WO2025111312A1

WO2025111312A1 - Di-sulfur triazole phosphate and thiophosphate fire retardants

Info

Publication number: WO2025111312A1
Application number: PCT/US2024/056619
Authority: WO
Inventors: Jun Yong Kang; Jeffrey ASH; Parsa AZAEI
Original assignee: University of Nevada Las Vegas; Nevada System of Higher Education NSHE
Current assignee: University of Nevada Las Vegas; Nevada System of Higher Education NSHE
Priority date: 2023-11-21
Filing date: 2024-11-20
Publication date: 2025-05-30
Anticipated expiration: 2026-05-21

Abstract

Described herein are di-sulfur triazole phosphate or thiophosphate compounds, methods for the synthesis thereof, and method for using the compounds as fire suppressants.

Description

DI-SULFUR TRIAZOLE PHOSPHATE AND THIOPHOSPHATE FIRE RETARDANTS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 63/682,522, filed on August 13, 2024, and U.S. Provisional Patent Application No. 63/601 ,377, filed on November 21 , 2023, each of which is incorporated by reference herein in its entirety.

BACKGROUND

The 2020 Nevada System of Higher Education (NSHE) Science and Technology Plan (STP) identified the wildfire processes, mitigation, and impacts as additional research focus areas. This research proposal directly contributes to the NSHE STP by providing novel fire-retardant systems through innovative synergistic effects. Nevada has been ranked 2^nd as a very high Wildland Fire Potential (WFP) state alongside its five neighboring states (CA, ID, OR, UT, AZ). Locating at the high fire potential zone, Nevada’s wildfire has a direct impact on Nevadans’ health and wellbeing regarding human smoke exposure and safety and ecosystem. Recent studies revealed that wildfire smoke exposure reduced students’ test scores; younger students were more vulnerable to these impacts. The study also projected a consequential negative effect on future economical earnings. Because of these widespread impacts of smoke plumes on the environment and human activities, the fire science research to control wildfires and smoke plumes is an unmet need to achieve the HDRFS (Harnessing the Data Revolution for Fire Science) goals, specifically Fire Emissions and their Atmospheric Aging (FEAA) field.

With adverse effects such as mutagenesis, carcinogenesis, and toxicity on human health and the environment, the brominated and chlorinated organic flame-retardants (BFRs and CFRs) were banned in 2010 following the “San Antonio Statement”. Since then, the efforts to develop eco-friendly, less-harmful alternatives have been expedited by this ban — once popular halogenated compounds. In addition, NIST (National Institute of Standards and Technology) Technical Note 1443, “Alternative Fire Suppressant Chemicals: A Research Review with Recommendations”, identified phosphate, sulfur, and inert gas (nitrogen gas) as promising chemical families with “High Priority.” As a result of this implementation, alternative halogen-free chemicals which contain phosphates, disulfides, and triazoles have been developed as promising flame suppressants.

FIG. 1 shows representative fire retardants containing the National Institute of Standards and Technology (NIST)-identified chemical families — A, organophosphates (Exolit 5060); B, disulfides; C, triazoles; and D, PTFM (phosphorus- and triazole-functionalized fire retardant monomer). These fire retardants have demonstrated discrete fire suppressing properties. For example, the phosphate fire retardant A serves as free radical scavenger to suppress flames by forming char layers which prevent combustible materials from generating flammable gases. Also, the disulfide-containing flame suppressant B is known for improving flame retardant properties by generating radical scavengers that subdue radical-mediated flame propagation. In addition, the triazole-containing flame retardant C generates inert nitrogen gas to quell the flames via thermal decomposition of the triazole group. Furthermore, with two functional groups of a phosphate and a triazole, the PTFM D demonstrated the generation of a phosphorus radical scavenger and nitrogen gas.

What are needed are phosphate-, thiophosphate-, sulfur-, and triazole-containing compounds that have synergistic effects in fire suppression.

SUMMARY

One embodiment described herein is a compound of formula (I), or a salt thereof,

wherein:

X¹ is O or S;

R¹, at each occurrence, is hydrogen, Ci_₆alkyl, G^x, Ci-6alkylene-G^x, or Ci_₆alkylene-OH, wherein:

G^x is a Ce-i2aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12- membered heterocycle, wherein G^x is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

R², at each occurrence, is hydrogen, Ci-ealkyl, G^Y, Ci-6alkylene-G^Y, or Ci-ealkylene-OH, wherein:

G^Y, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^Y is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci- ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

wherein: G¹, at each occurrence, is a Ce-izaryl, a 5- to 12-membered heteroaryl, a Ce i2carbocycle, or a 5- to 12-membered heterocycle, wherein G¹ is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi_₆alkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi_₄haloalkyl;

R³, at each occurrence, is hydrogen, Ci-salkyl, G^z, Ci-salkylene-G^z, or Ci-salkylene-OH;

G^z, at each occurrence, is a Cs-^aryl, a 5- to 12-membered heteroaryl, a Cs-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^z is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi-₄haloalkyl;

L¹ is Ci-salkylene, Ci-sheteroalkylene or Cy¹, wherein:

Cy¹, at each occurrence, is a C6-i2arylene, a 5- to 12-membered heteroarylene, a C3- scycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy¹ is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci-₄haloalkyl, and -OCi-₄haloalkyl;

n:

G², at each occurrence, is a Cs-^aryl, a 5- to 12-membered heteroaryl, a Cs-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G² is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci_₄haloalkyl , and -OCi_₄haloalkyl;

R⁴, at each occurrence, is Ci_salkyl, G^m, Ci-salkylene-G^m, or Ci-salkylene-OH, wherein:

G^w, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a Cs-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^w is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi_₄haloalkyl; and

L² is Ci-ealkylene, Ci-sheteroalkylene, or Cy², wherein:

Cy², at each occurrence, is a Cs-^arylene, a 5- to 12-membered heteroarylene, C3- 6cycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy² is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Cisalkyl, — OCi ealkyl, cyclopropyl, Ci ihaloalkyl , and -OCi ₄haloalkyl.

In one aspect, X¹ is O. In another aspect, X¹ is S. In another aspect, R¹ is G^x or Ci-ealkylene- G^x. In another aspect, G^x is Ce-^aryl. In another aspect, C₆-i2aryl is phenyl. In another aspect, R² is G^Y. In another aspect, G^Y is Ce-^aryl. In another aspect, Ce-^aryl is phenyl. In another aspect, L¹ is Ci-ealkylene. In another aspect, L¹ is Ci-3alkyene. In another aspect, L¹ is Gy¹.

In another aspect, Cy¹ is C6-i2arylene. In another aspect, C6-i2arylene is phenylene. In another aspect, Z¹ is G¹. In another aspect, G¹ is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Z¹ is

. In another aspect, R³ is hydrogen, Ci-ealkylene-OH, G^z, or Ci-6alkylene-G^z. In another aspect, R³ is Ci-salkylene-OH or Ci-3alkylene-G^z. In another aspect, G^z is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Y¹ is absent. In another aspect,

. In another aspect, X² is O. In another aspect, X² is S. In another aspect, L² is Ci-ealkyene. In another aspect, L² is Ci_3alkyene. In another aspect, L² is Cy². In another aspect, Cy² is C₆-i2arylene. In another aspect, C₆-i2arylene is phenylene. In another aspect, Z² is G². In another aspect, G² is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Z² is

In another aspect, R⁴ is hydrogen, Ci- ealkylene-OH, G^w, or Ci-6alkylene-G^w. In another aspect, R⁴ is Ci-salkylene-OH or Ci- 3alkylene-G^w. In another aspect, G^w is the C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, the compound is selected from:

Another embodiment described herein is a method for suppressing fire, the method comprising applying any of the compounds described herein or salts thereof to a fire or to the situs of a fire. Another embodiment described herein is the use of any of the compounds described herein or salts thereof for fire suppression.

Another embodiment described herein is a kit comprising any of the compounds described herein or salts thereof and optionally, directions or instructions for use. DESCRIPTION OF THE DRAWINGS

FIG. 1 shows representative fire retardants containing the National Institute of Standards and Technology (NIST)-identified chemical families: A, organophosphates (Exolit 5060); B, disulfides; C, triazoles; and D, PTFM (phosphorus- and triazole-functionalized fire retardant monomer).

FIG. 2 shows descriptions and key features of di-sulfur triazole phosphates and thiophosphates (DSTPs).

DETAILED DESCRIPTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. For example, any nomenclatures used in connection with, and techniques of biochemistry, molecular biology, immunology, microbiology, genetics, cell and tissue culture, and protein and nucleic acid chemistry described herein are well known and commonly used in the art. In case of conflict, the present disclosure, including definitions, will control. Exemplary methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the embodiments and aspects described herein.

As used herein, the terms such as “include,” “including,” “contain,” “containing,” “having,” and the like mean “comprising.” The present disclosure also contemplates other embodiments “comprising,” “consisting essentially of,” and “consisting of’ the embodiments or elements presented herein, whether explicitly set forth or not.

As used herein, the term “a,” “an,” “the” and similar terms used in the context of the disclosure (especially in the context of the claims) are to be construed to cover both the singular and plural unless otherwise indicated herein or clearly contradicted by the context. In addition, “a,” “an,” or “the” means “one or more” unless otherwise specified.

As used herein, the term “or” can be conjunctive or disjunctive.

As used herein, the term “and/or” refers to both the conjuctive and disjunctive.

As used herein, the term “substantially” means to a great or significant extent, but not completely.

As used herein, the term “about” or “approximately” as applied to one or more values of interest, refers to a value that is similar to a stated reference value, or within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, such as the limitations of the measurement system. In one aspect, the term “about” refers to any values, including both integers and fractional components that are within a variation of up to ± 10% of the value modified by the term “about.” Alternatively, “about” can mean within 3 or more standard deviations, per the practice in the art. Alternatively, such as with respect to biological systems or processes, the term “about” can mean within an order of magnitude, in some embodiments within 5-fold, and in some embodiments within 2-fold, of a value. As used herein, the symbol means “about” or “approximately.”

All ranges disclosed herein include both end points as discrete values as well as all integers and fractions specified within the range. For example, a range of 0.1-2.0 includes 0.1 , 0.2, 0.3, 0.4 . . . 2.0. If the end points are modified by the term “about,” the range specified is expanded by a variation of up to ±10% of any value within the range or within 3 or more standard deviations, including the end points.

As used herein, the terms “active ingredient” or “active pharmaceutical ingredient” refer to a pharmaceutical agent, active ingredient, compound, or substance, compositions, or mixtures thereof, that provide a pharmacological, often beneficial, effect.

As used herein, the terms “control,” or “reference” are used herein interchangeably. A “reference” or “control” level may be a predetermined value or range, which is employed as a baseline or benchmark against which to assess a measured result. “Control” also refers to control experiments or control cells.

Definitions of specific functional groups and chemical terms are described in more detail herein. The chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75^th ed., inside cover, and specific functional groups are generally defined as described therein. Additionally, general principles of organic chemistry, as well as specific functional moieties and reactivity, are described in Thomas Sorrell, Organic Chemistry, University Science Books, Sausalito, 1999; Smith and March, March’s Advanced Organic Chemistry, 5^th ed, John Wiley & Sons, Inc., New York, 2001; Larock, Comprehensive Organic Transformations, VCH Publishers, Inc., New York, 1989; and Carruthers, Some Modern Methods of Organic Synthesis, 3^rd ed, Cambridge University Press, Cambridge, 1987.

As used herein, the term “alkyl” refers to a straight or branched hydrocarbon radical having from 1 to 12 (e.g., C1-C12) carbon atoms and includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, terf-butyl, n-pentyl, iso-pentyl, n-hexyl, and the like.

As used herein, the term “alkenyl” refers to straight and branched hydrocarbon radicals having from 2 to 12 carbon atoms (e.g., C2-C12) and at least one double bond and includes, but is not limited to, ethenyl, 3-buten-1-yl, 2-ethenyl butyl, 3-hexen-1-yl, and the like. The term “alkenyl” includes cycloalkenyl, and heteroalkenyl in which 1 to 3 heteroatoms selected from O, S, N, or substituted nitrogen may replace carbon atoms.

As used herein, the term “alkynyl” refers to straight and branched hydrocarbon radicals having from 2 to 12 carbon atoms (e.g., C₂-Ci₂) and at least one triple bond and includes, but is not limited to, ethynyl, 3-butyn-1-yl, propynyl, 2-butyn-1-yl, 3-pentyn-1-yl, and the like.

As used herein, the term “cycloalkyl” refers to a monocyclic or polycyclic hydrocarbyl group having from 3 to 8 carbon atoms (e.g., Cs-Cs), for instance, cyclopropyl, cycloheptyl, cyclooctyl, cyclodecyl, cyclobutyl, adamantyl, norpinanyl, decalinyl, norbornyl, cyclohexyl, and cyclopentyl. Such groups can be substituted with groups such as hydroxy, keto, amino, alkyl, and dialkylamino, and the like. Also included are rings in which 1 to 3 heteroatoms replace carbons. Such groups are termed “heterocyclyl,” which means a cycloalkyl group also bearing at least one heteroatom selected from O, S, N, or substituted nitrogen. Examples of such groups include, but are not limited to, oxiranyl, pyrrolidinyl, piperidyl, tetrahydropyran, and morpholine.

As used herein, the term “alkoxy” refers to a straight or branched chain alkyl groups having

1-10 carbon atoms (e.g., C₂-C ) and linked through oxygen. Examples of such groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, pentoxy, 2-pentyloxy, isopentoxy, neopentoxy, hexoxy, 2-hexoxy, 3-hexoxy, and 3- methylpentoxy. In addition, alkoxy refers to polyethers such as -O- (CH₂)₂-O-CH3, and the like.

The alkyl, alkenyl, alkoxy, and alkynyl groups described herein are optionally substituted (i.e., may be substituted, but are not necessarily substituted), preferably by 1 to 3 groups selected from NR4R5, phenyl, substituted phenyl, thio Ci-Ce alkyl, Ci-Ce alkoxy, hydroxy, carboxy, Ci-Ce alkoxycarbonyl, halo, nitrile, cycloalkyl, and a 5- or 6-membered carbocyclic ring or heterocyclic ring having 1 or 2 heteroatoms selected from nitrogen, substituted nitrogen, oxygen, and sulfur. “Substituted nitrogen” means nitrogen bearing Ci-Ce alkyl or (CH₂)_pPh where p is 1 , 2, or 3. Perhalo and polyhalo substitution is also included.

Examples of substituted alkyl groups include, but are not limited to, 2-aminoethyl, 2- hydroxyethyl, pentachloroethyl, trifluoromethyl, 2-diethylaminoethyl, 2-dimethylaminopropyl, ethoxycarbonylmethyl, 3-phenylbutyl, methanylsulfanylmethyl, methoxymethyl, 3-hydroxypentyl,

2-carboxybutyl, 4-chlorobutyl, 3-cyclopropylpropyl, pentafluoroethyl, 3-morpholinopropyl, piperazinylmethyl, and 2-(4-methylpiperazinyl)ethyl.

Examples of substituted alkynyl groups include, but are not limited to, 2-methoxyethynyl, 2-ethylsulfanylethynyl, 4-(1-piperazinyl)-3-(butynyl), 3-phenyl-5-hexynyl, 3-diethylamino-3- butynyl, 4-chloro-3-butynyl, 4-cyclobutyl-4-hexenyl, and the like. Typical substituted alkoxy groups include aminomethoxy, trifluoromethoxy, 2- diethylaminoethoxy, 2-ethoxycarbonylethoxy, 3-hydroxypropoxy, 6-carboxhexyloxy, and the like.

Further, examples of substituted alkyl, alkenyl, and alkynyl groups include, but are not limited to, dimethylaminomethyl, carboxymethyl, 4-dimethylamino-3-buten-1-yl, 5- ethylmethylamino-3-pentyn-1-yl, 4-morpholinobutyl, 4-tetrahydropyrinidylbutyl, 3-imidazolidin-1- ylpropyl, 4-tetrahydrothiazol-3-yl-butyl, phenylmethyl, 3-chlorophenylmethyl, and the like.

As used herein, the term “anion” means a negatively charged species such as chloride, bromide, trifluoroacetate, or triethylammonium. The term “cation” refers to a positively charged species, such as sodium, potassium, or ammonium.

As used herein, the term “acyl” refers to alkyl or aryl (Ar) group having from 1-10 carbon atoms bonded through a carbonyl group, i.e., R-C(O)-. For example, acyl includes, but is not limited to, a Ci-Ce alkanoyl, including substituted alkanoyl, wherein the alkyl portion can be substituted by an amine, amide, carboxylic, or heterocyclic group. Typical acyl groups include acetyl, benzoyl, and the like.

As used herein, the term “aryl” refers to an aromatic monocyclic hydrocarbon ring system or a polycyclic ring system where at least one of the rings in the ring system is an aromatic hydrocarbon ring and any other aromatic rings in the ring system include only hydrocarbons. In some embodiments, a monocyclic aryl group can have from 6 to 14 carbon atoms and a polycyclic aryl group can have from 8 to 14 carbon atoms (e.g., Cs-Cu). The aryl group can be covalently attached to the defined chemical structure at any carbon atom(s) that result in a stable structure. In some embodiments, an aryl group can have only aromatic carbocyclic rings, e.g., phenyl, 1- naphthyl, 2-naphthyl, anthracenyl, phenanthrenyl groups, and the like. In other embodiments, an aryl group can be a polycyclic ring system in which at least one aromatic carbocyclic ring is fused (i.e., having a bond in common with) to one or more cycloalkyl or cycloheteroalkyl rings. Examples of such aryl groups include, among others, benzo derivatives of cyclopentane (i.e., an indanyl group, which is a 5,6-bicyclic cycloalkyl/aromatic ring system), cyclohexane (i.e., a tetrahydronaphthyl group, which is a 6,6-bicyclic cycloalkyl/aromatic ring system), imidazoline (i.e., a benzimidazolinyl group, which is a 5,6-bicyclic cycloheteroalkyl/aromatic ring system), and pyran (i.e., a chromenyl group, which is a 6,6-bicyclic cycloheteroalkyl/aromatic ring system). Other examples of aryl groups include benzodioxanyl, benzodioxolyl, chromanyl, indolinyl groups, and the like.

As used herein, the terms “halogen” or “halo” refer to fluorine, bromine, chlorine, or iodine.

As used herein, the term “haloalkyl” refers to an alkyl group having one or more halogen substituents. In some embodiments, a haloalkyl group can have 1 to 10 carbon atoms (e.g., Ci- Cs). Examples of haloalkyl groups include CF3, C2F5, CHF2, CH2F, CCI3, CHCh, CH2CI, C2CI5, and the like. Perhaloalkyl groups, i.e., alkyl groups wherein all the hydrogen atoms are replaced with halogen atoms (e.g., CF₃ and C2F5), are included within the definition of “haloalkyl.” For example, a C1-10 haloalkyl group can have the formula - CjH₂i+1- jXj, wherein is F, Cl, Br, or I, i is an integer in the range of 1 to 10, and j is an integer in the range of 0 to 21 , provided that j is less than or equal to 2i+1.

As used herein, the term “heteroaryl” refers to an aromatic monocyclic ring system containing at least one ring heteroatom selected from O, N, and S or a polycyclic ring system where at least one of the rings in the ring system is aromatic and contains at least one ring heteroatom. A heteroaryl group can have from 5 to 14 ring atoms (e.g., C5-C14), and contains 1- 6 ring heteroatoms (e.g., N, O, S, P, or the like). In some embodiments, heteroaryl groups can include monocyclic heteroaryl rings fused to one or more aromatic carbocyclic rings, non-aromatic carbocyclic rings, or non-aromatic cycloheteroalkyl rings. The heteroaryl group can be covalently attached to the defined chemical structure at any heteroatom or carbon atom that results in a stable structure. Generally, heteroaryl rings do not contain O-O, S-S, or S-0 bonds. However, one or more N or S atoms in a heteroaryl group can be oxidized (e.g., pyridine N-oxide, thiophene S-oxide, thiophene S,S-dioxide). Examples of such heteroaryl rings include pyrrolyl, furyl, thienyl, pyridyl, pyrimidyl, pyridazinyl, pyrazinyl, triazolyl, tetrazolyl, pyrazolyl, imidazolyl, isothiazolyl, thiazolyl, thiadiazolyl, isoxazolyl, oxazolyl, oxadiazolyl, indolyl, isoindolyl, benzofuryl, benzothienyl, quinolyl, 2-methylquinolyl, isoquinolyl, quinoxalyl, quinazolyl, benzotriazolyl, benzimidazolyl, benzothiazolyl, benzisothiazolyl, benzisoxazolyl, benzoxadiazolyl, benzoxazolyl, cinnolinyl, 1/7-indazolyl, 2/7-indazolyl, indolizinyl, isobenzofuyl, naphthyridinyl, phthalazinyl, pteridinyl, purinyl, oxazolopyridinyl, thiazolopyridinyl, imidazopyridinyl, furopyridinyl, thienopyridinyl, pyridopyrimidinyl, pyridopyrazinyl, pyridopyrdazinyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl groups, and the like. Further examples of heteroaryl groups include 4,5,6,7-tetrahydroindolyl, tetrahydroquinolinyl, benzothienopyridinyl, benzofuropyridinyl groups, and the like.

As used herein, the term “lower alkenyl” refers to alkenyl groups which contains 2 to 6 carbon atoms (e.g., C2-C6). An alkenyl group is a hydrocarbyl group containing at least one carbon-carbon double bond. As defined herein, it may be unsubstituted or substituted with the substituents described herein. The carbon-carbon double bonds may be between any two carbon atoms of the alkenyl group. It is preferred that it contains 1 or 2 carbon-carbon double bonds and more preferably one carbon-carbon double bond. The alkenyl group may be straight chained or branched. Examples include but are not limited to ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2- butenyl, 2-methyl-1-propenyl, 1 ,3-butadienyl, and the like.

As used herein, the term “lower alkynyl” refers to an alkynyl group containing 2-6 carbon atoms (e.g., C₂-C₆). An alkynyl group is a hydrocarbyl group containing at least one carboncarbon triple bond. The carbon-carbon triple bond may be between any two-carbon atom of the alkynyl group. In an embodiment, the alkynyl group contains 1 or 2 carbon-carbon triple bonds and more preferably one carbon-carbon triple bond. The alkynyl group may be straight chained or branched. Examples include but are not limited to ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl and the like.

As used herein, the term “carbalkoxy” refers to an alkoxycarbonyl group, where the attachment to the main chain is through the carbonyl group, e.g., -C(O)-. Examples include but are not limited to methoxy carbonyl, ethoxy carbonyl, and the like.

As used herein, the term “oxo” refers to a double-bonded oxygen (i.e., =0). It is also to be understood that the terminology C(0) refers to a -C=0 group, whether it be ketone, aldehyde or acid or acid derivative. Similarly, S(0) refers to a -S=0 group.

As used herein, the term “cycloalkyl” refers to a non-aromatic carbocyclic group including cyclized alkyl, alkenyl, and alkynyl groups. A cycloalkyl group can be monocyclic (e.g., cyclohexyl) or polycyclic (e.g., containing fused, bridged, and/or spiro ring systems), wherein the carbon atoms are located inside or outside of the ring system. A cycloalkyl group can have from 3 to 14 ring atoms (e.g., from 3 to 8 carbon atoms for a monocyclic cycloalkyl group and from 7 to 14 carbon atoms for a polycyclic cycloalkyl group). Any suitable ring position of the cycloalkyl group can be covalently linked to the defined chemical structure. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopentenyl, cyclohexenyl, cyclohexadienyl, cycloheptatrienyl, norbornyl, norpinyl, norcaryl, adamantyl, and spiro[4.5]decanyl groups, as well as their homologs, isomers, and the like.

As used herein, the term “heteroatom” refers to an atom of any element other than carbon or hydrogen and includes, for example, nitrogen, oxygen, sulfur, phosphorus, and selenium.

As used herein, the term “cycloheteroalkyl” refers to a non-aromatic cycloalkyl group that contains at least one (e.g., one, two, three, four, or five) ring heteroatom selected from O, N, and S, and optionally contains one or more (e.g., one, two, or three) double or triple bonds. A cycloheteroalkyl group can have from 3 to 14 ring atoms and contains from 1 to 5 ring heteroatoms (e.g., from 3-6 ring atoms for a monocyclic cycloheteroalkyl group and from 7 to 14 ring atoms for a polycyclic cycloheteroalkyl group). The cycloheteroalkyl group can be covalently attached to the defined chemical structure at any heteroatom(s) or carbon atom(s) that results in a stable structure. One or more N or S atoms in a cycloheteroalkyl ring may be oxidized (e.g., morpholine

A/-oxide, thiomorpholine S-oxide, thiomorpholine S,S-dioxide). Cycloheteroalkyl groups can also contain one or more oxo groups, such as phthalimidyl, piperidinyl, oxazolidinoxyl, 2,4(1 /7, 3/7)- dioxo-pyrimidinyl, pyridin-2(1/7)-onyl, and the like. Examples of cycloheteroalkyl groups include, among others, morpholinyl, thiomorpholinyl, pyranyl, imidazolidinyl, imidazolinyl, oxazolidinyl, pyrazolidinyl, pyrazolinyl, pyrrolidinyl, pyrrolinyl, tetrahydrofuranyl, tetrahydrothienyl, piperidinyl, piperazinyl, azetidine, and the like.

wherein:

X¹ is O or S;

R¹, at each occurrence, is hydrogen, Ci-salkyl, G^x, Ci-6alkylene-G^x, or Ci-ealkylene-OH, wherein:

G^x is a Ce-i2aryl, a 5- to 12-membered heteroaryl, a Cs-i2carbocycle, or a 5- to 12- membered heterocycle, wherein G^x is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-salkyl, -OCi_₆alkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi_₄haloalkyl;

R², at each occurrence, is hydrogen, Ci_₆alkyl, G^Y, Ci-6alkylene-G^Y, or Ci_₆alkylene-OH, wherein:

G^Y, at each occurrence, is a Cs-^aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^Y is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-ealkyl, cyclopropyl, Ci-₄haloalkyl , and -OCi-₄haloalkyl;

wherein:

G¹, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G¹ is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci_₄haloalkyl , and — OCi_₄haloalkyl ;

R³, at each occurrence, is hydrogen, Ci_₆alkyl, G^z, Ci_₆alkylene-G^z, or Ci-₆alkylene-OH; G^z, at each occurrence, is a Ce-izaryl, a 5- to 12-membered heteroaryl, a Ce i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^z is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi_₆alkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi_₄haloalkyl;

L¹ is Ci-salkylene, Ci-sheteroalkylene or Cy¹, wherein:

Cy¹, at each occurrence, is a Cs-^arylene, a 5- to 12-membered heteroarylene, a C3- scycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy¹ is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci-₄haloalkyl, and -OCi-₄haloalkyl;

n:

G², at each occurrence, is a Cs-^aryl, a 5- to 12-membered heteroaryl, a Cs-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G² is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-ealkyl, cyclopropyl, Ci_₄haloalkyl , and -OCi_₄haloalkyl;

R⁴, at each occurrence, is Ci-salkyl, G^m, Ci-salkylene-G^m, or Ci-salkylene-OH, wherein:

L² is Ci-salkylene, Ci-sheteroalkylene, or Cy², wherein:

Cy², at each occurrence, is a Cs-^arylene, a 5- to 12-membered heteroarylene, C3- 6cycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy² is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Cisalkyl, -OCi-salkyl, cyclopropyl, Ci_₄haloalkyl, and -OCi-₄haloalkyl.

In one aspect, X¹ is O. In another aspect, X¹ is S. In another aspect, R¹ is G^x or Ci-salkylene- G^x. In another aspect, G^x is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, R² is G^Y. In another aspect, G^Y is Cs-^aryl. In another aspect, Cs-^aryl is phenyl. In another aspect, L¹ is Ci-salkylene. In another aspect, L¹ is Ci-3alkyene. In another aspect, L¹ is Cy¹. In another aspect, Cy¹ is C6-i2arylene. In another aspect, C6-i2arylene is phenylene. In another aspect, Z¹ is G¹. In another aspect, G¹ is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Z¹ is

. In another aspect, R³ is hydrogen, Ci-ealkylene-OH, G^z, or Ci_₆alkylene-G^z. In another aspect, R³ is Ci_₃alkylene-OH or Ci_₃alkylene-G^z. In another aspect, G^z is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Y¹ is absent. In another aspect,

In another aspect, X² is O. In another aspect, X² is S. In another aspect, L² is Ci-salkyene. In another aspect, L² is Ci-₃alkyene. In another aspect, L² is Cy². In another aspect, Cy² is C5-i2arylene. In another aspect, C6-i2arylene is phenylene. In another aspect, Z² is G². In another aspect, G² is C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, Z² is

In another aspect, R⁴ is hydrogen, Ci- ealkylene-OH, G^w, or Ci-6alkylene-G^w. In another aspect, R⁴ is Ci-₃alkylene-OH or Ci- ₃alkylene-G^w. In another aspect, G^w is the C6-i2aryl. In another aspect, C6-i2aryl is phenyl. In another aspect, the compound is selected from:

Another embodiment described herein is a kit comprising any of the compounds described herein or salts thereof and optionally, directions or instructions for use.

It will be apparent to one of ordinary skill in the relevant art that suitable modifications and adaptations to the compositions, formulations, methods, processes, and applications described herein can be made without departing from the scope of any embodiments or aspects thereof. The compositions and methods provided are exemplary and are not intended to limit the scope of any of the specified embodiments. All of the various embodiments, aspects, and options disclosed herein can be combined in any variations or iterations. The scope of the compositions, formulations, methods, and processes described herein include all actual or potential combinations of embodiments, aspects, options, examples, and preferences herein described. The exemplary compositions and formulations described herein may omit any component, substitute any component disclosed herein, or include any component disclosed elsewhere herein. The ratios of the mass of any component of any of the compositions or formulations disclosed herein to the mass of any other component in the formulation or to the total mass of the other components in the formulation are hereby disclosed as if they were expressly disclosed. Should the meaning of any terms in any of the patents or publications incorporated by reference conflict with the meaning of the terms used in this disclosure, the meanings of the terms or phrases in this disclosure are controlling. Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments. All patents and publications cited herein are incorporated by reference herein for the specific teachings thereof.

Various embodiments and aspects of the inventions described herein are summarized by the following clauses:

Clause 1 . A compound of formula (I), or a salt thereof,

wherein:

X¹ is O or S;

G^x is a Ce-i2aryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12- membered heterocycle, wherein G^x is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

G^Y, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^Y is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl , -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

wherein:

G¹, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G¹ is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

R³, at each occurrence, is hydrogen, Ci-ealkyl, G^z, Ci-ealkylene-G^z, or Ci ealkylene— OH;

G^z, at each occurrence, is a Ce-^aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^z is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

L¹ is Ci_₆alkylene, Ci_₆heteroalkylene or Cy¹, wherein:

Cy¹, at each occurrence, is a C₆-i2arylene, a 5- to 12-membered heteroarylene, a C₃-ecycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy¹ is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

:

G², at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a Ce-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G² is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl; R⁴, at each occurrence, is Ci-ealkyl, G^m, Ci-6alkylene-G^w, or Ci-salkylene-OH, wherein:

G^w, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C₆-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^w is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl; and

L² is Ci-salkylene, Ci-6heteroalkylene, or Cy², wherein:

Cy², at each occurrence, is a C6-i2arylene, a 5- to 12-membered heteroarylene, Cs-ecycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy² is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl.

Clause 2. The compound of clause 1 , or a salt thereof, wherein X¹ is O.

Clause 3. The compound of clause 1 , or a salt thereof, wherein X¹ is S.

Clause 4. The compound of any one of clauses 1-3, or a salt thereof, wherein R¹ is G^x or

Ci-ealkylene-G^x.

Clause 5. The compound of clause 4, or a salt thereof, wherein G^x is C6-i2aryl.

Clause 6. The compound of clause 5, or a salt thereof, wherein C6-i2aryl is phenyl.

Clause 7. The compound of any one of clauses 1-6, or a salt thereof, wherein R² is G^Y.

Clause 8. The compound of clause 7, or a salt thereof, wherein G^Y is Ce-^aryl.

Clause 9. The compound of clause 8, or a salt thereof, wherein C6-i2aryl is phenyl.

Clause 10. The compound of any one of clauses 1-9, or a salt thereof, wherein L¹ is Ci- salkylene.

Clause 11. The compound of clause 10, or a salt thereof, wherein L¹ is Ci_₃alkyene.

Clause 12. The compound of any one of clauses, 1-9, or a salt thereof, wherein L¹ is Cy¹.

Clause 13. The compound of clause 12, or a salt thereof, wherein Cy¹ is Cs-^arylene.

Clause 14. The compound of clause 13, or a salt thereof, wherein C6-i2arylene is phenylene.

Clause 15. The compound of any one of clauses 1-14, or a salt thereof, wherein Z¹ is G¹. Clause 16. The compound of clause 15, or a salt thereof, wherein G¹ is C6-i2aryl.

Clause 17. The compound of clause 16, or a salt thereof, wherein C6-i2aryl is phenyl. Clause 18. The compound of any one of clauses 1-14, or a salt thereof, wherein Z¹ is

Clause 19. The compound of clause 18, or a salt thereof, wherein R³ is hydrogen, Ci_ 6alkylene-OH, G^z, or Ci_₆alkylene-G^z.

Clause 20. The compound of clause 19, or a salt thereof, wherein R³ is Ci-salkylene-OH or Ci-3alkylene-G^z.

Clause 21. The compound of clause 19 or 20, or a salt thereof, wherein G^z is C6-i2aryl.

Clause 22. The compound of clause 21 , or a salt thereof, wherein C6-i2aryl is phenyl.

Clause 23. The compound of any one of clauses 1-22, or salt thereof, wherein Y¹ is absent.

Clause 24. The compound of any one of clauses 1-22, or a salt thereof, wherein Y¹ is

Clause 25. The compound of clause 24, or a salt thereof, wherein X² is O.

Clause 26. The compound of clause 24, or a salt thereof, wherein X² is S.

Clause 27. The compound of any one of clauses 24-26, or a salt thereof, wherein L² is Ci_

₆alkyene.

Clause 28. The compound of clause 27, or a salt thereof, wherein L² is Ci-3alkyene.

Clause 29. The compound of any one of clauses 24-26, or a salt thereof, wherein L² is Cy².

Clause 30. The compound of clause 29, or a salt thereof, wherein Cy² is C6-i2arylene.

Clause 31. The compound of clause 30, or a salt thereof, wherein C6-i2arylene is phenylene.

Clause 32. The compound of any one of clauses 24-31 , or a salt thereof, wherein Z² is G².

Clause 33. The compound of clause 32, or a salt thereof, wherein G² is C6-i2aryl.

Clause 34. The compound of clause 33, or a salt thereof, wherein C6-i2aryl is phenyl.

Clause 35. The compound of any one of clauses 24-31 , or a salt thereof, wherein Z² is

Clause 36. The compound of clause 34, or a salt thereof, wherein R⁴ is hydrogen, Ci- 6alkylene-OH, G^w, or Ci-6alkylene-G^w.

Clause 37. The compound of clause 36, or a salt thereof, wherein R⁴ is Ci-salkylene-OH or Ci-3alkylene-G^w. Clause 38. The compound of clause 36 or 37, or a salt thereof, wherein G^w is C6-i2aryl.

Clause 39. The compound of clause 38, or a salt thereof, wherein Ce ^aryl is phenyl.

Clause 40. The compound of any one of clauses 1-39, wherein the compound is selected from:

Clause 41. A method for suppressing fire, the method comprising applying the compound of any one of clauses 1-40, or a salt thereof, to a fire or to the situs of a fire.

Clause 42. Use of the compound of any one of clauses 1-40, or a salt thereof, for fire suppression.

Clause 43. A kit comprising the compound of any one of clauses 1-40, or a salt thereof, and optionally, directions or instructions for use.

EXAMPLES

Example 1

Synthesis and Characterization of Example DSTPs

Scheme 1. Synthesis of DSTP-1

To a solution of phenylphosphinic acid 1 (5.29 mmol, 1.0 equiv) in acetonitrile (26.0 mL), 1 H-1 ,2,3-triazole-4-methanol 2 (5.29mmol, 1.0 equiv) was added. Coupling agent DCC (5.29 mmol, 1.0 equiv) was added portion wise to the round bottom flask at room temperature. The reaction was stirred for 21 h. The crude mixture was filtered to remove di-cyclohexyl urea byproduct, and the filter cake was washed with acetonitrile. The mother liquid was then concentrated under reduced pressure and the crude solid was washed with cold diethyl ether (20 mL, 2x) and cold ethyl acetate (20 mL, 2*). The product 3 was then dried under high vacuum to give 1.204 grams esterified phosphine oxide in a 73% yield. State: Sticky white solid. ¹H NMR (400 MHz, CDCh): 6 7.79-7.73 (m, 2H), 7.59-7.57 (m, 2H), 7.51-7.48 (m, 2H), 7.38-7.35 (m, 2H), 7.27-7.25 (m, 2H), 5.51 (s, 3H), 5.28-5.14 (m, 2H), 4.77 (S, 1 H). ¹³C NMR (100.5 MHz, CDCh): 6 143.6 (d, J = 6.7 MHz), 134.2, 133.3 (d, J = 3.0 MHz), 131.0 (d, J = 11.9 MHz), 129.9, 129.2, 129.1 , 128.8 (d, J = 14.8 MHz), 128.1 , 123.5, 58.6 (d, = 6.0 MHz), 54.2. ³¹P NMR: (162 MHz, CDCI³): 620.56.

Procedure

To a solution of secondary phosphine oxide 3 (1.0 mmol, 1.0 equiv) in DCM (5.0 mL) was added Ss (1.0 mmol, 1.05 equiv), followed by triethylamine (1.5 mmol, 1.5 equiv). The reaction was stirred for 23 h and the solvent was concentrated under reduced pressure. The crude mixture was then dissolved in ether and washed with 1 M HCI (3x). The organic layer was then washed with brine and dried with sodium sulfate. The dried organic extract was concentrated under reduced pressure to give 253 mg thiophosphinic acid 4 in a yield of 73%. State: Sticky yellow solid.

¹H NMR (400 MHz, CDCh): 5 7.95-7.90 (m, 2H), 7.50 (s, 1H), 7.45-7.41 (m, 1 H), 7.37- 7.32 (m, 5H), 7.22-7.19 (m, 2H), 5.45-5.39 (m, 3H), 5.20 (t, J = 12.8 MHz). ¹³C NMR (100.5 MHz, CDCh): 5 143.5 (d, J = 7.4 MHz), 135.3, 133.8, 133.5, 131 .7 (d, J = 3.0 MHz), 130.7 (d, J = 12.0 MHz), 129.2 (d, J = 15.6 MHz), 128.2, 128.0, 123.6. ³¹P NMR: (162 MHz, CDCh): 0 81 .31 .

Procedure (Pa- 1-92)

To a solution of thiophosphinic acid 4 (0.3 mmol, 1.0 equiv) in DCM (1.5 ml_), was slowly added iodine (0.15 mmol, 0.5 equiv). The reaction was stirred at room temperature for 40 minutes and concentrated under reduced pressure to give 123 mg DSTP-1 in a 99% yield. State: Sticky red solid.

¹H NMR (400 MHz, CDCI₃): 6 7.87-7.81 (m, 4H), 7.72 (s, 2H), 7.39-7.37 (m, 2H), 7.31- 7.27 (m, 10H), 7.23-7.21 (m, 3H), 5.44 (s, 4H), 5.37-5.31 (m, 2H), 5.20-5.13 (m, 2H). ¹³C NMR (100.5 MHz, CDCh): 5 142.5 (d, J = 7.5 MHz), 134.9, 133.4, 132.0 (d, J = 3.0 MHz), 130.7 (d, J = 11.9 MHz), 129.3, 128.6, 128.3, 128.2, 124.9, 57.3 (d, J = 4.5 MHz), 55.6. ³¹P NMR: (162 MHz, CDCh): 6 81.73.

Example DSTP Derivatives

Example 2

Preliminary Results and Design Principles Preliminary data for the synthesis of the proposed novel fire retardants is shown in

Scheme 2. Three key synthesis methods will be used for the novel fire retardants: the mixed phosphate synthesis using triethyl phosphates 1 ' and alkyne-phenols 2' afforded various mixed phosphate derivatives 3' (Scheme 2, eq 1), the triazole synthesis between phenyl alkynes 4' and benzyl azides 5' furnished triazoles 6' (Scheme 2, eq 2), and the disulfide synthesis using benzyl mercaptans T generated dibenzyl disulfides 8' (Scheme 2, eq 3). See Huang et al., Angewandte Chemie Int. Ed. 57(22): 6624-6628 (2018); Ryu and Emrick, Angewandte Chemie Int. Ed. 49(50): 9644-9647 (2010); Huang et al., Organ. Biomol. Chem. 16 (23): 4236-4242 (2018). With these streamlined-synthesis approaches, the construction of the proposed fire retardants shown in Scheme 3 will be facilitated.

Scheme 2. Preliminary Synthesis Results

Fe(PC) (3 mol %)

(3)

THF, RT, 20 min 99% yield

FIG. 2 describes the key features of di-sulfur triazole phosphates (DSTP) which are synthesized by using results discussed in Scheme 2. The three different functional groups (phosphate, triazole, and disulfide) have not only their unique fire-suppressing properties but also different bond dissociation energies (BDEs). The DSTPs may be applied for a wide range of temperatures. In addition, they may be readily synthesized and derivatized via a modular synthesis approach.

Scheme 3 describes the modular synthesis approach toward the DSTPs. This modular strategy enables the desired DSTPs in three steps to install the three active functional groups: phosphate, disulfide, and triazole. The advantages of this modular approach include its combinatorial nature and flexibility: this synthetic route is readily adjustable to optimize a high product yield and the various combination of R', R", and R³ groups rapidly increases the diversity of DSTPs. Accordingly, this modular protocol will significantly reduce the labor and time in the DSTP synthesis.

Scheme 3. Modular Synthetic Approach toward DSTP

Synthesize novel-fire retardants harnessing the synergistic effects via environmentally friendly synthesis methods. The proposed synthesis of DSTPs via a modular approach is described in Scheme 4.

First, phosphorothioic acid 8 is treated with alkyne 2' to synthesize a mixed phosphorothioic acid 9. Next, the alkyne group on thioic acid 9 reacts with azide 10 to generate triazole 11 via click chemistry. Finally, the coupling reaction of triazole 11 in presence of Fe(Pc) catalyst affords the target DSTP 12. This standard procedure will be used for the synthesis of different DSTPs. For example, the DSTP 13 which has a hydroxyl group will be synthesized for the potential polymerization reaction. Sykam et al., \CS Omega 4(1): 1086-1094 (2019). In addition, DSTPs 14 and 15 will be generated by the same procedure, and they carry the benefits of low-residue, eco-friendly flame retardants. Scheme 4. Proposed Synthesis of Novel Fire Retardants (DSTP) Di-sulfur triazole phosphate (DSTP) synthesis

Di-sulfur Triazole Phosphate (DSTP) Synthesis

DSTP Alternative Synthesis for DSTPs

Click chemistry, a reliable, tolerable reaction with a wide range of functional groups, will be used to generate a triazole functional group. However, if this second-step click chemistry reaction is inhibited by a thioic acid group on the intermediate 8, an alternative approach that installs the triazole group 16 in the first step will be examined and followed by the synthesis of mixed phosphonates 11 and the coupling reaction to afford DSTP 18 (Scheme 5). As such, any functional group compatibility issues of the proposed synthesis will be addressed by the proposed flexible, modifiable, combinatorial approach. In addition, if the proposed coupling reaction to form the disulfide 18 with Fe(Pc) catalyst provides a low product yield, different catalysts such as CuCI₂, FeCI₃, or MnO₂ will be examined. Huang et al., Organ. Biomol. Chem. 16 (23): 4236-4242 (2018).

Scheme 5. Alternative Synthesis Route

Di-sulfur Triazole Phosphate (DSTP) Synthesis

Assess the Flame Suppression Efficiency and the Synergistic Effects of DSTPs

Thermal properties and synergistic effects of the novel DSTPs will be analyzed in collaboration with Fortress. To study the thermolysis of DSTPs, melting point measurements will be used in our lab. This experiment will provide a specific temperature range of flame suppression for different DSTPs. To investigate the thermal property changes such as homolytic bond cleavages of P-0 and S-S bonds as well as releasing N₂ gas after thermolysis, Infrared Spectroscopy (IR) and Nuclear Magnetic Resonance (NMR) will be used to analyze the functional groups affected by the thermolysis in our lab. Fortress, an industry collaborator, will test our DSTPs with the industry testing methods. A detailed description of these methods is listed below, and they will be applied to test phosphonate-, sulfur-, and triazole containing DSTPs to assess the synergistic effects. Fortress Burn Testing

Fortress burn testing mimics the US Forest Service test chamber in the screening and evaluation of fire-retardant materials. The test formulations with novel fire-retardant materials (DSTPs) are applied at 7.6 L/30.5 m² (2 gallons/100 ft²) to both Aspen excelsior and Ponderosa pine needles at standard fuel densities. Test burns are timed, and the lateral travel rates are compared as a reduction compared to untreated fuel. The reduction index for the novel materials is compared to a standard fire retardant, 10.6% diammonium phosphate. Fire retardant material concentration within the applied coating and coating thickness can be changed to evaluate the performance of the DSTPs. This burn testing will be applied for the regionally significant sagebrush.

Corrosion Testing

Screening corrosion experiments are performed for DSTPs to demonstrate the corrosivity of the materials against 2024-T3 aluminum, 4130 steel, UNS C26000 yellow brass, and Az31 B- H24 magnesium. These corrosion experiments place coupons of the metals into solutions of the fire-retardant chemical and store them at 49 °C (120 F) in full or partial immersed conditions for up to 90 days. The coupons are removed, cleaned, and uniform corrosion rates are calculated. The corrosion rates are compared to the limits described by the US Forest Service (< 5 mils per year for steel and brass, < 4 mils per year for magnesium, and < 2 mils per year for aluminum).

Stability Testing

The DSTPs are stored for 14 days on the bench, and standard parameters are monitored, including homogeneity, pH, viscosity, refractive index, and density.

Example 3

Synthesis of Disulfide Triazole Thiophosphate Compounds

Scheme 6 describes the proposed FR synthesis via a modular approach. First, phosphorus pentasulfide 19 will be treated with propargyl alcohol 20 to synthesize dithiophosphoric acid 21. See Sinyashin et al., Phosphorus, Sulfur, Silicon Relat. Elem. 186(4): 997-998 (2011). This acid 21 , containing an alkyne group, may then undergo a click chemistry reaction with azides 22, under photochemical conditions (390 nm light source), to yield bis-triazole dithiophosphoric acids 23a-23c. See e.g., Tasdelen and Yagci, Tetrahedron Lett. 51(52): 6945- 6947 (2010); Khalili et al., Synlett 30: 2136-2142 (2019); Miao and Wang, Synthesis 2008: 363- 368 (2008); McBride et al., Polymer 55(23): 5880-5884 (2014). This step ensures the rapid diversification of FRs to study their effects. Finally, a photochemical homocoupling reaction of dithiophosphoric acids 23a-23c may be explored to synthesize the target FRs 24a-24c. Dethe et al., Adv. Syn. Catal. 360(16): 3020-3025 (2018). This versatile method allows for the synthesis of various FRs to be studied regarding their effectiveness.

Scheme 6. Modular Synthesis of Disulfide Triazole Phosphonate via Photochemical Flow

Reaction

This modular procedure may be utilized to synthesize different FRs, such as DSTP 25 and 26, to investigate the triazole effect on the release of N₂ gas (Scheme 7). To study the effect of alkyl substituents on the triazole moiety in releasing N₂ gas, compounds 26b-26c containing alkylsubstituted triazoles may also be synthesized. Furthermore, these alkyne-containing compounds can be used for polymerization reactions to synthesize FR polymers. See Sykam et al., TtCS Omega 4(1): 1086-1094 (2019). Notably, the DSTPs 27a-27c can generate eight firesuppressing chemical motifs per molecule, including two P- and two S-radical scavengers, as well as four N₂ molecules. Due to their high heteroatom (N, P, and S) ratio compared to combustible hydrocarbons, these FRs are expected to exhibit an enhanced synergy effect, allowing for a significant reduction in flame retardant loading. This reduction in flame retardant loading may be advantageous for space exploration missions.

Scheme 7. Proposed Flame Retardants (DSTP)

FR polymers are crucial materials for ensuring the safety of astronauts’ apparel and equipment in space by protecting them from fire hazards. To synthesize these novel FR polymers, the proposed synthesis depicted in Scheme 8 may be employed.

Scheme 8. Photochemical Alkyne Polymerization

Initially, phosphorus pentasulfide 19 may react with propargyl alcohol 20 to produce dithiophosphoric acid 21. See Sinyashin et al., Phosphorus, Sulfur, Silicon Relat. Elem. 186(4): 997-998 (2011). Subsequently, this acid 21 may undergo a homocoupling reaction under photochemical conditions (CuCI, K₂CO₃, 440 nm) to yield the desired product 28 via a polymerization reaction. See Sagadevan and Hwang, Adv. Syn. Catal. 354(18): 3421-3427 (2012). The development of this direct homocoupling reaction of alkyne is particularly significant as it is a challenging reaction to achieve. Finally, a click reaction between dialkyne 28 with NaN₃ 22a may be used to synthesize the triazole-containing polymer 29 under photochemical conditions (390 nm). See e.g., Tasdelen and Yagci, Tetrahedron Lett. 51(52): 6945-6947 (2010); Khalili et al., Synlett 30: 2136-2142 (2019); Miao and Wang, Synthesis 2008: 363-368 (2008); McBride et al., Polymer 55(23): 5880-5884 (2014). These triazoles are designed to release inert N₂ gas, effectively suppressing fire propagation. This proposed synthetic route is supported by existing precedent in photochemical reactions. It is important to note that these polymer products are expected to have a wide range of applications.

Scheme 9. Photochemical Alkyne Polymerization (Alternative Reaction Route 1)

Scheme 10. Photochemical Alkyne Polymerization (Alternative Reaction Route 2 - thiol-ene reaction)

32 If the proposed synthetic pathway is unsuccessful (Scheme 8), an alternative route will be explored for the alkyne polymerization (Scheme 9). In this alternative approach, alkynyl dithiophosphoric acid 19 will react with bromobenzene 30 to form a dialkyne benzene motif 31 using the precedent photochemical reaction. See Sagadevan and Hwang, Adv. Syn. Catal. 354(18): 3421-3427 (2012). Next, a click chemistry between dialkyne benzene 31 and NaNs 22a will be explored to synthesize the desired triazole-containing polymer product 32. This alternative pathway will not only address potential challenges in alkyne polymerization but also offer novel polymers with unique properties. Additionally, if the first alternative reaction route (Scheme 9) is unsuccessful, a thiol-ene reaction will be investigated (Scheme 10). The alkynyl dithiophosphoric acid 19 will be treated with benzenedithiol 33 to form a bis-vinylthio benzene motif 32. See Fang et al., Macromolecules 53(24): 125-131 (2020). Furthermore, this thiol-ene reaction will be carried out with alkene analogs if the initial approach with alkynyl compounds is unsuccessful.

Burn Tests for FRs

To measure flame retardancy and evaluate the synergy effect, the burn test compares a control sample (methyl vinyl phosphonate) with the FR compounds 21 , 23a-23c, 24a-24c, 25, 26a-26c, and 27a-27c (Schemes 6-8). The fabric burn test may be used to assess the selfextinguishment and the charring of the fabrics. See Hajj et al., Polym. Degrad. Stab. 166: 86-98 (2019). Additionally, an epoxy resin burn test may be conducted to evaluate the flame retardancy in electrical and electronic applications. See Jian et al., Ind. Eng. Chem. Res. 55(44): 11520- 11527 (2016). These comprehensive tests may provide insights into the effectiveness of DSTPs in suppressing flames and protecting materials from fire hazards.

Claims

CLAIMS What is claimed:

1. A compound of formula (I), or a salt thereof,

wherein:

X¹ is O or S;

R¹, at each occurrence, is hydrogen, Ci-ealkyl, G^x, Ci-6alkylene-G^x, or Ci-ealkylene-OH, wherein:

G^x is a Ce-izaryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12- membered heterocycle, wherein G^x is optionally substituted with 1-5 substituents selected from the group consisting of cyano, C-i-ealkyl, -OCi-salkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

G^Y, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C₆-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^Y is optionally substituted with 1-5 substituents selected from the group consisting of cyano, C-i-ealkyl , -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

wherein:

R³, at each occurrence, is hydrogen, Ci_₆alkyl, G^z, Ci-ealkylene-G^z, or Ci-ealkylene-OH;

G^z, at each occurrence, is a C₆-i2aryl, a 5- to 12-membered heteroaryl, a C₆-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^z is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci ₆alkyl , -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

L¹ is Ci_₆alkylene, Ci_₆heteroalkylene or Cy¹, wherein:

Cy¹, at each occurrence, is a C6-i2arylene, a 5- to 12-membered heteroarylene, a Cs-scycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy¹ is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

, n:

G², at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G² is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci-ealkyl, -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl;

R⁴, at each occurrence, is Ci-ealkyl, G^w, Ci-ealkylene-G^w, or Ci-ealkylene-OH, wherein:

G^w, at each occurrence, is a C6-i2aryl, a 5- to 12-membered heteroaryl, a C6-i2carbocycle, or a 5- to 12-membered heterocycle, wherein G^w is optionally substituted with 1-5 substituents selected from the group consisting of cyano, Ci__ealkyl , -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl; and

L² is Ci-ealkylene, Ci-sheteroalkylene, or Cy², wherein:

Cy², at each occurrence, is a C6-i2arylene, a 5- to 12-membered heteroarylene, Cs-ecycloalkylene, or a 4- to 6-membered heterocyclylene, wherein Cy² is optionally substituted with 1-4 substituents selected from the group consisting of cyano, Ci-ealkyl , -OCi-ealkyl, cyclopropyl, Ci-4haloalkyl, and -OCi-4haloalkyl.

2. The compound of claim 1 , or a salt thereof, wherein X¹ is O.

3. The compound of claim 1 , or a salt thereof, wherein X¹ is S.

4. The compound of any one of claims 1-3, or a salt thereof, wherein R¹ is G^x or

Ci-6alkylene-G^x.

5. The compound of claim 4, or a salt thereof, wherein G^x is the C6-i2aryl.

6. The compound of claim 5, or a salt thereof, wherein the C6-i2aryl is phenyl.

7. The compound of any one of claims 1-6, or a salt thereof, wherein R² is G^Y.

8. The compound of claim 7, or a salt thereof, wherein G^Y is the C6-i2aryl.

9. The compound of claim 8, or a salt thereof, wherein the C6-i2aryl is phenyl.

10. The compound of any one of claims 1-9, or a salt thereof, wherein L¹ is Ci_6alkylene.

11. The compound of claim 10, or a salt thereof, wherein L¹ is Ci-3alkyene.

12. The compound of any one of claims, 1-9, or a salt thereof, wherein L¹ is Cy¹.

13. The compound of claim 12, or a salt thereof, wherein Cy¹ is the C₆_i2arylene.

14. The compound of claim 13, or a salt thereof, wherein the C6-i2arylene is phenylene.

15. The compound of any one of claims 1-14, or a salt thereof, wherein Z¹ is G¹.

16. The compound of claim 15, or a salt thereof, wherein G¹ is the C6-i2aryl.

17. The compound of claim 16, or a salt thereof, wherein the Ce-^aryl is phenyl.

18. The compound of any one of claims 1-14, or a salt thereof, wherein Z¹ is

19. The compound of claim 18, or a salt thereof, wherein R³ is hydrogen, Ci_₆alkylene-OH, G^z, or Ci-ealkylene-G^z.

20. The compound of claim 19, or a salt thereof, wherein R³ is Ci-salkylene-OH or Ci-3alkylene-G^z.

21. The compound of claim 19 or 20, or a salt thereof, wherein G^z is the C6-i2aryl.

22. The compound of claim 21 , or a salt thereof, wherein the C6-i2aryl is phenyl.

23. The compound of any one of claims 1-22, or salt thereof, wherein Y¹ is absent.

24. The compound of any one of claims 1-22, or a salt thereof, wherein Y¹ is

25. The compound of claim 24, or a salt thereof, wherein X² is O.

26. The compound of claim 24, or a salt thereof, wherein X² is S.

27. The compound of any one of claims 24-26, or a salt thereof, wherein L² is Ci-ealkyene.

28. The compound of claim 27, or a salt thereof, wherein L² is Ci-3alkyene.

29. The compound of any one of claims 24-26, or a salt thereof, wherein L² is Cy².

30. The compound of claim 29, or a salt thereof, wherein Cy² is the C6-i2arylene.

31. The compound of claim 30, or a salt thereof, wherein the C6-i2arylene is phenylene.

32. The compound of any one of claims 24-31 , or a salt thereof, wherein Z² is G².

33. The compound of claim 32, or a salt thereof, wherein G² is the C6-i2aryl.

34. The compound of claim 33, or a salt thereof, wherein the C6-i2aryl is phenyl.

35. The compound of any one of claims 24-31 , or a salt thereof, wherein Z² is

36. The compound of claim 34, or a salt thereof, wherein R⁴ is hydrogen, Ci-ealkylene-OH, G^w, or Ci-6alkylene-G^w.

37. The compound of claim 36, or a salt thereof, wherein R⁴ is Ci_₃alkylene-OH or Ci_₃alkylene-G^w.

38. The compound of claim 36 or 37, or a salt thereof, wherein G^w is the C6-i2aryl.

39. The compound of claim 38, or a salt thereof, wherein the C6-i2aryl is phenyl.

40. The compound of any one of claims 1-39, wherein the compound is selected from:

41. A method for suppressing fire, the method comprising applying the compound of any one of claims 1—40, or a salt thereof, to a fire or to the situs of a fire.

42. Use of the compound of any one of claims 1-40, or a salt thereof, for fire suppression.

43. A kit comprising the compound of any one of claims 1-40, or a salt thereof, and optionally, directions or instructions for use.