HK1168589A - Improved process for the preparation of halo-olefins - Google Patents

Description

Improved process for preparing halogenated olefins

Background information

FIELD OF THE DISCLOSURE

This disclosure relates generally to methods for the synthesis of fluorinated olefins.

Description of related Art

Since the montreal protocol mandates the gradual cessation of the use of ozone depleting chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs), the fluorocarbon industry has been working for the past several decades to find alternative refrigerants. A solution for many applications is the commercialization of Hydrofluorocarbon (HFC) compounds for use as refrigerants, solvents, fire extinguishing agents, blowing agents and propellants. These novel compounds, such as HFC refrigerants, HFC-134a and HFC-125, which are currently most widely used, have zero ozone depletion potential and therefore are not affected by the current regulatory phase out due to the montreal protocol.

In addition to the ozone depletion problem, global warming is another environmental problem associated with many of these applications. There is therefore a need for compositions that meet both low ozone depletion standards and have low global warming potentials. It is believed that certain hydrofluoroolefins meet both goals. There is therefore a need for a process that can provide for the production of halogenated hydrocarbons and fluoroolefins that do not contain chlorine while having low global warming potential.

Summary of The Invention

Described herein is a process for preparing a halogenated olefin, the process comprising contacting a halogenated hydrocarbon with a metal dehalogenating agent in a solvent in the presence of a phase transfer catalyst under conditions sufficient to dehalogenate the halogenated hydrocarbon to produce a product stream comprising the halogenated olefin. In one embodiment, the halogenated hydrocarbon is trifluorotrichloroethane and the halogenated alkene is chlorotrifluoroethylene.

The foregoing summary, as well as the following detailed description, is intended to be exemplary and illustrative only, and is not intended to be limiting, as defined by the appended claims.

Detailed Description

Disclosed is a process for preparing a halo-olefin, the process comprising: contacting a halogenated hydrocarbon with a metal dehalogenating agent in a solvent in the presence of a phase transfer catalyst under conditions sufficient to dehalogenate the halogenated hydrocarbon to produce a product stream comprising the halogenated olefin. In one embodiment, the halogenated olefin is selected from the group consisting of chlorotrifluoroethylene, tetrafluoroethylene, difluoroethylene, and vinyl chloride. In one embodiment, the halogenated hydrocarbon is selected from trichlorotrifluoroethane, dichlorotetrafluoroethane, dichlorodifluoroethane, and trichloroethane. In one embodiment, the halogenated alkene is chlorotrifluoroethylene and the halogenated hydrocarbon is trichlorotrifluoroethane. In one embodiment, the presence of the phase transfer catalyst increases the yield of the halogenated olefin and reduces the amount of side reaction products.

Many aspects and embodiments have been described above and are merely exemplary and not limiting. After reading this description, the skilled person will realize that other aspects and embodiments are possible without departing from the scope of the invention.

Other features and advantages of any one or more embodiments will become apparent from a reading of the following detailed description and the claims.

Before addressing details of the embodiments described below, certain terms are defined or clarified.

For the purposes of the present invention, a phase transfer catalyst is a substance which promotes the transfer of ionic compounds (e.g. reactants or components) into the organic phase. The phase transfer catalyst facilitates the reaction of these dissimilar and incompatible components. Although various phase transfer catalysts may function in different ways, their mechanism of action is not a determining factor in their utility in the present invention.

As used herein, a metal dehalogenating agent refers to a metallic element that, when reacted with a halogenated hydrocarbon, reductively removes a halogen atom from adjacent carbon atoms, forming a double bond between two adjacent carbon atoms.

In one embodiment, the metal dehalogenating agent is a metal selected from the group consisting of tin, magnesium, zinc, iron, and aluminum. In one embodiment, the metal dehalogenating agent is zinc. Such agents are generally available in different grades and different particle sizes. Generally, smaller particle sizes have a greater amount of surface area, and correspondingly faster reaction rates. Conversely, smaller particle sizes are generally more difficult to handle and transfer (although particle size is not particularly critical). In one embodiment, the metal dehalogenating agent is sieved through a 40 mesh screen to leave a particle size of up to 420 microns. In another embodiment, the metal dehalogenating agent is sieved through a 100 mesh screen to leave a particle size of up to 150 microns.

In one embodiment, the metal dehalogenating agent is mixed with a solvent to form a heterogeneous mixture. In another embodiment, the metal dehalogenating agent is mixed with a solvent to form a homogeneous mixture. In one embodiment, the solvent should be miscible with the halogenated hydrocarbon feedstock and should also be capable of dissolving the metal halide formed in the dehalogenation reaction. In one embodiment, the solvent is selected from the group consisting of methanol, ethanol, acetonitrile, and tetrahydrofuran. In another embodiment, the solvent is methanol.

In one embodiment, an equimolar amount of metal dehalogenating agent relative to the halogenated hydrocarbon is used. In another embodiment, 1.05 moles of metal dehalogenating agent per mole of halogenated hydrocarbon are used. In another embodiment, 1.1 moles of metal dehalogenating agent per mole of halogenated hydrocarbon are used. In another embodiment, 0.9 moles of metal dehalogenating agent per mole of halogenated hydrocarbon are used.

In one embodiment, the halogenated hydrocarbon feedstock may be dehalogenated under conditions suitable to produce halogenated olefins. In one embodiment, the dehalogenation reaction is carried out at a temperature between 50 ℃ and 150 ℃. In another embodiment, the dehalogenation reaction is carried out at a temperature between 50 ℃ and 100 ℃.

In one embodiment, the dehalogenation reaction is carried out in a batch-type process. In another embodiment, the dehalogenation reaction is carried out in a continuous type process. In one embodiment of a batch type process, a slurry of metal dehalogenating agent is introduced into the reactor to initiate the reaction. The slurry is mixed with the halocarbon, the metal dehalogenating agent and the solvent prior to, simultaneously with or after addition of the one or more process components. In another embodiment, the slurry is mixed using any convenient means prior to the addition of the halogenated hydrocarbon.

The phase transfer catalyst may be ionic or neutral and is selected from crown ethers, methyl ethers, ethyl ethers, propyl ethers, butyl,Salts, cryptates and polyalkylene glycols and derivatives thereof, and mixtures thereof. An effective amount of phase transfer catalyst should be used to achieve the desired reaction; this amount can be determined by limited experimentation after the selection of reactants, process conditions and phase transfer catalyst. The effective amount may vary depending on the particular type of phase transfer catalyst being applied.

Crown ethers are cyclic molecules in which the ether groups are linked by dimethylene bonds; the compounds form molecular structures that are believed to "accept" or retain alkali metal ions in the hydroxide, thereby facilitating the reaction. Particularly useful crown ethers include 18-crown-6, especially in combination with potassium hydroxide; 15-crown-5, especially in combination with sodium hydroxide; 12-crown-4, especially in combination with lithium hydroxide. Derivatives of the above crown ethers are also useful, such as dibenzo-18-crown-6, dicyclohexyl-18-crown-6 and dibenzo-24-crown-8 and 12-crown-4. Other polyethers that are particularly useful for alkali metal compounds, especially lithium, are described in U.S. patent 4,560,759, which is incorporated herein by reference to the extent permitted. Other compounds similar to crown ethers and useful for the same purpose are different in that they are derived from othersCompounds of the type in which an electron donor atom, especially N or S, replaces one or more oxygen atoms, e.g. hexamethyl- [14]-4, 11-diene N₄。

Salts include quaternary phosphonium salts useful as phase transfer catalysts in the process of the inventionSalts and quaternary ammonium salts; such compounds may be represented by the following formulas I and II:

R¹R²R³R⁴P⁽⁺⁾X’^(-)(I)

R¹R²R³R⁴N⁽⁺⁾X’^(-)(II)

wherein R is₁、R₂、R₃And R₄May be the same or different, each is an alkyl group, an aryl group or an aralkyl group, and X' is a halogen atom. Specific examples of these compounds include tetramethylammonium chloride, tetramethylammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride (commercially available under the trade names Aliquat 336 and Adogen 464), tetra-n-butylammonium chloride, tetra-n-butylammonium bromide, tetra-n-butylammonium hydrogen sulfate, tetra-n-butylammonium chlorideTetraphenyl bromidesTetraphenyl chlorideTriphenylmethyl bromideAnd triphenylmethyl chlorideAmong them, benzyltriethylammonium chloride is preferably used under strongly alkaline conditions. Other useful compounds in this class include those that exhibit high temperature stability (e.g., up to about 200 degrees Celsius), and include 4-dialkylaminopyridinesSalts, e.g. tetraphenylarsonium chloride, bis [ tris (dimethylamino) phosphine]Ammonium chloride and tetrakis [ tris (dimethylamino) phosphinimine]Chlorination ofThe latter two compounds are reported to be stable also in the presence of hot concentrated sodium hydroxide and are therefore particularly useful.

The polyalkylene glycol compound useful as a phase transfer catalyst may be represented by the following formula:

R⁶O(R⁵O)_tR⁷(III)

wherein R is₅Is alkylene, R₆And R₇May be the same or different, each is a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, and t is an integer of at least 2. Such compounds include, for example, glycols (such as diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol and tetramethylene glycol) and monoalkyl ethers (such as monomethyl ether, monoethyl ether, monopropyl ether and monobutyl ether of such glycols), dialkyl ethers (such as tetraethylene glycol dimethyl ether and pentaethylene glycol dimethyl ether), phenyl ethers, benzyl ethers and polyalkylene glycols (such as polyethylene glycol (average molecular weight of about 300) dimethyl ether, polyethylene glycol (average molecular weight of about 300) dibutyl ether and polyethylene glycol (average molecular weight of about 400) dimethyl ether). Among them, preferred is the compound wherein R₆And R₇All are alkyl, aryl or aralkyl compounds.

Cryptates are another class of compounds useful as phase transfer catalysts in the present invention. These are provided by electron supply means including appropriate spacingThree-dimensional polymeric macrocyclic chelants formed by a bridge structure connected by a chain of atoms. For example, from a nitrogen bridgehead with (- -OCH)₂CH₂- -) chain groups bind the resulting bicyclic molecule, such as 2.2.2-cryptate (4, 7, 13, 16, 21, 24-hexaoxa-1, 10-diazabicyclo- (8.8.8) hexacosane; available under the trade names cryptand 222 and Kryptofix 222). The donor atoms in the bridge may all be either O, N or S, or the compound may be a hybrid donor macrocycle, wherein the bridge chain comprises a combination of such donor atoms.

It is also possible to use combinations of phase transfer catalysts from one of the abovementioned classes, and combinations or mixtures of phase transfer catalysts from more than one class, for example crown ethers andor from a combination or mixture of two or more classes of phase transfer catalysts, e.g. quaternary phosphoniumSalts and quaternary ammonium salts, and crown ethers and polyalkylene glycols.

In one embodiment, the phase transfer catalyst isAnd (3) salt. In another embodiment, the phase transfer catalyst is selected from the group consisting of tetramethylammonium chloride, tetramethylammonium bromide, benzyltriethylammonium chloride, methyltrioctylammonium chloride, tetra-n-butylammonium bromide, tetra-n-butylammonium bisulfate, tetra-n-butylammonium chlorideTetraphenyl bromidesTetraphenyl chlorideTriphenylmethyl bromideAnd triphenylmethyl chlorideIn another embodiment, the phase transfer catalyst is methyltrioctylammonium halide. In another embodiment, the phase transfer catalyst is tetrabutylammonium bromide.

In one embodiment, an effective amount of phase transfer catalyst is 1 gram of tetrabutylammonium bromide per 50 grams of halogenated hydrocarbon. In another embodiment, an effective amount of phase transfer catalyst is 1 gram of tetrabutylammonium bromide per 100 grams of halogenated hydrocarbon. In another embodiment, an effective amount of phase transfer catalyst is 1 gram of tetrabutylammonium bromide per 200 grams of halogenated hydrocarbon. In another embodiment, an effective amount of phase transfer catalyst is 1 gram of tetrabutylammonium bromide per 25 grams of halogenated hydrocarbon.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, unless expressly stated to the contrary, "or" refers to an inclusive "or" and not to an exclusive "or". For example, the condition a or B is satisfied in any of the following cases: a is true (or present) and B is spurious (or absent), a is spurious (or absent) and B is true (or present), and both a and B are true (or present).

Also, the use of "a" or "an" is used to describe elements and components described herein. This is done merely for convenience and to provide a general sense of the scope of the invention. Such description should be understood to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

The use of group numbers corresponding to columns in the periodic Table of elements is described in the "New nomenclature" convention described in "CRC Handbook of chemistry and Physics", 81 th edition (2000-2001).

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of embodiments of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety, unless a specific paragraph is cited. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Examples

The concepts described herein will be further described in the following examples, which do not limit the scope of the invention described in the claims.

Example 1

Example 1 demonstrates the conversion of CFC-113 to Chlorotrifluoroethylene (CTFE) with zinc.

16.4g (0.25mol) of zinc powder, 50g of methanol and 46.9g (0.25mol) of CFC-113 were charged into a 210mol of Hastelloy oscillating tube. The zinc powder had been activated under nitrogen, dried in a drying oven, and sieved through a 40 mesh screen to remove large particle agglomerates. Then using N₂The reactor is pressurized and N is added₂And emptying twice. The reactor was then cooled to-70 ℃ and the vacuum was pulled gently. The reaction mixture was heated and stirred at 65 ℃ for 3 hours. The reactor pressure increased from 179psig to 227psig at 65 ℃. After the reactor was cooled to room temperature, the vapor phase of the reaction was analyzed by GC-MS. Data are reported as GC-MS area percent (integration does not include methanol). Analysis of the liquid phase in the reactor showed 113The conversion was 90.6%.

Table 1 (steam phase)

Compound (I)		GC-MS area%
			CF2＝CH2	1, 1-difluoroethylene	0.056
CF2＝CFH	Trifluoroethylene	1.25
			CF2＝CFCl	Chlorotrifluoroethylene (CTFE)	97.124
CF2＝CHCl	1-chloro-2, 2-difluoroethylene	0.024
			CClF2-CClHF	1, 2-dichloro-1, 1, 2-trifluoroethane	0.772
CF2ClCFCl2	1, 1, 2-trichloro-1, 2, 2-trifluoroethane (CFC-113)	0.764
			Is unknown		0.01

Example 2

Example 2 demonstrates the conversion of CFC-113 to CTFE with zinc in the presence of tetrabutylammonium bromide (TBAB).

To a 210mol Hastelloy oscillating tube were added 16.4g (0.25mol) of zinc powder, 50g of methanol, 46.9g (0.25mol) of CFC-113, and 1g of TBAB. The zinc powder had been activated under nitrogen, dried in a drying oven, and sieved through a 40 mesh screen to remove large particle agglomerates. Then using N₂The reactor is pressurized and N is added₂And emptying twice. The reactor was then cooled to-70 ℃ and the vacuum was pulled gently. The reaction mixture was heated and stirred at 65 ℃ for 3 hours. The reactor pressure increased from 205psig to 229psig at 65 ℃. After the reactor was cooled to room temperature, the vapor phase of the reaction was analyzed by GC-MS. Data are reported as GC-MS area percent (integration does not include methanol). Liquid phase analysis of the reactor showed that the conversion of CFC-113 was 98.5%.

Table 2 (steam phase)

Compound (I)		GC-MS area%
			CF2＝CH2	1, 1-difluoroethylene	0.009
CF2＝CFH	Trifluoroethylene	0.28
			CF2＝CFCl	Chlorotrifluoroethylene	99.065
CF2＝CHCl	1-chloro-2, 2-difluoroethylene	0.045
			CClF2-CClHF	1, 2-dichloro-1, 1, 2-trifluoroethane	0.49
CF2ClCFCl2	1, 1, 2-trichloro-1, 2, 2-trifluoroethane	0.112

It should be noted that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity is not required, and that one or more other activities may be performed in addition to those described. Further, the order in which the acts are listed are not necessarily the order in which they are performed.

In the foregoing specification, various concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.

It is appreciated that certain features which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Furthermore, recitation of ranges of values herein are inclusive of each value recited within the range.

Claims (11)

1. A process for preparing a halo-olefin, the process comprising: contacting a halogenated hydrocarbon with a metal dehalogenating agent in a solvent in the presence of a phase transfer catalyst under conditions sufficient to dehalogenate the halogenated hydrocarbon to produce a product stream comprising the halogenated olefin.

2. The process of claim 1 wherein the halogenated olefin is selected from the group consisting of chlorotrifluoroethylene, tetrafluoroethylene, difluoroethylene, and vinyl chloride.

3. The process of claim 2 wherein the halogenated olefin is chlorotrifluoroethylene.

4. The process of claim 1 wherein the halogenated hydrocarbon is selected from the group consisting of trichlorotrifluoroethane, trichloroethane, dichlorodifluoroethane and dichlorotetrafluoroethane.

5. The process of claim 4 wherein the halogenated hydrocarbon is trichlorotrifluoroethane.

6. The process of claim 1 wherein the dehalogenating agent is selected from the group consisting of zinc, tin, magnesium, iron and aluminum.

7. The process of claim 6 wherein the dehalogenating agent is zinc.

8. The process of claim 1 wherein the phase transfer catalyst is selected from the group consisting of crown ethers, and mixtures thereof,Salts, cryptates and polyalkylene glycols and derivatives thereof, and mixtures thereof.

9. The process of claim 8 wherein the phase transfer catalyst isAnd (3) salt.

10. The process of claim 8 wherein the phase transfer catalyst is a quaternary ammonium salt.

11. The method of claim 10, wherein the quaternary ammonium salt is tetrabutylammonium bromide.