CA1095281A - Corrosion inhibited agricultural compositions - Google Patents

Abstract

CORROSION INHIBITED
AGRICULTURAL COMPOSITIONS

Abstract of the Disclosure Corrosion of metal surfaces contacted by aqueous agricultural compositions containing as an active ingredient an aminomethylenephosphonic acid, such as N-phosphonomethyl-glycine or an agriculturally acceptable salt or ester thereof is inhibited by the inclusion in the compositions of an inhibiting amount of a thiol compound or salt thereof.

Description

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CORR~SION INHIBITED
AGRICULT~R~L COMPOSITIONS

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This i~vention relates to the inhibition of metallic corrosion by aque~us agricultural compositions containing as an active agricultural ingredient an aminomethylenephosphonic acid, or an agriculturally acceptable salt or ester derivative : thereof. ~ore p~rtlcularly, this inven~ion re7a~es to the inhibition of corroslon of iron or zi~c surfaces contact~d by a~ueous ayricultural compositions wherein the actiYe agricultuxal ~ :
: ingredient, an aminomethylenephosphonic acid, or salt or ester derivatives thereo in the prese~ce of watex and in the absence o a~ inhibitor is corrvsi~e of such surfaces and evolves hydrogen gas. ~ccording to this invention, corrosion o iron '~
or zinc surfaces i~ inhibited by the inclusion in such agri-; cultural composition of a corrDsisn inhibiting amount o~ a - thLol compound or salt thereof as hereinafter described.
The ami~omethylanephosphonic acids employed in the compositions of this invention are encompassed by the ollowing : ~ormula ~oOC - C~ 2 ~ ~(3 wherei~ y and z are ~ach indi~idually 1 or 2, and x is 0 or 1, the sum of x, y and z bei.~g ~. A so use~ul in the compositions ~' o~ this invention are the agriculturally acceptable salt~ and esters o~ these acids~
The term "agricultural composition" as herein employed includes within its s~ope herbicidal and plant growth regulant ~`
: compositions. While such compositions are frequen~ly ~ormulated .~

. -2-as dry powder compositions and used in this form to dus~ plan~
foliage, more commonly they are formulated mto solutions, emulsions, suspensions or dispersions ~or wet application to plant foliage. These liquid formulations usually contain water and more water is added thereto at the tIme of application in order to dilute th~ concentration of the active ingredie~t in the formulation to le~els enabling khe application of predeterm m ed, controlLed amounts to plant foliage. Wormally, the dry powder formulations are generally non-corrosive of metal sur~aces whereas depending on ~he specific active ingredient in an aqueous liquid formulation and the surface active agent which may also be present in the formulation, mild to severe corrosion of metal surfac~s will oceur when contacted by the aqueous agricuLtural compositions.
The term " active agricultural ingredient" as herein employed is inclusive of any ingxedie~t ~unctioning as a plant phytotoxicant or a~ a plant growth regulant. The particular functio~ of an active lngredient can be that of a herbicide when appLied to the plant at moderate to high application rates and, on the other hand, function as a plant growth regulant at low to minute application rates. Such dual function capability is exhibited by some o~ the aminomethylenepho~phonic acids and their agriculturally acceptable saLts as described in U.S.
Pate~ts 3,455,675 and 3,556,762, the former being directed to phytotoxicant use and the lat er to plant ~rswth regulation.
The herbicidal activity of N-phosphonomethylglycine and its agriculturally acceptable salt and ester derivati~es is described in U.S. Patents 3,799,758; 3,863,407; 3,971,648 and 3,977,860.
P lant growth r egulant ut il ity f or N-pho sphcnomethylg lyc ine and its agriculturally acceptable salt and ester derivatives is described in U.S. Patents 3,853,530 arld 3,988,142.

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' The aqueous formulations of the aminomethylenephos-phonic acids, such as N-phosphonomethylglycine or derivatives thereof, and more particularly those formulations water-diluted to application le~els are corrosi~e to iron, steel or galvani ed metal surfaces of containers in which the concentrates or mlxtures are stored, and to steel or galvanized sur~aces of spraying equip~ent~ Hydrogen evolution is one aspect of the corrosion activity and can cause disruptive pressures in closed containers conta ming the aqueous agricultural compositions as well as constituting a ~ire hazard and explosion hazard.
:~ It is known that the application of various organic coatings, such as the phenolics, synthetic rub~er~, alkyds, vinyls as well as glass linLngs to metal surfaces is one : practical means for protecting or preventing corrosion o~ metal :~ surfaces but such coatings increase the cost of containers and other equipment used ~or application of herbicides or plant -~ growth regulants. Moreover, the integrity o~ such coatings is. subject to accidental or abrasive abuse under agricultural r application working conditions whereby the coating is mechanically ~ 20 abraded, scraped or otherwise detached ~rom the metal surace.
When this occuxs, the exposed metal surface is then readily attacked by the agricultural composition, and ~uch corrosion requently causes detachment or degradation o~ the protective coating material adjacent to the exposed metal surface thus acceLerating the overall corrosion o the equipment.
: Trabanelli et al reported on the performance of various .. .
organic sulfur compounds ~or inhibiting corrosion of iron immersed in sulfuric acid and noted that mercaptans were ; generally poor inhibitors of ixon corrosion and in some instances even functioned as corroslon stimulators (Chemical Abstxacts, Volume 7~, page 206, 58134~).

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It was thus most surprising to discoYer that thiol compour~s, e.g. mercaptans, as well as the ~mmonium and alkali metal thio salts vf inorganic polybasic acids and the thio : alkali metal salts are effective inhibitors of metal corrosion ~or aqueous agricultural compositions containing as an active agricultural ingrediellt an aminom~thylenephosph~nic acid, such as N-phosphonomethylglycine or the agriculturaLly acceptable saLt or ester derivatives thereof. Obviously, a satisfactory inhibitor of acldic corrosisn as measured by H2 evolution and metal coxrosion rate or a herbicidal compositioIl or plant :~ growth regulant composition should not deleteriously modify the agricultural activity of the composition. It was ound ~hat both re~e~tion of agricultural activity and adequate lnhi-bition o~ acidic corrosion ~as obtained by the addition to aqueous formulations of an aminomethylenephosphonic acid or the ag~iculturally acceptable de~ivatives of relati~ely small amounts of certain thio compounds, such as the alkane thiols and dithiols, alkali metal salts of the alkane thiols and dithiols, and the ammonium a~d alkali metal thio salts of poly~
20 basic inorganic acids, i.e., sulfuric acid and phosphoric acid.
Adequate inhibition of acidic corrosion as measured by H2 ; e~oluti.on can be obtained with a minimum o about 0.15 percent .; by weight o the thio compound on the weight o N-phosphonomethyl-glycine. To insure long term corrosion inhibition, it is pre-ferred to use the thio compound in amounts of 0.3 to 3 percent by weight on the weight of the N-phosphonomethylglycine or amino-methylenephosphonic acid ox derivatives thereof although the thio compound can be employ~d in amounts as high as 20 percent by weight . ~ased on the N~phosphonomethylglycine~ Not too infrequently, aqueous concentrates of the herbicidal or p.lant growth regulant com~
positions may be sto.red in the vendor's m~tal containers by the ;''' ,, _5.

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farmer for many months be~ore ~eing used and, hencel it is desirable to minimize corrosion o the co~tainer to the maximum extent in order to prevent any possible leakage of ~he concen-trate due to rusting of the container's metal walls. Amounts more than 5 percent by weight o~ the thio compound can be used if desired but no further commensurate advantage with respect -to corrosion is usually realized~
In the agriculkural formulations of this invention, one can employ anicnic, cationlc or non ionic surface-active agents. The surfactants which are useful in the compositions o this i~ention include those of the cationic, anionic, and non-ionic variety and also amine oxide, imidazolines, propoxylated ethoxylated ethylenediamine, quarternary ammonium compounds, betaine derivatives as well as ~mphoteric surfactants. Examples of the ~mine axides are lauryldim~thylamine oxide, cetyl-dimethylamine oxide, myristyldimethylamine oxide, bis(2-hydroxy-ethyl)coco2mi~e oxide and the like. Examples of quarternary :: , amin~ ~urfactants are cocotrimethylammonium chlorlde, alkylamLdo-ethyl aLkyl Lmidazolium methyl methosulfate. Examples of cationic surfactants ~re N,N-bis(2-hydroxyethyl~alkylamines where the alkyl groups are Cl~-C18 derived from tallow, N,N-bis(c~-ethyl-amega-hydroxy)-poly(oxyethylene)alkylamines having an a~erage of 3 oxyethylene groups, the alkyl beiny C14-C18 derived from tallow and (3-lauramidopropyl) trimethyl ammonium methyl sul~ate. Some anionic surface-active agents are the sulfated ~atty alcohols and the alkylarylsulfonates.
Representative of the sulfated fatty alcohols are the sodium or lower alkanol amine salts of the monoesters of sulfuric acid with N-aliphatic alcohols containing from 8 to 18 carbon atoms.
The alkylarylsulfona-tes are inclusive of the products derived rom the alkylation of an ar~matic hydrocarbon, e~g., ben~ene, . .

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naphthalene, diphenyl, diphenyl methane and phenoxybenzene, ~lfonation of the resulting al~ylated aromatic hydrocarbon and neutralization of the sulfonation product with NaOH or KOH, or with a primary or secondary amine.
Scme non-ionic surace-active agents are the ethoxyla~ed monoamines h~ving the structure (CH CH o) H
RN ~

(CH2 CH2 0 ) mH
wherein R is alkyl containing from about 8 to 16 carbon atoms and m is an integer from 2 to 25. Preferred anionic surface-active agents are the aLiphatic amine salts o~ monoalkyl (C8 C16) phenoxybenzene disulfonic acids.
All of the alkane thiols and dithiols containing ~rom

2 to 16 carbon atoms in the alkane moiety which have been exami~ed for corrosion inhibition were found e~fective in sub-stantially el~ninatirlg hydrogen evolution unde~ the test conditions herein described. The alkane thioLs particularly . those containi~s 8 or less carbon atom~ in the alkane moiety : have a p~onounced disagreeable odor. It is, therefore, preerable to employ alkane thiols having greater than 8 carbon .20 atoms in the alkane moiety. The higher alkane thiols are less odorous and, hence, are preerred in the interests o~ m m imizing worker and user discom~ort. The terms "alkane thiol" and ; "alkane dithiol" are intended to include ~he normal, secondary and tertiary isomers of these compounds. Represe~tative thiols and dithiols useful in the practice of this mvention include .; 1,2-ethanedithiolr ethanethiol, 1,3-propanedithiol, l-propanethiol, 2~propanethiol, 2-methyl-2-propanethiol, 1,4-butanedithiol, : l-butanethiol, 3-methyl-1-butanethiol, l-hexanethiol, 2-. hexanethiol, 3~hexanethiol, l-octanethiolt 2~octanethiol, .~

l-decanethiol, l-dodecanethiol and l-hexadecanethiol. Repre-sentative of the alkali metal salts of the alkane thiols and dlthiols are the sodium and potassium salts of l-ethanethiol l-butanethiol, l-hexanethiol and l-dodecanethiol. Represen-tative of the ammonium and al~ali metal thio salts o inorganic polybasic acids are ammonium thiosulfate, ammoni~m thiophosphate, ammonium thiocarbonate, sodium thiophosphate, potassium thio-phosphate, sodium dimethyldithioc~rbonate and s~dium thiocar-`~ bonate, which unliXe the alkane thiols do not co~tain in their structllre an -SH group but nevertheless do inhibit hydrogen evolution ~o a major exten~ from steel and zinc surfaces. One ; can also add compounds such as sodium sulfite to the thiosul~ate~
containlng compositions. Although no improvement m the corrosion inhibitio~ is obtained, this prevents dissociation o~ the ammonium thiosulfate in this composition.
The corrosion inhibited agricultural compositions o~
this invention, including concent~ates requiring dilution with water prior to plant applicatio~, contain from 5 to 95 par~s ~ by weight of an agriculkurally active agent, from about 5 to ;~ 20 95 parts by weight of an adju~ant comprising from 0.25 to 25 parts by weight of a non-ionic or anionic surface-active agent, ~rom 0 to 25 parts ky weight of a disp~rsant and rom about 4.5 to about 95 parts by weight of inert liquid ext~rlder, e.g~, - water and rom 0.1 to 2 parts by weight of a suitable thio compound~ The CGmpoSitiOns are prepared by admixing the active ingredient, the thio compound, the surface-~ctive agent and the liquid extender to provide liquid compositions in the form of solutions, suspensions~ dispexsions or emulsions. These liquid compositions immediately prior to application to plants are ~:.
diluted with water as required to obtain the desir~d erfects (herbicidal or plan. growth regulation).
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For determining hydrogen evolution~ concentrated liquid formulations were prepared according to the ollowing formula, all parts being by weight:
Monoisopropylamine salt41 parts of N-phosphonomethylglyc ine Surfactant 15 parts Inhibitor 1 part Wa~er 43 parts The li~uid concentrates wexe then diluted with water to actual spray use concentxations, i.e., 5 parts concentrate to 95 parts water and the diluted ormulations were tested for hydrogen evolutlon and corro s ion characteristics. T he d iluted concen-trates are noxmally more corrasive to metals than the concen-trates.
Hydrogen evolution ~as measured according to the following procedure. A metal coupon (mild steel or zinc) was horizontally supported within the mouth of an inverted plastic funnel, the support being toot.hpicks fastened to the rlm of `~ the fun~el. The dimensions of the steel coupon were 3.2 cm x .~ 20 1.4 cm x 0.6 cm; the z me coupons were 3.2 cm x 1.4 cm x 0.2 cm.
The funnel assembly with the supp~rted metal coup~n was placed into a 250 ml beaker, and enough dilute liquid agricultural formulation was paured into the beaker to completely submerge ~:l the ~unnel. A 100 mL aonical graduated glass centrifuge test tube was filled with the formulation, the end of the tube was then inger sealed, in~erted and placed over the neck of the Eunnel. Hydrogen gas evolving from attack on the metal coupon by the formulation ascends upwardly within the conical section of the funnel, then into the funnel neck a~d f inally into the test tube where it collects and displaces the liquid rormu-:- latian. The amount of collected gas is read directly off the ,i graduations on the test tube. The beaker and its contents axe g _ maintalned at room te~perature during the 24-hour test period.
The corrosion xate of the coupons was determined by i~nersing degreased rnild steel and zinc coupons in a given formulation at room temperature for 96 hours and then measuring weight }055 or galn of the coupon and extrapolating the result to an annual rate of corrosion.
Water-diluted concentrates prepared as described supra and contai~ing the monoisopropylam m e salt of N phosphono-methylglycina as the active a~ricultural ingredie~t were modi~ied by the inclusion o various thiol compounds and suractants as stated in subsequent Table I. Test data reported in Table I
was obta~ned at room temperature.

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* Surfactar~ "A" is a non-ionic type surfactant comprising an ethoxylated tallow amine having the structure ~CH2CH20)mH
RN
(C~I2CH20)mH
wherein m has an average vaLue of between 15 and 2 0 and R is alkyl having an average number of carbon atoms of about 17-18.
Suractant "B" is an anionic type surfactant compris~ng a mixture which averages about 8 0 percent or mor2 by weigh~ of a monoisopropylam~ne salt of a C10 alkyl phenoxy-: benzene disulfonic acid and up to about 20 percent by weight of dialkylated products of phenoxybenxene disulfonic acid~
Surfactant "C" is aLso a~ anionic ~urEactant and is . the triethanolamine salt of a (C8 -lO) alcohol sulfate;-(C8_l0) O5O2ON(CH2CH~OH)3.
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`i Inspection o the data presented in Table I shows i~ : that all the tested alkane thiols and dithiols (ExperLments . : 4~9 ) and the alkali metal salt o an alkane thiol (Experiment `~ 10) w~re 100 pexce~t effective in preventing evolution of hydrogen on test coupons o~ steel and zinc. Additionally, they exhibited the lowest corrosion rates o~ steel and æinc of all the te3ted inhibitor s being less corrosive than even distilled water per se (Exp~rim~nt 33).
~ Almo~t as efective as the thiol and dithiol~ and : alkali metal salts of the thiols in .reducing ~2 evolution was ~;~ ammonium thiosulfat~ (Experiments 16, 17 a~d 18), sodium thio-phosphate (Experi~ents 24, 25 and Z6), ~odium thioc~rbonate (ExperLments 30, 31 and 32) and sodium dimethyldithiocarbamate (Experiments 27, 28 and 29). Inhibition of corrosion, however, was only fair. The inhibition of H2 evolution i9 adequate ;. :
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-for safe storage of the ammoni~m thiosulfate, the sodium thiophosphate and the sodium thiocarbonate inhibited formu-lations in metal cans, tanks and other metal equipment.
Exper~ment 11 involved a herbicidal for.mulation containing ln ,~dditicn to the dodecanethiol inhibitor, the copresence o oxalic ac id in an amount equal to the weight of the isopropylamine salt of ~-phosphsnomethylglycine. The use of oxalic acid in herbicidal formuLations containing N phos-.
: phon~methylgly~cine or its derivatives is disclos~d in "Research Disclosure'l publication number RD15334, published January, 1977 by Industrial Opportunities Ltd~, Homewell-Havant-Hampshire P09 lEF, United Kinydom. ~ccording to said publication, when herbicidal formulations containing N-phosphonomethylglycine or its derivatives are diluted for applic~ion purposes with hard water, i. e. water conta m ing calcium or magnesium ions in the range of fxom 100 to 2000 or more parts by weight per , million parts by weight of water, the diluted formulations :
have dLmi~ished ~erbicidal activity as compared to the same ; formulations diluted with deionized water. The pubLication teaches the use o oxalic acid in hard water diluted herbicidal ; ~ormulation~ to restore the herbicidal activity and recommends ' the amount o~ oxalic acid be at least equivalent to S0 percent '~ of the calcium or magnesium ion to as much as 200 percent or more o such ions present in the diluting hard water. The weight ratio of the N-phosphonomethylglycine compound to oxalic ; acid ranges rom 1 to 10 parts by weight of the glycine compound ~ per 1 to 10 par~s by weight o~ oxalic acid. Oxalic acid is ^"J known to be corrosive of iron surfaces. As demonstrated by ; the data in Table I for Experimerlt 11, the nonmal corrosi~e action of oxalic acid on iron surfaces is satisfactorily inhibited when a thiol compound is present in the herbicidal .' `

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formulation.
That the use of thio compounds as L~hibitors of metaL
corrosion in herbicidal compositions containing an a}nine salt of W-phosphonomethylglyc m e does not significantly dLminish post-em~rgent herbicidal activity o~ the composition is quite evident from the data presented in Ta~le II on the post-emergence killing of quackgrass using formulations described in Table I, being Experiments 1 to 6 a~d 16 to 18. The experime~tal formulations were suitably diluted with water and applied to quackgrass plant~ established from vegetative propagules at a rate of 187 liters per hectare. Plants treated with the ~perImental Eormulations were placed in a greenhouse and obser~ed and recorded 12 days ater treatment with the herbic idal ormuLation.

Table II
. % Inhibitio~
Plant Responsa .~ (% Quackyrass :, Experiment Rate. 12 Days After - 20 Number Surfactant Inhibitor (Xg/h)* Treatment~
~ 1 A None 1.12 95 '. 0.56 95 0.28 40 , ...................................................................... .
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; 2 B None 1.12 99 : ~.5~ 99 ': 0.2~ So . 3 C None 1.12 99 0.28 60 ,- 30 4 A Dodecane- 1.12 98 thiol 0.56 98 0.28 4s B Dodecane- 1.12 99 thiol 0.56 98 .
0.28 70 ~5~

`~ Table II (Cont'd) % Xnhibition Plant Response (~ Quackgrass ExperimentRate 12 Days After ;~ Number Surfactant Inhibitor ~ T _ 6 C Dodecane~ 99 thiol 0.56 99 0.28 55 16 A ~mmonium 1.1~ 99 thiosul-; fate 0~56 98 : 0.~ 60 17 B Ammonium 1.12 ~9 :
;; thiosul-~ . fate 0.55 90 `~ 0.~8 60 . 18 C AImnonium 1 .12 9 9 . 2 0 thiosul-fate 0. S6 99 !~ .
~ . 0.28 40 : *Amount of monolsopropylami~e salt of N-phos-.. phonomethylglycine appliel per heckare.
In order to determine what effect on post-emergence herbicidal activity would result when the quantity o thiol , inhibitor i~ a herbicidal formulation containing the mono-isopropylamine salt o~ N-phosphonomethylglyc ine as the active ingxedient ~as increased many fold beyond that required or 30 adequate inhibition of hydrogen evolution and metal corrosion~ :
two control for~ulatio~s were pr~pared, one containing previously descxibed surfactant "A" and the other surfactant "C" according to the following formula, all parts being by weight:
Monoisopropylamine salt 41 paxts of N-phosphonome~hyl~lyc ine Surfactant 15 parts Water 44 parts The formulations were then diluted with water and sufficient additional sur~actant added to the diluted .
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formulations for the surfactant to constitute in each instance 1 percent by wsight of the diluted formulation. The amount of water used to prepare the diluted formulations was so adjusted :; that each diluted formulation could be spray applied to the plants at a common rate of 187 liters per hectare, even though the amount o~ active ingredient in each diluted formulation was mainta~ned at diff erent levels. The amount of t:hiol inhi-bitor in each diluted formulation was also adjusted to malntain a constant application o~ 4.48 kilograms per hectare when the ` 10 diluted formulation wa~ ~pray applied at 187 liters per hectare.
The diluted ~ormulations ~with and without ~nhibitor) were sprayed on 3 week old greenhouse grown Johnson grass and quackgrass and the ob~exvatio~s as to herbicidal efectiveness reported m Table III were made 28 days later.
. Table III
,......... Formulation Rate ~ Inhibition Surfactant Inhibitor (kg/h)* Joh~son Grass A Nolle 0.28 100 100 A None 0.14 65 98 A None 0. 07 35 25 A None 0. 085 0 20 ,,s~
: C None 0.28 95 100 C No~e 0.14 60 95 ~$~
C None 0.07 30 35 C None 0.035 .0 20 : A Octane- 0.28 85 100 ;- thiol A Octane- 0.14 55 65 thiol .~ 30 ~ Octan~- 0.07 30 15 thiol : A Octane- 0.035 0 0 thiol : ..
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Table II
Formulation Rate % Inhibition ~.
Surfact~;~;ibitor ~kg/h) * Johnson Grass Quack~rass __ C Octane- 0. 28 85 7 5 thiol C Octane- 0.14 35 45 ~hiol ;~
C Octal~e 0. 07 20 30 . thiol C Octane ~ a . 0350 o thiol A 1,12-3:)ode 0 . 2890 100 ~a~aed ithiol A 1,12-dode 0.14 60 90 canedithiol A 1,12-dode-- 0.07 15 25 canedithiol A 1,12~dode- 0~, 0350 15 canedithiol C 1/12-dode- 0.28 85 100 canedithiol C 1,12~dode- 0.14 35 70 ''.' c?nedithiol C 1~12-dode 0.07 20 40 ca~edi~hic: 1 C 1,12-dode-- 0. 035 û ?.0 caned ithio 1 ; *Amount of mo~oisopxopylamine salt of N-phos-phonometh~lglycine applied per h~ctare.
Although the amount o~ thiol inhibitor to ac~ive illgredient of the formulations described in Table III ranged .~ ~rom 164:1 at the 0.28 kg/h rate to a high of 131~:1 at the O. 03 5 kg/h rate of active ingredient, only a slight diminution of herbicidal effectiveness was observed and this occurr~l principally at xatios of thiol inhibitor to active ingredi~nt of more than 164 ~
Although the inhibitor ef f icacy OL various thio compounds was exemplif ied with the monoisopropylamine salt of N-phosphonomethylglycine in Table I, substantially similar .: --20--.

corrosion lnhib.ition can be expected when a thlo compound as herein disclosed is admixed with other salts and esters of ; N-p~osphonomethylglycine such as the alkali metal salts as are disclosed i.n U.S. Patent No. 3,977,8~0. Such salts and esters incLude but are not limited to the following:
monocyclohexylamine salt o N-phosphonomethylglycine di(methylamine) " " "
.. di(dimethylamine) di(ethylamine) . 10 di(n-propylamine) ~i di(morpholine) mono(stearlyamine) mono(tallowamine) mono(methylbutyl) mono(butylaml~e) n-di~utylamine n-octadecylamine methoxyethylamine .1 ethylened iamin8 " " 1-, ~, dipropanolamine chloroethylamine phenoxyethylamine mono(triethylamine) :: mono(diethylene~
triamine) monoisopropylamine monomorpholine ;; monoaniline monoethanolamine ~ 30 monodiethanolamine ~ "
- mono~mmonium monosodiwm ~ "
.~ disodium ~ , ~ -21-52~3~

trisodium salt of N-phosphon~methylglycine monopotassium salt of N-phosphonomethylglyci~e dipotassi~m " " "
tripotassium " " "
dilithium monosodi~m salt of ethyl N-phosphonomethylglyclnate monosodium salt of chloroethyl N-phosphonomethylglycinate m~thyl N-phosphonomethylglyclnate dimethyl N-phosphonomethylglycinate ethyl W-phosphonome~hylglycinate 2-chlorcethyl N-phosphonomethylglycinate n-propyl N-phosphonomethylglycinate ; n-butyl N-phosphonomethylglycinate n-hexyl N-phosphonomethylglycinate .;
cyclohexyl N-phosphonomethylglycinate n-octyl N-phosphonomethylglyclnate n~decyl N-phosphonomethylglycinate n-dodecyl N-phosphonomethylglycinate Repre~entative but no~ inclusive of the aminophosphonates described in ~.S. Patent No. 3,S56,762 and which in aqueous for-mulations cause corrosion of metal surfaces are the following compounds:
nitrilodi(acetic acid)(m~thylphosphonic acid) tris(dimethylammonium)Lminoacetate N-methylphosphonate : trisodium iminodiacetate N-methylphosphonate tetra(dimethyl~lmoniu~l)aminoacetate N,N~bis-methylphosphonate 2,2'-bisphosphonomethyliminoacetlc acid dipotassium iminodiacetate N-methyl-O-potassium~O-ethyl-phosphonate Data on hydxogen evolution and corrosion inhi-bition by dodecanethiol for several agricultuxal formulations conta m ing as an active ingredient N-phosphonomethyl-glycLne or salt or ester derivative thexeof or an -2~-aminophosphonat~ compound are tabulated in Table rv. The formu~
lations U5ed in Table IV were of two types, li~uid and dry powder. Experiments 34 and 3 5 were co~ducted on liquid formu-lations o~ the following compositions, all parts being by weigh~:

;~' ~
-:~ Di- (monoisopropylamine) salt of 41 N-phosphonomethylglycine Surfactant "C" 15 Water 44 , 10 ~
Di ~monoisopropylamine salt of 41 N ~phosphonomethylglyc ine Surfactarlt " C" 15 Dodecanethiol.

Water 43 The dry powder ormulations, Experiments 36 to 47 had - the following compositions, alL par~s being by weight:

:~ Disodium salt o~ N-~hosphono- 78 methylglycine Surf actant " D "

~; Urea 20 Disodium salt o~ N-phosphono-methylglycine 78 Surfactant "D " 2 Dodecanethiol - 9 . 2 - Urea Complex (2.1 parts thiol) (7.1 parts urea) Urea 10.9 .~ ~
Diammonium salt of N-phosphono- 74.6 ~ me~hylglycine .~ Sur~actant "D" 2 Urea 23.4 ., , . -23-~5 .

. .
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Diar~nonium salt o~ N-phosphono- 74 . 6 ;~ methylglyc ine Surfactant "D " 2 Dod e~ ane~hiol - 9 . 2 UreA Complex (2.1 parts thiol) (7.1 parts urea) Urea 14 . 3 !, ~ =
10Dipotassium salt of N-phosphono- 89.7 methylyl yc irle Surfactant "D " 2 - Urea ~ 3 Dipotassium salt of N phosphono- 87 . 7 methylglyc ine Surfactant "D "
;~ Dodecanekhiol - 9. 2 Urea Compl ex ~ 2 .1 parts thiol ) (7.1 parts urea) ~rea 1. 2 N-phosphonomethylglycine 64 . 4 Surfactant "D " 2 .
Urea 33. 6 ~eriment 43 N-phosphonomethylglycine 64 . 4 Surfactant "I:) " 2 ,:, i Dodecanethiol - 9 O 2 : 3 0 Ur ea Compl ex ( 2 . 1 part s t hio 1 ) (7.1 parts uxea) Urea 22~ 4 :: 2, 2 '-bisphosphonomethyl~mino- 51 ac et ic ac id Surf actarlt "D " 2 IJxea ~~ - - 47 ~-~
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Experiment 45 2,2' bisphosphonomethylimino- 51 ac etic ac id Surfactant "D" 2 Dodecanethiol - 9.2 Urea Complex (2.1 parts thiol) (7.1 parts urea) Urea 37.9 ,, E~
:
`. 10 Monoethyl ester of N~phosphono- 8 6 . 3 methylglycine Surfactant "~ " 2 Urea 11.7 Monoethy~ ester of N-phosphono- 8 6 .
methylglycine ~Dodecanethiol - 9.2 Urea Complex (2.1 part 9 thiol) (7 .1 parts urea ) Urea 2.5 Surfactant "C " is as previously described .
Suxfactant "D", an anionic sur~actant, is a complex of sodium dioctyl sulfosuccinate.
Experiments 34, 36, 38, 40, 42 and 44 were control experiments co~taining no inhibitor. Experiments 37, 39, 41, - 43 and 45 were dry solid formulations containing a comple~ of urea and dodecanethiol. Alkane thiols such as dodecanethiol are substantially water insoluble and although a surfactant is ~n aid in effecting dispersion of the thiol in an aqueous formulation, it has been found that a solid complex of urea and ~, a straight chain alkane thiol when mixed with a dry mixture of the active ingr~dient and surfacta~t enhances dispersibility of the thiol in aqueous agricultural formulations and minimizes separation o~ the thiol comFonent. The complex dissolves readily in water to reform the urea and the thiol with the : .

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~hiol being finely dispersed a~d remai~ing in suspension. The urea-thiol complex is prepared by dissol~ing the alkane thiol in a solvent such as isoctane and mixing the solution at room temperature with su~icient urea prewetted with methanol until the urea increases in volume; the reaction is slightly exothermic.
The molar ratio of urea ~o alkane thiol used to form the complex is proportional to the thiol's chain length being at least 6~1 for alkane thiols containing 6 carbon atoms, 10:1 moles for dcdecanethiol and about 16:1 for thiols of 16 carbon atoms.
~he solvents used in the reaction are removed by washi~g and drying. The corrosion ex~erlments reported in Table rv were all co~ducted with the liquid as well as the solid type formulations having b~en diluted with water in amount corresponding to normal : application dilutions, namely a dilution that would apply per hect~re 2.24 kilograms of active ingredient (calculated as N-phosphonomethylglycine or 2, 2 ' -bisphosphonomethylLminoacetic acid) at a spraying rate of 187 liters per hectare~

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; Thiols other tnan th~ alkane thiols have also been found effective in inhibiting corrosion by aqueous agricultural compositions as herein contemplated. Such thiols include the aromatic and cycloaliphatic thiols. For exa~lple, 2~ inhibiting amounts of p-chlorothiophenol, 2-ami~othiophenol, 2-furano-methanethiol, toluenethiol, 2 benzoxaz~lthiol and mercaptoben-zothiazole enable a dry disodium salt of N-phosphonomethylglycine formulation corresponding to Experiment 36 when diluted with water reduces the hydrogen evolution and the metal corrosion rate. SiMilar corrosion inhibition was obtained when fertili~er diluent i~gredients other than urea were included in the agricultural formulations, as, for example, monoammonium phosphate and disodi.um phosphate.
Although the inven~ion is described with respect to speciic modi~ications, the details thereo are not to be construed as limitations except to the extent indicated in the following cla~ms.

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Claims (24)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An agricultural composition comprising an active ingredient selected from the aminomethylenephosphonic acids of the formula wherein y and z are each individually 1 or 2, and x is O or 1, the sum of x, y and x being 3, and the agriculturally acceptable salts and esters thereof and a metal corrosion inhibiting amount of a thio compound selected from the alkane thiols and dithiols having from 2 to 16 carbon atoms in the alkane moiety, aromatic thiols, cycloaliphatic thiols, the alkali metal salts of said thiols and dithiols and the ammonium and alkali metal thio salts of polybasic inorganic acids.

2. An agricultural composition according to Claim 1 wherein the alkane thiol is l-dodecanethiol.

3. An agricultural composition according to Claim 1 wherein the alkane thiol is l-octanethiol.

4. An agricultural composition according to Claim 1 wherein the alkane thiol is l-hexadecylthiol.

5. An agricultural composition according to Claim 1 wherein the ammonium thio salt is ammonium thiosulfate.

6. An agricultural composition according to Claim 1 wherein the ammonium thio salt is ammonium thiophosphate.

7. An agricultural composition according to Claim 1 wherein the amount of the thio compound is between 0.15 and 3 percent by weight of the active ingredient.

8. A agricultural composition according to Claim 1 containing between 1 and 10 parts by weight of oxalic acid per 1 to 10 parts by weight of an amine salt of N-phosphono-methylglycine.

9. A dry agricultural composition according to Claim 1 wherein the thiol is a straight chain alkane thiol and complexed with urea.

10. An agricultural composition according to Claim 1 wherein the active ingredient is N-phosphonomethylglycine.

11. An agricultural composition according to Claim 1 wherein the active ingredient is 2,2'-bisphosphonomethylimino-acetic acid.

12. An agricultural composition according to Claim 1 wherein the active ingredient is a salt of N-phosphonomethyl-glycine.

13. An agricultural composition according to claim 12 wherein the salt is the monoisopropylamine salt of N-phosphono-methylglycine.

14. A method for inhibiting corrosion of iron and zinc metal surfaces in contact with an aqueous agricultural compo-sition comprising water, a surfactant and an active ingredient selected from the aminomethylenephosphonic acids of the formula wherein y and z are each individually 1 or 2, and x is 0 or 1, the sum of x, y and z being 3, and the agriculturally acceptable salts and esters thereof which comprises adding to the compo-sition an inhibiting amount of a thio compound selected from alkane thiols and dithiols having from 2 to 16 carbon atoms in the alkane moiety, aromatic thiols, cycloaliphatic thiols, the alkali metal salts of said thiols and dithiols and the ammonium and alkali metal thio salts of polybasic inorganic acids.

15. A method in accordance with Claim 14 wherein the alkane thiol is l-dodecanethiol.

16. A method in accordance with Claim 14 wherein the alkane thiol is l-octanethiol.

17. A method in accordance with Claim 14 wherein the alkane thiol is l-hexadecylthiol.

18. A method in accordance with Claim 14 wherein the thio compound is ammonium thiosulfate.

19. A method in accordance with Claim 14 wherein the thio compound constitutes between 0.15 and 3 percent by weight of the aminomethylenephosphonic acid, or the salts or esters thereof.

20. A method in accordance with Claim 14 wherein the thiol is an alkane thiol complexed with urea and the urea-thiol complex is admixed with a dry mixture of the active ingredient and the surfactant before dispersing in water.

21. A method which comprises contacting a plant with a phytotoxic amount of an aqueous herbicidal composition comprising an amine salt of N-phosphonomethylglycine, a sur-factant and a metal corrosion inhibiting amount of a thio compound selected from alkane thiols and dithiols having from 2 to 16 carbon atoms in the alkane moiety, aromatic thiols, cyclo-aliphatic thiols, the alkali metal salts of said thiols and dithiols and the ammonium and alkali metal thio salts of poly-basic inorganic acids.

22, A method according to Claim 21 wherein the thio compound constitutes between 0.15 and 3 percent by weight of the amine salt of N-phosphonomethylglycine.

23. A method according to Claim 21 wherein the amine salt is the monoisopropylamine salt of N-phosphonomethylglycine.

24. A method which comprises contacting a plant with a plant growth regulating amount of an aqueous plant growth regulating composition comprising a compound selected from the aminomethylenephosphonic acids having the formula wherein y and z are each individually 1 or 2, and x is O or 1, the sum of x, y and z being 3, and the agriculturally acceptable salts and esters thereof, a surfactant, and metal corrosion inhibiting amount of a thio compound selected from the alkane thiols and dithiols having from 2 to 16 carbon atoms in the alkane moiety, aromatic thiols, cycloaliphatic thiols, the alkali metal salts of said thiols and dithiols and the ammonium and alkali metal thio salts of polybasic inorganic acids.