GB2055827A

GB2055827A - Process for preparing chlorothiolformates

Info

Publication number: GB2055827A
Application number: GB8024185A
Authority: GB
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1979-07-25
Filing date: 1980-07-24
Publication date: 1981-03-11
Also published as: NL177308B; FR2462423B1; FR2462423A1; IT8068189A0; DE3025654C2; NL8501007A; IT1141615B; NL8002496A; DE3025654A1; GB2055827B

Abstract

Chlorothiolformates are prepared by reacting a mercaptan with phosgene in the presence of a catalytic amount of secondary anline, a secondary amine hydrochloride, a quaternary ammonium salt or a basic anion exchange resin. Preferably the resin has quaternary ammonium functionality.

Description

SPECIFICATION Process for preparing chlorothiolformates The catalytic preparation of alkyl and phenyl chlorothiolformates by reaction of the appropriate mercaptan, e.g., an alkyl or phenyl mercaptan, with phosgene has been described in the patent literature. In the absence of catalyst, the reaction can require several days to achieve substantially complete reaction. Exemplary of U.S. Patents directed to the preparation of chlorothiolformates are U.S. Patents 3,165,544, 3,093,537, 4,012,405 and 4,119,659, which describe the use of activated carbon for the preparation of alkyl and phenyl chlorothiolformates, and U.S. Patent 3,299,114, which describes the use of tertiary amines and heterocyclic amine compounds to catalyze the aforesaid reaction.

The present invention relates to the use of a catalyst for the reaction of a mercaptan with phosgene to produce chlorothiolformates. The reaction can be represented by the following balanced equation: (1) R-SH+COCl2

Certain chlorothiolformates, e.g. ethyl chlorothioformate, have been found useful as pesticides See for example U.S. Patent 3,093,537. In addition, chlorothiolformates, e.g. ethyl chlorothiolformate, have been found useful as intermediates for the preparation of herbicidally effective thiolcarbamates and similar compounds. See, for example, U.S. Patents 2,913,327, 3,126,406, 3,175,897 and 3,185,720. In the latter patents, thiolformates are reacted further which amines to produce the corresponding thiolcarbamate.

It has now been discovered that secondary amines and secondary amine hydrochlorides, quaternary ammonium salts and basic anion exchange resins can be used to catalyze the reaction of mercaptan with phosgene.

According to the present invention a process of preparing an organic chlorothiolformate by reacting an organic mercaptan having the general formula, R-SH with phosgene is provided which comprises conducting said reaction in the presence of a catalytic amount of (i) a secondary amine catalyst having the general formula, R1R2NH or R1R2NH.HCl wherein R is alkyl, cycloalkyl, cycloalkylmethyl, alkenyl having 2 to 5 carbon atoms, aryl, alkaryl, aralkyl, haloaryl, haloarylalkyl or carboalkoxyalkyl, and R, and R2 each represent C1-C,2 alkyl, C3-C4 alkenyl, C3-C6 cycloalkyl, C3-C6 cycloalkylmethyl, lower alkyl substituted C3-C6 cycloalkyl, C6-C10 aryl, halo-substituted C6-C10 aryl, lower alkyl substituted C6-C10 aryl, C6-C10 aralkyl or halo-substituted C6-C10 aralkyl or (ii) a quaternary ammonium salt or (iii) a basic anion exchange resin.

As used hereinafter in the specification and claims the term "secondary amine" is intended to include the corresponding secondary amine hydrochloride.

The use of the secondary amines as catalysts for the reaction of mercaptan with phosgene has the added benefit of not requiring separation of the catalyst from the chlorothioiformate when it is used as an intermediate for the preparation of thiolcarbamates for the reason that secondary amines are used typically as a reactant in the thiolcarbamate forming reaction. Thus, an appropriate secondary amine can be selected for use as the catalyst in the process described herein and any amine present in the chlorothiolformate product will serve as a reactant in the subsequentthiolcarbamate forming reaction, thereby avoiding the introduction of by-product impurities in the thiolcarbamate product.

Examples of secondary amine compounds useful as catalysts for the reaction of mercaptans with phosgene are secondary amines and secondary amine hydrochlorides having the general formulae, R1R2NH and R1R2NH HCi, wherein R1 and R2 are each selected from the group consisting of C1-C12 alkyl, C3-C4 alkenyl, C3-C6 cycloalkyl, C3-C6 cycloalkylmethyl, lower alkyl substituted C3-C6 cycloalkyl, C6-C10 aryl, halo-substituted C6-C10 aryl, lower alkyl, substituted C6-C10 aryl, C6-C1O aralkyl and halo-substituted C6-C1O aralkyl.As used in the specification and claims, the term "lower alkyl" is intended to mean and include alkyl groups having from 1 to 4 carbon atoms (C1-C4alkyl); and, the prefix "halo" is intended to mean and include a halogen substituent, e.g., chloro, bromo, fluoro and iodo, preferably chloro or bromo, on the aromatic ring. Preferred secondary amine and secondary amine hydrochlorides are those wherein R1 and R2 are each selected from the group C1-C6, more preferably C1-C4 and especially C2-C4, alkyl and C3-C6 cycloalkyl. Moreover, as used hereinafter in the specification and claims, the term secondary amine is intended to include the corresponding secondary amine hydrochloride. The secondary amine compounds represented by the above-described formulae can be prepared by methods well known in the art.

As further examples of secondary amines that are useful as catalysts for the process described herein, reference is made to U.S. patents 3,126,406 and 3,896,169 and particularly Table I of the latter patent. These patents describe thiolcarbamate compounds which contain the radical.

which, if a hydrogen atom were added to the nitrogen atom, denotes a variety of secondary amines. Such amines are exemplary of secondary amines that have been used in the art to prepare thiolcarbamates, and are examplary of the second amine catalysts described by the aforesaid general formulae.

As examples of C1-C12 alkyl radicals there can be mentioned methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, n-pentyl, neopentyl, hexyl, neohexyl n-heptyl, n-octyl 2-ethylhexyl, n-nonyl, n-decyl, and n-dodecyl. As examples of alkenyl radicals, there can be mentioned allyl, methallyl, and butenyl.

As examples of C3-C6 cycloalkyl, C3-C6 cycloalkyimethyl and lower alkyl substituted C3-C6 cycloalkyl radicals, there can be mentioned, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, 3-methyl cyclohexyl, dimethyl cyclohexyl, 1-methyl cyclopropyl, 3-methyl cyclobutyl, 2-ethyl cyclopropyl, cyclopropylmethyl, cyclopentyl methyl, cyclobutylmethyl, 1-methyl cyclopropylmethyl, 3-methyl cyclopentylmethyl, 3 methylcyclobutylmethyl and 2-ethyl cyclopropylmethyl.

Among the aryl, mono- and dihalo-substituted aryl, lower alkyl substituted aryl, aralkyl, and halosubstituted aralkyl radicals, there can be mentioned phenyl, 4-chlorophenyl, 2-tolyl, 3-tolyl, 2-naphthyl, 3-chloro-4-methyl phenyl, 4-bromophenyl, benzyl, 4-chlorobenzyl and 2-phenylethyl.

The amount of secondary amine catalyst used to catalyze the reaction of the mercaptan with phosgene is that amount which is required to accelerate the reaction to commercially acceptable rates, i.e., a catalytic amount. Whereas several days may be required to accomplish significant conversions of mercaptan, e.g., greater than 80 percent conversion, in the absence of catalyst, such conversions can be accomplished within 4to 16 hours with use of a secondary amine catalyst. Typically, from about 0.01 to about 10 mole percent of secondary amine, based on the mercaptan, can be used. More commonly, from about 0.05 to about 0.5 or 1 mole percent of secondary amine catalyst is used.It has been found, for example, that from 0.01 to 0.05 mole percent of di-n-propyl amine based on mercaptan, catalyzes the reaction of ethyl or n-propyl mercaptan with phosgene at economical rates and yields the corresponding chlorothiolformate of high quality.

The secondary amine catalyst can be added to the reactor separately, dissolved in the phosgene or mixed with the mercaptan. In a preferred embodiment, the amine catalyst is added slowly to a pool of phosgene or added slowly to the phosgene admixed with the mercaptan during the initial stages of the reaction rather than being added all at once.

Quaternary ammonium salts are the products of the final stage of alkylation of nitrogen. The salts can be represented by the formula R'(4) N+X-, wherein R'(4) represents the four organic groups bonded to the nitrogen forming an ion having a positive charge, wich is balanced by a negative ion, X. The four organic groups can be varied widely and thus quaternary ammonium salts that can be used in the present process will also vary widely.The more common quaternary ammonium salts that can be used in the present process are represented by the general formula, (B3B4B5B6N)+ X-, wherein R3, B4, R5 and B6 each represent C1-C22 alkyl, C2-C8 alkenyl, phenyl, C6-C9 alkaryl or C6-C9 aralkyl, and Xis a monovalent anion normally associated with quaternary ammonium salts. The particular anion associated with the salt depends on the method by which the quaternary ammonium salt is prepared, e.g., the anion associated with the alkylating agent. Typically, X is a halogen, e.g., chloride, bromide or iodide, hydroxyl, nitrate, methyl sulfate, etc.

Regardless of the anion associated with the quaternary ammonium salt initially, it is expected that during use as a catalyst in the present process, the anion will be exchanged for the chloride anion introduced with the phosgene reactant.

The particular aliphatic (saturated or unsaturated branched or straight chain) or aromatic radical selected for each of the R' groups of the quaternary ammonium salt, i.e. R3, R4, R5 or B6 can vary. Preferably, one of the R' groups is phenyl or aralkyl, one of the groups is a long chain (C8-C22) aliphatic hydrocarbon and two of the groups are shorter chain (C1-C7) aliphatic groups, and Xis a halogen, e.g., chloride ion. In particular, preferred quaternary ammonium salts of the above formula are those in which B3 is a C10-C22 alkyl, R4 and B5 are each C1 -C12 alkyl, B6 is selected from the group consisting of phenyl and benzyl, and Xis chloride.The alkyl groups can be branched or straight chain, and substituted or unsubstituted with functional groups that do not interfere with the catalytic activity of the quaternary ammonium salt.

As examples of C1-C22 alkyl radicals, there can be mentioned methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, n-pentyl, neopentyl, hexyl, neohexyl n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, undecyl, n-dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl and docosyl.

As examples of alkenyl radicals, there can be mentioned; allyl, methallyl, and butenyl.

Among the C6-Cg alkaryl and aralkyl radicals, there can be mentioned phenyl,4-chlorophenyl,2-tolyl, 3-tolyl, 3-chloro-4-methyl phenyl, 4-bromophenyl, benzyl, 4-chlorobenzyl and 2-phenylethyl.

The quaternary ammonium salts described herein are either commercially available or can be prepared by processes well known in the art. Typically, quaternary ammonium compounds are prepared by the alkylation of primary, seconary or tertiary amines. When primary or secondary amines are used, an alkaline reagent (acid acceptor) is used to neutralize the acid formed by the alkylation. Among the alkylating agents used, methyl halides, e.g., methyl chloride, dimethyl sulfate and benzyl chloride are used most frequently.

Examples of classes of quaternary ammonium salts commercially available include monoalkyl trimethyl quaternaries, dialkyl dimethyl quaternaries, monomethyl trialkyl quaternaries and dimethyl alkyl benzyl quaternaries.

Examples of specific quaternary ammonium salts include: ethyltrimethylammonium iodide, tetramethylammonium chloride, trimethyloctadecyl-ammonium chloride, dimethyldioctadecylammonium chloride, dimethyldicocoammonium chloride, trimethyldodecylammonium chloride, tricaprylylmethylammonium chloride, benzyltrimethylammonium chloride, methylallylphenylbenzylammonium iodide, benzyltriethylammonium chloride, soya trimethyl ammonium chloride, palmityl trimethyl ammonium chloride, coco trimethyl ammonium chloride, allyl trimethyl ammonium chloride, benzyl trimethyl ammonium chloride, dialkyl (C12-C18) dimethyl ammonium chloride, dialkyl (C14-C18) dimethyl ammonium chloride, dialkyl (C12-C16) dimethyl ammonium chloride, distearyl dimethyl ammonium chloride, trialkyl (C8-C18) monomethyl ammonium chloride, dimethyl alkyl (C12-C1s) benzyl ammonium chloride, dimethyl alkyl (C10C18) benzyl ammonium chloride, and dimethyl stearyl benzyl ammonium chloride.

The skilled artisan will recognize that quaternary ammonium salts other than described above are commercially available or can be routinely prepared. Typical commercial combinations include methyl groups, fatty alkyls, imidazolinium and amido amine substituents along with chloride or methyl sulfate anions. In the above specific salts, it is recognized that for example ethyl or propyl can be substituted for methyl, and hydroxyl or bromo substituted for the chloro anion. Such quaternary ammonium salts can be used as the catalyst for the process described herein and it is expected that results similar to that of Example VI will be obtained.

The amount of quaternary ammonium salt used to catalyze the reaction of mercaptan with phosgene is that amount which is required to accelerate the reaction to commercially acceptable rates, i.e. a catalytic amount. Whereas several days may be required to accomplish significant conversions of mercaptan, e.g., greater than 80 percent conversion, in the absence of catalyst, such conversions can be accomplished within 0.1 to 20 hours with use of a quaternary ammonium salt. Typically, from about 10 to about 0.01 mole percent of quaternary ammonium salt, based on the mercaptan, can be used. More commonly, from about 0.1 to about 1 or 5 mole percent of quaternary ammonium salt is used.It has been found, for example, that about 0.2 mole percent of benzyltriethylammonium chioride, based on mercaptan, catalyzes the reaction of ethyl mercaptan with phosgene at economical rates and yields the corresponding chlorothio[formate of high quality.

The quaternary ammonium salt can be added to the reactor in any convenient manner, e.g., before, after or simultaneously with one or both of the reactants. In a preferred embodiment, the ammonium salt is added to a pool of phosgene previously formed in the reactor, Basic anion exchange resins are well known in the art and many are commercially available. Such resins contain primary, secondary and tertiary amine groups, and quaternary ammonium groups on a three dimensional polymeric hydrocarbon backbone. The resins are typically divided into two groups, i.e. the strongly basic anion exchange resin having a quaternary ammonium functionality and weakly basic anion exchange groups having a polyamine functionality. Either can be used as catalysts in the practice of the present process.These ion exchange resins consist of two principal parts - a structural portion (polymer matrix) and a functional portion (the ion-active group). The wide variety of ion-exchange resin formulations and properties derives from various combinations of these parts.

The polymer matrix istypicallyformed from polymers (including copolymers) produced by condensation or addition polymerization. Condensation polymers useful as ion-exchange resin backbones are high molecular weight, cross-linked structures formed usually by an ionic organic reaction mechanism from small polyfunctional monomers e.g., by the condensation of phenol with formaldehyde or an epoxide, e.g., epichlorohydrin, with an amine or ammonia. Addition polymers useful as the backbone for ion-exchange resins are cross-linked structures formed by the free-radical polymerization of mixtures of olefinic and diolefinic compounds, e.g., by the polymerization of styrene and divinyl benzene. The addition polymers are generally more stable to hydrolysis or oxidative cleavage and therefore are preferred.

Commercially available basic anion exchange resins are typically of the styrene-divinyl benzene backbone type. The amount of divinyl benzene copolymerized with styrene commonly varies from about 1 to about 16, e.g., 4to 12, more usually about 8, percent of divinyl benzene. The copolymer product is usually prepared by the free-radical suspension polymerization of the monomers. The polymer is then modified by chlorination or chloromethylation using chioromethyl methylether and a Friedel-Crafts condensation catalyst. The resulting modified polymer is reacted with an amine, polyamine or ammonia to form the ion-exchange resin.

For example, the chlorinated polymer can be reacted with a tertiary amine in the presence of a polar solvent e.g. water to form a quaternary ammonium salt. Amination of the chlorinated polymer can be conducted with alkyl amines or alkaline polyamines to produce a variety of strong and weak basic anion exchange resins.

The resins which contain quaternary ammonium functionality are considered to be strong basic anion exchange resins; while the resins which possess an amine or polyamine functionality are considered to be weak basic anion exchange resins. Although the ionic form exhibited by the resin can vary, the ionic form most common for ion exchange resins is the chloride form, i.e., the anion associated with the amine functional group.

The basic anion exchange resins utilized in the present process will typically be in bead form and vary in size from about 400 mesh to about 16 mesh. Although gel-type resins can be utilized, the granular or spherical (bead) form are preferred for use as a catalyst in the present process. Also available are the macroporous or macroreticular resins which have pores of considerably larger size then the more conventional gel-type resins. The physical form of the catalyst chosen should be such that the resin resists physical degradation by the forces it encounters in the reaction, e.g., by attrition. Further, the resin should be somewhat chemically resistant to the chemical species encountered by the resin, i.e., the reactants and the reaction products of the mercaptan-phosgene reaction.

Use of a solid granular basic anion exchange resin as a catalyst in the present process has the advantage that the resin is substantially insoluble in the reaction medium and, because it is a solid, it can be separated easily by filtration or decantation when the reaction is completed. The solid resin can be put in a column and the present process operated continuously by charging mercaptan and phosgene continuously to the column. Alternatively, the solid resin can be charged to a continuously stirred reaction vessel and the reaction performed on a batch or semi-continuous basis. The resin catalyst should also provide a reduction in catalyst costs over the conventional amine catalysts for the reason that they can be used repeatedly and usually without regeneration.

Among the basic anion exchange resins that can be used in the present process, there can be mentioned those resins sold under the trade-Marks DUOLITE, DOWEX, IONAC, AMBERLITE and AMBERLYST.

Exemplary of the latter two commercial resins are the AMBERLITE IRA-900 series ion exchange resins, the AMBERLITE IRA-93 ion exchange resins, and the macroreticularAMBERLYSTA-26 and A-29 ion exchange resins.

The amount of basic anion exchange resin used to catalyze the reaction of the mercaptan with phosgene is that amount which is required to accelerate the reaction to commercially acceptable rates, i.e., a catalytic amount. Whereas several days may be required to accomplish significant conversions of mercaptan, e.g., greater than 80 percent conversion, in the absence of catalyst, such conversions can be accomplished within 0.1 to 5 hours with use of a basic anion exchange resin catalyst. Typically, from about 5 to about 40 grams, e.g., 20 grams, of resin per 100 grams of mercaptan will be used when the reaction is conducted in a stirred reactor.When the process is performed continuously, as in a column, the amount of resin used is less precise for the reason that the same catalyst is used for the continuously charged reactants and until the catalyst becomes deactivated. Stated differently, sufficient resin is used to provide from about 0.001 to about 0.2 moles of ion exchange capacity per mole of mercaptan charged. More typically the resin will provide from about 0.01 to about 0.1, e.g., 0.05 moles of ion exchange capacity per mole of mercaptan charged.

In the case of a batch or semi-continuous process, the basic anion exchange resin is typically added to the reactor separately from the phosgene or mercaptan. In a preferred embodiment, a pool of phosgene, i.e., the excess phosgene, is established in the reactor and the resin catalyst added to the phosgene before the introduction of the mercaptan and additional phosgene reactants.

Mercaptans that can be reacted with phosgene in the presence of the catalyst can be represented by the formula, R-SH, wherein R is alkyl, cycloalkyl, cycloalkylmethyl, alkenyl having 2 to 5 carbon atoms, aryl, alkaryl, aralkyl, haloaryl, haloaralkyl, and carboalkoxy alkyl. Such mercaptans are well recognised in the art, as can be seen by reference to the aforesaid described U.S. patents. Mercaptans, such as those described herein, can be prepared by methods known in the art. Among the methods described in the art for preparing mercaptans are the reaction of an alkali alkyl sulfate or alkyl halide with sodium or potassium hydrosulfide; the vapor phase reaction of the appropriate alcohol with hydrogen sulfide; and the addition of hydrogen sulfide to the appropriate unsaturated organic compound.

Typically, R in the formula R-SH is a branched or straight chain C-C15 alkyl, C2-C5 alkenyl, C3-C7 cycloalkyl or cycloalkylmethyl, C6C1O aryl, C6-C10 alkaryl or aralkyl, and C6-C10 haloaryl or haloaralkyl and C2-C10 carboalkoxyalkyl. The halo prefix includes the halogen substituents, i.e., chloro, bromo, fluoro and iodo, preferably chloro and bromo. Generally the aliphatic and aromatic radicals described with respect to the secondary amine catalyst are also suitable as substituents for the R group of the mercaptan.More typically, R is a C1-C10, preferably C1-C6 alkyl, C3-C4 alkenyl, C5-C6 cycloalkyl or cycloalkylmethyl, phenyl, C1-C4 alkyl substituted phenyl, chlorophenyl including mono- and polychlorinated phenyl, benzyl and chlorobenzyl, including mono- and polychlorinated benzyl, and C2-C5 carboalkoxyalkyl.

Examples of organic mercaptans which can be suitably used in the reaction of the present invention are alkyl mercaptans such as methyl-mercaptan, ethylmercaptan, isopropylmercaptan, n-propylmercaptan, isobutylmercaptan, secondary butylmercaptan, n-butylmercaptan, 2-pentylmercaptan, neopentylmercaptan, n-pentylmercaptan, n-hexylmercaptan, neohexylmercaptan, n-heptylmercaptan, n-octylmercaptan, and the like. As examples of cycloalkyl mercaptans, the following can be employed: cyclopentylmercaptan, cyclohexylmercaptan, 2-methylcyclohexylmercaptan, 3-methylcyclohexyl mercaptan, cyclopropylmethyl- mercaptan, cyclopentylmethylmercaptan, cyclohexylmethylmercaptan, and the like. Allyl mercaptan and butenyl mercaptan are typical examples of lower alkenyl mercaptans that can be used in the above defined reaction.

Also useful are aryl, alkaryl, aralkyl, haloaryl and haloaralkyl compounds exemplified by the following compounds: mercaptobenzene, 2-mercaptonaphthalene, 4-mercaptotoluene, 2-mercaptotoluene, 3- mercaptotoluene, 2,4-dimethylmercaptobenzene, 2,5-dimethylmercaptobenzene, 4-tert-butyl- mercaptobenzene, 1 -methyl-2-mercaptonaphthalene, 4-ethylmercaptobenzene, benzylmercaptan, mercaptoethyl benzene, mercaptopropyl benzene, triphenyl-methyl mercaptan, mercaptomethyl naphthalene, mercaptoethyl naphthalene, mercaptobutyl naphthalene, 2-chloromercaptobenzene, 3- chloromercaptobenzene, 4-chloromercaptobenzene, 2,5-dichloromercaptobenzene, 4 bromomercaptobenzene, 2-iodomercaptobenzene, 3-iodomercaptobenzene, 4-iodomercaptobenzene, 2- chlorobenzylmercaptan, 3-chlorobenzyl merca ptan, lorobenzyl mercaptan, 2,4-dichlorobenzylmercaptan, 3,4-dichlorobenzylmercaptan, 4-bromobenzylmercaptan, 4-chloro-1 -mercaptonaphthalene, 4-bromo-1 mercaptonaphthalene, and the like. Similarly, examples of carboalkoxyalkyl mercaptans that can be reacted with phosgene according to the present invention are those compounds typified as esters of mercapto-acids.

Suitable examples are methyl mercaptoacetate, ethyl mercaptoacetate, propyl mercaptoacetate, butyl mercaptoacetate, pentyl mercaptoacetate, hexyl mercaptoacetate, methyl 2-mercaptopropionate, ethyl 2-mercaptopropionate, pentyl 2-mercaptopropionate, methyl 3-mercaptopropionate, ethyl 3mercaptopropionate, hexyl 3-mercaptopropionate, methyl 2-mercaptobutyrate, propyl 2-mercaptobutyrate, hexyl 2-mercaptobutyrate, methyl 3-mercaptobutyrate, ethyl 3-mercaptobutyrate, hexyl 3mercaptobutyrate, methyl 4-mercaptobutyrate, ethyl 4-mercaptobutyrate, hexyl 4-mercaptobutyrate, methyl 3-mercaptovalerate, ethyl 3-mercaptovalerate, hexyl 3-mercaptovalerate, methyl 5-mercaptovalerate, ethyl 5-mercaptovalerate, hexyl 5-mercaptovalerate, and the like.

The amount of phosgene used in the reaction can vary; but is typically at least a stoichiometric amount based on equation (1). That is, at least one mole of phosgene is used for every mole of mercaptan. More usually, an excess of phosgene, e.g., from about 5 to about 50 mole percent excess phosgene, based on the mercaptan is used for the reasons that the phosgene can be removed readily from the reaction mixture and an excess of mercaptan will favor the production of by-product dithiolcarbonate. However, if the presence of dithiolcarbonate can be tolerated, the amount of phosgene used can be less than a stoichiometric amount, i.e., the mercaptan is used in excess.

Reaction of the mercaptan with phosgene is commonly conducted at atmospheric pressure, although subatmospheric or superatmospheric pressures can be used. Reaction temperatures should be maintained as low as possible, consonant with reasonable reaction rates since, at high temperatures, the dithiolcarbonate can be formed in significant amounts. Since the mercaptans described hereinbefore exhibit varying reactivities and varying decomposition temperatures such factors must be taken into account in selecting the reaction temperature. Commonly reaction temperatures will be less than about 70"C. With an excess of phosgene, the reaction temperature will typically range from about 0 C. to about 70"C. at atmospheric pressure and with refluxing phosgene.More typically, reaction temperatures will range from about 10 C. to about 50"C., e.g., from 10"C. to 35"C.

The reactants can be introduced into a suitable reactor in any order or simultaneously; however, it is preferable to add the mercaptan to a pool of phosgene. Thus all of the reactants can be added simultaneously with stirring to the reactor (as in a batch process) and permitted to react. Further, when carrying out the process on a batch or semi-continuous basis, it is preferred that the mercaptan be added slowly to the pool of phosgene so as to control the heat of reaction and minimize the formation of by-product dithiolcarbonate. When phosgene is added to a pool of mercaptan, the reaction commences at a higher temperature than when the order of reactant introduction is reversed, thereby increasing the opportunity for formation of by-product dithiolcarbonate. Preferably, the secondary amine catalyst is added mixed with the mercaptan; however, it can be added to the pool of phosgene.

More preferably, the phosgene and mercaptan are charged simultaneously and slowly to a pool of excess phosgene with stirring, e.g., over a period of 6-10 hours, followed by post stirring for about one hour. This latter method (semi-continuous) avoids the presence in the reactor of large amounts of unreacted material and permits the gradual build-up of product in the reactor. The post stirring period allows time for substantially complete reaction of the mercaptan and can be performed in a series of reactors, e.g., holding tanks, other than the principal reactor.

In the case of a continuous process, and where the catalyst is an anion exchange resin it is charged to a reactor, e.g., a column, and the mercaptan and phosgene charged to the reactor simultaneously. After a suitable residence time, the product is removed from the reactor. The continuous process can be operated as a plug flow system (as in the case of a column reactor) or a series of sequential reactors in which the effluent of a reactor is forwarded to the next reactor in the series. Sufficient residence time in the reactor(s) is provided to ensure substantially complete reaction of the mercaptan reactant.

The reaction can be conducted batch-wise or semi-continuously also by introducing the reactants to a heel of the chlorothiolformate, i.e., a portion of the reaction product of a previous preparation. Although the initial reaction temperature is higher than when mercaptan is added to a pool of phosgene, reaction times are shorter. Preparation of the chlorothiolformate by a continuous reaction is also contemplated.

The chlorothiolformate product prepared in accordance with the present process contains low levels of organic disulfide, i.e., R-S-S-R, and dithiolcarbonate by-products. The low level of disulfide impurity is in contrast to the significant quantities of such impurity that is found in chlorothiolformate prepared using activated carbon as the catalyst. See, for example, U.S. Patent 4,012,405 (column 1) wherein from 3 to 7 percent of diethyl disulfide is produced during preparation of ethyl chlorothiolformate by reaction of ethyl mercaptan with phosgene in the presence of activated carbon catalyst. Further, the catalyst of the present process does not appear to catalyze the reaction of the chlorothiolformate with further mercaptan to produce the dithiolcarbonate by-product.

In conducting the reaction of the present process, the reaction mixture is usually agitated to assist in removing heat from the reactor. At the end of the reaction, excess phosgene is removed, e.g., by stripping.

Phosgene can be stripped from the chlorothiolformate product by pulling a vacuum on the system - thereby permitting the phosgene to boil off; passing an inert gas, e.g., nitrogen, through the reaction mixture; or, heating the reaction mixture slightly to boil off the excess phosgene. Upon removal of the excess phosgene, any secondary amine catalyst, e.g., probably as the hydrochloride, will precipitate and can be removed from the chlorothiolformate by filtration; any quaternary ammonium salt catalyst can be removed from the chlorothiolformate by filtration or washing with water although the latter course is not preferred because water can react with the chlorothiolformate thereby decreasing the yield of the product; and any resin catalyst can be separated from the reaction product by decantation or filtration.If the chlorothiolformate is to be converted to a thiolcarbamate by reaction with further secondary amine, either the same or a different amine from the secondary amine catalyst, residual amine catalyst need not be removed from the chlorothiolformate before its further reaction with the appropriate further amine reactant.

If the chlorothiolformate product is to be converted to a thiolcarbamate and a secondary amine catalyst has not been used then secondary amine is mixed with the chlorothiolformate product in the presence of an acid acceptor, e.g., sodium hydroxide, in an amount sufficient to convert the thiolformate to the corresponding thiolcarbamate. The secondary amine can be represented by the formula R1R2NH wherein R and B2 have the meanings given above and particularly those compounds wherein R1 and R2 each represent C1-C4, preferably C2-C4, alkyl, cyclohexyl or allyl, e.g., diethylamine, di-n-propylamine, di-n-butylamine, di-isobutylamine, ethyl cyclohexylamine, or di-allylamine.

The degassed chlorothiolformate product is obtained in sufficient purity to be used in some commercial applications, e.g., as an intermediate for the preparation of thiolcarbamates. If further purification is desired, the chlorothiolformates can be distilled or recrystallized from a suitable solvent to obtain a more pure product.

In a typical embodiment of a batch process using a secondary amine catalyst about 0.6 mole of phosgene per mole of mercaptan used is condensed in a reactor to establish a pool of phosgene at about 10 C.

Thereafter, the ethyl mercaptan containing about 0.5 mole percent of di-n-propyl amine (based on mercaptan) is introduced slowly into the reactor simultaneously with the further addition of about 0.6 mole of phosgene per mole of mercaptan used. The additional phosgene and mercaptan reactant are added to the reactor over a period of about one hour and the reaction maintained under constant agitation. Vaporized phosgene is condensed in a reflux condenser connected to the reactor and condensed phosgene returned to the reactor. As the reaction takes places, the phosgene and ethyl mercaptan are consumed and the boiling point of the reaction mixture rises from about 10 C. to about 27"C. at the end of the reaction.At the end of about 5-6 hours, excess phosgene and unreacted ethyl mercaptan are stripped from the reactor by degassing, and the chlorothiolformate product removed from the reactor.

While the above embodiment has been exemplified by ethyl mercaptan and di-n-propyl amine, other of the above described mercaptans or secondary amines can be substituted for the ethyl mercaptan and di-n-propyl amine respectively of the exemplification and expect to obtain the corresponding chlorothiolformate.

In a typical embodiment of a batch process using a quaternary ammonium catalyst about 0.2 mole percent of quaternary ammonium salt (based on mercaptan) is introduced into the reactor. Thereafter, 0.6 mole of phosgene, per mole of mercaptan, used is condensed in the reactor to establish a pool of phosgene at about 10 C. Mercaptan is then added to the reactor together with the further addition of about 0.6 mole of phosgene per mole of mercaptan used. The additional phosgene and mercaptan reactant are added to the reactor over a period of about one hour and the reaction maintained under constant agitation. Vaporized phosgene is condensed in a reflux condenser connected to the reactor and condensed phosgene returned to the reactor.As the reaction takes place, the phosgene and mercaptan are consumed and the boiling point of the reaction mixture rises, e.g., from about 10 C. to about27'C. when using ethyl mercaptan. At the end of about 10 hours, excess phosgene and unreacted mercaptan are stripped from the reactor by degassing, and the chlorothiolformate product removed from the reactor.

In a typical embodiment of a batch process using a resin catalyst about 0.6 mole of phosgene per mole of mercaptan used is condensed in a reactor to establish a pool of phosgene at about 10"C. AMBERLYST A-26 basic anion exchange resin containing a total of 0.05 mole of ion exchange capacity per mole of mercaptan used is added to the phosgene and ethyl mercaptan is introduced slowly into the reactor simultaneously with the further addition of about 0.6 mole of phosgene per mole of mercaptan used. The additional phosgene and mercaptan reactant are added to the reactor over a period of about one hour and the reaction maintained under constant agitation. Vaporized phosgene is condensed in a reflux condenser connected to the reactor and condensed phosgene returned to the reactor. As the reaction takes place, the phosgene and ethyl mercaptan are consumed and the boiling point of the reaction mixture rises from about 10"C. to about 27"C. at the end of the reaction. At the end of about 2 to 3 hours, excess phosgene and unreacted ethyl mercaptan are stripped from the reactor by degassing and the chlorothiolformate product removed from the reactor.

While the above embodiment has been exemplified by ethyl mercaptan and AMBERLYST basic anion exchange resin, other of the described mercaptans or basic anion exchange resins can be substituted for the ethyl mercaptan, and AM BERLYST resin respectively of the exemplification and expect to obtain the corresponding chlorothiolformate.

The present invention is more particularly described in the following Examples which are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. In the Examples, the purity of the chlorothiolformate product is reported as peak area percent, i.e., by estimating the area under the peaks of the chart produced by gas liquid chromatographic analysis.

Example I Phosgene (0.194 mole) was condensed into a 30 ml. serum bottle which was capped with a Viton septum.

Ethyl mercaptan (0.171 mole) containing 0.01 mole of di-n-propylamine was then injected into the bottle by means of a syringe and hypodermic needle. The reaction mixture was stirred and allowed to warm from -70 C. to wet ice temperature (0"C.) and maintained there for 250 minutes. The reaction was followed by means of gas liquid chromatographic analysis (GLC) of the unreacted ethyl mercaptan. During the aforesaid period at 0 C., the reaction mixture was homogeneous and about 90 percent of the ethyl mercaptan reacted.

The reaction mixture was permitted to warm to room temperature overnight to remove excess phosgene.

The crude product was washed two times with 30 ml. of distilled water to remove the amine catalyst, dried with sodium sulfate and recovered by filtration. 13.7 grams of a water white product, which was identified by GLC as ethyl chlorothiolformate of about 90 to 95 percent purity, was recovered. This represented a 64.3 percent yield based on the theoretical conversion of all ethyl mercaptan to ethyl chlorthiolformate.

Example II Phosgene (4.8 moles) was condensed into a one liter, round bottom, three-neck flask. The flask was equipped with a stirrer and motor, thermometer, addition funnel, phosgene inlet tube and a dry ice-acetone condenser and cooled with a wet ice bath. A mixture of 4.0 moles of ethyl mercaptan and 0.2 moles of di-n-propylamine was placed in the addition funnel. When approximately one-half of the phosgene was condensed into the reaction flask, the addition thereto of the ethyl mercaptan-di-n-propylamine mixture was started at a rate of 2-3 cc./minute with stirring. The temperature of the phosgene in the reaction flask at the start of ethyl mercaptan addition was 7"C. The ice bath was not used during the addition of the ethyl mercaptan, which took 117 minutes.The temperature of the reaction mixture at the end of the addition of ethyl mercaptan was 7.5"C.

The reaction mixture was stirred overnight (about 17-1/2 hours and a GLC analysis the next morning showed that most of the ethyl mercaptan had reacted. Excess phosgene and unreacted ethyl mercaptan were then removed from the reaction mixture by degassing with nitrogen at the end of the degassing step, a white solid separated from the reaction mixture and was removed from the flask by filtration. The reaction product was identified by GLC as ethyl chlorothiolformate of about 97.7 percent purity. It was estimated that the ethyl chlorothiolformate product contained about 0.05 percent each of diethyl disulfide (DEDS) and diethyl dithiolcarbonate (DETC). The yield of degassed product was calculated to be 84.2 percent, based upon a theoretical conversion of all ethyl mercaptan to ethyl chlorothiolformate.The white solid was identified by melting point determinator to be di-n-propylamine hydrochloride.

Example Ill The procedure of Example II was repeated except that no di-n-propylamine was added to the ethyl mercaptan, and the ethyl mercaptan was added to the flask over a period of 89 minutes. Other than the refluxing phosgene, no signs that a reaction was taken place were observed. The temperature of the reaction mixture remained at 15"C. for at least 6 hours, and 12 hours after the addition of the ethyl mercaptan, the temperature was found to be 13"C. The reaction mixture was left stirring overnight.

The next morning (about 24 hours after the start of the run) it was found that the dry ice - acetone coolant in the reflux condenser was depleted, which allowed phosgene to escape from the reaction system. The reaction temperature was found to be 1 9"C. A GLC analysis of the reaction mixture indicated that there was no longer an excess of phosgene and only about one quarter of the ethyl mercaptan had reacted at that time.

92 grams of additional phosgene was added to the reactor at that time with stirring. The temperature of the reaction mixture dropped to about 17"C. and was left stirring for the rest of that day. The reflux condenser was cooled with a 50 percent ethylene glycol solution which was circulated through a refrigeration unit. The next afternoon, the reaction temperature was found to be 24"C. and a GLC analysis of the reaction mixture indicated that about one-half of the ethyl mercaptan had reacted. The following afternoon the reaction temperature was found to be 26"C. and a GLC analysis of the reaction mixture indicated that about three-quarters of the ethyl mercaptan had reacted.

The next day (after four days of reaction) the reaction mixture was degassed with nitrogen. The yield of ethyl chlorothiolformate was calculated to be 71.7 percent. Its identity was confirmed by GLC analysis which indicated that the ethyl chlorothiolformate was about 99.5 percent pure and contained about 0.1 percent DEDS and about 0.3 percent DETC as by-products.

Example IV The procedure of Example li was repeated except that 0.001 moles of di-n-propylamine was used as the catalyst, and 2.0 moles of ethyl mercaptan and 2.4 moles of phosgene were used. The ethyl mercaptan-catalyst mixture was added over a period of 50 minutes. The reaction temperature increased slowly from 8"C. (at the start of ethyl mercaptan addition) to 240C. over 9 hours indicating that significant reaction had taken place. The run was terminated at that time due to aspiration of sodium hydroxide from a scrubber in the reaction system into the reaction flask. A GLC analysis of the reaction mixture 6-1/2 hours after the start of ethyl mercaptan addition indicated that about 50% of the ethyl mercaptan had reacted.

Example V The procedure of Example IV was repeated except that 2.0 moles of n-propyl mercaptan, 2.2 moles of phosgene and 0.1 mole percent (based on n-propyl mercaptan) of di-n-propylamine catalyst was used. The n-propyl mercaptan was added slowly to the reaction flask over 108 minutes and the reaction temperature rose slowly from 9"C. to 26"C. over 9 hours. A GLC analysis of the reaction mixture 7 hours after the start of n-propyl mercaptan addition indicated that about 84 pecent of the mercaptan had reacted. About 12-1/2 hours following the start of n-propyl mercaptan addition, the reaction mixture was heated to 35"C. and degassed with argon for about 10 hours.The yield of degassed product was calculated to be 93.9 percent, based on the theoretical conversion of all the n-propyl mercaptan to the chlorothiolformate. The propylchlorothiolformade (the identity of which was confirmed by GLC) was determined by GLC analysis to be about 99.2 percent pure and to contain about 0.2 percent di-n-propyl dithiolcarbonate and about 0.6 percent unknowns.

The data of Examples I-V show that secondary amines, e.g., di-n-propyl amine, serve as catalyst for the preparation of organic chlorothiolformates by the reaction of organic mercaptans, e.g. ethyl or n-propyl mercaptan, with phosgene.

Example VI 0.6 grams (0.2 mole percent) of solid benzyltriethylammonium chloride was charged to a one liter, round bottom, three-neck flash containing about 100 grams of ethyl chlorothiolformate. The flask was equipped with a stirrer and motor, thermometer, addition funnel, phosgene inlet tube and a dry ice-acetone condenser and cooled with a wet ice bath. Thereafer, 1.37 moles of phosgene were condensed into the flask.

Seventy-five grams (1.208 moles) of ethyl mercaptan was placed in the addition funnel and added to the reaction flask in about 38 minutes with stirring. The temperature in the reaction flask at the start of ethyl mercaptan addition was 21"C. The ice bath was not used during the addition of the ethyl mercaptan. The temperature of the reaction mixture at the end of the addition of ethyl mercaptan was 170C. The reaction mixture was stirred for about 11 hours during which time 5 samples were taken and analyzed by means of gas liquid chromatographic analysis (GLC) of the unreacted mercaptan. The reaction mixture was stirred overnight (an additional 9 hours) at which time a further sample was taken. The temperature of the reaction mixture was maintained at 20"C. during the reaction.Analysis of the six samples taken was tabulated in Table I.

TABLE I Sample Elapsed Time, Peak Area Percent, Compoundsb No. Minutes COCI2 ETSH ECTF DETC 1 oa 35 25 39 0.1 2 45 26 17 57 0.1 3 150 14 11 75 0.3 4 4 330 8 6 85 0.1 5 670 5 3 91 0.1 6 1330 3 2 95 0.1 a. 17 minutes after all ETSH added to reaction flask.

b. COCI2 - phosgene ETSH - ethyl mercaptan ECTF - ethyl chlorothiolformate DETC - diethyl dithiolcarbonate Additional phosgene (1.01 moles) and 50 grams (0.81 moles) of ethyl mercaptan were added all at once to the reaction flask containing the aforesaid reaction product. The temperature of the reaction mixture was about 20"C. The reaction mixture was stirred for about 9-1/2 hours during which time 4 samples were taken.

The reaction mixture was stirred overnight (an additional 14 hours) and a final sample taken. The reaction mixture was maintained during this period at 20 C. Results are tabulated in Table II.

TABLE II Sample Elapsed Time, Peak Area Percent, CompoundsbC No. Minutes COCI2 ETSCH ECTF DETC 1 0 22 15 62 0.1 2 90 16 10 73 0.1 3 270 11 6 83 0.1 4 570 8 3 90 0.1 5 1410 5 1 94 0.1 c. Traces of diethyl disulfide were also found.

The data of Tables land II show that quaternary ammonium salt, e.g., benzyltriethylammonium chloride, catalyze the reaction of phosgene with mercaptan, e.g., ethyl mercaptan, to form chlorothiolformate. After 5-6 hours, the reaction mixture was found to be at least about 85 percent ethyl chlorothiolformate. After 10-11 hours, the reaction mixture was found to contain at least 90 percent chlorothiolformate.

Example VII (Comparative) Into a 30 milliliter serum bottle, with a Viton septum cap, was placed 24.5 grams (0.248 mole) of phosgene and 12.0 grams (0.193 mole) of ethyl mercaptan The mixture was held at 0 C. and 1.0 grams (0.01 mole) of triethylamine was added to the bottle. The mixture was stirred and held at 0 C. for 4.5 hours and the reaction followed by GLC analysis. In the aforesaid 4.5 hours, approximately 80 percent of the ethyl mercaptan disappeared and ethyl chlorothiolformate was found.

In a similar serum bottle was placed 21.0 grams (0.212 mole) of phosgene, 9.6 grams (0.155 mole) of ethyl mercaptan and 0.56 grams (0.01 mole) of ammonium chloride. The ammonium chloride did not dissolve to a significant extent. The reaction mixture was held at room temperature (about 23"C.) for 4 hours and at least 80 percent of the ethyl mercaptan remained unreacted at the end of that time period.

It was concluded from the data of this Example that ammonium chloride was at best a poor catalyst for the reaction of ethyl mercaptan with phosgene.

Example Vlil Phosgene (1.8 moles) was condensed into a one liter, round bottom, three-neck flask containing 17.74 grams of AMBERLYSTA-26 basic anion exchange resin having 0.075 moles of ion exchange capacity. The resin had been washed with methanol to remove moisture contained in the commercial product and the methanol removed by heating the washed resin in a nitrogen stream. The flask was equipped with a stirrer and motor, thermometer, additional funnel, phosgene inlet tube and a dry ice-acetone condenser and cooled with a wet ice bath. 1.5 moles of ethyl mercaptan was placed in the addition funnel and added to the reaction flask over a period of 20 minutes with stirring.The temperature of the phosgene in the reaction flask at the start of ethyl mercaptan addition was about 7"C. The ice bath was not used during the addition ofthe ethyl mercaptan. The temperature of the reaction mixture at the end of the addition of ethyl mercaptan was about 9'C.

The reaction mixture was stirred for about 2-1 2 hours. The reaction was followed by means of gas liquid chromatographic analysis (GLC) of the unreacted ethyl mercaptan. The temperature of the reaction mixture was controlled about 20 C. by means of the ice bath. The crude reaction product was identified by GLC as ethyl chlorothiolformate of about 90 percent purity. It was estimated that the ethyl chlorothiolformate product contained about 9.5 percent phosgene,0.25 percent ethyl mercaptan, and trace amounts of diethyl disulfide (DEDS) and diethyl dithiolcarbonate (DETC). Avery small amount of methyl chloroformate and dimethylcarbonate was found by GLC and mass spectrometer analysis of the chlorothiolformate product.

These materials are believed to have been formed from traces of methanol not removed from the washed resin.

Example IX Using the same resin and reaction mixture that was used in Example VIII, a further 1.5 moles of ethyl mercaptan and 1.8 moles of phosgene were added to the reaction mixture over a period of 13 minutes and the mixture maintained at about 20"C. The crude undegassed reaction mixture was stirred for about 3-1 2 hours. The reaction mixture was found to contain about 91 percent ethyl chlorothiolformate, 7.8 percent phosgene, 1.1 percent ethyl mercaptan and traces of diethyl disulfide and diethyl dithiolcarbonate.

Example X With the same resin and reaction mixture of Example IX still in the reaction flask, the reaction mixture was heated to about 40"C. and phosgene (0.76 mole) added to the flask until phosgene refluxing occurred. Ethyl mercaptan (0.63 mole) was then added to the flask in about 4 minutes and the reaction mixture stirred for about 1-1/2 hours. The reaction mixture was maintained at about 35"C. for 90 minutes to yield a crude product which, when analyzed, was found to contain 90 percent ethyl chlorothiolformate, 9 percent phosgene, 0.2 percent ethyl mercaptan, 0.1 percent diethyl dithiolcarbonate and a trace of diethyl disulfide.

The data of Examples Veil, IX and X show that basic anion exchange resin catalyzes the reaction of mercaptan with phosgene to produce chlorothiolformate with little by-product formation. The catalyst of Example VIII was used also in the runs described in Examples IX and X and was still catalytically active for those latter two experimental runs.

Although the present process has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims.

Claims

1. A process of preparing an organic chlorothiolformate by reacting an organic mercaptan having the general formula, R-SH with phosgene which comprises conducting said reaction in the presence of a catalytic amount of (i) a secondary amine catalyst having the general formula, R1R2NH or R1R2NH-HCi wherein R is alkyl, cycloalkyl, cycloalkylmethyl, alkenyl having to 5 carbon atoms, aryl, alkaryl, aralkyl, haloaryl, haloarylalkyl or carboalkoxyalkyl, and R1 and R2 each represent C1-Cq2 alkyl, C3-C4 alkenyl, C3-C6 cycloalkyl, C3-C6 cycloalkylmethyl, lower alkyl substituted C3-C6 cycloalkyl, and C6-C10 aryl, halo-substituted C6-C10 aryl, lower alkyl substituted C6-CsO aryl, C6-C10 aralkyl or halo-substituted C6-C0 aralkyl or (ii) a quaternary ammonium salt or (iii) a basic anion exchange resin.

2. A process according to Claim 1 wherein R is a C1-C15 alkyl, C2-Cs alkenyl, C3-C7 cycloalkyl, C3-C7 cycloalkylmethyl, C6-C,O aryl, C6-C10 alkaryl, C6-CrO aralkyl, C6-C10 haloaryl, Ce-C10 haloaralkyl or C2-C10 carboalkoxyalkyl.

3. A process according to Claim 2 wherein R is a C,-C,0 alkyl, C3-C4 alkenyl, Ce-Ce cycloalkyl or cycloalkylmethyl, phenyl, C1 -C4 alkyl substituted phenyl or benzyl radical.

4. A process according to Claim 3 wherein R is a C1-C6 alkyl.

5. A process according to Claim 4wherein R is ethyl or propyl.

6. A process according to any of Claims 1 to 5 wherein from 0.01 to 10 mole percent of secondary amine catalyst, based on the mercaptan, is used.

7. A process according to Claim 6 wherein from 0.05 to 1 mole percent of secondary amine catalyst is used.

8. A process according to any of Claims 1 to 7 wherein the secondary amine catalyst is a secondary amine having the general formula R1R2NH or the general formula B1B2NH.HCl wherein R1 and R2 each represent C1 -C4 alkyl, cyclohexyl or allyl.

9. A process according to Claim 8 wherein R1 and B2 each represent C2-C4 alkyl.

10. A process according to Claim 8 or 9 wherein the catalyst is diethylamine, di-n-propylamine, di-n-butylamine, di-isobutylamine, ethyl cyclohexylamine, or di-allylamine.

11. A process according to any of Claims 1 to 10 wherein secondary amine catalyst is mixed with the mercaptan.

12. A process according to any of Claims 1 to 4 wherein the quaternary ammonium salt has the general formula: (R3R4RSRSN)f Xwherein R3, R4, R5 and B6 each represent C1-C22 alkyl, CrCe alkenyl, phenyl, C6-Cg alkaryl, or Ce-C9 aralkyl, and Xis a monovalent anion normally associated with quaternary ammonium salts.

13. A process according to Claim 12 wherein the anion X is chloride, bromide or hydroxyl.

14. A process according to Claim 12 or 13 wherein from 0.01 to 10 mole percent of quaternary ammonium salt, based on the mercaptan, is used.

15. A process according to Claim 14 wherein from 0.1 to 5 mole percent of quaternary ammonium salt is used.

16. A process according to any of Claims 12 to 15 wherein R3, R4, B5 and Be each represent C1-C22 alkyl, allyl, phenyl or benzyl, and X is chloride, bromide or hydroxyl.

17. A process according to any of Claims 12 to 15 wherein B3 is a C10-C22 alkyl, R4 and Rtare each C1-C12 alkyl, Be is phenyl or benzyl, and X is chloride.

18. A process according to any of Claims 1 to 4 wherein the ion exchange resin has quaternary ammonium functionality.

19. A process according to claim 18 wherein the resin is in the chloride ionic form.

20. A process according to any of Claims 1 to 4 wherein the ion exchange resin has polyamine functionality.

21. A process according to Claim 18, 19 or 20 wherein the resin has a styrene-divinylbenzene copolymer backbone.

22. A process according to any of Claims 18 to 21 wherein the amount of basic anion exchange resin used contains from about 0.001 to about 0.2 moles of ion exchange capacity per mole of mercaptan used.

23. A process according to any of Claims 1 to 22 wherein from about 5 to about 50 moles percent excess phosgene is used.

24. A process according to any of Claims 1 to 23 wherein the reaction is conducted by adding the mercaptan to a pool of phosgene.

25. A process according to any of Claims 1 to 24 wherein the reaction product is degassed to remove excess phosgene, and secondary amine is added to the degassed reaction product in an amount sufficient to convert the alkyl chlorothiolformate to the corresponding alkyl thiolcarbamate.

26. A process according to Claim 25 wherein the secondary amine added to the degassed product has the formula R,R2NH wherein R1 and R2 have the meanings given in Claim 1.

27. A process according to Claim 25 wherein the secondary amine added to the degassed product has the formula B1B2NHwherein R and R2 each representC1-C4alkyl,cyclohexyl or alkyl.

28. A process according to Claim 27 wherein the secondary amine added to the degassed product is diethylamine, di-n-propylamine, di-n-butylamine, di-isobutylamine, ethyl cyclohexylamine, or di-allylamine.