GB1573357A

GB1573357A - Production of perchloromethyl mercaptan

Info

Publication number: GB1573357A
Application number: GB52417/77A
Authority: GB
Original assignee: Stauffer Chemical Co
Current assignee: Stauffer Chemical Co
Priority date: 1976-12-22
Filing date: 1977-12-16
Publication date: 1980-08-20
Also published as: JPS5379812A; IT1092244B; FR2375202A1; CH639364A5; NL7713849A; IL53443A0; IL53443A; FR2375202B1; MX5809E; DE2755186A1

Abstract

Perchloromethyl mercaptan is prepared catalytically from chlorine and carbon disulphide. The reagents are brought into contact with I. a carbonyl compound of the formula (A) or (B), or II. a phosphate or a phosphite, or a mixture of these, or III. a phosphonate or a phosphonite, or a mixture of these, in a quantity which suppresses the formation of carbon tetrachloride and sulphur monochloride. <IMAGE>

Description

(54) PRODUCTION OF PERCHLOROMETHYL MERCAPTAN (71) We, STAUFFER CHEMICAL COMPANY, a corporation organised under the laws of the State of Delaware, United States of America, of Westport, Connecticut 06880, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which is to be performed, to be particularly described in and by the following statement:- This invention relates to the production of perchloromethyl mercaptan; more particularly, it relates to the use of carbonyl compounds or phosphates and/or phosphites or phosphonates and or phosphonites as additives which serve to improve the yield of perchloromethyl mercaptan.

Perchloromethyl mercaptan, C13CSCI, also known as trichloromethanesulphenyl chloride, has commercial importance as an intermediate in the manufacture of fungicides, bactericides, germicides, herbicides, soil fumigants and pharmaceuticals.

Perchloromethyl mercaptan was first described in a production scheme by Rathke in Annalen, Volume 167, at Page 195 (1873). Rathke's method, which is still in use today, utilizes an iodine catalyst. The reaction scheme operates most efficiently at temperatures below 400 C. in accordance with the following equations: CS2+3CI2eCC13SCI+SCi2 (1) 2CS2+5CI2 < 2CC13SCl+S2Cl2 (2) CS2+ 3Cl2CCl4+S2Cl2 (3) In addition to sulphur dichloride, sulphur chloride (also known as sulphur monochloride) and carbon tetrachloride, the reaction may also form thiophosgene and other compounds as unwanted by-products. Although more volatile byproducts, such as carbon tetrachloride and sulphur dichloride, may be removed from the reaction mixture by distillation, it is extremely difficult to separate perchloromethyl mercaptan from sulphur chloride by this method. This is due to the fact that the boiling points of perchloromethyl mercaptan and sulphur chloride are very close to each other.

The prior art has proposed several methods for improving the basic Rathke method. For example, U.S. Patent No. 3,544,625 discloses a method for producing perchloromethyl mercaptan by chlorinating carbon disulphide in the presence of a solution of inorganic acids, such as hydrochloric acid. U.S. Patent No. 3,673,246 discloses a continuous process for producing perchloromethyl mercaptan wherein carbon disulphide is reacted with chlorine on or in intimate contact with activated carbon at temperature of from -5 to +100"C. U.S. Patent No. 3,808,270 discloses a continuous process for producing perchloromethyl mercaptan by reacting carbon disulphide and chlorine in a reaction zone filled with granular active carbon completely immersed in the liquid reaction mixture while maintaining temperatures of from 40 to 1350C. U.S. Patent No. 3,878,243 discloses a homogeneous catalyst system comprising a lead salt of a carboxylic acid which is soluble in carbon disulphide.

Notwithstanding the effectiveness of the above methods for producing perchloromethyl mercaptan (PMM), they do not deal with preventing the tendency of PMM to react with chlorine or sulphur dichloride to form carbon tetrachloride, sulphur and sulphur monochloride. Mixtures of carbon disulphide, sulphur dichloride and perchloromethyl mercaptan also react in a similar fashion. The reactions which form carbon tetrachloride are believed to be accelerated by trace amounts of rnetals, such as iron, tin and bronze, in the reaction mixture.

Small quantities of iron are generally present in the commerical carbon disulphide and chlorine used as reactants for PMM at levels of the order of parts per million. The chlorine may be treated by passing it through a glass wool filter to remove most of the iron. However, the presence of iron at levels as low as one part per million may be deleterious and capable of effecting significant reductions in the yield of perchloromethyl mercaptan. It has, therefore, been an objective of industry to develop agents capable of ameliorating the effect of metallic impurities present in the reactants and/or catalyst so that the formation of carbon tetrachloride, sulphur monochloride and other undesirable by-products is suppressed.

Another problem in the production of perchloromethyl mercaptan occurs in the decomposition of sulphur dichloride to sulphur chloride and chlorine in the following manner: 2SCI2aS2C12tCl2 (4) This reaction is undesirable due to the fact that the boiling points of perchloromethyl mercaptan and sulphur chloride are so close to each other that it is impractical to separate them by distillation. Thus, it has also been an objective of industry to develop agents for stabilizing sulphur dichloride to thereby prevent it from forming sulphur chloride and chlorine.

In accordance with the present invention, improved yields of perchloromethyl mercaptan or suppression of undesired by-products may be achieved by addition of certain additives to the reaction system.

In general terms, the present invention provides a process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst and in the presence of: (a) one or more difunctional carbonyl compounds; (b) one or more phosphates and/or one or more phosphites; or (c) one or more phosphonates and/or one or more phosphonites; when one or more difunctional carbonyl compounds are present, the catalyst being iodine, activated carbon or a lead salt; or when one or more phosphates and/or one or more phosphites or one or more phosphonates and/or one or more phosphonites are present, the catalyst being activated carbon.

In a first embodiment, the present invention provides a process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst selected from iodine, activated carbon or a lead salt and in the presence of one or more difunctional carbonyl compounds.

In a second embodiment, the present invention provides a process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst which is activated carbon and in the presence of one or more phosphates and/or one or more phosphites.

In a third embodiment, the present invention provides a process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst which is activated carbon and in the presence of one or more phosphonates and/or one or more phosphonites.

The carbonyl compounds that have been found to be most effective in accomplishing the purposes of the present invention are difunctional in nature and preferably correspond to one of the following general formulae:

wherein R independently represents alkoxy or optionally substituted hydrocarbyl; R indepedently represents alkyl or hydrogen; and X independently represents hydrogen or halogen; and n represents zero or an integer of from 1 to 3.

Typical examples of hydrocarbyl groups are C1-C20 preferably C1-C10 alkyl, cycloalkyl, aralkyl, alkarvl and aryl.

Typical examples of substituted alkyl and substituted aryl groups are alkyl or aryl groups having attached thereto at least one substituent selected from halogen, cyano, carboxyl, carboxylate, amido, amino, nitro, hydroxy or alkoxy, with the proviso that the substituent(s) does/do not adversely affect the preparation of perchloromethyl mercaptan. The preferred substituent is halogen, most preferably chlorine.

A typical example of an aryl group is phenyl. Typical alkaryl groups may be cresyl or xylyl; and a typical aralkyl group may be benzyl. Typical examples of the preferred difunctional carbonyl compounds and derivatives thereof found to be especially effective in increasing the yield of perchloromethyl mercaptan, are the alkyl diones having from 4 to 10 carbon atoms, i.e. the butane diones, pentanediones, hexane diones, heptanediones, octane diones, nonane diones, decane diones, mixtures thereof and isomers thereof.

Improved yields of perchloromethyl mercaptan have also been achieved by the addition of small amounts of phosphates and/or phosphites to the reaction system.

The particularly effective phosphates and phosphites preferably respectively correspond to the following general formulae:

wherein R, R', and R", independently represent hydrogen or optionally substituted hydrocarbyl, provided that at least one of R, R', and R" represents other than hydrogen.

The above description regarding preferred substituents applies equally to the present case.

Typical examples of the preferred phosphates and/or phosphites found to be especially effective in increasing the yield of perchloromethyl mercaptan have alkyl and/or substituted alkyl groups having 4 to 10 carbon atoms.

Improved yields of perchloromethyl mercaptan have also been achieved by the addition of small amounts of phosphonates and/or phosphonites to the reaction system.

The particularly effective phosphonates and phosphonites preferably respectively correspond to the following general formula:

wherein R independently represents hydrogen optionally substituted hydrocarbyl or chlorine R' and R" independently represents hydrogen or optionally substituted hydrocarbyl; provided that in (E) at least one of R, R' and R" represent other than hydrogen.

Typical phosphonates and/or phosphonites found to be especially effective in increasing the yield of perchloromethyl mercaptan have alkyl and/or substituted alkyl groups having from 4 to 10 carbon atoms.

The addition of the additives in the production of perchloromethyl mercaptan is accomplished most effectively by contacting the compounds in situ with carbon disulphide and catalyst, followed by addition of chlorine.

The phosphates and/or phosphites and the phosphonates and/or phosphonites must be used with a catalyst chosen to be inert to these compounds. For example, these compounds will not function with an iodine catalyst.

For the carbonyl compounds the reaction temperatures required for batch process production of PMM are generally lower than the temperatures which may be maintained in a continuous process. For example, batch process temperatures are generally from 10 to 400C when using a carbon or iodine catalyst. At above 400C in a batch process PMM would tend to decompose into CCI4 and S2CI2. The iodine-catalyzed system is preferably run below 40"C in either a batch or continuous reaction. The carbon-catalyzed system may operate in a continuous mode at temperatures above 400C if carried out in accordance with U.S. Patent No. 3,808,270.

For the phosphorus-containing compounds, it has been found that activated carbon is most effective as a catalyst. The activated carbon catalyst is contacted with the carbon disulphide and chlorine reaction mixture over an extended period of time while maintaining the reaction temperature between 0 and 135"C. Again, for operation with these compounds it should be noted that the reaction temperatures required for batch process production of PMM are generally lower than the temperatures which may be maintained in a continuous process. For example, batch process temperatures are generally from 10 to 400C when using a carbon catalyst.

The additives are generally added in amounts of from 0.01 to 10%, preferably from 0.1 to 5% by weight based on the carbon disulphide feed. Larger amounts may be used, however, no advantage is accrued thereby.

In the Examples which follow, all parts and percentages are by weight, unless otherwise indicated.

Examples 1 to 8 and 10 illustrate the practice of the present invention using the difunctional carbonyl compounds.

EXAMPLES 1 to 9 In a 250-millilitre glass jacketed flask fitted with a chlorine inlet tube, dry ice condenser and mechanical stirrer, 76 grams (1 mole) of carbon disulphide and 0.3 gram of iodine were contacted with 0.5 gram of 2,3-hexanedione. This mixture was then contacted with 182 grams (2.6 moles) of chlorine, bubbled in over a 4+ hour period. During the chlorine contacting, the reaction temperature was maintained, using external cooling, at a temperature of from 20 to 240 C. The reaction mixture was then vacuum distilled at temperatures of from 70 to 1000C. at 200 mm. of mercury. 141.4 grams (0.76 mole) of perchloromethyl mercaptan were obtained.

This is an 89% yield based upon the chlorine reacted. The above procedure was repeated successively except for the use of different difunctional carbonyl additives. The results are tabulated below: Example Additive Amount, Grams PMM Yield /n 2 Ethyl acetoacetate 0.5 82

CH3C-CH2C-CH2CH3 II II O 0 3 Diethyl malonate 0.5 86 CH3CH20CCH2COCH2CH3 II 11 00 4 Dimethyl oxalate 0.5 83 CH3OC-COCH3 II /I OO 5 Acetyl acetaldehyde 0.5 85 dimethyl acetal CH3C-CH2-CHOCH II I O OCH3 6 Acetylacetone 0.5 91 CH3C-CH2-C-C113 II II O 0 7 Acetylacetone 0.1* 93 8 Benzoin 0.5 85 0 yo t)H 9 80 (for comparison purposes only) * 0.2 gram of iodine used EXAMPLE 10 76 grams (1 mole) of carbon disulphide, 28 grams of charcoal (CXAL coconut charcoal from Union Carbide), and 0.5 gram of acetylacetone were placed into a 250 ml. glass jacketed flask fitted with a chlorine inlet tube, dry ice condenser and mechanical stirrer. Thermostated water (250C.) was continuously cycled through the reactor jacket. The solution was stirred and 182.0 grams (2.6 moles) of chlorine was bubbled through the reaction mixture over a 4-hour period. A total of 198 grams of liquid was separated from the charcoal by vacuum distillation at temperatures of from 70 to 1000C. under a vacuum of from 50 to 60 mm. Hg. A total of 119 grams was obtained as a distillate, 74 grams as a dry ice trap condensate and an additional 5 grams were obtained by washing the charcoal with chloroform.

Analysis of the various fractions of liquid indicated a yield of 122 grams of PMM, which is a 78% yield based on the chlorine reacted. The yield of side product CCl4 was 2% of the theoretical amount.

EXAMPLE 11 (For Comparison Purposes Only) The same procedure as Example 10 was repeated without an additive. After the reaction was completed, 219 grams of liquid were obtained comprising 128 grams of distillate, 85 grams as a dry ice trap condensate and 5.7 grams obtained by washing the charcoal with chloroform. Analysis of the various fractions by gas chromatography indicated a yield of 128.5 grams of PMM, which is a 69% yield based on the chlorine reacted and a 19% yield of CCl4.

Examples 12 to 15 illustrate the practice of the present invention using the phosphate and phosphite compounds.

EXAMPLE 12 (Continuous Reaction) A l+" I.D. glass tube was filled to a height of 30" with 812 mesh size granular activated carbon (CXAL coconut charcoal from Union Carbide). The glass reactor was fitted with a top inlet for CS2 feed and a bottom inlet for Cl2 feed, as well as a bottom drain for collecting the crude product. A reflux condenser was fitted to the vapour outlet of the column in order to avoid the loss of CS2. CS2 was added to the reactor in an amount sufficient to cover the catalyst bed. C12 was then metered to the reactor until about 90% of the CS2 had been reacted (by gas liquid chromatographic analysis). Cl2 and CS2 were then fed to the reactor simultaneously in the ratio of 3 moles CVmole CS2. Crude PMM was withdrawn from the bottom of the reactor at a rate such that the liquid level in the reactor was maintained at the top of the catalyst bed. The maximum temperature in the reactor was maintained at not more than 110"C. by limiting the CS2 feed rate to about 0.16 gm.

CS2/gm. catalyst per hour.

This run was then repeated except for the addition of 3% weight (based on CS2) tributyl phosphate (TBF) to the CS2 with the following results: Without With 3% TBF TBF % CS2 conversion 98.0 98.2 % Selectivity for PMM 78.8 96.4 % Selectivity for CCI4 21.2 3.6 % S2Cl2 in distilled product 11.0 2.4 % PMM yield on CS2 77.2 94.7 % CCl4 yield on CS2 20.8 3.5 EXAMPLES 13 to 15 76 grams of carbon disulphide (1 mole), 30 grams of activated carbon (CXAL coconut charcoal from Union Carbide), and 0.38 gram of tributoxyethylphosphate were placed into a 250-ml. glass jacketed flask fitted with a chlorine inlet tube, dry ice condenser and mechanical stirrer. Thermostated water at a temperature of 35"C. was continuously cycled through the jacket. The solution was stirred and 182.9 grams of chlorine were bubbled through the solution over a 4-hour period. A total of 247 grams of liquid residue was recovered from the jacketed flask after separation from the charcoal. This material was analyzed by gas liquid chromatography (glc). The results are shown in - the- Table below. The above procedure was repeated except for different additives with the results shown in the Table.

TABLE Example Additive PMM Yield, %"' % CCI4 13 Tributoxyethyl phosphate 95 5 (C4H9OCH2CH2O)2NO 14 Tris(betachloroethyl) phosphate (CICH2CH20)3P=O 99.3 0.7 15 Dibutyl acid phosphate'2' 99.8 0.2

(1 All yields based upon C12 consumed, analysis by glc.

(2) Charcoal was washed with HCI, then neutralized.

Examples 16 to 20 illustrate the practice of the present invention using the phosphonate and phosphonite compounds.

EXAMPLE 16 (Continuous Reaction) A l+" I.D. glass tube was filled to a height of 30" with 8--12 mesh size granular activated carbon (CXAL coconut charcoal from Union Carbide). The glass reactor was fitted with a top inlet for CS2 feed and a bottom inlet for C12 feed, as well as a bottom drain for collecting the crude product. A reflux condenser was fitted to the vapour outlet of the column in order to avoid the loss of CS2. CS2 was added to the reactor in an amount just sufficient to cover the catalyst bed. Cl2 was then metered to the reactor until about 90% of the CS2 had been reacted as determined by gasliquid chromatographic analysis. Cl2 and CS2 were then fed to the reactor simultaneously in the ratio of 3 moles Cl2/mole CS2. Crude PMM was withdrawn from the bottom of the reactor at a rate such that the liquid level in the reactor was maintained at the top of the catalyst bed. The maximum temperature in the reactor was maintained at not more than 110"C. by limiting the CS2 feed rate to about 0.16 gm..CSJgm. catalyst per hour. The above procedure was then repeated, except that dimethyl methylphosphonate (DMMP) was added to the CS2 feed at a level of 0.5%, by weight, based on CS2. The results are tabulated below: No Additive 0.5% DMMP % CS2 Conversion 98.0 98.8 % Selectivity for PMM 78.8 94.8 % Selectivity for CCI4 21.2 5.2 % S2Cl2 in distilled product 11.0 1.9 % PPM yield on CS2 77.2 93.7 % CCl4 yield on CS2 20.8 5.1 EXAMPLES 17 to 21 (Batch Reaction) 76 grams of carbon disulphide (1 mole), 30 grams of activated carbon (CXAL coconut charcoal from Union Carbide), and 0.28 gram of dimethyl ethyl phosphonoacetate were placed into a 250-ml. glass jacketed flask fitted with a chlorine inlet tube, dry ice condenser and mechanical stirrer. Thermostated water at a temperature 350C. was continuously cycled through the jacket. The solution was stirred and 182.9 grams of chlorine were bubbled through the solution over a 4hour period. A total of 247 grams of liquid residue was recovered from the jacketed flask after separation from the charcoal. This material was analyzed by gas-liquid chromatography (glc). The results are shown in the Table below. The procedure was again successively repeated using different additives and using no additive with the results shown in the Table.

TABLE Example Additive PMM Yield, O/,''' CCI4

17 Dimethyl ethyl phosphonoacetate 85 1 (CH3O)2PCH2COOC2H5 0 18 Dimethyl methyiphosphonate'2' 100 0 (CH2O)2PCH3 0 19 Tetra(,B-chloroethyl)ethylene 99.8 0.2 bisphonate [(ClCH2CH2O)2PCH2i2 0 20 Tetraethyl methylene bisphosphonate 99.8 0.2 [(CH3CH2O)2Pi 2CH2 0 21 None 77 21 (for comparison purposes only) '1} All yields based upon Cl2 consumed, analysis by glc.

12} Charcoal was washed with HCI, then neutralized.

WHAT WE CLAIM IS: 1. A process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst and in the presence of: (a) one or more difunctional carbonyl compounds; (b) one or more phosphates and/or one or more phosphites; or (c) one or more phosphonates and/or one or more phosphonites; when one or more difunctional carbonyl compounds are present, the catalyst being iodine, activated carbon or a lead salt; or when one or more phosphates and/or one or more phosphites or one or more phosphonates and/or one or more phosphonites are present, the catalyst being activated carbon.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. from the bottom of the reactor at a rate such that the liquid level in the reactor was maintained at the top of the catalyst bed. The maximum temperature in the reactor was maintained at not more than 110"C. by limiting the CS2 feed rate to about 0.16 gm..CSJgm. catalyst per hour. The above procedure was then repeated, except that dimethyl methylphosphonate (DMMP) was added to the CS2 feed at a level of 0.5%, by weight, based on CS2. The results are tabulated below: No Additive 0.5% DMMP % CS2 Conversion 98.0 98.8 % Selectivity for PMM 78.8 94.8 % Selectivity for CCI4 21.2 5.2 % S2Cl2 in distilled product 11.0 1.9 % PPM yield on CS2 77.2 93.7 % CCl4 yield on CS2 20.8 5.1 EXAMPLES 17 to 21 (Batch Reaction) 76 grams of carbon disulphide (1 mole), 30 grams of activated carbon (CXAL coconut charcoal from Union Carbide), and 0.28 gram of dimethyl ethyl phosphonoacetate were placed into a 250-ml. glass jacketed flask fitted with a chlorine inlet tube, dry ice condenser and mechanical stirrer. Thermostated water at a temperature 350C. was continuously cycled through the jacket. The solution was stirred and 182.9 grams of chlorine were bubbled through the solution over a 4hour period. A total of 247 grams of liquid residue was recovered from the jacketed flask after separation from the charcoal. This material was analyzed by gas-liquid chromatography (glc). The results are shown in the Table below. The procedure was again successively repeated using different additives and using no additive with the results shown in the Table. TABLE Example Additive PMM Yield, O/,''' CCI4 17 Dimethyl ethyl phosphonoacetate 85 1 (CH3O)2PCH2COOC2H5 0 18 Dimethyl methyiphosphonate'2' 100 0 (CH2O)2PCH3 0 19 Tetra(,B-chloroethyl)ethylene 99.8 0.2 bisphonate [(ClCH2CH2O)2PCH2i2 0 20 Tetraethyl methylene bisphosphonate 99.8 0.2 [(CH3CH2O)2Pi 2CH2 0 21 None 77 21 (for comparison purposes only) '1} All yields based upon Cl2 consumed, analysis by glc. 12} Charcoal was washed with HCI, then neutralized. WHAT WE CLAIM IS:

1. A process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst and in the presence of: (a) one or more difunctional carbonyl compounds; (b) one or more phosphates and/or one or more phosphites; or (c) one or more phosphonates and/or one or more phosphonites; when one or more difunctional carbonyl compounds are present, the catalyst being iodine, activated carbon or a lead salt; or when one or more phosphates and/or one or more phosphites or one or more phosphonates and/or one or more phosphonites are present, the catalyst being activated carbon.

2. A process for the preparation of perchloromethyl mercaptan which

comprises reacting chlorine and carbon disulphide in the presence of a catalyst selected from iodine, activated carbon or a lead salt and in the presence of one or more difunctional carbonyl compounds.

3. A process as claimed in claim 2 in which the carbonyl compound(s) correspond(s) to one of the following general formulae:

wherein R independently represents alkoxy, or optionally substituted hydrocarbyl, R' independently represents alkyl or hydrogen; and X independently represents hydrogen or halogen; and m represents zero or an interger of from 1 to 3.

4. A process as claimed in claim 3 in which the carbonyl compound(s) is/are (an) alkyl dione(s) having from 4 to 10 carbon atoms.

5. A process as claimed in claim 3 or claim 4 in which the carbonyl compound(s) is/are present in an amount of from 0.01 to 10%, by weight, based on the carbon disulphide.

6. A process as claimed in claim 5 in which the carbonyl compound(s) is/are present in an amount of from 0.1 to 5%, by weight, based on the carbon disulphide.

7. A process as claimed in claim 2 substantially as herein described.

8. A process as claimed in claim 2 substantially as herein described with reference to any one of Examples I to 8 or 10.

9. Perchloromethyl mercaptan when prepared by a process as claimed in any of claims 2 to 8.

10. A process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst which is activated carbon and in the presence of one or more phosphates and/or one or more phosphites.

II. A process as claimed in claim 10 in which the phosphate(s) and/or phosphite(s) respectively correspond(s) to the following general formulae:

wherein R, R', and RN independently represent hydrogen or optionally substituted hydrocarbyl; provided that at least one of R, R' and RH represents other than hydrogen.

12. A process as claimed in claim 10 or claim 11 in which the phosphate(s) and/or phosphite(s) is/are alkyl and contain(s) from I to 10 carbon atoms.

13. A process as claimed in any of claims 10 to 12 in which the phosphate(s) and/or phosphite(s) is/are present in an amount of from 0.01 to 10%, by weight based on the carbon disulphide.

14. A process as claimed in claim 13 in which the phosphate(s) and/or phosphite(s) is/are present in an amount of from 0.1 to 5%, by weight of the carbon disulphide.

15. A process as claimed in claim 10 substantially as herein described.

16. A process as claimed in claim 10 substantially as herein described with reference to any one of Examples 12 to 15.

17. Perchloromethyl mercaptan when prepared by a process as claimed in any of claims 10 to 16.

18. A process for the preparation of perchloromethyl mercaptan which comprises reacting chlorine and carbon disulphide in the presence of a catalyst which is activated carbon and in the presence of one or more phosphonates and/or one or more phosphonites.

19. A process as claimed in claim 18 in which the phosphonate(s) and/or phosphonite(s) respectively correspond(s) to the following general formulae:

wherein R independently represents hydrogen chlorine or optionally substituted hydrocarbyl, R' and R" independently represent hydrogen or optionally substituted hydrocarbyl; provided that in the former case, at least one of R, R' and R" represents other than hydrogen.

20. A process as claimed in claim 19 in which the phosphonate(s) and/or phosphonite(s) is/are alkyl and contain(s) from 1 to 10 carbon atoms.

21. A process as claimed in any of claims 18 to 20 in which the phosphonate(s) and/or phosphonite(s) is/are present in an amount of from 0.01 to 10%, by weight, based on the carbon disulphide.

22. A process as claimed in claim 21 in which the phosphonate(s) and/or phosphonite(s) is/are present in an amount of from 0.1 to 5%, by weight based on the carbon disulphide.

23. A process as claimed in claim 18 substantially as herein described.

24. A process as claimed in claim 18 substantially as herein described with reference to any one of Examples 16 to 20.

25. Perchloromethyl mercaptan when prepared by a process as claimed in any of claims 18 to 24.