Synthesis of Dithiocarboxylic Acids

Synthesis of Dithiocarboxylic Acids.—Several methods of long standing have been applied recently, although a procedure which is appropriate in all, or even most, cases is still lacking. 

Thiolysis of phenyl trichloroacetate, ClaCOgPh, yields potassium trithio-oxalate, KaiSgCCOS], and the reaction of benzyl chlorides or bromides with elemental sulphur and methoxide ion has proved to be a very convenient method for the preparation of pure dithiocarboxylic acids.  

The most important synthetic route now, as before, is the addition of Grignard reagents to carbon disulphide. 3 -3  

Activated methylene, or methyl groups, e.g. in A-methylpicolinium iodide and related compounds, are readily attacked by CSa. The resulting dithio-carboxylate ion is methylated by excess of A -methylpicolinium iodide to yield (166).  

Various attempts to achieve reductive dimerization of CSg in order to obtain tetrathio-oxalates have been unsuccessful, the product isolated after methylation always being the l,3-dithiole-2-thione (167). Carbon monosulphide, CS , is involved in the formation of (167), and has been detected as the stable complex Rh(CS)(PPh3)2.  

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Several methods for the synthesis of dithiocarboxylic acids and esters have been pub-lishedJ84-86 They have been summarized by Ramadas et alJ8T ... 

Synthesis of Dithiocarboxylic Acids and their Derivatives.—The preparation of thioterephthalic acid from l,4-di(chloromethyl)benzene, sulphur, and sodium methoxide (see Vol. 5, p. 179) has beeil reported by another group. In a similar reaction, the addition of chloroacetonitrile to sulphur and triethylamine in DMF, followed by alkylation, gave methyl and ethyl cyanodithioformates. These were not isolated, but they condensed when water was added, giving EfZ mixtures of l,2-di(alkylmercapto)-l,2-dicyanoethylenes. Ethylene dithioacetals from aromatic aldehydes are decomposed by sodium hydride in DMF containing HMPA, with elimination of ethylene and the liberation of an aryIdithiocarboxylate anion this may be alkylated to give the dithioester (Scheme 8). ... 

Dithiocarboxylate salts of Group 1 elements are an important class of compounds for the synthesis of dithiocarboxyhc acid derivatives. Anhydrous alkali salts of the dithiocarboxyhc acid of 4-methyldithiobenzoic acid, such as 1-5, are obtained in solid form by the reaction of the dithiocarboxyhc acid 6 with alkali... 

This method is not general and only a limited number of 5-alkyl-l,2,3,4-thiatriazoles were prepared by this reaction. Ikeda and co-workers have described a convenient method for the synthesis of both 5-alkyl- and 5-aryl-l,2,3,4-thiatriazoles 9 by reaction of l-methyl-2-thioacylpyridinium salts 143 with sodium azide (Scheme 33). Compound 143 can be prepared from pyridium salt 142 by reaction with dithiocarboxylic acid derivatives. The synthesis can conveniently be carried out as a one-pot reaction from 2-chloro-l-pyridinium salt 142 and carbodithioate leading to final compounds 9 in high yields. The 5-alkyl-l,2,3,4-thiatriazoles 9 were isolated as oils <1990S415, 1990ZC67>. 

The addition of amine to the bicyclic salt (96) initially takes place not in position 3, but in position 5, as in the reaction with mercaptans the reaction then proceeds by the same steps to yield the ester of the 1-aminocyclopent-l-ene 2-dithiocarboxylic acid (118). This ester (118) is obtained in yields of 30-65% its structure has been confirmed by independent synthesis from 119. This reaction course is again confined to the special system 118, the homologous tetramethylene-trithionium salts yielding Schiff s bases on reaction with primary amines under the same conditions.50... 

Contrary to carboxylic acids which, under normal conditions, only give salts with amines, dithiocarboxylic acids, RCS2H, are quite reactive in nucleophilic displacement reactions. However, the compounds are unpleasant to handle and, due to their limited stability, often give only low yields of thioamides in the reaction with amines.The approach was successfully employed in the synthesis of thiobenzoyl azolides, e. g. in the formation of (7) according to equation (4). °... 

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