Mercaptan, acidity addition reactions

The striking effect of the catalyst is exemplified by the reaction of pregna-4, 16-diene-3,20-dione (10) with benzyl mercaptan. In the presence of piperidine only conjugate addition occurs to give (11) whereas with pyridine hydrochloride only the 3-benzyl thioenol ether (12) is formed. In the presence of p-toluenesulphonic acid both reactions take place to yield (13). 

Mercaptoacetone reacts with methyl propiolate to give a 1 1 adduct, which then cyclizes to a substituted thiophene. Similar addition reactions of mercaptans with acetylenic acids have also been reported by Owen and Sultanbawa. ... 

Cassaday (1950), Shostakovski et al. (1951) and Melnikov et al. (1952) investigated extensively the addition reactions of dialkyl phosphorodithioic acids to unsaturated dicarbonic acid esters, and found that the dialkyl phosphorodithioic acids are added at the double bond in the same way as are mercaptans. This reaction was used by Cassaday (1950) who prepared 0,0-dimethyl-S-(l,2-dicarbethoxy)-ethyl phosphorodithioate by the addition reaction of dimethyl phosphorodithioic acid and maleic acid diethyl ester. This compound, known by the name malathion (89), became one of the most important phosphorus ester insecticides because of its low toxicity to warm-blooded animals. 

With this kind of assignment of bond energy we can go on to have a look at some of the chemical reactions in which both of these molecules (mer-captans and disulfides) would be involved. The rather obvious one of the redox system between some mercaptans and disulfides will be reserved for a later part of the discussion. We shall first look at the acidity of the mercaptans and then at some of the ordinary addition reactions which mercaptans can undergo. 

Mercaptans can also add to other types of unsaturation—simple C=C unsaturation. It is a common procedure now to use mercaptans and thiol acids to add to olefins, and it is a common method of introducing a sulfur into the compounds containing the olefinic group. However, in general, those reactions are much slower and require more vigorous catalytic conditions than do the ordinary carbonyl additions. There is more that could be described on the addition reactions, but I think that there are too many other items of interest to us, which will prohibit our spending any more time on them. 

Besides polar additions, radical additions such as the photochemical (287) or peroxide-catalysed (121, 122) mercaptan addition have been investigated. Catalytic hydrogenation has been the object of particularly thorough study. In cases where optical induction is possible, addition reactions afford a means of synthesizing optically active amino acids. 

Other additives that may be incorporated include sodium hydrogen phosphates as buffering agents to stabilise that pH of the reaction medium, lauryl mercaptan or trichlorethylene as chain transfer agents to control molecular weight, a lubricant such as stearic acid and small amounts of an emulsifier such as sodium lauryl sulphate. 

Ethylene oxide polymerization may be initiated similarly by substances (alcohols, amines, mercaptans) capable of generating a hydroxyl group through reaction with the monomer. In the presence of strongly acidic or basic catalysts, successive addition of ethylene oxide molecules proceeds rapidly in the following manner ... 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

Ethyl mercaptan reacts with DMAD to give a 1 1 adduct through a trans mode of addition. WeibulP has reported that a mixture of both fumarate and maleate is formed from cyclohexyl mercaptan with propiolic acid. A similar observation has been made in the reaction of cyclohexyl mercaptan with acetylenedicarboxylic acid. ... 

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... 

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