Thio-thiocarboxylation

Crystalline adducts from thioamides and aromatic acid chlorides ate well known. A very convenient synthesis of diacyl sulfides and thiocarboxylic acids - proceeds via adducts of thio-DMF with acid chlorides. 

Thiols and sulfides are protonated on sulfur in superacid media and give mono- and dialkylsulfonium ions, respectively49. Thiocarboxylic acids, S-alkyl esters, thio-esters, dithioesters and thiocarbonates in similar media also form stable protonated ions179 such as... 

A method of preparing alkanethiols and thiophenols by means of thio-carboxylic acids consists of converting, preferably, thioacetic or thiobenzoic acid by an alkyl (or aryl) halide into an 5-alkyl (or 5-aryl) thiocarboxylate and hydrolysing this by acid or alkali this method, and that described in the following paragraphs, have the advantage that the thiols can be obtained free from sulfide.268... 

Historically, the first chalcogenocarboxylic acid discovered was thiocarboxylic acid - thioacetic acid - reported by Kekule in 1854 [1]. Since then, chalcogenocarboxylic acids, and particularly numerous thio- and dithiocarboxylic acid esters, have been synthesized and summarized in several review articles [2-9]. In contrast, until very recently, little has been known about the chemistry of the congeners containing heavier chalcogen atoms, such as selenium and tellurium, probably due to their instability and the handling difficulties associated with them. In this chapter, the chemistry of chalcogenocarboxylic acids, their syntheses, structures, spectral features and reactions are reviewed. 

The structures of thio- and dithiocarboxylic acids have been studied extensively using IR, UV/Vis and NMR spectra, and molecular orbital calculations for many decades now [3, 7-9]. Thiocarboxylic acids are considered to exist as fast tautomeric equilibrium mixtures of thiol (I) and thioxo (II) forms... 

The required imidoyl chlorides can also be prepared in situ from nitriles and hydrogen chloride. For example, Ishikawa ( ) obtained thio amides in the reaction of nitriles with hydrogen chloride and thiocarboxylic S-acids CII. 

The syntheses of 5-thio-D-arabinose and -lyxose have been achieved conventionally by thiocarboxylate displacements on 5-sulphonate ester derivatives of these sugars, and their methyl glycosides were also prepared, both anomers being obtained. Methyl 5-thiopentopyran-osides (D-arabino. L-lyxo, D-ribo. and D-lyxo derivatives) have also been prepared from methyl 5-thio-3-0-tosyl-o<-D-xylopyranoside as outlined in Scheme 1. The syntheses of S-(5 -deoxy-5 -adenosyl)-(+)-2-methylhomocysteine (14.) has been achieved in two steps from (+)-2-methyl-homocysteine. Methyl 2-0-tosyl-4,6-thioanhydro-K-... 

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