Preparation of thiocarbonic acid derivatives

This Section consists of a review of the most important methods of preparing thiocarbonic acid derivatives. The space available suffices for details of the processes in only a few cases, and for others the literature cited must be consulted. 

Since carbonyl sulfide and thiophosgene are used particularly often for preparation of these compounds, convenient methods of obtaining them in the laboratory will be described first. For the preparation of dicyanogen see page 105. 

When pure, carbonyl chloride is a colorless, odorless, easily flammable gas with a strong narcotic action. It is soluble in organic solvents, and water dissolves about its own volume of the gas. Carbonyl sulfide decomposes gradually in aqueous solution to carbon dioxide and hydrogen sulfide. 

Dry tetrahydronaphthalene (182 g) is heated in flask A to 195-200°. Then dry trichloromethanethiol (465 g) is added from the dropping funnel at a steady rate during 4-5 h a gentle, regular reaction ensues, with evolution of a stream of brown vapors of which hydrogen chloride forms part. Most of the thiophosgene condenses in flask B the hydrogen chloride 

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Carbon disulfide is a useful synthon for the preparation of thiocarbonic acid derivatives (see Chapter 8, p. 135). Carbon disulfide will react with alkynes (18) under forcing conditions the reaction is facilitated by the presence of electron-... 

Methods for the preparation of organic sulfur compounds by alteration of sulfur-containing groups already present include reduction, oxidation, and cleavage. The preparation of thiocarbonic acid and its derivatives is treated at the end of the present Chapter. For the rearrangement of sulfur compounds see the Section on p. 1074. 

The Schiff bases (18) are metallated under kinetically controlled conditions to give mostly the enamines (19), whereas under thermodynamic conditions the corresponding Z-isomers predominate. The thiocarbonic acid derivatives (20, R = CHaPh, R = Et) react with electrophiles at the a-position, after metalla-tion however, for (20, R=H or Ph) metallation and alkylation take place exclusively at the R group. This latter sequence has been used for the preparation of the oxathiolanes (21) from ketones [R R C(O)] and (20, R = R = Me). ... 

For many years, the carbohydrate esters of carbonic acid and thiocar-bonic acid have found important application as intermediates in the synthesis of otherwise difficultly accessible derivatives. A review of these esters is particularly opportune, because both their preparation and properties are considerably influenced by stereochemical factors which require interpretation in the light of modem concepts of reaction mechanisms and conformational analysis. Although the historical development of the chemistry of the carbonic and thiocarbonic esters of carbohydrates has been independent, it is appropriate to give a comparative treatment of their closely related structures and properties. 

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