Thiocarbonic half esters

For the preparation of thiocarbonic half esters, alkoxides or thiolates are added to carbon disulfide or carbonyl sulfide to the following scheme (where M = a metal)  

The xanthates are formed with extreme ease, so that almost all alcoholic hydroxyl groups can be brought into reaction in this way. 

General directions for preparation of xanthates 755 Finely powdered potassium hydroxide (56 g, 1 mole) is dissolved in the requisite amount of an alcohol, the solution is cooled to room temperature, and carbon disulfide (76 g, 1 mole) is added with stirring during 30 min. After a further hour s stirring, ether is added to complete the precipitation of the xanthate, which is then filtered off and recrystallized from ethanol. Yields are 80-95 %. 

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The carbonates and thiocarbonates may be classified quite simply into the following types, (i) Mixed Esters. In these esters, the carbonic acid or thiocarbonic acid is esterified with both an alcohol and a carbohydrate, (ii) Acid Esters. Here, a metal salt of a half-ester of a carbohydrate has been formed, (iii) Intermolecular Esters. Here, an ester has been formed between one molecule of the acid and two molecules of carbohydrate, (iv) Cyclic or Intramolecular Esters. Here, one molecule of the acid is di-esterified with one molecule of carbohydrate. 

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