Xanthates, Carbanilates

The sugars react with methyl (or ethyl) chloroformate at 0°C. in the presence of alkali to give a mixture of cyclic carbonate and acyclic 0-meth-oxycarbonyl (or 0-ethoxycarbonyl) derivatives 91), The cyclic carbonate structures resemble those of the isopropylidene cyclic acetals as shown in the formulas. 

In the presence of pyridine and methyl or ethyl chloroformate, the sugars are converted to fully acylated 0-methoxycarbonyl or 0-ethoxycarbonyl derivatives 92), 

A better method for the preparation of the carbonates utilizes the action of carbonyl chloride (phosgene) at 0°C. on pyridine solutions of the sugars. By this method, n-glucose, D-fructose, n-mannose, and L-arabinose dicarbonates have been obtained (P5). 

When the sugar molecule contains only one free hydroxyl group, two moles of the sugar derivative may react with one mole of carbonyl chloride 95). The following formulas illustrate the reaction of 1,2,3,4-tetra-0-acetyl-D-glucopyranose and phosgene to form bis( 1,2,3,4-tetra-O-acetyl-D-glucopyranose) 6-carbonate. 

The xanthates, or dithiocarbonates, are important substances in cellulose technology. They have been studied to some extent with the simple sugars. Their sodium salts are formed from the alcohol, carbon disulfide, and alkali and may be converted to the alkyl esters. 

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