Carbohydrates thiocarbonates

The most significant discovery in the history of carbohydrate thiocarbonates was reported in 1892 by Cross, Bevan, and Beadle, who found that cellulose reacts with a mixture of aqueous sodium hydroxide and carbon disulfide to give a soluble dithiocarbonate derivative, from which cellulose can be regenerated. This observation, the basis of the Viscose process, was made at a time when only one other polyhydric alcohol thiocarbonate, that of glyceritol, was known. The subsequent industrial development of... 

Of the many possible types of carbohydrate thiocarbonates, only a few have been synthesized. The essential difference between the preparations of carbonates and thiocarbonates is that, in the former case, one method may introduce different types of substituents, whereas, with the thiocarbonates, this complication has not so far arisen. The methods are thus classified according to the different types of thiocarbonate. 

The rearrangement of carbohydrate thiocarbonates has also been reported by Doane and co-workers [46,47]. As depicted in Scheme 26, thionocarbonate 89 was treated with potassium iodide in acetonitrile to give monothiolcarbonate 90 in 84% yield. This method was also successfully applied to furanoses bearing other protecting groups as well as similar pyranoside derivatives. 

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. 

A need exists for a systematization of the nomenclature used for carbonate and thiocarbonate esters of carbohydrates, and the nomenclature employed in this review, based on modern chemical usage, shows clearly and unambiguously the nature of the groups described (see Table I). 

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. 

Tables III and IV record the melting points, specific rotations, and methods of preparation of some carbonates and thiocarbonates of carbohydrates.

Carbohydrates, allyloxycarbonates, 123 carbonates of, 151 chloroformyl esters of, 102 conformational analysis of, 12 reaction of, with carbon dioxide, 129 with carbon disulfide, 135 with carbonic acid, 129 with phosgene in acetone, 105 thermochemical properties of, 21 thiocarbonates of, 157 Carbonic acid, esters, 91,92,151 bis(methyl 3,4-0-isopropylidene-/3-D-arabinopyranoside), 2,2 -, 96 bis(1,2,3,4 - tetra - O - acetyl -/J - D - glucose), 6,6 -, 104 cyclic, 103... 

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