Decomposition of alkyl dixanthogens in aqueous solutions |
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| Authors: | MH Jones JT Woodcock |
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| Institution: | CSIRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria 3207 Australia |
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| Abstract: | Alkyl dixanthogens, (ROCSS)2, decompose in aqueous solution in the presence of nucleophiles in many ways.It is proposed here that in alkaline solution the principal methods of decomposition of ethyl dixanthogen are by simultaneous attack of OH? ions on the sulphur-sulphur bond to give products which include xanthate ion (ROCSS?) and peroxide (H2O2) and on the carbon-sulphur bond to give products which include monothiocarbonate ion (ROSCO?), sulphide ion (S2?), and sulphur (S0). Above pH 12 reaction is complete in a few minutes, and more monothiocarbonate than xanthate is formed. At pH 9 the reaction takes over 20 h and more xanthate than monothiocarbonate is formed.The primary products react further to give various ions which depend in part on the pH of the system. In alkaline solution some of the xanthate and peroxide react to give perxanthate (ROCSSO?). In acid solution both xanthate and monothiocarbonate decompose rapidly; CS2 is formed from xanthate and OCS from monothiocarbonate.In the presence of other nucleophiles at pH 9.2, dissolved dixanthogen decomposes much more quickly than with OH? alone, and other reactions occur. With thiosulphate a higher proportion of xanthate is formed together with some xanthyl thiosulphate and monothiocarbonate but no perxanthate. With sulphite (in the absence of oxygen) or cyanide the products include xanthate and monothiocarbonate but no perxanthate. With sulphite in the presence of oxygen, perxanthate is also formed.Suspensions of dixanthogens react slowly but in a similar fashion to dissolved dixanthogens.Longer-chain dixanthogens are much less soluble than ethyl dixanthogen but, in general, react in a similar way. Higher temperatures increase the rate of decomposition by OH?.This work has various implications in operating plants. |
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