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S-Methyl Dithizone and the Structure of Metal Dithizonates

1952; Nature Portfolio; Volume: 169; Issue: 4305 Linguagem: Inglês

10.1038/169756a0

1476-4687

H. M. N. H. Irving, Charles Bell,

Chemical Reaction Mechanisms

ALTHOUGH diphenylthiocarbazone (‘dithizone’, I or II, X = H) is probably the most widely used of all organic reagents for trace-metal determinations, its structure, and more particularly the structure of its metal complexes, are still in doubt. Several metals form two dithizone complexes, that with the lower proportion of metal being termed the keto-form, the metal-rich complex being known as the enol form. Following Hellmut Fischer1, it is commonly supposed that in the keto form it is a hydrogen atom from the imido group of dithizone that is replaced by a metal (I, X = monovalent metal; IV, Y = divalent metal); whereas in the enol form the hydrogen atom from the sulphydryl group of the tautomeric form of the reagent (II, X = H) is replaced by metal as well (II, X = monovalent metal; V, Y = divalent metal). There is virtually no experimental evidence for these formulations, which are nevertheless reproduced in standard text-books2, though some of them are impossible on steric grounds alone.