Thallium triacetate in acetic acid gave clean regeneration of both aldehydes and ketones from their toluene-p-sulphonylhydrazones. The reagent gave N-aroyl-N' -acetyl-NV-phenylhydrazines from aromatic aldehyde phenylhydrazones without prior dehydrogenation to nitrilimine intermediates.
Considerable recent interest1 -4 has focussed on reagents which can regenerate carbonyk compounds from crystalline hydrazone derivatives. Thallium triacetate in acetic acid has now proved an effective reagent for this purpose with toluene-p-sulphonylhydrazones. While thallium trinitrate in methanol has previously been used to regenerate carbonyl compounds from oximes, 5 the reactions of thallium triacetate with hydrazone systems have not been reported despite extensive studies of the reactions of hydrazones with the isoelectronic oxidising agents lead tetraacetate 6 and, more recently, mercuric acetate. 7 -10
Treatment af a range of ketone and aldehyde toluene-p-sulphonylhydrazones with T~(OAC)~ in acetic acid gave a clean high-yield regeneration of the carbonyl compound at ambient temperatures for aldehydes and reflux temperatures for ketones.11 For the corresponding toluene-p-sulphonylhydrazones (Scheme) the results were, Rl, R2 , per cent yield of carbonyl compound (l?lR2CO): Ph, H, 80; p-ClC6H4, H, 82;
p-MeC6H4, H, 90; Ph, Me, 76(90 min. reflux); Ph, Ph, 4Q(2 h. reflux); cyclohexanone, 'X)(30 min. reflux); camphor, (2 h. reflux) 50 %.
In each case the remaining products were hydrazones recovered and thallium (I) toluene-p-sulphonate and the reactions were generally clean and without decomposition. By analogy with lead tetraacetate 12 -14 and mercuric acetate 7 the reaction probably involved the intermediate m. Acetolysis of this to the unstable acetal w would regenerate the carbonyl compound. A similar acetolysis has been suggested recentl$5 for cleavage of N-bromotoluene-p-sulphonylhydrazones. When benzophenone toluene-p-sulphonylhydrazone was treated with T~(OAC)~ in dry methanol, the products contained a 7 : 1 ratio of benzophenone and its dimethylketal,