2-methyl-3-thiosemicarbazone formation

Fig. 11.7 (A) E1cB mechanism for the elimination reactions of 4-nitrophenylethylpyridinium ions catalysed by OH deprotonation is rate limiting at pKa s below the breakpoint data are from reference [16] and the line is calculated from Eqaution 11.11. (B) Effect of increasing 3-quinuclidinol buffer concentration on the rate constants for 2-methyl-3-thiosemicarbazone formation from 4-chlorobenzaldehyde at pH 11.10 results are consistent with a change in the rate-limiting step from proton transfer to formation of the intermediate data from reference [8],...

See footnote 56 in J.M. Sayer and W.P. Jencks, Mechanism and Catalysis of 3-Methyl-3-thiosemicarbazone Formation. A Second Change in Rate-Determining Step and Evidence for a Stepwise Mechanism for Proton Transfer in a Simple Carbonyl Addition Reaction, J. Am. Chem. Soc., 1973,95, 5637. 

Recent studies have been directed towards the synthesis of heterocyclic hydrazones which have lower toxicities than thiosemicarbazones [44], It has been proposed that the hydrazinic N-H group is essential for activity since it might be involved in a crucial radical formation step important in the mechanism of RDR. This is supported by the loss of antileprotic activity for this series of compounds when the hydrazinic hydrogen is replaced by a methyl group [44]. The heterocyclic hydrazones, like thiosemicarbazones, behave as tridentate ligands. 

Methyl pyruvate thiosemicarbazone in the presence of zinc chloride or acetate resulted in the formation of complexes with the ligand hydrolyzed or transesterified. The complexes with pyruvate thiosemicarbazone, ZnL2, or ethyl pyruvate thiosemicarbazone, ZnLCl2 were structurally characterized by single-crystal X-ray crystallography showing respectively a distorted octahedral and distorted square pyramidal geometry.874... 

Copper Complex formation with 5,5-di-methyl-1,3-cyclohexanedione bis(4-phenyl-3-thiosemicarbazone) 0.8-8 Reaction medium 2.5-3.0moir HCI. Both fixed time and initial rate were used... 

Irradiation of 2-methyl-4-phenyl-substituted benzaldehyde thiosemicarbazones (171) leads to the corresponding A -l,2,4-triazohne-5-thione derivatives (173) through the formation of stable 1,2,4-tria-zoHdine-5-thione derivatives (172) (Scheme 27). Irradiation of N-acylthiourea (174) in the presence of triethylamine gives thiourea (175) and benzothiazoles (176) via an electron-transfer mechanism. A photochemicaUy induced Dimroth rearrangement has been reported in the l,2-thiazolino[5.4-d]-l,2-thiazoline-3,6-dithione (177) and yields the 3ff,6ff-l,2-dithiolo[4.3-c]-l,2-dithiole (178). ... 

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