Synthesis and structure of dihydrazones obtained from the dihydrazide of S,S′-(1,3,4-thiadiazole-2,5-diyl)bis(2-mercaptopropionic acid)

Abstract

It has been established by PMR spectroscopy that dihydrazones obtained by the condensation of the dihydrazide of S,S'-(l,3,4-thiadiazole-2,5-diyl)bis(2-mercaptopropionic acid) with aldehydes, ketone.s, and B-dicarbonyl compounds exist in solution as a mixture of stercoisomeric forms, the ratio of which depends on the structure of the carbonyl compound used in the condensation. E',Z'-conformational (twisting) isomerism due to hindered rotation about an N--CO amide bond and E,Zgeometric syn-and anti-isomerism relative to a C=N bond in bisacyl hydrazone derivatives of 2-mercaptoacetic acid have already been studied by us [1, 2]. However, there are no data in the literature on hydrazones of or-substituted 2-mercaptoacetic acid. With the aim of filling the gap existing in this area we have synthesized and studied the structure 9 f dihydrazones from the dihydrazide of S,S'-(1,3,4-thiadiazole-2,5-diyl)bis(2-mercaptopropionic acid). In the present work the dihydrazide (II) was isolated from the condensation of S,S'-(1,3,4-thiadiazole-2,5-diyl)bis(2-mercaptopropionic acid) dimethyl ester (I) with liydrazine hydrate in 2-propanol. Compound (II) reacts with aldehydes or ketones to form bisacyl hydrazones (IIIa-1), (IV), and (V) (Scheme 1).Scheme 1 llla-j R 1 = H, 1 R t = CH3; a R 2 = 2,3-(MeO)2C6H3; b R 2 = 2,4-(HO) 2C6H3; c R 2 = 2-HO-3-Me0C6H3; dR 2 = 4-(Me)2NC6H4; e'R 2 = 4-CIC6H4; f R 2 = 3-NO2C6H4; g R 2 = 2-BrC6H4; h R 2 ~ 3,4-(OCH20)C6H3; i R 2 = C4H30; j R 2 = 5-(Me)2NC4H20; kR l =R 2 = C3H7; I R 2 = 3,4-(OCH20)C6H3CH2

Synthesis and isomerism of hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide

“…Conformational isomerism of hydrazones obtained from 2,5-dimercapto-1,3,4-thiadiazole has been studied previously [12,13]. Hydrazones in solution exist as a mixture of two conformers (anti/syn), as exemplified by doubled proton resonances assigned to the CH 2 CO, =CH and NH groups in 1 H NMR spectra.…”

“…The percentages of anti -and syn -conformers are calculated from the ratio of integral intensities of these signals. It was found that syn -conformers dominate in DMSO solution [12][13][14].…”

“…Syn -conformers can have two complexation sites and should form dimeric or polymeric structures upon complexation with iron(III), but not monomeric complexes. It was noticed that the percentage of anti -conformer in the DMSO solution of hydrazone prepared from 2,5-dimercapto-1,3,4-thiadiazole and 2-hydroxybenzaldehyde has increased compared to that of hydrazones obtained from benzaldehydes [12,13]. It was suggested that formation of intramolecular hydrogen bonds (IMHB) with the participation of the imino nitrogen lone electron pair and the proton of the 2-hydroxy group is responsible for this effect [11,12].…”