Synthesis and structure of dihydrazones obtained from the dihydrazide of 1,3,4-thiadiazole-2,5-dithioglycolic acid

Abstract

Using PMR spectroscopy we have established that dihydrazones, obtained by condensation of the dihydrazide of 1,3, 4-thiadiazole-2,5-dithioglycolic acid with aldehydes, ketones, or b-dicarbonyl compounds, exist in solutions as a mixture of stereoisomeric forms due to conformational and geometric isomerism.E',Z'-conformational (rotational) isomerism as a result of hindered rotation about the N-CO amide bond and E,Zgeometric syn-, anti-isomerism relative to the N=C bond in hydrazones [1, 2] and aroylhydrazones [3] have been studied in sufficient detail. However, no data are available in the literature on such a phenomenon in ambifunctional compounds containing two hydrazone groups. With the goal of filling in the existing gap in this area, we synthesized and studied the structure of dihydrazones based on the dihydrazide of 1,3,4-thiadiazole-2,5-dithioglycolic acid (I).In patent [4], the starting dihydrazide (I) is obtained by esterification of the corresponding acid followed by condensation of the diester formed (lla) with hydrazine hydrate.We proposed a more convenient and simple method for synthesis of dihydrazide I. The diesters lla, b were obtained as a result of direct alkylation of 2,5-dimercapto-l,3,4-thiadiazole by the corresponding esters of monobromoacetic acid in the presence of potassium hydroxide, both in an isopropanol medium and in water under phase transfer catalysis conditions in the presence of triethylbenzylammonium chloride (TEBA). Compounds IIa, b easily react in isopropanol with hydrazine hydrate, forming dihydrazide I, the condensation of which with aldehydes or ketones leads to dihydrazones (Ilia-s). Their characteristics are presented in Tables 1 and 2.

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].…”

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

“…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.…”

Succinic acid dihydrazide: a convenient N,N-double block for the synthesis of symmetrical and non-symmetrical succinyl-bis[5-trifluoro(chloro)methyl-1H-pyrazoles]

“…In the same year, Al-Talib et al 13 reported that the reaction of oxalic, malonic and succinic acid dihydrazide with 2,4-pentanedione gave smoothly the corresponding oxalyl-, malonyl-and succinyl-N,N'-bis(3,5-dimethyl-1H-pyrazole). It is also important to mention that aroyl and heteroaroyl spacer bispyrazoles have been synthesized employing 1,3-dicarbonyl compounds or derivatives thereof and, for example, isophthalic acid dihydrazide 14 or 1,3,4-thiadiazole-2,5-dithioglycolic acid dihydrazide, 15 respectively.…”