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.

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

R was found by ESR spectroscopy that asymmetric azines obtained from 3-methyl-2-benzothiazolinone hydrazone can exist in solutions in the form of a mixture of syn and anti isomers, depending on the structure of the carbonyl compound introduced into the condensation reaction.E,Z-Geometric syn and anti isomerism of azines of aliphataic and aromatic carbonyl compounds has been treated in several papers [1][2][3][4]. Asymmetric azines based on 3-methyl-2-benzothiazolinone hydrazone were prepared for the purpose of further synthesis of cyanine dyes [5], but the literature lacks any data on their structure. In order to fill the existing gap in this area, we expanded the number of asymmetric azines based on 3-methyl-3-benzothiazolinone hydrazone and studied the structure of the azines obtained.Azines I-XIII were isolated in the reaction of condensation of 3-methyl-2-benzothiazolinone hydrazone with aldehydes and ketones containing different functional groups.

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