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.

Hydrazones obtained from the known isonicotinic acid hydrazide and also their complexes with metals are used as antibacterial and antitubercular preparations [1], analytical reagents [2], and dyestuffs [3]. However there are no literature data on hydrazones obtained from 2-mercapto-5-(4-pyridyl)-1,3,4-oxadiazole (1).In the present work a method of synthesis of hydrazides is proposed from compound 1 using direct alkylation of monobromoacetic or 2-chloropropionic acid methyl esters in the presence of an alkaline component both in 2-propanol and in water under interphase catalysis conditions in the presence of triethylbenzylammonium chloride (TEBA) with the formation of the corresponding methyl esters 2,3. These esters then condensed readily with hydrazine hydrate forming the hydrazides 4,5. The latter condense with aldehydes and ketones giving the acylhydrazones 6a-i (Scheme 1).Conformational (rotating) isomerism due to hindered rotation around an N-CO double bond and geometric s.vn,anti isomerism relative to an N=C bond has already been studied by us in certain heterocyclic hydra,zones [4,5]. We have established analogously to the data in the cited works that acylhydrazones 6a-i in DMSO solution exist as a mixture of two stereoisomers, what follows from the doubling of the proton signals of the CH2CO, CHCO, =CH, and NH groups in the ~H NMR spectra. These signals coalesce on heating the solutions to 120~ In agreement with the data of [4,5] the proton signals of the CH2CO, CHCO, and NH groups of the Z-conformer of acylhydrazones 6a-i are also found at higher field, but the proton signal of the =CH group is at lower field compared to the signal of the E-isomer. The reaction products of 13-dicarbonyl compounds with acid hydrazides may form systems with hydrazone, enehydrazine, 5-hydroxypyrazoline, or pyrazole forms [4,6,7]. The interaction of acetylacetone with the hydrazides of (2-benzothiazolylthio)-and (2-benzoxazolylthio)acetic acids leads to the formation of a pyrazole system [4], however on studying the JH NMR spectrum of the condensation product of hydrazide 4 with aeetylacetone a doublet was detected for the CH2 group protons corresponding to a pyrazole ring with a chemical shift of 2.80 ppm and a singlet for a hydroxyl group proton at 6.41 ppm. An intense absorption

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

Das Mercaptobenzothiazol (I) reagiert mit Formalin zu der N‐Hydroxymethylverbindung (H), die mit Halogenalkylsulfonaten oder 1,3‐Propansulton zu den Derivaten (III).oder über das Chlorid (IV) zu Dithiocarbamaten (V) umgesetzt wird.

Reaction o/" 2,5-dimercapto-l,3,4- mono-and dialka,l-suhstituted 2.5-dimercapto-l,3,4-thiadiazoles. Keywords: monoammonium, monopyridinium, monohydrazine, and dihydrazine salts of 2,5-dimercapto-1,3,4-thiadiazole, mono-and dialkylation of salts of 2,5-dimercapto-1,3,4-thiadiazole.The formation of monohydrazine salt of 2, 5-dimercapto-l,3,4- The reaction of compound 1 with excess of hydrazine hydrate at roorn temperature leads to compound 2a, which melts with decomposition at 117~ Similar reaction in boiling ethanol leads to compound 2b, which melts with decomposition at 168~ The boiling of an ethanolic solution of compound 2a results in the release of gas and the formation of compound 2b. If it is assumed that compound 2a is hydrazine salt and 2b is hydrazide, then the last should form hydrazones by reaction with aldehydes. However, the reaction of compound 2b with 2-hydroxybenzaldehyde leads to a compound which corresponds in its physical parameters and LH NMR spectrum to the physical parameters and spectrum of 2,2'-dihydroxybenzalazinc, obtained by the reaction of 2-hydroxybenzaldehyde with hydrazine hydrate [6]. On the basis of these data, the proposal is made that compound 2a is dihydrazine salt of 2,5-dimercapto-l,3,4-thiadiazole, and 2b is monohydrazine salt. Compound 1 formed salt 2c in the reaction with ammonia. Salt 2d was obtained by analogy [2].The UV spectra of compounds 2a-d show a strong absorption band at 336 nrn, which is probably associated with electronic transitions of the thiadiazole ring.