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The title 1,3,4-oxadiazole derivative crystallizes as a hemihydrate, C8H6N2O2S·0.5H2O, with the water molecule located on a twofold rotation axis. The 1,3,4-oxadiazole molecule is essentially planar, the r.m.s. deviation of the non-H atoms being 0.0443 Å. The dihedral angle between the mean planes of the phenyl and oxadiazole rings is 6.101 (17)°. In the crystal, molecules are linked via O—H...S and N—H...O hydrogen bonds involving the water molecule, the N—H group and the thione S atom into undulating ribbons. Additional π–π interactions generate a two-dimensional supramolecular framework extending parallel to (001).

3- .4-oxadiazole-2(3H)-thiones were synthesized. The direction of alkvlation aJ 5-atTl-1,3.4-oxadiazoline-2-thiones and their potassium salts was studied relative to the substrate, al~,lating agent, solvent, and reaction conditions.We have previously studied alkylation of 5-substituted 1,3,4-oxadiazole-2(3H)-thiones by various alkyl halides in solvents differing in polarity such as acetone, ethanol, acetonitrile, DMF, and HMPTA at 56-8 I~ Our results showed that the S-alk'yl derivatives were the predominant if not exclusive products in all the cases [1, 2] although the literature data on these reactions are very contradictory [3, 4].In continuation of these studies, we investigated the previously unexamined reaction of 5-aryl-l,3,4oxadiazole-2(3H)-thiones with some chloromethyl alkyl ethers. The extremely labile halogen atom in ot-halodialkyl ethers is the most important feature of these compounds. Strong polarization of the C-CI bond in the or-halo ether molecule occurs under the influence of the alkoxy ~oup [6], leading to the increase of the positive charge on the carbon atom and to the decrease of its polarizability. According to Pearson's theory of hard and soft acids and bases [6], such a carbon atom becomes a more hard electrophile. An increase in the hardness of the electrophilic site of the alkylating agent facilitates the proceeding of reaction at the atom of the ambident anion, which possesses the ~eatest electron density [7]. Such a site in the ambifunctional NH-C=S group in 5-aryl-l,3,4oxadiazole-2(3H)-thione molecule is the nitrogen atom.Hence, we would expect that the reaction of these thiones with chlorometbyl alkyl ethers should lead to N-substituted oxadiazolinethiones, whose analogs could not be obtained in the course of alkylation of these thiones by alkyl halides. The reactions of oxadiazolinethiones with chloromethyl alkyl ethers were carried out under the conditions of the alkylation of the same thiones by haloalkanes, namely, by heating a mixture of the reagents in dry acetone or acetonitrile in the presence of K_,CO3 [I, 2]. 5-Aryl-l,3,4-oxadiazole-2(3H)-thiones (aryl = phenyl, 2-chlorophenyl, 2,4-dichlorophcnyl, and 2-methoxyphenyl) were taken as thc thiones. Chloromethyl mcthyl, chloromcthyl ethyl, and chloromctbyl 1-butyl ethcrs wcrc used as the halo cthcrs. The rcaction conditions were varied principally in the case ofchloromethyl methyl cthcr (Tablc I).

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Methylation of a series of 5-aryl-l,3,4-oxadiazoline-2-thiones with various methylating agents has been described [1][2][3][4]. Radha Vakula and Srinivasan [1] carried out the methylation of the indicated thion~s with dimethyl sulfate in an alkaline medium and thus obtained S-methyl derivatives exclusively. We studied the alkylation of thiones with methyl iodide and other alkyl halides under various conditions [3, 4]. Continuing these studies, we investigated the reaction of the potassit~m salt of 5-(2, .4-dichlorophenyl)-l,3,4-oxadiazoline-2-thione (I) with dimethyl sulfate in a protic (water) and aprotic (HMPT) solvent. When the reaction was carried out in the HMPT medium (equimolar ratio of reactants, 60-80~ 5 h) a mixture of products of S-(IIa) and N-methylation (Ma) was obtained in a high yield (86% based on the thione used); the ratio Ha : ma (according to ESR data) was 85:15.