Synthesis of 5-Phenyl-(5,6-Diphenyl-)-2,3-Dihydro-1,2,4-Triazine-3-Thions and Investigation of Their Reactions with 1,2-Dibromoethane

Abstract

5-Phenyl-(5,6-diphenyl-)-1,2,4-triazine-3(2H)-thions (1,2) were synthesized by condensation of phenylglyoxal monohydrate with thiosemicarbazide and benzyl with thiosemicarbazide hydrochloride, respectively. Phenylglyoxal monohydrate was obtained by oxidation of acetophenone with selenous acid by the Riley reaction, while benzyl (1,2-diphenylethane-1,2-dione) waw obtained by oxidation of (2-hydroxy-1,2-diphenylethanone) benzoin with nitric acid by the known procedure. The compounds 1 and 2 were studied in reactions with 1,2-dibromoethane in various ratios. The interaction of triazinethione 1 with 1,2-dibromoethane in molar ratios of 1:1 and 1:2 led to the formation of a previously unknown 3-[(2-bromoethyl)sulfanyl]-5-phenyl-1,2,4-triazine (3а). Using a double excess of 1,2-dibromoethane increased the yield of compound 3а by 11 %. The interaction of triazinethione 2 with 1,2-dibromoethane in molar ratios 1:1 and 2:1 led to the formation of 3-[(2-bromoethyl)sulfanyl]-5,6-diphenyl-1,2,4-triazine (3b). In the 1H NMR spectra of compounds 3a,b there are signals of aromatic ring protons in the region of 7.23-8.81 ppm, a triplet of protons of the SCH2 group at 3.22 and 4.06 ppm, and a triplet of protons of the CH2Br group at 4.39 and 5.28 ppm. It is of interest that1,2-bis-(5-phenyl-[1,2,4]triazinyl-3-sulfanyl)-ethane is formed in the case of the reaction of compound 1 with 1,2-dibromoethane in the 2:1 ratio of reagents. In the 1H NMR spectra of the latter, in contrast to the spectrum of compound 3a, there is a signal of the S-CH2 group protons, which are equivalent in this structure and form a singlet at 3.79 ppm. Compound 3a was also studied by chromatography-mass spectrometry (direct sample insertion). It should be noted that under the conditions of mass spectrum imaging, the bromine atom is split off and the mass spectrum shows a peak with m/z 216 with an intensity of 38% and no peak of the molecular ion. The peak with the maximum intensity (m/z 116, 100 %) seems to correspond to 4-thia-6,7-diaza-1-azoniumbicyclo[3.2.0]hept-1(5)-ene. Its high intensity is due to the fact that the structure of the 1,2-dihydrotriazetium cation is aromatic.