Experimental and computational investigations of the products of halogenation of 1,2-chalcogenazole 2-oxides

Reactions with Cl, Br, and I yield products formed by one or more of three processes: halogenation of the chalcogen, protonation, and halogenation of the heterocycle. The halogenation reactions of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide, benzo-1,2-selenazole 2-oxide and benzo-1,2-tellurazole 2-oxide were investigated in organic solution. The products were identified by single-crystal X-ray diffraction, and characterized by NMR, IR spectroscopies and mass spectrometry. The outcomes of the reactions resulted from one or more of three processes: (i) halogenation of the chalcogen, (ii) protonation, and (iii) halogenation of the heterocycle. Molecules in which the chalcogen was halogenated and protonated behaved as very weak Brønsted acids and displayed a strong affinity for bromide ions, crystallizing with tetraalkyl ammonium cations. In the case of benzo-1,2-selenazole 2-oxide, the heterocycle was chlorinated before the selenium atom. Chalcogen and hydrogen bonding are structural features that determine molecular arrangement in these crystals.