N-Arylation of azoles with low basicity by 1,4-dimethoxybenzene during undivided electrolysis

The reactions of 1,4-dimethoxybenzene with 4-nitropyrazole, 3,4-dinitro-5-methylpyrazole, 1,2,4-triazole, 3-nitro-1,2,4-triazole, and tetrazole were studied during undivided amperostatic electrolysis on a Pt electrode in MeCN, CH₂Cl₂, and MeOH. The main reaction products were 2-azolyl-1,4-dimethoxybenzenes and (or) 1,4-diazolyl-1,4-dimethoxycyclohexa-2,5-dienes. In all cases except 1,2,4-triazole, N-arylation occurs only in the presence of the Alk₄N⁺ salts of azoles or 2,4,6-trimethylpyridine as a base. The mechanism of the reactions is discussed.     

On the nature of the mobile charge in passivating coatings based on lead-borosilicate glasses

The temperature dependences of the mobile charge in lead-borosilicate glass passivating coatings are investigated. Mechanisms are proposed for the formation of the mobile charge in the structure of the glass. It is shown that the temperature dependence of the mobile charge becomes stronger with increasing content of the crystal phase in the interior volume of a passivating coating. Zh. Tekh. Fiz. 69, 141–142 (August 1999)     

N-Dimethoxyphenylation of highly basic pyrazoles during undivided electrolysis

The reactions of pyrazole, 3,5-dimethylpyrazole, and its 4-nitro derivatives with 1,4-dimethoxybenzene during undivided amperostatic electrolysis in MeCN (CH₂Cl₂) were studied. The basicity of the medium, which depends on the solvent nature, the nature and concentration of pyrazole and the acid-base properties of additives, and the amount of electricity passed determine the yield and relative content of the target products, viz., 1,4-dimethoxy-2-(pyrazol-1-yl)benzenes (1) and 1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-dienes (2). The process occurs mainly through the interaction of the nonionized solvato complex of pyrazole with the 1,4-dimethoxybenzene radical cation and affords radical intermediates structurally similar to compounds 1 and 2. The key stage of the process determining the 1 : 2 ratio is the rearrangement of the intermediately produced 1,4-dimethoxy-1-(pyrazol-1-yl)arenonium cation to the 1-(pyrazol-1-yl)-2,5-dimethoxyarenonium cation.