Key words: 2-,3-, and 4-methylbiphenyls, 4,4'-dimethylbiphenyl, 4-tert-butylbiphenyl, 4,4'-di-tert-butylbiphenyl, thermal stability, critical temperatures, kinetic parameters
The kinetics of gas-phase thermal transformations of 4-methyl-, 4,4'-dimethyl-, 4-tert-butyl-, and 4,4'-di-tert-butylbiphenyls in the temperature ranges 813 ÷ 848, 733 ÷ 793, 703 ÷ 763, 703 ÷ 763 K, respectively, is studied. It is found that in the case of tert-butyl-bi phenyls a competition between сracking and isomerization of alkyl substituents in aromatic rings of initial substance and products is taking place. Kinetic parameters of overall conversion of alkyl-biphenyls (ABF) are determined and used for the prediction of their thermal behavior in the conditions of synthesis, processing, and exploitation. It is experimentally stated that 2-, 3-, and 4-methylbiphenyls and their mixtures with toluene in the whole range of compositions are thermally unstable at critical temperatures (600 ÷ 780 K).