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The esters PhCH(OT)CO2T (2), PhCH2CO2T (5), PhCO2T, (6), and 1-AdCO2T (7, Ad = 1adamantyl), T = 2,2,6,6-tetramethyl-N-piperidinyl, undergo thermal decomposition at 120 °C in toluene with the formation of carboxylic acids, 2,2,6,6-tetramethylpiperidine (TH), and bibenzyl in all cases, indicative of the formation of 2,2,6,6-tetramethylpiperidinyl radicals, but excluding the formation of the radicals PhCH2CO2• and 1-AdCO2•. Qualitative kinetic measurements show that 5-7 react much faster than expected for rate-limiting bond-homolysis, suggesting the occurrence of induced decomposition. Addition of 2,6-di-tert-butyl-4-methylphenol (BHT) to the reaction of PhCH2CO2T in hexane accelerates the reaction, with a first-order dependence on [BHT], and leads to the formation of the characteristic dimers 9 and 10 from 2,6-di-tert-butyl-4methylphenoxyl radical (12). These reactions of the esters 5-7 are interpreted to occur by molecule-induced homolysis, in which a hydrogen atom from toluene or BHT is transferred to oxygen forming RCO2H and the 2,2,6,6-tetramethylpiperidinyl radical T• in a concerted process. Comparable behavior is observed for reactions in chloroform. PhCH(OT)CO2T (2) is proposed to form an intermediate PhCH(•)CO2T (1) which gives α-lactone 19. Density functional calculations are used to model the overall energy changes in these reactions.

Thermolysis of N-tetramethylpiperidinyl esters: homolytic fragmentation and induced decomposition