Comparison of the mechanisms of the thermal decompositions of 2,2′-azisobutane and azoisopropane

Abstract

The gas phase pyrolyses of 2,2′-azoisobutane and azoisopropane have been investigated in the temperature range 471–573 K. The products of 2,2′-azoisobutane (AIB) decomposition result from the following elementary reactions. AIB [graphic omitted] 2t-C₄H₉+ N₂(1), 2t-C₄H₉ [graphic omitted] iC₄H₁₀+ iC₄H₈(2), 2t-C₄H₄ [graphic omitted] 2,2,3,3-tetramethylbutane (3)

The disproportionation-combination rate constant ratio, k_d/k_c, for t-butyl radicals has been determined as 2.60 ± 0.04 in the temperature range 483 to 515 K.

In addition to the corresponding reactions (1) to (3) involving isopropyl radicals, azoisopropane (AIP) decomposition involves the abstraction reaction, iC₃H₇+ AIP [graphic omitted] C₃H₈+ AIP (4). In the temperature range, 518–573 K, k_a is given by the expression, log₁₀k_a/(k_c)^½/cm mol^–½ s^–½= 5.26 ± 0.22 –(41.64 ± 2.31) kJ mol^–1//_{2.303 RT}, and the disproportionation-combination rate constant ratio for isopropyl radicals has been found to fall from 0.52 at 518 K to 0.49 at 573 K.