The thermal and photochemical decomposition of cis -1,2-cyclobutanedicarboxylic anhydride in the vapour phase

Abstract

The thermal decomposition of cis-1,2-cyclobutanedicarboxylic anhydride (CBA) has been studied in a static system in the range 625–725 K. The major process observed was a homogeneous unimolecular decomposition to form ethylene and maleic anhydride, with first-order rate parameters A = 1.14(± 0.1) × 10 14 s −1 and E = 55.1 ± 1 kcal/mol. A very minor decomposition channel yielding butadiene, CO 2 , and CO was also observed, with A = 8.4 (± 0.1) ×10 14 s −1 and E = 67.5 ± 1 kcal/mol.The decomposition induced by a pulsed CO 2 laser was also studied briefly; the same two decomposition channels were observed and their dependence on fluence and pressure examined.The ultraviolet photolysis of CBA was also investigated between 210 and 365 nm. In addition to the products found in the thermal reaction, cyclobutene was also a major product, and product ratios were measured as a function of wavelength and added CO 2 . Mechanisms in the three systems are discussed and compared.