Kinetic and mechanistic study on the pyrolysis of 1,3-dihydroisothianaphthene-2,2-dioxide toward benzocyclobutene using RRKM and BET theories

Abstract

The kinetics and mechanisms of pyrolysis of 1,3-dihydroisothianaphthene-2,2-dioxide toward benzocyclobutene have been theoretically studied using canonical transition state theory (CTST), statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory, and bonding evolution theory (BET) in conjugation with M06-2X/aug-cc-pVTZ calculations. The CTST slightly breaks down to estimate the reaction rate of the cheletropic extrusion. RRKM results indicated that the cheletropic extrusion and electrocyclic reaction require energy barriers of 171.3 and 122.2 kJ/mol to be overcome; and can be characterized respectively by 7 and 3 phases associated to the sequence of catastrophes C8H8SO2(1):7-[FF]C†C†FFF-0:C8H8+SO2 and C8H8(2):3-[F†F†]C-0:C8H8(3). For the cheletropic extrusion, breaking of the C7-S and C8-S bonds begins respectively at Rx=−2.7434 amu1/2Bohr and Rx=−1.7458 amu1/2Bohr, and formation of the sulfur dioxide is completed at Rx=−0.2494 amu1/2Bohr. For the electrocyclic reaction, formation of new C7-C8 bond occurs at Rx=1.6214 amu1/2Bohr from C- to C- coupling between the generated pseudoradical centers at Rx=0.1474 amu1/2Bohr on the terminal carbon atoms.