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

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 C 8 H 8 SO 2 ( 1 ): 7-[FF]C † C † FFF-0: C 8 H 8 + SO 2 and C 8 H 8 ( 2 ): 3-[F † F † ]C-0: C 8 H 8 ( 3 ). For the cheletropic extrusion, breaking of the C 7 –S and C 8 –S bonds begins respectively at Rx = −2.7434 amu 1/2 Bohr and Rx = −1.7458 amu 1/2 Bohr, and formation of the sulfur dioxide is completed at Rx = −0.2494 amu 1/2 Bohr. For the electrocyclic reaction, formation of new C 7 –C 8 bond occurs at Rx = 1.6214 amu 1/2 Bohr from C- to C- coupling between the generated pseudoradical centers at Rx = 0.1474 amu 1/2 Bohr on the terminal carbon atoms.