Thermal Reactions of Benzoxazole. Single Pulse Shock Tube Experiments and Quantum Chemical Calculations

Abstract

The thermal decomposition of benzoxazole diluted in argon was studied behind reflected shock waves in a 2 in. i.d. single-pulse shock tube over the temperature range 1000-1350 K and at overall densities of approximately 3 x 10(-5) mol/cm(3). Two major products, o-hydroxybenzonitrile at high concentration and cyclopentadiene carbonitrile (accompanied by carbon monoxide) at much lower concentration, and four minor fragmentation products resulting from the decomposition were found in the postshock samples. They were, in order of decreasing abundance, benzonitrile, acetylene, HCN, and CH=C-CN and comprised of only a few percent of the overall product distribution. Quantum chemical calculations were carried out to determine the sequence of the unimolecular reactions that led to the formation of o-hydroxybenzonitrile and cyclopentadiene carbonitrile, the major products of the thermal reactions of benzoxazole. A potential energy surface leading directly from benzoxazole to cyclopentadiene carbonitrile could not be found, and it was shown that the latter is formed from the product o-hydroxybenzonitrile. In order that cyclopentadiene carbonitrile be produced, CO elimination and ring contraction from a six- to a five-membered ring must take place. A surface where CO elimination occurs prior to ring contraction was found to have very high barriers compared to the ones where ring contraction occurs prior to CO elimination and was not considered in our discussion. Rates for all the steps on the various surfaces were evaluated, kinetic schemes containing these steps were constructed, and multiwell calculations were performed to evaluate the mole percent of the two major products as a function of temperature. The agreement between the experimental results and these calculations, as shown graphically, is very good.

Spectroscopic and theoretical characterization of 2-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-oxide

“…In the present case the bond length of C 22 -C 24 and C 21 -C 23 are 1.4988 and 1.4923 Å, the bond length is very high due to the presence of methyl group. The bond length of C 21 -C 22 is 1.383 Å which is agreement with the reported value [67]. Bigotto et al [68] reported the bond length of C 21 -C 22 as 1.3827 Å.…”

“…Lifshitz et al [67] reported the bond lengths for C 22 -C 24 , C 21 -C 23 as 1.374 and 1.4 Å. In the present case the bond length of C 22 -C 24 and C 21 -C 23 are 1.4988 and 1.4923 Å, the bond length is very high due to the presence of methyl group.…”

UV-Induced Photochemistry of 1,3-Benzoxazole, 2-Isocyanophenol, and 2-Cyanophenol Isolated in Low-Temperature Ar Matrixes

“…However, the studies performed at −40 °C (in methylcyclohexane) seemed to indicate the formation of a different photoproduct, 2-isocyanophenol 4 , which promptly decayed back to 1 upon heating to room temperature . The thermal reaction of benzoxazole under single-pulse shock-tube conditions was also studied . Under those conditions, the main isomerization product was 2-cyanophenol 3 , which subsequently decomposed to cyano-cyclopentadiene and CO.…”

“…18 The thermal reaction of benzoxazole under single-pulse shock-tube conditions was also studied. 19 Under those conditions, the main isomerization product was 2-cyanophenol 3, which subsequently decomposed to cyano-cyclopentadiene and CO.…”

Decomposition, Isomerization, and Ring Expansion in 2-Methylindene: Single-pulse Shock Tube and Modeling Study

“…Moreover, the ring expansion and isomerization products are found to be of very high yield. Experimental results were obtained, modeling and quantum chemical calculations of potential energy surfaces have been performed on molecules such as methylpyrrole, [1][2][3] dimethylpyrrole, 4 methylindole, 5 methylcyclopentadiene, [6][7][8] methylindene (quantum chemical calculations) 9 and others. Some of the studies have been published and some are still in the process of data reduction.…”