TY - JOUR
T1 - Thermal reactions of benzoxazole. Single pulse shock tube experiments and quantum chemical calculations
AU - Lifshitz, Assa
AU - Tamburu, Carmen
AU - Suslensky, Aya
AU - Dubnikova, Faina
PY - 2006/4/6
Y1 - 2006/4/6
N2 - 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 ∼3 × 10 -5 mol/cm3. 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.
AB - 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 ∼3 × 10 -5 mol/cm3. 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.
UR - http://www.scopus.com/inward/record.url?scp=33646383868&partnerID=8YFLogxK
U2 - 10.1021/jp057063u
DO - 10.1021/jp057063u
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
AN - SCOPUS:33646383868
SN - 1089-5639
VL - 110
SP - 4607
EP - 4613
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 13
ER -