Reaction of NO3 Radicals with 1,3‐Cyclohexadiene, α‐Terpinene, and α‐Phellandrene: Kinetics and Products

Abstract

AbstractThe gas‐phase reaction of NO3 radicals with 1,3‐cyclohexadiene, α‐terpinene, and α‐phellandrene has been studied in a flow system at 298 K in the pressure range 8<P(mbar)<250 using GC‐MS/FID, MS, and long‐path FT‐IR as detection techniques. At a total pressure of 15 mbar N2 rate constants for the primary attack of NO3 were determined with the relative rate method to be (1.08±0.02) 10−11, (1.03±0.06) 10−10, and (5.98±0.20) 10−11, respectively (unit: cm3 molecule−1 s−1).As buffer gas in the product studies served N2 or He as well as O2/N2 mixtures. In the case of 1,3‐cyclohexadiene the formation of the corresponding oxirane (7‐oxa‐bicyclo[4.1.0]hept‐2‐ene) up to a yield of 90% at P<35 mbar and the formation of benzene (about 6%) was observed. The oxirane yield was independent on the amount of added O2 and decreased with increasing total pressure. In the case of α‐terpinene and α‐phellandrene no indication of oxirane formation was found. However, the corresponding aromatic compound (p‐cymene) was detected for both terpenes, maximum yield 6% for α‐terpinene and 22% for α‐phellandrene. For all reaction systems investigated the formation of organic nitrate‐compounds was proved by means of long‐path FT‐IR measurements. In the case of the 1,3‐cyclohexadiene degradation with [O2]>5·1015 molecule cm−3 an absorption band was detected in addition assigned to a carbonylic group. There were no indications for a reaction of O2 with the adduct radical (NO3/diene).