Gas phase reaction of selected isothiocyanates with OH radicals using a smog chamber-mass analyzer system

Relative rate constants for the gas phase reaction of methyl isothiocyanate (1), ethyl isothiocyanate (2), allyl isothiocyanate (3), phenyl isothiocyanate (4), 2-methylphenyl isothiocyanate (5), benzoyl isothiocyanate (6), and 4-methoxyphenyl isothiocyanate (7) with OH radicals have been determined at 297±2 K and 9.21×10^-2 Atm in a 20 L smog chamber-coupled online with a quadrupole mass analyzer, in which the concentration of the reaction partners could be determined online every minute. Some of the photoproducts could be detected and identified by HRGC-MS and HRGC-FTIR spectroscopy. The rate constants of the isothiocyanates obtained for the OH radical reactions ranged between 12.8 and 99.5×10^-12 cm³ molecule^-1 s^-1. The indicated errors were of 2-least-squares standard deviations. The lifetimes of the investigated compounds in the troposphere due to reactions with the OH-radicals were calculated and ranged from 3.5 to 18.8 h by using the tropospheric concentration of OH radicals of 8.0×10⁵ molecules cm^-3 over a period of 24 h.