Atmospheric chemistry of isopropyl formate and tert-butyl formate

Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH₃)₂, and tert-butyl formate, HC(O)OC(CH ₃)₃. Product distributions are reported from both Cl- and OH-initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the α-ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15-20%). The OH radical initiated oxidation of tert-butyl formate gives acetone, formaldehyde, and CO₂ as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10^-12, and with Cl (1.75 ± 0.35) × 10^-11, and for tert-butyl formate with Cl (1.45 ± 0.30) × 10^-11 cm³ molecule^-1 s^-1. Simple group additivity rules fail to explain the observed distribution of sites of H-atom abstraction for simple formates.