Formate Ester Norrish Type II Elimination:  Diode Laser Probing of Gas-Phase Yields

Abstract

Time-resolved infrared absorption spectroscopy was utilized to monitor the production of HCOOH, CO2, and CO following ultraviolet laser excitation of gas-phase formate esters. Excitation of ethyl formate at 227.5 nm resulted in formation of HCOOH and CO2. The CO2 quantum yield was estimated to be 0.5 ± 0.1. No evidence for CO formation was obtained at this wavelength. Relative quantum yields for the Norrish Type II elimination of HCOOH from ethyl, n-propyl, n-butyl, isopropyl, isobutyl, and tert-butyl formate were obtained at 227.5 and 222 nm. Normalization of the observed HCOOH yields with respect to the number of γ-hydrogen atoms resulted in reactivity trends at 227.5 nm of 1:3:9 for the abstraction of primary, secondary, and tertiary hydrogen atoms, respectively. At 222 nm, a similar reactivity trend was observed with yields per available γ-hydrogen of 1:3:7 for abstraction of primary, secondary, and tertiary hydrogen atoms. Yields were found to be independent of ester pressure over the range 100−550 mTorr. Semiempirical and ab initio calculations of the excited state hydrogen abstraction step were performed and enthalpies of activation of 8−12 kcal/mol were obtained using AM1 with configuration interaction.

A mechanistic model of fast pyrolysis of glucose-based carbohydrates to predict bio-oil composition

“…This formate ester undergoes Norrish type II elimination to form formic acid and a double bond between C4 and C5 (20). 48 It is to be noted that pericyclic dehydration and formic acid elimination involve a cyclic, six-membered transition structure.…”

Valence and Ionic Lowest-Lying Electronic States of Isobutyl Formate Studied by High-Resolution Vacuum Ultraviolet Photoabsorption, Photoelectron Spectroscopy, and Ab Initio Calculations

“…This is important in precombustion CO 2 capture in coal-fired power plants . Isobutyl formate undergoes Norrish Type II elimination, leading to the formation of relatively high yields of formic acid at 5.4 and 5.6 eV incident radiation energy, that upon further photolysis may lead to CO, CO 2 , and free radical formation . Isobutyl formate has also been found as a trace constituent of Los Angeles smog …”

Direct Investigation of the Validity of Vertical Approximation in the Calculation of Transition Moment Matrix Elements: n → π* Transition in Methyl Formate

“…Despite its importance, little attention has been paid to the photochemistry of this class of compounds. New theoretical and experimental insights would be desirable in order to improve the current knowledge on the weak n → π* transition for model compounds such as methyl formate. , As far as we are aware, there is only one experimental study recently published for UV photoabsorption cross-sections of formates . However, there is not any theoretical study for comparing and validating these experimental studies.…”