Photolytic cleavage of 1-(2-nitrophenyl)ethyl ethers involves two parallel pathways and product release is rate limited by decomposition of a common hemi-acetal intermediate

J E T Corrie, A Barth, V R N Munasinghe, D R Trentham, M C Hutton

Research output: Contribution to journalArticlepeer-review

120 Citations (Scopus)

Abstract

Time-resolved FTIR spectroscopic studies of the flash photolysis of several 1-(2-nitrophenyl)ethyl ethers derived from aliphatic alcohols showed that a long-lived hemiacetal intermediate was formed during the reaction. Breakdown of this intermediate was rate-limiting for product release. One of these compounds (methyl 2-[1-(2-nitrophenyl)ethoxy]ethyl phosphate, 9) was studied in detail by a combination of time-resolved FTIR and UV-vis spectroscopy. In addition, product studies confirmed clean photolytic decomposition to the expected alcohol, 2-hydroxyethyl methyl phosphate, and the 2-nitrosoacetophenone byproduct. At pH 7.0, 1 C, the rate constant for product release was 0.11 s-1, very much slower than the 5020 s-1 rate constant for decay of the photochemically generated aci-nitro intermediate (pH 7.0, 2 C). Time-resolved UV-vis measurements showed that the hemiacetal intermediate is formed by two competing pathways, with fast (~80% of the reaction flux) and slow (~20% of the flux) components. Only the minor, slower path is responsible for the observed aci-nitro decay process. These competing reactions are interpreted with the aid of semiempirical PM3 calculations of reaction barriers. Furthermore, AMSOL calculations indicate that the pKa of the nitronic acid isomer formed by photolysis is likely to determine partition into the alternate paths. These unusual results appear to be general for 1-(2-nitrophenyl)ethyl ethers and contrast with a related 2-nitrobenzyl ether that photolyzed without involvement of a long-lived hemiacetal.
Original languageEnglish
Pages (from-to)8546 - 8554
Number of pages9
JournalJournal of the American Chemical Society
Volume125
Issue number28
DOIs
Publication statusPublished - 16 Jul 2003

Fingerprint

Dive into the research topics of 'Photolytic cleavage of 1-(2-nitrophenyl)ethyl ethers involves two parallel pathways and product release is rate limited by decomposition of a common hemi-acetal intermediate'. Together they form a unique fingerprint.

Cite this