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Radiation‐induced oxidation of substituted benzaldehydes: a pulse radiolysis study
Author(s) -
Geeta S.,
Rao B. S. M.,
Mohan H.,
Mittal J. P.
Publication year - 2004
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.713
Subject(s) - radiolysis , chemistry , radical , reaction rate constant , adduct , radiation chemistry , medicinal chemistry , oxidizing agent , substituent , absorption spectroscopy , absorption (acoustics) , photochemistry , chemical reaction , kinetics , organic chemistry , physics , quantum mechanics , acoustics
The reactions of the oxidizing radicals hydroxyl radical ( . OH), azidyl radical $({\rm N}_3^\cdot)$ and sulfate radical anion $({\rm SO}_4^{-\cdot})$ with hydroxy‐, methoxy‐, chloro‐ and nitro‐substituted benzaldehydes were studied by pulse radiolysis. The rate constants for the . OH reaction [ k ≈ (2.6–12.0) × 10 9 l mol −1 s −1 ] with these compounds are higher than those for the ${\rm N}_3^\cdot$ or ${\rm SO}_4^{-\cdot}$ reactions [ k ≈ (0.01–4.2) × 10 9 l mol −1 s −1 ]. The . OH reaction shows a significant substituent effect which is reflected in the rate constants ( k ≈ 12.0 × 10 9 dm 3 mol −1 s −1 with hydroxybenzaldehyde and k ≈ 3.0 × 10 9 dm 3 mol −1 s −1 with nitrobenzaldehyde). The transient species produced by the reaction of . OH with the m ‐substituted benzaldehydes shows an absorption maximum at 370–400 nm, whereas the p ‐substituted isomers exhibit two absorption peaks centred around 325 and 410 nm, except in the case of p ‐nitrobenzaldehyde, which shows only a single peak at 330 nm. These spectra are identical with the spectra obtained for the $({\rm N}_3^\cdot)$ or ${\rm SO}_4^{-\cdot}$ reactions with substituted benzaldehydes. . OH adduct formation and subsequent decomposition to the corresponding phenoxyl radicals is the main reaction channel for the . OH‐induced oxidation of substituted benzaldehydes. One‐electron oxidation by $({\rm N}_3^\cdot)$ or ${\rm SO}_4^{-\cdot}$ of substituted benzaldehydes proceeds via an electron transfer process producing the corresponding radical cations. Copyright © 2004 John Wiley & Sons, Ltd.