Redox chemistry ofhydroxycinnamic acids: A pulse radiolysis study

Journal of Chemical Sciences

P Yadav²  J P Mittal2¹  H Mohan¹  B S M Rao1² 

[1] Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India$$;National Centre for Free Radical Research, Department of Chemistry, University of Pune, Pune 411 007, India$$

关键词: Pulse radiolysis;    transient absorption spectra;   

DOI  :  

来源: Indian Academy of Sciences

【 摘 要 】

Radiation chemical reactions of ${}^{ullet}$OH, O$^{ullet -}$, N$_{3}^{ullet}$ and $e^{-}_{aq}$ with 𝑜- and 𝑚-hydroxycinnamic acids were studied. The second-order rate constants for the reaction of ${}^{ullet}$OH with ortho and meta isomers in buffer solution at 𝑝H 7 are 3.9 ± 0.2 × 109 and 4.4 ± 0.3 × 109 dm3 mol-1 s-1 respectively. At 𝑝H 3 the rate with the ortho isomer was halved (1.6 ± 0.4 × 109 dm3 mol-1 s-1) but it was unaffected in the case of meta isomer (𝑘 = 4.2 ± 0.6 × 109 dm3 mol-1 s-1). The rate constant in the reaction of N$_{3}^{ullet}$ with the ortho isomer is lower by an order of magnitude (𝑘 = 4.9 ± 0.4 × 108 dm3 mol-1s-1). The rates of the reaction of $e^{-}_{aq}$ with ortho and meta isomers were found to be diffusion controlled. The transient absorption spectrum measured in the ${}^{ullet}$OH with 𝑜-hydroxycinnamic acid exhibited an absorption maximum at 360 nm and in meta isomer the spectrum was blue-shifted (330 nm) with a shoulder at 390 nm. A peak at 420 nm was observed in the reaction of O$^{ullet-}$ with the 𝑜-isomer whereas the meta isomer has a maximum at 390 and a broad shoulder at 450 nm. In the reaction of $e^{-}_{aq}$, the absorption peaks were centred at 370-380 nm in both the isomers. The underlying reaction mechanism is discussed.

【 授权许可】

Unknown