Abstract
Studies on the antioxidant activity of two model phenols containing either an electron withdrawing (p-nitrophenol) or electron donating (p-aminophenol) group and p-hydroxyacetophenone in different solvents are reported using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay by spectrophotometry and stopped-flow techniques. The second-order rate constants measured with p-nitrophenol were found to be (1.2–5.5) × 10−2 dm3 mol−1 s−1 but the DPPH radical reacts much faster with p-aminophenol (k = 0.5–1.1 × 104 dm3 mol−1 s−1). The normal kinetic solvent effect in H atom transfer was seen in the case of p-nitrophenol with the solvent independent rate constant k o = 0.1 dm3 mol−1 s−1. The IC50 values in p-nitrophenol are similar to those measured in p-hydroxyacetophenone. On the other hand, much lower IC50 values of more than four orders of magnitude with p-aminophenol were observed. This work demonstrates that the phenol with the electron donating –NH2 substituent is a better antioxidant.
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Acknowledgments
BSMR would like to thank the DAE-BRNS for the award of the Raja Ramanna Fellowship and P. Gaikwad is thankful to the BARC for financial support under the BARC—PU Collaborative Research Program.
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Gaikwad, P., Barik, A., Priyadarsini, K.I. et al. Antioxidant activities of phenols in different solvents using DPPH assay. Res Chem Intermed 36, 1065–1072 (2010). https://doi.org/10.1007/s11164-010-0220-8
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DOI: https://doi.org/10.1007/s11164-010-0220-8