title: A spectroelectrochemical and chemical study on oxidation of 7,8-dihydroxy-4-methylcoumarin (DHMC) and some related compounds in aprotic medium.
abstract: Electrochemical and chemical oxidation of 7,8-hydroxy-4-methylcoumarin (DHMC 1) and 7,8-diacetoxy-4-methylcoumarin (DAMC 4) were studied to investigate the mechanisms occurring in their antioxidant activities in acetonitrile, under electron transfer and H-atom transfer conditions. Electrolysis and chemical reactions were followed on-line by monitoring the UV spectral changes with time. The anodic oxidation of DHMC, studied by cyclic voltammetry and controlled potential electrolysis, occurs via a reversible one-step two-electrons process, yielding the corresponding stable phenoxonium cation. Moreover, the chemical oxidation with an H-atom acceptor also follows a similar path, yielding the stable neutral quinonic product. Intermediates were never evidenced in both cases. Only in the presence of a strong base, an anodic oxidation product mono-electronic was evidenced, likely the DHMC radical anion. However, the anodic oxidation of the acetoxy derivative DAMC occurs at very high potential values, ruling out the possibility that the antioxidant activity observed in vivo might occur via an electron transfer mechanism; no reactions were evidenced with an H-atom acceptor.
authors.affiliation: Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Università di Roma, Via del Castro Laurenziano 7, I-00161, Rome, Italy. rita.petrucci@uniroma1.it
authors.forename: Rita
authors.initials: R
authors.lastname: Petrucci
authors.forename: Luciano
authors.initials: L
authors.lastname: Saso
authors.forename: Vineet
authors.initials: V
authors.lastname: Kumar
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Prasad
authors.forename: Sanjay V
authors.initials: SV
authors.lastname: Malhotra
authors.forename: Virinder S
authors.initials: VS
authors.lastname: Parmar
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Marrosu
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry; D003374:Coumarins / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet
chemical_list: C114369:7,8-diacetoxy-4-methylcoumarin; D000097:Acetonitriles; D016227:Benzoquinones; D003374:Coumarins; C025232:semiquinone radicals; C032159:acetonitrile