A spectroelectrochemical and chemical study on oxidation of 7,8-dihydroxy-4-methylcoumarin (DHMC) and some related compounds in aprotic medium.
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.
Petrucci
Rita
R
Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Università di Roma, Via del Castro Laurenziano 7, I-00161, Rome, Italy. rita.petrucci@uniroma1.it
Saso
Luciano
L
Kumar
Vineet
V
Prasad
Ashok K
AK
Malhotra
Sanjay V
SV
Parmar
Virinder S
VS
Marrosu
Giancarlo
G
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
C114369:7,8-diacetoxy-4-methylcoumarin; D000097:Acetonitriles; D016227:Benzoquinones; D003374:Coumarins; C025232:semiquinone radicals; C032159:acetonitrile