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4084220 
Journal Article 
Kinetics and mechanism of oxidation of tyrosine by vanadium(V) in aqueous hydrochloric and ethanoic acid medium 
Onkar, AS; Naik, PN; Gunagi, SD; Nandibewoor, ST; Chimatadar, SA 
2012 
1 
Indian Journal of Chemistry. Section A
ISSN: 0376-4710
EISSN: 0975-0975 
51 
11 
1574-1579 
WOS:000311463400007 
Vanadium(V) and tyrosine does not react in sulpuric acid or perchloric acid media at 25 degrees C. However, in aqueous hydrochloric and ethanoic acid media vanadium(V) is reduced to vanadium(IV) and tyrosine oxidized to 4-hydroxyphenyl acetaldehyde. In this reaction, two moles of vanadium(V) consume one mole of tyrosine. The reaction is first order with respect to vanadium(V) and less than unit order with respect to tyrosine concentrations. Increase in hydrochloric acid concentration increases the rate. The order with respect to acid concentration is found to be less than unity. The effect of ionic strength and dielectric constant of the medium have been studied and a suitable mechanism is proposed. The activation parameters and frequency factor have been determined on the basis of the rate law:



Rate = -d[VO2+]/dt = k K1K2 [VO2+] [tyrosine] [H+]/1 + K-1[H+] + K1K2 [tyrosine] [H+]