Kinetics of the diazotization and azo coupling reactions of procaine in the micellar media

Abstract

The kinetics of the diazotization reaction of procaine in the presence of anionic micelles of sodium dodecyl sulfate (SDS) and cationic micelles of cetyltrimethyl ammonium bromide (CTAB), dodecyltrimethyl ammonium bromide (DDTAB) and tetradecyltrimethyl ammonium bromide (TDTAB) were carried out spectrophotometrically at λmax=289nm. The values of the pseudo first order rate constant were found to be linearly dependent upon the [NaNO2] in the concentration range of 1.0×10−3moldm−3 to 12.0×10−3moldm−3 in the presence of 2.0×10−2moldm−3 acetic acid. The concentration of procaine was kept constant at 6.50×10−5moldm−3. The addition of the cationic surfactants increased the reaction rate and gave plateau like curve. The addition of SDS micelles to the reactants initially increased the rate of reaction and gave maximum like curve. The maximum value of the rate constant was found to be 9.44×10−3s−1 at 2.00×10−3moldm−3 SDS concentration. The azo coupling of diazonium ion with β-naphthol (at λmax=488) nm was found to linearly dependent upon [ProcN2+] in the presence of both the cationic micelles (CTAB, DDTAB and TDTAB) and anionic micelles (SDS). Both the cationic and anionic micelles inhibited the rate of reactions. The kinetic results in the presence of micelles are explained using the Berezin pseudophase model. This model was also used to determine the kinetic parameters e.g. km, Ks from the observed results of the variation of rate constant at different [surfactants].