title: Spectrophotometric kinetic and determination of quinones and barbiturates.
abstract: The kinetics of 1,3-dimethylbarbituric acid with some quinones, namely 1,4-benzoquinone, 1,4-naphthoquinone and p-chloranil in 50% methyl alcohol-water mixture have been investigated spectrophotometrically at 30-50 degrees C. The reaction follows overall second-order kinetics, first order each in reactant. From the dependence of the rate constants on temperature, activation parameters have been calculated. A plot of deltaH# versus deltaS# for the reaction gave a good straight line with an isokinetic temperature of 387.66 K. The rate of reaction increases with increasing dielectric constant of the medium. Based on this reaction, a spectrophotometric determination method of quinones is described. Beer's law was obeyed within the concentration range 2.7-61.5 microg ml(-1) quinone. The method was applied for determination of barbituric, thiobarbituric and 1,3-dimethylbarbituric acids with 1,4-naphthoquinone within a concentration range of 3.2-39.5 microg ml(-1) barbiturate. The reaction mechanism and reactivity have been discussed.
authors.affiliation: Department of Chemistry, Faculty of Science, Ain Shams University, Cairo, Egypt. hmadian59@yahoo.com
authors.forename: H A
authors.initials: HA
authors.lastname: Medien
authors.forename: A A
authors.initials: AA
authors.lastname: Zahran
mesh_terms: D001463:Barbiturates / Q000737:chemistry*; D002703:Chloranil / Q000737:chemistry; D007700:Kinetics; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D011809:Quinones / Q000737:chemistry*; D013053:Spectrophotometry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D001463:Barbiturates; D011809:Quinones; D002703:Chloranil; D014867:Water; C018924:1,3-dimethylbarbituric acid; D000432:Methanol