NOPR Collection:

Highly selective chloride poly(vinyl chloride) membrane electrode based on vanadium(IV) oxide acetylacetonate

2013-07-24T16:40:08Z

Title: Highly selective chloride poly(vinyl chloride) membrane electrode based on vanadium(IV) oxide acetylacetonate Authors: Mahajan, Rakesh Kumar; Sood, Pallavi Abstract: The response characteristics of a new solvent-polymeric membrane electrode with unique selectivity and detection limit towards chloride anion is reported here. The electrode is prepared by incorporating vanadium(IV) oxide acetylacetonate into a plasticized PVC-membrane. The resulting sensor exhibits high selectivity for chloride anion over other anions, including lipophilic inorganic anions like nitrate and perchlorate, etc. The electrode has a linear dynamic range 2.5×10^-5-1.0×10^-1 M with a Nernstian slope -55.0±2 mV per decade and a low detection limit 4.27×10^-6 M. The potentiometric response has been found to be independent of pH of the solution in the pH range 3.5-9.0. The electrode can be used for at least 9 months without any considerable divergence in its potential. It can be used as an indicator electrode in the potentiometric titration of silver ions. Page(s): 2446-2449

Kinetics and mechanism of oxidation of secondary alcohols by benzyltriethylammonium chlorochromate

2013-07-31T16:39:47Z

Title: Kinetics and mechanism of oxidation of secondary alcohols by benzyltriethylammonium chlorochromate Authors: Kaur, Ravdeep; Soni, Neelam; Sharma, Vinita Abstract: Oxidation of several aliphatic secondary alcohols by benzyltriethylammonium chlorochromate in dimethylsulfoxide leads to the formation of corresponding ketones. The reaction is first order each in benzyltriethylammonium chlorochromate and the alcohols. The reaction is catalysed by hydrogen ions. Hydrogen-ion dependence has the form: k_obs = a+b [H⁺]. The oxidation of benzhydrol-α-d exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.12 at 288 K). Oxidation of 2-propanol has been studied in nineteen different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The reaction has been subjected to both polar and steric effects of the substituents. A mechanism involving transfer of hydride ion from alcohol to the oxidant via a chromate ester is also proposed. Page(s): 2441-2445

Kinetics of oxidation of thymine by t-butoxyl radical — Protection and repair by caffeic acid

2013-07-27T16:37:27Z

Title: Kinetics of oxidation of thymine by t-butoxyl radical — Protection and repair by caffeic acid Authors: Charitha, Lingareddy; Adinarayana, Mundra Abstract: The kinetics of oxidation of thymine and caffeic acid by t-BuO^• has been studied by the photolysis of t-butyl hydroperoxide in presence of t-butanol. The rates and the quantum yields (φ) of oxidation of caffeic acid by t-BuO^• radicals have been determined by varying concentrations of thymine. An increase in [thymine] has been found to decrease the rate of oxidation of caffeic acid suggesting that thymine and caffeic acid compete for t-BuO^• radicals. From competition kinetics, the rate constant of t-BuO^• - thymine reaction has been calculated to be 5.3×10⁷ dm³ mol^-1 s^-1. The experimentally determined quantum yields (φ_expt) and the calculated yields (φ_cal) of oxidation of caffeic acid, assuming that caffeic acid reacts only with t-BuO^• radicals, suggest that caffeic acid not only protects thymine from t-BuO^• radicals but also repairs thymine radicals formed by the reaction of t-BuO^• radicals. Page(s): 2435-2440

Cu(II) catalysed oxidation of o-mercapto-benzoic acid by methylene blue in acidic medium: A kinetic study

2013-07-24T16:39:59Z

Title: Cu(II) catalysed oxidation of o-mercapto-benzoic acid by methylene blue in acidic medium: A kinetic study Authors: Gupta, R; Chaturvedi, R; Mishra, K K Abstract: Kinetics of oxidation of o-mercaptobenzoie acid by methylene blue catalyzed by Cu(II) in presence of sulphuric acid and in aqueous ethanol medium (4% v/v) have been studied. Two moles of the substrate are oxidized by one mole of methylene blue forming the disulphide and the leuco dye as the end products. The order in methylene blue is 3/2 which increases to two at lower concentrations of Cu(II). The older in o-mercaptobenzoic acid is nearly zero. The rate is independent of variation in [H⁺] but at higher concentrations, the rate decreases to give a limiting value. The rate is not influenced on varying [Cu(II)] at higher levels but at lower concentrations (ca. < 6.0×10^-6 M), there is a linear relationship between the rate and [Cu (II)]. The addition of reaction products does not influence the rate. Activation parameters have been evaluated and a plausible reaction scheme, presuming the reaction between metal - TSA complex and MB dimer as the rate determining step, has been proposed. Page(s): 2431-2434