The kinetics of the oxidation of a number of aliphatic and aromatic secondary alcohols with Nbromo succinimide has been investigated. Electron-withdrawing substituents retard the reaction considerably and electron-releasing substituents increase the rate of oxidation. The Taft p* value is -2.56. Cis-and tram-4-t-butyl cyclohexanols arc oxidized at nearly the same ratcs. There is also a good correlation between the rates of the NBS oxidations and Br, oxidations of these alcohols. The results are interpreted in ternis of a cyclic mechanism involving a rate-determining abstraction of the alpha hydrogen as a hydride anion. For personal use only.

No abstract

No abstract

Kinetics of chlorination of substituted phenols with a particular emphasis on p-nitrophenol (PNP) have been extensively studied using chloramine T (CAT). The effect of added mineral acids, neutral salts, and chloride have been investigated in detail. In aqueous acetic acid a t high acidities the reactive phenols follow a zero-order process, while PNP or the disubstituted derivatives give a fractional-order dependence on substrate concentration. The concentration dependence of rate with respect to PNP, the chlorinating agent, and acid reveals the rate lawgave a straight line with a finite intercept. In aqueous dimethylformarnide (DMF) and dimethylsulfoxide (DMSO) the reaction shows a second-order dependence on CAT and a first-order dependence on PNP in the case of DMF and a slight increment in order in DMSO. Addition of water increases the rate both in aqueous acetic acid and in dipolar aprotic solvents such as D M F and DMSO. The order of the reaction with respect to C A T is found to be dependent on pH as well as the reactivity of the phenols. In buffered acetic acid medium a second-order dependence on CAT was followed up to pH 7. The rate variations with temperature in the range of 30"-50°C have been studied for all the substituted phenols, and the respective activation parameters have been calculated. The empirical rate law is accounted for by a mechanism involving sprcies generated from CAT complexing PNP. Protonated CAT, H20C1, CIOAcH, and dichloramine T (DCT) are considered important depending on reaction media. The effect of salts, pH, structural variations, and solvent dependence have been accounted for by the proposed mechanism. An attack by positive chlorine on oxygen of the phenol is thc preferred mode of attack.

<p>The flow path of a conceptual hypersonic air-breathing scramjet engine integrated with the vehicle (without combustion) has been simulated numerically using ANSYS CFX software with the SST turbulence model. The computations were performed for the free stream Mach number of 6 and angle-of-attack of 5°. A strong separation bubble was observed on the bodyside wall in the internal compression region where the reflected cowl shock impinges on body which in turn increases the static pressure substantially. The external-internal flow field of the hypersonic mixed compression intake, shock-boundary layer interactions, and the shock-shock interactions present in the internal compression region have qualitatively been obtained and analysed. The variation of centreline pressure along the bodyside wall close to the symmetry plane obtained from numerical simulation centreline has been compared with the experimentally measured data. It has been observed that the computed wall pressure matches fairly well with the measured values in the external ramp compression region, internal compression region and in the combustion chamber. The flow patterns and the pressure variations near the middle wall and the fuel injecting strut locations have also been analysed.</p><p><strong>Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 272-278, DOI: http://dx.doi.org/10.14429/dsj.65.6979</strong></p>