NOPR Collection:

A flash photolysis study of the oxidation of aliphatic amines by phosphate radical

2017-06-07T12:09:56Z

Title: A flash photolysis study of the oxidation of aliphatic amines by phosphate radical Authors: Subramanian, P; Rajaram, J; Ramakrishnan, V; Kuriacose, J C Abstract: Rate constants for the reaction of the phosphate radical (PO) with various aliphatic amines have been measured by flash kinetic spectrophotometry. Phosphate radical can react with aliphatic amines by hydrogen atom abstraction or electron transfer, the general reactivityorder being tertiary secondary primary. For tertiary amines,a gOlodcorrelation has been obtained when the logarithm of rate constraints are plotted against 'the oxidation peak potentials of the amines, providing clear evidence for an electron transfer mechanism. In the case of tertiary amines, electron transfer from the nitrogen takes place. The identification of aminium cation radicals in the case of cyclic tertiary amines like, 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,3,6,8-tetraazatricyclo[4.4.1.1]dodecane (TATCD) provides additional proof for electron transfer. Primary and secondary amines get oxidized mainly by hydrogen atom abstractor as shown by the poor correlation with Taft substituent constants, but electron transfer cannot be completely ruled out. In the case of t-butylamine, electron transfer takes place and t-butylalcohol has been identified as the end product. Page(s): 913-919

Standard potentials of Ag-AgX (X = Br and I) electrodes at different temperatures and the related transfer energetics of HX in quasi-isodielectric aqueous ethylene carbonate solvents

2017-06-06T10:45:17Z

Title: Standard potentials of Ag-AgX (X = Br and I) electrodes at different temperatures and the related transfer energetics of HX in quasi-isodielectric aqueous ethylene carbonate solvents Authors: Sinha, Subrata; Kundu, Kiron K Abstract: Ag-AgI electrodes have been determined in quasiisodielectric aqueous mixtures of 10, 30, 50 and 70 (wt %) dipolar aprotic ethylene carbonate (EC) at 25°,30°,35°,40° and 45°C. These E⁰ values have been utilized to compute transfer free energies (∆G) and entropies (∆S) of HBr and HI. These values when coupled with previously determined transfer energetics of H⁺ yield the transfer energetics of Br^- arid I^-. The chemical parts of transfer free energies ∆G_,ch (i), obtained after correcting the cavity effect and Born-type and ion-dipole type electrostatic effects, are found to be in accord with the dictates of increased destabilizing chemical effect of dipolar aprotic nature of EC and the superimposed soft-soft interactions on these large sized halide ions. The observed T∆S (i) versus composition profiles as well as those of T∆G_,ch (i) versus composition, as obtained after correcting for the cavity effect and Born-type electrostatic effects, have been examined in the light of Kundu et al.'s semiquantitative theory based on a four-step transfer process, It is found that addition of cosolvent EC induces breakdown of three dimensional water structure due to possible formation of H-bonded EC-(H₂O)_x complexes and EC-EC aggregates and the packing imbalance in solvent mixtures containing higher proportion of EC. Page(s): 920-928

Kinetics of the reaction between triphenylphosphine and some haloalkanes

2017-06-06T10:36:54Z

Title: Kinetics of the reaction between triphenylphosphine and some haloalkanes Authors: Jain, D V S; Chadha, R Abstract: Kinetics of reactions RX + (C₆H₅)₃P -> (C₆H₅)₃PR⁺X^- (R = CCI₃,CBr₃,CH₂Br, C₄H₉ and X = Br, Cl,I) have been studied at different temperatures and in different dielectric media. The values of second order rate constants of the reactions with tetrahalomethanes are much higher than those with partially halogenated alkanes. This suggests that the reaction may be of charge transfer type with tetrahalomethanes while with other haloalkanes it is simple nucleophilic substitution reaction of S_N2 type. Page(s): 929-935

Kinetics and mechanism of oxidation of some substituted 4-piperidones by pyridinium fluorochromate (PFC)

2017-06-06T10:34:43Z

Title: Kinetics and mechanism of oxidation of some substituted 4-piperidones by pyridinium fluorochromate (PFC) Authors: Dhar, R K; Varadarajan, R Abstract: The kinetics of oxidation of several 3-alkyl and 3,5-dimethyl substituted 2,6-diphenylpiperidin-4- ones (1-6) by pyridinium fluorochromate (PFC) in the presence of perchloric acid in aqueous acetic acid medium have been investigated. Direct second order kinetics is observed, first order each in [oxidant] and [substrate]. A primary isotope effect, k_C-H/k_C-D = 4.2, suggests that the α_C-H bond is cleaved in the rate determining step. An interesting order of reactivity has been found to be: 3-ethyl > 3-methyl > 3- isopropyl > 3-H > 3,5-dimethyl. An explanation has been presented to justify the above rate differences. Further, the effect of electron-withdrawing NO₂ group or electron-donating OCH₃ group present at the para position of the phenyl ring of these piperidones (7,8) on the rate of oxidation suggests participation of the phenyl group. 3-Hydroxy-substituted piperidin-4-ones and substituted pyrrolidine-3-carboxylic acids are the major products of oxidation. Activation energies and related thermodynamic parameters have been determined and compared. Aprobable mechanism consistent with experimental observations has been proposed. Page(s): 936-940