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|Title:||KINETICS AND MECHANISM OF OXIDATION OF CERTAIN ORGANIC COMPOUNDS BY PERIODATE ION|
|Keywords:||CHEMISTRY;ORGANIC COMPOUNDS;PERIODATE ION;AQUEOUS ACETIC ACID|
|Abstract:||Results of kinetic investigation of hitherto unreported non-Malaoaradian oxidation of 2,3- and 2,5- dimethy1aniline with periodate in aqueous acetic acid under various conditions are presented and discussed. The reaction in both the cases shows secpnd order behaviour, being first with respect to each reactant. Various kinetic oarameters for these reactions have been evaluated. Low energy of activation and high negative value of entropy of activation characterize these reactions. The rates decrease with decrease in dielectric constant and plots of log (dA/dt). vs D*"* or D-1/2D+1 are linear. The rate-pri profile shows a sharp increase in rate with increase in pH in the ranie 4,0-5.8, after which it remains almost constant. No effect of free radical scavengers such as acrylamide and allylacetate could be observed. Reaction stoichiometry is as follows: 1 mole of aromatic amine; 2 moles of periodate. Main prpducts isolated by solvent extraction and Preparative t.l.c. and characterized by varipus spectral studies Vi ii were the corresponding o-benzoquinones. Effect of various substituents ( uS ji)—NH«, X=H, P-Cl, £-Br, £-1, £-CH3, £-OCH3, £-OC2H5, o-OCH3 and o-CFU) on the rate of reaction, was systematically studied under identical conditions for testing the validity of linear free energy relationships. In all cases, the kinetic runs were carried out at four different temperatures. Linear relationship (Hammett) between log (k/k^) vs a for electron rich substituents exists (/°= -3.0) however, the p-methyl group shows deviation from the linearity. Further, a plot of log (JS'Ah ^ vs a+ (3rown and Okamoto) w?s linear (/*= -2.4), which is suggestive of the development of considerable amount of opsitive charge in the transition state. The negative value of reaction ccnstant F is interpreted in terms of relative ease of stabilisation of the transition state by electron donar groups. No correla tion with Taft, Van Bekkum and Sekigawa constpnts could be observed. A A fhe olot of AH' vs & S was linear, demonstra ting thereby the validity of isokinetic relationship Ill (£ = 275 K), an indication that similar interaction mechanism is operative in the oxidation of these substituted anilines. The reactions have been explained in terms of a bimolecular interaction mechanism. Tentative reaction pathways have been proposed.|
|Research Supervisor/ Guide:||Bhattacharyajee, G.|
Srivastava, S. P.
|Appears in Collections:||DOCTORAL THESES (chemistry)|
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