University of Khartoum

Studies of the Reactions of Arylpropene Oxides on Basic Media.

Studies of the Reactions of Arylpropene Oxides on Basic Media.

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Title: Studies of the Reactions of Arylpropene Oxides on Basic Media.
Author: Issam El Din Abdel Wahid, Mohamed
Abstract: The reaction of aryl propene oxides, with different single -substituent at Para - , meta -, or ortho - positions, with excess potassium tert - butoxide in tert - butanol, was investigated at 60°C The reaction was followed kinetically by quenching appropriate aliquots of the reaction mixture by aqueous ethanol, and running the solutions obtained in an ultra-violet spectrometer (SP -800 A); using l cm. -wide cell, and ethanol in the reference cell. These solutions were found to show increased absorbance with time in the region between 245 and 250 millimicrol wavelengths. The observed rates of these reactions were found to follow pseudo first order kinetics as calculated from a plot of log A/A –At versus time; where A represents absorbance at infinity and At represents absorbance at time t. The order of reactivity for the different substituents has been found to have the following sequence: p- NO2 o-Cl m-F m-Br p-Br m-OCH3 o- CH3 p-CH (CH3)2 o-O CH3. which is consistent with the polar effect of the substituent. Hammett plot, rendered a straight line with a ρ value of +2.50; a positive value of ρ is in accordance with the determined sequence of reactivity. The small value of ρ indicates that the effect of substituents on the reaction centre is small, which is due to an evident proximity effect. The postulated mechanism of reaction is a concerted mechanism involving a proton-abstraction from the carbol atom  to the phenyl group, followed by the epoxide ring-opening via the carbanion to give the corresponding cinnamyl alcohol.
URI: http://khartoumspace.uofk.edu/handle/123456789/14645
Date: 2015-06-23


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