Evaluation of Steric Effect of Hydroquinone, Tert-Butyl Hydroquinone and 2, 5-Ditert-Butyl Hydroquinone by using a Briggs-Rauscher Oscillator

Abstract

This article indicated a novel methodology of evaluation of steric effect of (hydroquinone (HQ), tert-Butyl hydroquinone (TBHQ) and 2, 5-ditert-butyl hydroquinone (DTBHQ)) by using a Briggs-Rauscher chemical oscillating system. The macro cyclic [NiL](ClO 4) 2 complex catalyst with 5,7,7,12,14,14-hexamethyl-1,4,8,1,1-tetraazacyclotetradeca-4,1,1-diene as ligand is used. The calculated experimental data confirmed the diverse perturbation effects of all three additives towards the active Briggs-Rauscher oscillator in their concentration ranges from 5.0 × 10-7 M to 1.25 × 10-5 M. Hydroquinone generate inhibition time (t in) higher than t-BHQ, whereas, no influence of 2,5-DBHQ were observed in Briggs-Rauscher system. Our claim for such differences in perturbation is due to the strong steric hindrance effect of these additives. The presence of bulky group (tertiary butyl) reduces the reactivity of the antioxidants by covering the active sides (OH-group) from the attack of HOO • radical. Thus, Hydroquinone produced larger t in because of absence of bulky group, the shorter t in of t-BHQ due to the presence of one bulky group whereas, no t in of 2, 5-DBHQ because of two bulky groups attached. The perturbation reaction mechanism was discussed on the basis of FCA (Furrow-Cervellati-Amadori) model. The explanation mechanism is that both HQ and t-BHQ is oxidized by HOO • into their respective Quinone.

pH-Responsive, Thermoset Polymer Coatings for Active Protection against Aluminum Corrosion

“…Initial attempts to remove the color through activated carbon filtration was only partially successful (Figure , image b), so an investigation was conducted to identify the source of color formation. Chromatographic separation of the reaction components revealed that mixed aromatic derivatives (of tert -butyl hydroquinone) were the likely cause of the discoloration, formed at the elevated reaction temperature (80 °C). − It was found that by reducing the reaction temperature to 50 °C and increasing the mole percentage of K 2 CO 3 from 5 to 10%, the reaction could deliver a 75% yield of BOC-Gly-MA on a multigram scale, as a clear and colorless product (Figure , image c). Optimal conditions for the synthesis found that separation of any unreacted GMA from the BOC-Gly-MA product was not necessary since GMA was an ingredient in all of the functional polymers synthesized (all at 28% w/w GMA).…”