ISSN:
0268-2575
Keywords:
photocatalysis
;
p-cresol
;
BHT
;
alkyl phenols
;
titanium dioxide
;
primary processes
;
Chemistry
;
Biochemistry and Biotechnology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Aerobic irradiation of organic compounds in aqueous suspensions of titanium dioxide (TiO2) generally leads to rapid mineralization with little accumulation of intermediates. This environmentally advantageous feature, however, hinders attempts to obtain mechanistic information and, while expansion of the field continues unabated, details of reaction pathways in many cases remain obscure. We have developed a procedure that allows the identification and monitoring of principal primary products, and the outcome with p-cresol is reported. Extrapolation of primary product yield profiles to zero conversion enables us to account for approximately 50% of the initial mass loss of p-cresol. At least four pathways are in competition, including nuclear substitution by OH, side-chain oxidation, radical dimerization, and the hitherto undetected nuclear addition of OH. These findings allow the conflicting results reported by previous workers to be reconciled. Changing the solvent from water to 20% acetonitrile in water has little effect on the initial rate, but ring coupling is more favoured and there is some addition of O2. Preliminary measurements with 2,6-di-tert-butyl-4-methylphenol (butylated hydroxytoluene, BHT), however, indicate that ortho-disubstitution with bulky tert-butyl groups substantially enhances the initial rate and changes the product profile significantly. The importance of both the extent of adsorption and substrate orientation on the catalyst surface is implicated in these results. © 1997 SCI.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
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