PHENOL CONVERSION AND DIMERIC INTERMEDIATES IN HORSERADISH PEROXIDASE-CATALYZED PHENOL REMOVAL FROM WATER

Phenol was removed from water by horseradish peroxidase-catalyzed poly merization. Five dimeric and one trimeric products from the reaction w ere identified in the aqueous solution. The trimer had a structure of 4-(4-phenoxyphenoxy)phenol (VI) determined from its NMR spectrum. The dimers such as p,p'-biphenol (I), o,o'-biphenol (II), and p-phenoxyphe nol (III) were the reaction intermediates. With more than 95% phenol r emoval from an initial phenol concentration of 188 mg/L, the final con centrations of the three dimers were each below 1 mg/L. About 7% of th e precipitate mass was attributed to the three dimers (I, II, III), an d the rest consisted mainly of the compounds of higher hydrophobicity and molecular mass. With an equimolar ratio of phenol to hydrogen pero xide, the phenol conversion behaved as a first-order reaction with res pect to phenol concentration. A peroxidase inactivation model for the reaction in the presence of poly(ethylene glycol) (PEG) was proposed, and the inactivation rate constant was found to have a logarithmic rel ationship with the ratio of PEG to enzyme doses. The three dimers were the substrates of peroxidase, and their conversion could also be depi cted with a first-order model with respect to the dimer concentrations . A comparison of the specific reaction rates indicated that p-phenoxy phenol was the best substrate of peroxidase (2.172 nM(-1) min(-1)) fol lowed by p,p'-biphenol (0.671 nM(-1) min(-1)), phenol (0.0105 nM(-1) m in(-1)), and o,o'-biphenol (0.00453 nM(-1) min(-1)). Therefore, the pr edominant polymerization bonds in the products may be the oxygen-para connection whereas the ortho-ortho connection would hardly be found in the higher oligomers.