HYDROXYLATION OF CHLOROTOLUENES AND CRESOLS - A PULSE-RADIOLYSIS, LASER FLASH-PHOTOLYSIS, AND PRODUCT ANALYSIS STUDY

The reactions of (OH)-O-., O.- and SO4.- with 2-, 3-, and 4-cresols we re studied by pulse radiolysis, laser flash photolysis, and product an alysis techniques. The rates of OH reaction with cresols are very high (k approximate to 1 x 10(10) M-1 s(-1)), whereas O.- was found to be less reactive (k approximate to 2.4 x 10(9) M-1 s(-1)). The second-ord er rate constants for SO4.- reaction with cresols are in the range (3- 6) x 10(9) M-1 s(-1). The transient absorption spectra measured in OH reaction exhibited peaks in the range 295-325 nm with a red shift for the meta isomer. The absorption spectra obtained for O.- reaction with 2-cresol has a peak at 360 nm, which is different from those measured with the m and p isomers (lambda(max) = 310 and 380 nm). The absorpti on spectra of the transient species in SO4.- reaction obtained by puls e radiolysis and flash photolysis techniques are similar, with absorpt ion maxima centered around 290 and 390 nm in all three isomers. The in termediates formed in (OH)-O-., O.-, and SO4.- reactions are assigned to OH adducts, substituted benzyl radicals, and radical cations, respe ctively. The rates for oxygen addition to OH adducts of 2-, 3-, and 4- chlorotoluenes and cresols are high, with k(f) values lying in the ran ge (1-2.7) x 10(8) M-1 s(-1). The relatively higher stability constant s of peroxyl radicals formed with cresols (K = k(f)/k(r) = (2-5) x 10( 4) M-1) than with chlorotoluenes suggest that the product-forming reac tion competes effectively with the reverse reaction in cresols. Dihydr oxytoluenes with OH groups ortho to each other were only formed in oxy genated solutions of cresols, and the mechanism involves the addition of oxygen to 1,3-type OH adducts at the carbon carrying the hydroxyl f unction.