Radiation chemical oxidation of aniline derivatives

The reactions of (OH)-O-., O.- and N-3(.) with chloro- and hydroxy-anilines were studied by pulse radiolysis. The rates of the OH radical reaction are higher (k similar to 5x10(9) dm(3) mol(-1) s(-1)) than those found for the O.- and N-3(.) reactions (k similar to 2x10(9) dm(3) mol(-1) s(-1)). Neith er the position of the substituent nor the introduction of an additional Cl to monochloroanilines has any significant effect on the rates of the (OH)- O-. reaction. The intermediates formed in all the aniline derivatives studi ed herein have lambda (max) values around 310-320 and 350-380 nm. The OH ra dical reacts both by addition and direct H abstraction giving rise to OH ad ducts (350-380 nm) and anilino radicals (310-320 nm). The extent of these t wo reactions depends on the position of the substituent, the former being m ore predominant in the meta than in the ortho and para isomers. The initial ly-formed OH adducts subsequently undergo dehydration, leading to anilino r adicals in the case of chloroanilines and phenoxyl radicals with hydroxyani lines. The OH attack at the carbon bonded to Cl in all three monochloroanil ines is not significant (less than or equal to 15%). Semi-empirical quantum calculations using the PM3 method were carried out to evaluate the possibl e sites of the OH radical attack. The charge distribution and the heats of formation data reveal that the (OH)-O-. attack extends over more than one c arbon center. The relative stabilities of the isomeric OH adducts formed fr om the attack at the unsubstituted carbons of chloro- and hydroxy-anilines are nearly the same, their respective heats of formation being approximatel y -70 and -230 kJ mol(-1).