Autoxidation of n-alkylisoindolines : Solvent effects and mechanisms

Abstract

The autoxidation of N-butylisoindoline at 38 ° is markedly dependent on the solvent. Oxidation proceeds readily in solvents which can be considered hydrogen donors, such as methyl isopropyl ketone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexane, octene-1 and isopropyl alcohol. In a variety of other solvents such as benzene, toluene, cumene, pyridine, benzaldehyde, acetonitrile and isobutyronitrile, autoxidation of N-butylisoindoline is either very slow or does not occur. The oxidation is demonstrated to be free radical chain process, in which N-butylisoindole is formed by oxidative dehydrogenation. N-butylisoindole is synthesized and autoxidation is shown to be rapid in methyl isopropyl ketone as well as in benzene. The same products are formed from both the autoxidation of N-butylisoindoline and N-butylisoindole. N-butylphthalimidine and N-butylphtalimide constitute greater than 90% of the material balance in methyl isopropyl ketone, together with small amounts of N-butyl-3-hydroxy-phthalimidine. N-Butylisoindole iniatiates autoxidation of the isoindoline and is probably responsible for the auto- catalysis observed. A mechanism is proposed for the autoxidation.