A flash photolysis study of the oxidation of aliphatic amines by phosphate radical

Abstract

Rate constants for the reaction of the phosphate radical (PO<img src='http://www.niscair.res.in/jinfo/four1.gif' border=0>) with various aliphatic amines have been measured by flash kinetic spectrophotometry. Phosphate radical can react with aliphatic amines by hydrogen atom abstraction or electron transfer, the general reactivityorder being tertiary <img src='http://www.niscair.res.in/jinfo/greaterequal.gif' border=0> secondary <img src='http://www.niscair.res.in/jinfo/greaterequal.gif' border=0> primary. For tertiary amines,a gOlodcorrelation has been obtained when the logarithm of rate constraints are plotted against 'the oxidation peak potentials of the amines, providing clear evidence for an electron transfer mechanism. In the case of tertiary amines, electron transfer from the nitrogen takes place. The identification of aminium cation radicals in the case of cyclic tertiary amines like, 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,3,6,8-tetraazatricyclo[4.4.1.1]dodecane (TATCD) provides additional proof for electron transfer. Primary and secondary amines get oxidized mainly by hydrogen atom abstractor as shown by the poor correlation with Taft substituent constants, but electron transfer cannot be completely ruled out. In the case of <i>t</i>-butylamine, electron transfer takes place and <i>t</i>-butylalcohol has been identified as the end product.