Mechanistic Studies of Some Phosphite Antioxidants

  • Kenneth J. Humphris

Student thesis: Doctoral ThesisDoctor of Philosophy


A number of esters of phosphorous acid were shown to be
effective inhibitors for hydrocarbon oxidation catalysed by
azobisisobutyronitrile and by hydroperoxides after an initial
rapid, but short-lived, pro-oxidant stage. Cyclic compounds derived
from catechol were particularly effective, exhibiting autoretardation
even at low concentrations.

The reactions of some phosphites with cumene hydroperoxide
were examined kinetically and by subsequent product studies, and
their kinetic parameters determined. Common to all compounds studied
was an initial second order reaction which showed features consistent
with a redox process. This reaction led to stoichiometric reduction
of hydroperoxide with concomitant formation of phosphate. This
phosphite/hydroperoxide system showed features in common with the
better known amine/peroxide systems, including the ability to initiate
the polymerisation of vinyl monomers, and to absorb oxygen.

After this stage the linear phosphates formed were inert to
hydroperoxide whilst the (5-membered) cyclic compounds underwent
further reaction(s) with peroxide to yield an unidentified species
which was an extremely powerful catalyst for destruction of
hydroperoxide by a pseudo-first order process. Product studies
and solvent effects suggested a Lewis acid for this unknown compound.

The effects of ring strain were not marked in these reactions
nor in their rates of hydrolysis which were briefly examined. This
contrasts strongly with the large rate enhancements often
encountered in other cyclic systems.

The phosphites examined did not inhibit the polymerisation of
styrene initiated by azobisisobutronitrile. The catechol phosphates were shown to be as effective as the
(patented) phosphites in stabilising polypropylene against thermooxidative
degradation, and both types of compounds were shown by
induction=period measurements to compare favourably with a
commercial synergistic stabiliser composition.
Date of Award1971
Original languageEnglish


  • phosphite antioxidants

Cite this