Antioxidant Behaviour of Phosphate Esters and Derived Metal Complexes

Abstract

A series of aromatic and aliphatic cyclic phosphate esters have been prepared and the reactions of these with hydroperoxides investigated.

While acyclic aliphatic phosphates are inert towards hydroperoxides aliphatic cyclic phosphates were found to react with hydroperoxides in near stoichiometric proportions. The products from cumene hydroperoxide included phenol, acetone, α-methyl styrene and amyl alcohol indicating ionic and free-radical pathways for the reaction. Five-membered cyclic phosphate esters based on catechol were shown to be very powerful catalysts for the decomposition of hydroperoxides. With cumene hydroperoxide, the products were mainly acetone and phenol reflecting a non-radical mechanism. The effect of substituents, temperature and solvent on the reaction has been investigated in detail and thermodynamic ‘parameters calculated. The mechanism has been shown to involve alternative ring opening and ring closure of the catechol phosphate. Restricted rotation of the C-C bond in the five-membered cyclic phosphate, the stability of the intermediate phenolate anion and the activity of the vicinal hydroxy group are important factors governing the reaction.

These esters were found to be very effective thermal stabilisers in decalin and they improved the u.v. stability of polypropylene by virtue of their reaction with hydroperoxide forming non-radicalproducts.

A number of novel metal complexes derived from acyclic and cyclic phosphato-ligands were synthesised. The catechol phosphate metal complexes (ferric and copper) were very effective catalysts for the decomposition of hydroperoxides and they did so almost exclusively by an ionic mechanism. These complexes, particularly the copper complex, were very effective photo stabilisers for poly propylene.

Attempts to prepare the nickel complex of catechol cyclic phosphate were not successful,

Date of Award	Sept 1977
Original language	English
Awarding Institution	Aston University