Abstract: Aryl phosphonites and thiophosphonites of the formula, ##STR1## in which the or each R, independently, is alkyl, alkoxy, chlorine or dialkylamino, there being at the most one dialkylamino group, at the 4-position and unaccompanied by any other substituents, on the benzene nucleus,n is zero, 1, 2 or 3,each X, independently, is oxygen or sulphur,and each R.sub.1, independently, is alkyl or optionally substituted phenyl,are useful as antioxidants. Organic material, e.g. polypropylene, which are susceptible to the degradative effects of oxygen, are treated with one or more of such compounds, e.g. by incorporation into the body of the organic material, in order to be stabilized against such effects.

Abstract: Fluorene phosphonites and thiophosphonites of the formula, ##STR1## in which each R, independently, is alkyl or optionally substituted phenyl, each Y, independently, is oxygen or sulphur, and n is zero or 1, are useful as antioxidants. Organic materials, which are susceptible to the degradative effects of oxygen, are treated with one or more of such compounds e.g. by incorporation into the body of the organic material, in order to be stabilized against such effects.

Abstract: Novel compounds based on a hydroxybiphenyl nucleus in which the hydroxy group is in the para position relative to the other phenyl ring and has an adjacent tertiary alkyl radical, are useful stabilizers for organic compounds against heat, light or oxygen.