N - (1,3 - dimethyl - 3 - methoxybutyl)-N1-R-p-phenylene diamines in which R is an alkyl or alkoxyalkyl group of 3-12 carbon atoms, a phenalkyl group of 7-14 carbon atoms, a phenyl or alkyphenyl group of 6-10 carbon atoms, or a cycloalkyl group of 5 or 6 carbon atoms, are used for stabilizing organic substances against oxidative deterioration. Specified organic substances which may be stabilized include gasoline, hydro-reformed gasoline, thermally-cracked and catalytically cracked gasolines, coker gasoline, polymer gasoline, naphtha, kerosene, jet fuel, gas oil, diesel oil, lubricating oil, fuel oil, grease, edible mineral oils, edible and non-edible animal and vegetable fats and oils, e.g. lard, beef tallow, soya bean oil, linseed oil, castor oil, menhaden oil, hydrogenated oils, and solid food products containing oils or fats. The anti-oxidant may be incorporated in a proportion of 0.0001 to 5% by weight of the substance to be stabilized. The preferred phenylene diamine is N,N1-bis-(1,3 - dimethyl - 3 - methoxybutyl) - p - phenylene diamine, and examples describe the use of this substance for stabilizing gasoline, dioctyl sebacate to be used as a high temperature lubricant, and a grease comprising mineral oil and lithium stearate.ALSO:Substituted phenylene diamines of the constitution N - (1,3 - dimethyl - 3 - methoxybutyl) - N1 - R - p - phenylene diamine in which R is an alkyl or alkoxyalkyl group of 3-12 carbon atoms, a phenalkyl group of 7-14 carbon atoms, a phenyl or alkphenyl group of 6-10 carbon atoms, or a cycloalkyl group of 5 or 6 carbon atoms, are used for stabilizing organic substances which are subject to oxidative deterioration, including natural rubber, butyl rubber, neoprene rubber, styrenebutadiene copolymer rubber, silicone rubber, thiokol rubber, polyethylene, polypropylene, and polybutylene. The natural rubber may be Hevea rubber, caoutchouc, balata, or guttapercha. The preferred phenylene diamine compound is N,N1 - bis - (1,3 - dimethyl - 3 - methoxybutyl) -p-phenylene diamine. The proportion of stabilizer incorporated may be in the range of 0.0001 to 5% by weight of the substance to be stabilized. It may be used together with other stabilizers and additives.ALSO:N - (1,3 - dimethyl - 3 - methoxybutyl) - N1 - R - p - phenylene - diamines in which R is an alkyl or alkoxyalkyl group of 3-12 carbon atoms, a phenalkyl group of 7-14 carbon atoms, a phenyl or alkphenyl group of 6-10 carbon atom, or a cycloalkyl group of 5 or 6 carbon atoms, are used for stabilizing organic substances which are subject to oxidative deterioration. The preferred anti-oxidant is N,N1-bis-(1,3-dimethyl - 3 - methoxy - butyl) - p - phenylenediamine. This compound may be obtained by reductive alkylation of p-phenylene diamine, p-nitroaniline, or 1,4-dinitrobenzene with 4-methyl - 4 - methoxy - 2 - pentanone in presence of a catalyst such as a mixture of oxides of chromium, cobalt, and barium. Other catalysts containing cobalt, nickel, platinum, or molybdenum may be used. The reaction may be effected at 93-260 DEG C. and at a hydrogen pressure of 3.4 to 204 atmospheres. In an example, a platinum-alumina catalyst is used. Other substituted p-phenylenediamines specified are those in which the group R in the general formula is a phenyl, tolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl, isopropyl, sec.-butyl, sec. alkyl of 5-12 carbon atoms, benzyl, phenethyl, phenalkyl of 9-14 carbon atoms, cyclopentyl, or cyclohexyl group, Substances stabilized by the phenylene diamines include mineral oils and spirits, greases, natural and synthetic rubber, animal and vegetable oils. Dioctyl sebacate to stabilized may be used as a lubricating oil under high temperature conditions. N,N1-bis-(1,3-dimethyl-3-methoxy-butyl)-p-phenylenediamine may be resolved into two isomers by fractional crystallization from its solutions in pentane-acetone solvent.