Anti-ozonants and use thereof in rubber compositions

Cracking of articles made of natural rubber and sulphur-vulcanizable and sulphur-vulcanized unsaturated synthetic rubbers is inhibited by incorporating into the rubber batch, from which the articles are prepared, an anti-ozonant in the form of a N,N1-dialkyl phenylenediamine hydrogenated in the benzene nucleus to an average extent equal to at least 40% of full hydrogenation of the nucleus, or a salt thereof. Anti-ozonants of the type described are particularly suitable for white rubber articles; for they do not impart coloured stain to the rubber. It is especially advantageous to utilize compounds in which the benzene nucleus is fully hydrogenated, i.e. the N,N1-dialkyl cyclohexylenediamines. Among those specified are:-N-N1-di-2-isoheptyl-m-cyclohexylenediamine, N,N1-di-2-cyclohexyl-p-cyclohexylenediamine, and N,N1-di-3-octyl-o-cyclohexylenediamine. The anti-ozonant is utilized in proportions in the range of 0,1 to 5% by weight of the rubber. The anti-ozonants also function to some extent as vulcanization-accelerators and anti-oxidants. They also function as tackifiers so that, when used in compositions containing rubber and wax, excellent protection against ozone is provided without blooming out.ALSO:The invention comprises N,N1-dialkyl-cyclohexylenediamines and other N,N1-dialkyl-phenylenediamines which are hydrogenated in the benzene nucleus to an average extent equal to at least 40% of full hydrogenation of the nucleus, and salts thereof. The compounds are prepared by hydrogenating a mixture of a nitroaniline, or dinitrobenzene, or phenylenediamine, and an alkyl or cycloalkyl ketone in the presence of Raney nickel catalyst or of rhodium metal deposited in carbon. In an example, N,N1-di-2-isoheptyl-m-cyclohexylenediamine is obtained by hydrogenating a mixture of m-phenylenediamine, methyl isoamyl ketone and rhodium-on-carbon catalyst at a pressure of 300 to 500 p.s.i.g. and a temperature of 100 DEG -280 DEG F. Among other cyclohexylenediamines referred to are:-N,N1-di-2-cyclohexyl - p - cyclohexylenediamine and N,N1-di-3-octyl-o-cyclohexylenediamine. Specified salts are the phthalates, benzoates, hydroxybenzoates, maleates, fumarates, sulphates, chlorides and nitrates. The compounds are anti-ozonants for rubber (see Group IV(a)).