Nitrile rubber hydrogenation

An improved process for the production of hydrogenated nitrile rubber wherein a nitrile rubber which is a polymer comprising a conjugated C.sub.4 -C.sub.6 diolefin and a C.sub.3 -C.sub.5 unsaturated nitrile is hydrogenated in the presence of a divalent ruthenium catalyst selected from compounds of the general formula:

• RuXY(CO)ZL.sub.2, or RuDE(CO)M.sub.n, or RuGJM.sub.3, or RuK.sub.2 N.sub.2
• wherein X is selected from a halogen atom or a carboxylate group, Y is selected from a halogen atom, a hydrogen atom, a phenyl group, a carboxylate group or a styryl group, Z is selected from CO, pyridine., benzonitrile or no ligand and L is selected from the phosphine ligands of the general formula PR.sub.3 in which R is selected from alicyclic or alkyl groups, n is 2 or 3 and when n is 3, D is a halogen atom and E is a hydrogen atom and when n is 2, D is selected from a halogen atom or a carboxylate group and E is selected from a halogen atom, a hydrogen atom a phenyl group or a carboxylate group and M is selected from the phosphine ligands of the formula PA.sub.3 in which A is a phenyl group or a C.sub.1 to C.sub.4 alkyl group or mixtures thereof, G is selected from a halogen atom or a hydrogen atom, J is selected from a halogen atom or a carboxylate group, K is a carboxylate group and N is triphenylphosphine, the improvement being that said nitrile rubber is provided in an aqueous emulsion, an organic compound which is miscible with the aqueous phase and is also a solvent for the polymer and for the catalyst is added to said aqueous emulsion and an organic additive is added to the mixture before hydrogenation is initiated, said additive being selected from monocarboxylic acids of formula R.sub.1 --COOH, from dicarboxylic acids of formula HOOC--R.sup.1 --COOH and from tartaric, citric and ascorbic acids, where R.sub.1 is selected from Q--(CH.sub.2).sub.m -- where m is an integer from 1 to 6 and Q is selected from hydroxy and phenoxy or R.sub.1 is selected from T--C(CH.sub.3).sub.2 --, T--CH.sub.2 --(CH.sub.2).sub.p --, T.sub.2 CH--(CH.sub.2).sub.p --, T.sub.3 C--(CH.sub.2).sub.p --, CH.sub.3 --CHT--(CH.sub. 2).sub.p-1 --, CH.sub.3 --(CH.sub.2).sub.y --CHT--(CH.sub.2).sub.p-1-y --, or CH.sub.3 --(CH.sub.2).sub.p-1 --CHT-- where T is fluorine or chlorine, p is 0 or an integer from 1 to 5 and y is an integer from 1 to 3, or R.sub.1 is selected from the aromatic group C.sub.6 H.sub.4 Y where Y is selected from chlorine and hydroxy, and wherein R.sup.1 is selected from --(CH.sub.2).sub.q -- where q is 0 or an integer from 1 to 5, from --CH.dbd.CH-- and from (p) C.sub.6 H.sub.4, the weight of said additive per 0.01 parts by weight of ruthenium in the catalyst being from about 0.3 to about 1.5.