Process for hydrogenating unsaturated compounds

In a process for hydrogenating a hydrogenatable unsatuated organic compound having carbon-carbon, carbon-oxygen, carbon-nitrogen or nitrogen-oxygen multiple bonds, in substantially homogeneous, organic liquid phase, wherein said compound is hydrogenated with hydrogen, in the presence of a hydrogenation catalyst which is substantially soluble in said organic liquid phase,

• the improvement which comprises using as said catalyst the product obtained by reacting at least one tri-hydrocarbyl aluminum reducing agent with (a) at least one carboxylate of a transition metal and (b) at least one organic carboxylic acid whose pK.sub.a in water at 25.degree. C. is lower than 7.