A process for the manufacture of pent-3-enoic acid and its alkyl esters, of the general formulaCH.sub.3 --CH.dbd.CH--CH.sub.2 --CO--ORwhere R is hydrogen or alkyl of 1 to 4 carbon atoms, comprising carbonylating butadiene with carbon monoxide and a compound ROH at from 300 to 1,000 bars CO pressure and from 100.degree. to 160.degree. C. in the presence of cobalt catalysts and nitrogen bases, wherein C.sub.4 cuts are used as starting materials and a tertiary amine having a pK.sub.A of from 3 to 11 is used as the nitrogen base. The pent-3-enoic acid or alkyl esters produced may be used for the manufacture of adipic acid or its alkyl esters, which compounds are starting materials for the manufacture of nylons.