Preparation of alkyl pentenoates

Alkyl pentenoates are prepared by (a) reacting butadiene or a butadiene-containing hydrocarbon mixture with carbon monoxide and an alkanol in the presence of a tertiary aromatic heterocyclic nitrogen base and a cobalt carbonyl catalyst at from 80 DEG to 160 DEG C. under from 100 to 1,000 bar to obtain a reaction mixture which contains alkyl pentenoate, C6-diester, tertiary nitrogen base, alkanol, butadiene, hydrocarbon and by-product, (b) substantially removing from the reaction mixture obtained any excess hydrocarbon, nitrogen base, alkanol and alkyl pentenoate by distillation to obtain a residue which contains cobalt carbonyl catalyst, (c) bringing the residue which contains cobalt carbonyl catalyst into contact with a mixture of carbon monoxide and hydrogen at elevated temperature and elevated pressure, and (d) recycling the residue which contains cobalt carbonyl catalyst into alkyl pentenoate synthesis stage (a).