Preparation of cyclic lactams

In the process for the preparation of cyclic lactams of formula (II)

• in which n and m can individually have a value of 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9, the sum of n and m is at least 3 and R1 and R2 denote C1-C6 alkyl, C5-C7 cycloalkyl or C6-C12 aryl groups by reaction of a compound (I) of the formula
• in which R1, R2, m and n have the meanings stated above and R denotes nitrile, carboxamido and carboxy groups,
• with steam in the vapor phase, the improvement wherein
• a) compound (I) is caused to react with steam in the vapor phase, an organic diluent (III) which is an aliphatic, cycloaliphatic or aromatic hydrocarbon, being added after the reaction, which diluent exhibits a miscibility gap with water under certain conditions of concentration, pressure and temperature, to give a mixture (IV) containing lactam (II)
• b) mixture (IV) is subjected, before or after separation of ammonia, to conditions of concentration, pressure and temperature under which diluent (III) and water are present in the liquid state and exhibit a miscibility gap, to give a two-phase system comprising a phase (V) in which the content of diluent (III) is higher than that of water and a phase (VI) in which the content of water is higher than that of diluent (III),
• c) phase (V) is separated from phase (VI), and
• d) from phase (V) diluent (III) and optionally by-products comprising low boilers (VIII), high boilers (VII) and/or uncoverted compound (I) are separated, to give lactam (II).