N-Alkyl-lactam purificn - comprises removing cycloalkylene imine by passing carbon dioxide at ambient temp

Purifcn. of N-alkyl lactams of formula (I) (where R = straight or branched, 6-20C satd. aliphatic hydrocarbyl, n = 414) is by using a current of CO2 at ambient temp. to ppte. cycloalkylene imine (II) as carbonate. (I) are prepd. by reacting corresp. alkali metal lactomate with alkyl halide in organic solvent. Pref. compds (I) are N-heptyl-,N-nonyl-,N-decyl-,N-dodecyl- and N-2ethyl-hexyl-dodecyl- and N-2-ethyl-hexyl-dodecalactam. CO2 is passed for 10-60 mins. Cpds. (I) are monomers, esp. for copolymerisation with lactams, e.g. caprolactam, and (II) binders or prevents copolymerisation, thus method gives improved polymer yield and properties.