however too much enamine is wasteful as the excess takes no part in the reaction the reaction will take place over a wide range of temperatures for example from 0 u00b0 to 140 u00b0 c more preferably from about ambient temperature to 60 u00b0 c in general temperatures as close to ambient as possible are preferred for industrial processes in order to minimize energy costs but this may sometimes be impractical as higher temperatures in general speed chemical reactions and too long a reaction time may be required unless an elevated temperature is employed it is a particular advantage of the present invention that chlorinated aliphatic hydrocarbons such as methylene chloride may be used as the reaction solvent since these permit the reaction to be effected efficiently at a relatively low temperature e g from ambient temperature to 40 u00b0 c within a reasonably short period for example up to 5 or 6 hours when chloroform is used as the solvent similar conditions apply e g a reaction temperature from ambient to 50 u00b0 c and a period up to about 5 hours the time required for the reaction will vary depending upon many factors including the reaction temperature and other reaction conditions notably as mentioned above the reaction solvent in general a period of from 30 minutes to 30 hours will suffice although of course it is preferred that.