which the nitrogen maybe activated to promote the elimination addition mechanism one approach is treatment with an acid for example a carboxylic acid at a sufficiently high temperature such as heating with propionic acid e g under reflux this reaction is suitably conducted in an inert solvent such sa toluene the racemisation can optionally be accelerated by the judicious addition of amounts of additives such as water or inorganic salts that will favour the charge separation in the transition state of the elimination this reaction may also be promoted by the addition of an aldehyde or ketone e g butyraldehyde or 2 cyclohexen 1 one as indicated above conditions are known that will epimerise erythro ritalinic acid at the benzylic centre only on the basis of the evidence herein it will readily be apparent to the man of ordinary skill in the art that conditions can be adopted in order to give all 4 stereoisomers of methylphenidate by racemisation at both chiral centres following racemisation and prior to resolution it is necessary to enrich the mixture in the threo enantiomers for example the racemic methylphenidate is hydrolysed e g using as such as alkali metal hydroxide this can be done such that there is also epimerisation work up with acid gives predominantly threo ritalinic acid x co 2 h which can be esterified e g by reaction with methanol to give the appropriate substrate for resolution alternatively the erythro isomers can be separated by precipitation and then subjected to sequential epimerisation esterification and resolution the following experiment was.