the same or different from the antisolvent used for precipitation of the salt ob h x u2212 the amount of antisolvent used for washing should be kept as low as possible to result in a sufficient purity of the product while maintaining a good yield after the salt ob h x u2212 has been removed preferably by precipitation and filtration the product of formula i is usually recovered by distillation particularly preferred is a fractional distillation under reduced pressure where the boiling point of the antisolvent used during precipitation and washing of the salt ob h x u2212 is sufficiently below the boiling point of the desired compound of formula i it is preferred to strip off the antisolvent before the remaining mixture is subjected to further purification in an alternative embodiment the salt ob h x u2212 is not precipitated by addition of an antisolvent but the reaction medium still comprising the salt ob h x u2212 is directly subjected to fractional distillation however while in this embodiment it is possible to omit the use of the antisolvent generally purity and yield of the desired product are improved if the salt ob h x u2212 is first removed preferably by precipitation and filtration before the desired.