Spontaneous transformation of one crystalline solvate of a succinic acid to another has been observed by Japanese and South African chemists. 

Koichi Tanaka and colleagues at Kansai University in Japan and the University of Cape Town in South Africa detected this rare phenomenon while studying the properties of succinic acid crystals containing ethanol. 

The researchers found that when succinic acid is recrystallised from a saturated ethanol solution pale yellow needles containing an equal number of acid and ethanol molecules form. When these crystals are left in ethanol solution for one day they change to become orange prisms which contain acid and ethanol in a 1:2 ratio. 

Solvate formation and crystallisation is an area of intense interest, particularly in the pharmaceutical sector where different solvate forms of a drug may have different solubilities, processabilities and reactivities. 

Caroline A Moore