Separation and Identification of the Main Impurity in Erythromycin Oxime

The oximation of erythromycin is studied. The main impurity involved in the synthesis of erythromycin oxime was separated and purified, which was identified as the very compound formed in the acidic hydrolysis of erythromycin A, i.e erythromycin A 8,9 dehydro 6,9 hemiketal. This result shows that the oximation of erythromycin is always accompanied with its acidic degradation, and therefore that it is important to control the amount of acid used as catalyst.