Scheme 4.10 The effect of ultraviolet light on chlorpromazine (CLP).

The first step of the photodegradation is the loss of an electron to yield the semiquinone free radical R. Further stages in the degradation yield the phenazathonium ion P, which is thought to react with water to yield chlorpromazine sulfoxide (CPO). The chlorpromazine sulfoxide is itself photolabile and further decomposition occurs. Other products of the photooxidation include chlorpromazine N-oxide and hydroxychlorpromazine. Reproduced from F. H. Merkle and C. A. Discher, J. Pharm. Sci., 53, 620 (1964).

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