Hydrochloric Acid → L-Cysteine hydrochloride monohydrate

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500 ml of a purified L-cysteine-containing solution (eluate with 1N HCl) of example 7 or 9 (L-cysteine content=17 g/l) are concentrated to 25 ml. After adding concentrated HCl or introducing HCl gas, chlorides of inorganic alkali metal and alkaline earth metal ions and ammonium chloride may be crystallized, preferably at 20-60° C. After filtration, the L-cysteine-containing mother liquor is cooled to −10° C. and L-cysteine hydrochloride monohydrate crystallizes. Depending on the purity of the L-cysteine-containing solution used, L-cysteine hydrochloride monohydrate may be obtained in crystalline form in yields of >80% and purities of >90% from these solutions. It is possible to achieve purities of up to >98% by suitable control of the crystallization conditions, fractionated crystallization and/or recrystallization.

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