Hi Viktor

Yes, I think you are on the right track.

Dissolution of L-histidine hydrochloride monohydrate in a minimum volume of water will give you the aqueous protonated form of L-histidine, chloride and a water molecule. Addition of a molar equivalent of a strong base such as NaOH will give you aqueous L-histidine. Partial evaporation of the water should lead to the crystallization/precipitation of L-histidine (full evaporation will give L-histidine and NaCl).

Alternatively, you may also be able to obtain L-histidine directly from L-histidine hydrochloride monohydrate by mild heating at 100 oC, liberating HCl(g) and H2O(g). If you are going to try this, do the experiment in a fumehood due to liberation of HCl(g).

Geoff

Hi Viktor

Yes, I think you are on the right track.

Dissolution of L-histidine hydrochloride monohydrate in a minimum volume of water will give you the aqueous protonated form of L-histidine, chloride and a water molecule. Addition of a molar equivalent of a strong base such as NaOH will give you aqueous L-histidine. Partial evaporation of the water should lead to the crystallization/precipitation of L-histidine (full evaporation will give L-histidine and NaCl).

Alternatively, you may also be able to obtain L-histidine directly from L-histidine hydrochloride monohydrate by mild heating at 100 oC, liberating HCl(g) and H2O(g). If you are going to try this, do the experiment in a fumehood due to liberation of HCl(g).

Geoff

Thank you, Mr. Waterhouse!

Best regards.

The L-histidine hydrochloride monohydrate could be dissolved in water (approx. 10 wt%) and neutralized with either sodium hydroxide or sodium hydrogen carbonate sol. (e.g. 1 M), from the original acidic pH (3.5―4.5) to the L-histidine isoelectric point (7.5―7.6); hence minimizing the L-histidine solubility. The alkali could be dissolved in water, methanol, or in water―methanol solution. Adding methanol and/or chilling (to approx. 0 ºC) further promotes L-histidine precipitation from the solution. The precipitate could be washed with methanol and/or with diethyl ether, what would facilitate drying. For neutralization with sodium hydrogen carbonate: C6H9N3O2·HCl·H2O + NaHCO3 → C6H9N3O2 ↓ + NaCl + 2 H2O + CO2(g)↑.