Fractional crystallisation evaporation

The separation of cystine and tyrosine as they are obtained by hydrolysis with hydrochloric acid was described by Morner in I901. The protein—hair, keratin from horn, eggshells, etc.—was boiled with five times its quantity of 13 per cent hydrochloric acid under a reflux condenser on a water bath for six to seven days. The solution was then decolorised with charcoal and evaporated in vacuo, and the residue dissolved in 60 to 70 per cent, alcohol. The two acids then crystallised out on neutralising with soda, and were separated by fractional crystallisation from ammonia if much tyrosine was present it separated out first, but if cystine exceeded tyrosine in quantity this compound crystallised out first the remainder was only separated with difficulty. Embden separated the mixture of the two acids by means of very dilute nitric acid, in which tyrosine is very easily soluble, but cystine with difficulty. Their separation may also be effected by precipitation with mercuric sulphate in 5 per cent, sulphuric acid solution in which the mercury compound of tyrosine is soluble (Hopkins and Cole). 

Proline.—This is the only product of hydrolysis obtained from an ester fraction which is soluble in alcohol it is also much more easily soluble in water than the other products with which it is present and therefore is somewhat easily separated, as it remains in the mother-liquor after these have crystallised out. The solution, in which it is contained, is evaporated to dryness and extracted with absolute alcohol the combined alcoholic extracts from the several fractions are evaporated to dryness and taken up by absolute alcohol several times, so as to remove small amounts of the other amino acids, which, though insoluble in alcohol, are dissolved when proline is present. 

The mass is mixed with water and the calculated quantity of sodium hydrogen sulphate, and heated under pressure after filtration the solution of sodium chromate is fractionally crystallised. If the dichromate is required, the solution of sodium chromate is slightly acidified with sulphuric acid and evaporated until it crystallises. 

Phthalic anhydride [85-44-9] M 148.1, m 132", h 295. Distil the anhydride under reduced pressure. Purify it from the acid by extracting with hot CHCI3, filtering and evaporating. The residue is crystallised from CHCI3, CCI4 or benzene, or sublimed. Fractionally crystallise it from its melt. Dry it under vacuum at 100". [Saltiel J Am Chem Soc 108 2674 1986, Beilstein 17/11 V 253.]... 

---