1000 ml of polystyrene-trimethylbenzylammonium ion exchange resin were
converted into the chloride form by passing aqueous hydrochloride acid over
the resin. The resin was washed with distilled water to remove all traces of passed over the resin. A 10% excess of the calcium aspartate solution over
the theoretical ion-exchange capacity of the resin was used and the resin was
then washed with water until the wash water was free of chloride ions. At the
end of this treatment, the resin was in the aspartic acid form.
An aqueous solution containing 168.56 g of calcium aspartate and 49.44 g of
arginine dihydrochloride per litre was prepared, and this solution was passed
slowly over the aspartic acid form resin. The effluent liquid was collected in
fractions of 200 ml, then of 100 ml, and towards the end, in fractions of 50
ml. After about 1000 ml of eluate had been collected, the succeeding fractions
were examined very carefully for the presence of chloride ion. All the eluate
fractions prior to the first one containing traces of chloride, i.e. all the
chloride-free eluate fractions, were combined, the combined chloride eluates
amounted to about 1300 ml. The arginine present was determined by
Sakaguchis method and the total nitrogen in the combined eluates was also
determined. These determinations showed that the eluates contained from
270 to 300 g of arginine aspartare per litre. The combined eluates were
evaporated to a volume of about 500 ml and allowed to crystallize at a low
temperature (0°-4°C). After seeding with a crystal of arginine aspartate,
colourless crystals were obtained, they were filtered off, washed with aqueous
ethanol, and then dried. About 210 g, i.e. 70% of the theoretical yield, of
crystals having a decomposition point of 220°C was obtained. The mother
liquor from the first crystallization was evaporated down to a volume of about
150 ml. Ethanol was added to the solution until cloudiness which persisted
was obtained, the solution was cooled to 0°C and a second crop of crystals
was obtained. The size of this second crop was increased by adding further
ethanol after the major portion of the second crop had crystallized and
allowing the mixture to stand for 48 hours at 0°C. After separation, the
second fraction consisted of 75 g of a crystalline mass which had the same
physico-chemical and chemical properties as the main fraction.
