In a
2-l., three-necked, round-bottomed flask (Note
1) fitted with a
sealed stirrer having a Teflon® blade and, on the two side necks, with
gas-outlet tubes connected by rubber or plastic tubing to an efficient hydrogen chloride absorption trap (Note
2),
464 g. (2 moles) of D,L-10-camphorsulfonic acid (Note
3) is mixed with
416 g. (2 moles) of phosphorus pentachloride (Note
4). The flask is immersed in ice water and, as soon as the mixture has liquefied sufficiently, the stirrer is started but must be run slowly at first because of lumps. When the vigorous reaction has subsided, the
cooling bath is removed and stirring continued until the chloride is completely dissolved (Note
5). The mixture is then allowed to stand for 3 or 4 hours. It is poured (
Hood!) onto 500 g. of crushed ice contained in a
2-l. beaker. This mixture is immediately poured into a second beaker containing a similar quantity of crushed ice. The mixture is then poured back and forth between the two beakers until all evidence of reaction has disappeared (Note
6). The fine white product is collected on a
suction filter and washed several times with cold water. The yield is essentially quantitative (500 g.) of moist sulfonyl chloride which is pure enough to be used for the preparation of
D,L-ketopinic acid (
p. 55). When carefully dried, the crude material has m.p.
81–83° (Note
7) and (Note
8) and may be preserved in a
desiccator.