1. Moisture in the reagents affects the yield seriously because of the ease with which the intermediate
imido ether is hydrolyzed. The
hydrogen chloride must be thoroughly dried by passing it through two
wash bottles containing
sulfuric acid. If the wash bottles are not effective, a tube containing
glass beads mixed with
phosphorus pentoxide should be used after the wash bottles. It is well to protect the side arm of the flask by means of a calcium chloride tube. The absolute
alcohol used should be at least 99.5 per cent (p. 249).
2. If commercial
acetonitrile is used directly, the yields are poor. It should be dried over
calcium chloride for at least a week, filtered, and distilled, the fraction boiling at 76–81° being used.
7. By a similar procedure
benzamidine hydrochloride can be prepared. Dry
hydrogen chloride is passed into a cooled solution of
51.5 g. (51 cc., 0.5 mole) of benzonitrile in
25 g. of absolute ethyl alcohol until 21.3 g. of the gas is absorbed. The reaction mixture is allowed to stand for forty-eight hours, and the solid cake of
imido ether hydrochloride is quickly crushed in a dry mortar. The solid is transferred to a
liter flask, and an
8 per cent solution of dry ammonia in absolute
ethyl alcohol containing
12 g. of ammonia is added slowly in small portions. The reaction mixture is shaken for twenty-four hours, then allowed to stand for forty-eight hours and filtered to remove the
ammonium chloride which has precipitated. (During the shaking the solution may develop a faint pink color. This is probably due to the presence of traces of
glyoxal in the alcohol for this material in basic solution furnishes colored condensation products with
benzamidine.) The filtrate is allowed to evaporate to dryness in the open air, and the
benzamidine hydrochloride thus obtained is dissolved in water. The solution is acidified with concentrated
hydrochloric acid, decolorized with charcoal, filtered, and the filtrate is evaporated almost to dryness at room temperature. The crystals of
benzamidine hydrochloride dihydrate are filtered and air-dried. The yield is
60–70 g. of material which melts at
70–73°. The filtrate on evaporation to dryness furnishes
15–30 g. of less pure product, melting at
74–82°, which contains a small amount of
ammonium chloride but which can be used satisfactorily in most reactions. The total yield is
80–95 per cent. (A. R. Ronzio and J. B. Ekeley, private communication.)