B.
o-Anisaldehyde. In a
3-l. three-necked flask fitted with a
mechanical stirrer and a
nitrogen inlet tube are placed
60 g. (0.35 mole) of sulfanilic acid (Note
5),
18 g. (0.17 mole) of anhydrous sodium carbonate, and 400 ml. of water. Stirring is started, and the resulting solution is cooled to 0–5° in an
ice bath.
Nitrogen is passed into the reaction flask, and a
nitrogen atmosphere is maintained throughout the reaction. To the cooled solution is added three-quarters of a solution of
24.2 g. (0.35 mole) of sodium nitrite in 75 ml. of water, followed by
32 ml. of concentrated hydrochloric acid. During the diazotization the temperature of the solution is maintained below 5° by the addition of ice in small pieces. After a few minutes another
32 ml. of acid is added. Further additions of the
sodium nitrite solution are made slowly until a positive test for excess
nitrous acid is observed (Note
6). The diazonium solution is buffered to pH

6 by the addition of a cooled solution of
50 g. of sodium acetate in 125 ml. of water. A solution of
52 g. (0.20 mole) of 4-dimethylamino-2'-methoxybenzhydrol in 500 ml. of acetone is added rapidly, followed by an additional
500 ml. of acetone. The reaction mixture becomes red almost immediately, and stirring is continued for 30 minutes. at 0–5°. The cooling bath is replaced by a warm
water bath (50–60°), and stirring is continued for an additional 30 minutes. The reaction mixture is diluted with an equal volume of water and extracted with three
750-ml. portions of ether. The combined ethereal extracts are washed with water until all the dissolved
methyl orange is removed, then dried over
calcium sulfate. The
ether is removed under reduced pressure, and the residue is distilled to yield
19–20.5 g. (
69–75%) of colorless liquid, b.p.
79–80° (1.5 mm.),
n25D 1.5586 (Note
7).