A solution of
170 g. (1.0 mole) of silver nitrate in 1 l. of water in a
2-l. beaker is treated, with stirring, with a solution of
44 g. (1.07 moles) of 97% sodium hydroxide in 400 ml. of water (Note
1). The mixture is stirred for 5 minutes, and the
silver oxide is collected on an
11-cm. Büchner funnel with suction and washed free of nitrates with water (Note
2). The wet, freshly precipitated
silver oxide is transferred to a
4-l. beaker (Note
1), covered with 2 l. of water, and treated with
200 g. (4.85 moles) of 97% sodium hydroxide pellets with vigorous stirring. If the temperature of the mixture at this point is below 55°, the mixture is warmed to 55–60°. With continued stirring at 55–60° (Note
3),
152 g. (1.0 mole) of vanillin (Note
4) is added; the reaction begins after a few minutes. The
silver oxide is transformed to fluffy metallic
silver, and considerable heat is evolved. Stirring is continued for 10 minutes, the mixture is filtered, and the precipitated
silver is washed with 100 ml. of hot water. A rapid stream of
sulfur dioxide gas (Note
5) is passed into the combined filtrate and washings for 2 minutes, and the resulting solution is poured into
1.1 l. of 1:1 hydrochloric acid with vigorous stirring. The resulting mixture, which should be acid to Congo red, is cooled to 15–20°. The
vanillic acid is collected on a Büchner funnel, pressed to remove the mother liquor, washed with 150 ml. of ice water (Note
6), sucked as dry as possible, and air-dried. The yield is
140–160 g. (
83–95%) of white needles melting at
209–210°. This product is pure enough for most purposes, but it may be purified by recrystallization from water containing a little
sulfur dioxide, 1.2 l. of water being used per 100 g. of product. Pure white needles melting at
210–211° are obtained with a recovery of
90–97%.