In a
3-l. flask is placed a solution of
184 g. (4.6 moles) of sodium hydroxide in 300–400 cc. of water; sufficient ice is added to make the total volume about 1.5 l.
Chlorine is passed into the solution, the temperature being kept below 0° by means of a
salt-ice bath, until the solution is neutral to litmus, then a solution of
34 g. of sodium hydroxide in 50 cc. of water is added (Note
1) and (Note
2). The flask is now supported by a clamp and equipped with a
thermometer and an
efficient stirrer. The solution is warmed to 55°, and
85 g. (0.5 mole) of methyl β-naphthyl ketone (Note
3) is added. The mixture is vigorously stirred, and, after the exothermic reaction commences, the temperature is kept at 60–70° (Note
4) by frequent cooling in an
ice bath until the temperature no longer tends to rise. This requires thirty to forty minutes. The solution is stirred for thirty minutes longer and then the excess hypochlorite is destroyed by adding a solution of
50 g. of sodium bisulfite in 200 cc. of water (Note
5). After cooling to room temperature, the reaction mixture is transferred to a
4-l. beaker and carefully acidified with
200 cc. of concentrated hydrochloric acid. The crude colorless acid is collected on a Büchner funnel, washed with water, and sucked as dry as possible with a
rubber dam. After drying, the acid is crystallized (Note
6) from
600 cc. of 95 per cent alcohol, giving
75–76 g. (
87–88 per cent of the theoretical amount) of
β-naphthoic acid melting at
184–185° (corr.). By distilling 450 cc. of solvent from the mother liquor, an additional
9 g. (
10 per cent of the theoretical amount) of acid, m.p.
181–183° (corr.), is obtained (Note
7).