3,3'-Dimethoxybiphenyl2 (8 g., 0.037 mole) is dissolved in
120 ml. of methylene chloride in a
250-ml. conical flask, and the flask is placed in an
acetone-dry ice bath at −80°. The flask is fitted with an
air condenser. A solution of
15.9 g. (6.0 ml., 0.063 mole) of boron tribromide (Note
1), (Note
2) in
40 ml. of methylene chloride (Note
3), (Note
4) is added carefully to the stirred solution through the condenser. When the addition is complete, a
calcium chloride tube is fitted to the top of the air condenser in order to protect the reaction mixture from moisture. As the solution of
boron tribromide is added, a white precipitate is formed. The reaction mixture is allowed to attain room temperature overnight with stirring, when a clear, brownish yellow solution is obtained. The reaction mixture is then hydrolyzed by careful shaking with 130 ml. of water, thus precipitating a white solid which is dissolved by the addition of
500 ml. of ether. The organic layer is separated and extracted with
240 ml. of 2N sodium hydroxide; the alkaline extract is neutralized with dilute
hydrochloric acid, extracted with
300 ml. of ether, and the
ether extract is dried over anhydrous
magnesium sulfate. On removal of the
ether under reduced pressure, a brownish yellow oil remains which soon crystallizes to give an off-white solid; this is recrystallized twice from hot
benzene, the first time with the addition of charcoal, and gives
3,3'-dihydroxybiphenyl as white needles with a pinkish tint, m.p.
126–127° (Note
5). The yield is
5.4–6.0 g. (
77–86%).