Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

338 BENZOHYDKOL AND TKIPHENYLCAKBINOL
distilled benzaldehyde mixed with 10 c.c. of ether are rapidly added
drop by drop, at first with continued cooling.
To complete the reaction the solution is boiled for fifteen minutes
under reflux and again cooled. External cooling is continued,
20-30 g. of ice are then added in one portion, followed by sufficient
hydrochloric acid to dissolve the magnesium hydroxide which is
precipitated (about 10 c.c. of concentrated acid plus 10 c.c. of water).
The ether layer is now separated in a funnel and the aqueous layer
is extracted with a little fresh ether. If a glass rod after dipping into
the ethereal solution still smells of benzaldehyde, half of the ether is
evaporated and the remaining solution is vigorously shaken for five
minutes with a few cubic centimetres of 40 per cent bisulphite solution,
then with a little sodium carbonate solution to remove dissolved
sulphur dioxide ; the ethereal solution is next dried for a short time
with calcium chloride. On evaporating the ether the benzohydrol
remains as an oil which soon solidifies. Yield, after pressing on
porous plate, 12-14 g. The alcohol can be recrystallised from ligroinor
from a little spirit. Beautiful colourless prisms; melting point 68°.
If the formation of the Grignard compound proceeds too violently
the reaction product usually contains considerable amounts of diphenyl
because of the reaction :
C6H5MgBr + BrC6H5 — •> C6HS.C6HS + MgBr2 .
(6) TRIPHENYLCARBINOL FROM ETHYL BENZOATE AND
PHENYL MAGNESIUM BROMIDE
Ethyl benzoate (15 g.) mixed with 15 c.c. of absolute ether is
dropped into a Grignard solution prepared as just described from
6-4 g. of magnesium and 40 g. of bromobenzene. The conditions
are the same as those observed in the preceding preparation;
at the end the solution is boiled for half an hour and worked up as
before. Colourless prisms of triphenylcarbinol, melting point 162°,
are obtained by recrystallising the solid residue from hot alcohol.
Yield over 20 g. For further information about this important
alcohol see p. 355.
2. SYNTHESIS OF A KETONE FROM A NITRILE.
ACETOPHENONE 1
An ethereal solution of phenyl magnesium bromide is prepared
1 Blaise, Compt. rend., 1901, 133, 1217.