A well-stirred
(Note 1) and
(Note 2) mixture of
740 ml. of glycerol and
216 g. of boric acid, in a
2-l. three-necked round-bottomed flask fitted with a
thermometer and a
condenser for downward distillation, is dehydrated by heating in an
oil bath to
exactly
170°. This temperature is maintained for 30 minutes and then allowed to
drop. When the temperature has fallen to 150°, a mixture of
154 g. (1 mole) of pyrogallol-1,3-dimethyl ether and
154 g. (1.1 moles) of hexamethylenetetramine (Note 3)
is added as rapidly as possible through the neck holding the
thermometer. The temperature drops to approximately 125°. Rapid heating
is immediately started but is slowed down when the temperature begins
to reach 145° and stopped at 148°. The reaction must be watched and
controlled
very carefully when this temperature is reached, since the reaction becomes exothermic at this point
(Note 4),
(Note 5), and
(Note 6). The temperature is maintained at 150–160° for approximately 6 minutes
(Note 7). At the end of this reaction time the mixture is cooled to 110° as rapidly as possible
(Note 6) and
(Note 8), and a previously prepared solution of
184 ml. of concentrated sulfuric acid in 620 ml. of water is added to the reaction mixture. After being stirred for 1 hour, the mixture is cooled to 25° in an
ice bath. The
boric acid, which separates from the solution, is removed by filtration
(Note 9) and washed free of mother liquor with 400 ml. of water. The filtrate and washings are combined and extracted with three
500-ml. portions of chloroform (Note 10),
(Note 11), and
(Note 12).
The
chloroform solution is then extracted with a filtered solution of
180 g. of sodium bisulfite in 720 ml. of water
(Note 13) by stirring rapidly with a
Hershberg stirrer for 1 hour. The separated bisulfite solution is washed twice with
chloroform, filtered, and acidified in a
hood with a solution of
55 ml. of concentrated sulfuric acid in 55 ml. of water. After careful heating on a
steam bath for a short time, air is bubbled through the hot solution until all the
sulfur dioxide has been expelled. The product, which separates as a mixture of crystals and oil, readily solidifies upon cooling
(Note 14). The
syringic aldehyde is collected by filtration, washed with cold water, and dried in an
oven at 40° to give
62.5–66 g. of light-tan material, melting at
110.5–111°,
which still contains a small amount of foreign material that does not
melt at 300°. Recrystallization of the crude product from aqueous
methanol using 30 ml. of water and
3 ml. of methanol for each 10 g. of aldehyde gives
56–59 g. (
31–32%) of product melting clear at
111–112° (uncor.). A second extraction of the
chloroform solution with a filtered solution of
60 g. of sodium bisulfite in 240 ml. of water gives an additional
3–4 g. of product.