Org. Synth. 1941, 21, 27
DOI: 10.15227/orgsyn.021.0027
3,5-DIHYDROXYBENZOIC ACID
[α-Resorcylic acid]
Submitted by Arthur W. Weston and C. M. Suter.
Checked by C. F. H. Allen and John W. Gates, Jr..
1. Procedure
To 200 g. (1.64 moles) of benzoic acid in a 1-l. Kjeldahl flask, in the top of which is inserted a loosely fitting cold finger (Note 1), is added 500 ml. of fuming sulfuric acid (Note 2). The mixture is heated in an oil bath for 5 hours at 240–250° (bath temperature).
After standing overnight the syrupy liquid is poured slowly with stirring into 3 kg. of ice in a 3-gal. crock (Note 3). The solution is then neutralized by adding barium carbonate in 100-g. portions, stirring occasionally until the gas evolution slackens before each addition: 2.4–2.5 kg. is required. The pasty mass is filtered by suction on a 30-cm. Büchner funnel, and the barium sulfate is washed with five 300-ml. portions of water. The combined filtrates are evaporated nearly to dryness on a steam bath and finally dried in an oven at 125–140° (Note 4). The yield of crude barium salt is 640–800 g.
The operator should wear goggles and long-sleeved gloves during the next two operations. The dried, pulverized barium salt is introduced in 200-g. portions into a melt of 600 g. each of sodium and potassium hydroxides contained in a 14 by 20 cm. copper beaker. The mixture is stirred with a copper stirrer and the temperature determined with a thermometer in a copper well. (Note 5). Each portion is well stirred in before the next is added. The temperature is then slowly raised to 250–260°, at which point a vigorous reaction occurs with copious evolution of gas. After this has slackened (about 30 minutes) the temperature is raised to 280–310° and maintained there for 1 hour, then allowed to drop to 200°. The melt is ladled into 6 l. of water (Note 6) and (Note 7). The barium sulfite is filtered by suction, and the filtrate is acidified with concentrated hydrochloric acid (about 2.5 l. is required).
The resulting solution (about 9 l.) is divided into two portions and each is extracted three times, 600 ml. of ether being used each time (Note 8). The combined extracts are concentrated to about 1 l. and dried overnight over 150 g. of anhydrous sodium sulfate. After filtration and evaporation of the ether, there remains 137–160 g. (58–65%) of a slightly colored product, melting with decomposition at 227–229°. It is sufficiently pure for most purposes (Note 9) and (Note 10).
2. Notes
1.
An ordinary
glass funnel suspended in the neck serves less satisfactorily, whereas with a water condenser solidification of the
sulfur trioxide causes difficulty.
2.
This acid, approximately
30% sulfur trioxide, is made by mixing
500 g. each of fuming sulfuric acid containing
60% free sulfur trioxide and concentrated
sulfuric acid (sp. gr. 1.84); 500 ml. of this mixture is used.
3.
The reaction product may solidify at first, but it dissolves later.
4.
The evaporation of the solution is most conveniently done overnight. The final drying is best done in flat metal trays; the length of time required depends upon the temperature. The checkers left trays on a steam coil over a week end.
5.
An
18-cm. piece of 10- to 12-mm. copper tubing, pounded together at the lower end, is used. The stirrer can be made of the same tubing.
6.
The addition of the hot melt causes some spattering.
7.
Alternatively, the melt may be poured into shallow metal trays and allowed to cool and solidify. It is then pulverized and dissolved. Grinding is difficult and unpleasant. The melt should not be allowed to solidify in the reaction vessel.
8.
A large automatic extraction apparatus may be used if available.
9.
The color can be removed by recrystallization from hot
acetic acid, using a
decolorizing carbon. A solution of 16 g. of the crude acid in
85 ml. of hot acetic acid deposits
13.4 g. of white needles after filtration through a 2-mm. layer of Darco in a hot funnel and cooling. These are anhydrous after drying at 100° at 35 mm. for 2 hours; m.p.
234–235° with decomposition (cor.). The melting point varies with the rate of heating.
10.
This material is partially hydrated.
1 The melting point is unchanged after recrystallization from water.
3. Discussion
3,5-Dihydroxybenzoic acid is most conveniently prepared by alkaline fusion of the disulfonic acid obtained by sulfonation of
benzoic acid.
1,2,3 It has also been prepared by alkaline fusion of the
3,5-dihalobenzoic acids4,5 or of
3-bromo-5-sulfobenzoic acid.
6 Benzoic acid has been sulfonated using various strengths of
sulfuric acid with or without catalysts.
7,8
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
barium salt
potassium hydroxides
3,5-dihalobenzoic acids
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
acetic acid (64-19-7)
ether (60-29-7)
sulfur trioxide (7446-11-9)
sodium sulfate (7757-82-6)
Benzoic acid (65-85-0)
barium sulfate (7727-43-7)
decolorizing carbon (7782-42-5)
sodium (13966-32-0)
barium carbonate (513-77-9)
3,5-Dihydroxybenzoic acid,
α-Resorcylic acid (99-10-5)
barium sulfite
3-bromo-5-sulfobenzoic acid
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