Org. Synth. 1940, 20, 92
DOI: 10.15227/orgsyn.020.0092
TEREPHTHALALDEHYDE
Submitted by J. M. Snell and A. Weissberger.
Checked by R. L. Shriner and N. S. Moon.
1. Procedure
A. α,α,α',α'-Tetrabromo-p-xylene. A 1-l. three-necked flask is fitted with an oil-sealed mechanical stirrer, a 500-ml. dropping funnel, and a reflux condenser, the top of which is connected to a gas-absorption trap. A 300-watt tungsten lamp is clamped in such a position that its bulb is within 1 in. of the flask (Note 1). Into the flask is introduced 100 g. (0.94 mole) of dry p-xylene (m.p. 11–12°), and the flask is heated in an oil bath maintained between 140° and 160°. The stirrer is started, and, when the xylene starts boiling, 700 g. (224 ml., 4.38 moles) of dry bromine (Note 2) is gradually added through the dropping funnel at such a rate that there is never any large amount of unreacted bromine in the flask. Stirring and heating are continued throughout the reaction, which requires 6–10 hours. After all the bromine has reacted, the mixture is cooled and dissolved in 1 l. of warm chloroform. The chloroform solution is cooled in an ice bath and the product removed by filtration. It is light gray, melts at 165–169°, and weighs 250–258 g. After a second recrystallization from 1 l. of chloroform, 190–200 g. of light-gray crystals melting at 168–170° is obtained. An additional 15–20 g. may be obtained by concentrating the chloroform filtrate to 250 ml. and recrystallizing the precipitate from fresh chloroform. The total yield is 205–220 g. (51–55%).
B. Terephthalaldehyde. A 2-l. round-bottomed flask is fitted with a still head, capillary ebullition tube, and receiver in an assembly for a vacuum distillation. Into the flask are introduced 84.3 g. (0.2 mole) of finely powdered tetrabromo-p-xylene and 200 ml. of concentrated sulfuric acid (95%). The reactants are thoroughly mixed by shaking. A vacuum is applied by means of a water pump, and a stream of air is allowed to pass through the capillary tube in order to facilitate the rapid removal of hydrogen bromide. The flask is heated in an oil bath to 70°, and, as the evolution of gas becomes less vigorous, the temperature of the bath is gradually raised to 110° (Note 3). The reaction is complete when a perfectly clear solution is obtained and no more gas is evolved (about 2.5 hours). The flask is then cooled and the contents are poured on 600 g. of crushed ice. The crystalline solid is collected on a filter, washed with a little water, and recrystallized from 600 ml. of 10% methanol with the aid of 1 g. of decolorizing carbon to remove the yellow color. The small amount of tetrabromoxylene which remains undissolved is separated with the carbon and washed on the filter with two 100-ml. portions of hot 10% methanol. The yield of pure product, m.p. 115–116°, is 21.7–22.5 g. (81–84%).
2. Notes
1.
It is important to have light shining on the reaction mixture throughout the bromination. The bromination may also be accomplished by placing the flask in direct sunlight.
2.
The
bromine is dried by shaking it with two
200-ml. portions of concentrated sulfuric acid.
3.
The mixture foams considerably and must be watched. The foaming can be controlled by raising the temperature slowly and regulating the vacuum. For this reason it is difficult to hydrolyze larger amounts of the tetrabromide.
3. Discussion
Terephthalaldehyde has been made by the action of
lead nitrate on
α,α'-dichloro-p-xylene1 or
α,α'-dibromo-p-xylene;
2 by the action of fuming
nitric acid on
dibromo-p-xylene;
3 by the hydrolysis of
terephthaldehyde tetraacetate;
4 by the action of
phosphorus pentachloride on
p-xylyleneglycol monoethyl ether;
5 by the hydrolysis of
α,α,α',α'-tetrachloro-p-xylene;
6 by the hydrolysis of
α,α,α',α'-tetrabromo-p-xylene;
7 and by the Sommelet procedure.
8 The method described here is essentially the modification described by Weissberger and Bach.
9
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
sulfuric acid (7664-93-9)
methanol (67-56-1)
phosphorus pentachloride (10026-13-8)
chloroform (67-66-3)
nitric acid (7697-37-2)
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
decolorizing carbon,
carbon (7782-42-5)
lead nitrate (10099-74-8)
xylene,
p-xylene (106-42-3)
Terephthalaldehyde (623-27-8)
α,α,α',α'-Tetrabromo-p-xylene,
a,a,a',a'-Tetrabromo-p-xylene (1592-31-0)
terephthaldehyde tetraacetate
p-xylyleneglycol monoethyl ether
α,α'-dichloro-p-xylene (623-25-6)
dibromo-p-xylene,
α,α'-dibromo-p-xylene
α,α,α',α'-tetrachloro-p-xylene
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