Org. Synth. 1930, 10, 90
DOI: 10.15227/orgsyn.010.0090
PYROMELLITIC ACID
Submitted by E. Philippi and R. Thelen.
Checked by H. T. Clarke and S. Graff.
1. Procedure
In a 5-l. round-bottomed flask, set on a wire gauze in a hood and provided with a thermometer, are placed 100 g. of finely powdered pine or spruce charcoal (Note 1), 650 cc. of 82–88 per cent sulfuric acid (sp. gr. 1.76–1.80) (Note 2), and a small drop of mercury (Note 3). The mixture is heated with a small flame so that the temperature is raised to 250° during four hours. During another half hour the temperature is raised to 290°, when the acid begins to volatilize and the reaction mixture froths and expands greatly (Note 4). During the next hour the temperature is raised to 300°, and during the following hour to 315°. The mixture thickens somewhat, then much bubbling and spurting take place and fine white needles of pyromellitic anhydride begin to collect in the neck of the flask (Note 5). Fifty cubic centimeters of sulfuric acid is now added—the acid being poured in so as to rinse the walls of the flask; the syrupy reaction mixture is again heated to 250° for a few minutes and is transferred while still hot to a 1-l. tubulated retort (Note 6). The flask is rinsed with the minimum amount of water and the washings are added to the retort.
The material in the retort is heated with a free flame until the water present has distilled, then 30 g. of acid potassium sulfate is added and the distillation is continued. At first almost colorless sulfuric acid distils. As soon as crystals of pyromellitic anhydride appear, the receiver is replaced by one containing 50 cc. of water and the distillation is continued until nothing more passes over. The retort is then rinsed with 100 cc. of water and the rinsings are filtered and evaporated on the steam bath to 25 cc. (Note 7). The last distillate is also evaporated to 25 cc. On cooling, pyromellitic acid crystallizes. The product from both portions is collected on a suction funnel, using hardened filter paper, washed with two 10-cc. portions of ice water (Note 8), and recrystallized from four parts of boiling water. After drying at 105° the product (containing 2 moles of water of crystallization) melts at 271° (262° uncorr.). The yield is 6–8 g. (Note 9).
2. Notes
1.
The yield of
pyromellitic acid depends considerably on the kind of charcoal used. An experiment with ordinary willow charcoal gave none of the desired product.
2.
The specific gravity of the acid used should not vary from the limits indicated.
3.
A series of experiments has proved the helpful action of
mercuric sulfate.
4.
If the time for the first stage (temperature below 250°) is shortened, the frothing is greater at this point, and the final yield is lowered.
5.
The end of the reaction can be readily detected by the bubbling and spurting which take the place of the quiet boiling. If the mixture is not fairly thick, less
sulfuric acid should be used in the next run. If it is solid, more acid should be used.
6.
The transfer to the retort must be made before the mixture solidifies. The best method of closing the tubulure of the retort (unless this consists of
Pyrex glass) is by means of a
glass stopper too small for the hole and wrapped with asbestos paper moistened with
sodium silicate solution.
7.
If much
pyromellitic anhydride collects in the neck of the retort, it should be rinsed into a clean dish rather than into the receiver for the receiver contains considerable
sulfuric acid.
8.
In recovering
pyromellitic acid from the mother liquor it is advisable first to remove the
sulfuric acid by adding a slight excess of
barium hydroxide and acidifying to
Congo red with
hydrochloric acid.
9.
The anhydride of
pyromellitic acid may be obtained by boiling the dry anhydrous acid with
acetic anhydride.
3. Discussion
Pyromellitic acid may be obtained by the oxidation of benzene derivatives containing organic substituents in the 1-, 2-, 4-, and 5-positions: by the oxidation of
durene with
nitric acid;
1 by condensing
benzene with
diethylmalonyl chloride, reducing to the hydrocarbon, again condensing in the same way, and finally oxidizing the resulting
tetraethylbenzodihydrindenedione;
2 by an analogous synthesis from
m-xylene, involving condensation with
acetyl chloride, reduction, and oxidation;
3 and by the oxidation of
tetrahydro-5,6-benzindan-1-one.
4
Mellitic acid can be decarboxylated to yield
pyromellitic acid, either by the action of heat alone
5 or in the presence of
sulfuric acid.
6
The oxidation of wood charcoal by means of
sulfuric acid leads to
mellitic acid and its decarboxylation products;
7 nitric acid may also be employed.
8 Pyromellitic acid has also been obtained by the electrolytic oxidation of graphite in an alkaline medium.
9
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Congo red
tetraethylbenzodihydrindenedione
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
acetic anhydride (108-24-7)
acetyl chloride (75-36-5)
sodium silicate
nitric acid (7697-37-2)
mercury (7439-97-6)
barium hydroxide (17194-00-2)
mercuric sulfate (7783-35-9)
Durene (95-93-2)
Pyromellitic acid (89-05-4)
pyromellitic anhydride (89-32-7)
diethylmalonyl chloride (54505-72-5)
tetrahydro-5,6-benzindan-1-one
Mellitic acid (517-60-2)
m-xylene (108-38-3)
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