Here pyrogallol reacts with Acetic Anhydride in presence of Zinc Chloride (Lewis Acid) and acetic acid as a solvent.
Pyrogallol:
- IUPAC Name: benzene-1,2,3-triol
- Chemical Formula: C6H6O3
- Exact Mass: 126.03
- Molecular Weight: 126.11
- m/z: 126.03 (100.0%), 127.04 (6.7%)
- Elemental Analysis: C, 57.14; H, 4.80; O, 38.06
- Boiling Point: 309°C
- Melting Point: 131-134 °C
- Critical Temp: 792.92 [K]
- Critical Pres: 99.8 [Bar]
- Critical Vol: 311.5 [cm3/mol]
- Gibbs Energy: -342.18 [kJ/mol]
- Log P: 0.87
- MR: 30.72 [cm3/mol]
- Henry’s Law: 12.61
- Heat of Form: -451.1 [kJ/mol]
- tPSA: 60.69
- CLogP: 0.211
- CMR: 3.1479
Gallacetophenone:
- IUPAC Name: 1-(2,3,4-trihydroxyphenyl)ethanone
- Chemical Formula: C8H8O4
- Exact Mass: 168.04
- Molecular Weight: 168.15
- m/z: 168.04 (100.0%), 169.05 (8.9%), 170.05 (1.2%)
- Elemental Analysis: C, 57.14; H, 4.80; O, 38.06
- Boiling Point: 705.05 [K] (Calc)
- Melting Point: 171-172 °C
- Critical Temp: 828.83 [K]
- Critical Pres: 76.28 [Bar]
- Critical Vol: 429.5 [cm3/mol]
- Gibbs Energy: -463.89 [kJ/mol]
- Log P: 0.18
- MR: 41.97 [cm3/mol]
- Henry’s Law: 15.35
- Heat of Form: -616.43 [kJ/mol]
- tPSA: 77.76
- CLogP: 0.861434
- CMR: 4.1112
Synthetic Procedure:
In a 250-cc. round-bottomed flask, fitted with a reflux condenser, 28 g. (0.21 mole) of freshly fused zinc chloride is dissolved in 38 cc. of glacial acetic acid by heating in an oil bath at 135–140°. Try to make sure that the quality of Zinc Chloride used is good. It is always preferred to freshly fused Zinc Chloride. The temperature of the solution remains close to about 132 °C. Once the temprature reaches this point, forty grams (0.37 mole) of 95 per cent acetic anhydride is then added to the clear, pale brown liquid, followed by the addition in one lot of 50 g. (0.4 mole) of distilled pyrogallol. The addition should be done only after about 30 minutes of free stirring of pale brown liquid. The mixture is heated at 140–145° (Note 3) for forty-five minutes with frequent and vigorous shaking. Once again, due to the acetic acid synthesized in the reaciton, the temprature of the flask should not exceed 138 °C. You can try to maintain the bath temperature at 150°. The unused acetic anhydride and acetic acid are removed by distilling under reduced pressure. The temperature should NOT exceed 150 °C. The red-brown cake is broken up by the addition of 300 cc. of water with mechanical stirring for a few minutes. The mixture is cooled in ice water, filtered with suction, and washed with cold water. The crude material, 45–50 g., is crystallized from 500 cc. of boiling water saturated with sulfur dioxide. The yield of straw-colored needles melting at 171–172° is 36–38 g. (54–57 per cent of the theoretical amount). On saturating the mother liquor with salt and cooling to 10°, 4–5 g. of crude material is obtained, which on recrystallization yields 3–4 g. of pure material.
The method described above is a modification of the process of Nencki and Sieber. Gallacetophenone has also been prepared by treating pyrogallol with acetyl chloride, and from 2-formyl-4-acetylresorcinol by treatment with hydrogen peroxide and alkali.
Related References:
- Witt and Braun, Ber. 47, 3227 (1914).
- Cheema and Venkataraman, J. Chem. Soc. 1932, 919.
- Nencki and Sieber, J. prakt. Chem. (2) 23, 151, 538 (1881);
- Nencki, Ber. 27 2737 (1894).
- Crabtree and Robinson, J. Chem. Soc. 121, 1038 (1922).
- Einhorn and Hollandt, Ann. 301, 107 (1898);
- Fischer, Ber. 42, 1020 (1909).
- Nakazawa, J. Pharm. Soc. Japan 59, 297 (1939) [C. A. 33, 8186 (1939)].
