A New Method for the Preparation of m-Iodobenzoic Acid
Abstract Generated abstract
A method is described for preparing m-iodobenzoic acid by direct iodination of benzoic acid with elemental iodine in the presence of ozone. The study examines how ozone concentration, temperature, solvent amount, gas flow rate, iodine addition, reaction time, and acid additive affect product yield, and compares sulfuric and phosphoric acids as activators. The optimized procedure uses acetic acid, a small amount of concentrated sulfuric acid, ozonized air or oxygen, and portionwise iodine addition at about 85 to 90°C, giving m-iodobenzoic acid in approximately 70 to 75% yield. Phosphoric acid showed no activating effect under the tested conditions.
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PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR
POLYTECHNIC INSTITUTE
Vol. 163 1970
A NEW METHOD FOR OBTAINING m-IODOBENZOIC ACID
A. N. NOVIKOV, T. A. KHALIMOVA
(Presented by the scientific seminar of the departments of the organic profile)
Iodobenzoic acid was described long ago. The methods proposed for its preparation, based on replacing the diazonium group by iodine, and the use of phthalimide, are inconvenient because of the multistage nature of the processes. Direct introduction of iodine into benzoic acid in the presence of fuming nitric acid (1) or fuming nitric acid saturated with sulfuric anhydride (2), owing to side reactions of oxidation and nitration, gives a low yield of m-iodobenzoic acid. The use of sulfuric acid and silver sulfate is uneconomical (3), while the use of a nitrating mixture (4) complicates purification of the acetic-acid solvent. More convenient proved to be the method we proposed for obtaining m-iodobenzoic acid, based on the reaction of direct iodination of benzoic acid in the presence of ozone. In developing this method we determined the effect on the yield of m-iodobenzoic acid of the percentage content of ozone in oxygen or in air, the process temperature, the amount of solvent, the rate of passage of ozonized air through the reaction mixture, the method of charging iodine, and the amount of sulfuric acid, and compared the activating properties of sulfuric ($d$ 1.84) and phosphoric acids.
The results of the studies carried out are presented in Tables 1, 2, 3, and 4.
Table 1
Effect of the amount of sulfuric acid on the yield of m-iodobenzoic acid.
Iodine 2.1 g, ozone concentration in oxygen 0.8%
| Sulfuric acid, ml | Moles of sulfuric acid per mole of benzoic acid | Yield of m-iodobenzoic acid, % |
|---|---|---|
| 50.0 | 57.2 | 40.5 |
| 10.0 | 11.4 | 40.5 |
| 5.0 | 5.7 | 40.5 |
| 1.0 | 1.14 | 40.5 |
| 0.5 | 0.57 | 39.3 |
| 0.25 | 0.28 | 38.1 |
| 0.10 | 0.114 | 30.9 |
| 0.05 | 0.057 | 10.7 |
Table 2
Influence on the yield of m-iodobenzoic acid: percentage content of ozone in air, reaction temperature, amount of solvent, reaction time, and flow rate of ozonized air. In experiment 17 iodine 1.0 g
| No. of experiments | Ozone in air, % | Air flow rate, l/hour | Reaction temperature, °C | Synthesis time, hour | Acetic acid, ml | Yield of iodobenzoic acid, % |
|---|---|---|---|---|---|---|
| 1 | 0.42 | 13 | 90 | 1.3 | 20 | 44 |
| 2 | 0.38 | 13 | 90 | 1.3 | 20 | 44 |
| 3 | 0.30 | 13 | 90 | 1.3 | 20 | 42 |
| 4 | 0.20 | 13 | 90 | 1.3 | 20 | 29 |
| 5 | 0.38 | 13 | 90 | 1.3 | 20 | 44 |
| 6 | 0.38 | 13 | 80 | 1.3 | 20 | 51 |
| 7 | 0.38 | 13 | 70 | 1.3 | 20 | 17 |
| 8 | 0.38 | 13 | 90 | 1.3 | 10 | 48 |
| 9 | 0.38 | 13 | 90 | 1.3 | 20 | 44 |
| 10 | 0.38 | 13 | 90 | 1.3 | 30 | 44 |
| 11 | 0.38 | 13 | 90 | 1.3 | 40 | 24 |
| 12 | 0.30 | 13 | 90 | 1.3 | 20 | 43 |
| 13 | 0.30 | 13 | 90 | 2.0 | 20 | 55 |
| 14 | 0.30 | 13 | 90 | 2.5 | 20 | 48 |
| 15 | 0.38 | 13 | 90 | 2.0 | 10 | 55 |
| 16 | 0.38 | 7.8 | 90 | 2.0 | 10 | 65 |
| 17 | 0.38 | 5.2 | 90 | 2.0 | 10 | 72 |
Table 3
Influence of the iodine charge on the yield of iodobenzoic acid. Flow rate of ozonized air with an ozone concentration of 0.38%, 5.2 l/hour
| Synthesis time | Amount of iodine, g | Amount of iodine, moles | Portions of iodine when charged, g | Molar ratio benzoic acid : iodine | Yield of iodobenzoic acid, g | Yield of iodobenzoic acid, % |
|---|---|---|---|---|---|---|
| 2 hr. 50 min. | 2.15 | 0.0082 | 2.15 | 1:0.5 | 1.8 | 44 |
| 2 hr. 50 min. | 2.15 | 0.0082 | 0.5; 0.5; 0.55; 0.60 | 1:0.5 | 2.1 | 50 |
| 2 hr. 30 min. | 1.50 | 0.0069 | 0.5; 0.5; 0.5 | 1:0.42 | 2.1 | 72 |
| 2 hr. | 1.00 | 0.0039 | 0.5; 0.5 | 1:0.21 | 1.4 | 72 |
Table 4
Comparison of the activating properties of sulfuric and phosphoric acids
| Oxidant | Acid | Yield of iodobenzoic acid, % |
|---|---|---|
| Ozonized oxygen with an ozone concentration of 0.8% | Without acid | Benzoic acid is not iodinated |
| —,— | Phosphoric acid | Benzoic acid is not iodinated |
| —,— | Sulfuric acid | 40.5 |
Experimental Part
Synthesis of m-iodobenzoic acid. Into a three-necked round-bottom flask equipped with a reflux condenser and a tube for introducing ozonized oxygen or air were placed 2.0 g of benzoic acid, 10.0 ml of glacial acetic acid, 1.0 ml of concentrated sulfuric acid (d 1.84), 0.5 g of iodine, and 2.0 ml of carbon tetrachloride. At a glycerol-bath temperature of 85–90°C, ozonized oxygen or air, obtained in an ordinary laboratory ozonizer, was passed through the mixture at a rate of 5.2 l/hr. The remaining amount of iodine (1.0 g) was added periodically in 0.5-g portions as the coloration of the reaction mass characteristic of free iodine disappeared. After 2.0–2.5 hr the synthesis was stopped. The reaction mass was diluted with water; the m-iodobenzoic acid was filtered off and crystallized from aqueous alcohol. The yield of m-iodobenzoic acid was 70–75%; melting point 186°C.
Conclusions
- Benzoic acid is readily iodinated by elemental iodine in the presence of ozone with a small addition of sulfuric acid.
- Under the optimum reaction conditions, the yield of m-iodobenzoic acid is 72%.
- Phosphoric acid does not possess activating properties in this reaction.
LITERATURE
- A. P. Kreshkov, I. N. Kurbatov. Laboratory Work on the Synthesis and Analysis of Organic Compounds. Goskhimizdat, Moscow, p. 109, (1940).
- P. Varma, A. Panicker. Ch. A., 24, 5740 (1930).
- D. Derbyshire, W. Waters. J. Chem. Soc., 1950, 3694.
- B. V. Tronov, A. N. Novikov. ZhOKh, XXIII, 1022–1024, (1953).