Preparation of 5-Bromo-8-Hydroxyquinoline
Abstract Generated abstract
This paper addresses the preparation of 5-bromo-8-hydroxyquinoline for use in syntheses of polychelate polymers, noting limitations of a previously reported acetic acid method. The authors examine bromination of 8-hydroxyquinoline in sulfuric acid, varying reaction temperature and acid concentration, and compare the resulting yields of mono- and dibromo derivatives. The study finds that concentrated sulfuric acid at about 0 to 5°C gives the best yield of the monobromo compound, approximately 55 to 57%, while higher temperatures or lower acid concentrations reduce this yield and increase formation of 5,7-dibromo-8-hydroxyquinoline. An experimental procedure is provided for isolating 5-bromo-8-hydroxyquinoline with a reported melting point of 124°C.
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PREPARATION OF 5-BROMO-8-HYDROXYQUINOLINE
L. I. ARISTOV, T. I. KOSTINA
(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)
To carry out a number of syntheses in the series of polychelate polymers, we required 5-bromo-8-hydroxyquinoline.
The literature describes the synthesis of 5-bromo-8-hydroxyquinoline in acetic acid medium [1]. Carrying out this synthesis under laboratory conditions requires a tenfold amount by weight of acetic acid, and the yields of the 5-bromo derivative are insignificant.
In 1962 A. F. Sukhina showed that, upon chlorination of 8-hydroxyquinoline in sulfuric acid, 5-chloro-8-hydroxyquinoline is obtained in good yield [2]. Bromination of 8-hydroxyquinoline under these same conditions, as our experiments have shown, also proceeds with better yields than in acetic acid medium. Experimental data on the bromination of 8-hydroxyquinoline in sulfuric acid medium are given below.
Table 1
| No. of experiments | 8-Hydroxyquinoline, g/mole | Bromine, ml/mole | Reaction temperature, °C | Sulfuric acid concentration, % | Yield, % of monobromo derivative |
|---|---|---|---|---|---|
| 1 | 10,0/0,069 | 3,6/0,069 | −17 | 94 | 42,8 |
| 2 | ” | ” | −0 | 94 | 52,6 |
| 3 | ” | ” | −5 | 94 | 55,2 |
| 4 | ” | ” | 0 | 94 | 57,9 |
| 5 | ” | ” | +10 | 94 | 32 |
| 6 | ” | ” | −5 | 70 | 16,3 |
| 7 | ” | ” | −5 | 57 | 16,3 |
As can be seen from the experiment, the yield of the monobromo derivative is affected by the reaction temperature and by the concentration of the acid taken.
The best yields of the monobromo derivative (57–55%) are obtained at a reaction-medium temperature of 0–5°C.
With an increase in temperature, as well as with a decrease in the concentration of sulfuric acid, the yield of the monobromo derivative decreases, while the yield of the dibromo derivative increases.
Experimental Part
10 g of 8-hydroxyquinoline is dissolved in 25 ml of sulfuric acid \((d = 1.84)\) in a porcelain beaker; the reaction mixture is cooled to \(-5^\circ\mathrm{C}\), and, with mechanical stirring, 3.6 ml of bromine is added from a dropping funnel at such a rate that the temperature of the reaction mixture does not exceed \(0^\circ\mathrm{C}\). After all the bromine has been added, the contents are stirred for another 10 minutes and poured onto ice (100 g). The sulfate salts of mono- and dibromo-8-hydroxyquinoline precipitate. Upon addition of 100 ml of water, the solution is filtered from the poorly soluble salt of 5,7-dibromo-8-hydroxyquinoline. The filtrate is neutralized with ammonia; the precipitate that forms is filtered off, washed with water, dried, and recrystallized from ethyl alcohol. Yield 55% of theory, m.p. \(124^\circ\mathrm{C}\).
From the insoluble salt of the dibromo derivative, after conversion to the base and recrystallization from benzene, 5,7-dibromo-8-hydroxyquinoline is obtained in 10–15% yield, m.p. \(196^\circ\mathrm{C}\).
Conclusions
Upon bromination of 8-hydroxyquinoline in concentrated sulfuric acid medium, 5-bromo-8-hydroxyquinoline is obtained in 57% yield.
REFERENCES
- Rosenmund, Doring, Arch. Pharm., 277, 266, (1928).
- A. F. Sukhina, ZhOKh, XXXII, 1356, 1962.