Comparison of methods for the preparation of dioxychonolylmethane
Abstract Generated abstract
This study compares sulfuric acid and hydrochloric acid condensation methods for preparing 5,5′-bis-8-hydroxyquinolylmethane, a compound relevant to polymeric and biologically active materials, in light of conflicting reported melting points. The authors vary reaction temperature and heating time, examine yields after recrystallization, and compare purified products by melting point, nitrogen analysis, and X-ray diffraction. The sulfuric acid method gives its best yield near 0°C but produces material requiring repeated recrystallization, apparently because of isomeric impurity, whereas the hydrochloric acid method reaches maximum yield after about 90 minutes of reflux and affords material melting at 279 to 280°C after recrystallization. The results indicate that preparation in hydrochloric acid medium is preferable.
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COMPARISON OF METHODS FOR THE PREPARATION OF DIOXYCHINOLYLMETHANE
L. I. ARISTOV, R. T. CHUPRINA, V. N. LINKO
(Presented by the scientific-methodological seminar of the Chemical-Technological Faculty)
Dioxychinolylmethane is of interest as a starting material for the synthesis of polymeric products and biologically active compounds; however, the literature contains contradictory indications concerning the melting point of this substance. Thus, H. Schuller, who obtained this compound by sulfuric-acid condensation, gives a m.p. of 246°C [1]. With this melting point it was used by V. V. Korshak and co-workers for the synthesis of polychelate compounds [2]. Burkhalter, who obtained this substance by condensation of 8-oxyquinoline with formaldehyde in hydrochloric acid medium, gives a melting point of 280°C for dioxychinolylmethane [3].
We have studied in more detail the conditions for obtaining dioxychinolylmethane both by Schuller’s method and by Burkhalter’s method, and have determined the factors affecting the yield of this product.
Table 1
Sulfuric-acid method (according to Schuller)
| No. | 8-oxyquinoline taken, g | 40% formaldehyde taken, ml | Reaction temperature, °C | Yield after first recrystallization, % | Melting point after first recrystallization, °C | Melting point after fourth recrystallization, °C |
|---|---|---|---|---|---|---|
| 1 | 10 | 44 | −10 | 63.9 | 244–246 | 276 |
| 2 | " | " | −5 | 64.5 | " | " |
| 3 | " | " | 0 | 72.5 | " | " |
| 4 | " | " | +5 | 68.4 | " | " |
| 5 | " | " | +15 | 62.5 | " | " |
| 6 | " | " | 0 | 73.7 | " | " |
As is evident from the experiment, in obtaining dioxychinolylmethane in concentrated sulfuric acid medium, the best yields (72%) are obtained at a temperature of 0°C. With an increase, as well as with a decrease ...
temperatures, the yields of the product decrease. However, the quality of the dioxyquinolylmethane obtained in all experiments was low, judging from the increase in melting point after each recrystallization.
Table 2
Hydrochloric-acid method (according to Burkhalter)
| No. | 8-Hydroxyquinoline taken, g | 40% formaldehyde taken, ml | Reaction temperature, °C | Reaction time, min | Yield, % after one recrystallization | Melting point, °C |
|---|---|---|---|---|---|---|
| 1 | 5 | 1.5 | boiling of the reaction mixture | 60 | 51.6 | 272—274 |
| 2 | ” | ” | ” | 90 | 70.3 | 272—274 |
| 3 | ” | ” | ” | 120 | 70.3 | 272—274 |
| 4 | ” | ” | ” | 150 | 62.5 | 272—274 |
Only after four recrystallizations from dimethylformamide was it possible to raise the melting point of dioxyquinolylmethane to 276°C. It should be noted that the elemental analyses for nitrogen of the products with m.p. 246 and 276°C coincided. Found, %: N — 9.51, 9.32; calculated, %: N — 9.24.
In the preparation of dioxyquinolylmethane in hydrochloric acid medium, the yield of the product depends on the duration of heating. Heating the reaction mixture for 1.5 h is already sufficient to obtain the maximum yield of product. After a second recrystallization from dimethylformamide, the product obtained had a melting point of 279—280°C. The X-ray diffraction patterns of the pure substances (with m.p. 276 and 280°C) obtained by both methods were identical. The lower melting point of the dioxyquinolylmethane obtained in concentrated sulfuric acid medium can apparently be explained by a larger admixture of the isomer—7,7′-bis-8-hydroxyquinolylmethane—from which, probably, it is freed only by repeated recrystallization.
On the basis of the experiments carried out, it may be concluded that preparation of dioxyquinolylmethane in hydrochloric acid medium is preferable.
Experimental Part
Dioxyquinolylmethane (hydrochloric-acid method). To 30 g of 8-hydroxyquinoline (0.2 M), placed in a 0.5-l flask, are added 9 ml of a 40% formaldehyde solution (0.108 M) and 105 ml of concentrated hydrochloric acid. The contents of the flask are connected to a reflux condenser and heated on an air bath at a gentle boiling of the solution for 90 min. The reaction mixture is left for a day to allow the precipitate to mature. The yellow-green precipitate formed is filtered off and transferred to a beaker, where it is dissolved with gentle heating in 500 ml of distilled water. The solution is neutralized with caustic soda to a neutral reaction according to universal indicator. The precipitated solid is filtered off, washed with water, and dried. After three recrystallizations from dimethylformamide, 19.3 g (62%) of a substance with a melting point of 279—280° (on the block) is obtained.
Conclusions
The conditions for preparing 5,5′-bis-8-hydroxyquinolylmethane in sulfuric and hydrochloric acid media were investigated. The advantages of obtaining the substance in hydrochloric acid are shown.
References
- H. Schuller, I prakt Chemie [2], 88, 180, 1913.
- V. V. Korshak, S. V. Vinogradova, V. S. Artemova, T. M. Babchinitsher. Vysokomolekulyarnye soedineniya, 2, 974, 1960.
- J. N. Burckhalter, R. I. Leib, J. org. Chem. 26, 4078, 1961.