ON THE INTERACTION OF OLEFIN OXIDES WITH AROMATIC COMPOUNDS

V. A. Levin, B. V. Tronov, V. P. Lopatinskii, E. E. Sirotkina

(Presented by the scientific-methodological seminar of organic departments and problem laboratories)

β-Phenylethyl alcohol and its homologues are known as important constituents of essential oils—for example, rose oil—and have long found broad application in perfumery [1]. In recent years the range of application of these compounds has expanded still further, since their physiological action has been discovered, as well as the possibility of using them as surface-active substances. The usual methods for their preparation are the multistage Grignard synthesis [2] from phenols and dibromoethane, and Shorygin’s synthesis [3] from phenylmagnesium bromides and olefin oxides. A more promising approach is the preparation of phenylalkanols by the condensation reaction of olefin oxides with various aromatic hydrocarbons and their derivatives.

A number of papers and patents [4–10] describe methods for the synthesis of β-phenylethanol using the Friedel–Crafts reaction in the presence of aluminum chloride, as well as several other catalysts. In them it is recommended to use the catalyst in an amount of from one to three moles per mole of ethylene oxide, and also to dilute the oxide with an inert gas and to remove the product and hydrogen chloride from the reaction mixture by purging with nitrogen or air.

In the work of Cologne and Roesch [11] it was found that, in the reaction of ethylene oxide with aromatic compounds, aluminum chloride is the best catalyst; ferric chloride and zinc chloride are less active, while on stannic chloride ethylene oxide is converted mainly into ethylene chlorohydrin. Later, N. Shorygina [12] obtained similar yields (40–45%) of arylethanols, while V. Likhterov and V. Etlis [13] achieved yields of arylpropanols of up to 40% in the condensation of propylene oxide with aromatic compounds in the presence of aluminum chloride. In the present work the action of ethylene oxide and propylene oxide on a series of aromatic compounds (benzene, m-xylene, anisole, 9-ethylcarbazole) was studied in the presence both of aluminum chloride and of other Lewis acids—antimony pentachloride, titanium tetrachloride, and stannic chloride. The reaction conditions were worked out on benzene and then on other aromatic reagents. It was established that, among the catalysts tested, aluminum chloride and titanium tetrachloride are the least active. Antimony pentachloride caused mainly chlorination of benzene and polymerization of ethylene oxide. The best results were obtained using stannic chloride. It was established that, in this case, no appreciable amounts of...

the amount of by-products, for example diphenylethane, which is usually inevitable in the presence of aluminum chloride. Oxypropylation of benzene in the presence of SnCl₄ proved especially effective. In studying the influence of conditions on this process it was found that a stable yield of 1-phenylpropan-2-ol reaches 40–44% and changes little in the temperature range from 5 to 40°C. However, owing to the exothermic nature of the process, it is more advantageous to maintain the temperature in the range 10–15°C, so that there is no significant overheating of the reaction mass. The amount of catalyst should be equimolar relative to the amount of propylene oxide. Holding the reaction mass after completion of the reaction for 18 hours slightly increases the yield of phenylpropanol. Purging the reaction mass with nitrogen or air is not necessary. The results of some experiments are given in Table 1. It should be noted that the results of oxyethylation

Table 1

Results of experiments on the synthesis of arylalkanols in the presence of tin chloride

of m-xylene and anisole are preliminary and will be refined. An attempt to carry out direct oxyethylation of 9-ethylcarbazole in the presence of SnCl₄ was unsuccessful, while in the presence of aluminum chloride a noticeable amount of a crystalline reaction product with m.p. 97°C (m.p. of the picrate 195°C) was isolated, probably 3,3′-di(9-ethyl)carbazylethane.

Experimental Part

Phenylethanol

Into a three-necked flask equipped with a thermometer, a dropping funnel, and a tube connected to a water-jet pump, a homogeneous mixture consisting of 40 ml of SnCl₄ and 100 ml of benzene is introduced. The flask is placed in a bath with a cooling mixture and shaken continuously and vigorously (a mechanical stirrer may be used).

With the water-jet pump operating, a solution of 22 ml of ethylene oxide in 100 ml ...

benzene. The rate of addition is regulated so that the temperature of the reaction mixture remains within 2–5°C.

After completion of the reaction, the product is poured into 150 ml of water; the hydrocarbon layer is separated, washed twice with water, and dried over potash. After distilling off the benzene, the reaction product is distilled.

At 215–218°C, 23% of phenylethanol was isolated—a colorless oily liquid with \(n_D^{17}\) 1.5320 (lit. \(n_D^{17}\) 1.5337 [14]) and a pleasant odor.

Analyses. Found, %: C 78.45; H 8.60. \(\mathrm{C_8H_{10}O}\)
Calculated, %: C 78.70; H 8.20.

1-Phenylpropanol-2.
By the above procedure, from 34 ml of tin chloride in 200 ml of benzene and 10 ml of propylene oxide in 200 ml of benzene, at 10–14°C, there was obtained at 219–223°C 8.8 ml of 1-phenylpropanol-2 (44% of theory, calculated on the reacted propylene oxide), in the form of a viscous oily liquid with \(n_D^{20}\) 1.5230 (lit. \(n_D^{20}\) 1.5210 [13]) and a characteristic odor.

Analyses. Found, %: C 79.78; H 8.95. \(\mathrm{C_9H_{12}O}\).
Calculated, %: C 79.41; H 8.82.

Conclusions

1. The interaction of benzene and certain other aromatic compounds with ethylene and propylene oxides in the presence of aluminum, titanium, antimony, and tin chlorides has been investigated.

2. A high catalytic activity of tin chloride in the reaction of propylene oxide with benzene has been established.

3. The optimal conditions for the oxypropylation reaction of benzene have been determined, under which a yield of 1-phenylpropanol-2 of 40–44% is achieved.

References

1. E. Grimal. C. r., 144, 434, 1907.
2. A. Wohl, E. Betthold, Ber., 43, 2184, 1910.
3. P. P. Shorygin. Synthesis of Fragrant Substances. Pishchepromizdat, 1939.
4. A. Schaarschmidt, Z. Hermann, Ber., 58, 1914, 1925.
5. R. Smith, S. Natelson, J. Am. Chem. Soc., 53, 3476, 1931.
6. Z. Valik, I. Valik. Engl. pat. 398136 (1933); C. A. 28, 1047, 1934.
7. Klipstein. Can. pat. 340555 (1934); C. A. 28, 4067, 1934.
8. M. Carpenter. U.S. pat. 2013710 (1935); C. A. 29, 6901, 1935.
9. H. Davis. U.S. pat. 2125490 (1938); C. A. 32, 7477, 1938.
10. W. Kalkotta, I. Tinner, J. Am. Chem. Soc., 61, 1010, 1939.
11. J. Colonge, P. Rochas, Bull. Ch. Soc. Fr., 818, 1949.
12. N. V. Shorygina. ZhOKh, 21, 1273, 1951.
13. V. R. Likhterov, V. S. Etlis. ZhOKh, 27, 2867, 1957.
14. Brief Handbook of Chemistry, GKhI, 196, 1954.