On the Interaction of Olefin Oxides with Aromatic Compounds

V. A. Levin, V. P. Lopatinskii

(Presented by the Scientific-Methodological Seminar of the organic departments and problem laboratories)

In a previous communication (1) we showed the effectiveness of anhydrous tin chloride as a catalyst for the oxyethylation and oxypropylation of benzene.

In the present work we investigated the reaction of ethylene oxide, and especially propylene oxide, with certain homologs and substituted benzenes (toluene, xylenes, mesitylene, chlorobenzene, and anisole) in the presence of \(\mathrm{SnCl}_4\).

With the exception of chlorobenzene and anisole, all the benzene homologs tested in oxypropylation gave reaction-product yields equal to 40–49% of theoretical. Lower yields of reaction products were obtained in the oxypropylation of anisole (30–36%) and chlorobenzene (10%).

In searching for the optimal synthesis conditions, the following reaction parameters were varied: temperature from \(-25^\circ\) to \(100^\circ\mathrm{C}\), the amount of catalyst from 1 to 3 moles per mole of propylene oxide, and the ratio between the aromatic reagent and propylene oxide. The aromatic reagents were dried with sodium, and the propylene oxide with calcium hydride. The action of several proton acceptors (dimethylaniline, diethylamine, and diethyl ether) was tested. The results of the experiments are summarized in a table, in which \(o\)-xylene was chosen as the model when varying the reaction parameters.

The experimental results showed that in the temperature range from \(-10\) to \(60^\circ\mathrm{C}\) the yield of the reaction product changes little, and almost no side reactions, such as isomerization or transalkylation, are observed. At temperatures below \(-10^\circ\mathrm{C}\) a decrease in yield is noticeable, while at \(100^\circ\mathrm{C}\) arylpropanols are formed in such quantities that it is practically impossible to isolate them. In contrast to experiments with benzene, where increasing the amount of \(\mathrm{SnCl}_4\) to more than one mole per mole of olefin oxide does not affect the yield of the reaction product, in experiments with \(o\)-xylene such an increase in yield is observed when \(\mathrm{SnCl}_4\) is increased from 1 to 3 moles per mole of propylene oxide. It was established that, in the case of benzene homologs as well, the optimal ratio is 10–15 moles of aromatic reagent to 1 mole of propylene oxide. In experiments using proton acceptors it was established that, in their presence, the yield of arylpropanols decreases. Analyses of the crude products of all experiments showed the presence in them of small amounts of aliphatically bound

chlorine, which was readily hydrolyzed by a 0.5% solution of caustic soda on boiling. This indicates the side formation of arylchloropropanes, which, during distillation of the product, undergo thermal dehydrochlorination and lead to the formation of unsaturated propenyl derivatives. A more detailed elucidation of the mechanism of formation of styrene homologs will be carried out in a subsequent study.

The experimental procedure was described in the preceding communication (1).

Table

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

Notes. 1. In experiment 55, 1 mole of diethylamine is added; in experiment 56, dimethylaniline is added; and in experiment 57, diethyl ether is added.
2. In experiments 35, 62, and 36, 150 ml of chlorobenzene was added as solvent.

Conclusions

1. The interaction of several homologs and substituted benzenes with propylene oxide in the presence of stannic chloride has been investigated.

2. The optimum conditions for the oxypropylation of benzene homologs have been established, under which yields of arylpropanols amounting to 40–49% of theory are achieved.

Literature

1. V. A. Levin, B. V. Tronov, V. P. Lopatinskii, E. E. Sirotkina. Izv. TPI (the present collection).