Methylenation of catechol
J. Org. Chem. 16, 1739 (1951)
The most satisfactory results were obtained by the following procedure: A solution of 0.1 mole of catechol in 15 ml. of methanol was placed in a thick-walled Pyrex bomb tube, together with 3 g. of Tobin bronze shavings (Cu 6O%, Zn 38%, Sn 1.5%, Fe 0.2%, Pb 0.3%) and 10.2 g. (0.12 mole) of methylene chloride or the equivalent amount of the bromide. Methanol (40 ml.) was then added in such fashion that the minimum amount of mixing occurred. The bomb was clamped vertically in an ice-bath and a cold solution of 11.0 g (0.2 mole) of potassium hydroxide in 15 ml. of water was added quickly, so that very little mixing occurred. The bomb tube was now about 90% full; it was sealed immediately and heated in a shaking furnace for 18 hours at 105-115°C. The product was isolated by steam-distillation and purified by distillation under reduced pressure. The methylenedioxybenzene obtained had bp 172-175°C/755 mmHg. Numerous modifications of this method were tried. It was found that unless the bomb tube was carefully charged as described above, and unless it was at least 90% full before sealing, the yields of product mere lower, and more oxidative deconiposition occurred. It was also found that use of less than the stoichiometric aniount of potassium hydroxide (0.2 mole) led to lower yields in contrast t o the report of Rao (2). Methylene sulfate gave very poor results by this method; methylene iodide gave the highest yields, but since the pressure in the bomb tubes was much higher when the iodide was used, more of the tubes broke during the heating period, and so this reagent was not used in subsequent work. Methylene chloride and methylene bromide gave comparable results. Some of the results are given in Table I.
Attempts to repeat the procedure of Rao and Seshardi (2) were unsuccessful. This method involves treating the ortho-dihydroxybenzene with methylene sulfate in acetone-potassium hydroxide solution at atmospheric pressure, in a stream of illuminating gas, at 60°C for several hours. Despite many attempts, no appreciable amount of methylenedioxybenzene could be obtained, and extensive oxidation occurred with the formation of large amounts of tarry by-products.
Attempts to use methylene sulfate under pressure in acetone solution were abandoned because of the highly exothermic reaction which frequently led to destruction of the bomb tube.
(2) Rao and Seshardri, Proc. Indian Acad. Sci., 23A, 147 (1946)