DE525836C - Process for the preparation of unsaturated ethers - Google Patents

Description

Process for the preparation of unsaturated ethers It is known that by passing acetals in gaseous form at a higher temperature over pottery shards can reach unsaturated ethers with elimination of alcohol; also finely divided Nickel has already been used. With such a procedure, however, certain by-products fall and the reactions cannot be made economical as a result.

It has now been found that acetals can advantageously be converted into unsaturated ones Ether can be converted if the noble metals of the i. or B. Group of the periodic table, i.e. silver, gold and the platinum metals, in finely divided form used alone or in a mixture with each other. The metals are expediently used on carriers; as such are the usual inert ones mineral, ceramic or metallic substances, as well as active gels such as clay gel, Silica gel, etc., active coals, charcoal, etc., called. Even under mild ones In this way, the elimination of alcohol is achieved without significant amounts of by-products. In certain cases it is advantageous to use the catalysts incorporate activating or stabilizing substances, e.g. B. finely divided metals, easily or difficultly reducible metal oxides or salts.

The fixation of the noble metals and the activating or stabilizing additives is done in a known manner, for. B. by soaking or spraying the mostly porous carrier materials with salt solutions and by subsequent thermal decomposition or reduction of these salts, also by applying precipitated or otherwise finely divided metals, metal oxides; Hydroxides, carbonates or salts with the help of binders such as water glass, dextrin solution, colloidal silica, etc., on the carrier materials, and also by the action of metal salt solutions on carrier materials with a precipitating effect, such as calcium carbonate, magnesia, etc.

The reaction can be carried out in particular with those acetals of aliphatic or aromatic aldehydes or ketones which can be evaporated without decomposition at ordinary or reduced pressure. The elimination of alcohol is generally endothermic and is expediently carried out at temperatures between 100 and 450.degree. The vaporized acetals can be used alone or in a mixture with inert gases or vapors. You can work under normal or reduced pressure. Example i 40 g of palladium asbestos (10%) are distributed evenly over a reaction space of 0.4 l. At a temperature of 270 ° C., the vapors of the diethyl acetal of acetaldehyde are sent over the catalyst at a rate of about 50 g per hour. : The vapors escaping from the Räktönsräum are continuously fractionated. Below 40 ° C., almost pure vinyl ethyl ether is obtained in good yield. The part of the reaction product boiling above 40 ° C. consists of alcohol and unchanged acetal; Since there are no contaminating by-products in this mixture, it can easily be used, for example, for the preparation of acetal.

Example 2 The vapors of acetaldehyde di-n-butyl acetal are, like given in example z, passed over palladium masbestos at 300 °. From the condensate wins vinyl n-butyl ether with a boiling point of 92 to 93 ° in a yield of about 75 0/0 of theory.

Example 3 40 g of 10% strength silver asbestos, produced with the aid of ammoniacal Silver carbonate solution; is distributed over a reaction space of 0.4 l. At a At a temperature of 28o ', the vapors of acetone diethyl acetal are sent over the catalyst at a rate of 4o to 6o g per hour. Gains from the condensate one by distillation the isopropenyl ether (a-methyl vinyl ethyl ether), which for the removal small amounts of alcohol are treated with metallic sodium; the one so cleaned Ether boils at 61 to 62 ° under 735 mm pressure and is produced in a yield of about 6o0 / 0 of theory.

Example 4 The vapors of propionaldehyde diethylacetal are, as indicated in Example 3, passed over silver asbestos at 280 °. The n-propenyl ethyl ether (β-methyl vinyl ethyl ether) is obtained from the condensate and boils in its pure state at 69 °. Yield about 75% of theory. EXAMPLE 5 A cold solution of 75 g of silver carbonate in aqueous ammonia is dried with 0.6 kg of diatomaceous earth with constant mixing to form a paste. The measure is now formed and heated to Zoo ° in the air stream. A reaction space of 0.4 l is filled with the catalyst prepared in this way. After a brief pretreatment of the catalyst with hydrogen at 250 °, the vapors of butyraldehyde dimethyl acetal are passed over the same at the same temperature at a rate of 60 g per hour. Most of the methyl alcohol split off is removed from the condensate with the aid of calcium chloride. The n-butenyl methyl ether (ß-ethyl vinyl methyl ether) is purified by distillation over sodium. The ether boils at 73 to 74 'under 749 mm of pressure. Yield: 75% of theory. EXAMPLE 6 O.45 kg of small pieces of pottery shards are moistened with an aqueous solution of = 5 g uranyl nitrate and dried. After prolonged heating to 400 ', the pottery shards pretreated in this way are soaked with a cold solution of 45 g of carbonate in aqueous ammonia. The vapors of acetophenone diethyl acetal mixed with nitrogen are passed over the dried catalyst which has been pretreated in a stream of hydrogen at 270 'at 220'. The a-ethoxystyrene (a-phenyl vinyl ethyl ether) with a boiling point of 93 to 96 ' at a pressure of 2.5 mm is obtained from the condensate by distillation. Yield: 850/0 of theory.

Example 7 The vapors of acetaldehyde di (2-ethoxyethyl) acetal (glycol monoethyl ether acetaldehyde acetal) are under the conditions mentioned in example z at 26o 'above platinum asbestos directed. From the condensate, which still contains 3o to 4o ° /, p unchanged acetal, wins the vinyl (2-ethoxy) ethyl ether (a-vinyl-ßäthyläthyläthyläther) with a Yield of about 60% of theory. The ether boils at 128 'under 757 mm of pressure.

Claims (1)

PAT9NTANSPRU.CH Process for the representation of unsaturated ethers from acetals, characterized in that the acetals are in gaseous form at increased Temperature passes over catalysts, which finely divided precious metals of z. or B. Group of the periodic table included.