DE947474C - Process for the preparation of 1-methylcyclohexene (1) - Google Patents

Description

Process for the preparation of 1-methylcyclohexene (I) The invention relates to a catalytic process for the production of I-methylcyclohexene (I) by elimination of water from 1 -methylcyclohexanol- (2).

When r-methylcyclohexanol- (2) with the help of the usual dehydrating Medium, such as sulfuric acid or aluminum oxide, is heated, a mixture is obtained of the three isomeric methylcyclohexenes, which usually do not contain more than 500/0 r-methylcyclohexene (x) contains.

It has already been proposed to use cycloaliphatic alcohols to dehydrate them with acid activated earths at temperatures from 2590 and above, i.e. H. in the vapor state, heated to unsaturated cyclic Obtain hydrocarbons. When using this procedure on 1 -Methylcyclohexanol- (2) it has been found that this results in a yield of less than 30% of the desired I-methylcyclohexene- (I) gives and that at the same time considerable amounts of the other isomeric methylcyclohexenes arise.

It has now been found that excellent yields of I-methylcyclohexene (I) obtained when the elimination of water is carried out in the presence of an acid-activated bleaching earth performs in a liquid state.

To prevent the fuller's earth from becoming ineffective, it is advantageous to to remove the water formed during the reaction from the reaction mixture. this can be done in a simple manner by heating the mixture to such a temperature he- follow that the water and the I-methylcyclohexene (I) distill off and unreacted I-methylcyclohexanol- (2) and the fuller's earth as a residue stay behind. Suitable temperatures for the reaction are between 120 and 1500.

By adding fresh I-methylcyclohexanol- (2) as much as it is consumed, the method can be carried out continuously.

The amount of I-methylcyclohexene- (r) in the product depends in part on the ratio of cis to trans isomers in the I-methylcyclohexanol- (2). From pure trans-I-methylcyclohexanol- (2) - a product is obtained which is 77% 1 -Methylcyclohexen- (i) contains, while using a 1 -Methylcyclohexanols- (2) with a content of 75% of the cis compound and 25% of the trans compound leads to a product with a content of 93% I-methylcyclohexene (r).

At the beginning of the elimination of water with a mixture of 35 to 400/0 of the cis compound and 60 to 650 / e of the trans compound in the starting material the crude I-methylcyclohexene (I), which is easily removed from the water with which it is is immiscible, separates 950 / o or even more I-methylcyclohexene (l). By doing As the implementation progresses, the content of I-methylcyclohexene (I) decreases slowly to 85 to 90%.

The crude product can be purified or purified by fractional distillation also in unpurified form, e.g. B. for the production - of oxidation retarders after of German patent application I 6702 IVc / 120 by reacting 2 mol with 1 mol Bis- (2-oxy-5-methylphenyl) methane in the presence of an acidic condensing agent be used.

In the following examples, in which parts mean parts by weight, the invention is explained.

Example I 36 parts of 1-methylcyclohexanol- (2) containing from 35 to 40% of the cis compound and 60 to 650/0 of the trans compound by catalytic hydrogenation of o-cresol in the presence of Raney nickel at 200 at pressure and I40 to I600, and 10 parts of an acid-treated fuller's earth (s. Thorpe: Dictionary of Applied Chemistry, 4th Edition, Vol. IV, p. 248) are in a Reaction vessel gégeMen, which is equipped with a stirrer and a short, with a water-cooled Liebig cooler connected fractionation attachment is provided. There's one on the radiator connected with a measuring device for the distillate provided template. The mixture is heated to a temperature of 120 to 1500, so that a mixture of I-methylcyclohexene (I) and water distilled off and unchanged r-methylcyclohexanol- (2) in the reaction vessel remains, the temperature - at the top of the column being 82 to go0.

After the start of the distillation, further I-methylcyclohexanol- (2) is advantageously fed at the same rate as the cycloolefin-water mixture is distilled off. The distillate separates into two layers, of which the upper layer consists of 1-methylcyclollexene (I) exists. After 2 hours, 86 parts of I-methylcyclohexanol- (2) are added and 67 parts of a colorless liquid have been obtained, the 96% I-methylcyclohexene (I) contains. After a total of 12¼ hours, 364 parts of I-methylcyclohexanol (2) obtained a total of 375 parts of a colorless liquid containing 89 0 / o 1 -Methylcyclohexen- (1) while leaving parts of I-methylcyclohexanol- (2) in the flask. The content of the amount that is transferred during the fifth and sixth hours of the operating period Product of I-methylcyclohexene (I) is 860/0> and during the last two Hours of operating time SSe / o. The crude I-methylcyclohexene (I) can be fractionated be cleaned and. then boils at IIoO.

Example 2 300 parts of a prepared according to the instructions in Example I. 1 -Methylcyclohexanols- (2) with a content of 35 to 400/0 of the - cis compound and 60 to 650/0 of the trans compound and 60 parts of an acid activated one Bleaching earth are placed in an enamel-lined autoclave at I400 for 3 hours stirred at a pressure of 5.3 kg per cm2. After cooling, the reaction product becomes filtered and distilled in a fractionating column. The first one passing to 110 ° Fraction separates into two layers. The top layer is made up of the bottom layer of water separated, dried over calcium chloride and distilled again, 32.5 Parts of 1 -Methylcyclohexen- (1) obtained from a boiling point of 110 °.

Claims (5)

PATENT CLAIMS: I. Process for the preparation of I-methylcyclohexene (I); characterized in that one liquid I-methylcyclohexanol- (2) in known Way in the presence of an acid activated fuller's earth on preferably I20 bis I500 heated. 2. The method according to claim I, characterized in that the during water formed during the reaction by azeotropic distillation from the reaction mixture Will get removed. 3. The method according to claim I to 3, characterized in that one an I-methylcyclohexanol- (2) used as starting material, which is 35 to 40 percent by weight the cis compound and 60 to 65 percent by weight of the trans compound. Publications Considered: Berkman, Moreill and Egloff, Catalysis, 1940, p. 743; Beilstein's Book of Organic Chemistry, Vol. V, I930, I. Supplementary work, p. 34; Bull: Soc. Chim. France, I952, 5th series, pp. 2II to 213.