DE1793037B1 - Process for the production of 2,3,6-trimethylphenol - Google Patents

Description

23, 6-Trimethylphenol is known to be an important precursor for the synthesis of vitamin E.

In the previously known processes for the production of 2,3,6-trimethylphenol Benzene derivatives are used as starting materials. such as pseudocumene or dimethylphenols used. However, these processes are very expensive because they result in mixtures of isomers, from which the desired isomer is difficult and with losses in pure form can be won.

It has now been found. that 2,3,6-trimethylphenol is advantageous can be produced. when using diethyl ketone in the presence of basic agents Crotonaldehyde or a compound that converts to crotonaldehyde in the presence of basic agents will. converts and the resulting 2,5,6-trimethyl-2-cyclohexen-1-one. in itself as is known, preferably in the gas phase. dehydrated.

According to the method of the invention is 2.3.6-trimethylphenol under Use of easily accessible starting materials in good yield and high purity obtain.

When using crotonaldehyde as the starting substance, the reaction can be represented by the following reaction scheme: It was surprising that derivatives of cyclohexen-2-one-1 can be prepared in a smooth reaction by the process of the invention. from the work of J. Colonge et al, Bulletin de la Société Chimique de France 1954. p. 1444 and Bulletin de la Société Chimique de France. 1959, p. 450. It is known that, in the reaction of trioxane or unsaturated ketones with aliphatic ketones, derivatives of cyclohexen-2-one-1 only when methyl ketones are used. but in no case can be obtained when using diethyl ketone, and that even when methyl ketones are reacted, only yields of at most 40% are achieved.

In the connections. those in the presence of basic agents in crotonaldehyde are converted, it is generally butyraldehydes. those in the ß-position carry a substituent caused by the action of basic substances is eliminated together with an α-hydrogen atom. Such substituents are, for example, the hydroxy, alkoxy, aryloxy. Alkyl mercapto, aryl mercapto, Acyloxy-. Dialkylamino group, halogen atoms or residues of so-called onium salts like the remainder of a quaternary ammonium salt or a trialkylsulfonium salt.

Suitable compounds are, for example, the; -hydroxy, ß-methoxy, ß-phenoxy, ß-acetyloxy, ß-benzyloxy, ß-methylsulfonyloxy, ß-dimethylamino- and -; - chlorobutyraldehyde.

Alkali or alkaline earth metals, for example, can be used as basic agents Hydroxides, oxides, alcoholates, amides, hydrides, carbonates or organometallic compounds the alkali and alkaline earth metals or quaternary ammonium hydroxides can be used.

The following are mentioned here, for example: sodium, potassium and calcium hydroxide. Sodium, potassium carbonate, sodium methylate, sodium amide, sodium hydride, sodium, Phenyllithium. Methyl lithium and tetramethyl ammonium hydroxide.

The condensation of the starting materials can be in a solvent or in the absence of one Solvent are run. In the absence of a solvent it is expedient to use excess diethyl ketone as a diluent.

The solvents used are, for example, organic solvents, such as aliphatic or aromatic hydrocarbons. Ethers, sulfoxides. preferably Alcohols and water. Of the alcohols, those with 1 to 10, particularly 1 to 6 carbon atoms are preferred. Suitable solvents are e.g. 13. Ligroin. Benzene toluene. Diethyl ether. Tetrahydrofuran. Dimethyl sulfoxide. methylglycol, Methanol. Ethanol, isopropanol. Isobutanol, ethylene diglycol. is generally the weight ratio of solvent to crotonaldehyde or its precursor 1 : 10 to 10: 1.

The condensation is generally carried out at temperatures between - 20 and 200 ° C. preferably carried out between 20 and 120 ° C. Usually applies one feels at atmospheric pressure. However, Nian can also be used under reduced pressure, e.g. 100 Torr, or under increased pressure, e.g. B. the pressure. which when using a below the reaction temperature sets the boiling solvent. work.

Diethyl ketone and crotonaldehyde or its precursor are expedient in a ratio of 1: 1 to 50: 1. preferably 2: 1 to 10: 1. implements.

The amount of basic agent can vary within wide limits. In general it will be between 0.1 equivalent percent and the equivalent amount, based on crotonaldehyde. used.

The condensation is carried out, for example, by going to Mixture of diethyl ketone. basic agent and optionally added solvent at the reaction temperature crotonaldehyde or its precursor is added in the Ntaße. how it is consumed. Crotonaldehyde or its precursor is advantageous diluted with a solvent or additional diethyl ketone prior to addition.

The implementation generally decreases depending on the Reaction temperature 15 minutes to 5 hours to complete.

The reaction mixture is worked up, for example, in the manner that it is first neutralized and then through fractional distillation that 2,5,6-trimethyl-2-cyclohexen-1-one of any excess present Separates diethyl ketone and any solvent added.

The 7.5,6-trimethyl-2-cyclohexen-one obtained is then dehydrogenated in a manner known per se to give 2,3,6-trimethylphenol. for example in the liquid phase by heating with sulfur, selenium or chloranil as well as in the liquid phase Phase or in the gas phase by heating in the presence of metals of the 8th group of the periodic table like iron. Cobalt, nickel. Rhodium. Platinum, palladium or from Metals or metal oxides of the 1st subgroup of the periodic table such as copper or Silver. The metals of the 8th group and the 1st subgroup of the Periodic table. especially palladium is used. The metallic delyrogenation catalysts are expediently on a conventional carrier material such as aluminum oxide, silica gel or activated carbon.

The dehydrogenation can be carried out in an inert solvent. However, the 2,5,6-trimethyl-2-cyclohexen-1-one is advantageously dehydrogenated in the gas phase. for example by making it gaseous at the dehydrogenation temperature over a Palladium-silica gel catalyst conducts. The 2,5,6-trimethyl-2-cyclohexen-1-one is preferred in the case of gas phase dehydrogenation in a mixture with a foreign gas such as nitrogen, water vapor, Carbon dioxide, but especially hydrogen, passed over the catalyst, with one generally has a volume ratio of foreign gas to gaseous 2,5,6-trimethyl-2-cyclo-hexen-1-one selects from about t: 2 to 5: 1. In general, in the gas phase dehydrogenation Temperatures between 200 and 400 ° C., preferably 250 to 350 ° C., are used. the Residence times on the catalyst are generally from 0.5 to 50, preferably 2 up to 10 seconds. In the gas phase dehydrogenation, the 2,3,6-trimethylphenol is in more than 95 () io'iger yield obtained.

Example 1 A. Preparation of 3.S, G-trimethyl-2-cyclohexen-one, Zu a boiling mixture of 1000 g of diethyl ketone, 250 g of isobutanol and 5 g of 50% Oiger Sodium hydroxide solution is refluxed with 70 g of crotonaldehyde in the course of half an hour added dropwise. The mixture is then heated to the boil for another half an hour.

After neutralizing with glacial acetic acid and separating the resulting aqueous layer is first excess diethyl ketone by fractional distillation and isobutanol separated, and then are at a transition temperature obtained between 74 and 76 ° C. at 12 torr 106 g of 2,5,6-trimethyl-2-cyclohexen-1-one. The yield is 77% based on crotonaldehyde.

B. Production of 2,3,6-trimethylphenol a) By an externally heated Tube with a capacity of 250 ccm, which is equipped with a palladium-silica gel catalyst (0.1% by weight Palladium) is filled, 1000 g of 2,5,6-trimethyl-2-cyclo- hexen-1-on passed per liter of catalyst per hour at normal pressure. The yield is 96% 2,3,6-trimethylphenol. 4% starting material is recovered and the reaction fed back. The melting point of the 2,3,6-trimethylphenol obtained is 62 ° C, the boiling point 215 C. b) Through an externally heated pipe with a volume of 250 ccm. which is filled with a platinum-carbon catalyst (0.2 percent by weight platinum), are at 300 C 1000 g of 2'5,6-trimethyl-2-cyclohexen-1-one per liter of catalyst and Hour passed at normal pressure.

The yield of 2,3,6-trimethylphenol is 92%. c) One moves as under a), with a nickel-copper-chromium-carbon catalyst instead of the palladium catalyst (100 g each of coal, 8 g of nickel, 3 g of copper and 1 g of chromium) are used. Be at 3502C 500 g of 2,5'6-trimethyl-2-cyclohexen-1-one per liter of catalyst and hour as a mixture with hydrogen (molar ratio of hydrogen to cyclohexenone 2: 1) over the catalyst directed. The yield of 2,3,6-trimethylphenol is 89%.

Example 2 To a boiling mixture of 400 g of diethyl ketone and 10 g of a 30% solution of sodium methylate in methanol are refluxed 70 g of crotonaldehyde were added dropwise over the course of one hour.

The reaction mixture is then under for a further half an hour Heated to reflux. It is neutralized with glacial acetic acid and the mixture obtained is filtered.

By distilling the filtrate, 325 g of diethyl ketone are recovered; 55 g of 2,5,6-trimethyl-2-cyclohexen-1-one with a boiling point of 74 ° to 76 ° C. are also obtained.

The yield based on crotonaldehyde is 40%. The 2,5,6-trimethyl-2-cyclohexene As described in Example 1, 1-one is converted into 2,3,6-trimethylphenol.

Example 3 To a boiling mixture of 250 g of diethyl ketone. 80 A mixture of g isopropanol and 5 g sodium hydroxide powder is refluxed 88 g of hydroxybutyraldehyde and 150 g of diethyl ketone were added dropwise over the course of one hour. The mixture is then heated to boiling for a further 1 hour. After neutralization with Glacial acetic acid and separating the aqueous phase, the organic layer is fractionated. 65 g of 2,5'6-trimethyl-2-cyclohexen-1-one with a boiling point of 74 to 76 ° C. are obtained. The yield is 47% based on i-hydroxybutyraldehyde. The 2,5,6-trimethyl-2-cyclohexen-l-one is, as described in Example 1, converted into 2'3,6-trimethylphenol.

Example 4 To a boiling mixture of 500 g of diethyl ketone and 10 g of a 30% solution of sodium methylate in methanol are refluxed 102 g of ii-methoxybutyraldehyde were added dropwise over the course of one hour. Then will heated under reflux for half an hour. After working up the reaction mixture, as described in Example 2, 77 g of 2,5,6-trimethyl-2-cyclohexen-1-one are obtained, that is 56% yield based on d-methoxybutyraldehyde. The 2,5,6-trimethyl-2-cyclohexen-1-one is, as described in Example 1, converted into 2,3,6-trimethylphenol.

Claims (1)

Claim: Process for the production of 2,3,6-trimethylphenol, characterized. that you diethyl ketone in the presence of basic agents with crotonaldehyde or a compound. which in the presence of basic agents in Crotonaldehyde is converted. converts and the 2,5,6-trimethyl-2-cyclohexen-l-one obtained, in a manner known per se, preferably in the gas phase. dehydrated.