DE1668874C2 - Process for the production of 2,3,6-trimethylphenol - Google Patents

Description

2,3,6-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 are used as starting materials Benzene derivatives such as pseudocumene or dimethylphenols are used. However, these procedures are very expensive, since they result in isomer mixtures from which the desired isomer is difficult and can be obtained in pure form with losses.

It has now been found that 2,3,6-trimethylphenol can be prepared in a simple manner if one Diethyl ketone in the presence of basic agents with methyl vinyl ketone or a compound in the presence is converted by basic agents into methyl vinyl ketone, and the resulting 2,3,6-trimethyl-2-cycIohexen-l-one preferably dehydrated in the gas phase.

According to the process of the invention there is 2,3,6-trimethylphenol using easily accessible starting materials in good yield and high purity obtain.

When using methyl vinyl ketone as the starting material, the reaction can be carried out as follows Represent reaction scheme:

55

60 It was surprising that derivatives of cyclohexen- (2) -one- (l) can be prepared in a smooth reaction by the process of the invention, since it is described in Bulletin de la Societe Chimique de France, 1954, p. 1444, that in the reaction of trioxane with ketones to derivatives of cyclohexene (2) -one- (l) these compounds are obtained only when using methyl ketones, but in no case when using diethyl ketone.

In the case of compounds that are converted into methyl vinyl ketone in the presence of basic agents are, it is generally about methylethyl ketones, which are in the / f-position of the ethyl group carry a substituent which, through the action of basic substances, together with a «- Hydrogen atom is eliminated. 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 such as the remainder of a quaternary Ammonium salt or a trialkylsulfonium salt. For example, mated connections are that / i-Hydroxyäthyl-, / i-Methoxyäthyl-, / i-Phenoxyäthyl-, / i-Acetyloxyäthyi-, / J-Benzoyloxyäthyl, / i-Methylsulfonyloxyäthyl-, / i-Phenylsulfonyloxyäthyl-, / i-Dimethylaminoäthyl-, / i-chloroethyl methyl ketone, dimethyl (/ i-acctylethyl) sulfonium bromide, Trimethyl (/ i-acetylethyl) ammonium iodide. Because of economical reasons of these compounds is the / ^ - Hydroxyäthylmethylketon preferred. Alkali or alkaline earth metals, for example, can be used as basic agents, Hydroxides, oxides, alcoholates, amides, hydrides, carbonates or organometallic compounds of the Alkali and alkaline earth metals or quaternary ammonium hydroxides can be used. Let it be here, for example called sodium, potassium, calcium hydroxide, sodium, potassium carbonate, sodium diethylate, Sodium amide, sodium hydride, sodium, phenyllithium, methyllithium, tetramethylammonium hydroxide.

The condensation of the starting materials can be in an inert solvent or in the absence of one Solvent are run. In the absence of a solvent, it is expedient to use excess diet hyiketone as a diluent. Organic solvents, for example, can be used as inert solvents Solvents such as alcohols, ethers, aromatic or aliphatic hydrocarbons, sulfoxides or water. Suitable solvents are e.g. B. methanol, diethyl ether, tetrahydrofuran, Benzene, toluene, ligroin, dimethyl sulfoxide.

The condensation is generally carried out at temperatures between -20 and 200.degree. C., preferably 50 and 150 ° C. As a rule, atmospheric pressure is used. However, you can also use reduced pressure, e.g. 100 torr, or under increased pressure, e.g. B. the pressure, which is in the Use of a solvent boiling below the reaction temperature adjusts to work.

Diethyl ketone and methyl vinyl ketone or its precursor are expediently in a molar ratio of 1: 1 to 50: 1, preferably 2: 1 to 10: 1, reacted. The amount of basic agent can be further within Limits vary. In general, it will be between 0.1 equivalent percent and the equivalent amount, based on methyl vinyl ketone. When using compounds as starting materials,

which can be converted into methyl vinyl ketone when exposed to basic substances is expedient the amount of alkali required in the elimination to the vinyl group is additionally used.

The condensation is carried out, for example, by adding to the mixture of diethyl ketone and basic Adding agent at the reaction temperature methyl vinyl ketone or its precursor to the extent that how it is consumed. The methyl vinyl ketone or its precursor is advantageous before the addition an inert solvent or additional diethyl ketone diluted.

In addition, it is advantageous to add a polymerization inhibitor such as these starting materials Stabilize hydroquinone or hydroquinone monomethyl ether. The water produced during the reaction is conveniently removed from the reaction mixture, for. B. by putting it together with a suitable Diluents such as benzene or toluene or with excess diethyl ketone as an azeotropic The mixture is separated off and, if appropriate, the diluent is returned.

The reaction generally takes from 0.5 to 10 hours, depending on the reaction temperature.

The reaction mixture is worked up, for example, in such a way that it is first neutralized and then separating off the 2,3,6-trimethyl-2-cyclohexen-1-one by fractional distillation.

Depending on the reaction conditions, more or less is obtained as a by-product in the condensation large amounts of -t-methyl-S-ethyl ^ -cyclohexen-1-one. However, this can be achieved by treatment with aqueous bases, e.g. B. aqueous sodium or potassium hydroxide, in be rearranged in a manner known per se, after an equilibrium has been established a mixture of about 4 percent by weight of the by-product and about 96 percent by weight 2,3,6 - trimethyl - 2 - cyclohexen-1-one arises. Due to the isomerization, it is therefore possible to convert the by-product almost quantitatively into the to convert isomeric 2,3,6-trimethyl-2-cyclohexen-l-one.

The isomerization can be carried out, for example, by adding 4-methyl-3-ethyl-2-cyclo-hexen-1-one separated by fractional distillation from the reaction mixture and then with aqueous sodium hydroxide solution, e.g. B. a 10 weight percent solution at elevated temperature, e.g. B. at the Reflux temperature, treated. The isomer mixture is then expediently fractionated by Separated distillation and the unrearranged compound isomerized again. But you can too carry out the isomerization in such a way that the reaction mixture obtained in the condensation some time, e.g. B. 5 hours, treated at elevated temperature with aqueous bases.

The 2,3,6-trimethyl-2-cyclohexen-l-one obtained is then used in a manner known per se 2,3,6-trimethylphenol dehydrated, for example in wet phase by heating with sulfur, selenium or chloranil as well as in the liquid or in the gas phase by heating in the presence of metals from group VIII of the periodic table such as iron, cobalt, Nickel, rhodium, platinum, palladium or of metals and metal oxides of the I. subgroup of the periodic table like copper or silver. The metals of group VIII and subgroup 1 are preferred of the periodic table, in particular palladium, is used. The metallic dehydrogenation catalysts are expediently used on a conventional basis Carrier material such as aluminum oxide, silica gel or activated carbon is used.

You can do the dehydrogenation in an inert solvent carry out. 2,3,6-Trimethyl-2-cyclohexen-1-one is advantageous however, dehydrogenated in the gas phase, for example by converting it in gaseous form at the dehydrogenation temperature over a palladium-charcoal catalyst directs. Preferably that will

ι ο 2,3,6-trimethyl-2-cyclohexen-1-one in the gas phase dehydrogenation in a mixture with a foreign gas such as nitrogen, steam, carbon dioxide, but especially hydrogen, passed over the catalyst, in general, a volume ratio of foreign gas to Selects 2,3,6-trimethyl-2-cyclohexen-l-one from about 1: 2 to 5: 1. In general, in the gas phase dehydrogenation temperatures between 200 and 400 ⁰ C, preferably 250 to 35O ⁰ C, applied. The residence times on the catalyst are generally from 0.5 to 50, preferably from 2 to 10, seconds. In the gas phase dehydrogenation, the 2,3,6-trimethylphenol is obtained in 95% yield.

example 1
A. Preparation of 2,3,6-trimethyl-2-cyclohexen-1-one

To a boiling mixture of 1000 g of diethyl ketone and 5 g of sodium hydroxide powder, a mixture of 70 g of methyl vinyl ketone, 200 g of diethyl ketone and 0.1 g of hydroquinone is added dropwise over the course of one hour. The reaction mixture is then refluxed for a _{further V for 2 hours.} The water (17 g) formed during the reaction is removed from the reaction mixture with the aid of a separator. After neutralization with glacial acetic acid and after filtration, the mixture is distilled, 1120 g of diethyl ketone being recovered. Fractional distillation of the residue gives 81 g of 2,3,6-trimethyl-2-cyclohexen-1-one with a boiling point of ₁₂ 89 ° C and 29 g of 4-methyl-3-ethyl-2-cyclohexen-1-one with a boiling point of _u 102 ⁰ C. The total yield of cyclohexenones is 80%, based on methyl vinyl ketone.

B. Preparation of 2,3,6-trimethylphenol

a) Through an externally heated tube with a volume of 250 ecm, which is filled with a palladium-silica gel catalyst (0.07 percent by weight palladium), 1000 g of 2,3,6-trimethyl-2-cyclohexene ^{are introduced at 300 ° C.} 1-one per liter of catalyst and hour

Normaldiruck passed through. The yield of 2,3,6-trimethylphenol is 95%. 5% starting material is recovered and returned to the reaction.

The melting point of the obtained 2,3,6-trimethylphenol is 62 ° C, the boiling point is 215 ° C.

b) Through an externally heated tube with a volume of 250 ecm, which is filled with a platinum-carbon catalyst (0.2 percent by weight platinum), 1000 g of 2,3,6-trimethyl-2-cyclohexene ^{are introduced at 300 ° C.} 1-one passed through per liter of catalyst and hour at normal pressure. The yield of 2,3,6-trimethylphenol is 92%.

c) The procedure is as described under b), a nickel-copper-chromium / carbon catalyst being used instead of the platinum catalyst (100 g each of coal, 8 g of nickel, 3 g of copper and 1 g of chromium) are used. 500 g of 2,3,6-trimethyl-2-cyclohexen-1-one are obtained at 350.degree per liter of catalyst and hour in the mixture with

Hydrogen (molar ratio of hydrogen to cyclohexenone 2: 1) passed through the contact. The yield of 2,3,6-trimethylphenol is 89%.

Example 2 _s

To a boiling mixture of 400 g of diethyl ketone and 10 g of a 30% strength by weight methanolic sodium methylate solution, a mixture of 70 g of methyl vinyl ketone, 10 g of water and 0.1 g of hydroquinone is added dropwise over the course of one hour. The mixture is then refluxed for a further two hours. The mixture obtained is neutralized with glacial acetic acid and then filtered. The excess diethyl ketone and the water present are distilled off and the residue is fractionated in vacuo. This gives 81 g of 2,3,6-trimethyl-2-cyclohexen-l-one of boiling point _and 89 ° C and 9 g of 4-MethyJ-3-ethyl-2-cyclohexen-l-one, bp. _12, 102 'C The total yield of cyclohexenones is 65%, based on methyl vinyl ketone.

The further processing of the 2,3,6-trimethyl-2-cyclohexen-1-one to 2,3,6-trimethylphenol is carried out as described in Example 1.

E xample 1 3

To a mixture of 250 g of diethyl ketone and 10 g of a 30% strength by weight methanolic sodium methylate solution a mixture of 88 g of 3-ketobutan-l-ol, 150 g of diethyl ketone and is refluxed 0.1 g of hydroquinone added dropwise over the course of 2 hours. It is then refluxed for a further 2 hours heated. During the reaction, 37 g of water are removed from the reaction mixture. The work-up takes place as described in example 1. There are 73 g of 2,3,6-trimethyl-2-cyclohexen-1-one and 10 g of 4-methyl-3-ethyl-2-cyclohexen-1-one obtain. The total bulging of cyclohexenones is 60%, based on 3-ketobutan-1-ol. The 2,3,6-trimethyl-2-cyclohexen-1-one is, as described in Example 1, in 2,3,6-trimethylphenol convicted.

Example 4

A mixture of 138 g of 4-methyl-3-ethyl-2-cyclohexen-1-one and 500 g of 7 percent strength by weight sodium hydroxide solution are refluxed for 5 hours with stirring heated. After the reaction mixture has cooled down, the resulting cyclohexenone mixture is poured into 500 ml Hexane taken up and separated from the aqueous layer. From the organic phase obtained the hexane is distilled off. 135 g of one are obtained The residue, which is 96% from 2,3,6-trimethyl-2-cyclohexen-1-one and 4% from 4-methyl-3-ethyl-2-cyclohexen-1-one consists. The 2,3,6-trimethyl-2-cyclohexen-1-one is, as described in Example 1, in 2,3,6-trimethylphenol convicted.

Example 5

To a boiling mixture of 400 g of diethyl ketone and 5 g of a 30 weight percent methanolic Sodium methylate solution is added dropwise to 152 g of 1-methoxybutan-3-one over the course of one hour. The reaction mixture is then refluxed for a further 1 hour. The reaction mixture has been neutralized with glacial acetic acid is fractionated. There are 70 g of 2,3,6-trimethyl-2-cyclohexen-1-one and 9 g of 4-methyl-3-ethyl-% cyclohexen-l-one are obtained. The total yield Cyclohexenones is 57% based on 1-methoxybutan-3-one. The 2,3,6-trimethyl-2-cyclohexen-1-one is, as described in Example 1, converted into 2,3,6-trimethylphenol.

Example 6

130 g of 1-acetoxybutan-3-one are added to 400 g of boiling diethyl ketone from separate feed vessels with stirring and methanolic sodium methylate solution was added dropwise in one hour so that the reaction mixture always remains alkaline. There are a total of 190 g of a 30 weight percent sodium methylate solution consumed. The mixture is then refluxed for a further hour and then neutralized with glacial acetic acid. The precipitated sodium acetate is filtered off. The filtrate is subjected to fractional distillation subject. 81 g of 2,3,6-trimethyl-2-cyclohexen-1-one are obtained in addition to only traces of 4-methyl-3-ethyl-2-cyclohexen-1-one. The yield based on l-acetoxy-butan-3-one, is 59%. The 2,3,6-trimethyl-2-cyclohexen-1-one is, as described in Example 1, converted into 2,3,6-trimethylphenol.

Example 7

The procedure is as described in Example 6, except that 107 g in place of the l-acetoxybutan-3-one l-chloro-butan-3-one can be used. 76 g of 2,3,6-trimethyl-2-cyclohexen-1-one are obtained along with traces 4-methyl! -3-ethyl-2-cyclohexen-1-one. The yield is 55% based on l-chlorobutan-3-one. That 2,3,6-trimethyl-2-cyclohexen-1-one obtained is, as described in Example 1, in 2,3,6-trimethylphenol convicted.

Example 8

The procedure is as described in Example 5, 115 g of 1-dimethylamino-butan-3-one being used in place of the 1-methoxybutan-3-one begins. 78 g of 2,3,6-trimethyl-2-cyclohexen-1-one and 7 g of 4-methyl-3-ethyl-2-cyclOhexen-1-one are obtained. The yield of cyclohexenones is 62%, based on 1-dimethylaminobutan-3-one. The 2,3,6-trimethyl-2-cyclohexen-1-one obtained 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 in that one diethyl ketone in the presence of basic Agents with methyl vinyl ketone or a compound which in the presence of basic agents in Methyl vinyl ketone is converted, and the resulting ^, o-trimethyl ^ -cycIohexen-l-one dehydrogenated in a manner known per se, preferably in the gas phase. IO