DE1956382A1 - Process for the preparation of 2.3.6.-trimethylphenol by methylation of 2.6-dimethylphenol - Google Patents

Description

Wesseling, October 6, 1969 VP / Dr Sch-B / Ne

Our reference: UK 228

Process for the preparation of 2.3 · 6-trimethylphenol

The invention relates to a process for the production of 2.3 · 6-trimethylphenol by methylation of 2,6-dimethylphenol.

2. 3 · 6-trimethylphenol is of considerable importance as a starting product for the synthesis of vitamin E. In the conventional alkylation of phenol, the 2.3 · 6-trimethylphenol is only obtained in such small amounts and in a mixture with other alkylphenols, that isolation from the crude alkylate in the required purity is not economically feasible. In general, the known solid alkylation catalysts cause ortho substitution of the phenols, so that in addition to o- and p-methylphenol, 2,6- and 2,4-dimethylphenols and 2.4.6-trimethylphenol are obtained. This also applies in particular to the aluminum oxide catalysts, for example in the conversion of o-cresol (Brit. Pat. 717 588), 3.5-dimethylphenol (US Pat. 2,678,951), o-cresol, 2.5-, 3 · 5-dimethylphenol (BeIg .Pat. 649 671) with alcohols. Also in the presence of other solid oxidic catalysts, eg magnesium oxide and uranium oxide (DAS 1 248- 666), the oxides of thorium, zirconium, zinc, magnesium, calcium or barium (Brit.Pat. 717 588) or in the usual way as a carrier Oxides used, for example aluminum silicates, (US Pat. 2,684,389) 1, o-substitution is preferred. Also, when 3 · 5-dimethylphenol was reacted with methanol in the presence of aluminum oxide, o-substitution was found primarily, and 2,3,5-trimethylphenol was mainly formed (US Pat. 2,678,951).

It has now been found that in the methylation of 2,6-Di ... othylphenol in the presence of the aluminum oxides usually used as solos or carriers, surprisingly, preference is given to 2,3,6-trimethylphenol forms although a preferred formation of the 2,4,6-trimethylphenol was to be expected.

109821/2188

Our reference: UK 228

The invention accordingly relates to a process for the preparation of 2,3 · 6-trimethylphenol, in which 2,6-dimethylphenol is alkylated with methanol in a manner known per se in the presence of aluminum oxide. The alkylation can be carried out in a customary manner both in the gas phase and in the plus phase. The reaction temperatures are in the range of about 250-4OO ⁰ , in particular about 280-380 ⁰ . Depending on the choice of procedural conditions, the use of pressure is appropriate or necessary. The residence times in the reactor are also different depending on how the process is carried out and can range from a few seconds when working in the gas phase to over an hour when working in the positive phase. ^{A 1} molar ratio of 2,6-dimethylphenol: methanol, such as about 1: 0.2 to 1: 0.8, in particular one of about 1: 0.3 to 1: 0.6, is advantageously selected. By-products obtained in the alkylation, such as methyl anisole, m-cresol, 2,3- and 2,5-dimethylphenol, can optionally be returned to the reactor in order to increase the yield of 2,3.6-trimethylphenol. The catalysts can be activated, for example with small amounts of zinc chloride or zinc chloride or duroh pretreatment with oxygen or air at 450 °, for example. If necessary, they can be regenerated in an appropriate manner. They can also be present in conjunction with other oxides, such as nickel oxide and magnesium oxide. The process according to the invention for obtaining 2,3 · 6-trimethylphenol has the particular advantage that the starting product 2,6-dimethylphenol is available in sufficient quantity and inexpensively as a by-product of the cresol syntheses.

example 1

2.6-Dimethylphenol was in the gas phase with methanol (molar ratio 1: 0.3) alkylated over aluminum oxide. The reaction temperature was 300-320 °, the residence time in the reactor was about 10 seo. It was a raw alkylate obtained which - free of 2,6-dimethylphenol - reohnet the following Composition showed:

109821/2188

Our reference: UK 22β

o-KreBol

p-cresol

2,5-dimethylphenol 2,4-dimethylphenol 2.3 · 5-trimethylphenol 2.4.6-trimethylphenol 2.3 6-trimethylphenol 2,6-dimethyl anisole Tetramethylphenols Higher alkylated phenols

Weight -ή

6.2

0.6

1.2

3.1

1.2

13.6 48.8

2.5 13.6

9.2

Example 2

It was 2,6-dimethylphenol in the liquid phase "at about 350-370 ° and alkylated under a pressure of approx. 50 atm with methanol (molar ratio 1: 0.6) in the presence of aluminum oxide, whereby the residence time time in the reactor was 1 hour. The 2,6- »dimethylphenol-free obtained calculated alkylate had the composition:

o-cresol

2.4 · 6-trimethylphenol 2.3 x 6 Trimethylphenol__ · 2.6 dimethylanisol tetramethylphenols higher alkylated phenols

Weight %

7.7

4.1

57.7 11.5 13.6

5.4

Example 3

Various catalysts were used in the gas phase process

in fact:

A) ^ -Alumina

B) regenerated several times by treatment with air "at 4ΟΟ-5ΟΟ ⁰

Alumina

C) Alumina activated with ZnCl £

D) for comparison: $ 78 MgO + $ 22 VO ₃

E) for comparison: 90% SiO ₂ +

109821/2188

Our reference: UK 226

Reaction temperature wt. -Fo 2.4 6 wt .- ^ 2.3.6-

⁰ C trimethylphenol trimethylphenol

in the alkylate

Δ 280 23.1 40.2

300 21.3 48.0

B 300. 15.5- 41.5

320 14.5 _. 39.9

C 270 12.5 37.6

280 20.1 35.6

300 27.8 34.7

Ί> 330 74.1 1.6

340 68.7 0.6

E 300 42.5 5.2

320 28.9 ^ι 7.4

109821/2188

Claims (2)

Our sign; UK 228 . _Λ _ Claims; Process for the production of 2. 3 «6-trimethylphenol, characterized in that that you get 2,6-dimethylphenol in the presence of aluminum oxide alkylated with methanol in a manner known per se. 2. The method according to claim 1, characterized in that the catalyst before it is used, treatment with oxygen or air at around 400 - 450 ° is activated. 109821/2188