DE1543943A1 - Process for the production of cresol mixtures - Google Patents

Description

Wesseling, April 25, 1966 BWi / Dr Sch-B / Ne

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Process for the production of cresol mixtures

The invention relates to the production of a mixture of o- and p-cresol, which is essentially free of ra ~ cresol.

It is known that cresols can be obtained by alkylating phenol with methanol can get. Normally, skeletons of the three positional isomers are formed, with ra-cresol in particular often being a problem is felt. It is known that it is difficult to separate from the reaction mixture and it is therefore not easy to obtain pure isomers.

For the alkylation of phenol with methanol, it has already been proposed to use aqueous solutions of zinc halides, in particular zinc bromide, as catalysts, the water content being set within wide limits. In this process, the catalyst is appropriately activated with small amounts of hydrogen halide. The reaction is carried out in the temperature range from about 150 to 250 ^° C., if appropriate under increased pressure.

It has also already been proposed that the response in a predetermined To allow the concentration range of the catalyst solution to run off and, if this is exceeded, to terminate the reaction, for example or if too much dilution by the water of reaction obtained this z. B. to evaporate.

It has now been found that, when certain reaction conditions are observed, the final water content set in the catalyst is expediently set by metered addition of the methanol of aqueous zinc bromide solutions as a catalyst which contain 2.5 to 10 mol, preferably 3 to 8 mol of water and 0.05 to 0.50, preferably 0.2 to 0.3 mol of hydrogen bromide, based on one mole of zinc bromide, at temperatures of about 200 to 2 ^ 0 °, the water content of the during the sowing reaction

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Zinc broaid solution keeps in said area, characterized in that, that the amount of methanol fed to the reaction mixture is kept so low that that through the water formed during the reaction, the said upper> Water content of the catalyst solution is not exceeded

It has also been shown that the predetermined amount of water in the catalyst at the start of the reaction is not critical. Rather, it is only, depending on the Auegangekatalyeator, to choose the amount of methanol to be used so that the predetermined final water content does not exceed " It can be advantageous to work with an excess of phenol to suppress the formation of multiply methylated phenolic compounds.

When mixing phenol, methanol and catalyst according to the invention a homogeneous solution forms »The mixture obtained after the reaction, which contains, in particular, the unreacted phenol, cresols and xylenols, segregates at temperatures below 100 to 130 °, so that the water-containing catalyst phase can be separated off. The fact that homogeneous reaction mixtures are always present at the reaction temperatures, allows the homogeneous mixture to be implemented in a simple manner To conduct pressure coils or similar reaction vessels which are kept at the reaction temperature. For better separation after the reaction An inert solvent can be added to the reaction mixture in two phases. Examples are benzene, xylene, hexane, or cyclohexane similar. The resulting organic liquid phase can, for. B. can then be washed with water. The wash water can be mixed with the separated aqueous catalyst phase and from this mixture, the water created by the ron'ation and brought in by the washing water removed. In this way, the catalyst can be restored to its original water content.

The process according to the invention allows practically m-free mixtures • to obtain ms o- and p-cresol with very high yields

Example:

In an autoclave, 515 g of phenol (5.5 mol) were mixed with 112 g of methanol (3.5 mol) in the presence of a catalyst solution containing 1 mole of zinc bromide, 5 moles of water and 0.25 Hol of hydrogen bromide, reacted · During the reaction time

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a pressure of 25 atm was maintained by forcing in nitrogen. The reaction temperature was approx. 220 ° C. After the reaction, the water content in the catalyst solution was 8.4 mol. The yields of o- and p-cresol and dimethylphenols were approx. 98% based on converted phenol and approx. 76% based on methanol. The content of more highly alkylated products in the reaction mixture was 1.5 #

If, under otherwise identical conditions, instead of 3.5 moles of methanol, 7 moles were used Brought conversion and the reaction terminated as soon as the water content of the catalyst solution was 11 mol per mol of zinc bromide, so was the Yield of o- and p-cresol and dimethylphenols based on converted Phenol only 83.5 # and, based on methanol, about 50 #. The content of more highly alkylated products in the reaction mixture was in this case about 1Ί.

Claims (2)

Patent claims: 1 · Process for the production of o- and p-cresol by converting phenol with methanol in the presence of aqueous zinc bromide solutions as a catalyst, the 2.5 to 10 moles, preferably 3 to 8 moles of water and 0.05 to 0.50, preferably 0.2 to 0.3 mol of hydrogen bromide, based on one mole of zinc bromide, at temperatures of about 200 to 2 ^ 0 °, with one during the entire reaction keeps the water content of the zinc bromide solution in the range mentioned, characterized in that the reaction mixture keeps the amount of methanol supplied so low that the water produced during the reaction causes the above-mentioned upper water content of the catalyst solution is not exceeded 2. The method according to claim 1, characterized in that one with a Excess of phenol works 3 · The method according to claim 1 and 2, characterized in that the Reaction product after cooling to a temperature of about below 1300c an inert solvent to facilitate the separation of the adding aqueous catalyst phase 909887/1732 BATHROOM 0W6 «nal