CS230842B1 - Process for chemical refining of technical 2,6-xylenol - Google Patents

Abstract

The invention relates to the chemical refining of technical 2,6-xylenol, containing as impurities in various proportions other products of phenol methylation, by heating with an aqueous solution of formaldehyde in an amount of 10 to 500% by weight, converted to anhydrous 100% formaldehyde, based on the weight content of impurities, in the presence of metal salts of fatty acids with 1 to 30 carbon atoms in an amount of 0.1 to 10% by weight based on the technical 2,6-xylenol used. The above-mentioned fatty acid salts act as selective catalysts promoting the reaction of formaldehyde with the free ortho-position of phenol or its methyl derivatives.

Description

The invention relates to a process for the chemical purification of crude 2,6-xylenol by heating it with an aqueous formaldehyde solution.

It is known that 2,6-xylenol is used to prepare polyphenylene oxide. A certain degree of purity is required for its polymerization.

The source of 2,6-xylenol is a phenol methylation reaction mixture containing predominantly methylphenols (o-, m- and p-cresols), di- and trimethylphenols. To a lesser extent, irrelevant from a quantitative point of view, also other phenol methylece products. Depending on the phenol methylation reaction conditions, the reaction mixture contains a different ratio of o-cresol and 2,6-xylenol, depending on whether the major methylation product is to be o-cresol or 2,6-xylenol. the major and most important component of 2,6-xylenol. Of the other methyl phenol derivatives, the o-, m- and β-cresols alone account for 90-95% of the impurities.

Until now, 2,6-xylenol has been isolated from this mixture and isolated by physical procedures such as rectification, crystallization, or a combination thereof. All these processes are characterized by being very energy intensive, time consuming and requiring complex and costly equipment.

Chemical refining of industrial 2,6-xylenol by heating with paraformaldehyde in the presence of fatty acids can be successfully accomplished.

The present invention provides a process for the chemical refining of industrial 2,6-xylenol in which phenol derivatives having at least one free ortho position relative to the phenolic OH group are impurities by heating this mixture with an aqueous formaldehyde solution in the presence of 1 up to 30 carbon atoms in an amount of 0.01 to 10 weight percent for the industrial 2,6-xylenol used.

The reaction of phenols with an aqueous formaldehyde solution takes place when boiling the reaction mixture only in the presence of catalysts. At pH 4 to 7 of the reaction mixture and use of alkali salts e.g.

Zn, Mg, Al, Mn, Cd, Co, Pb, Cr, Ni and Cu are mainly formed by o-o'-isomers. A 15 to 30% excess of phenol leads almost exclusively to the ó-o´-structure of the reaction products. Traces of acids give rise to β-β-isomers.

The reaction products, especially phenolic impurities with formaldehyde, are characterized by higher molecular weights. During the distillation of refined 2,6-xylenol, they do not volatilize and remain in the distillation residue.

The amount of formaldehyde solution used depends on the content of phenolic impurities. Generally, it does not exceed five times the impurity content (calculated on anhydrous 100% formaldehyde). A smaller excess of formaldehyde requires longer reaction times.

Of the metal salts of fatty acids, the most suitable salts are the most accessible acids, formic, acetic, lauric, etearic, acrylic and oleic. The most suitable chemical refinement temperature of the technical 2,6-xylenol with an aqueous formaldehyde solution is the boiling point of the reaction mixture, i.e. about 100 ° C, depending on the ratio of the aqueous formaldehyde solution and its concentration to the technical 2,6-xylenol.

After distilling off the water and unreacted formaldehyde from the reaction mixture, the distilled 2,6-xylenol is almost completely free of the above impurities, phenol derivatives containing at least one free ottho position relative to the phenolic OH group.

Compared to the same process, but using paraformaldehyde, this process has the advantage that more readily available and cheaper aqueous formaldehyde solutions of various concentrations can be used.

Characteristic features of this new process for the purification of technical 2,6-xylenol are the simplicity and speed of execution, the simplicity and the low-cost production equipment with considerable energy savings. Moreover, the obtained 2,6-xylenol is fully suitable for the polymerization and preparation of polyphenylene oxide. The following examples illustrate the invention.

He did

A 500 ml three-necked flask equipped with a stirrer, thermometer and reflux condenser was charged with 244 g of industrial 2,6-xylenol containing 8.2 wt. % of other phenol methylderivatives resulting from the phenol methylation, 30 ml of a 36% aqueous formaldehyde solution and 2.5 g of zinc acetate. The mixture was heated at boiling point for 8 hours. Then the reaction water along with unreacted formaldehyde is distilled off and 2,6-xylenol is distilled off. 208 g are obtained

2,6-xylanol containing 1.2 wt. % impurities.

Example 2

The procedure of Example 1 is followed, except that 265 g of 2,6-xylenol of 6.5 wt. % impurities and 40 ml of the same aqueous formaldehyde solution. 230 g of 2,6-xylenol having a content of 0.7% by weight are obtained. % impurities.

Example 3

The procedure of Example 1 was followed using only 305 g of 2,6-xylenol containing 5.5 wt. % impurities, 40 ml of a formaldehyde solution of the same concentration and 5 g of lead acetate are used instead of zinc acetate and the reaction mixture is refluxed for 3 hours. 285 g are obtained

2,6-xylenol containing 1.4 wt. % impurities.

Example 4

The procedure of Example 1 was followed using only 305 g of 2,6-xylenol having a content of 3.3 wt. % impurities, 40 ml of an aqueous solution of formaldehyde of the same concentration, 5 g of calcium stearate are used instead of zinc acetate and the mixture is reflexed for 2 hours. 292 g of 2,6-xylenol having a content of 0.2% by weight are obtained. % impurities.

Example 5

The procedure of Example 4 was followed, except that the same amount of lead laurate was used instead of calcium stearate. 290 g of 2,6-xylenol of 1.0 wt. % impurities.

Example 6

The procedure of Example 4 is followed, except that 3 g of sodium acetate is used instead of calcium stearate. 286 g of 2,6-xylenol having a content of 1.1% by weight are obtained. % impurities.

Example 7

The procedure of Example 4 is followed, except that 30 g of zinc stearate is used instead of calcium stearate. 290 g of 2,6-xylenol having a content of 0.4% by weight are obtained. % impurities.

Example 8

The procedure of Example 4 was followed, except that 0.1 g of zinc acetate was used instead of calcium stearate. 286 g of 2,6-xylenol are obtained having a content of 1.4% by weight of impurities.

Example 9

The procedure of Example 4 is followed. 3 g of sodium formate is used instead of calcium stearate. 285 g of 2,6-xylenol having a content of 1.2% by weight are obtained. % impurities.

Example 10

The procedure of Example 1 was followed except that 5 g of zinc oleate was used instead of zinc acetate. 210 g of 2,6-xylenol are obtained with a content of 0.9% by weight. % impurities.

Example 1 d

The procedure of Example 1 was followed except that 2.5 g of zinc acrylate was used instead of zinc acetate. 204 g of 2,6-xylenol of 1.3 wt. % impurities.

Claims (1)

SUBJECT OF THE INVENTION Process for the chemical refining of industrial 2,6-xylenol, containing, in varying proportions, other phenol methylation products such as cresols, xylenols, trimethylphenols, polymethylphenols, anisole, as well as unreacted phenol and characterizing these impurities as phenol derivatives with at least one free ortho- to the phenolic OH group, by heating with an aqueous formaldehyde solution in an amount of 10 to 500% by weight, calculated on the anhydrous 100% formaldehyde, to an impurity content by weight, characterized in that the above mixture of phenolic substances with an aqueous formaldehyde solution is heated With a condenser in the presence of metal salts of C 1 -C 30 fatty acids in an amount of 0.1 to 0% by weight based on the technical 2,6-xylenol used, the reaction water together with unreacted formaldehyde is distilled off and then, without or under vacuum, 2.6. -xylenol distils.