CS238026B1 - Method of 2,6-dialkyl phenols cleaning - Google Patents

Abstract

Method of purifying 2,6 dialkylphenols of (C 1 -C 4) alkyl containing phenol and other accompanying phenolic impurities characterized by greater reactivity with formaldehyde, by 2.6 dialkylphenol heating to 50 to 180 ° C with a suitable a source of formaldehyde, which may be polymeric formaldehyde or formaldehyde releasing with or without catalysts optionally an aqueous formaldehyde solution with catalysts of the selected type aE acidic, or basic. The amount of these moves between 0.005 and 6% by weight reacting phenol mixtures. Added amount formladehydu is 1.01 to 15 fold excess relative to the phenolic present impurities. 2,6 dialkylphenol was reacted the mixture by distillation or rectification at atmospheric pressure or vacuum, optionally crystallization.

Description

The present invention relates to a process for the chemical purification of 2,6-dialkylphenols, in particular 2,6-xylenol.

The oxidation polycondensation of 2,6-dialkylphenols requires a relatively high purity of monomers. in the case of 2,6-xylenol, the source is a phenol methylazo reaction mixture containing a mixture of methylphenols (O-, m-, and p-cresol), dl- and trimethylphenols.

It contains, in smaller quantities, other methylation products and unreacted phenol. Depending on the phenol methylation reaction conditions, the reaction mixture contains mainly o-cresol and 2,6-xylenol in varying proportions.

After the o-cresol has been distilled off, 2,6-xylenol remains in the remainder of the reaction mixture as the main and most important component in addition to the abovementioned mono-, di- and trimethylphenols. From this mixture, 2,6-xylenol is isolated by physical processes such as rectification or crystallization from solution or melt. Due to the close physical properties of the accompanying impurities, these processes are inefficient, lengthy, energy intensive and require expensive and complex equipment. Especially fractionated distillation, used for the isolation and refining of 2,6-xylenol, is uneconomical and the raw material in this operation is exposed to long-term high temperatures, which cause the formation of further impurities which are detrimental to xylenol polymerization.

These impurities arise, in particular, from the isomerization, dealkylation and disproportionation reactions under the conditions mentioned. The yield of pure 2,6-xylenol in the rectification is lower and the recycle from the distillation the greater the lower starting concentration of 2,6-xylenol in the feed.

The purity of the 2,6-xylenol obtained also depends on the composition of the feed. For example, by rectifying crude xylenol containing about 80% by weight of 2,6-xylenol, a product with a purity of 95-97% by weight is obtained industrially with a yield generally lower than 50% by weight, with an increase in the 2,6-xylenol content of the feed above 90% by weight. %, it is possible to obtain 2,6-xylenol with a purity of 98% by weight with a yield of more than 80% by weight, and thus it is easy to obtain pure 2,6-xylenol by rectification to produce a feed which already contains the highest percentage of product obtained.

O-cresol, whether as a major product or as an alkylation by-product, may be due to its. . boiling point (191 ° C) largely separated by rectification. Other impurities, in particular m- and β-cresol, cannot be completely removed by rectification, since their boiling points are practically the same as the boiling point of the 2,6-xylenol obtained (202 ° C).

It has now been found that refining and concentrating 2,6 alkylphenols can also be accomplished on the basis of the different reactivity of the alkylated phenols to formaldehydes. Due to the increased reactivity of the phenolic compounds accompanying the 2,6 alkyl-substituted phenols, they react preferentially with formaldehyde, resulting in higher molecular weight products.

These products can then be easily separated by distillation as they have a substantially higher yarpoint than 2,6-dialkylphenols. For example, alkylphenol impurities accompanying 2,6 xylenol can be converted to low molecular weight resins by heating with a suitable source of formaldehyde by condensation. The alkyls on the phenol are generally up to C5.

SUMMARY OF THE INVENTION The present invention provides a process for the purification of 2,6 dialkylphenols having from 1 to 4 carbon atoms in an alkyl containing unreacted phenol and other phenol alkylation products characterized by higher reactivity, formaldehyde condensation by heating said mixture of phenols to form temperature of 50 to 180 ° C with a suitable source of formaldehyde, which may be an aqueous solution of formladedehyde and / or polymeric form of formaldehyde or formaldehyde releasing compounds or their mixtures in an excess of 1.01 to 15 times relative to the impurities content without catalysts or from the group comprising acids and acid-reacting salts of both inorganic and organic origin and / or basic catalysts, also of inorganic or organic origin, and mixtures thereof, with the exception of metal salts of fatty acids and of divalent and trivalent oxides in an amount of 0,005 to 6 %, based on the weight of the phenol mixture, after which the 2,6-alkylphenol is isolated from the reaction mixture by distillation or rectification under atmospheric pressure or vacuum or by crystallization.

In the purification of 2,6 dialkylphenoids, the resulting low molecular weight resin fractions are non-volatile, so that after distilling off the reaction water and further distilling the resulting reaction mixture, it is possible to obtain in high yield 2,6 dialkylphenols with substantially lower undesirable impurity content than the starting mixture. As the formaldehyde source, either an aqueous solution of formaldehyde or a polymeric form of formaldehyde, for example paraformaldehyde, polyoxymethylenes, trioxane and the like, from which formaldehyde is released by heat, or other substances from which formaldehyde is released, or mixtures thereof may be used.

The condensation reaction can be accelerated by the addition of both acid and base reacting catalysts commonly used in the condensation reactions of phenols with formaldehyde. Likewise, the other reaction conditions can be applied from the commonly or industrially used condensation reactions of phenols with formaldehyde, with the molar ratio of formaldehyde to phenolic impurities being favored in favor of formaldehyde. Generally, 1.01 to 15 times pure formaldehyde can be used due to the amount of phenolic impurities.

It is known that in the reaction of phenols with formaldehyde, other substituents on the phenol nucleus, in particular alkyls, halogens, methylols and the like, have a large influence on the reaction. Particularly important is their position relative to the phenolic hydroxyl. In the condensation of substituted phenols with formladehyd, the principle is that only those phenols having a free ortho or para position react. If these positions are already occupied, then such phenols do not react at all.

The substituents on the phenolic core also influence the rate of the condensation reaction with formaldehyde. For example, the meta-alkyls to the phenolic hydroxyl accelerate the reaction (e.g., m-cresol, 3,5-xylenol, and others). However, when the alkyl is in the ortho or para position to the phenolic hydroxyl, their reactivity to formaldehyde decreases (e.g. o- and p-cresol, 2,6-xylenol and the like).

For example, if under certain conditions the reactivity of 2,6 xylenol to formaldehyde equals 1, then for o-cresol 1,6 1,6 p-cresol 2,2 3,4 3,4-xylenol 5,2 fen phenol 6,2 2 2, 3,5-trimethylphenol 9.2 m-cresol 18.0 l 3,5-xylenol 48.0.

Thus, the worst-off method of the present invention separates o-cresol, which in turn is best separable by rectification due to different boiling points (2,6-xylenol 202-203 ° C, o-cresol 191 ° C).

Another important factor influencing the condensation of phenolic compounds with formaldehyde is the suitability of the reaction regime and the possible method of catalysis. The reactions take place in both acid and i-basic catalysis, which affects the mechanism of the condensation reaction.

For example, using some metal salts of organic acids or metal oxides II. and III. For example, the addition of formaldehyde to the phenol core (AO 230 842, AO 231 085) can be controlled by adhering to certain reaction conditions and the ratio of reactants.

OF '

The catalyst systems conduct rofmaldehyde only predominantly into the o-positions, while the β-position on the phenyl is very difficult to react - but this is a certain disadvantage for the complete removal of any accompanying phenolic impurities, especially those with a free only para position.

Sometimes an aqueous formaldehyde solution is stabilized - for example, formic acid, which is often enough to condense this formaldehyde with phenols relatively well.

Likewise, the ratio of formaldehyde to reacting phenols plays an important role. In the condensation reactions of phenolic impurities accompanying 2,6 dialkylphenols with formaldehyde, care must be taken that the condensation, whether acid-catalyzed (oH less than 7) or basically (pH greater than 7), and the formed condensate is novolak or resol type distilling off

2.6 dialkylphenol always hot enough to be drained from the reaction vessel without difficulty.

Since the distillation residues contain some reactive phenol-alcohols in addition to the low molecular weight resin moiety, these residues need not be carefully removed from the reaction vessel, since these may contribute to some extent to the condensation reaction of the following batch of 2,6 dialkylphenol. _;

Due to their composition, distillate residues from the reaction vessel which have been deaerated can be used as additives in the production of some types of phenolic oils.

Among the many possibilities of condensation of formaldehyde with phenolic impurities accompanying 2,6 dialkylphenols without or using different catalyst systems, several examples are given to illustrate the invention.

In the examples, the percentages are by weight unless otherwise indicated.

He did

Weigh 275 g of 97% pure 2,6-ethylene-phenol for technical purposes and heat to 50 to 60 ° C in a 500 ml three-neck ground reaction flask equipped with a reflux condenser, stirrer, thermometer interfering with the reaction mixture and a dropping funnel.

0.4 ml of hydrochloric acid (36%) is added as a condensation reaction catalyst and 16 g of formaldehyde (36.5% concentration) is added through the side tube with stirring. At the same time, the mixture is slowly heated up to its boiling point. It is around 104 ° C. Heating is continued for about 3 1/2 hours at moderate reflux. During this time, the temperature of the reaction mixture rises to 110 ^and C.

The reaction was terminated by replacing the reflux condenser with a descending condenser and distilling virtually all the water from the mixture. The mixture is heated so that its temperature does not exceed 140-150 ° C. Thereafter, distillation is adjusted to vacuum distillation.

In the first phase of this distillation, a first fraction containing still water residues and possibly 1 part of the unreacted o-cresol present is collected. Vacuum distillation of 2.6 xylenol was continued after changing the flask.

17 g of xylenol were obtained in the first fraction and 195 g of 2.6 xylenol in the main fraction. This fraction was collected at 81-82 [deg.] C. at a pressure of 10 to 50 psi. The distillation residue in the flask was 50 g.

The purity of the 2.6 xylenol main fraction was determined to be 99.5% by melting point and chromatography. Some losses are due to the entrainment of a portion of 2,6 xylenol when the water from the reaction mixture is distilled off.

Example 2

The procedure was as in Example 1, but using 0.6 ml of formic acid instead of hydrochloric acid. The shaft was the same. Technical 2,6 xylenol contained 7% impurities in the form of methylated phenols.

After condensation, water was distilled off from the mixture and 20 g of 2.6 xylenol were obtained in the first fraction and 99 g of 99% pure 2.6 xylenol in the main fraction.

Example 3

Weigh 275 g of technical xylenol of 94.4% into a three-neck reaction flask.

2,6 xylenol. For the condensation reaction, a mixture of an aqueous solution of formaldehyde and paraformaldehyde was used, namely 12 g of an aqueous formaldehyde solution of 36.5% and 4 g of paraformaldehyde.

0.4 ml of 85% phosphoric acid was used as catalyst. The reaction conditions remained the same as in Example 1. After the water was distilled off from the reaction mixture, 37 g of 2.6 xylenol in the first fraction and 210 g of 2.6 xylenol in the main fraction with a purity of 98.2 t were obtained.

Example 4

The procedure was as in Example 1, except that 20 g of 36.5% aqueous formaldehyde solution was used and 0.5 g of dllumide phosphate was used as catalyst. Under the same reaction conditions, after distilling off the water, 16 g of 2.6 xylenol were obtained in the first fraction and in the main fraction 241 g of 2.6 xylenol with a purity of 99.1% were obtained.

Example 5

To a 250 mL three necked flask equipped with a reflux condenser and a thermometer was weighed 140 g of technical 2.6 xylenol containing 5.6% phenolic impurities. To this was added 2 g of triethanolamine as a catalyst, and after heating to 65 ° C, stirring and addition of 18 g of an aqueous 36.5% formaldehyde solution was started.

Heating was continued until the heated mixture was refluxed. After heating for 3 hours, the reaction was discontinued and, after replacing the condenser with a condenser, the water was distilled off from the mixture.

The temperature of the reaction mixture reached about 110 ° C during this operation.

Then, after switching on to vacuum, 2.6 xylenol was distilled off. In the first fraction 7 g of 2,6 xylenol were obtained, in the second fraction 123 g of 2,6 xylenol with a purity of 98,9% were obtained.

Example

The procedure was the same as in Example 5, including the amount of reacting components, but the catalyst of the condensation reaction was another base - morpholine at 1.4 g. In the same procedure, the reaction time was 3 1/2 hours. 8 g of 2,6 xylenol and in the second fraction 122 g of 2,6 xylenol of 98,9% purity.

Example 7

The apparatus and procedure were the same as in Example 5 except that 1 g of boric acid was used for catalysis. The reaction was complete after 4 hours of boiling. By distillation, 9 g of 2.6 xylenol was obtained from the dewatered reaction mixture in the first fraction and 118 g of the product with a purity of 99.0% was obtained in the second fraction.

Example 8

The procedure was the same as in Example 5, except for the condensation of phenolic impurities in the technical process

2.6 g of xylenol was used with 45 g of an aqueous formaldehyde solution at a concentration of 36.5%, and a mixture of 1.2 g of acetic acid and 5 g of sodium acetate was used as the reaction catalyst.

The condensation time at moderate reflux of the reaction mixture lasted only 100 / min. After distilling off the water from this mixture, 6 g of product was obtained in the first fraction of the vacuum distillation and in the second fraction 120 g of 2.6 xylenol having a purity of 98.1% were obtained.

Example 9

120 g of 2.6 xylenol containing 5.1% phenolic impurities were weighed into a 500 ml three-neck ground reaction flask equipped with a descending condenser, a thermometer reaching into the reaction mixture, and a stirrer.

4.8 g of paraformaldehyde were added to remove them. The reaction was not catalyzed.

After the mixture was melted, it was stirred and its temperature gradually increased to 105-110 ° C. After a short delay at this temperature, the temperature was raised to 115-125 ° C while distilling off the water formed.

The total reaction time was 5 1/2 hours and the final condensation temperature was 145 ° C. Distillation yielded 5.5 g of 2.6 xylenol in the first fraction and 107 g of the product with a purity of 99.2% in the second fraction.

Example 10

The procedure was similar to that of Example% except that 120 g of 2.6 xylenol containing 3.3% phenolic impurities were used for purification. Pure paraformaldehyde (2.5 g) was used for the reaction. The mixture of 2.6 xylenol was heated to 110 ° C with stirring and then 150 ° C was reached over a further 4 hours while distilling off the resulting water.

Distillation yielded 5 g of product in the first fraction and 108 g of 2.6 xylenol in the second fraction with a purity of 99.3%.

They did

The procedure, the ratio of the reacting components and the temperature regime were the same as in Example 9. The reaction was catalysed by 0.2 g magnesium carbonate and 0.2 g lactic acid (80%).

After completion of the reaction for a total of 5 hours, 6.5 g of 2.6 xylenol and 105 g of product having a purity of 99.4% were obtained by vacuum distillation in the first fraction.

Example 12

The procedure was the same as in Example 8, except that 170 g of 2.6 diethylphenol with a purity of about 95% were purified. Its melting point was 36.1 ° C. 6 g paraformaldehyde was added to condense the impurities present.

The reaction was carried out at 110-145 ° C for 4 hours. The condensation products were crystallized after cooling the mixture. The procedure was followed by dissolving the phenol mixture after condensation in 50 ml methanol / water by heating to 40 ° C.

The methanol in the mixture was 60%, the water 40%. The solution was then cooled to 3 ° C, filtered, and 500 ml of cold water were gradually added to the filtrate. Part of the solvents was decanted from the deposited crystals, then 500 ml of water was added again.

The crystalline slurry was then aspirated and dried under vacuum at normal temperature. The product with a melting point of 37.4 ° C was obtained, which corresponds to a purity of more than 98%.

Claims (1)

Process for the purification of 2,6 dialkylphenols having 1 to 4 carbon atoms in an alkyl, containing unreacted phenol and other phenol alkylation products characterized by higher reactivity in condensation with formaldehyde, by reacting with formaldehyde, characterized in that said phenol mixture is heated to a temperature of 50 to 180 ° C with a suitable source of formaldehyde, which may be an aqueous solution of formaldehyde and / or polymeric form of formaldehyde or formaldehyde-releasing substances, or mixtures thereof in 1.01 to 15 times the excess of the impurities, without or without catalysts from the group comprising acids and acid-reacting salts of both inorganic and organic origin and / or basic catalysts, also of inorganic or organic origin, and mixtures thereof, with the exception of metal salts of fatty acids and trivalent oxides, in an amount of 0.005 to 6 wt. and the 2,6-alkyl-phenol is isolated from the reaction mixture by distillation or rectification under atmospheric pressure or vacuum, or by crystallization.