Method for selective preparing ortho-alkylphenols

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of phenols alkylated at ortho-position as parent substances used in preparing organic compounds. Method for preparing o-alkylphenols is carried out by interaction of phenol with alkanol at increased temperature in gaseous phase in the presence of metal oxide as a catalyst. Process is carried out for at least two stages in the molar ratio alkanol : phenol about ≤0.4, preferably, from 0.2 to 0.4 at each stage. Methanol is used as alkanol usually using aluminum gamma-oxide as a catalyst and process is carried out at temperature 300-400°C. Reaction products are separated by distillation. Invention provides increasing yield the end product due to enhancing selectivity with respect to o-alkylphenol.

EFFECT: improved method for preparing.

9 cl, 4 tbl, 2 ex

 

The invention relates to a multistage method o-alkylation of phenol by reaction of phenol with alkanol at elevated temperature in the gas phase in the presence of an acidic catalyst of a metal oxide.

Clean o-ALKYLPHENOLS are important compounds that are used in large quantities as initial substances for the chemical synthesis of organic compounds. Clean o-cresol (2-METHYLPHENOL) finds special application upon receipt of plant protection products.

o-Cresol can be obtained by methylation of phenol with methanol in the gas or liquid phase. Because of the low reactivity of methanol interaction occurs at elevated temperatures in the presence of a catalyst. As catalysts are the oxides of metals, such as aluminum oxide, silicon oxide, mixed aluminum oxide and magnesium oxide. The choice of reaction temperature depends on the catalyst utilized in the region from 250 to 460°C. Thus, magnesium oxide exhibits high selectivity in the case of o-cresol in the temperature range from 420 to 460°while γ-aluminium oxides catalyze the methylation of phenol at a temperature of from 200 to 400°C.

Known also receive o-cresol as a byproduct in the synthesis of 2,6-dimethylphenol and the subsequent allocation of o-cresol is and through additional stages of purification. Methods of obtaining o-cresol in other ways described in H.G. Franck, J.W. Stadelhofer, INDUSTRIELLE AROMATENCHEMIE, S.170-177, Springer Verlag 1987.

In the application DE 2756461 A1 describes a method of this kind which is carried out at a temperature of from 250 to 330°With alumina as the catalyst. When the ratio of methanol to phenol of 0.5:1 to reach the exit of o-cresol up to 26%. The product contains 2,6-dimethylphenol approximately 6%.

At high conversions of phenol in addition to o-cresol always produce large quantities of 2,6-dimethylphenol. Selective receipt of o-cresol in the methylation of phenol is problematic. Often as by-products occur in significant amounts of m-cresol and p-cresol or higher alkylated products.

All known methods of industrial synthesis of o-alkyl phenols in General are characterized by high content of by-products.

Therefore, the object of the invention is to develop a possible selective suitable for implementation on an industrial scale method of producing o-alkylphenol.

The problem is solved by o-alkylation of phenol with alkanol at elevated temperature in the gas phase in the presence of a catalyst of a metal oxide, in which the interaction is conducted in at least two reaction stages, and the molar ratio of alkanol/phenol in the tech is the only way has a value of approximately 1.

The method according to the invention can be carried out in several stages, for example, from two to five. Particularly preferred three-stage method. Each stage of the interaction can be carried out in a different reactor. But it is also possible to carry out several stages of the reaction in the same reactor. With this type of method in the reactor are several spatially separated from each of the drop zones of the active catalyst. Between the locations of catalyst can be located in the zone with the lower activity of the catalyst or without a catalyst.

The research on which this invention is based, showed that the methylation of phenol occurs anisole and o-cresol is formed, on the one hand, by alkylation of the phenol anisole and, on the other hand, through intramolecular rearrangement of anisole to o-cresol. This result is new and is in contradiction with the existing still knowledge. The new course of the reaction, see end of text.

Unexpectedly shown that multistage carrying out the method with the previously mentioned conditions leads to a clearly higher selectivity of the reaction in relation to o-cresol and the associated increase in the yield of this compound. Take that with small local concentrations of methanol and thereby also anisole required for the realizatsii this way, achieve high selectivity to o-alkylation. In addition, it is preferable that the highly exothermic reaction through the distribution of two, in particular three of the reactor, it becomes much more manageable. The formation of the so-called hot spots when it is suppressed.

Through a multi-stage reaction, the ratio of alkanol to phenol in each reactor or at each stage of the reaction can be set particularly low. Consequently limit the conversion of phenol, and can be reached particularly high selectivity for o-alkylphenol, for example, o-cresol. The molar ratio of alkanol to phenol during the entire method is preferably set to 0.9, particularly preferably 0.6 or in the range between them. Thus, the molar ratio of alkanol to phenol with three-stage performing method in each reaction stage is preferably from 0.3 to 0.2.

Alternative conversion of phenol can be set at a value of approximately from 35 to 43%, for example, from 38%to 42%, to ensure the desired high selectivity.

For carrying out the method according to the invention is suitable catalysts are acidic metal oxides and their mixtures. Such metal oxides are, for example, aluminum oxide, silicon oxide/mixed oxides of aluminum and magnesium oxide. Especially preferred γ-alumina. The surface of the catalysts is preferably about 250 m2/g or more, especially preferably from 250 to 300 m2/, These catalysts receive by known methods, for example, by ammonia hydrolysis of aluminium nitrate and subsequent separation, drying and calcination of the resulting sludge (J. Amer. Chem. Soc. 82 (1960) 2471).

The catalyst may be placed in the usual form, for example, in the form of a fixed layer, moving or fluidized bed. Preferably the catalyst is placed in a fixed bed.

Used according to the invention with alkanols in particular are1-4-alkanols, i.e. methanol, ethanol, n-propanol, isopropanol, n-butanol and Isobutanol.

The method according to the invention can be carried out at temperatures ranging from 250 to 400°C. When using γ-aluminium oxide as catalyst, the temperature in the reactor is set to preferably 300-400°S, especially preferably 300-340°With, for example, 330°C.

The following describes an exemplary form of the method according to the invention when using methanol as the alkylating agent. The method is carried out in three stages.

For this phenol through the metering device is sent to the mixer/evaporator. In the same mixer/evaporator through the metering at trojstvo is methanol. The mixture of the source compounds are served in a tubular reactor, heated to 330°C. Downward flow reactor contains, in addition to the products, the original phenol and may come at the bottom of the reactor. Downward flow is served at the next mixer/evaporator which is installed before the next tubular reactor. This mixer to re-establish the ratio of methanol/phenol required for the method according to the invention, and the resulting mixture was fed to the second reactor. Descending stream from the second reactor is sent or in the refrigerator, or in a third mixer/evaporator, which is located before the third reactor. In the third mixer to re-establish the ratio of methanol/phenol required for the method according to the invention, and the resulting mixture was fed into the third reactor.

Downward flow from the third reactor, if necessary, from the second reactor to condense in the refrigerator, and the condensate is directed into the tank.

The processing of the raw alkylate may occur preferably by continuous distillation in a system of three adjacent distillation columns.

In the first column, for example, 20-35 plates, which operate at normal pressure, is the separation of the reaction water in the column head at a temperature of from 90 to 100°C. Water contains a small number of f is Nol, alkyl phenol and anisole, since these compounds are distilled with water in the form of an azeotrope.

VAT residue first column continuously served in the second column. This column is about 100 plates and also works at normal pressure. From the head of the column select phenol with a small fraction of o-cresol at a temperature of the head of the column 180-185°C. This mixed stream can again be fed to the stage of alkylation as raw materials.

Free from phenol VAT residue column 2 is continuously fed into the loading mixture to the third pillar, for example, with 70-95 plates when the pressure in the column head 300 mbar and a temperature of about 145-155°S. Of the head of the column can be obtained pure o-cresol with a purity of >99.5%pure.

VAT residue columns containing a small amount of o-cresol, can be used as raw material to obtain a mixture of a cresol/Xylenol.

Obtained according to the invention the o-alkylated compounds are cresol and ethyl-, n-propyl-, isopropyl-, n-butyl and isobutylpyrazine phenol.

Further explain the invention the following examples.

Example 1

From literature it is known that the anisole through intramolecular rearrangement forms o-cresol. Proceeding from this position, to increase product yield in the method provides a high concentration of anisole. To do this, in one way the e was introduced pure anisole in a tubular reactor with a temperature of 330° With the bulk flow velocity (LHSV) of 1.25 h-1. As the catalyst used γ-alumina with a surface of about 250 m2/, Obtained products and their concentrations in mixtures of products listed in the following table 1.

Table 1
ConnectionConcentration %
The anisole7,1
Phenol32,2
o-Cresol28,6
2,6-Xylenol16,1
2,3,6-trimethylphenol4,0
Pentamethylene3,3
Conversion of anisoleof 92.9%
The selectivity of o-cresol30,8%

The results of table 1 show that the anisole conversion of 92.9% at the chosen conditions is highly reactive. A high concentration of phenol and more vysokolegirovannyh phenols, as 2,6-Xylenol and 2,3,6-trimethylphenol shows that

only part of anisole programmirovaniya in o-cresol. A large part of anisole reacts as alkylating agent.

To confirm this assumption was made experience for alkylation in the same conditions as previously described, in which the methanol is completely substituted anisole. Paul is the results obtained are shown in table 2.

Table 2
Alkylating agent
The anisoleMethanol
ConnectionConcentration %Concentration %
The anisole--
Phenolof 76.872,3
o-Cresol18,820,5
2,6-Xylenol2,6the 3.8
2,3,6-trimethylphenol-0,4
The selectivity of o-cresol81,0%74,0%

Values show similar behavior of methanol and anisole. The use of anisole is characterized by an even higher selectivity than the use of methanol as the alkylating agent.

It can be assumed that the selectivity for o-cresol with both alkylating agents are approximately equal. A slightly higher selectivity of o-cresol under the action of anisole can be explained by the fact that simultaneously with the alkylation of the phenol anisole is regrouping of anisole with the formation of o-cresol.

The study of the share of o-cresol, which is formed by the intramolecular paragraphi ovci, it was conducted in a similar experience with 4-methylanisole as model compounds. The concentration of individual products in a mixture of products (in%) and the conversion of 4-methylanisole are shown in table 3.

Table 3
ConnectionConcentration %
Phenol57,7
o-Cresol12,8
p-Cresol18,6
2,6-Xylenol1,5
2,4-Xylenol6,4
Conversion of 4-methylanisole100%

The results show that along with o-cresol were obtained from p-cresol and 2,4-Xylenol in significant concentrations. p-Cresol is formed when 4-methylanisole acts as meteorologi agent. 2,4-Xylenol is a product of intramolecular rearrangements of 4-methylanisole. The calculation shows that about 70% of 4-methylanisole are meteorous agent and about 30% regroup with the formation of 2,4-Xylenol. It was assumed that when using anisole as the alkylating agent are equal proportions.

Example 2

Phenol with methanol is pumped into the reactor at a temperature of reactor 330°With a molar ratio of methanol/phenol 0.2 and volumetric flow rate (LHV) of 3.75 h -1. As catalyst, use γ-alumina with a surface of about 250 m2/, next the second stage of methanol in a molar ratio of 0.2 to lead to downward flow of the first reactor and continue alkylation. Equally carry out the third stage of alkylation.

For comparison phenol with methanol was subjected to interaction in single-stage tubular reactor at a temperature of reactor 330°With a molar ratio of methanol/phenol 0.6 and volumetric flow rate of 1.25 h-1. Used the same catalyst. In General, the ratio of methanol/phenol and volumetric flow rate (LHSV) were the same as in the three-stage reactor. The concentration of products in a mixture of products, the conversion of phenol and selectivity of o-cresol in both reactions is presented in table 4.

Table 4
ConnectionOne

alkylation
Three-stage

alkylation
The anisole0,020,9
Phenol53,758,6
o-Cresol27,929,4
m/p-Cresol1,50,8
2,6-Xylenol9,56,8
2,4/2,5-Xylenol2,00,9
2,3,6-trimethylphenol1,70,9
The conversion of phenol46,341,4
The selectivity of o-cresol60,371,1

These results show that multi-stage method, the selectivity of o-cresol is clearly higher than in the single-stage method, despite the fact that the conversion of phenol in the three-stage method is similar. The essence is that the number of products in a one-step method is clearly higher than in the three-stage method. Although the content of anisole 0.9% in this experiment is not yet optimal, receive increasing the selectivity of o-cresol from 60.3 per cent in one-step way to 71.1% in the three-stage method.

1. The method of obtaining o-alkyl phenols by reacting phenol with alkanol at elevated temperature in the gas phase in the presence of a catalyst of a metal oxide, characterized in that the interaction is conducted in at least two stages and the molar ratio of alkanol/phenol at each stage of the reaction is approximately0,4.

2. The method according to claim 1, characterized in that the interaction is carried out in three stages.

3. The method according to claim 1, characterized in that the molar ratio of alkanol/f is Nol at each stage of the reaction is about 0.2 - 0,4.

4. The method according to claim 3, characterized in that the molar ratio of alkanol/phenol at each stage of the reaction is approximately 0.3.

5. The method according to claim 1, characterized in that the conversion of phenol in the reaction time at each stage is 35 - 43%.

6. The method of claim 1, characterized in that as alkanol use methanol.

7. The method of claim 1, characterized in that the catalyst used γ-alumina with a surface of more than 250 m2/year

8. The method according to claim 7, characterized in that the reaction is carried out in the temperature range from 300 to 400°C.

9. The method according to one of claims 1 to 8, characterized in that the mixture of products obtained after alkylation, separated by distillation to obtain the desired product.



 

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