JPH05186390A - Production of p-hydroxybenzoic acid - Google Patents

Abstract

PURPOSE:To obtain the subject compound in high yield by subjecting potassium salicylate to rearrangement reaction in the presence of a specific compound. CONSTITUTION:Potassium salicylate is subjected to rearrangement reaction in the presence of one or more compounds expressed by the formula [R is substituent group required for the rearrangement reaction of the potassium salicylate; n is 1-5] (preferably potassium mono-, di- and trialkylphenoxides) at 230-450 deg.C in an inert solvent in an atmosphere of carbon dioxide and/or an inert gas while preferably removing substituted phenols, etc., formed as by-products and acidifying treatment is carried out. Thereby, the objective compound is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel method for producing parahydroxybenzoic acid. More particularly, it relates to a method for producing para-hydroxybenzoic acid, which is useful as a raw material for liquid crystal polymer compounds, preservatives and antifungal agents, by a novel rearrangement reaction method using potassium salicylate as a raw material in a higher yield than ever before.

[0002]

2. Description of the Related Art A conventional industrial production method of parahydroxybenzoic acid is as follows. First, phenol is converted into potassium salt, and carbon dioxide (carbon dioxide) is reacted with this under high temperature and pressure, followed by Kolbe-Schmidt reaction. The mainstream method is to acidify the obtained potassium salt of carboxylic acid with a mineral acid or the like to obtain a free carboxylic acid according to a conventional method. In such a method, the Kolbe-Schmidt reaction
When carried out at around 0 ° C, salicylic acid becomes the main product,
It is known that para-hydroxybenzoic acid becomes the main product when the reaction temperature is set to a relatively high temperature of about 200 ° C. or higher.

In the Kolbe-Schmidt reaction, salicylic acid is likely to be formed as a monopotassium salt, so that it is often produced almost quantitatively (90% or more), but parahydroxybenzoic acid is likely to form a dipotassium salt. Approximately half of the charged phenol potassium is liberated as phenol, and the amount of parahydroxybenzoic acid produced is 50% based on the molar number of charged phenol potassium.
It is general that it becomes a degree.

By the way, it is also well known that potassium salicylate, which can be obtained almost quantitatively in this way, is a rearrangement intermediate of such Kolbe-Schmidt reaction (for example, Journal of Industrial Chemistry, 64, 1317, 1961).
However, despite the fact that the amount of by-products often becomes a problem, there are very few techniques for actively utilizing this to produce para-hydroxybenzoic acid. Kolbe
There are only a few academic studies dealing with the rearrangement reaction of potassium salicylate to investigate the mechanism of the Schmidt reaction.

The matters clarified in the conventional studies on the rearrangement reaction of potassium salicylate are as follows.

For example, the above-mentioned document (Industrial Chemistry Magazine, 64
(Vol. 1317, 1961), the rearrangement reaction of potassium salicylate was carried out under the conditions that the initial pressure of carbon dioxide was 0, 2.5, 5 and 10 kg / cm ² and the reaction temperature was 190 to 250 ° C. As a result, the yield of para-hydroxybenzoic acid was high at about 37-39%, the residual salicylic acid was at 3-22%, and the degradation product mainly composed of phenol was 4%.
It was reported to be 2 to 58%.

Also, Journal of Industrial Chemistry, 63, 1410
Page, 1960, reports a rearrangement reaction in a system in which potassium salicylate is allowed to coexist with equimolar phenol potassium. According to this, in the rearrangement reaction under pressure of carbon dioxide, the highest yield of parahydroxybenzoic acid was 71.8%, and the residual salicylic acid at this time was 2%.
It was reported to be 1.1%. However, in this reaction system, the coexisting phenol potassium undergoes carbonation, so the generated parahydroxybenzoic acid contains a rearrangement reaction and a carbonation reaction, and therefore, the molar amount of the charged potassium salicylate is increased. It is reasonable to evaluate the above-mentioned rearrangement yield based on the number as about 1/2 of the above-mentioned yield.

[0008] Furthermore, the study of rearrangement reaction of potassium salicylate by microthermal analysis was carried out by The Chemical Society of Japan, 1974.
Volume, 798. However, since the amount of parahydroxybenzoic acid produced is shown as the ratio of the total carboxylic acids excluding the released phenol, the absolute rearrangement yield based on the number of moles of potassium salicylate charged is used. The rate is unknown. However, para-hydroxybenzoic acid, by its nature, easily forms a dipotassium salt because the hydroxy group also exhibits strong acidity, and the document also states that dipotassium para-hydroxybenzoate is produced from potassium salicylate. Therefore, the absolute rearrangement yield of para-hydroxybenzoic acid is still similar to those in the above-mentioned two documents, and it is reasonable to assume that it does not exceed 50%.

[0009]

As described above, in the conventional technique for producing para-hydroxybenzoic acid through the step of rearrangement reaction of potassium salicylate, the yield of para-hydroxybenzoic acid is as low as less than 50%, It was not possible to produce para-hydroxybenzoic acid in a higher yield than this.

The present invention provides a potassium salt of parahydroxybenzoic acid in a high yield in comparison with the conventional rearrangement reaction method of potassium salicylate. Therefore, it is possible to obtain parahydroxybenzoic acid in a high yield. It is an object of the present invention to provide a method for producing parahydroxybenzoic acid, which comprises a novel rearrangement reaction as one step.

[0011]

Means for Solving the Problems The present inventors have noticed that when potassium salicylate undergoes a rearrangement reaction, potassium is insufficient because dipotassium parahydroxybenzoate is produced. Therefore, it was thought that the yield would be improved in the production of parahydroxybenzoic acid through the step of rearrangement reaction of potassium salicylate. And
We have studied the method of supplementing potassium.

In the course of the research, the inventors of the present invention have found that the compound represented by the following formula I alone may react with carbon dioxide to give the corresponding carboxylic acid. It was found that it was not as reactive as potassium.

[Chemical 2] (In the above formula I, R is a substituent inert to the rearrangement reaction of potassium salicylate, n is an integer of 1 to 5. When n is 2 to 5, R may be the same or different from each other. Good.)

Therefore, when the rearrangement reaction of potassium salicylate was carried out in the coexistence of the compound represented by the formula I, the compound represented by the formula I was extremely unlikely to undergo carbonation in such a coexisting system, and parahydroxybenzoic acid was thus obtained. The present invention has been completed by finding that it acts as a potassium carrier for potassium acid and, after the reaction, most of it is converted into the corresponding free substituted phenols.

That is, the present invention is a process for producing parahydroxybenzoic acid, which comprises a step of causing rearrangement reaction of potassium salicylate in the presence of at least one compound represented by the following formula I: Is provided.

[Chemical 3] (In the above formula I, R is a substituent inert to the rearrangement reaction of potassium salicylate, n is an integer of 1 to 5. When n is 2 to 5, R may be the same or different from each other. Good.)

The step of carrying out the rearrangement reaction on potassium salicylate is carried out at 230 to 450 ° C., under a carbon dioxide and / or inert gas atmosphere, or
It is preferably carried out in a medium inert to the reaction.

As the compound represented by the above formula I, mono,
It is preferred to use at least one of potassium di and trialkylphenol.

The present invention will be described in detail below. In the step of rearrangement reaction of potassium salicylate in the present invention, at least one of the compounds represented by the following formula I is allowed to coexist.

[Chemical 4] (In the above formula I, R is a substituent inert to the rearrangement reaction of potassium salicylate, n is an integer of 1 to 5. When n is 2 to 5, R may be the same or different. Good.)

The substituent R in the compound of formula I is
It is a substituent that is inactive in the rearrangement reaction of potassium salicylate. That is, it must not be an aliphatic hydroxy group having 4 or less carbon atoms, an aliphatic mercapto group having 4 or less carbon atoms, or a substituent containing these functional groups as a part thereof.

Examples of the substituent R include an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an amino group, an imino group, a halogen atom, a hydroxy group (aromatic), a nitro group and a phenyl group.

Further, as the substituent R having a plurality of functional group moieties, isopropyl group, aminoalkyl group, monoalkylaminoalkyl group, dialkylaminoalkyl group, acylamino group, halogenated alkyl group, nitroalkyl group, phenylalkyl group. , Methoxy group, alkylamino group, dialkylamino group, acyl group, alkylphenyl group, alkoxyphenyl group, aminophenyl group,
Examples thereof include halogenated phenyl group, hydroxyphenyl group, nitrophenyl group and styryl group.

As the compound represented by the above formula I, which is suitable for use in the present invention, the substituent R is an electron-donating compound such as an alkyl group such as a methyl group or an isopropyl group or an alkoxy group such as a methoxy group. Compounds,
Further, a compound in which the substituent R is a phenyl group or the like is also suitable.

The number n of the substituents R in the compound represented by the above formula I is an integer of 1 to 5, but a compound in which n is 1 to 3 is preferable. When n is 2 or more, the plurality of substituents R may be the same or different from each other.

The compound of the above formula I has the substituent R 1
When it has one, the substitution position of R may be any of ortho, meta or para position with respect to -OK (potassium oxy group). Further, in the case of having 2 to 5 substituents R, the positions of the respective substituents R may be in any positional relationship with respect to -OK or with each other.

Specific examples of the compound represented by the above formula I include cresol potassiums and phenylphenol potassiums in which n is 1, 2,3-, 2,4 in which n is 2.
-, 2,5-, 2,6-, 3,4- and 3,5-xylenol potassium, etc., wherein n is 3, 2,3,4-,
2,3,5-, 2,3,6-, 2,4,5-, 2,4
6- and 3,4,5-trimethyl potassium phenoxide and the like.

In the present invention, as the compound represented by the above formula I, potassium 2,4,6-tri-substituted phenol having substituents at least at 2,4 and 6-positions may be used. Unlike other substituted phenol potassiums, they are inert to carbonation by themselves, which makes potassium supplementation easier.

Further, as the compound represented by the above formula I,
A compound derived from tar dry acid by-products of coal carbonization or cresylic acid can also be preferably used.

Further, in recent years, as a by-product in the synthesis of orthoalkylphenol or 2,6-dialkylphenol, which is a raw material for polymer, these positional isomers and polyalkyl compounds have been obtained. Since such a by-product is inexpensive, it can be used as the compound represented by the above formula I after forming a potassium salt, which is also an effective use of such a by-product.

As will be described later, the potassium atom in the compound represented by the formula I is transferred to potassium parahydroxybenzoate produced by the rearrangement reaction of potassium salicylate,
This produces dipotassium parahydroxybenzoate. Therefore, as the compound represented by the above formula I, a compound whose pKa value of its free acid is larger than the pKa value of the hydroxy group of parahydroxybenzoic acid (pK2 = 9.23) is
Such potassium transfer is preferable because it is advantageous.

In the present invention, the compounds represented by the above formula I may be used alone or in combination of two or more kinds.

The amount of the compound represented by the formula I used is not particularly limited, but is preferably 0.5 to 3 times equivalent, more preferably 0.8 to 1.2 times, as the number of equivalents of potassium with respect to potassium salicylate. Use equivalent amount. If it is less than this, the effect will be small, and if it is more, it will be useless.

In the present invention, the step of causing rearrangement reaction of potassium salicylate in the presence of the compound represented by the above formula I is performed. Next, this rearrangement reaction will be described.

The rearrangement reaction is carried out under heating. The reaction temperature at that time is usually 200 ° C. or higher, but 230
The temperature is preferably ~ 450 ° C. According to the research conducted by the present inventors, potassium salicylate has a peak at 246 ° C.
Decomposes above ℃. When the reaction is carried out in the temperature range of 230 ° C. or higher, potassium salicylate is decarboxylated or the rearrangement to potassium parahydroxybenzoate is more advantageously carried out. The potassium parahydroxybenzoate produced by such rearrangement obtains potassium derived from the compound represented by the above formula I and becomes dipotassium parahydroxybenzoate (main product) having high heat stability. Even the di-potassium salt of para-hydroxybenzoic acid becomes unstable in the temperature range higher than around 454 ° C, and decomposed products increase. Therefore, at 230-450 ° C,
It is advisable to carry out the rearrangement reaction of potassium salicylate.

Further, the rearrangement reaction is carried out by carbon dioxide and / or
Alternatively, the rearrangement reaction is preferably performed in an atmosphere of an inert gas. This is also effective in preventing the raw materials and products from being decomposed by oxidation or moisture. Examples of such a gas inert to the reaction include nitrogen, helium, argon, hydrocarbons and the like, but nitrogen and the like are preferable. On the other hand, from the viewpoint of the rearrangement reaction, a lower partial pressure of carbon dioxide is more advantageous in order to make the elimination of the carboxyl group from potassium salicylate advantageous, but the eliminated carbon dioxide is paralyzed again in the phenol ring. A higher carbon dioxide partial pressure seems to be advantageous in order to attack the position. Therefore, in the method of the present invention, it is preferable to carry out the rearrangement reaction under a certain carbon dioxide pressure.

The preferable partial pressure of carbon dioxide is 0 to 50 kg / cm ² (G), and the more preferable partial pressure of carbon dioxide is 0 to 10 kg / cm ² (G). I can.

The rearrangement reaction may be carried out using a reaction medium inert to the reaction, but can also be carried out without using a reaction medium. In particular, when the reaction temperature is equal to or higher than the mixed melting point of potassium salicylate and the compound represented by the above formula I,
Since the raw material system becomes liquid due to the melting point lowering phenomenon, not only the method using the reaction medium but also the method not using the reaction medium provides easy reaction because satisfactory stirring can be obtained.

When an inert medium is used in the reaction, for example, an aromatic hydrocarbon, an aromatic ether, an aromatic alkane, an aromatic alkene, or a hydride thereof,
Alternatively, an aliphatic petroleum hydrocarbon, an aprotic polar solvent, an aromatic alcohol, a higher alcohol or the like may be used. These reaction media may be used alone or in combination of two or more as a mixed medium.

Specific examples of the reaction medium include biphenyl, terphenyl, naphthalene, anthracene, ditolylethane, dibenzyltoluene, methylnaphthalene, isopropylnaphthalene, GS250 (a mixture of aromatic compounds containing methylnaphthalene as a main component) and NeoSK. −
oil (media made by Soken Chemical Industry Co., Ltd.), Dowtherm (mixture of biphenyl and diphenyl ether), ethylbiphenyl,
Diphenyl ether, hydrogenated terphenyl, benzoylphenyl ether, benzophenone, acetophenone,
Kerosene and / or gas oil with a boiling point of 150 ° C or higher, N, N-
Examples thereof include dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, higher alcohols having 5 to 15 carbon atoms, and mixtures thereof.

The reaction medium used in the rearrangement reaction is preferably one in which potassium salicylate, the compound represented by the above formula I or the potassium salt of parahydroxybenzoic acid is difficult to dissolve. If a substance that dissolves these is used, the control of the orientation becomes stronger, and the selectivity is lowered. Further, in consideration of the treatment after the reaction, it is insoluble or hardly soluble in water,
Those which are liquid at a temperature of ℃ or above are preferable, and those which are liquid at room temperature or above are more convenient. Further, from the viewpoint of easy control of the reaction pressure, one having a high boiling point is preferable, and one having a boiling point of 200 ° C. or higher is more preferable.

Specifically, light oil having a boiling point of 250 ° C. or higher,
NeoSK-oil, Dowtherm, isopropylnaphthalene, hydrogenated terphenyl, etc. are exemplified as suitable reaction media.

It is preferable to stir the reaction system regardless of the presence of the reaction medium, and it is preferable to perform high-speed rotation and / or vigorous shaking in order to improve the contact of the contents and to reduce the temperature distribution. It is more preferable to set the conditions for producing turbulent flow.

In the rearrangement reaction, the compound represented by the above formula I becomes a corresponding free acid (substituted phenols) after releasing potassium, and the presence of this forms a new equilibrium system. Therefore, it is preferable to remove the generated free acid out of the system. This also facilitates control of the carbon dioxide partial pressure when the rearrangement reaction is carried out in a carbon dioxide atmosphere. Therefore, in the method of the present invention,
The rearrangement reaction is carried out in the circulation and / or circulation system of carbon dioxide and / or a gas inert to the reaction, and the substituted phenols and / or phenol, which are by-produced as the reaction proceeds, are collected outside the system. It is preferable to carry out while removing.

The free acids (substituted phenols) and phenol corresponding to the compound of the above formula I removed outside the system can also be recovered and reused.

In the present invention, the step of carrying out the rearrangement reaction of potassium salicylate may be carried out by either a batch method, a continuous method or a combination of both methods.
From the viewpoint of industrial significance, the continuous method is preferable.

When a reaction product containing dipotassium parahydroxybenzoate as a main product is thus obtained, it is acidified with a mineral acid or the like by a generally known method to give a free carboxylic acid. Parahydroxybenzoic acid is obtained.

The compound represented by the above formula I can be prepared by reacting the corresponding free acid with potassium hydroxide, potassium carbonate and / or potassium hydrogen carbonate in water or a lower alcohol and then drying. Since it can be prepared by the method, the step of removing the free acid from the above-mentioned rearrangement reaction system, derivatizing it to the compound represented by the above formula I, and returning it again to the rearrangement reaction system is also continuous to the production method of the present invention. Can be taken into.

[0046]

EXAMPLES The present invention will be specifically described below based on examples. In addition, the quantification in the examples was performed by chromatography, and displayed based on the number of moles of potassium salicylate charged.

Example 1 8.81 g of potassium salicylate in the form of dry powder, 8.74 g of potassium 2,4,6-trimethylphenol and 27 ml of NeoSK-140.
0 was charged in a pressure resistant reactor and reacted at a carbon dioxide pressure of 6 kg / cm ² (G) at 250 ° C. for 1 hour while stirring at 1000 rpm. After the reaction, the reaction product was acidified and analyzed by a conventional method. As a result, the yield of parahydroxybenzoic acid was 75.4%.

Example 2 8.80 g of potassium salicylate in the form of dry powder and 7.33 g of potassium orthocresol
And 25 ml of NeoSK-1400 were charged into a pressure resistant reactor at 300 ° C. under a carbon dioxide pressure of 4 kg / cm ² (G).
The reaction was carried out for 1 hour with stirring at 1000 rpm.
After the reaction, the reaction product was acidified and analyzed by a conventional method. As a result, the yield of parahydroxybenzoic acid was 75.7%.

(Example 3) 8.81 g of potassium salicylate in the form of a dry powder, 7.35 g of metacresol potassium and 25 g of NeoSK-1400 were charged into a pressure resistant reactor, and 300 kg of carbon dioxide was applied under a pressure of 9 kg / cm ² (G). 1 at ℃
The reaction was carried out while stirring at 1000 rpm for a period of time. After the reaction, the reaction product was acidified and analyzed by a conventional method. As a result, the yield of parahydroxybenzoic acid was 73.1%.

(Example 4) 8.82 g of potassium salicylate in the form of dry powder, 7.35 g of para-cresol potassium and 25 ml of NeoSK-1400 were charged into a pressure resistant reactor, and 300 kg of carbon dioxide was applied under a pressure of 3 kg / cm ² (G). The reaction was carried out at 1000C for 1 hour with stirring at 1000 rpm. After the reaction, the reaction product was acidified and analyzed by a conventional method. As a result, the yield of parahydroxybenzoic acid was 89.9%.

(Example 5) Dry powdery potassium salicylate (8.83 g), paracresol potassium (7.34 g) and 25 g of NeoSK-1400 were charged into a pressure resistant reactor, and carbon dioxide pressure of 14 kg / cm ² (G) was applied to 290. The reaction was carried out at 1000C for 1 hour with stirring at 1000 rpm. After the reaction, the reaction product was acidified and analyzed by a conventional method. As a result, the yield of parahydroxybenzoic acid was 71.8%.

[0052]

INDUSTRIAL APPLICABILITY The present invention provides a novel method for producing para-hydroxybenzoic acid, which is useful as a raw material for polymer materials and medicines and agricultural chemicals, in an unprecedentedly high yield, using potassium salicylate as a raw material. Is. Therefore, according to the present invention, parahydroxybenzoic acid can be efficiently obtained from potassium salicylate, which was an intermediate or by-product of the Kolbe-Schmidt reaction.

Claims (5)

[Claims] 1. A process for producing parahydroxybenzoic acid, which comprises a step of causing a rearrangement reaction of potassium salicylate in the presence of at least one compound represented by the following formula I. [Chemical 1] (In the above formula I, R is a substituent inert to the rearrangement reaction of potassium salicylate, n is an integer of 1 to 5. When n is 2 to 5, R may be the same or different from each other. Good.) 2. The process for producing para-hydroxybenzoic acid according to claim 1, wherein the step of rearrangement reaction of potassium salicylate is carried out at 230 to 450 ° C. 3. The method for producing para-hydroxybenzoic acid according to claim 1, wherein the step of causing rearrangement reaction of potassium salicylate is carried out under an atmosphere of carbon dioxide and / or a gas inert to the rearrangement reaction. 4. The method for producing parahydroxybenzoic acid according to claim 1, wherein the step of causing rearrangement reaction of potassium salicylate is carried out in a medium inert to the reaction. 5. The method for producing parahydroxybenzoic acid according to claim 1, wherein the compound represented by the formula I is at least one kind of mono-, di-, and trialkylphenol potassium.