DE2044705B2 - PROCESS FOR THE PREPARATION OF THE ALKALINE METAL SALT FROM P-HYDROXYBENZOIC ACID ESTERS - Google Patents

Description

p-Hydroxybenzoic acid esters, especially their anhydrous To develop forms that are simple and economical to carry out and that produce good yields leads

The invention relates to a process for the preparation of the alkali metal salts of p-hydroxybenzoic acid esters the general formula

wherein R is an alkyl radical with up to 10 carbon atoms, an aryi radical with 6 to 10 carbon atoms or an aryi radical with 7 to 10 carbon atoms and M is an alkali metal, characterized in that a p-hydroxybenzoic acid ester of the general formula

wherein R has the meaning given above, with an alkali metal phenoxide at a temperature from room temperature to 250 ⁰ C in an inert organic solvent from the group of hydrocarbons, ethers and ketones or in an excess of up to 20 mol »based on the alkali metal phenoxide, the p -Hydroxybenzoic acid ester converts.

It has now been found that when a p-hydroxybenzoic acid ester is reacted with an alkali phenoxide, which is represented by the following equation Reaction:

ONa

COOCH,

40

45

55

60

runs quantitatively quickly and is hardly influenced by the temperature or the type of solvent and thus an alkali salt of p-hydroxybenzoic acid ester is obtained

The esters of the formula (I) are methyl, ethyl, propyl, phenyl, benzyl and tolyesters of p-hydroxybenzoic acid generally useful, but the methyl and ethyl esters are generally preferred

Sodium phenoxide is used as an alkali phenoxide. Potassium phenoxide or lithium phenoxide is used

The reaction can be carried out either in an inert organic solvent or without use any organic solvent. When not using organic solvent it is preferred that a p-hydroxybenzoic acid ester with an alkali phenoxide is used an excess of up to 20 mol, based on the alkali metal phenoxide, of the p-hydroxybenzoic acid ester is implemented. In this case, the reaction proceeds with the excess of the p-hydroxybenzoic acid ester as Reaction medium and the formed alkali salt of p-hydroxybenzoic acid ester as a mixture with the not obtained converted p-hydroxybenzoic acid, while on the other hand the PHenol formed as a by-product easily separated and removed by distillation under reduced or atmospheric pressure can. The mixture obtained from the p-hydroxybenzoic acid ester alkali salt and the p-hydroxybenzoic acid ester Can be used as such with ethylene oxide or ethylene dihalide to produce 4- (2-hydroxyethoxy) benzoic acid ester or 4,4'-ethylenedioxybisbenzoic acid diester are reacted.

An organic solvent is used as the inertLS organic solvent, which the Phenol dissolves, but not the p-hydroxybenzoic acid ester alkali salt dissolves, for example hydrocarbons such as benzene, toluene, xylene or petroleum hydrocarbons, Ethers, such as ethyl ether, isopropyl ether, isobutyl ether or anisole or ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone or diisobutyl ketone. By These inert organic solvents can be used for the p-hydroxybenzoic acid ester alkali salt formed are generally recovered as a precipitate and the phenol remains in the dissolved state in the inert organic solvent and can be so easily and without great loss by separation with Solvent or by evaporation.

Since no water is formed in this reaction, an alkali salt of an anhydrous p-hydroxybenzoic acid ester can be used using an anhydrous alkali phenoxide. For example the raw material alkali phenoxide does not contain an easily hydrolyzable ester residue, it can at high Temperatures are dried and dehydrated and so an anhydrous alkali phenoxide easily and in can be generated for a very short period of time. Furthermore, the reaction between the alkali phenolate and a p-Hydroxybenzoic acid ester rapidly at low temperatures, making an alkali salt of an anhydrous p-hydroxybenzoic acid ester can be obtained easily.

Furthermore, according to the invention, a water-containing alkali metal phenoxide with up to 50 wt .-%, preferably up to 40% by weight of water can be used as alkali metal phenoxide.

It has been found that in the process of the invention, unlike in the case of direct Reaction of a p-hydroxybenzoic acid ester with an alkali hydroxide, the hydrolysis of the ester residue does not take place, even if an alkali phenoxide with a content of a comparatively large amount of water, z. B. up to 50 wt .-% water, is heated to over 100 ° C. Accordingly, a hydrous

Alkali salt of a p-hydroxybenzoic acid ester easily a water-containing alkali metal phenoxide, which is then essentially converted into a anhydrous alkali salt of a p-hydrobenzoic acid ester can be converted.

The reaction temperature is not particularly limited, and a temperature of from room temperature to 250 ^° C. is generally used; However, if an anhydrous alkali metal phenoxide is used, the reaction temperature should not exceed 150 ° C. ι ο

The invention is illustrated in more detail by the following examples

3 e i s ρ i e 1 1

11.6 g (0.1 mol) of anhydrous sodium phenoxide, 35 g of toluene and 15.2 g (0.1 mol) of methyl p-hydroxybenzoate were mixed with one another, and the mixture was ^{stirred at 100 °} C. for about 15 minutes. After cooling the mixture, the insoluble fraction was separated off by filtration, washed with a small amount of: o toluene and then the remaining toluene was removed by evaporation. There was thus obtained 17.1 g of anhydrous methyl p-hydroxybenzoate sodium salt.

Example 2

61 g (0.4 mol) of methyl p-hydroxybenzoate were melted by heating to 140 ° C, 11.6 g (0.1 mol) anhydrous sodium hydroxide was added and the mixture was allowed to stir at 140 ° C for about Stirred for 15 minutes. By distilling off the free phenol under reduced pressure (1 to 5 mm Hg) was a mixture of 45.7 g of methyl p-hydroxybenzoate and 17.4 g of the sodium salt of anhydrous methyl p-hydroxybenzoate obtain.

Example 3

13.2 g (0.1 mol) of anhydrous potassium phenoxide, 40 g of benzene and 16.6 g (0.1 mol) of ethyl p-hydroxybenzoate were mixed together, the mixture was heated and stirred up for about 30 minutes refluxed in a water bath. After cooling, the insoluble portion was removed by filtration separated, this washed with a small amount of benzene and then evaporated the remaining benzene. Thus 20.9 g of the potassium salt of anhydrous ethyl p-hydroxybenzoate was obtained.

Example 4

58 g (0.35 mol) of ethyl p-hydroxybenzoate were melted by heating to 130 ° C, 11.8 g (0.1 mol) Sodium phenoxide (water content: 2.0%) was added, and the mixture was kept at 130 ° C during stirred for about 15 minutes. By distilling off the free phenol under reduced pressure (1 to 5 mm Hg) was a mixture of 41.5 g of ethyl p-hydroxybenzoate and 18.5 g of the sodium salt of ethyl p-hydroxybenzoate obtain.

Example 5

fio

184 g (1.0 mol) of a 63% strength aqueous solution of sodium phenoxide were mixed with 608 g (4.0 mol) of methyl hydroxybenzoate, and then the mixture was by heating at 120 ° C with stirring while distilling off the water and the implemented free phenol. Then the temperature was increased to 140 ^° C. and the water and the phenol were distilled off further under reduced pressure (1 to 5 mm Hg). Thus 454 g of methyl p-hydroxybenzoate and 171 g of the sodium salt of anhydrous methyl p-hydroxybenzoate were obtained.

Example 6

! 3.2 g (0.1 mol) of anhydrous potassium phenoxide, 40 g of acetone and 19.4 g (0.1 mol) of butyl p-hydroxybenzoate were mixed together, and the mixture was allowed to stand at room temperature for about an hour stirred. The insoluble matter was separated by filtration, it was mixed with a small amount Acetone washed, and then the remaining acetone was evaporated obtained anhydrous butyl p-hydroxybenzoate.

Example 7

11.6 g (0.1 mol) of anhydrous sodium phenoxide, 40 g of isobutyl ether and 25.6 g (0.1 mol) of octyl p-hydroxybenzoate were mixed together, and the mixture was heated and stirred for about Refluxed on a water bath for 30 minutes. After cooling, the insoluble component became separated by filtration, washed with a small amount of isopropyl ether and then the remaining Isopropyl ether evaporated. There was thus obtained 26.4 g of anhydrous octyl p-hydroxybenzoate sodium salt.

Example 8

86 g (0.4 mol) of phenyl p-hydroxybenzoate were melted by heating to 180 ° C, 11.6 g (0.1 mol) anhydrous sodium phenoxide was added and the mixture was allowed to stir at 180 ° C for about Stirred for 15 minutes. By distilling off the free phenol under reduced pressure (1 to 5 mm Hg) was a mixture of 64.2 g of phenyl p-hydroxybenzoate and 23.3 g of the sodium salt of anhydrous phenyl p-hydroxybenzoate obtain.

Example 9

11.6 grams (0.1 moles) of anhydrous sodium phenoxide, 35 grams of methyl ketone, and 22.8 grams (0.1 moles) of benzyl p-hydroxybenzoate were mixed together, the mixture was heated and stirred up for about 30 minutes refluxed in a water bath. After cooling, the insoluble portion was removed by filtration separated, washed with a small amount of methyl ethyl ketone and then the remaining methyl ethyl ketone evaporated. There was thus obtained 24.5 g of anhydrous benzyl p-hydroxybenzoate sodium salt.

Comparative experiments

1. Comparison of the manufacturing processes

the anhydrous sodium salts

of the methyl p-hydroxybenzoate by reaction

of sodium hydroxide or sodium methoxide or

Sodium phenoxide with p-hydroxybenzoic acid methyl

ester

A. 45.7 g of methyl p-hydroxybenzoate (purity 99.8%) became (1) 12.4 g sodium hydroxide (purity 96.8%), (2) 16.4 g sodium methoxide (purity 98.8%) and (3) Added to a mixture of 35.0 g of sodium phenoxide (purity 99.4%) and 139 g of toluene. Each of the three mixtures was ^{heated to 100 °} C. for 15 min with stirring. The insoluble fraction was separated off by filtration, the product with a small

Washed amount of ethyl ether and then dried at 1 torr.

The purity of the sodium salt of methyl p-hydroxybenzoate was calculated as follows: First, the content of sodium p-hydroxybenzoate was calculated by titration in an acetone-methanol

Table 1

Solution (volume ratio 9: 1) with 0.1 n-HCl (in a Methanol-benzene mixture, volume ratio 1: 4) measured. Then the water content according to the Karl Fischer method determined. The purity was shown by forming the difference against 100%. The results are given in Table 1.

Test run
No.

Sodium salt of p-hydroxybenzoic acid methyl ester Weight purity

Sodium p-hydroxybenzoate

Water content

yield

(0/0)

51.2
51.6
51.7

88.8
92.1
99.7

10.7 7.3 0.2 1.08
0.56
0.09

87.1
91.0
98.8

From Table 1 it can be seen that the yield and purity of the product drop significantly when the Alkali salt of the ester using alkali hydroxide or alkali alcoholate and a solvent (like toluene) is produced.

B. 35.0 g of sodium phenoxide (purity 99.4%) were added to (a) 100 g of methanol or (b) 300 g of methanol dissolved 45.6 g of methyl p-hydroxybenzoate (purity 99.8%) were added to each solution. then the mixture was stirred at room temperature for one hour. In experiment (a) a small amount fell Sodium salt of p-hydroxybenzoic acid methyl ester. This was filtered off and the hydrate was with washed a small amount of ethyl ether, dried at 1 torr and at a certain temperature and concentrated under a certain vacuum. 140 g of ethyl ether were added to the residue. the Mixture was washed, filtered and at 1 torr

Table 2

dried.

Since no precipitate formed in experiment (b), the filtrate was vacuum and at a certain Temperature concentrated. 140 g of ethyl ether were added to the residue; the mixture was washed, filtered and dried at 1 torr.

The purity of the obtained sodium salt of methyl p-hydroxybenzoate became as follows Calculated: First the content of sodium p-hydroxybenzoate was determined by titration in a Acetone-methanol solution (volume ratio 9: 1) with 0.1 N HCl (in a methanol-benzene mixture; volume ratio 1: 4) measured. The water content was then determined by the Karl Fischer method The purity was determined by subtracting from 100%. The results obtained are in the table 2 compiled

solvent

Unusual Na salt des
methyl p-hydroxybenzenate

Purity yield

weight
(G)

Conditions of mother liquor concentration

Pressure temperature time (mm Hg) ( ⁰ C) (h)

Mother liquor (Na salt des
methyl p-hydroxybenzoate

Weight purity yield
(g) (%) (%)

(a) 10.2
10.2 99.3
99.3 19.6
19.6 100-1
200-1 20th
50 21
6th 40.3
39.4 91.5
75.9 72.1
58.6 (b) 0
0 100-1
200-1 20th
50 21
6th 51.3
50.2 91.9
76.1 90,:?
73.2

From Table 2 it can be seen that the use of alcohol, dimethanol as a solvent in the implementation of methyl p-hydroxybenzoate with sodium phenolate is not appropriate

From the experiments under A. and B. it follows that at the preparation of the alkali salt of p-hydroxybenzoic acid ester with alkali hydroxide or alkali alcoholate and a solvent according to the present invention, the yield and purity of the product are extraordinarily bad. Besides, the Use of alcohol, such as methanol, on sodium phenate unsuitable as an alkalizing agent

IL Manufacture of disodium p-hydroxybenzoate

by converting sodium phenolate

with monosodium p-hydroxybenzoate

A. 48.2 g of monosodium p-hydroxybenzoate (purity 39%) and 35.0 g of sodium phenolate (purity 99.4%) were poured into 40 g of toluene with stirring. Isopropyl ether and methyl isobutyl ketone at 100 ⁰ C and 50 ⁰ C and 110 ⁰ C heated after cooling was the undissolved substance was filtered off, to remove the Nairiumphenolats with a mixture of ethyl ether and methanol (volume ratio 20: 1), and then: when 1 Torr dried. The proportions of monosodium p-hydroxybenzoate and disodium p-hydroxybenzoate in the residue were determined by titration with 0.1 η-HCl (in a methanol-benzene mixture; volume ratio 1: 4) in an acetone-methanol solution (Volume ratio 9: 1) determined ^

B. 45.7 g of p-Hydroxvbenzoesäuremethylester (purity 99.8%) and 35.0 g of sodium (purity 99.4%) was one hour with stirring in 140 g of toluene, isopropyl ether and methyl isobutyl ketone at 100 ⁰ C and 50 ° C and RO ⁰ C heated. After cooling, the undissolved substance was filtered off, washed with a small amount of ethyl ether and then dried at 1 Torr.

980

The salt of p-hydroxybenzoic acid methyl ester was determined by titration with 0.1 N HCl (in a methanol-benzene mixture; Volume ratio 1: 4) in an acetone-methanol solution (volume ratio 9: 1) geTable 3

10

measure up. Then the yield was calculated.

The results of experiments A. and B. are compiled in Tables 3 and 4.

solvent temperature Time Monosodium p-hydroxy
benzoate Disodium p-hydroxy
benzoate (° / o) (• C) (H) (Mol%) (Mol%) toluene
Isopropyl ether
M ethyl isobutyl ketone 100
50
110 1
1
1 59.8
65.5
58.2 40.2
34.5
41.8 Table 4 solvent temperature Time Na salt of p-hydroxybenzoic acid methyl ester
Weight purity yield CQ (H) (g) (%)

toluene 100 1 51.5 99.5 98.1 Isopropyl ether 50 1 51.9 99.6 99.0 Methyl isobutyl ketone 110 1 51.2 99.1 97.2

From Tables 3 and 4 it can be seen that the salt formation of the phenolic OH groups by Conversion of monosodium p-hydroxybenzoate with sodium phenolate in the three specified solvents only progresses to a level of about 40%. In contrast, the neutralization of the p-hydroxybenzoic acid methyl ester gives with sodium phenolate a yield of more than 97%.

980

Claims (2)

Patent claims: 1. Process for the preparation of the alkali metal salts of p-hydroxybenzoic acid esters of the general formula COOR where R is an alkyl radical with up to 10 carbon atoms, an aryl radical with 6 to 10 carbon atoms or an aralkyl radical with 7 to 10 carbon atoms and M is an alkali metal, characterized in that a p-hydroxybenzoic acid ester of the general formula COOR 25th OH wherein R has the meaning given above, with an alkali metal phenoxide at a temperature from room temperature to 250 ⁰ C in an inert organic solvent from the group of hydrocarbons, ethers and ketones or in an excess of up to 20 mol, based on the alkali metal phenoxide, of the p -Hydroxybenzoic acid ester converts 2. The method according to claim 1, characterized in that the alkali metal phenoxide is an anhydrous alkali metal phenoxide or an alkali metal phenoxide contains no more than 50% by weight of water. 50 There are various processes for preparing alkali salts of p-hydroxybenzoic acid esters, particularly their anhydrous forms, but so far have been no process for the preparation of alkali salts of anhydrous p-hydroxybenzoic acid esters known which can be carried out easily and with little effort. For example, an alkali salt becomes an anhydrous p-Hydroxybenzoic acid ester in the production of 4,4 '- (ethylenedioxy) -bisbenzoic acid ester and 4- (2-hydroxyethoxy) -benzoic acid ester, which raw materials for synthetic fibers and plastics are used. To produce this alkali salt of p-hydroxybenzoic acid esters, a p-hydroxybenzoic acid ester is reacted with an alkali metal hydroxide solution and subsequently dehydrated. The drying of the reaction product occurs at as low as possible temperature while preventing hydrolysis of the reaction product. However, since this Method limits the working temperature to comparatively low temperatures, such as the Rauini temperature a large amount of water is required due to the solubility of the desired compound and the amount of water to be evaporated large, so that thermal economic problems arise and a require long periods of time in excess of 20 hours for operation, which brings complications Further, a process for the preparation of the alkali salts of p-hydroxybenzoic acid esters is by Conversion of metal alcoholates with phenol esters is known, the salt formation taking place with the aid of alkali metal. The metal alcoholate is produced by dissolving the alkali metal in alcohol and then dissolving it Solution for the preparation of the alkali salt is reacted with the p-hydroxybenzoic acid ester. In this process, the alkalizing agent used is alkali hydroxide or alkali alcoholate By using alcohol as a solvent, the alkali salt of the ester formed remains in solution, so that subsequent precipitation or distillation is necessary In this known process, losses in yield arise as a result of saponification and the necessary Distillation of the solvent through local overheating. In addition, relatively impure products are obtained. For the reasons mentioned, this method is unsuitable for large-scale production The phenolic OH group is also known of sodium salicylate to neutralize with sodium phenoxide. However, this is a salt of Salicylic acid and not an ester, whereby here the neutralization of the phenolic OH group with Sodium phenate is not quantitative Tests have shown that the known processes and reactions do not affect the technical preparation of alkali salts of p-hydroxybenzoic acid esters can be used because impure products or low yields are obtained, like the comparative experiments show at the end of this description. Finally, there is a method from DT-OS 19 07 230 known for the preparation of sodium or potassium salts of anhydrous p-hydroxybenzoic acid esters by catalytic neutralization of a p-hydroxybenzoic acid ester with sodium hydroxide. Here is a Sodium or potassium hydrate of p-hydroxybenzoic acid ester obtained, which then on a Temperature below the melting point of the hydrate must be dried under reduced pressure in order to get to the End product to arrive. As the examples of this publication show, it is necessary to prepare the sodium salt hydrate of p-hydroxybenzoic acid methyl ester to 3 ° C to - 10 ° C to cool, which takes a long time of about Takes 15 hours. In addition, the hydrate must then over the course of 11 to 18 hours to be dried. So in order to get from the starting compounds to the end product, this is required Total procedure approximately 26 to 33 hours. In addition, this known process results in relatively low yields of the sodium salt hydrate of the p-hydroxybenzoic acid ester obtained, which are of the order of about 65%. This product must then still be isolated from the mother liquor. Overall, this process is time-consuming and leads to low yields. The object of the invention is to provide a technical process for the production of alkali salts of