DE2101992A1 - 4-alkyl-pyrocatechols prodn - by oxidation of 4-alkyl- phenols - Google Patents

Abstract

4-Alkylpyrocatechols of formula (I):- (where R is Me, Et, n.Pr or t-Bu), which are useful as antioxidants, are prepared by reacting a corresponding 4-alkylphenol with a mixture of H2O2 and a saturated is not >4 C aliphatic carboxylic acid (pref. formic or acetic acid) at 50-150 degrees C (pref. 60-110 degrees C). The 4-alkylphenol should be used in large excess so as to avoid over-oxidation of (I). The presence of catalytic amounts of H3PO4 increases teh yield of (I).

Description

Process for the preparation of 4-alkyl-substituted catechols The present invention relates to a process for the preparation of 4-alkyl-substituted catechols of the formula where R = methyl, ethyl, n-propyl, n-butyl or tert-butyl.

In chemical engineering, 4-alkyl catechols have antioxidants big meaning. They are used to stabilize organic compounds such as e.g. aldehydes, gasolines and olefin hydrocarbons to prevent their self-oxidation and prevent their polymerization. For the stabilization of gasoline is 4-methylpyrocatechol is particularly suitable (DBP 1 016 264), while e.g. 4-tert.-butylpyrocatechol mainly used to stabilize monomereo butadiene and styrene.

So far, 4-methylpyrocatechol has been obtained by isolation made from brown coal tar, which is also a natural source of catechol represent. Since the process of brown coal smoldering is increasing technical Losing importance, in the future it will be necessary to use 4-methylcatechol synthetically produced.

The production of 4-tert-butyl pyrocatechol, that of all 4-tert-alkyl pyrocatechols Has the greatest technical importance, takes place mainly through the alkylation of Pyrocatechol with tert-butyl chloride or isobutylene in the presence of Frsedel-Crafts catalysts in many variants, the formation of di-tert-butyl catechol as undesirable By-product is difficult to prevent using this method.

Furthermore, 4-tert-butylpyrocatechol from 2-chloro- or bromo-4-tert-butylphenol can be obtained by exchanging the halogen for a hydroxyl group. By cooking of 1 mol of 2-bromo-4-tert-butylphenol with 5.2 mol of NaOH in an approximately 5% aqueous solution in the presence of Cu2 0, 4-tert-butylpyrocatechol is obtained in the above yield (U.S. Patent 1,942,827).

The use of the expensive bromine compound and the need to be in Working with great aqueous dilution make such a process economical unprofitable.

The hydrolysis of 2-chloro-4-tert-butylphenol to tert-butylpyrocatechol takes place at 10-30 Atü and a temperature of 190-260 ° C in the autoclave in the presence of lead hydroxide or of calcium or barium hydroxide (British patent 1 130 188).

Since tert. -Butyl catechol at the required high Hydrolysis temperature is decomposed, stabilization through the formation of the metal salts is necessary. This process is very labor-intensive and requires a lot of equipment Expenditure.

The preparation of the intermediate 2-chloro-4-tert. -butylphenol takes place by chlorination of 4-tert-butylphenol.

It has now been found that 4-alkyl-substituted catechols of the formula mentioned at the outset can be prepared by using a compound of the formula in which R has the meaning given at the outset, with a mixture of hydrogen peroxide and a saturated aliphatic carboxylic acid with up to 4 carbon atoms at temperatures of 50 to 1500C, preferably 60-1100C.

As a short-chain aliphatic carboxylic acid with up to 4 carbon atoms preferably formic acid or acetic acid is used.

The reaction is carried out in such a way that there is a mixture of hydrogen peroxide and a saturated aliphatic carboxylic acid to one Melt or a solution of p-cresol or 4-tert-butylphenol in an oxidation-resistant organic solvents at temperatures from 50 to 1500C, preferably 60 to 1DoOC, can act. It is necessary, the corresponding starting phenol to be used in large excess, otherwise further oxidation of what has already been formed Alkyl catechol takes place. The presence of catalytic amounts of phosphoric acid has the effect of increasing exploitation.

The formed alkyl catechols can from the starting product through fractional distillation can be separated without difficulty; the recovered Alkylphenol can be returned to the oxidation process again. The invention is demonstrated by the following examples.

Example 1: In a 1 liter three-necked flask fitted with a stirrer, internal thermometer and a dropping funnel is provided, 376 g of p-tert-butylphenol are melted and heated to 1000C with the addition of 10 g of formic acid.

A mixture of 39 g of hydrogen peroxide is then added dropwise over the course of 30 minutes (Content 35 percent by weight) and 40 q formic acid and allowed to stir for a further 2 hours. A gas chromatographic analysis of the reaction mixture shows a content of 8% tert-butyl catechol. The reaction product is subjected to fractional vacuum distillation subject. 340 q p-tert-butylphenol is obtained back, which is again used in the oxidation process can be traced back. In addition, 29 g of p-tert-butyl pyrocatechol are obtained Fp. 54t, based on reacted p-tert-butylphenol, this corresponds to a yield of 72.5% of theory of p-tert-butyl catechol.

Example 2: In a 2 liter three-necked flask equipped with a stirrer, reflux condenser and dropping funnel is provided, 376 g of p-tert-butylphenol are added with the addition of 10 g of formic acid dissolved in 400 ml of toluene and heated to 80.degree.

A mixture of 39 g of hydrogen peroxide is then added dropwise over the course of 30 minutes (Content 35 percent by weight) and 40 g of formic acid and stirred for a further 2 hours. After removal of the solvent, the gas chromatographic analysis shows a Content of 8.2% tert-butyl pyrocatechol.

Fractional vacuum distillation gives 336 g of p-tert-butylphenol return. In addition, 30 g of p-tert-butyl pyrocatechol are obtained. Based on what has been implemented p-tert-butylphenol corresponds to a yield of 68% of theory.

Example 3: Using the same procedure as in Example 2, however, with the addition of 2 q orthophosphoric acid, the gas chromatographic results Analysis shows a content of 8.9% tert-butyl catechol. By vacuum distillation 335 g of p-tert-butylphenol are obtained back. In addition, 32 g of tert-butyl catechol are obtained. Based on converted p-tert-butylphenol, this corresponds to a yield of 71% d.Th.

Example 4: In a 2 liter three-necked flask equipped with a stirrer, reflux condenser and a dropping funnel is provided, 270 g of p-cresol are added with the addition of 10 g of formic acid dissolved in 400 ml of toluene and warmed to 080.degree.

A mixture of 39 g of hydrogen peroxide is then added dropwise over the course of 30 minutes (Content 35 percent by weight) and 40 g of formic acid and stirred for a further 2 hours. After removal of the solvent, the gas chromatographic analysis shows a Content of 7.4% 4-methylpyrocatechol.

Fractional vacuum distillation gives back 239 g of p-cresol. In addition, 18 g of 4-methylcatechol are obtained.

Based on converted p-cresol, this corresponds to a yield of 50.6% of theory

Claims (5)

P a t e n t a n s p r ü c h e 1. Process for the preparation of compounds of the formula in which R = methyl, ethyl, n-propyl, n-butyl or tert-butyl, characterized in that a compound of the formula with a mixture of hydrogen peroxide and a saturated aliphatic carboxylic acid with up to 4 carbon atoms at 0 temperatures of 50 to 150 C. 2. The method according to claim 1, characterized in that the implementation is carried out at temperatures of 60 to 1100C. 3. The method according to claims 1 to 2, characterized in that that the starting phenol is used in molten form. 4. The method according to claims 1 to 2, characterized in that that the reaction is carried out in an oxidation-resistant organic solvent will. 5. Process according to claims 1 to 4, characterized in that that the reaction is carried out in the presence of phosphoric acid.