DE1643348C3 - Process for the preparation of phenyl esters from benzene - Google Patents

Description

15th

In DT-PS 15 43 582 there is already a method for Preparation of a »mixture of a phenyl ester and phenol has been proposed in which a mixture of Benzene and saturated aliphatic carboxylic acids as well as oxygen in the gas phase on a supported catalyst is implemented, the palladium and / or platinum and a salt containing a strong base and a weak acid or forms a buffer system with the carboxylic acid used.

It has now been found that phenyl esters can be produced alone if one is in the liquid phase works and uses a palladium catalyst that also contains bismuth and / or tellurium.

The process according to the invention for the preparation of phenyl esters by reacting benzene, saturated aliphatic carboxylic acids and molecular oxygen in the presence of metallic Palladium and a salt formed from a strong base and a weak acid or with the used carboxylic acid forms a buffer system, is characterized in that the reaction in liquid Phase takes place and the palladium bismuth and / or tellurium is or are added.

The oxygen can be supplied in elemental form or in the form of air. With circulation of the reaction components, it is best to use pure or largely pure oxygen.

The starting materials can also be used by others who are profitable of the claimed reaction products contain non-impairing substances, such as, for example saturated hydrocarbons. Noble gases or carbon oxides.

The promoter metals bismuth and tellurium are advantageously obtained in amounts of up to 20 atomic percent on the palladium. A particularly good activity and selectivity of the catalyst can be found achieve when it contains 20 to 40 atomic percent of the promoter metal, based on the palladium.

The metal mixture can be used on its own, but advantageously on a carrier substance which it is as finely distributed as possible. Particularly suitable carrier materials are those with a large size Surface, for example aluminum oxide, aluminum uo silicate, silica gel, coal, zeolites, pumice stone, clays. Feldspars, molecular sieves.

The concentration of the precious metal on the carrier can vary within wide limits. In many cases are extremely low concentrations of the precious metal, e.g. B. 0.1 to 10 percent by weight, based on the total weight of the carrier and catalyst system. However, you also get even phenyl esters at concentrations which are below 0.1 percent by weight, for example down to 0.05 percent by weight or at even lower concentrations. Of course you can also use concentrations work successfully above 10 percent by weight. The application of the precious metal to the carrier takes place according to known methods. The total concentration of active metal (consisting of precious metal and Promoter metal) should be appropriate depending on the nature of the support and its textural properties be chosen so that there is an optimal carrier coverage

In order to achieve the most homogeneous possible distribution between noble metal and promoter metal, the Catalyst expediently prepared by reducing a solution containing both the reducible compounds Noble metal as well as the promoter metal contains, for example, aqueous solutions which contain, side by side, noble metal chlorides or nitrates and chlorides or nitrates of the promoter metals. Of course, one can also start from corresponding salts of these metals with other acids.

In particular, various can be used for the production of the metals or metal mixtures from their salts Use reduction processes. One can in the liquid phase or in the gas phase with inorganic Substances such as sodium borohydride, hydrazine hydrate. Hydrogen or with organic substances such as ethylene. Reduce methanol or ethanol. The salt mixture can also either directly or only after a suitable one Conversion into other, more easily reducible compounds, such as oxides, hydroxides or hydrated oxides Metal level can be reduced.

The additionally used activators can be salts from a strong base and a weak acid, such as B. carbonates or acylates of alkali or alkaline earth metals represent. But you can use it as a Activators also use salts that form a buffer system with the carboxylic acid used in each case form, such as B. sodium phosphates or borax. It has proven to be particularly advantageous if as Activator an alkali salt of the carboxylic acid used in each case is used. In the case of implementation of acetic acid, for example, an alkali acetate is often used. The amount of activator, based on the benzene-carboxylic acid mixture, depending on the solubility of the activator between 5 and 30 percent by weight. It is advantageously between 10 and 20 percent by weight.

The carboxylic acids should as far as possible be anhydrous or used in a mixture with their anhydride will. For example, when using glacial acetic acid, the addition of acetic anhydride in amounts of up to 30 percent by weight, preferably 10 to 15 percent by weight, proven to increase exploitation.

The mixing ratios of the individual reactants can vary within wide limits. In many cases, an excess of benzene and oxygen is used.

The unreacted reaction components benzene, carboxylic acid and oxygen are expedient guided in a cycle.

The pressures are between 1 and 10 atmospheres. The reaction temperature can vary depending on the type of used carboxylic acid and the benzene / carboxylic acid ratio, but also under the influence of others Conditions such as pressure or decomposition temperature of the phenyl ester formed (hydrolysis) vary.

Appropriate course? the reaction at temperatures between 75 and 150 ^° C., preferably not below 90 ^° C. The upper temperature limit depends on the pressure used. She is z. B. in the reaction of benzene and acetic acid at normal pressure and the weight ratio of 1: 4 at 95 to 100 ⁰ C, but can be shifted to higher temperatures by using higher pressures.
The reaction mixtures are worked up by known methods. The catalyst is separated from the reaction mixture and reacted again with the unchanged starting materials. If the activity has decreased after repeated use of the catalyst, it can be reactivated by re-impregnation with appropriate amounts of metal salts and their reduction to the free metals.

Example 1 to

The catalyst is first prepared by reducing an aqueous ethanolic solution or slurry containing palladium chloride and the chloride dos concerned promoter with an excess of sodium borohydride initially at 40 ^° C. and then at 80 to 90 ^° C. and the mixture of the reduced metals isolated

A solution of 20 g benzene, 80 g acetic acid and 9.6 g potassium acetate or a mixture of potassium acetate with another potassium salt is used together with the finely divided catalyst consisting of 2.16 g

Table I.

Palladium and 10 or 20 atomic percent of the promoter metal in question, while stirring and passing through heated under reflux (96 to 98 ° C) of 2.5 1 oxygen per hour

After a reaction time of five hours, after filtering off the catalyst, depending on the used promoter metal different amounts of phenyl acetate from the unreacted benzene-acetic acid mixture Separate by distillation, as can be seen from Table I:

example

Promoter
metal

Aiomprozcni

Phenyl.) Ccuii

yield

(g / 5h) activator

2
3
4th
5
6th

Te
Bi
Bi
Bi
Bi

10
10
10
10
20th

0.15 0.42 0.77 0.88 0.55 1.53 9.6 g KOAc

9.6 g KOAc

9.6 g KOAc

6.2 g KOAc + 3.4 g KHSO4

6.2 g KOAc + 3.4 g KHjPO *

9.6 e KOAc

Apart from traces of CO ₂ , there are no other by-products.

Examples 7 to

20 g of silica gel (grain size 0.075 to 0.25 mm) are impregnated with a solution of 4.75 g of palladium acetate and varying amounts, e.g. 10 atomic percent = 0.985 g of bismuth nitrate · 5 H ₂ O) in 22 ml of semi-concentrated nitric acid while stirring Steam bath dried and then dried in a heatable reaction tube at 200 to 220 ⁰ C while passing through about 5 l / hour nitrogen. The nitrogen is then saturated with methanol at room temperature and the mixture thus obtained is initially a

Table Il

Hour then passed a further hour at 400 to 450 ⁰ C by the impregnated carrier containing raw ·· at 200 to 220 ° C and. The catalyst is ready for use after this reaction and is reacted together with a solution of 80 g of acetic acid, 20 g of benzene and 9.56 g of potassium acetate while passing through 2.51 of oxygen per hour at 97 to 100 ^° C. and with vigorous stirring.

Table II gives the results of Examples 7 to 10 with increasing bismuth concentration:

example

Promolor

Insurance duration atomic percent (hours) Phenyl acetate

Bulge

(G)

Space-time uusbeutc

(g / l K;> l./hour)

7th Bi 10 10 1.64 3.0 8th Bi 20th 10 1.9V 3.7 9 Bi 30th 15th 2.30 4.3 10 Bi 50 10 1.75 3.2

As by-products arise z. B. in Example 9 0.01 g 6s of unreacted acetic acid-benzene mixture.

Phenol and 0.8 g CO ₂ . The work-up is carried out by The filtered catalyst can again for the

Filtering off the catalyst and distillative separation reaction are used, tion of the reaction products phenyl acetate and phenol

Claims (1)

6 43 Claim: Process for the preparation of phenyl esters by converting benzene, saturated aliphatic carboxylic acids and molecular oxygen into Presence of metallic palladium and a salt consisting of a strong base and a weak base Acid has formed or forms a buffer system with the carboxylic acid used, as a result characterized in that the reaction takes place in the liquid phase and the palladium bismuth and / or tellurium is or are added.