DE1518350B - Process for the production of phenol by the oxidative decarboxylation of benzoic acid - Google Patents

Description

The invention relates to the production of phenol by the oxidative decarboxylation of benzoic acid.

U.S. Patents 2,762,838 and 2,766,294 describe a process in which aromatic Monocarboxylic acids in the liquid phase with the help of gases containing molecular oxygen in Presence of a copper compound can be oxidized to esters, from which phenols are formed by hydrolysis will. A separate hydrolysis stage can be avoided by carrying out the reaction in Presence of water. Furthermore, the required copper connection, in particular Copper (II) oxide, are formed in the reaction zone from metallic copper.

U.S. Patents 2,727,924, 2,727,926 and 2,852,567 with the same filing date relate also on the production of phenols from aromatic carboxylic acids with the help of copper compounds.

Of these patents, 2,727,924 relates to the oxidative decarboxylation of certain dicarboxylic acids and substituted benzoic acids a reaction which occurs in both the liquid phase and the gas phase can be carried out using a copper (II) compound as the copper compound; the The oxidation state of the copper (II) compound is maintained by the presence of oxygen. Furthermore, the presence of water vapor reduces the amount of undesired by-products and the Limited tar formation. The oxidative decarboxylation of benzoic acid is described in this patent not treated.

US Pat. No. 2,852,567 particularly describes the oxidative decarboxylation of monocarboxylic acids described, which can also take place in both the liquid and the gas phase, wherein as copper (II) compound, in particular copper (II) oxide is used. According to this procedure, the monocarboxylic acid in the absence of molecular oxygen at a temperature of 200 to 400 ° C brought to react with copper (II) oxide, the copper (II) oxide to copper (I) oxide and Copper is reduced, after which this reduced product in a separate oxidation zone with molecular Oxygen is oxidized again to copper (II) oxide, which is again one with the carboxylic acid Response received. The formation of undesired by-products can be reduced by using the Performs reaction in the presence of water vapor.

In the aforementioned US Pat. No. Π21926 (Reissue 24 848) it is reported that in the case of a production of phenol according to the process of the aforementioned US Pat. No. 2,852,567 by reaction of benzoic acid with cupric oxide at a temperature of 200 to 400 ° C phenol yields of 20 to 65%, based on reacted benzoic acid, can be achieved; so there are considerable losses due to the formation of tar-like products.

ίο This very annoying and disadvantageous tar formation can, as can be seen in US Pat. No. 2,727,926, be reduced by reducing the oxidation and the decarboxylation of aromatic monocarboxylic acids, especially benzoic acid, in the liquid Phase with molecular oxygen in the presence of water vapor and a copper (II) compound dissolved in the liquid reaction mixture. The dissolved copper (II) compound, in particular the benzoate, is formed in the reaction mixture Addition of metallic copper, copper (I) oxide, copper (II) oxide or a copper salt to this Mixture, whereupon at least partially by reaction with the oxygen and the carboxylic acid to be oxidized a conversion to the required dissolved copper (II) compound takes place.

Although the aim of the process of the last-mentioned patent specification is to reduce tar formation is, a noticeable tar formation sets in anyway, so that with one of the phenol production detrimental accumulation of tar is to be expected in the reactor (see column 4, lines 33 to 41).

U.S. Patent No. 2,954,407, according to which this tar can be extracted with water in order to avoid losses of the valuable substances contained in the tar to restrict.

It has now been found that it is possible to avoid this disruptive tar formation, which thus means a solution to this difficult problem which occurs in the oxidative decarboxylation of benzoic acid and which has significant advantages when it is carried out on an industrial scale. It has been found that in the production of phenol by oxidative decarboxylation of benzoic acid with the aid of a molecular oxygen-containing gas and water vapor at temperatures of 200 to 400 ⁰ C in the presence of a copper catalyst, the advantages mentioned are obtained if benzoic acid vapor is used together with the oxygen-containing gas and brings water vapor into contact with metallic copper.

The copper provided as a catalyst in the process according to the invention is preferably used in finely divided form used. It is advisable to apply this finely divided copper metal to a carrier, which is not detrimental to the reaction, such as the oxides of zinc, calcium, aluminum, titanium, Cadmium, magnesium, barium, cerium or silicon. Some of these oxides are from those mentioned above Patents known that they act as a promoter of copper compounds reacting with the oxygen-containing Pumping gas.

Preferably, the copper metal is applied to magnesium oxide because such a catalyst is a has a large catalytic surface and good stability.

The copper content of the catalyst can vary within wide limits and, for example, 5, 10, 25,

1 Ö1Ö DOU

3 4

40, 50, 75 or 100 percent by weight. The B e i s d i e 1 1

Copper content is usually 40 to 60 weight

Percent applied. In a tubular reactor (diameter

In the method according to the invention, the 22 mm) acts as a 50 cm ³ of copper on magnetic-metallic copper as a catalyst; it remains unchanged after the ammonium oxide (50 percent by weight copper) has existed during the reaction. Catalyst at a temperature of 250 ° C

Benzoic acid can easily be kept in vapor form, while benzoic acid vapor (formed when bringing, for example, water vapor or an inert gas such as nitric acid), water vapor and air through the pipe through molten benzoic acid led fabric, leads. Also molecular oxygen-containing io. There are given every hour: gases for which z. B. oxygen, air or other 35.8 g of benzoic acid, 5.51 nitrogen, 3.25 liters of air and mixtures of oxygen and inert gases, such as water vapor (gas quantities measured at 2O ⁰ C nitrogen, can be used by molten and 1 at).

zene benzoic acid or with the Ben- As can be seen, 2.0 g of the hourly

zoesäuredampf be mixed. If desired, 15 given benzoic acid can be implemented, resulting in sales

the vapors and gases also correspond individually in the reaction of 5.5 ° / _0,

space can be introduced. The result of the implementation per hour is:

The reaction in which the oxidation and the _{DepheQol 1Q2 (3? Mol ent)}

carried out carbonylation of benzoic acid, in _D ip _{henyläther 0,} 03 g 0.12 mole)

carried out at a temperature of 200 to 400 C Be ₁ * o _Diph 1 _{0 09 0 39 mol percent} )

a reaction takes place at higher temperatures phenyl benzoate 0.37 g (1.28 mol percent)

instead, it is then however undesirable with the formation.

Tar products to be expected. An increased pressure is over- Calculated on the converted benzoic acid amounts

liquid, because the reaction takes place in a simple manner at atmo- the phenol yield (an additional half of the

spherical printing can be performed. 25 phenyl benzoate yield) to 89.5 ° / ₀ .

Furthermore, the method according to the invention
can easily be carried out in continuous operation, for example by adding benzoic acid vapor, water vapor Example 2 and the oxygen-containing gas together in the

mentioned temperature by a catalyst mass 30 The experiment described in Example 1 is repeated, which in a reaction chamber on the required, but with the difference that the temperature borrowed temperature is maintained. is now 275 ^° C.

The phenol can be in a known manner, e.g. B. by It shows that in this way 3.4 g of the hourly

Condensation and distillation, converted from the reaction abandoned amount of benzoic acid (35.8 g)

win product. Furthermore, benzoic acid can become from the 35, corresponding to a degree of conversion of

Reaction product excreted and anew 9.6%.

be set. The result of this implementation per hour is:

The phenol reaction product contains 1 93 g (7 mol percent) as by-products

mostly phenyl benzoate, diphenyl ether and diphenyl. Diphenyl ether '.'. '.'. '.'. '.'. 0 ^ 03 g (0.11 mole percent)

You need these valuable products per se not 40 _D i _phenyl i _0, 07 g (0.29 mol)

can be obtained individually because these products, like the phenyl benzoate, 0.65 g (22-22 mole percent)

unreacted benzoic acid, preferably again m

The yield of phenol (an additional half of the

the phenol yield leads. Phenyl benzoate yield) amounts to 95.4%

Claims (2)

Patent claims: 1. Process for the preparation of phenol by oxidative decarboxylation of benzoic acid with Using a gas containing molecular oxygen and water vapor at temperatures of 200 to 400 ° C in the presence of a copper catalyst, characterized in that one benzoic acid vapor together with the oxygen-containing gas and water vapor with metallic Brings copper into contact. 2. The method according to claim 1, characterized in that the copper is on a carrier, preferably made of magnesium oxide.