DE2513952C2 - PROCESS FOR THE PRODUCTION OF MONOCHLOROBENZOIC ACIDS - Google Patents

Description

From US-PS 18 78463 it is known o- and p-chlorobenzotrichloride in the presence of iron (III) chloride as a catalyst in a first stage with the saponify equimolar amount of water to o- and p-chlorobenzoyl chloride and then in one second stage to saponify with water or aqueous alkali solution to o- and p-chlorobenzoic acid. Here is the Addition of the catalyst only necessary for the reaction of the chlorobenzotrichloride to chlorobenzoyl chloride; It is, however, essential that anhydrous iron (III) chloride is added to the chlorobenzene trichloride before the addition of water. rid is added, since iron (III) chloride dissolved in water shows no catalytic effect The overall yield of the process is about 78% of theory, the yield of the first catalyzed stage of the process being about 83% of theory

There has now been a process for the preparation of monochlorobenzoic acids by reacting monochlorobenzotrichlorides with water in the presence of iron salts found, which is characterized by that the iron salts are water-soluble iron (H) salts begins and the reaction is carried out in the presence of water-immiscible solvents

In general, the erfmdungsgemäße method in the temperature range of 80 to 14O ⁰ C, preferably between ■ SO and 13O ⁰ C _1, in particular between 95 and 125 C carried out

Take p-chlorobenzotrichloride as an example Process according to the invention explained by the following reaction scheme:

Cl

+ 2H ₂ O

COOH + 3HCI

45

(- 3cnen be in the form of water-soluble ,, 4Eisen {!!} !!) - The Monochlorbenzotrichloride, namely o-, m- and p-Chlorbenzotrichlorkl known ι Eissn Sa zen used ", the associated anion is not essential!. That will be advantageous; f Iron (II) salt in the required amount before the start of the reaction dissolved in the water to be used in the reaction, so that iron (H) ions and water in the form of a dilute aqueous iron (! I) salt! Find solution use, preferably with a content of about 0.005 to 0.5 percent by weight, in particular between 0.01 and 0.5 percent by weight of Etsen (II) -SaIz; solutions with a higher content can also be used, but this is generally neither necessary nor expedient.

AJs water-soluble iron ^ ü ^ Saize, the use can be found, for example: Fe (NO3 ^, FeCOi, FeBr ?, FeJ ?, Iron (II) salts are useful used that are easily accessible; FeCb and FeSOi are therefore preferred for use.

In general, the amount of the dilute aqueous iron (ii) salt solution is such that at least the stoichiometrically required amount of 2 moles of water per mole of chlorobenzotrichloride is present. The amount of the aqueous solution is advantageous dimensioned that the excess of water up to 1, OMoI, preferably 0.5, in particular 0.2 mol of water per mol Benzotrichloride is

As a solvent immiscible with water preferably aliphatic and aromatic halogenated hydrocarbons and nitrohydrocarbons such as 1,1,2,2-tetrachloroethane, 1,1,1,2-tetrachloroethane, 1,2-dibromoethane, chlorobenzene. Bromobenzene and nitrobenzene called It can also be advantageous o-, m- and / or to use p-chlorobenzaldehyde as a solvent.

In general, the water-immiscible solvent in an amount of 0.5 to 2.0 is preferred 0.8 to 1.75, in particular 0.9 to 1.6 mol of solvent Chlorobenzotrichloride is used per moi

The starting compounds ο-, m- and p-chlorobenzo-

'trichlond can be used both in pure form and in the form of their ¹ raw products used v / earth; is self-evident

it is also possible to use mixtures of chlorobenzotrichlorides to be used as starting material.

Compared to the known prior art, the method according to the invention has the following advantages.

The hydrolysis of monochlorobenzotrichloride to monochlorobenzoic acid takes place in a one-step process Process whereby the intermediate isolation of the monochlorobenzoyl chloride is saved.

The hydrogen chloride obtained as a by-product in the process according to the invention is pure and can therefore easily be put to further use, for example after absorption in dilute Hydrochloric acid as concentrated hydrochloric acid.

The conversion of the monochlorobenzotrichloride is practically quantitative and that of the monochlorobenzoic acid is obtained in such a purity that further purification is not necessary

Another particular advantage is that instead of the catalyst known from the prior art, namely anhydrous ferric chloride, ferrous ions used in the form of iron (II) salts in aqueous solution; anhydrous iron (III) chloride leaves Because of its well-known hygroscopicity, it is difficult to manufacture and store.

If parts are given in the examples below, they are parts by weight.

example 1

120 parts of p-chlorobenzotrichloride and 50 parts of 1,1,1,2-tetrachloroethane are placed in a 500 ml glass flask equipped with a stirrer, dropping funnel, thermometer and reflux condenser with gas discharge through two water-filled gas collecting bottles connected in series Normaldruch heated to a temperature of about 110 to 12O ⁰ C in the hot reaction mixture, 20 parts of water, are dissolved in which 0.01 part of iron (H) -chIorid, added dropwise, keeping the reaction temperature is maintained at about 110 to 120 ⁹ C . During this process, the splitting off of hydrogen chloride begins immediately and p-chlorobenzoic acid separates out in finely divided form. At a stirrer speed of about 800 rpm, the hydrolysis reaction is over after about 1.6 hours.

34.5 parts (»95% of theory!) hydrogen chloride are collected. Substance and p-chlorobenzoic acid separate out in finely divided form. Depending on the intensity of stirring, the hydrolysis reaction is over after 1.5 to 2 hours. 54.5 parts (-95% of theory) of hydrogen chloride are collected in the absorption traps. The p-chlorobenzoic acid is then filtered off from the solvent, washed with 50 parts of 1,1,1,2-tetrachloroethane and dried. 81 parts (= 99% of theory) of p-chlorobenzoic acid are obtained in the form of a white, fine-grained powder.
Gas chromatographic analysis:

Ρ chlorobenzoic acid content: 99.7%;

Dichlorobenzoic acid content: <0.0.4%.

Example 2

In the apparatus described in Example 1, 120 parts of p-chlorobenzotrichloride with 80 parts of bromobenzene are heated to a temperature of about 115 to 120 ° C. under normal pressure. 20 parts of water, in which 0.03 part of Etsen (H) sulfate are dissolved, are added dropwise to the hot reaction mixture, the aforementioned temperature being maintained. During this process, the splitting off of hydrogen chloride begins immediately and p-chlorobenzoic acid separates out in finely divided form. At a stirrer speed of about 800 rpm, the hydrolysis reaction is complete after about 1.2 hours. 54.0 parts of HCl are collected in the absorption traps. The crude p-chlorobenzoic acid is then taken up in 350 parts of 7 weight percent aqueous sodium hydroxide solution, the organic solvent phase is separated off and the aqueous phase is acidified with 50 weight percent sulfuric acid. The solution is then nitrated, the precipitate is washed free of acid and dried. 80 parts («98% of theory) of p-chlorobenzoic acid are obtained as a snow-white, finely crystalline powder.
Gas chromatographic analysis:

P-chlorobenzoic acid content: 9935%;

Dichlorobenzoic acid content: <9.04%.

Example 3

In the manner described in Example 1 Apparatus 12OTeIIe be o-chlorobenzotrichloride and lOOTeile nitrobenzene under atmospheric pressure to a temperature of about 120 to 125 ⁰ C is heated in the hot reaction mixture is 22 parts of water in which 0.03 part of iron (I I) chloride are dissolved, given while maintaining the temperature. This immediately starts ίο splitting off of hydrogen chloride and o-chlorobenzoic acid separates out in fine crystalline form. At a stirrer speed of about 800 rpm, the hydrolysis reaction has ended after 23 hours. The o-chlorobenzoic acid is then filtered off from the solvent, washed with 30 parts of bromobenzene and dried. 79 parts (97% of theory) of o-chlorobenzoic acid are obtained in the form of a finely crystalline powder.
Gas chromatographic analysis:

O-chlorobenzocic acid content: 99.75%;

Dichlorobenzoic acid content: 0.08%.

Example 4

In the apparatus described in Example 1, 120 parts of m-chlorobenzotrichloride and 90 parts of 1,2-dibromoethane are mixed under normal pressure with 19 parts of water, in which 0.02 parts of ferric chloride are dissolved, to a temperature of initially about 95 ° C. later heated to about 12O ⁰ C In a stirrer speed of about 800 rev / min, the hydrolysis reaction is completed after 1.5 hours after cooling, the precipitated m-chlorobenzoic acid is filtered off from the solvent, with

40 parts of 1,2-dibromoethane were washed and dried. 79 parts (97% of theory) of m-chlorobenzoic acid are obtained in the form of a finely crystalline powder.
Gas chromatographic analysis:
M-chlorobenzoic acid content: 993%;

Dichlorobenzoic acid content: <0.05%.

Claims (1)

Claim: Process for the preparation of Wonochlorbenzoic acids by reacting monochlorobenzotrichlorides with water in the presence of iron salads, characterized in that as Iron salts water-soluble iron (II) salts are used and the reaction in the presence of water immiscible solvents IO