DE1543952B - Process for the production of nitrophenols - Google Patents

Description

The invention relates to a process for the production of nitrophenols by hydrolysis of nitrohalobenzenes, especially for the production of p-nitrophenol by hydrolysis of p-nitrochlorobenzene.

In the commercial production of p-nitrophenol by hydrolysis of p-nitrochlorobenzene with aqueous Alkali and acidification of the sodium p-nitrophenolate formed become intense even in small amounts colored impurities are formed, which greatly reduce the value of the product. So far one is generally proceeded so that air in the process, e.g. B. by purging with nitrogen excluded in order to hold back unwanted side reactions that result from the formation of highly colored Are accompanied by substances which have been attributed to the presence of oxidation products. It was now, however found that the undesirable side reactions resulting in an inferior colored product lead, in fact, practically by the presence of a certain amount of a suitable oxidizing agent can be switched off in the reaction mixture.

The production of nitrophenols by saponification of nitrochlorobenzenes with additives is known of bichromate to protect against resinification. However, this will cause staining Fabrics not prevented.

The invention was based on the object of preventing undesirable formation in the production of nitrophenols By-products which contaminate the product and reduce its value, essentially turn off.

Accordingly, the invention relates to a process for the preparation of nitrophenols, especially p-nitrophenol, by hydrolysis of nitrohalobenzenes, especially p-nitrochlorobenzene, with aqueous alkali metal hydroxide solution at elevated temperature in the presence of an oxidizing agent and subsequent acidification of the alkali nitrophenolate obtained, the characterized in that the hydrolysis is carried out at a temperature in the range from about 100 to 200 ° C while passing through a gas containing molecular oxygen or in the presence of a inorganic or organic peroxide, preferably in an amount of about 0.001 to 0.1 percent by weight, based on the nitrohalobenzene.

A preferred embodiment of the invention consists in that p-nitrochlorobenzene and Sodium hydroxide in intimate contact with either air or with hydrogen peroxide at a temperature converts from about 140 to 180 ° C and wins the p-nitrophenol obtained.

The nitrophenols which can be prepared according to the invention have a benzene ring or fused benzene rings with at least one hydroxyl group attached, in general no more than three nitro groups and one lower alkyl substituent. Examples of nitrophenols that can be prepared according to the invention are p-, m- or o-nitrophenol, 2,4,5- or 2,4,6-trinitrophenol, 2,3-, 2,4-, 2,5- or 2,6-dinitrophenol, 2,4-dinitro-1,3-dihydroxybenzene, 2,4,6-trinitro-1,3-dihydroxybenzene, 2-methyl-3-nitrophenol, 2-methyl-4-nitrophenol, 4-methyl-5-nitrophenol, 2-methyl-5-nitrophenol, 2-methyl-6-nitrophenol, 2-methyl-4,6-dinitrophenol, 3-methyl-4-nitrophenol, 3-methyl-5-nitrophenol, 3-methyl-6-nitrophenol, 3-methyl-2,4,6 -trinitrophenol, 4-methyl-2,6-dinitrophenol, 4-methyl-2-nitrophenol, 4-methyl-3-nitrophenol.

The nitrophenols are produced by hydrolysis of a corresponding halonitrobenzene. To a preferred feature of the invention is e.g. B. p-nitrophenol by hydrolysis of p-nitrochlorobenzene manufactured. Other suitable compounds are 2,3-dinitrochlorobenzene, 2,4- dinitrochlorobenzene, 2,5 - dinitrochlorobenzene,

2,6 - dinitrochlorobenzene, 2,4,5 - trinitrochlorobenzene, 2,4,6 -trinitrochlorobenzene, 2,4- dinitro -1,3 - dichlorobenzene, 2,4,6-trinitro-1,3-dichlorobenzene, 2-methyl

3 - nitrochlorobenzene, 2 - methyl - 4 - nitrochlorobenzene, l-methyl-S-nitrochlorobenzene, 2-methyl-6-nitrochlorobenzene, 2-methyl-4,6-dinitrochlorobenzene, 3-methyl-

4 - nitrochlorobenzene, 3 - methyl - 5 - nitrochlorobenzene, 3 - methyl - 6 - nitrochlorobenzene, 3 - methyl - 2,4,6 - trinitrochlorobenzene and preferably o-, m- and p-nitrochlorobenzene.

In addition to the halogenated nitrobenzene compounds explained above, corresponding Bromine, fluorine or iodine compounds are used. However, these other halogen compounds are im generally not as readily available as the chlorine compounds.

The hydrolysis of the nitrohalobenzene can be done by treating it with an alkali hydroxide in Contact with an oxidizing agent. The starting compound, preferably p-nitrochlorobenzene, can be reacted with an at least stoichiometric amount of the alkali hydroxide. in the In general, a molar excess of about 2: 1 or 3: 1 is appropriate. Used preferably one sodium hydroxide, although potassium, lithium, cesium or rubidium hydroxide if desired can also be used. In general, the alkali metal hydroxide is used as an aqueous solution.

Pressure does not appear to play an important role in the method of the invention, and one can simply work under the autogenous pressure developed in the course of the reaction, which is based on Due to the temperature used, the aqueous phase of the reaction mixture forms. The reaction is carried out at about 100 to 200 ° C. A temperature of about 140 is preferably used up to 180 ° C.

The nitrohalobenzene compound and the alkali hydroxide are passed through a molecular Oxygen-containing gas or reacted in the presence of an inorganic or organic peroxide, which is able to have an oxidizing effect in an alkaline reaction medium. To the appropriate Peroxide compounds include those of an organic nature such as methyl hydroperoxide, dimethyl peroxide, ethyl hydroperoxide, Diethyl peroxide, diisopropyl peroxide, dit-butyl peroxide, acetyl peroxide, butyryl peroxide, lauroyl peroxide, Benzoyl peroxide, benzyl hydroperoxide, 2,4-dichlorobenzoyl peroxide, tetralin hydroperoxide, Urea peroxide, t-butyl perbenzoate, t-butyl hydroperoxide, Methylcyclohexyl hydroperoxide, diisopropylbenzoyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, Cyclohexanone peroxide. Inorganic peroxide compounds represent a preferred class of peroxide compounds. Suitable examples of these are the persulfates, perborates and Percarbonates of ammonium and alkali. Hydrogen peroxide is particularly suitable as is the alkali

peroxides and alkali hydroperoxides, e.g. B. sodium peroxide, sodium hydroperoxide, potassium peroxide, potassium hydroperoxide, Lithium peroxide, lithium hydroperoxide, cesium peroxide, cesium hydroperoxide, rubidium peroxide, Rubidium hydroperoxide.

The unwanted side reactions that lead to the formation of ammonia and dark colored substances lead, are essential due to the presence of only small amounts of the oxidizing agents mentioned here switched off. In most cases the oxidant involved is in amounts in the range of about 0.001 to about 0.1 weight percent of the present nitrohalobenzene compound is effective.

The hydrolysis of the nitrohalogenobenzene to the corresponding nitrophenol by the process according to the invention can be carried out in any suitable manner respectively. According to a convenient method, the desired amount of starting materials, for. B. at p-nitrochlorobenzene and aqueous sodium hydroxide solution, placed in a suitable reaction vessel, which is equipped with heating and mixing devices is provided, and at the same time an oxidizing agent, such as aqueous hydrogen peroxide, admitted. The reaction mixture is heated and stirred to intimate the reactants to mix and distribute the oxidant throughout the reaction mixture. After suitable Reaction time, the mixture is cooled to about room temperature and filtered. The residue is washed with aqueous alkali hydroxide, dried and then acidified to the desired Obtain nitrophenols.

If air or another oxygen-containing gas, e.g. B. in a mixture with nitrogen or an inert gas is used, the oxygen-containing gas is continuously introduced into the reaction mixture initiated in such a way that intimate contact is ensured. They are appropriate Take measures to ensure that the oxygen-containing gas is used throughout the duration the reaction is fully dispersed in the reaction mixture because of a simple surface contact of the mixture does not produce the desired effect with the atmosphere.

The following examples serve to further illustrate the process of the invention.

example 1

acidified in hot dilute hydrochloric acid, the mixture cooled and filtered.

Example 2

2270 g of p-nitrochlorobenzene and 2309 g of sodium hydroxide in about 131 ml of water were introduced into an autoclave with a capacity of about 19 l and provided with a stirrer. The contents were brought in the course of one hour to a temperature of 16O ⁰ C and

ίο kept at this temperature for 4 hours with stirring. During the course of the reaction, air was constantly blown into the reaction mixture and dispersed therein. The pressure was not allowed to rise ^{above about 5.6 kg / cm 2.} After the 4 hours had elapsed, the contents were cooled to approximately room temperature and filtered. The residue was washed with aqueous 30 ° / ₀ strength alkali metal hydroxide solution and dried. Sodium p-nitrophenolate was obtained as a yellow crystalline material with no evidence of coloring impurities in a yield of 98 ° / _0th p-Nitrophenol was obtained by acidifying the phenolate as in Example 1.

Example 3

About 10 grams of t-butyl hydroperoxide was added to about 2270 grams of p-nitrochlorobenzene and placed in a rotary autoclave along with about 1725 grams of sodium hydroxide and 6900 ml of water. The reaction mixture was ^{heated to 140 to 180 °} C. for 4 to 6 hours, then cooled and filtered. The residue was washed alkaline and dried. The sodium p-nitrophenolate thus obtained was treated with hydrochloric acid to produce p-nitrophenol without discoloration.

Example 4

About 2270 g of p-nitrochlorobenzene and 1725 g of sodium hydroxide in 6900 ml of water were placed in an autoclave with a suspended stirrer together with about 10 g of sodium peroxide in aqueous solution. The reaction mixture was ^{heated to 140 to 180 °} C. for 4 to 6 hours. The reaction mixture was then cooled and filtered. The residue was washed alkaline and dried. The sodium p-nitrophenolate was treated with hydrochloric acid to give uncolored p-nitrophenol.

2270 g of p-nitrochlorobenzene and 1725 g of sodium hydroxide and 6900 ml of water were placed in a glass insert, which was enclosed in a rotary autoclave, together with 23 g of a 30% strength by weight aqueous water / substance peroxide solution. The contents were slowly heated to a temperature of about 160 ^° C. and kept at this temperature for 4 hours. The autoclave was rotated continuously. Then the contents were cooled to room temperature and filtered. The residue was washed with small amounts of 30 ⁰ / ^he o'g aqueous alkali metal hydroxide solution and dried. To give sodium p-nitrophenolate in a yield of 96.3 ° / o ^m the form of yellow crystals that showed no contamination with staining substances. To recover the p-nitrophenol, the sodium p-nitrophenolate was introduced by introducing it

Claims (1)

Claim: Process for the preparation of nitrophenols, especially p-nitrophenol, by hydrolysis of nitrohalobenzenes, especially p-nitrochlorobenzene, with aqueous alkali metal hydroxide solution at elevated temperature in the presence of an oxidizing agent and subsequent acidification of the alkali nitrophenolate, characterized in that the hydrolysis is carried out at a temperature in the range of about 100 to 200 ⁰ C while passing through a molecular oxygen-containing gas or in the presence of an inorganic or organic peroxide, preferably in an amount of about 0.001 to 0.1 percent by weight, based on the nitrohalogenobenzene.