DE2708914A1 - Prepn. of hydrazobenzene by catalytic redn. of nitrobenzene - with hydrogen in alkaline alcoholic soln. under turbulent motion - Google Patents

Abstract

Prepn. of hydrazobenzene by alkaline catalytic hydrogenation of nitrobenzene in alcoholic soln. contg., as alkaline agent, an alkali alcoholate and/or alkali hydroxide, under a press. of >=1 bar at a temp. of =120 degrees C., whilst maintaining the reaction mixt. in turbulent movement. Pref. the reaction mixt. is atomised with H2 in an H2 atmos. and is effected under increasing press. at =90 degrees C., without addn. of any water and using a 1-5C alkanol as solvent, e.g. methanol. High yields of prod. of high purity are obtd. withofast reaction times. Costly purificn. steps required in previous catalytic processes are avoided. The formation of poisoned catalyst in the present process is strongly retarded or even completely avoided.

Description

1Process and apparatus for the production of hydrazobenzene

The present invention relates to the in the preamble of Claim 1 specified subject matter.

Another object of the invention is a device for implementation Des. In claim 1 specified method.

It is known that by catalytic reduction of nitrobenzene with Hydrogen is formed in the presence of hydrazobenzene hydrogenation catalysts.

r. Brandt and J. Steiner, Reports 55, 886, performed the hydrogenation on a laboratory scale in dilute, weakly alkaline aqueous alcoholic tOH solution in the presence of a palladium-carbon catalyst. The response time was despite the small approach 4 hours. Neutralized to separate off the hydrazobenzene K. Brandt et al the reaction mixture first with acetic acid, after which the hot solution was freed from the palladium catalyst by filtration. Separated from the filtrate the hydrazobenzene in a yield of 80% d. Th. From.

In SU-PS 165 174 it is proposed to increase the yields, the hydrogenation of nitrobenzene with hydrogen in a solution of pyridine and KOH to be carried out in Xtbanol.

The catalyst Pt02 was used to prepare the reaction mixture filtered off, the solution neutralized with sulfuric acid, the precipitated pyridine sulfate filtered off and the alcohol is distilled off. That filtered off after the solution had cooled down Hydralobenzene had to be used to produce a high-purity hydrazobenzene by recrystallization getting cleaned.

The technical preparation of hydrazobenzene by catalytic hydrogenation is according to the method described in the yields achieved and expensive Work-up and purification process uneconomical, so that the reduction of Ritrobenzene on an industrial scale almost exclusively by electrochemical means with sodium amalgam or with metals such as zinc and iron.

However, these known methods also have considerable disadvantages. The reduction of the nitrobenzene to hydrazobenzene is incomplete and it results By-products that reduce the yield. Hicrby as well as by the deployed Auxiliary materials, such as pyridine, mercury or zinc, are used in the production process Hydrazobenzene is very difficult or impossible on an industrial scale.

To remedy these disadvantages we have not yet published this in the German patent applications P 26 34 861.8 and P 26 34 862.9 proposed the hydrogenation at elevated pressure and at temperatures up to 1200C, preferably up to 900C, below To carry out metered addition of hydrogen, the reaction mixture in turbulent Movement is kept.

Alkali alcoholates are used as alkaline agents in these processes and / or alkali hydroxide is used, and the reaction is carried out in a R5hrautoklav carried out under strong pipes in order to achieve the best possible exchange of substances between To achieve gas base and liquid.

It has been found that when applying this procedure on the industrial scale (tons) with a longer reaction time a considerable amount Reduction in yield occurs.

There was therefore the object in the preparation of hydrazobenzene on an industrial scale to improve the yield, the space / time yield to increase and at the same time suppress undesired side reactions.

Ze has now found that the above-mentioned difficulties can be eliminated can, if you consider the catalytic hydrogenation of nitrobenzene in alkaline-alcoholic Carries out solution in an apparatus in which the reaction mixture with the help of a Circulation pump pushed through a nozzle and mixed with hydrogen into the hydrogen atmosphere of the reactor is atomized.

The invention therefore provides a process for the production of Hydrazobenzene by catalytic alkaline hydrogenation of ditrobenzene with hydrogen in alcoholic solution, which is characterized in that the reaction mixture mixed with hydrogen is atomized in a hydrogen atmosphere.

Another object of the invention is a device for implementation of the process for the preparation of hydrazobenzene characterized by a temperature controlled Reactor and an outgoing from the reactor in the area of the liquid column, provided with a pump circuit, which in a the reaction material in the gas space the reactor's finely distributing nozzle opens.

Essential components of the hydrogenation device according to the invention are a temperature-controlled reactor, a pump, an atomizing nozzle, e.g. according to Art the Venturi-DUse or water jet pump, as well as temperature and pressure regulators.

Surprisingly, with the help of the DUse and subsequent atomization a particularly good mass transfer between gas phase, liquid and catalyst achieved.

In the procedure according to the invention it is possible to reduce the reaction time to 1/10 of the 6 hours observed in large stirred autoclaves on s.B. 35 to 40 minutes.

It is also advantageous that the yield despite twice the nitrobenzene concentration, compared to previously known methods, is improved by 25%.

With the method according to the invention, the production of a highly pure Hydrazobenzene with a purity greater than 99.7 * with a high yield, e.g. 97% on nitrobenzene used. The used alcohol sol is almost converted quantitatively to hydrazobenzene and 2 to 3% aniline. An elaborate work-up the reaction solutions by acidifying the impulses separated from the catalyst, The salts formed are filtered off and the hydrazobenzene is recrystallized superfluous, as there hydrasobenzene from the alkaline catalyst freed from the catalyst The solution crystallizes out with a high degree of purity as it cools. The education the catalyst poison which interferes with the reaction is in the process according to the invention strongly pushed back or it is almost entirely avoided.

The hydrogenation takes place at hydrogen pressures from 1 bar.

It is expedient and preferred to react at elevated hydrogen pressures > 1 bar to be carried out. Pressures at which boiling of the reaction mixture is avoided will be preferred.

The maximum pressure to be maintained is not per se for the reaction critical, but only depends on the maximum pressure for which the pressure vessel is constructed. Preference is given to working with increasing, preferably, during the reaction steadily increasing, printing.

In principle, it is also possible to work at constant pressure, with right at the beginning of the reaction, the pressure is adjusted so that it is when it is reached the maximum temperature is at least so high that the boiling of the reaction mixture is avoided.

In general, hydrogenation at 20 ° to 1200 ° C. is preferred to 9000. However, one works with caution during the reaction of 20 to 12000, in particular 20 to 900C, increasing temperatures.

The temperature of the reaction solution as well as the hydrogen supply are this coordinated so that the temperature of the solution during the course the reaction of about 20 to 1200C, preferably about 20 to 90C, increases.

The pressure rises, for example, from 1 to 60 bar.

In general, the reaction has ended after about 30 to 45 minutes.

In general, one works in such a way that the reactor with the alkaline-alcoholic solution of nitrobenzene and a hydrogenation catalyst charged, the reaction mixture being used in an amount that at most 80 to 90% of the volume of the reactor is filled, so that there is a gas space above the liquid remains. The liquid flow is now circulated with the help of a pump, by taking the liquid stream, preferably at the lowest end of the reactor and is fed to the nozzle arranged at the head of the reactor.

Preference is given to the one that immerses the reaction solution in the hydrogen atmosphere atomized, fed with hydrogen, so that the reaction solution and the hydrogen are intimately mixed with each other in the shower and together in the finest distribution enter the hydrogen gas space of the reactor. Collects in the lower part of the reactor the reaction solution, which is then continuously fed to the nozzle by the circulation pump will.

The hydrogen required for the reaction is optionally from the Nozzle sucked out of the reactor and / or directly via a line US to a hydrogen extraction container inserted into the nozzle.

If necessary, the DUse can be a mixture of hydrogen and reaction solution are fed.

The hydrogenation and the work-up of the reaction mixture take place with the exclusion of atmospheric oxygen.

i the method according to the invention is precautionary worked so that ate the components used or the reaction mixture no additional water is admitted.

The alkyl radical of the alcoholates used can be any Chain length and branching, but generally 1 to about 6, preferably 1 to about 4, have carbon atoms.

Such alkali metal alcoholates, especially taklima, are preferred. or sodium used, which release the same alcohol in the reaction, which was used as a solvent for the nitrobenzene. Preference is given to sodium or potassium methylate.

The amount of alkaline agent is generally between 2 Up to 20% by weight, preferably 5 to 15% by weight, based on the alcohol used.

There. Nitrobenzene to be hydrogenated can be 8 to 60% by weight, preferably be used as a 20 to 45% strength by weight solution in an alcohol. Become useful those alcohols used in which both the nitrobenzene and the alkaline Means that are soluble.

Suitable alcohols and e.g. lower aliphatic saturated monohydric, optionally branched alcohols with up to 5 carbon atoms.

Methanol is preferred.

Hydrogenation catalysts known per se are used as catalysts, preferably noble metal catalysts, e.g. platinum or palladium catalysts and the like. Palladium-carbon catalysts, e.g. about 1 to 5% by weight of Pd, are preferably used containing palladium-carbon catalysts.

Me tatalyeatoren are generally used in amounts of 0.001 wt.% To 0.01% by weight, preferably 0.002% by weight to 0.004% by weight, based on the nitrobenzene used and calculated as metal.

As soon as the hydrogenation is complete, the hot reaction wipe becomes filtered to separate the catalyst and then, preferably under Stir, cooled down. There. Crystallized hydrazobenzene is known per se Methods, e.g.

by centrifugation or filtration, separated in a simple manner and washed with aqueous alcohol.

The alcohol is removed from the mother liquor by distillation. The organic phase remaining in the bottom becomes the aqueous alkaline phase after separation Phase fed back to the next approach.

The figure shows a device for implementing the invention Process with a temperature-controllable reactor and a circulation starting from this for the reaction material, which: via a nozzle together with hydrogen into the reactor is returned.

The reactor 1 is dimensioned so that at least 10 to 20% of its Volume are available as a gas space. The reactor can be via a jacket 9 tempered, i.e. optionally heated or cooled. The circulation 5 with the pump 2 leads to the nozzle 3, which is located in the upper part of the reactor in the area of the gas space is attached and extends into the hydrogen gas space of the reactor 1. The supply line of hydrogen into the nozzle 3 takes place via the side suction port 6, which Fresh hydrogen via feed line 4b and / or hydrogen via feed line 4a is fed from the gas space of the reactor.

The reactor is via the feed line 8 with the alkaline, the Catalyst-containing nitrobenzene solution is charged while removing the product takes place via the drain valve 7.

The circulation 5 is equipped with temperature control.

The operation of the device can generally be as follows described.

In the reactor 1 is an alcoholic solution of nitrobenzene, alkaline Agent and hydrogenation catalyst via feed line 8 under a nitrogen atmosphere submitted. After displacing the nitrogen with hydrogen, the reaction mixture becomes Heated to approx. 30 ° C via the heat exchanger 9 and pumped through the DUse 3. By the line 4a is subjected to a hydrogen pressure of e.g.

2 to 4 bar set. The hydrogen supplies and the temperature of the reaction mixture are controlled so that during the hydrogenation with increasing Pressure the temperature rises to approx. 900C. After the hydrogenation is complete - About Mob 30 to 40 minutes, the reaction mixture is over the drain valve 7 under Nitrogen atmosphere removed from the reactor and filtered hot. After cooling down the crystallized hydrazobenzene is centrifuged off and washed with aqueous alcohol, preferably methanol, washed.

All these known per se can be used as atomizer nozzles be, especially nozzles, an intimate mixing of the liquid, solid and allow gaseous phases within the DUse.

The following examples demonstrate the high yields and the good purity of hydrazobenzene and the short reaction times.

Example 1 The approximately 2 m3 reactor is loaded with 800 kg of a 10 % strength methanolic sodium methylate solution, 400 kg of nitrobenzene and 600 g of palladium carbon loaded. After displacing the nitrogen with hydrogen, the reaction solution becomes pumped through the nozzle. The hydrogen supply and the temperature of the reaction mixture is controlled so that the temperature during the hydrogenation with increasing pressure increases from 20 - 900C. After about 35 minutes, the hydrogenation is complete, the solution is filtered hot, cooled and the hydrazobenzene which has crystallized out is centrifuged off. The filter cake is washed several times with aqueous methanol and the washing liquid combined with the filtrate. After the methanol has been distilled off, the aqueous Phase separated and the organic phase fed to the next batch who. To the aniline was removed by distillation in about 10 batches. Per approach were on average 290 kg of Hdrazobenzene obtained with a purity of 99.7%. That corresponded to a yield of 97% of theory based on the nitrobenzene used.

Melting point 12700.

Example 2 The reactor is loaded with 800 kg of a 10g methanolic Potassium methylate solution, 500 kg of ititrobenzene and 700 g of td coal are charged.

The hydrogen supply and the temperature of the reaction mixture is regulated so that during the hydrogenation with increasing pressure the temperature up to rises about 90 ° C. The hydrogenation is complete after about 40 minutes. The solution will be filtered hot, cooled and the hydrazobenzene which had crystallized out was centrifuged off.

The filter cake is washed several times with aqueous methanol and the Jaschiquid combined with the filtrate. Reconditioning and reuse the mother liquor is carried out as described in Example 1. The average yield each set was 96% (360 kg) hydrazobenzene. Scan point 127 to 12800.

Example 3 The reactor is charged with 800 kg of methanol, 80 kg of KOH, 350 kg Nitrobene sol and 600 g of Pd carbon are charged. After displacing the nitrogen through Hydrogen the solution is hydrogenated. The hydrogen supply and the cooling of the The reaction mixture is regulated so that the temperature of the solution is from 20.degree. To 900.degree increases. The hydrogenation is complete after about 35 minutes, the solution is filtered hot, cooled and the hydrazobenzene which had crystallized out was centrifuged off. The cleaning of the hydrazobenzene and the work-up of the filtrate is carried out as described in Example 1. An average of 246 kg of hydrazobenzene with a reaunit> 99.5 were used per batch % obtained. This corresponds to a yield of 94% hydrazobenzene based on the Nitrobenzene used. Melting point 127 ° C.

Example 4 The reactor is filled with 800 kg of methanol, 80 kg of NaOH, 400 kg Nitrobenzene and 600 g of Pd-Iohle charged. The hydrogenation is as described in Example 1 described carried out. The reduction is complete after 35 minutes. The solution will be filtered hot, cooled and the hydrazobenzene which had crystallized out was centrifuged off. The pilter cake washed with methanol is dried at 70-80C. There were 280 kg hydrazobenzene with a purity> 99.5% and a melting point of t270C (Yield 93.5% of theory). Example 5 A solution of 1,200 kg of a 10% strength Sodium ethylate solution and 400 kg of nitrobenzene are added in the presence of 800 g of Pd-charcoal hydrogenated, the cooling of the reaction mixture is regulated so that the temperature the solution rises slowly from 30 to 90 ° C.

The reduction is complete after about 45 minutes. The solution becomes the separation the Pd-charcoal filtered hot. After adding water, it crystallizes out Hydrazobenzene centrifuged off. The filter cake is washed with aqueous ethanol and the hydrazobenzene dried at 70-80 ° C. The yield based on that used. Nitrobenzene is 92% of theory

Melting point 125 to 126 ° C.

L e r s e i t e

Claims (4)

P a t e n t a n s p r ü c h e 1. Process for the preparation of hydrazobenzene by catalytic alkaline hydrogenation of nitrobenzene with hydrogen in alcoholic Solution that indicates that the reaction mixture with hydrogen mixed ht is atomized in a hydrogen atmosphere. 2. The method according to claim 1, characterized in that the hydrogenation is carried out at 20 to 120 ° C. 3. The method according to claim 2, characterized in that the hydrogenation is carried out at increasing temperatures. 4. Apparatus for performing the method according to claim 1, characterized by a temperature-controllable reactor and one of the reactor in the area of the liquid column outgoing, provided with a pump circuit, which in a the reaction material A finely distributing nozzle opens into the gas space of the reactor.