DE2634861A1 - 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

Process for the preparation of hydrazobenzene

The invention relates to a process for the preparation of hydrazobenzene by catalytic alkaline hydrogenation of nitrobenzene with hydrogen in alcoholic Solution.

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

K. Brandt and J. Steiner, Reports 55, 836, carried out the hydration on a laboratory scale in dilute, weakly alkaline aqueous alcoholic KOH solution in the presence of a palladium-carbon catalyst. The reaction time was a mixture of only 2 g of nitrobenzene in 30 cm3 of alcohol, 8 cm3 of water and 5 cm3 of 2N potassium hydroxide solution in the presence of 0.2 g of palladium-carbon for 4 hours.

The liquid is used for processing immediately after the end of the reduction acidified with acetic acid to accelerate the oxidation of the hydrazobensol To cancel the influence of the alkali. After rewarming, the solution was filtered.

The hydrazobenzene separated in one form from the cooled filtrate Yield of 80% of theory the end.

According to V.P, Schmonina and D.V. Sokolski (SU-PS 165 174.) is used for the purpose increase of the yields suggested to carry out the reduction in the presence of pyridine. Laboratory approaches are reduced in batches in quantities of 0.5 g of nitrobenzene The work-up takes place after reduction of 2 to 3 batches by the from the Catalyst separated by decantation filtered solution and treated with sulfuric acid acidified. In a further stage, the pyridine sulfate is filtered off. The one in this The patented yield of 97% hydrazobenzene was polarographically indicated of the decanted solution. The actual yields of pure However, hydrazobenzene are much lower.

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 Nitrobenzene on an industrial scale almost exclusively on electrochemical goat with sodium amalgam or with metals such as zinc and iron,.

he follows.

However, these known methods also have considerable disadvantages. The reduction of the nitrobenzene to hydrazobenzene is incomplete and it results By-products that narrow the yield. As a result, as well as through the Additives such as pyridine, mercury or zinc, the manufacture is pure Hydrazobenzene is very difficult or impossible on an industrial scale.

The task was therefore to increase the reaction rate, nevertheless suppress side reactions and an expensive work-up of the reaction mixtures to avoid.

The object is achieved according to the invention in that the hydrogenation of nitrobenzene in the presence of alkali alcoholate at elevated pressure and at temperatures is made up to 1200C.

The invention therefore relates to a method for producing Hydrazobenzene by catalytic alkaline hydrogenation of nitrobenzene with hydrogen in alcoholic solution, which is 1 characterized in that as alkaline Means an alkali alcoholate is used or is also used, and that the hydrogenation at elevated pressure and at temperatures up to 120 ° C., preferably up to 90 ° C., with metered addition carried out by hydrogen, the reaction mixture in turbulent Movement is kept.

In the process according to the invention, alkali alcohol-1 is preferred lat used as the only basic remedy, although it is fundamentally possible is, a part of the alkali alcoholate, for example up to 50%, by alkali hydroxide, preferably potassium hydroxide, surprisingly to replace it by using of the alkali alcoholate as a basic agent suppressed the formation of aniline and that of the undesired by-products is almost completely prevented.

The water produced during the reaction is combined with the alkali alcoholate to alkali hydroxide and alcohol. Through the Custom of water the solubility of hydrazobenzene is ranked and thus the space-time yield 50% better than an alcoholic solution that is used as the sole alkaline solution Agent contains an alkali hydroxide.

The process according to the invention enables hydrazobenzene to be prepared in up to 98% yield in relatively short reaction times.

The nitrobenzene used becomes hydrazobenzene almost quantitatively and 2 to 5% aniline reacted.A complex work-up of the reaction solutions by acidifying the solutions separated from the catalyst, filtering off the resulting salts, recrystallization of the hydrazobenzene are unnecessary, since the Hydrazobenzene from the alkaline solution freed from the catalyst as it cools crystallized out with an average purity of 99.7%.

The method according to the invention is also characterized by that the nitrobenzene to be hydrogenated as a relatively concentrated solution in an alcohol can be used, whereby the space-time yields compared with the previous known methods, in which aenen is carried out in dilute solutions, considerably increase.

In general, the nitrobenzene to be hydrogenated is 8-60% by weight, preferably as a 20-45% strength by weight solution in an alcohol.

The amount of alkali alcoholate or alkali alcoholate-alkali hydroxide mixture ranges from 2 to 20% by weight, preferably 5 to 15% by weight, based on the quantity on the alcohol used.

The alcohols used are those in which both the nitrobenzene as well as the alkali alcoholate are soluble.

Suitable alcohols are, for example, lower aliphatic saturated monohydric, optionally branched alcohols with up to 5 carbon atoms. Methanol is preferred.

Preferred alkali alcoholates are those of sodium or potassium used. The alkyl radical of the alcoholates used can be any Chain length and branching, but generally 1 to about 10, preferably up to have about 5, carbon atoms.

Such alkali metal alcoholates, in particular potassium, are preferred or sodium used, which release the same alcohol in the reaction, which was used as a solvent for the nitro-1benzene. Preference is given to sodium or potassium alcoholates, in particular sodium or potassium methylate.

Noble metal catalysts are expediently used as catalysts e.g. platinum or palladium catalysts and the like. Preference is given to using them for hydrogenation purposes palladium-carbon catalysts known per se, e.g. containing approx. 1 to 5% by weight of Pd Palladium-carbon catalysts.

The amount of catalyst is generally in the range from 0.001 % By weight to 0.01% by weight, preferably 0.002% by weight to 0.004% by weight, based on the amount used Nitrobenzene and calculated as metal.

To achieve the best possible exchange of substances between the gas phase and the liquid to achieve, the reaction mixture is expediently kept in constant motion, for example, with a fast-moving driver.

The hydrogenation and expediently also the work-up of the reaction Gesches take place with the exclusion of atmospheric oxygen. The equipment used are used for this purpose with an inert gas, e.g. nitrogen, flushed. The nitrogen is then displaced by hydrogen.

The method according to the invention is preferably carried out in such a way that that the components used or the reaction mixture do not contain any additional water is admitted. However, small amounts of water do not generally do not disturb, so that the individual components are not used as completely anhydrous components have to.

The method according to the invention can be used, for example, in one with heating and cooling devices equipped autoclave with a high-speed stirrer, an inlet opening for the hydrogen supply as well as a temperature and pressure measurement Is provided.

The reactor expediently has a maximum capacity of up to about 80% charged with the reaction mixture.

The method according to the invention is preferably carried out in such a way that the hydrogenation is initially carried out by heating the hydrogen-containing reaction mixture is initiated at approx. 300C and that is followed by the further hydrogenation with cooling of the reaction mixture and with regulation of the hydrogen supply of this kind it is made that the formation of aniline is largely suppressed. Included the pressure increases, for example, from 1 to 10 bar.

In principle, the method according to the invention can also be used with constant Pressure can be worked, the pressure being set at the beginning of the reaction that when the maximum temperature is reached it is at least so high that the Boiling the reaction mixture is avoided.

However, preference is given to increasing, preferably continuously increasing, Pressure worked.

One variant of the process, although not preferred, is that Reaction mixture to the reaction end temperature before introducing the hydrogen to bring, preferably 70 to 9000, and then the hydrogen continuously supplying rapid stirring of the reaction mixture, the supply of hydrogen and the cooling of the reaction mixture can be controlled so that the temperature in remains essentially constant.

The optimal response times to be observed when performing the inventive Procedure, are expedient in preliminary tests, according to the size of the respective Pressure vessel, the capacity of the stirring device and the like. Determine. the Guide values for a 5-1 autoclave can be found in the examples.

The maximum pressure to be maintained is not per se for the reaction critical, but only depends on the maximum pressure for the pressure vessel is constructed.

For example, when carrying out the process of the invention so before that the autoclave after displacing the oxygen with nitrogen with a Alcoholic Alkalialko holatlösung, nitrobenzene and palladium-carbon charged will.

After displacing the nitrogen with hydrogen, the reaction mixture becomes heated with vigorous stirring. The hydrogen supply and cooling are then regulated so that the temperature of the reaction solution up to 1200C, preferably 900C - within a time of approx. 20 to 40 minutes (however, depending on the amount to be hydrogenated) increases. The pressure increases from 1 to e.g. 10 bar. After releasing the pressure, the still hot reaction mixture is used to separate off the catalyst Filtered hot and then cooled, advantageously with stirring. The filtering and the subsequent stirring are expediently excluded from atmospheric oxygen, preferably carried out in a nitrogen atmosphere. The crystallized hydrazobenzene is separated off by centrifugation or filtration and expediently with aqueous Alcohol washed. The alcohol is removed from the mother liquor by distillation and fed to the next batch. The organic phase remaining in the bottom becomes separated and fed back to the next batch. Generally there is a recrystallization not required, since hydrazobenzene with degrees of purity from> 99 to about 99.7% is incurred.

The invention is illustrated by the examples.

The solvents used for the alcoholates in Examples 99 % By weight alcohols used.

Example 1 A 5 liter stirred autoclave flushed with nitrogen is with 2,400 g of a 10% strength by weight methanolic sodium methyl acetate solution, 1,000 g nitrobenzene and 2 g palladium-carbon (2 wt.% Pd = 0.04 g Pd) charged. After this Displacement of the nitrogen with hydrogen causes the mixture to stir vigorously (1,400 rpm) heated to about 30 to 4000. The supply of hydrogen as well as the Cooling of the reaction mixture is then regulated so that the temperature of the solution from 30 to goQc and the pressure increases from 2 to 10 bar. After about 30 minutes the Hydrogenation ended.

The solution is filtered hot under a nitrogen atmosphere and cooled and the hydrazobenzene which has crystallized out is centrifuged off.

The filter cake is washed several times with aqueous methanol and then dried. The washing liquid is combined with the filtrate. To When the methanol is distilled off, the separated organic phase becomes the next Approach added again. After about 10 batches, the aniline was removed by distillation. On average, 730 g of hydrazobenzene with a purity of 99.7% were obtained per batch. This corresponded to a yield of 97.6% hydrazobenzene, based on the amount used Nitrobenzene.

Example 2 In the same apparatus as in Example 1, 1,230 g of nitrile benzene in 2,400 g of a 9% strength by weight methanolic sodium methylate solution hydrogenated in the presence of 2 g of Pd-charcoal (as in Example 1).

The hydrogen supply and the cooling of the reaction mixture are regulated so that the temperature of the solution increases slowly to -about 900C. To The reduction is completed in about 30 minutes. The solution is ztir Separation of the Pd coble filtered hot under a stick atmosphere. After addition the hydrazobenzene which has crystallized out is filtered off from water. The filter cake is washed with aqueous methanol and the hydrazobenzene is dried at 70-80C. The yield, based on the nitrobenzene used, is 94% (864 g) of theory. Melting point 126 ° C.

Example 3 As in Example 1, a solution of 2,000 g of nitrobenzene in 2,400 g of methanolic sodium methylate (approx. 10% strength by weight) with the addition of 2 g of Pd carbon (as in Example 1) hydrogenated. Here, the internal temperature of the autoclave rises to 90 ° C. The reduction is complete after about 45 minutes. The solution is filtered, cooled and the hydrazobenzene which had crystallized out was centrifuged off. The work-up of the filtrate and the purification and drying of the hydrazobenzene is carried out in the same way described in example 1. On average, 1,437 g of hydrazobenzene were used per batch obtained with a melting point of 127-12800.

Example 4 As in Example 1, a solution of 1,000 g of nitrobenzene in 2,000 g of a 10% strength by weight methanolic potassium methylate solution in the presence hydrogenated by 2 g of Pd carbon (as in Example 1). The hydrogen supply and the cooling are controlled so that the temperature of the solution rises to about 900C. After approx. The reduction is completed in 30 minutes. The filter cake is washed with methanol and dried at 60 - 800C. The work-up of the filtrate corresponds to the example 1. The yield is 95% of theory. Th. Based on nitrobenzene.

Example 5 As in Example 1, a solution of 500 g of nitrobenzene in 1,500 g of a 10% strength by weight ethanolic sodium ethylate solution in the presence of 2 g of Pd carbon (as in Example 1) hydrogenated. The cooling of the reaction mixture is regulated so that the temperature of the solution rises slowly from 30 to 90 ° C. To The reduction is completed in about 30 minutes. The solution is used to separate the Pd carbon filtered hot. After adding water, the hydrazobenzene which has crystallized out becomes centrifuged off. The filter cake is washed with aqueous ethanol and the hydrazobenzene dried at 73 - 800C. The yield, based on the nitrobenzene used, is 93% d. Theory, melting point 125 - 126 ° C.

Example 6 500 g of nitrobenzene are dissolved in a 5% strength by weight isopropanol Sodium isopropoxide solution hydrogenated in the presence of 2 g of Pd carbon (as in Example 1), The cooling of the reaction mixture is regulated so that the temperature of the solution rises to 800C.

The reaction has ended after 50 minutes. The filter cake is washed and dried at 80 ° C. The work-up of the filtrate corresponds to Example 1. The yield is 91% of theory.

based on nitrobenzene.

Claims (10)

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 is not shown as an alkaline agent Alkali alcoholate is used or is also used and that the hydrogenation is increased Pressure and at temperatures up to 1200C, preferably up to 9000, with the addition of Hydrogen is carried out, the reaction mixture in turbulent motion is held. 2. The method according to claim 1, d a d u r c h g e k e nn z e i c h n e t that the hydrogenation increases at up to 120.degree. C., preferably up to 900.degree Temperatures is carried out with the addition of hydrogen 3. Procedure according to Claim 1 or 2, d a d u r c h g e k e n n -z e i c h n e t that the hydrogenation with increasing: pressure is carried out. 4..Method according to one of the speeches 1 to 3, d a d u r o h g e k e n n s e i c h e t that the nitrobenzene to be hydrogenated as 8 - 60 wt.%, is preferably present as a 20-45% strength by weight solution in an alcohol that is 2-20% by weight % By weight, preferably 5-15% by weight, of alkali metal alcoholate in solution, where appropriate part of the alcoholate has been replaced by alkali metal hydroxide. 5. The method according to any one of claims 1 to 4 d a d u r c h g g e It is not noted that the catalyst used is a noble metal catalyst in quantities from 0.001% by weight to 0.01% by weight, preferably 0.002% by weight to 0.004% by weight, based on on nitrobenzene used and calculated as metal. 6. The method according to claim 5, d a d u r c h g e k e n n -z e i c h n e t that as a catalyst Ealladium carbon, preferential prices palladium carbon with 1 - 5% by weight palladium is used. 7. The method according to any one of claims 1 - 6, d a d u r c h g e k e It is not stated that reaction mixtures are used which do not contain any additives contained by water. 8. The method according to any one of claims 1-7, d a d u r c h g e k e It is not stated that the alkali metal alcoholates differ from monovalent saturated aliphatic Derive alcohols with 1-5 carbon atoms, preferably methanol. 9. The method according to any one of claims 1 - 8, d a d u r c h g e k E nn z e i c h n e tX that sodium alcoholates or potassium alcoholates are used. 10. The method according to any one of claims 1-9, d a d u r c h g e k It is noted that the alkali metal alcoholates used in the reaction are the release the same alcohol that is used as the solvent.