DE2634862A1 - 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 hydrazbenzene by catalytic hydrogenation of nitrobenzene with hydrogen in alcoholic solution in the presence of alkali hydroxide, subsequent separation of the catalyst and Isolation of the hydrazobenzene.

X, Brandt and. Steiner, Reports 55, 886, carried out the hydrogenation Borum grade in dilute, weakly alkaline aqueous-alcoholic KOH solution in Presence of palladium carbon catalyst. The reaction time was for one Mix on only 2 g nitrobenzene in 30 cm3 alcohol, 8 cm3 water and 5 potassium hydroxide solution in Presence of 0.2 g palladium-carbon for 4 hours.

The liquid is used for processing immediately after the end of the reduction with acetic acid to accelerate the oxidation of hydrazbenzene Cancel the influence of the alkali. After rewarming, the solution was filtered, From the filtrate obtained, the hydrazolobenzene separated in a yield of 80% of theory the end.

Esch V. P .Schmonina and D.V. Sokolski (SC-PS 165174) is used for the purpose Increase the yields suggested that the reduction be carried out 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 one filtered the separated from the catalyst by decanting solution and with Acidifies sulfuric acid. In a further stage, the pyridine sulfate is filtered off. The yield of 97% hydrazobenzene given in this patent was polarographic measured on the decanted solution. The partially achieved 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 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. As a result, as well as through the Auxiliary materials, such as pyridine, mercury or zinc, the production is pure Hydrazolbenzene is very difficult or impossible on an industrial scale.

The task was therefore to increase the reaction rate, Nevertheless, to suppress side reactions and a laborious work-up of the reaction mixtures to avoid.

The object is achieved according to the invention in that the hydration of nitrobenzene in the presence of alkali hydroxide at elevated pressure and at elevated Temperatures is made.

The subject of the invention is therefore a method for producing of hydrazobenzene by catalytic hydrogenation of nitrobenzene with hydrogen in alcoholic solution, in the presence of alkali metal hydroxide, subsequent separation of the catalyst and isolation of the hydrazobenzene, which is characterized is; that the hydrogenation at elevated pressure and at up to 120 ° C, preferably up to carried out to 900C, increasing temperatures with the addition of hydrogen is, wherein the reaction mixture is kept in turbulent motion, and that the hydrazobenzene from the alkaline solution freed from the catalyst without Acidification is obtained by crystallization.

Surprisingly, in the method according to the invention, a up to 94% yield obtained. Nevertheless the nitrobenzene in high concentration is used, you get hydrazobenzene and 6-8% aniline, and almost no by-products.

(<0.3%).

An expensive work-up of the reaction solutions was required by An-C'au? Rn the solution separated from the catalyst, filtering off the salts formed, recrystallization , there is no need for hydrazobenzene, since the hydrazobenzene is from the catalyst freed alkaline solution with an average purity of 99.6 when it cools down % crystallized out. The process according to the invention succeeds in producing it of hydrazobenzene in up to 94% yield in relatively short reaction times.

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, which work in more 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 hydroxide is in the range of 2 - 20% by weight, preferably 5-15% by weight, based on the alcohol used.

The alcohols used are those, including nitrobenzene as well as the alkali hydroxide are soluble.

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

The preferred alkali hydroxides are those of sodium or potassium used.

Noble metal catalysts are expediently used as the catalyst, e.g. platinum or ra: iiadium catalysts and the like. Preference is given to using 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 of 0.01 % By weight to 0.01% by weight, preferably 0.002% by weight to 0.004% by weight, based on the Nitrobenol 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 high-speed stirrer.

The hydrogenation and, appropriately, also the work-up of the reaction mixture take place with the exclusion of atmospheric oxygen. The equipment used will be for this purpose with an inert gas, e.g. I3. Nitrogen, purged. 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. Minor watermels, however, generally not gray, so the Individual components do not have to be used as completely hydrogen components.

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.

In a preferred embodiment of the method according to the invention one proceeds in such a way -that the hydrogenation is carried out with increasing- --- -the pressure and with up to to 1200C, preferably up to 90 ° C increasing temperatures.

In a further preferred mode of operation it is provided that the First hydrogenation by heating the hydrogen-containing reaction mixture about 30 ° C is initiated and that then send the further hydrogenation at up to 120 ° C, preferably up to 9000 increasing temperatures with cooling of the reaction mixture and is carried out with control of the hydrogen supply so that the formation is largely pushed back by aniline. For example, the pressure increases from 1 to 10 bar.

In principle, however, you can also work at constant pressure, the pressure 80 being set right at the beginning of the reaction so that it is when it is reached the maximum temperature is at least high enough to avoid boiling of the reaction mixture will.

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

The optimal response times to be observed when performing the according to the invention Procedure, are expedient in preliminary tests according to the size of the respective Pressure vessel of the capacity of the stirring device and the like. Determined. the Guide values for a 5 l 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 which the pressure vessel is constructed.

For example, when carrying out the process of the invention so before that the autoclave after displacing the .Sauerstoffs by nitrogen with a alcoholic alkali hydroxide solution, nitrobenzene and palladium-carbon is charged.

After displacing the nitrogen with hydrogen, the reaction mixture becomes heated with vigorous stirring. The hydrogen supply and the cooling are then regulated so that the temperature of the reaction solution up to 100C, preferably 9000 within a time of approx. 20 to 40 minutes (however, depending on the Amount) increases. The pressure increases from 1 to e.g. 10 bar. After relaxing the still hot reaction mixture is filtered hot to separate off the catalyst and then cooled, advantageously with stirring.

The filtration and the subsequent stirring are expedient under Exclusion of atmospheric oxygen, preferably in a nitrogen atmosphere, carried out. The hydrazobenzene which has crystallized out is separated off by centrifugation or filtration and conveniently washed with aqueous alcohol. The mother liquor becomes the alcohol removed by distillation and added to the next batch leads. The organic phase remaining in the bottom is separated off and used for the next batch reintroduced. In general, recrystallization is not necessary, since that hydrazobenzene generally has degrees of purity from> 99 to about 99.6 % accrues.

The invention is illustrated by the examples.

The alcohols used as solvents in the examples had a hydrogen content of 0.1 to 1%.

As can be seen from Example 4, this procedure leads only to yields of 84%. So it is an essential feature of the invention Process, the hydrogenation at increasing temperatures until reaching the final temperature carry through.

Example 1 A 5 liter autoclave flushed with nitrogen, which is equipped with a fast-running stirrer, a heating and cooling device and a feed opening is equipped for the hydrogen as well as pressure and temperature measuring device with 1,000 g nitrobenzene, 2,400 g ethanol, 250 g KOH and 2 g palladium-carbon (2nd % By weight = 0.04 g Pd) charged. After displacing the nitrogen with hydrogen the hydrogen-containing mixture is carefully raised to 3000 with rapid stirring (1,400 rpm) heated.

The further supply of hydrogen and the cooling of the reaction mixture are then regulated so that the temperature of the solution rises steadily from 30 to 9000. After about 30 minutes of rapid stirring, counted from reaching 3000, the Hydrogenation ended. The solution is filtered hot, cooled and the crystallized Centrifuged rydrazobenzene. The filter cake is washed several times with aqueous methanol washed and the washing liquid combined with the filtrate.

After distilling off the methanol, the organic phase is the nobsten approach fed back. After about 10 batches, the aniline becomes distillative removed. Each batch produces an average of 700 g of ilydrazobenzene with a purity 99.5% preserved.

This corresponds to a yield of 94% based on hydrazobenzene the nitrobenzene used. Melting point 127 ° C.

Example 2 As in Example 1, a solution of 1,000 g of nitrobenzene and 200 g of KOH in 2,000 g of methanol in the presence of 2 g of Pd carbon (as in Example 1) hydrogenated. The supply of hydrogen and the cooling of the reaction mixture will be regulated so that the temperature of the solution rises from about 30 to 900C. After approx. The reaction has ended in 30 minutes. The solution is filtered hot, cooled and the hydrazobenzene which has crystallized out is filtered off.

The filter cake washed with methanol is dried at 70-80 ° C. The mother liquor is worked up as described in Example 1. The yield is 696 g of hydrazobenzene (93%, based on the nitrobenzene used) with a melting point of 126-127 ° C.

Example 3 As in Example 1, a solution of 1,000 g of nitrobenzene and 200 g NaOH dissolved in 2,000 g methanol and in the presence of .2 g Pd carbon (such as Example 1) hydrogenated. The cooling of the reaction mixture is regulated so that the The temperature of the solution slowly rises from 30 to 9090. The reduction takes place after about 30 minutes completed. The solution is filtered hot, cooled and the hydrazobenzene crystallized out filtered off. The filter cake, washed with methanol, is dried at 70 to 80 ° C. The mother liquor is worked up as described in Example 1.

694 g of hydrazobenzene (93%, based on the nitrobenzene used with a purity> 99.5% and a melting point of 127 ° C.

Example 4 As in Example 1, a solution of 1,000 g of nitrobenzene and 240 g of KOH in 2,400 g of methanol and 2 g of palladium carbon and charged to about 800C heated. After displacing the nitrogen with hydrogen, the stirrer turns switched on. The hydrogen supply and the cooling of the reaction mixture is regulated so that the temperature remains at approx. 800G. The hydrogenation takes place after 35 minutes completed. The solution is filtered hot, cooled and the hydrazobenzene crystallized out filtered off. The filter cake is washed several times with methanol and the water liquid combined with the filtrate. Work-up is carried out as described in Example 1.

On average, 630 g of hydrazobenzene were obtained per batch corresponds to a yield of 84% of theory, based on nitrobenzene. Melting point 126 ° C.

Claims (8)

Pat e n t a n s p r ii e hwe Process for the production of hydrazobenzene by catalytic hydrogenation of nitrobenzene with hydrogen in alcoholic solution in the presence of alkali hydroxide, subsequent separation of the catalyst and Isolation of the hydrazobenzene, that the Hydrogenation at elevated pressure and at up to 120 ° C, preferably up to 90 ° C increasing Temperatures is carried out with metered addition of hydrogen, the reaction mixture is kept in turbulent motion, and that the hydrazobenzene from the alkaline The solution freed from the catalyst is obtained by crystallization. 2. The method according to claim 1, d a d u r o hS g e k e n u -z e i c It should be noted that the hydrogenation is carried out with increasing pressure. 3. The method according to claim 1 or 2, d a d u r c h g e k e n n -z It is true that the nitrobenzene to be hydrated is 8-50% by weight, preferably is present as a 20-45% by weight solution in an alcohol, which is 2-20% by weight, preferably 5-15% by weight, dissolved alkali hydroxide. 4. The method according to any one of claims 1 to 3, d a d u r c h g e k It is noted that the catalyst used is a noble metal catalyst in amounts of 0.001% by weight to 0.01% by weight, preferably 0.002% by weight to 0.004% by weight, based on Nitrobenzene used and calculated as the metal. ' 5. Process according to Claim 4, 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 Palladium carbon, preferably palladium carbon with 1 - 5 wt% Pd is used. 6. The method according to any one of claims 1 to 5, d a d u r c h g e k It is noted that the hydrogenation is initially carried out by heating the hydrogen-containing The reaction mixture is passed in at about 30 ° C. and then the other Hydrogenation at up to 120 ° C., preferably up to 9000 increasing temperatures with cooling of the reaction mixture and with regulation of the hydrogen supply in such a way it is made that the formation of aniline is largely suppressed. 7. The method according to any one of claims 1 to 6, d a d u r c h g e k It is noted that reaction mixtures are used which do not contain any additives contained by water. 8. The method according to any one of claims 1 to 7, d a d u r c h g e k It is noted that the alkali hydroxide used is KOH and / or lfaOH.