GB1560004A

GB1560004A - Process for producing hydrazobenzene

Info

Publication number: GB1560004A
Application number: GB3185877A
Authority: GB
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1976-08-03
Filing date: 1977-07-28
Publication date: 1980-01-30
Also published as: FR2360563A1; HU178508B; NL7708542A; IT1115946B; CS204007B2; FR2360563B1; ES470767A1; ES461272A1; JPS5318522A; CH629752A5

Abstract

The preparation of hydrazobenzene by a catalytic alkaline hydrogenation of nitrobenzene with water vapour in alcoholic solution is effected using an alkali that is an alkali metal alcoholate (alkoxide) and/or an alkali metal hydroxide, hydrogenation pressures of >/= 1 bar and temperatures of up to 120 DEG C, and keeping the reaction mixture in turbulent agitation. Industrial practice is by means of an apparatus comprising a temperature controllable reactor and a pump-equipped recirculation loop emanating from the reactor in the region of the liquid column and ending in nozzles which disperse the reacting material finely into the gas space of the reactor.

Description

(54) A PROCESS FOR PRODUCING HYDRAZOBENZENE (71) We, DYNAMIT NOBEL AKTIEN GESELLSCHAFT, a Germany Company of 521 Troisdorf bez Koln, Postfach 1209 Germany, do hereby declare the invention, for which we pray that a patent may be granted lo us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for producing hydrazobenzene.

K. Brandt and J. Steiner, Reports 55, 8!! described the production of hydrazobenzene on a laboratory scale by the hydrogenation of nitrobenzene in dilute, slightly alkaline aqueous alcoholic KOH-solution in the presence of a palladium-carbon catalyst. The reaction time, with a composition of )ably 2 g nitrobenzene in 30 cm alcohol, 8 cm water and 5 cm ' 2-n-potassium hydroxide solution, in the presence of 0.2 g palladiumcarbon, amounted to 4 hours. For the preparation the liquid was acidified with acetic acid directly after the conclusion of the reduction in order to counter-balance the effect of the alkali accelerating the oxidation of the hydrazobenzene. After renewed heating the solution was filtered. The hydrazobenzene was precipitated from the cooled filtrate in a yield which was 80'to of the theoretical value.

According to V. P. Schmonina and D. V.

Sokolski (Soviet Pat. Spec. 165 174), in order to increase the yield it has been proposed to carry out the reduction in the presence 0.' pyridine. In this instance laboratory-scale compositions containing 0.5 g amounts of m';trobenzene are reduced in batches. The preparation is effected after reduction of 2 to 3 batches by decanting the solution from the catalyst, filtering and acidifying the liquid with sulphuric acid. In a further stage the pyridine sulphate is filtered off. The yield of 97% hydrazobenzene given in this Soviet patent specification was measured polarographically on the decanted solution.

The yields of pure hydrazobenzeile actually dbtained, however, are very much lower.

The industrial preparation of hydrobenzene through catalytic hydrogenation according to the described process is uneconomical because of the low yields obtained and the costly isolation of the pro sLtict and purification processes required.

Thus the reduction of nitrobenzene on an industrial scale is carried out almost ex clusively electrochemically, using sodium amalgam or metals such as zinc and iron.

These known electrochemical processes also have considerable disadvantages, however.

The reduction of nitrobenzene to hydrazobenzene is incomplete and by-products which reduce the yields are formed. For this reason, and also because of the auxiliary substances used, for example pyridine, mercury or zinc, the preparation of pure hydrazobenzene on an industrial scale is rendered extremely difficult or even impossilble.

There ib thus a need for a process W11iCh has a high reaction speed, which suppresses secondary reactions and which avoids the costly preparation of reaction mixtures.

According to the present invention, there is provided a process for producing hydrazobenzene, which comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of hydrogenation catalyst and of an alkaline agent selected from alkali metal alcoholates, alkali metal hydroxides and mixtures thereof, and the reaction being carried out in the absence or substantial absence of water (other than the water formed by the reaction).

Preferably the reaction mixture is kept in turbulent motion throughout the reaction to ensure good contact between the phases of the mixture; in a preferred embodiment this turbulent motion is achieved by atoms ing the liquid reactants and catalyst into an atmosphere of hydrogen. The liquid react ants and catalyst are preferably admixed with hydrogen before atomising the admixture into the hydrogen atmosphere.

It has been found that in the case where an alkali metal hydroxide is used as the sole agent it is possible to obtain a yield of up to 94% of hydrazobenzene together with some 6-8% of aniline and less than 0.3% of other by-products, even though the nitrobenzene is used in a high concentration.

It has been found that even better results are possible in the case where an alkali metal alcoholate alone is used as the alkaline agent, although similar results are ob tainable when a proportion of the alkali metal alcoholate, for example up to 50% by v.-ci,,ht, is replaced by an alkali metal hydroxide, preferably potassium hydroxide or sodium hydroxide. The alkali metal of the alcoholate is also preferably potassium or sodium.

Surprisingly, it has been found that by using an alkali metal alcoholate as the alkaline agent the formation of aniline is repressed and the formation of other undesired by-produots is almost completely prevented. The water which is produced during the reaction is converted by the alkali metal alcoholate into alkali metal hydroxide and alcohol. The solubility of the hydrazobenzene in the reaction mixture is undesirably increased when water per se is present, and thus when the water which forms is removed by the alcoholate, as outlined above, the space-time-yield is improved, for example by 500/,, compared with the process .where an alkali metal hydroxide is used as the sole alkaline agent.

The process of the invention using an alkali metal alcoholate alone as the alkaline agent has been found to produce hydrazobenzene in yields of up to 98% in relatively short reaction times. That is, the nitrobenzene is converted almost quantitatively to hydrazobenzene, together with some 2 to 3% aniline.

The process, using as alkaline agent an alkali metal alcoholate, an alkali metal hydroxide or a mixture thereof renders unnecessary the hitherto essential and costly treatment of the product solutions comprising acidifying the solutions after separating them from the catalyst, filtering off the resulting salts and recrystallizing the hydrazobenzene. The present invention simply requires that the catalyst be filtered off, whereafter the hydrazobenzene crystallizes out of the alkaline filtrate on cooling in a purity which has been found to average 99.6 to 99.7%. The formation of catalyst poisons which affeot the reaction has been found to be considerably suppressed or almost completely avoided by the process of the in invention.

The space-time-yields of the present process may be considerably increased in comparison with previously known processes, wherein work is carried out in dilute solution, by the faot that the nitrobenzene to be hydrogenated can be used as a relatively concentrated solution in the alcohol. It is preferred that the nitrobenzene is hydrogenated as an 8 to 60% by weight, more preferably a 20 to 45% by weight, solution in the alcohol. The amount of alkaline agent used is preferably from 2 to 20% by weight, more preferably from 5 to 15% by weight, related to the weight of alcohol used.

The alcohols which may be used are those in which both the nitrobenzene and also the alkali metal alcoholate and/or alkali hydroxide are soluble. Preferred alcohols are lower aliphatic saturated monovalent. optionally branched, alcohols, preferably having up to 5 carbon atoms. Methanol is particularly preferred.

The alkali metal alcoholates used, preferably those of sodium or potassium, may contain an alkyl radical of any desired chain length and branching; however the chain preferably contains 1 to 10 carbon atoms, more preferably 1 to 4. In a preferred embodiment the alkyl group of the alcoholate is the same as the alkyl group of the alcohol in which the reaction is performed, i.e. the particularly preferred alcoholates are the methylates.

As alkali metal hydroxides there are preferably used the hydroxides of sodium or potassium, although in principle those of lithium, rubidium and caesium can be used.

Precious metals, for example platinum or palladium, are preferably used as the hydrogenation catalyst. Palladium is preferably used in the form of palladium-carbon, con taining for example from 1 to 5% by weight of palladium. The amount of catalyst used is preferably from 0.001 to 0.01% by weight, more preferably from 0.002 to 0.004% by weight, related to the nitrobenzene used and caluculated as metal.

The process is preferably carried out with the exclusion of atmospheric oxygen. Thus the apparatus used is flushed with an inert gas, e.g. nitrogen which is subsequently expelled by the hydrogen.

No water is added to The components used or to the reaction mixture, i.e. each reaction component is anhydrous. However small quantities of water do not generally disturb the reaction, so it is not essential for the individual components to be completely anhydrous.

The reaction is preferably carried out at a temperature of from 20 to 120"C, more preferably from 20 to 900C, and at a pressure of from 1 to 60 bars, more preferably from 1 to 10 bars. In a preferred embodiment both temperature and pressure are increased over the course of the reaction.

The process may be carried out e.g. in an autoclave, equipped with a heating and cooling device, a high-speed stirrer, an inlet for the hydrogen gas and a temperature and pressure gauge. Expediently such a reactor is charged to approximately 80% of its capacity with the reaction mixture.

In one embodiment hydrogenation is initiated by heating the hydrogen-contaiiing reaction mixture to about 30"C, with further hydrogenation being effected with cooling of the reaction mixture and regulation of the supply of hydrogen gas in a manner such that the formation of aniline is largely suppressed. The hydrogen pressure may rise for example from 1 to 10 bars. In principle, the process can also be carried out at a constant hydrogen pressure provided that the pressure is initially set at a value such that on reaching the maximum reaction temperature it is at least high enough to prevent the reaction mixture from boiling. Preferably, however, the reaction is carried out with a rising, preferably steadily rising, pressure.

Another embodiment, although not one that is preferred, comprises heating the reaction mixture to the final reaction tem perature, preferably 70 to 900 C, before introducing the hydrogen, and subsequently supplying the hydrogen continuously whilst stirring the reaction mixture at high speed, the supply of hydrogen and the cooling of the reaction mixture being regulated such that the ;temperature remains substantially constant.

The optimum reaction times are expediently determined in preliminary experiments and depend inter alia on the size of the pressure vessel and the effectiveness of the stirring device. The determining factors for a 5 litre autoclave can be derived from the Examples.

The maximum pressure to be attained during the reactions is not critical, but depends only on the maximum pressure for which the reaction vessel is constructed.

In a preferred small scale embodiment of the process, after expulsion of the oxygen by flushing with nitrogen, the autoclave is charged with an alcoholic alkali metal alcoholate solution, an alkali metal hydroxide solution or an alkali metal hydroxide/ alkali metal alcoholate admixture, nitrobenzene and palladium carbon as catalyst.

Residual nitrogen is flushed out with hydrogen and the reaction mixture is then heated with vigorous stirring. The supply of hydrogen and the cooling of the mixture are then regulated such that the - temperature of the reaction solution rises to up to 1200C, preferably 90"C, within a period of about 20 to 40 minutes (depending on the amount to be hydrogenated). The pressure rises at the same time from 1 to 10 bar. On completion of the reaction, after pressure reduction, the still hot reaction mixture is filtered to separate out the catalyst, and the filtrate is subsequently cooled, preferably whilst being stirred. The filtering and subsequent stirring are expediently carried out with the exclu sion of atmospheric oxygen, preferably in a nitrogen atmosphere. The hydrazobenzene which crystallises out is separated from the liquid phase by centrifuging or filtering, and is expediently washed with aqueous alcohol.

The alcohol is removed from the mother liquor by distillation and is reused in another batch. The remaining organic phase of the mother liquor is separated from the aqueous alkaline phase and again may be reused in another batch. Generally a recrystallization is not necessary since it has been found that the hydrazobenzene formed has a degree of purity of 99% and up to about 99.7%.

It has been found that difficulties occur when the small scale process described above is carried out on a large industrial scale in metric ton quantities. Thus even with a longer reaction time a considerable reduction in yield occurs. Hence there is a need to provide a means whereby the process of the invention may be performed on an industrial scale in a manner which improves the yield, increases the space-timeyield and simultaneously suppresses undesired subsidiary reaction.

The process of the invention can be carried out in an apparatus which comprises a temperature controllable reactor provided with an atomising nozzle, for containing the liquid reactants, catalyst and hydrogen; means for supplying hydrogen to the reactor to provide an atmosphere of hydrogen above the reaction mixture; and means for removing reaction mixture from the reactor and returning the same thereto via the atomising nozzle so as to atomise -the reaction mixture into the atmosphere of hydrogen. Any known nozzle which makes possible a uniform mixing of the liquid, solid and gaseous phases therein may be used as the atomiser nozzle, for example a Venturi-nozzle or a water jet pump type nozzle. Surprisingly, a particularly efficient material exchange between gas phase, liquid and catalyst is obtainable by means of the nozzle and subsequent atomising.

Using the apparatus, it has been possible to reduce the reaction time to 1/10 of the time observed in large stirring autoclaves. for example from 6 hours to 35 Ito 40 minutes. Further, the yield is improved by some 25% compared with hitherto knonw processes, in spite of the increased nitrobenzene-concentration.

The apparatus and process make possible the production on an industrial scale of hydrazobenzene with a purity greater than 99.7% and in a high yield, e.g. 97% related to the nitrobenzene. The nitrobenzene is converted almost quantitatively to hydrazobenzene with only some 2 to 3% of aniline; Preferably the reactor of the apparatus is charged with the liquid reactants and catalyst to some 80 to 90% of its capacity, leaving a gas space above the liquid. In use of the apparatus a stream of liquid and catalyst is circulated by means of a pump, the stream preferably being removed from the lowest end of the reactor and being delivered to the nozzle disposed at the top of the reactor. In a preferred embodiment the nozzle is provided with means for admixing hydrogen with the stream before it passes out of the nozzle. This enables the reaction solution and the hydrogen to be uniformly mixed with one another in the nozzle and passed into the hydrogen atmosphere of the reactor as a very fine distribuv tion. The reaction solution accumulates in the lower part of the reactor and is then steadily recirculated to the nozzle by way of the circulating pump.

The hydrogen supplied to the nozzle may be withdrawn from the hydrogen atmosphere at the top of the reactor and/or fresh hydrogen may be introduced into the nozzle directly via a line from a hydrogen reservoir. If desired a mixture of hydrogen and reaction solution can be supplied to the nozzle.

For a better understanding of ;the inven- tion, and to show how the same may be carried into effect, reference will now be made, by way of example. to the accom- panying drawing. the single Figure of which is a schematic cross section of an apparatus according to the invention.

In the Figure there is shown a tcmpr?- ture controllable reactor 1 which may be selectively heated or cooled by means o-f a jacket 9. In use, the reactor is charged such that some 40 to 20% of its volume is available as gas space. The reactor 1 is provided with a temperature controlled circulation system 5 having a pump 2, the circulat- ing system commencing at the bottom of the reactor and terminating at a nozzle 3, which nozzle is mounted in the upper part of the reactor 1 and extends into the hydrogen gas space thereof. A supply of hydrogen into the nozzle 3 is effected by means of a lateral intake pipe 6, to which fresh hydrogen is supplied from a reservoir via a supply line 4b and/or hydrogen from the gas space of the reactor is supplied via a supply line 4a.

The reactor is charged with The alkaline nitrobenzene/ alcohol solution containing the catalyst via a supply line 8, whilst the pro duct mixture is removed via an outlet valve 7.

In a preferred embodiment the apparatus is used for effecting the process by first supplying to the reactor 1 an alcoholic solu tion of nitrobenzene, alkaline agent and hy drogenation catalyst under nitrogen atoms sphere via the supply line 8. After expulsion of the nitrogen with hydrogen, the reaction mixture is heated by means of the heat exchanger jacket 9 to about 35) C, and is pumped through the nozzle 3. A hydrogen pressure in the gas space of the reactor of e.g. 2 to 4 bar is supplied from a reser- voir through the lines 4b and 4a. The supply of hydrogen and the temperature of the reaction mixture are regulated such that dur i g the hydrogenation, with increasing pressure, the temperature rises to about 900C After the hydrogenation reaction is concluded i.e. after approximately 30 to 40 minutes, the product mixture is removed from the reactor via the outlet valve 7 under a nitrogen atmosphere, and is filtered whilst hot. After cooling, the hydrazobenzene which crystallises out is centrifuged off and washed with aqueous alcohol, preferably methanol.

The following Examples illustrate the invention.

EXAMPLE I An autoclave of 5-litre capacity, equipped with a stirrer, was flushed with nitrogen and charged with 2,400 g of a 10% by weight methanolic sodium methylate solution, 1,000 g nitrobenzene and 2 g palladium carbon (2% by weight Pd=0.04 g Pd). After the residual nitrogen had been expelled by hydrogen the mixture in the autoclave was heated to about 30 to 40 C whilst being stirred vigorously at 1,400 r.p.m. The supply of hydrogen and the cooling of the reaction mixture was then controlled in a manner such that the temperature of the solution increased from 30.to 90"C and the pressure increased from 2 to 10 bar. After about 30 minutes the hydrogenation was concluded.

The solution was filtered under nitrogen whilst hot, cooled, and then the hydrazobenzene which crystallized out was centrifuged off. The filter cake was repeatedly washed with aqueous methanol and subsequently dried, the washing liquid being combined with the filtrate. The separated or ganic phase was then supplied to the follow ing batch after the methanol contained therein had been distilled off. After approximately 10 batches the aniline formed was removed by distillation. There was obtained on average per batch, 730 g hydrazobenzene in a purity of 99.7%. This corresponded to a yield of 97160J, hydrazobenzene related to the nitrobenzene used.

EXAMPLE In the same apparatus as in Example 1, 1,230 g nitrobenzene in 2,400 g of a 9% by weight methanolic sodium methylate solution were hydrogenated in the presence of 2 g Pd-carbon. The supply of hydrogen and the cooling of the reaction mixture were regulated such that the temperature -of the-solution increased slowly to about 900C.

After about 30 minutes the reduction was concluded. The solution was filtered under nitrogen whilst hot to separate the Pdcarbon; after the addition of water the hydraiobenzene which crystallized out was filtered off. The filter cake was then washed with aqueous methanol and the hydrazobenzene dried at 7800C. The yield, related to the nitrobenzene used, amounted to 94% (864g) of theoretical. The melting point of the product was l260C. EXAMPLE 3 As in Example 1, a solution of 2,060 g nitrobenzene in 2,400 g methanolic sodium methylate (about 10% by weight) was hy drogenated in the presence of - 2 g Pdtemperature of the autoclave rose to 90 carbon. During the reaction the internal temperature of the autoclave rose to 'i C.

After about 45 minutes the reduction was concluded. The solution was filtered and cooled, and the hydrazobenzene which crystallised out was centrifuged off. The further processing of the filtrate and the purification and drying of the hydrazobenzene was effected as described in Ex- ample 1. On average per batch 1.437- g of hydrazabenzene with a melting point of 127 128 C were obtained.

EXAMPLE 4 As in Example 1. a solution of 1,000 g nitrobenzene in 2,000 g of a 10% by weight methanolic potassium methylate solution was hydrogenated in the presence of 2 g Pdcarbon. The supply of hydrogen and the cooling were regulated such that the temperature of the solution rose to approximately 90"C. The. reduction was concluded after about 30 minutes. The filter cake was washed with methanol and dried at 60 80 C; The further processing of the filtrate was as described in Example 1. The yield of hydrazobenzene amounted to 95% of the theoretical value based on nitrobenzene.

EXAMPLE 5 As in Example 1, a solution of 500 g nitrobenzene in 1,500 g of a 10% by weight ethanolic sodium ethylate solution was hydrogenated in the presence of 2 g Pd-carbon, The cooling of the reaction-mixture was regulated such that the temperature of the solution slowly increased from 30 to 90"C.

The reduction was concluded after about 30 minutes. The resulting solution was -fil-. tered whilst hot to separate out the Pdcarbon. The hydrazobenzene which crystallized-out after the -addition of water was centrifuged off, the filter cake being washed with aqueous ethanol and the hydrazobenzene dried at - 70-800C. The yield, related to the nitrobenzene used, amounted to 93% of the theoretical value; the melting point of the product was 125-126 C.

EXAMPLE 6 500g nitrobenzene were hydrogenated in a 5% by weight isopropanolic sodium isopropylate solution in the presence of 2 g Pd-carbon (as Example 1). The cooling of the reaction mixture was regulated such that the temperature of the solution increased to 800C, the reaction being concluded after 50 minutes. The solution was then -filtered, the filter cake being washed and dried at 80"C, and the .further- pro cessing of the filtrate being as doscribed in Example 1. The yield of hydrazobenzene amounted to - 91% of the theoretical value c!culated - 6n the nitrobenzene.

EXAMPLE 7 A 5-litre autoclave equipped with a high speed stirrer, a - heating and cooling device, a feed opening for the hydrogen and a pressure and temperature gauge, was flushed with nitrogen and charged-with 1,000 g nitrobenzene, 2,400 g methanol, 250 gKOH and 2 g palladium carbon by weight=0.04 g Pd). After the nitrogen had been expelled with hydrogen the hydrogen containing mixture was carefully heated to 300C whilst being stirred vigorously at 1,400 r.p.m. The further supply of hydrogen and cooling of the reaction mixture were - then regulated such that the temperature of the solution rose steadily from .30. to 90"C After high-speed stirring for about .30 minutes. calculated from - the. time when 30"C was- reached, the hydrogenation was concluded. The solution was filtered whilst hot, and cooled, and the hydrazobenzene which crystallized out was centrifuged offi The filter cake was washed repeatedly with aqueous methanol and the washing liquid combined with the filtrate. The separated organic phase was then supplied to the fQl- lowing batch after the methanol contained therein had been distilled off. After about 10 batches. the aniline formed was removed by distillation. There was obtained on aver age per batch 700 g hydrazobenzene with a purity of > 99.5%. This corresponded to a yield of 94%. hydrazobenzene, related to the nitrobenzene used. The melting point of the product was 127 C.

EXAMPLE 8 As in Example 7 a solution of 1,000 -g nitrobenzene and 20Q g KOH in 5000 g methanol. was hydrogenatedin the presence of 2 g Pd-carbon. The supply of hydrogen and the cooling of the reaction mixture were regulated such that the temperature - of the solution rose from about 30 to 909C- - After about 30 minutes the reaction was - con duded. The - solution was. filtered whilst hot and cooled, and the hydrazobenzene which crystallised out was filtered off. The filter cake, after washing with methanol, was dried at 7080 C. The preparation of the mother liquor was carried out as described in Example 7. The yield amounted to 6% g hydrazobenzene (93% related to the nitrobenzene used), The product had a melting point of I2127.

EXAMPLE 9 As in Example 7, a solution of 1,000 g nitrobenzene and 200 g NaOH was dissolved in 2,000 g methanol and hydrogenated in the presence of 2 g Pd-carbon. The cooling of the reaction mixture was regulated such that the temperature of the solution rose slowly from 30 to 90"C. The reduction was concluded after about 30 minutes. The solution was filtered whilst hot and cooled, and the hydrazobenzene which crystallized out was filtered off. The filter cake after washing with methanol, was dried at 70 to 80"it. The preparation of the mother liquor was carried out as des- cribed in Example 7.

694 g hydrazobenzene (93% related to the nitrobenzene used) were oDtained with a purity > 99.59 and a melting point of 1-270C.

EXAMPLE 10 As in Example 7, a solution of 1,000 g nitrobenzene and 240g KOH in 2,400 g methanol, and also 2 g palladium carbon, was charged into the autoclave and heated to about 8uC. After the flushing nitrogen had been expelled with hydrogen, the stirrer was switched on. The supply of hydrogen and the cooling of the reaction mixture were regulated such that the temperature re rained at abo 94% hydrazobenzene related to the nitrobenzene used. The melting point of the product was 127"C.

EXMPLE 14 The reactor of Example 11 was charged with 800 kg methanol, 80 kg NaOH, 400 kg nitrobenzene and 600 g Pdearlbon, and the hydrogenation was effected as described in Example 1:1. The solution was filtered whilst hot, cooled and the hydrazabenzene which crystallized out was centrifuged off. The filter cake, after washing with methnaol, was dried at 70-800C. 280 kg hydrazobenzene with a purity > 99.5% and a melt ing point of 127so (yield 93.5gO of theoretical) were obtained, EXAMPLE :15 A solution of 1,200 kg of a 10% sodium ethylate solution and 400 kg nitrobenzene were hydrogenated in the presence of 800 g Pd-carbon. The cooling of the reaction mixture was regulated such that the temperature of the solution rose slowly from 30 to 900C.

After about 45 minutes the reduction was concluded. The solution was filtered whilst hot to separate the Pd-carbon. Thereafter water was added and the hydrazabenzene which crystallized out was centrifuged off, The filter cake was washed with aqueous ethanol and the hydrazdbenzene dried at 70 to 800C. The yield, related to the nitrobenzene used, amounted to 92% of the theoretical value. The melting point of the product was 125 to 126 C, WHAT WE CLMM IS : - 1. A process for producing hydrazo. benzene, whioh comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent selected from alkali metal alcoholates, alkali metal hydroxides and mixtures thereof, and the reaction being carried out in the absence or substantial absence of water (other than the water formed Iby the reaction).

2. A process for producing hydrazobenzene, which comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent comprising an alkali metal alcoholate, and the reaction being carried out in the absence or sub sandal absence of water (other than the water formed by the reaction).

3.. A process for producing hydrazobenzene, which comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent comprising an alkali metal hydroxide, and the reaction being carried out in the absence or substantial absence of water (dther than the water formed by the reaction).

4. A process according Q claim 1. wherein the reaction is carried out in the presence of both an alkali metal alcoholate and an alkali metal hydroxide, and the weight of hydroxide is not greater than the weight of alcoholate.

5. A process according to claim 1, 2 or 4, wherein the alkali metal alcoholate contains an alkyl radical having from 1 to 10 carlbon atoms.

6. A process according to claim 5. wherein the alkyl radical of the alcoholate contains from 1 to 4 carbon atoms.

7. A process according to claim 6, wherein the alcoholate is a methylate.

8. A process according to any of claims 1, 2, 4, 5, 6 and 7, wherein the alkyl group of the alcoholate is the same as the alkyl group of the alcohol in which the reaction is performed.

9. A process according to any of the preceding claims, wherein the reaction is carried out at a temperature of from 20 to 1200C.

10. A process according to claim 9. wherein the reaction is carried out at a temperature of from 20 to 9QeC.

11. A process according to any of the preceding claims, wherein the hydrogen pressure is from 1 to 60 bars.

12. A process according to claim 11, wherein the hydrogen pressure is from 1 to 10 bars, -13. A process according to any of the preceding claims, wherein the catalyst is a precious metal.

14. A process according to claim 13. wherein the catalyst is platinum or pal. ladium.

15. A process according to claim 14, wherein palladium used as catalyst is in the form of palladium-carbon.

16. A process according to claim 15, wherein the palladium-carbon contains from 1 to 5% by weight of palladium.

17. A process according to any of claims 1Z3 to 16, wherein the catalyst is present in a concentration of from 0.001 to 0.01% byweight, calculated as metal, based on the weight of nitrobenzene.

If8. A process according to claim 17, wherein the catalyst is present in a concen- tration of from 0.002 to 0.0040/, by weight, calculated as metal, based on the weight of nitrobenzene.

19. A process according to any of the preceding claims, wherein the alcohol con

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

94% hydrazobenzene related to the nitrobenzene used. The melting point of the product was 127"C.

EXMPLE 14 The reactor of Example 11 was charged with 800 kg methanol, 80 kg NaOH, 400 kg nitrobenzene and 600 g Pdearlbon, and the hydrogenation was effected as described in Example 1:1. The solution was filtered whilst hot, cooled and the hydrazabenzene which crystallized out was centrifuged off. The filter cake, after washing with methnaol, was dried at 70-800C. 280 kg hydrazobenzene with a purity > 99.5% and a melt ing point of 127so (yield 93.5gO of theoretical) were obtained, EXAMPLE :15 A solution of 1,200 kg of a 10% sodium ethylate solution and 400 kg nitrobenzene were hydrogenated in the presence of 800 g Pd-carbon. The cooling of the reaction mixture was regulated such that the temperature of the solution rose slowly from 30 to 900C.

After about 45 minutes the reduction was concluded. The solution was filtered whilst hot to separate the Pd-carbon. Thereafter water was added and the hydrazabenzene which crystallized out was centrifuged off, The filter cake was washed with aqueous ethanol and the hydrazdbenzene dried at 70 to 800C. The yield, related to the nitrobenzene used, amounted to 92% of the theoretical value. The melting point of the product was 125 to 126 C, WHAT WE CLMM IS : - 1. A process for producing hydrazo. benzene, whioh comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent selected from alkali metal alcoholates, alkali metal hydroxides and mixtures thereof, and the reaction being carried out in the absence or substantial absence of water (other than the water formed Iby the reaction).
2. A process for producing hydrazobenzene, which comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent comprising an alkali metal alcoholate, and the reaction being carried out in the absence or sub sandal absence of water (other than the water formed by the reaction).
3.. A process for producing hydrazobenzene, which comprises reacting nitrobenzene with hydrogen at a pressure of 1 bar or above in an alcohol to form the desired compound, the reaction being carried out in the presence of a hydrogenation catalyst and of an alkaline agent comprising an alkali metal hydroxide, and the reaction being carried out in the absence or substantial absence of water (dther than the water formed by the reaction).
4. A process according Q claim 1. wherein the reaction is carried out in the presence of both an alkali metal alcoholate and an alkali metal hydroxide, and the weight of hydroxide is not greater than the weight of alcoholate.
5. A process according to claim 1, 2 or 4, wherein the alkali metal alcoholate contains an alkyl radical having from 1 to 10 carlbon atoms.
6. A process according to claim 5. wherein the alkyl radical of the alcoholate contains from 1 to 4 carbon atoms.
7. A process according to claim 6, wherein the alcoholate is a methylate.
8. A process according to any of claims 1, 2, 4, 5, 6 and 7, wherein the alkyl group of the alcoholate is the same as the alkyl group of the alcohol in which the reaction is performed.
9. A process according to any of the preceding claims, wherein the reaction is carried out at a temperature of from 20 to 1200C.
10. A process according to claim 9. wherein the reaction is carried out at a temperature of from 20 to 9QeC.
11. A process according to any of the preceding claims, wherein the hydrogen pressure is from 1 to 60 bars.
12. A process according to claim 11, wherein the hydrogen pressure is from 1 to 10 bars, -
13. A process according to any of the preceding claims, wherein the catalyst is a precious metal.
14. A process according to claim 13. wherein the catalyst is platinum or pal. ladium.
15. A process according to claim 14, wherein palladium used as catalyst is in the form of palladium-carbon.
16. A process according to claim 15, wherein the palladium-carbon contains from 1 to 5% by weight of palladium.
17. A process according to any of claims 1Z3 to 16, wherein the catalyst is present in a concentration of from 0.001 to 0.01% byweight, calculated as metal, based on the weight of nitrobenzene.
If8. A process according to claim 17, wherein the catalyst is present in a concen- tration of from 0.002 to 0.0040/, by weight, calculated as metal, based on the weight of nitrobenzene.
19. A process according to any of the preceding claims, wherein the alcohol con tains from 8 to 60% by weight of nitrobenzene.
20. A process according to claim 19, wherein the alcohol contains from 20 to 45% by weight of nitrobenzene.
21. A process according to any of the preceding claims, wherein the alcohol contains from 2 to 20% by weight of the alkaline agent.
22. A process according to claim 21, wherein the alcohol contains from 5 to 15% by weight of the alkaline agent.
23. A -process according to - any - qf the preceding claims, wherein the alcohol has from 1 to 5 carbon atoms.
24. A process according - to - claim 23, wherein the alcohol is methanol.~
25. A process according to any of the preceding claims, wherein the alkali metal is sodium or potassium.

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26. A process according - to any -of the preceding clainis, wherein the hydrogen pressure is increased- over thecourse of the reaction.
27. A process according to any of the preceding claims. wherein the temperature is increased over the course of the reaction.
28. A process according to any of the preceding claims. which includes the additional step of isolating- the desired compound from the product mixture.
29. A process according to any of the preceding claims, wherein the reaction - is carried out by atomising the liquid-reactants and catalyst into a hydrogen atmosphere, by means of an atomising nozzle.
30. A process according to claim 30, wherein the liquid reactants and catalyst are admixed with hydrogen before atomising the admixture into the hydrogen atmosphere.
31. A process according to claim 29 or 30, wherein reaction mixture is rcmoved from the reactor in which the reaction is carried out, and wherein the removed reaclion mixture is recycled to the reactor via the alomising nozzle.
32, A process according to any of claims 29- to 31, wherein hydrogen is removed from the reactor in which the reaction is carried out, and wherein the removed hydrogen is recycled to the reactor via the atomising nozzle.
33. A process according to claim 1, sub- stantially as described in any one of Examples 1 to 15.
34. A process according to claim 1, substantially as described with reference to the accompanying drawling.
35. Hydrazobenzene whenever produced bp the process according to any of the preceding claims.