GB1569302A - Diazotization/coupling or aromatic amines - Google Patents

Description

PATENT SPECIFICATION ( 11) 1 569 302

M",1 ( 21) Application No 9425/79 ( 22) Filed 24 Nov 1976 ( 19) ( 62) Divided Out of No 1569301 ( 31) Convention Application No's 635059 ( 32) Filed 25 Nov 1975 in / 635058 ( 33) United States of America (US) ( 44) Complete Specification Published 11 Jun 1980 ( 51) INT CL 3 C 07 C 107/06 107/08 ( 52) Index at Acceptance C 2 C 220 227 22 Y 30 Y 322 325 32 Y 456 Y 620 660 680 699 712 FG NX ( 72) Inventors: JOHN KENT DETRICK FRANK EDWARD HERKES ( 54) DIAZOTIZATION/COUPLING OR AROMATIC AMINES ( 71) We, E I DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware United States of America located at ?ll Wilmington, State of Delaware, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: 5

The present invention relates to the control of nitrogen oxide reactions in off-gases from diazotization-coupling reactions in the preparation of 1 3-diarvl triazenes.

1,3-Diaryl triazenes (also referred to as diazoamino arvl compounds) can be made to undergo rearrangement by heating, e g in the presence of a Friedel-Crafts catalyst, to form aromatic amino azo compounds The latter are useful for the preparation of aromatic 10 diamines by reduction with hydrogen The diamines in turn, are useful as intermediates in the preparation of polymers, anit-oxidants etc.

: U S Patent 2,894,942 describes the formation of aromatic amino azo compounds by adding an inorganic nitrite to a mixture of an excess of a primary aryl monoamine, a mineral 1 $ acid, and a Friedel-Crafts catalyst while the temperature is 050 C ( 20-30 C preferred), 15 and thereafter heating up to about 40-75 C ( 45-55 C preferred) A portion of the amine is diazotized and the diazonium salt couples with unreacted amine to form the diazoamino aryl compound, which rearranges to the amino azo compound under the combined influence of the catalyst and heat One of the disadvantages of this process when considered in terms of large-scale operations is the need for separating and disposing of the 20 salt, e g sodium chloride, produced as a by-product of the diazotization reaction.

Over a period of a century or more, publications occasionally have appeared describing the diazotization of primary aromatic amines bv the use of certain nitrogen oxides For example, Griess, in 1862 (Ann 121 No 3 257-280) reported the synthesis of diazoaminobenzene by passing what he called "a weak stream of nitrous acid" into a cold 25 solution of aniline in alcohol until all of the aniline was consumed Griess used the formula "NO 3 " to denote the nitrous acid, but did not describe the composition or derivation of his diazotizing agent.

U.S Patent 2 622078 (Klaassens el al) describes carrying out the diazotization of amino aromatic sulfonic acids to diazonium compounds in water-ketone mixtures Although 30 nitrous gas (described as N 2,03 or a mixture of NO and NO 2 of a composition approximating that of N 203) was disclosed to be useful in the Klaassens et al process the gas was introduced at 20 C into a mixture of acetone or butanone water, and nitric acid, and the amino compound was added to the mixture while the temperature was maintained below 35 C Thus, Klaassens et al used conditions which led to the formation of nitrous acid 35 " 1 Furthermore, Klaassens et al operated with full consumption of their amine to produce the l diazonium compound and effected no coupling of the diazonium compound.

Lovejoy et al, J Chem Soc (A) 1968, 2325-8 reported the formation of a diazonium { nitrite by the reaction of a primary aromatic amine in an organic solvent with liquid, undissociated dinitrogen trioxide at -85 C as well as the isolation of a small amount of the 40 1 569 302 diazoamino compound in some cases However, the authors did not describe the action of gaseous nitrogen trioxide on the amines, nor did they disclose the conditions that would be required to produce a diazoamino compound as a major product.

The diazotization of aromatic amines by means of N 203 gas in the absence of water solvent, followed by coupling of the resulting diazo compound with phenols or naphthols 5 also in the absence of water solvent is described in Japanese Patent Application Publication 15,631/61 (September 7 1961).

Primary aromatic amines also have been diazotized in solvents by means of pure nitrogen tetroxide O N Witt, Tagbl Natf -Vers Baden-Baden 1879, 194 (Chem Zentr 1880, II, 226) reported obtaining benzenediazonium nitrate by the reaction of anhydrous pure 10 nitrogen tetroxide with aniline in an anhydrous benzene solution: and B Houston et al J.

Am Chem Soc 47, 3011-3018 ( 1925), obtained a diazoaminobenzene derivative as well as the corresponding diazonium nitrate by the action of pure anhvdrous nitrogen tetroxide on o-, m-, and p nitroaniline in an anhvdrous benzene solution.

Our copending Application No 48973/76 (Serial No 1569361) describes and claims a 15 process for the diazotization-coupling of primary aromatic monamines by means of a nitrogen oxide-containing gas mixture derived from the oxidation of ammonia.

The process of that invention comprises, in sequence, catalytically oxidizing ammonia by means of a gas comprising diluted molecular oxygen preferably air, so as to produce a gas mixture comprising a dilute nitrogen oxide component selected from nitrogen dioxide 20 (NO 2) and mixtures of nitrogen dioxide and nitric oxide the nitrogen oxide component being represented by the formula NO, wherein x is ( 1 + n) N being the NO, fraction of the nitrogen oxide component and generally has a value of 1 1 to 2 0: and contacting the gas mixture, preferably at a temperature in the range of about from 25 -350 C with a preferably neat primary aromatic monoamine, e g aniline, in the liquid phase so as to give 25 a monoamine temperature in the range of about from 25 to 90 C preferably 40 to 60 C, during contact, while maintaining at least 5, and preferably at least 40, percent by weight of unreacted monoamine during and at the termination of the reaction.

The accumulation of an aromatic diazonium nitrate anvwhere in the reaction system in the present process is undesirable because of the potential explosion hazard created 30 thereby The excess monoamine present in the reaction mixture enables the initially formed diazonium nitrate to couple instantaneously with the monoamine to form the triazene and thereby prevents the build-up of uncoupled diazonium nitrate in the reaction mixture In addition, a residual gas consisting chiefly of the diluent usually nitrogen present in the oxygen-containing gas used to produce the nitrogen oxide-containing gas mixture from 35 ammonia, and containing possibly unreacted NO, and oxygen as well as water, monoamine, and 13-diaryl triazene in the vapor phase, is separated from the triazenecontaining reaction liquid, and is conducted through a pipeline to a waste-gas disposal system under conditions such that an aromatic diazonium nitrate fails to deposit on the walls of the pipeline 40 Therefore, according to the present invention we provide a process, useful in conjunction with any procedure wherein a primary aromatic monoamine is diazotized leaving a residual gas containing unreacted monoamine and one or more nitrogen oxides, which process comprises conducting the residual gas through a pipeline to a waste-gasdisposal system and performing at least one of the following steps so that an aromatic diazonium nitrate fails to 45 deposit on the walls of the pipeline: (a) heating the walls of the pipeline during the passage of the residual gas therethrough e g to a temperature in the range of from 55 to 125 C: (b) conducting the residual gas out of the pipeline before an aromatic diazonium nitrate deposits on the walls thereof i e allowing a limited residence time of the gas in the pipeline, dependent on the rates of the reactions which must occur in the gas before the 50 conditions for diazonium salt formation are reached e g the rate of oxidaton of nitric oxide to nitrogen dioxide when molecular oxygen is present: or (c) preventing the substantial entry or formation of nitrogen dioxide in the pipeline The term -residual gas-' as used herein denotes the spent gas from a gas/liquid reaction system as well as the vapor produced by the volatilization of a reaction liquid For example, the process of the invention can be 55 employed in systems wherein amines are diazotized with an inorganic nitrite and a mineral acid, whereby vapors containing unreacted monoamine and one or more nitrogen oxides may be present in the ventilating flues of the reaction vats (Filippuichev, S F et al, Anilinokrasochnaya Prom 3 351-5 Chemical Abstracts 28 3720) However, as will be explained, the diazotization/coupling process as described in Application No 48973/76 60 (Serial No 1569301) is preferred over methods described in the prior art, and the nitrogen oxide off-gas reaction control process is used to particular advantage with this diazotization/ coupling process.

The Diazotizationl Coupling Process of Application No 48973/76 (Serial No 1569301) Although hot ammonia oxidation gases have heretofore been absorbed in inorganic 65 1 569 302 liquids, e g, to produce ammonium nitrite (U S Patents 2797144 and 2,805, 122) and sodium nitrite (British Patent 1,347,909), the bringing together of a primary aromatic monoamine, i e, a strong reducing agent, and the hot gas obtained by the oxidation of ammonia is contrary to the natural inclination of those skilled in the art because of doubts concerning the controllability of the reaction between such materials Contrary to 5 expectations, however, it has been found that the reaction between hot ammonia oxidation gas and an aromatic monoamine can be effected smoothly and controllably.

In addition to the nitrogen oxide component, the NO,-containing gas mixture produced by the oxidation of ammonia also contains an inert diluent e g nitrogen, and water vapor, the NO, concentration usually being about 10-12 mole percent and x generally having a 10 value of from 1 1 to 2 This gas mixture can be contacted intact with the monoamine, and this is the preferred practice There is no advantage in removing water vapor from the mixture prior to contacting it with the monoamine.

From the viewpoint of maximizing the yield of 1 3-diaryl triazene the diazotisation/ coupling process preferably is carried out using ( 1) NO, wherein x is in the range of from 1 3 15 to 1 7; ( 2) an amount of gas mixture contacted with the monoamine and a time of contact such that at least about 60 percent by weight of the monoamine remains unconsumed: and ( 3) a temperature of the gas mixture just prior to its contact with the monoamine which is in the range of about from 1100 to 275 C.

In the process, ammonia gas and a gas comprising diluted molecular oxygen, preferably 20 air, are passed over a catalyst at elevated temperature whereby the ammonia is oxidized to nitric oxide (NO); and the resulting gas comprising a mixture of nitric oxide oxygen water vapor, and diluent, e g, nitrogen, is cooled whereby the nitric oxide is oxidized, either completely but preferably only in part, to nitrogen dioxide (NO,) resulting in a gas mixture t 25 comprising nitrogen dioxide (NO,) preferably also nitric oxide, the diluent water vapor, 25 and, depending on the specific conditions used possibly some residual oxygen Under the usual circumstances, the NO, concentration of the gas mixture produced is 10-12 mole percent, but it can be adjusted as will be described hereinafter to span the range of from 1 to mole percent, and even up to 30 mole percent and such concentrations can be used for the diazotization/coupling reaction 30 In the present process of Application No 48973/76 (Serial No 1569301) the nitrogen oxide(s) used in the diazotization/coupling reaction are present in diluted form As such, the diazotization/coupling gas of that process is readily distinguishable from the pure N 203 and N 204 which have been described in the art relating to diazotization reactions The use of the dilute gas mixtures not only has the advantage that the diazotizing gas is more readily 35 obtainable, but also is beneficial in allowing a smoother more easily controllable reaction and therefore reducing the possibility of yield lossess associated with an uncontrolled reaction at the gas-liquid interface Also as contrasted to the prior art nitrite/acid diazotization method, the process of Application No 48973/76 (Serial No 1569301) produces no salt by-products requiring troublesome salt separation procedures 40 The oxidation of ammonia, and subsequently of the resulting nitric oxide by air at elevated temperature to produce gas mixtures containing no, as defined above has been amply described in the literature For the oxidation to nitric oxide usually a platinum or platinum alloy catalyst is used, together with temperatures in the range of about from 8000 to 950 'C Pressures of about from atmospheric to 120 psig ( 9 16 atm) have been used 45 Oxygen-enriched air also can be used The ammonia content of the ammonia/air mixture generally ranges about from 11 to 13 mole percent and the oxygen/ammonia mole ratio about from 13/1 to 17/1 Further details can be learned bv reference to Mellor's Comprehensive Treatise on Inorganic and Theoretical Chemistry Vol V 111 Suppl 11 Sec.

t; 50 XXIX; or Riegel's Handbook of Industrial Chemistr Y Ed 7 Van Nostrand, 1974 pp 50 94-98.

In contrast to the oxidation of ammonia the oxidation of nitric oxide occurs at a less elevated temperature e g in the range of about from 100 ' to 500 'C the rate of oxidation being higher at lower temperatures and higher pressures The value of x in the NOX component, which is a measure of the state of oxidation of the nitrogen oxide component, 55 can be varied by suitable selection of the pressure temperature and contact time of the gases in the NO oxidizer, the NO, fraction of the NO, produced increasing with the contact time The contact time required to produce a desired NO, fraction can be determinedf from know rates of oxidation at various temperatures and pressures.

68 tlt The NO component can be NO, alone but preferably is a combination of NO, and NO 60 When NO, is NO, alone i e when x is 2 the yield of 1 3-diarvl triazene is apt to be lower owing to ( 1) a competing nitration reaction which results for example in the formation of p and o nitroanilines when the reaction is aniline and ( 2) rearrangement of the triazene to the amino azo compound catalyzed by nitric acid produced as a by-product Although the At q$ nitro and amino azo produces are also useful in that they can be reduced to diamines, it is 65 A 1 569 302 preferred that as much as the monoamine as possible be converted to the triazene in the diazotization/coupling step, and for this reason an NO, wherein x is less than 2 is preferred.

Minimizing the formation of the amino azo compounds during the diazotization-coupling decreases the likelihood of the formation of by-products which could subsequently prove troublesome 5 The value of x in NO, will usually be at least about 1 1 and preferably at least about 1 3.

As the NO, fraction of the mixture decreases more of the nitric oxide is unutilized and conversion to the triazene consequently is low At very low NO 2 fractions excessive quantities of unutilized nitric oxide would have to be handled Preferablv x has a value no greater than about 1 7 so as to avoid the increased chance that rearrangement, nitration, 10 and/or oxidation reactions will occur, which reactions could subsequently prove troublesome, as mentioned previously On the basis of good utilization of the nitric oxide as well as the minimizing of side-reactions, an NO, wherein x is close to a value of about 1 5 ( 50/50 N 0,/NO mixtures), e g about 1 4 to 1 6 is especially preferred.

The NO, concentration of the gas mixture produced bv the air oxidation of nitric oxide 15 usually is about 10-12 mole percent and depends on the oxvgen/ammonia mole ratio and the yield, higher oxygen/ammonia ratios and yields being associated with higher NO, concentrations In theory, up to about 17 % NO, is attainable A range of about from 1 to 20 mole percent NO, can be achieved by dilution or water vapor removal, for example and mixtures having such concentrations can be used in the diazotization/coupling step 20 Mixtures having a higher NO, concentration e g up to about 30 mole percent are attainable by combining the I-20 percent mixtures with more highly concentrated mixtures, and also can be used in the diazotization/coupling step However concentrations above about 12 mole percent are not preferred owing to the added expense of achieving such concentrations and the loss of the beneficial effects of dilution with respect to reaction 25 control Also, in the diazotization/coupling there appears to be no benefit resulting from diluting or removing water vapor from, the mixture produced by the nitric oxide oxidation, and accordingly the 10-12 mole percent NO, concentration is preferred.

The temperature of the NO,-containing gas mixture just prior to its contact with the monoamine preferably is in the range of from 250 to 350 'C and more preferably from 1100 30 to 2750 C When, as in the usual case water vapor is present in the mixture a gas temperature of at least about 1100 C prevents the condensation of water vapor from the gas with the attendant formation of nitric acid, which catalvzes the rearrrangement of the 1,3-diaryl triazene to the amino azo compound Above about 350 'C oxidative degradation of the monoamine occurs, and furthermore, it becomes more difficult to maintain higher 35 states of oxidation of the NO, at such temperatures owing to the increased rate of decomposition of nitrogen dioxide into nitric oxide and oxygen Temperatures above about 2750 C are not preferred when oxygen is to be excluded and also because strenuous cooling measures are required to maintain the amine in the required temperature range as will be described later The present process involves advantageously contacting the monoamine 40 with a considerably hotter gas for diazotization than was employed in the procedures described in the prior art.

The diazotization-coupling temperature or the temperature at which the monoamine is maintained while it is in contact with the NO,-containing gas mixture, is in the range of from 25 to 90 'C and preferably 400 to 60 'C Temperatures above 90 'C are not employed 45 owing to the instability of the triazene and consequent vield losses The specific temperature employed will depend on various factors First, the temperature of the amine rises when it is contacted with the hot NO, gas mixture as a result of the heat of reaction as well as of the heat transferred to the amine from the hot gas Consequently it will be convenient to employ a reaction temperature in the vicinity of the temperature which 50 results from these exothermic and transfer conditions and which can be maintaned easily by modest cooling techniques e g water cooling.

The reaction temperature used may be selected also on the basis of the solubilitv of the triazene and the amount of amine consumed If a homogeneous product is desired, it may be desirable to employ a temperature at which the triazene is soluble in the amine at the 55 operating consumption level For example 1,3-diphenvl-triazene is sufficiently soluble in aniline at 50-550 C that at such temperature the product is homogeneous when about 20-40 %-c of the aniline has been consumed At consumption levels above 40 % higher temperatures are required for homogeneity Therefore in the diazotization/coupling of aniline, a temperature of about 50-550 C is especially preferred at consumption levels up to 60 about 40 %, and higher temperatures levels e g up to about 900 at consumption levels above about 40 % Cc.

Temperatures as low as about 250 C can be employed in the diazotizationcoupling reaction, homogeneity in the case of aniline still being attainable at this temperature at a 20 % consumption level The range of from 40 ( to 600 C is preferred on the basis of all 65 1 569 302 factors considered, i e, yield, ease of maintaining temperature, homogeneity of product, etc.

The diazotization-coupling process operates satisfactorily at atmospheric pressure although elevated pressures, usually those employed in the nitric oxide oxidation e g, up to about 20 psiga can be used 5 In the process described above, the NO,-containing gas mixture is contacted with an excess of monoamine so that the initially formed diazonium salt (nitrite or nitrate) can couple instantaneously with unreacted monoamine to form a 1 3-diarvl triazene ' Excess" monoamine means that unconsumed or unreacted monoamine is present in the reaction mixture at all times, with at least 5 percent and preferably at least 40 percent of the 10 monoamine remaining unconverted to products If the contact between the NO, and the reaction mixture is interrupted while at least 5 percent of the monoamine remains unconsumed, the build-up of uncoupled diazonium nitrate in the reaction mixture can be avoided.

S The monoamine is reacted in the liquid phase A solvent or diluent is not required with 15 monoamines which are liquid under the reaction conditions, and for economic reasons these preferably are employed in the neat condition If the monoamine is a solid under the reaction conditions, a solvent therefor can be used e g an aromatic hydrocarbon such as benzene or xylene or a halogenated aliphatic hydrocarbon such as carbon tetrachloride or '20 methylene chloride The presence of a solvent or a diluent liquid such as water with a liquid 20 monoamine has no adverse effect on the reaction.

There should be sufficient liquid in the reaction mixture to form a stirrable slurry or slush, or a solution, with the solid triazene formed Otherwise, even if excess monoamine is present, the diffusion of the gas through the reaction mixture may be so slow that the diazonium nitrate can accumulate on the surface of the solid triazene as a result of a 25 reaction between the gas and the triazene For this reason when the amount of unconsumed monoamine is at a level as low as 5 % another solvent is employed to maintain stirrability With larger amounts of unconsumbed monoamine present the required mobility of the reaction mixture may be achieved with neat monoamine bv employing 1 i 30 higher reaction temperatures Preferably, the reaction product is a homogeneous liquid and 30 for this reason, when neat monoamine is used, the amount thereof remaining unconsumed is sufficient to act as a solvent for the triazene.

In any case, whether neat, dissolved, or diluted monoamine is used, the contact between the N Ox gas and the reaction mixture preferably is broken while at least 40 percent and most preferably at least 60 percent by weight of the monoamine remains unconsumed The 35 yield of triazene drops off sharply owing to rearrangement when the consumed monoamine falls below 40 percent, and the yield drop may even become significant when the consumed monoamine falls below 60 percent Preferably the consumed monoamine will not exceed about 85 percent to avoid the handling and work-up of excessively large volumes of l" 11 40 materials containing low concentrations of the triazene In a semi-batch-type operation, the 40 N Ox gas is added to the monoamine, and the addition stopped when the selected monoamine consumption has been reached, as can be determined by analysis of the reaction mixture In a continuous operation the product stream is separated from the gas stream when the selected monoamine consumption has been reached, as can be determined by analysis of the product stream 45 Agitation of the reaction mixture has not notable effect on the course of the reaction per se, but helps to disperse the gas in the monoamine and promote good contact between gas and liquid phases.

The process described above is applicable to the diazotization-coupling of unsubstituted primary aromatic monoamines e g aniline and cu and J 3 naphthylamine as well as of 50 primary aromatic monoamines having substituents which are inert to NO,, e g alkyl halo, haloalkyl, alkoxy and nitro substituents Preferred alkvl haloalkvl and alkoxy substituents have 1 to 4 carbon atoms Suitable substituted monaomines include, for example oand m toluidines; 23-, 2,5- 26- and 35-dimethvlanilines trifluoromethvlaniline and oand m-chloro-, bromo- fluoro- and nitroanilines 55 Nitrogen Oxide Reaction Control in the Offt-Gas The residual gas separated from the triazene-containing reaction liquid from the above-described reaction consists chiefly of the diluent present in the molecular-oxygenl containing gas used to produce the nitrogen oxide-containing gas mixture from ammonia.

6 Since the oxygen-containing gas usually is air, the residual gas from the diazotization/ 60 l coupling reaction usually is chiefly nitrogen and additionally contains small quantities of " water, the monoamine, the 13-diaryl triazene unreacted NO,, and possibly oxygen The amount of water, monoamine, and triazene in the residual gas depends on the temperature and pressure in the reaction vessel When the NO, contacted with the monoamine is a mixture of nitric oxide and nitrogen dioxide unreacted NO, in the residual gas is usually 65 1 569 302 6 only NO Unreacted NO 2 may appear in the residual gas when the starting NO, is NO, and the degree of gas/liquid contact in the reaction vessel is not adequate for complete reaction of the NO 2 The nitric oxide concentration in the residual gas depends on the state of oxidation of the initial gas mixture, i e, on the value of x in the NO, contacted with the monoamine, higher NO concentrations in the residual gas being encountered with lower 5 values of x The NO concentration in the residual gas has been found to vary from 0 07 to 3.2 percent by volume over the range of x values of the starting NO, from 1 3 to 2 0 a concentration of 0 44 percent by volume being encountered when the value of x in the starting NO, is 1 65.

It has been found that, contrary to prior teachings (e g Drago R S et al, J Am, 10 Chem, Soc 83, 1891-1822 ( 1961)), primary aromatic monoamines do not react with nitric oxide, and that the formation of a diazonium salt in the residual gas does not occur unless nitrogen dioxide is present therein Although as explained above, nitrogen dioxide usually will not be present in the residual gas as it is separated from the reaction liquid, the dioxide can form if molecular oxygen and nitric oxide are present Therefore in one embodiment of 15 the present process substantial entry or formation of nitrogen dioxide in the pipaline is prevented in that molecular oxygen is excluded from the residual gas by employing a substantially oxygen-free NO x-containing gas mixture for the diazotization/coupling reaction, i e, a gas mixture containing less than about 500 parts per million oxygen In this way, the rate at which the nitric oxide in the residual gas can be oxidized to nitrogen dioxide 20 is minimized owing to the low concentration of oxygen therein To achieve the substantial absence of oxygen in the gas mixture to be used in the diazotization/coupling reaction, the ammonia concentration of the ammonia/oxvgen-containing gas mixture in the ammonia oxidation step of the process preferably is as high as possible within the safe operating range, e g about from 11 to 13 mole percent ammonia Also in the nitric oxide oxidation, 25 the contact time is sufficient to permit full consumption of the oxygen and the temperature of the gas mixture produced does not exceed about 275 'C at atmospheric pressure thereby minimizing the chances that the reverse reaction i e nitrogen dioxide decomposing into nitric oxide and oxygen will occur.

In other embodiments of the process moleclar ox Ygen is present in the residual gas, and 30 diazonium nitrate deposition on the walls of the pipeline through which the gas is conducted to a treatment system is prevented either by (a) limiting the residence time of the gas in the pipeline so that the gas has gone into the disposal system (e g wherein the amine isseparated out of the gas, or wherein the gas is exposed to high abatement temperatures) before the diazonium nitrate can form; or (b) maintaining the walls of the pipeline at a 35 temperature at which the rate of diazonium nitrate decomposition is at least as high as the rate of diazonium nitrate formation e g above about 500 C in the case of benzenediazonium nitrate.

The time that will elapse before the diazonium nitrate begins to form depends on the components of the gas and their concentrations and on the rates of the reactons which must 40 occur in the gas before the conditions for diazonium nitrate formation are reached.

Diazonium nitrate will form soonest in the rate circumstance in which nitrogen dioxide is present in the residual gas as the gas is separated from the reaction liquid This is because the nitrogen dioxide, along or with nitric oxide which usually is present reacts rapidly with the monoamine to form the 1 3-diaryl triazene if the monoamine is in excess or the 45 diazonium nitrate if the nitrogen oxide(s) are in excess Since the monoamine is rapidly consumed so as to result in the excess of the nitrogen oxide(s) the diazonium nitrate rapidly becomes the product of the monoamine-nitrogen oxide reaction In such a situation the diazonium nitrate may deposit on the walls of the pipeline instantaneously, thereby necessitating measures to decompose the salt as it is formed to prevent its accumulation 50 Therefore, when the residual gas as it is separated from the reaction liquid contains nitrogen dioxide, the walls of the pipeline are maintained at a temperature above the decomposition temperature of the diazonium nitrate (above about 50 'C for benzenediazonium nitrate) e g a temperature in the range of about from 550 to 1250 C.

If the residual gas as it is separated from the reaction liquid contains molecular oxygen, 55 but no nitrogen dioxide and therefore the presence of nitrogen dioxide in the gas in the pipeline results from the reaction of nitric oxide and oxygen in the gas diazonium nitrate accumulation can be prevented by controlling the residence time of the gas in the pipeline.

The reaction of nitric oxide and oxygen is slow relative to the reaction of the amine to form the diazonium salt or the triazene and diazonium nitrate deposition may not occur for 60 several seconds the exact time depending on the conditions prevailing in the pipeline For example when a residual gas at a temperature of 500 C and a pressure of one atmosphere and containing (by volume) l % nitric oxide 39 Ä oxygen ad O 5 % aniline passes through an off-gas line having a 25 to 350 C wall temperature the deposition of benzenediazonium nitrate on the walls occurs in about 5 seconds Therefore in this case the present process 65 r 1 569 302 can be carried out by limiting the residence time of the gas in the pipeline to 4 seconds or less The higher the pressure of the gas or the higher the nitric oxide or oxygen concentration, the lower the residence time requied to prevent diazonium nitrate deposition For example under the just-described conditions, as the nitric oxide concentration is increased to 1 5 % the maximum residence time should be lowered to 2 5 seconds.

It has been found that aromatic diazonium nitrates can be made to undergo smooth thermal decomposition as fast as they form in the off-gas linle if the walls of the pipeline are heated to a temperature above the decomposition temperature of the nitrate Therefore, in f 10 the present process, when oxygen is present in the residual gas and the residence time of the 10 gas in the pipeline is long enough for the diazonium nitrate to form the walls of the pipeline are maintained above the decomposition temperature of the nitrate The minimum wall temperature that will/e used will be one which will assure the instantaneous decomposition of the particular diazonium salt that can form i e about 55 C for benzenediazonium nitrate The maximum temperature will depend mainly on the thermal behaviour of other 15 materials in the off-gas e g the triazene and on economic considerations Based on these factors, the wall temperature generally will be in the range of from 55 to 125 C a range of from 55 to 75 C being preferred in the case in which benzenediazonium nitrate is involved.

In a preferred embodiment of this process when oxygen is present in the residual gas the walls of the pipeline are heated as described and the residence time of the gas in the pipeline 20 is limited as described This provides a redundancy factor in the means taken to avoid diazonium nitrate accumulation in the pipeline a potentially hazardous condition as was mentioned previously Of course one or both of these measures can be adopted even when the residual gas contains less than 500 parts per million of oxygen especially at higher l, 25 pressures and NO concentrations in the residual gas and oxvyen concentrations close to the 25 500 parts per million point With an oxygen concentration of about 200 () parts per million.

more than 17 seconds may elapse before diazonium nitrate deposition occurs when the NO concentration is 2 % and the pressure is 5 psiga ( O 3 atmosphere) In such a case measures to limit the residence time to a level below that normally prevailing in off-gas trains usually 0 will be unnecessary However under other combinations of gas concentrations and 30 pressure, control of residence time and/or wall temperature mav be used.

The invention is illustrated by the following Examples.

Example 1

A gas mixture having the composition (molar) 4 5 % NO 6 8 %' NO, 68 8 % nitrogen.

and 19 9 % water vapor ( 11 3 % NO, concentration: x = 1 6) is obtained when an 35 ammonia/air mixture containing 12 1 mole percent ammonia 181 mole percent oxygen, and 1 7 mole pecent water vapor (from ambient air) is passed over a platinum-rhodium alloy ( 10 % rhodium) gauze catalyst heated to 900 C at a pressure of 120 psi ( 8 16 atmospheres) and the resulting gas mixture is cooled to a temperature of 200 C and held at about the same pressure Under the latter conditions, all of the oxygen is consumed in 40 about 3 seconds.

Aniline ( 132 4 grams) at room temperature is charged to a 150-milliliter glass reactor equipped with an agitator an outer condenser sleeve a heated side-arm capillary gas inlet tube (near the bottom of the reactor) a thermocouple and a 150-millimeterlong upper exit tube connected to a 150-millimeter-long water-cooled condenser 45 The above-described gas mixture, at an average temperature of 200 C ( 175-225 C) and a pressure of one atmosphere is fed into the room-temperature aniline via the heated gas inlet tube at a rate of 342 milliliters per minute During the addition of the gas the aniline is stirred at about 2000 revolutions per minute The bulk temperature of the aniline rises to 4-50 C and is maintained there by cooling Off-gases (containing O 5-0 7 vol %/ NO no 50 NO 2, and no oxygen) leave the reactor through the exit tube and condenser at a rate of 274 millilieters per minute, and are vented to the atmosphere Hold-up time in the 25 C exit tube and condenser is about 11 sec No benzenediazonium nitrate deposition is observed in the off-gas line.

The gas flow is stopped after 180) minutes whereupon the reaction mixture is allowed to 55 cool to 30 C, and the organic layer separated from the aquous laver The composition of the organic layer ( 133 2 grams) after neurtralization bv weight is as follows: 19 8 % 1,3-diphenyltriazene, 1 63 % p-aminoazobenzene ( O 121 % i oaminoazobenzene, O 177 % o-, m-, and p-aminodiphenyls O 086 %, HN Ol 1 9 % HO and 73 1 c% aniline Based on total 6 l "accountable organic products 21 7 % of the aniline has been converted to products after 60 minutes On this basis the yield of 1 3-diphenvltriazene is 91 1 %/ (weight of triazene divided by the weight of total accountable solids derived from aniline).

When o or m-toluidine is substituted for aniline in the above procedure 1, 3-di-o or 1,3-dim-tolyltriazene respectively is obtained with similar results.

06 1 569 302 8 Example 2

The procedure described in Example I is followed with the exception that the bulk aniline temperature is maintained at 25 C with water cooling The weight of the organic layer is 139 8 grams Based on an aniline conversion of 20 3 % the yield of 13diphenyltriazene is 96 1 %, p-aminoazobenzene 3 8 % and o-aminoazobenzene 0 26 % The 5 off-gas at 25 C contains 0,5-7 % NO, nitrogen, aniline, and water (no NO, or oxygen) No benzenediazonium nitrate deposition is observed on the 25 C wall of thie exit tube and condenser in the 11 second hold-up time.

Example 3

The procedure described in Example 1 is repeated with the exception that a 300-milliliter 10 reactor is employed and the gas mixture used has the composition (molar) 10 % NO, and % nitrogen This mixture is obtained when the ammonia molar concentration is 10 7 % and oxygen 18 1 %, and water vapor is subsequently removed from the product gas In this case, the gas mixture, at a temperature of 25 C is fed into the aniline ( 199 5 grams) at a rate of 375 milliliters per minute the bulk temperature of the aniline rising to 35 C Gas 15 flow is stopped after 204 minutes The weight of organic layer is 206 7 grams Based on an aniline conversion of 16 4 % the yield of 1 3-diphenyltriazene is 42 2 %, paminoazobenzene 31 6 %, p-nitroaniline 16 3 %, and onitroaniline 9 9 % The off-gases (nitrogen, 700 parts per million NO 2, aniline, water vapor, no oxygen) are chilled to 10 C.

in the condenser to condense out aniline and triazene vapors and are vented The hold-up 20 time in the off-gas train maintained at about 15 C is 8 5 seconds No diazonium nitrate deposition is observed.

Example 4

The procedure described in Example 1 is repeated with the exception that the gas mixture used has the composition (molar) 5 7 % NO 5 7 % NO 2, 20 5 % water vapor, and 68 1 % 25 nitrogen This mixture is obtained when the ammonia content is 12 6 %' and oxygen 18 0 %.

In this case, the gas mixture at 200 C ( 175 -225 C) is fed into aniline ( 120 grams) at a rate of 750 milliliters per minute the bulk temperature rising to 50 C Gas flow is stopped after minutes Based on an aniline conversion of 31 3 % the vield of 1 3diphenyltriazene is 90 4 % p-aminoazobenzene 7 9 % o-aminoazobenzene O 49 %, p-nitroaniline O 20 %, and 30 o-nitroaniline 0 15 %.

Example 5

The procedure described in Example 1 is repeated with the exception that the gas mixture used has the composition (molar) 7 4 % NO 3 6 % NO, and 89 % nitrogen This mixture is obtained when 13 7 % ammonia and 17 8 % oxygen are used in the ammonia oxidation, and 35 water vapor is subsequently removed from the product gas In this case, the gas mixture, at an average temperature of 200 C ( 175 -225 C) is fed into a mixture consisting of 66 5 grams of aniline and 3 5 grams of nitrobenzene (internal standard) at a rate of 150 milliliters per minute the bulk temperature being maintained at 50 -55 C Gas flow is stopped after 121 minutes The weight of recovered organic laver is 68 1 grams Based on an aniline 40 conversion of 12 6 %, the yield of 1, 3-diphenyl-triazene is 96 8 % and paminoazobenzene 3.7 %.

Example 6

Aniline ( 69 9 grams) at room temperature is charged to a 15 ( 0milliliter glass reactor equipped with an outer condenser sleeve, two heated side-arm capillary gas inlet tubes 45 (near the bottom of the reactor), a thermocouple and a 15 () millimeterlong water-cooled condenser.

A gas mixture having the composition 5 4 %c NO, 2 9 % NO 17 'c water vapor and 74.7 % nitrogen at an average temperature of 200 C ( 175 -225 C) and a pressure of 1 atmosphere is fed into the room temperature aniline via one of the heated gas inlet tubes at 50 a rate of 150 milliliters per minute A second gas mixture having the composition of 3 % oxygen and 97 % nitrogen at an average temperature of 2000 C and a pressure of 1 atmosphere is fed into the aniline via a second heated gas inlet tube at a rate of 125 milliliters per minute such as to produce a final composition of 2 9 % NO 2, 1 6 % NO 9 1 % water vapor, 1 4 % 0, and 85 % nitrogen This mixture simulates a gas which has been 55 produced by the oxidation of ammonia according to the process of Application No.

48973/76 Serial No 15693 ( 01 followed by dilution with nitrogen to give a concentration of 4.5 % N Ox During the addition of the gases the aniline is stirred at about ( 1000 revolutions per minute The bulk temperature rises to 45 -50 C and is maintained there by air cooling.

The gas flow is stopped after 211 minutes The weight of organic laver is 68 2 grams 60 Based on an aniline conversion of 24 8 % the vield of 1 3-diphenyltriazene is 76 6 %.

p-aminoazobenzene 19 3 % o-aminoazo-benzene 1 6 %c p-nitroaniline 1 5 %, and onitroaniline 1 0 %.

The off-gas contains 0 5 volume percent NO and 1 4 volume percent oxygen No benzenediazonium nitrate deposits on the 25 C walls of the off-gas line in the approximately 65 1 569 302 9 seconds the gas is held up therein.

Example 7

A portion of the nitrous gas stream from a commerical ammonia oxidation process (AOP) unit engaged in the production of nitric acid is continuously withdrawn and reacted with aniline for a period of 155 minutes In the AOP unit an ammonia-air mixture routinely 5 containing 11 4-11 6 mole percent ammonia by analysis is catalytically burned over a platinum gauze catalyst at about 900 'C and 125 psig ( 9 8 atmospheres) to produce a nitrous gas containing nitric oxide, water vapour, some unreated oxygen ( 3 % by vol) and the rest nitrogen At a point in the AOP unit where the gas has been cooled to about 540 'C a portion of the gas is tapped off by pipeline at a rate of 140 pounds ( 63 6 kilograms) per 10 our, through a heat exchanger where it is cooled to 190 'C in about 1 5 seconds before being fed to a reactor tube wherein it is contacted with recirculating aniline solution at a flow rate of 25 gallons ( 95 liters) per minute The exit of the reactor tube is in a gas/liquid separator designed for continuous drawoff The reaction product solution ( 13diphenyltriazene dissolved in aniline) and gases produced in the reactor pass into the 15 separator, liquid being withdrawn from the separator continuously Fresh aniline is continuously fed mt the liquid stream emanating from the separator at a rate of 480 pounds ( 261 kilograms) per hour and product solution is continuously withdrawn to maintain constant inventory in the reactor and separator Part of the withdrawn liquid is recovered, l'20 and part of it is recirculated through a cooler (to remove heat of reaction from the system 20 and maintain a temperature of 50-550 C in the reactor and separator) and then to the reactor The temperature at the reactor tube inlet is 47-500 C: the pressure at the reactor inlet is 35 psig ( 3 4 atmospheres) and at the exit (in the gas/liquid separator) 4 psig ( 1 3 atmosphere) The volume of the reaction tube is ( 1186 cubic feet ( 5 2 liters) A liquid holdup of about 3 gallons ( 11 liters) is maintaned in the separator whose total volume is 25 about 12 gallons ( 45 liters).

Analyses of samples of the product solution are given in the following table The yield of 1,3-diphenyl-triazene based on aniline is 89 percent ( 17 %/s aniline conversion).

wt %' 30 1.3-Diphenyltriazene 16 3 p-Aminoazobenzene 1 77 35 o-Aminozaobenzene O 16 Aminodiphenyls ( O 07 Off-gas ( 50-550 C) leaving the separator comprises nitrogen ( 4 volume percent NO 3 40 volume percent oxygen water and aniline vapor (no NO 2) This gas is passed through a 'C wall off-gas line at 4 psig ( 1 3 atmosphere) with a residence time of O 05-0 1 second before entering a water scrubber to remove aniline No benzenediazonium nitrate deposition is observed.

Control Experiment 45 If the preceding off-gas contains 1 % NO the wall temperature is 250 C and the pressure 1 atmosphere, benzenediazonium nitrate deposition occurs in 5 seconds If, in addition, the temperature of the off-gas leaving the separator is 250 C benzenediazonium nitrate deposits on the wall of the off-gas line also in 5 seconds.

Claims (1)

1. so WHAT WE CLAIM IS: 50

   1 A method or preparing a 13-diaryl triazene by contacting an excess of a primary aromatic monoamine in the liquid phase with a diazotizing agent therefor and separating a residual gas from the triazene-containing reaction liquid comprising conducting said residual gas through a pipeline to a waste-gas-disposal system and performing at least one of the following steps: heating the walls of the pipeline during the passage of the residual gas 55 therethrough, conducting the residual gas out of the pipeline before an aromatic diazonium nitrate deposits on the walls thereof or preventing the substantial entry or formation of nitrogen dioxide in the pipeline.

   2 The method of Claim I wherein said residual gas is conducted to a wastegas disposal system through a pipeline whose walls are maintained at a temperature in the range of from 60 550 to 1250 C.

   3 A method of Claim 2 wherein the residence time of said gas in said pipeline is up to 4 seconds.

   4 The method of Claim 1 2 or 3 wherein said residual gas as it is separated from said reaction liquid contains nitrogen dioxide and the walls of said pipeline are maintained at a 65 1 569 302 temperature in the range of from 55 to 125 C.

   The method of Claim 1, 2 or 3 wherein said residual gas as it is separated from said reaction liquid contains nitric oxide, substantially no nitrogen dioxide, and is essentially free of molecular oxygen.

   6 The method of Claim 1 2 ot 3 wherein said residual gas as it is separated from said 5 reaction liquid contains nitric oxide, molecular oxygen and substantially no nitrogen dioxide, and the walls of said pipeline are maintained at a temperature in the range of from to 125 C.

   7 The method of Claim 1 2 or 3 wherein said residual gas as it is separated from said reaction liquid contains nitric oxide, molecular oxvgen and substantially no nitrogen 10 dioxide, and the residence time of said gas in said pipeline is up to 4 seconds.

   8 The method of any one of the preceding claims wherein said primary aromatic monoamine is aniline and the walls of the pipeline are maintained at a temperature in the range of from 55 to 75 C.

   9 The method of any one of the preceding claims wherein said primary aromatic 15 monoamine is unsubstituted or has one or more substituents which are inert to said diazotizing agent.

   The method of Claim 9 wherein said primary aromatic monoamine is an unsubstituted, alkyl-substituted or halo-substituted aniline or naphthylamine.

   11 A method of preparing a 1,3-diaryl triazene according to Claim 1 substantially as 20 described herein.

   12 A method of preparing a 13-diaryl triazene according to Claim 1 substantially as described herein with reference to Example 6.

   13 1,3-diaryl triazenes when prepared by the method of any one of the preceding claims 25 For the Applicants.

   CARPMAELS & RANSFORD.

   Chartered Patent Agents.

   43 Bloomsburv Square 30 London W Ci A 2 RA.

   Printed for Her Majesty's Stationery Office by Croydon Printing Company Limited Croydon, Surrey 1980.

   Published by The Patent Office 25 Southampton Buildings, London WC 2 A l AY from which copies may be obtained.