CA1204737A - Production of azo compounds - Google Patents

Abstract

Abstract of the Disclosure Production of Azo Compounds The invention provides a continuous process for the production of azo compounds, wherein the coupling including laking of metal salt pigments or precipitating of soluble azo compounds is carried out in a multicompartment mixer, wherein the residence time in the first compartment is from 5 to 200 seconds. The diazo compound may also be made continuously using a multicompartment mixer.

Description

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The present invention relates to the production of azo compounds, e.g. water insoluble azo compounds like pigments, including azo metal salt pigmen~s, sparingly water soluble azo compounds like disperse dyestuffs and water soluble azo compounds. More particularly it re-lates to the diazotisation of aromatic ~mines followed by azo coupling, and laking if a laked dye is being produced or optionally precipi-tating water soluble azo compounds ater they have been formed, in a continuous process.

Azo compounds are nGrmally manufactured by batch processes. Although such parameters as temperature and pH can be held substantially con-stant during a reaction the concentrations of reactants and products formed change from start to finish of a batch. This can lead to some variations in the quality of the desired products.

Processes for making azo pigments continuously have been proposed.
European Patent No. 10219 describes the production of azo pigments in a jacketed reactor column designed to give laminar flow condi-tions i.e. good mixing at right angles to the direction of flow but little or no axial miY.ing~ The coupling reaction residence time is 0.2 to 4 hours and the diazo component is introduced into the reactor which conta;ns the coupling component at 2 to 50 separate points along the length of the reactor. Thus the concentration of coupling component is different at each point of introduction of the diazo compound.

In the publication by M. Badzynski et al., Przemysl Chemiczny Vol. 57 (1978), No. 3, pp. 134-136 there is disclosed the continuous diazotation of sulphanilic acid and coupling with ~-naphthol (Acid Orange II) in vertical cylindrical reactors equipped with stirrers.

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_ 3 _ However the continuous preparation of azo compounds according to this publication as well as according to European Patent No. 10219 suffers from the serious drawback that due to the respective devices used the risk of backmixing of the reaction flow between sub-sequent reaction segments along the reaction zone may not be excluded. This affects the quality of the endproducts as well as the economical preparation of the desired azo compounds in general.

British Patent Specification No. 2014597 describes the continuous pro-duction of an aqueous dispersion of a water insoluble azo compound direc~ from a slurry, using membranes to remove salt. Large amounts of surfactants are used in this process. The tendency of freshly formed pigment to adhere to surfaces is discussed. It is claimed that the addition of surfactant and ultrasonic vibrators serve to protect the coupling reactor against pigment deposition We have also found that freshly formed pigment tends to adhere to the surface of the reactor when an attempt is made to produce an azo pigment continuously. This adhering pigment rapidly clogs up the reactor and th~ process soon comes to a halt.

We have surprisingly found that all the above mentioned disadvantages can be overcome, and a continuous production is possible, if the coupling reaction, and laking if a laked dye is being produced or pre-cipitation of a water soluble azo compound if desired, is carried out in a multicompartment mixer. It may be desirable that the residence time o~ the reactants in the first compartment is longer than the minimum time which would be needed to complete the reaction in the whole multicompartment mixer if the reactants flowed through at the fastest possible speed which allowed for complete reaction.

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A multicompartment mixer comprises a series of reactors or compart-ments axially linked to each other, each of which has a stirrer, pre-ferably a high speed stirrer from a common shaft. There is complete mixing in each of the compartments and the flow through the multi-compartment mixer approaches plug-flow i.e. there is a narrow resi-dence time distribution. This means that one can scale-up with con-fidence and it is easy to change the actual flow rate to suit the product being made.

Thus the use of a multicompartment mixer enables the process to be carried out compactly under consistently controlled conditions. This results in the production of a more consistent and better quality product compared to the product from a batch process.

We have also found that the use of a multicompartment mixer leads to a surprising decrease in the time needed for coupling to take place.
Since the volume in which the reaction occurs is very small compared to that in a normal batch operation, it is possible to have accurate control over the pH and excess coupling component. Under these accura-tely controlled conditions, the reaction can be allowed to take place adiabatically without the need for ice or refrigeration.

Accordingly the present invention provides a process for the continuousproduction of aæo compounds -~hich comprises continuously coupling a diazo compound and a coupling component, optionally in the presence of a metal salt if a laked dye is being produced, in a multi-compart-ment mixer, wherein the residence time of the reactants in the first stage of the reactor may be from 5 to 200 seconds, preferably S0 to 200 seconds.

The diazotisa~ion reaction for producing the diazo compound may also take place continuously, preferably in a separate multicompartment mixer, and the resulting diazo compound continuously fed to the ~az [?9~37 coupling reactor, or eventually also in the first compartment of the multicompartment mixture which is used for obtaining the azo com-pound. If the diazotisation reaction is carried out in a multicom-partment mixer, the reaction may be carried out adiabatically from ambient or higher temperature. We have found that the diazo (or tetrazo) solutions formed in this way contain few decomposition pro-ducts, and, if coupled immediately, do generally not need to be filtered or cooled. If a relatively impure amine is used solid im-purities may be removed by an automatic in-line filter placed be-fore or after the diazctisation reactor.

Diazotisation reactions which do not involve a precipitation of a solid diazo may be carried out in a multicompartment mixer which may contain from 3 to 12 compartments, but preferably from 5 to 8. The residence time in each compartment may be from 3 to 50 seconds.

The multicompartment mixer used for the coupling, laking and preci-pitation reactions may contain from 3 to 10 compartments,preferably from 5 to 8. The residence time in the first compartment is from 5 to 200 seconds, preferably from 50 to 200 seconds, more preferably from 60 to 180 seconds and especially from 90 to 140 seconds.
The residence times in subsequen~ compartments may be rom 5 to 200 seconds, preferably from 10 to 200 seconds and more preferably from 40 to 120 seconds.

The actual residence times chosen will depend on the particular amine being diazotised and on the coupling component used. In the case o preparing pigments normally the residence time in the first compart-ment of the coupling/laking reactor is longer than the time needed for the pigment precipitation process to be completed in the reactor, so that the build-up of solid pigment in the reactor is kept at a low level.

312q~737 The properties of reaction products, such as filterability, colouristics and application properties can be optimised during production by controlling the pH of the reaction mixtures, parti-cularly the coupling reaction mixture, by further pH adjustments and by subjecting ~he pigment to a heat treatment. The pH control and heat treatment may be readily carried out in the process of the invention. pH adjustment may also be a means to precipitate water soluble azo compounds. Such precipitation may also be achieved by the addition of brine.

The pH adjustment can be,achieved by adding acid or alkali as required into a compartment of a multicompartment mixer. The addition of acid or alkali may be controlled by a pH electrode, such as a brush-cleaned pH electrode situated in a circulating pump loop around one of the compartments, preferably the second, of the coupling reactor.

Preferably the number of compartments used for pH adjustment(s) plus holding time after precipitation is 1 to 7; the time required may be from 20 to 350 seconds.
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The heat treatment may be carried out, for example, by injecting steam into the reactor or by using a heat exchanger. The injection of steam is preferred and this is conveniently effected after the pH adjustmentts). Steam may be injected into a compartment of the multicompartment mixer used for product formation and precipitation or the reaction mixture may be passed to one or more subsequent multicompartment mixers in which the heat treatment iscarried out.

It should be noted that treatments such as pH control and heat treatmen~ may be carried out in the same multicompartment mixer as is used for the coupling reaction by providing more compartments than are needed to complete the coupling reaction.

The hot product slurry may be cooled either by a heat exchanger, or, preferably, by adding cold water. The addition of cold water enables the heat treatment to be controlled precisely.

The product slurry may then be filtered to recover the product.

The coupling reaction itself may be controlled precisely by the use of an autoanalyser, such as is described and claimed in British Patent Specification No. 1547759. This is used to ensure a minimal excess of coupling component during the coupling reaction.

Additives commonly added to azo compounds, such as resins, fatty amines, surfactants, and dyestuffs, may be dosed into ~he system at any desired point.

The process of the present invention may use all amines which are normally used for preparing azo compounds.

Such diazotisable amines are, for example, primary aromatic amines or polyamines derived from benzene, or from biphenyl, or from con-densed benzenoid structures such as naphthalene or anthracene, or from structures in which benzene is condensed with a heterocyclic ring, in which the carbocyclic or heterocyclic aromatic nucleus can be unsubstituted or substituted with one or more of the ~ollowing groups: alkyl; alkoxy, halogen, nitro, cyano, acylamino, sulphonamido, carboxylic acid, and sulphonic acid. Examples of diazotisable amines are 2,5-dichloraniline, 3,3'-dichlorbenzidine, 5-nitro-2-aminoanisole, 3-nitro-4-aminotoluene, 4-chloro-2-nitroaniline, 4-aminotoluene-3-sulphonic acid, 4-chloraniline, 2,4-dichloraniline, 4-nitroaniline, 3-nitro-4-aminoanisole, 2-chloro-4-nitroaniline, 2-amino-anisole-4-sulphodiethylamide, 5-chloro-2-amino-toluene, 4-chloro-2-amino-toluene, 4-nitro-2-amino-~oluene, 5-nitro-2-amino-toluene, 4-nitro-2-amino-anisole, 3,3'-dimethoxybenzidine, 3,3'-dimetho~y-696'-dichlor-~.Z~37 .
benzidine, anthranilic acid methyl ester, 2-chloro-4-amino-toluene-5-sulphonic acid, 2-chloro-5-amino-toluene-4-sulphonic acid, 4-chloro-aniline-3-sulphonic acid, aniline-2,5-disulphonic acid, 2-chloro-5-aminoethylbenzene-4-sulphonic acid, 5-amino-6-methyl-benzimidazolone, 4-methyl-6-chloro-7-amino-quinolone, 4(-2'-methoxy-4'-amino-5'-chlorophenylamino~-quinazoline, 3-amino-dibenzfuran,6-methyl-7-amino-phenomorpholone(3), 2-amino-benzoic acid, 2-amino-4-nitro-phenol, 2-amino-4-nitro-6-sulfo-phenol, 2-amino-5-nitro-phenol, 2-amino-4-sulphonamido-phenol, 2-chloro-4,6-dinitro-aniline, 2-amino-5-nitro-benæoic acid.

The coupling component may be any coupling component normally used for the production of azo compounds. Such components are5 for example, acetoacetanilide and derivatives thereof, such as acetoacet-2-toluidide, acetoacet-4-toluidide, acetoacet-2-anisidide, acetoacet-

2-chloranilide, acetoacet-2,4-dimethylanilide, acetoacet-2,5-di-methoxy-4-chloranilide; l-aryl pyrazolones such as 1-phenyl-3-methyl -5-pyrazolone, 1-4'-tolyl-3-methyl-5-pyrazolone, and 1-phenyl-3-carbethoxy-5-pyrazolone; l-naphthol; 2-naphthol; 2-hydroxy-3-naphthoic acid and arylides thereof such as (2',3'-hydroxy-naphthoylamino)-benzene, 1-(2',3'-hydroxy-naphthoylamino)-2-methyl-benzene, 1-~2l,3'-hydroxy-naphthoylamino)-2,4-dimethoxy-5-chloro-benzene, and 1-(2',3'-hydroxy-naphthoylamino)-2-methyl-5-chloro-benzene, 4-hydroxycoumarin, barbituric acid, 2,4-dihydroxyquinoline, 4-hydroxy-~-methyl-quinolone, 4-methyl-7-acetoacetamido-quinolone, 7-acetoacetamido-phenomorpholone

(3), 5-acetoacetamido-benzimidazolone, 3-methyl-1-[3'-chlorophenyl]
-5-pyrazolone, a mixture of 1-propionamido-4-methoxy-3-[~-mono-and ~,~-dicyanoethoxyethyl]-benzene, 2-amino-5-naphthol-7-sulphonic acid.

If the azo compound is a pigment it may also be a laked dye formed by precipitating a water soluble dyestuff with a metal salt. Among the metal salts which are suitable for theprecipitation process are 3~

g the water-soluble inorganic or organic salts of the following metals:
aluminium, cadmium, chromium, cobalt, copper, iron, lead, magnesium, mercury, nickel, tin, ~itanium, ~inc and, preferably, calcium, barium, strontium and manganese. The metal salt may be added to the diazotisation reactor or into a compartment of the coupling reactor.

The invention is illustrated by reference to the accompanying drawing which shows one fonm of apparatus for carrying out the process of the invention.

Referring to the drawing, diazotisation reactor 8, with a residence time of 150 to 300 seconds, is used as the first stage of diazoti-sation i the diazo product is a precipitated solid; otherwise, multicompartment mixer 10, which provides a residence time of be-between 3 and 30 seconds/compartment, is the only diazotisation reactor and 8 is bypassed. Thus, amine to be diazotised and sodium nitrite is fed into either inlet 6orll and hydrochloric acid, to-gether with a metal salt, if appropriate, is fed via inlet 7 or 12.
Alternatively, amine and hydrochlori~ acid may be fed into inlet 11 and sodium nitrite fed into inlet 12. The reactants are mixed by stirrers. The diazotisation reaction end point may be controlled by the polarovoltametric method described in United States Patent No. 4246171. The diazotised amine passes out of reactor 10 and is led to reactor 14 ha~ing 8 compartments by condui~ 15, into the first compartment. Coupling component is also added to the first compart-ment of reactor 14 at inlet 16.

The pH of the reaction mi~ture is measured by a brush-cleaned pH
electrode in loop 17, and is used to control the addition of alkali or acid as required7 e.g. caustic potash or hydrochloric acid, into the first co~partment directly or into the coupling component o~ diazo solution just befo~e it enters the reactor at 16; the pH is thereby main-~L2g)9~73~

tained at the desired value.

The reaction is controlled by using an Auto Analys~r to measure the excess of coupling component in loop 18, which may be connected to compartment 3 or 4~

Compartments 4 and/or 5 may be used for pH adjustment(s), i.e.
measurement of pH and addition of acid and/or alkali, and/or addition of brine.

Live steam inlet 19 is provided to allow for heat trea~ment of the product. Thus the reaction product may be kept at an elevated tempera-ture during passage through three compartments. It is then cooled by cold water added at 20 and is passed to a slurry receiver via con-dui~ 21; the reaction product may then be recovered by filtration.

The flow rates of the reactants into the apparatus may be regulated by the use of metering pumps or flow meters~controllers.

The invention is further illustrated by the following Examples. For the first three examples the apparatus shown in the accompanying drawing was used; for the others a similar equipment was used as described in the respective examples.

Example 1: 21 litres/~our of a 0.1746 molar ammoniacal solution of 2-chloro-4-amino-toluene-5-sulphonic acid and sodium nitrite, pH > 7.0, is fed by a metering pump into diazotisation first stage reactor 8 at 6, together with 12 l/h of a solution of hydrochloric acid and calcium chloride at 7, containing enough acid to hold the pH below pH 1.5 in reactor 10, and enough calcium chloride to subsequently lake the dyestuff and form the calcium salt of the resin. Pump 9 transfers the reaction mixture from reactor 8 to reactor 10 and is regulated so as to maintain a volume of 2 litres in reactor 8, corresponding to an ~Z~73~

average residence time of 218 seconds. Reactor 10 is a 7-compartment mixer with a total volume of 1.3 litres; each 60 mm diameter compar;-ment is f;tted with 3 baffles and a 38 mm diameter straight-bladed impeller running at 800 rpm. The pH and temperature are measured in compartment 5. A spot test on a sample taken from compartment S shows the diazotisation reaction to be complete and the slurry to contain a slight excess of nitrous acid. In compartment 1 of reactor 14, which is an 8-compartment mixer, each compar~ment has a capacity of 1.93 litres, a diameter of 13~ mm and 2 baffles and is fitted with a straight-bladed impeller, diameter 50 mm, rotating at 1200 rpm, the diazo is mixed with 19 litres/hour of a 0.1949 molar solution of 3-hydroxy-2-naphthoic acid in caustic potash which enters at 16; the solution also contains 1.3% by weight of the tall oil rosin known as Primarex ~ resin. The pH is measured at 17 and is used to control addition of 5% by weight aqueous caustic potash solution into the coupling component solution just before entering the mixer at 16, thereby maintaining the pH at 17 at pH 8.7-0.3.

A pump loop which provides a sampling point at 18 with a sample for automatic analysis of coupling component is connected around compart-ment 3. In compartment 4, the pH is reduced to ~ pH 3.5 by addition of dilute hydrochloric acid~ In compartment 5, addition of 2% by weight of aqueous ammonia raises the pH to pH 7.0 - 8Ø Live steam is injected into compartment 6 at 19, raising the temperature of the slurry to 80 - 85C. Addition of cold water at 20 lowers the tempera-ture to < 60C. The slurry is collected and the product (Pigment Red 48.2) is isolated from the slurry by filtration9 washlng the filter-cake free of water-soluble impurities and drying.

EYample 2. 12 litres/hour of a 0.2727 molar solution of 4-amino-toluene-3-sulphonic acid and sodium nitrite in an aqueous potassium hydroYide solution is pumped to diazotisation reactor 10 and is di-luted just before entry of a flow of 25 l/h of hot water; the tempera-ture of the water is adjusted to ensure that the temperature in the ~Z~4~37 reactor, as measurecl in compartment 5, is > 25C. Approximately 9 l/h of an aqueous solution of hydrochloric acid and calcium chloride also flow into compartment 1 of reactor 10, thereby maint~ining the pH (as measured in compartment 5) at C pH 1.5 and providing a small excess of calcium chloride over that required for laking and forming the calcium salt of the resin which is added via the coupling component solution. The latter is added into compartment 1 of reactor 14 at a rate and composition of 17 litres/hour of a solution of 0.1949 molar 2 hydroxy-3-naphthoic acid and 0.02/kg/1 hydrogenated rosin known as Staybelite resin dissolved with potassium hydroxide. pH is measured by means of a brush-cleaned electrode in a circulating pump loop around compartment 2, and is controlled to pH 10.0 by addition of 5~ by weight aqueous potassium hydroxide solution into the coupling compo-nent solution at 16.

The coupling reaction is substantially complete by compartment 4, and a sample is ta~en from this compartment ~ia lB on a pump loop for automatic analysis o~ excess 2-hydroxy-3-naphthoic acid.

5% by weight of aqueous hydrochloric acid is added into compartment 5 and pH is controlled to 7.5. Steam is injected into compartment 6 to raise the temperature to 85C. At 20, addition of cold water reduces the slurry temperature to < 60C. before collection of the product (Pigment Red 57;l~

The process has bee~ run continuously for up to 2 weeks before de-posits in Reactor 14 needed to be removed by flushing with dilute hydrochloric acid and water.

Example 3: Example 2 was repeated, except that 2.5% by weight of the

4-amino-toluene-3-sulphonic acid was replaced with the molar equiva-lent of 3-amino-naphthalene-4-sulphonic acid and the temperature of the heat treatment was 90C. The product was Pigment Red 57 l of a slightly bluer shade than the product of Example 2.

~Z~)4737 Example 4_ 250 r~ min of a 0.~33 molar solution of 2-amino-benzoic acid in hydrochloric acid and 16.7 mL/min of a 5 molar aqueous solution of sodium nitrite both at 20C are pumped into the first compartment of a diazotisation reactor with 7 compartments and a total volume of 1280 ml. The temperature increases adiabatically to 30C. After a mean residence time of 4.8 minutes the diazo solution leaves the reactor and is continuously fed to a coupling reactor with 9 compart-ments and a total volume of 1760 ml. In the first compartment, the diazo solution is mixed with 66.7 mL/min of a 1.3 molar solution of 3-methyl-1-phenyl-5-pyrazolone dissolved in a aqueous sodium hydroxide solution. Th~ coupling reaction is carried out at pH 7.5 whereby the temperature raises adiabatically to 3~C. Live steam is injected into compartment 6 raising the temperature to 80C. In compartment 7 the monoazo dyestuff is precipitated boy reducing the pH to 2 with hydro-chloric acid. The slurry is collected and the monoazo dyestuff isolated by filtration with a yield of 96% of theory.

Exa ple 5- 250 mL/min of a 0.333 molar solution of 2-amino-4-nitro-phenol in hydrochloric acid and 16.7 ml/min of a 5 molar aqueous solu-tion of sodium nitrite both at 20C are pumped into the first compart-ment of a diazotisation reactor with 7 compartments and a total volume of 1280 ml. The temperature increases adiabatically to 31C. After a mean residence time of 4.8 minutes, the diazo solution leaves the reactor and is continuously fed to a coupling reactor with 9 compart-ments and a total volume of 1760 ml. In the first compartment the solution of the diazonium compound is mixed with 66.7 mL/min of a 1.3 molar solution of 3-methyl-1-phenyl-5-pyrazolone dissolved in an aqueous sodium hydroxide solution. The pyrazolone solution also contains 0.19% by weight of a condensation product of naphthalene sulphonic acid with Iormaldehyde. The coupling reaction is carried out at pH 7.2 whereby the temperature raises adiabatically to 33C.
90 mL/min of a saturated solution of sodium chloride is injected in compartment 6 simultaneously with live steam raising the temperature to 40C. The slurry is collected and the monoazo compound isolated by filtration with a yield of 93% of theory.

Example 6: 240 mL/~in of a 0.347 molar solution of 2-amino-4-nitro-6-sulfo-phenol at pH 4.5, 10 mL/min of 30% by weight aqueous hydro-chloric acid and 16.7 ml of a 5 molar aqueous solution of sodium nitrite are pumped into the first compartment of a diazotisation reactor with 7 compartments and a total volume of 1280 ml. The tempera-ture increases adia~atically to 34C. After a mean residence time of 4.~ min. the diazonium sal~ solution leaves the reac~or and is continuously fed to a coupling reactor with 9 compartments and a total volume of 1760 ml. In the,first compartment, the diazonium salt solution is mixed with 66,7 ml/min of a 1.3 molar solution of 3 methyl-l-phenyl-S-pyrazolone dissolved in an aqueous sodium hydroxide solution. The pyrazolone solution also con~ains 0.19% by weight of a condensation product of aaphthalene sulphonic acid with formaldehyde. The coupling reaction is carried out adiabatically at pH 7.4. After a mean residence time of 5.3 minutes, the slurry leaves the reactor and is collected. The monoazo compound is isolated by filtration with a yield of 96% of theory.

Example 70 212.5 mL/min of a 0.392 molar solution of 2-amino-5-nitro-phenol and sodium nitrite in an aqueous sodium hydroxide solution and 54.4 ml of a 4.9 molar aqueous solution of l-naphthalenesulfonic acid both at 20C are pumped into the first compartment of a diazotisation reactor with 7 compartments and a total volume of 1280 ml. The temperature increases adiabatically to 37~C. After a mean residence time of 4.8 minutes, the diazonium salt solution leaves the reactor and is continuously fed to a coupling reactor with 9 compartments and a total volume of 1760 ml. In the first compartment, the diazonium salt solution is mixed with 66.7 mL/min of a 1.3 molar aqueous solution of 3-methyl-1-phenyl-5-pyrazolone dissolved with an aqueous sodium hydroxide solution. Approximately 3 ml/min of a 30% aqueous sodium hydroxide solution also flow into the firs~ compartment ,_ thereby maintaining the pH at 7.6. The coupling reaction is carried out adiabatically whereby the temperature raises to 40C. The slurry is collected and the monoazo dyestuff is isolated by filtration with a yield of 94% of theory.

Example 8: 143 mL/min of a 0.6 molar aqueous solution of 1-diazo-6-nitro-4-sulfo-2-naphthol and 37.7 mL/min of a 2.34 molar aqueous solution of the potassium salt of l-naphthol both at 20C are pumped into the first compartment of a coupling reactor with 9 compartments and a total volume of 1760 ml. 86 mL/min of a saturated solution of sodium chloride is injectéd into compartment 2. The coupling reaction is carried out at pH 9.6 whereby the temperature raises adiabatically to 28C. Live steam is injected into compartment 4 raising the temperature to 50C. 143 ml/min of water and 57 m Vmin of a saturated solution of sodium chloride are injected in compartment 8.
The dyestuff is precipitated:in compartment 9 by ~educing the pH to 3.0 with approximately 9 ml/min of 30% aq~eous hydrochloric acid. The slurry is collected and the dyestuff isolated by flltration with a yield of 94% of theory.

Example 9: 33.8 ml/min of a 1.76 molar aqueous solution of the sodium salt of 2-naphthol and 9I m Vmin of a 1.135 molar aqueous solution of calcium chloride both at 20C are pumped into the first compartment of a coupling reactor with 9 compartments and a total volume of 1760 ml. The calcium chloride solution also contains 0.14% by weight of a condensation product of naphthalene sulphonic acid with formaldehyde. 91 mL/min of a 0.6 molar solution of 1-diazo-6-nitro-4-sulfo-2-naphthol at 20C is injected into compartment 2. The coupling reaction is carried out at pH 9.8 and adiabatically in compartments 2 and 3. Live steam is injected in compartment 4 and ~ raising the temperature respectively to 60C and 80C. In compartment 8 the pH
is reduced to 1.5 with 114 mL/min of a 1.94~ by weight of a aqueous solution of hydrochloric acid also containing 16.3% by weight of 473~

potassium chloride. The slurry is collected and the monoa~o dyestuff isolated by filtration with a yield of 92% of theory.

Exa~lple 10: 266.7 mL/min of 0.3125 molar solution of diazoti~ed 2-amino-phenol~4-sulphonamide in hydrochloric acid at 55C, and 66.7 mL/min of a 1.3125 molar aqueous solution of a 3-methyl-1-[3'-chloro-phenyl]-5-pyrazolone dissolved in an aqueous solution of sodium hydroxide are pumped into the first compartment of a coupling reactor with 9 compartments and a total volume of 1760 ml. The pyrazolone solution also contains 0.18% by weight of a condensation product of naphthalene sulphonic acid with formaldehyde. The coupling reaction is carried out at pH 9.5 - 10.0 whereby the temperature raises adiabatically to 56C. In compartment 8, the monoazo dyestuff is precipitated completely by reducing the pH to 8 with 30% by weight of aqueous hydrochloric acid. The slurry is collected and the monoazo compound isolated by filtration with a yield of 97% of theory.

Example 11: 2.45 mL/min of 1.83 molar solution of diazotized 2-chloro-4,6-dinitro~aniline in about 80% by weight sulfuric acid at 20~C and 3.46 m Vmin of a 1.198 molar aqueous solu~ion of a equimolar mixture of N-cyanoethoxyethyl-2-amino-4-propionamido anisole and bis-(N-cyano-ethoxyethyl)-2-amino-4-propionamidO anisole in 20% sulfuric acid at 5C are pumped simultaneously with 52.6 m Vmin water at 5C in the first compartment of a coupling reactor with 6 compartments and a total volume of 270 ml. Approximately 15.2 mL/min of a 5% aqueous sodium hydroxide solution at 0C - 2C also flow into the first compartment thereby maintaining the pH at 1Ø The coupling reaction is carried out adiabatically whereby the temperature raises to 13C.
The slurry is collected and the dyestuff isolated by filtra~ion and washed.

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Example 12: 44.4 ml/min of 0.272 molar aqueous solution of 2-amino-5-nitro-benzoic acid which contains 2.72% by weight of naphthalene-2-sulfonic acid and sodium nitrite at pH 7.6 and 60 C i5 pumped simultaneously with ~4.5 ml/min of o.1% by weight of aqueous hydrochloric acid solution at 26C into the first compartment of a diazotisation reactor with 6 compartments and a total volume of 270 ml. The diazotisation reaction is carried out adiabatically at a temperature of 53 C. After a mean residence time of 4.6 minutes, the diazonium salt solution leaves the reactor and is continuously cooled down to 36C and fed to a coupling reactor with 6 compartments ~d a total volume of 780 ml. In the first compartment the di~zo solution is mixed with 45.6 mllmin of a 0.269 molar aqueous solution of the sodium salt of 2-amino-5-naphthol-7-sulfonic acid at pH 6;5-7 and containing 0.52~ by weight of the ammonium salt of a condensation product of nonylphenol and two moles of ethylene oxide esterified with sulfuric acid. The coupling reaction is carried ou~ adiabatically at 27C and p~ 1.6.
After a mean residence ~ime of 7.7 minutes th~ slurry is collected and the monoazo dyestuff isolated by filtration with a yield over 90~ theory.

Claims (16)

CLAIMS:

1. A process for the continuous production of azo compounds which comprises continuously coupling a diazo compound and a coupling com-ponent, optionally in the presence of a metal salt if a laked dye is being produced, in a multicompartment mixer, wherein the residence time of the reactants in the first stage of the reactor is from 5 to 200 seconds.

2. A process as claimed in claim 1 in which the residence time in the first stage of the reactor is from 60 to 180 seconds.

3. A process as claimed in claim 1 in which the multicompartment mixer has from 3 to 10 compartments.

4. A process as claimed in claim 1 in which the residence time in compartments other than the first is from 5 to 200 seconds.

5. A process as claimed in claim 1 in which the reactions are carried out adiabatically.

6. A process as claimed in claim 1 in which the coupling reaction is controlled by an automatic chemical analyser which continuously measures and adjusts the concentration of unreacted diazo compound or coupling component in the reaction medium.

7. A process as claimed in claim 1 in which the product is a water soluble azo compound which is precipitated by adjusting the pH-value or by addding brine solution.

8. A process as claimed in claim 1 in which the product is a laked dye, using a metal selected from aluminium, cadmium, chromium, cobalt, copper, iron, lead, magnesium, mercury, nickel,tin,titanium, zinc, calcium, barium,strontium, manganese.

9. A process as claimed in claim 8 in which the laked dye is formed by adding a metal salt to the diazotisation reactor or to a compart-ment of the coupling reactor.

10. A process as claimed in claim 1 in which a resin, fatty amine, surfactant and/or dyestuff is added to the reaction system at any desired point.

11. A process as claimed in claim 1 in which the diazo compound is in solution and is continuously produced by diazotising an amine in a multicompartment mixer before being continuously coupled.

12. A process as claimed in claim 1 in which the diazo compound is a solid and is continuously produced by diazotising an amine in a multi-compartment mixer which is preceded by a stirred vessel of volume sufficient to provide a residence time for the diazotisation reactants of 150 to 300 seconds.

13. A process as claimed in claim 11 in which the multicompartment mixer used for diazotisation contains from 3 to 12 compartments.

14. A process as claimed in claim 12 in which the multicompartment mixer used for diazotisation contains from 3 to 12 compartments.

15. A process as claimed in claim 11 in which the residence time of the reactants in each compartment of the diazotisation mixer is from 3 to 50 seconds.

16. A process as claimed in claim 11 in which the end-point of the diazotisation reaction is controlled by a polarovoltametric method.