GB1578732A

GB1578732A - Process for the manufacture of cyano azo dyes

Info

Publication number: GB1578732A
Application number: GB2228376A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1976-05-28
Filing date: 1976-05-28
Publication date: 1980-11-05
Also published as: FR2352864A1; BR7703412A; JPS52146432A; DE2724117A1; IT1078992B; NL7705742A; CH626647A5; BE854903A; FR2352864B1; ES459246A1

Abstract

Azo dyes of the formula D-A-N=N-B where A is an aromatic or heteroaromatic radical, B is an N-substituted p-aminophenyl radical, and D is iodine, bromine or chlorine ortho to the azo grouping, are reacted with a) copper (I) cyanide or b) another metal cyanide in the presence of a copper compound. The reaction is carried out in the presence of a phase transfer catalyst. The product obtained are azo dyes of the same formula, except that D is cyano. The dyes are suitable for dyeing or printing textiles.

Description

(54) PROCESS FOR THE MANUFACTURE OF CYANO AZO DYES (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED., Imperial Chemical House, Millbank, London SWIP 3JF a British Company 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:- This invention relates to a chemical process and more particularly to an improved process for the manufacture of azo dyes containing cyano groups and to the use of that process in the dyeing of textile materials.

It is known to manufacture certain azo dyes containing cyano groups by reacting the equivalent halogeno dye with cuprous cyanide in a solvent medium. It has also been proposed in UK Patent Specification No. 1387728 to perform this reaction from the bromo dye in aqueous suspension. However, when the reaction is carried out in aqueous suspension the replacement of the bromine atom by the cyano group tends to be slow so that in most cases the reaction needs to be carried out at temperatures in excess of 1 100C under superatmospheric pressure with obvious attendant operational disadvantages. One method of overcoming this problem has been disclosed in UK Patent Specification No. 1412922 and entails the addition of an organic base, especially pyridine, to the aqueous suspension.

However, this method has the disadvantage that it can cause degradation of alkalisensitive dyes, for example those having hydrolysable ester groups, which are partly hydrolysed under the process conditions. Further, the high usage of organic base required, typically, for pyridine, from 70 to 100% of the weight of the dye, introduces undesirable environmental hazards and discomforts.

According to the present invention we provide a process for the manufacture of azo dyes of the formula D-A-N = N-B wherein A is an aromatic radical, B is an optionally substituted benzenoid ring carrying a substituted nitrogen atom in the para position to the azo link and D is a cyano radical ortho to the azo group, which comprises reacting an azo dye of the same formula except that D is an iodine, bromine or chlorine atom in the presence of a phase transfer catalyst (as hereinafter defined) with an alkali metal or alkaline earth metal cyanide in the presence of a catalytic amount of a copper compound.

While a phase transfer catalyst may be used to advantage when the process is carried out in an organic solvent, our invention is of particular value for the manufacture of these azo dyes in aqueous medium especially where the dyes are free of water-solubilising groups. In this latter case the reaction proceeds with the dyes held in aqueous suspension. The reaction normally proceeds at the boil and sometimes at lower temperatures thereby obviating the use of the pressure equipment hitherto employed.

By the expression "phase transfer catalyst" we mean a substance which being at least partly present in or "wetted" by a first (usually organic) phase, promotes reaction by transferring a reactant from a second (usually aqueous) phase to the first phase where it undergoes reaction thereby releasing the phase transfer catalyst for re-use in transferring further reactant.

Phase transfer catalysts are reviewed by E.V. I)ehmlow in Angewante Chemie (International Edition) Vol 13, No. 3, 1974, page 170.

Other reviews are by Jozef Dockx in Synthesis 1973 at pages 441456, and by C. M. Starks in the Journal of the American Chemical Society 93:1 Jan 13, 1971 at pages 195-199.

Suitably the phase transfer catalyst is a quaternary ammonium salt which may be of the general formula:

wherein R, R', R" and R"', which may be the same or different, are alkyl, hydroxyalkyl, aryl, aralkyl, for example benzyl, or cycloalkenyl groups, or alternatively two of these may together form a ring system containing 5-7 carbon atoms. The positively charged nitrogen atom may be part of an aromatic system, as for example, in cetyl pyridinium bromide. X- is an anion. Conveniently it is a halogen, a bisulphate or a half-sulphate or a third phosphate ion. Further, double or multifunctional quaternary salts in which the formula (RR'R"R"'N)+X- is repeated a plurality of times may also be used. In such salts the nitrogen atoms are linked by an aralkyl group or long chain alkyl groups containing upwards of 10 carbon atoms.

Essentially a phase transfer catalyst of this type is a cationic species which contains bulky organic groups to make it soluble in organic media, and which when dissolved in an organic medium increases by virtue of its positive charge the solubility in the organic medium of anionic species required for reaction therein.

The molecular geometry of the quaternary ammonium moiety is not of prime importance, but to confer preferential solubility in the organic phase rather than the aqueous phase it is preferred that the total number of carbon atoms per positively charged atom in the molecule should be greater than 10, and there is little advantage in the number being above 70. It is especially preferred that the number should lie between 16 and 40. The nature of the anion, provided it is inert, is not important.

Although, surprisingly, the phase transfer catalyst accelerates the reaction of the invention when carried out in organic solvents, it is particularly efficacious when the reaction medium is largely aqueous.

The quaternary ammonium salt may be prepared in situ, for example by including in the reaction mixture a tertiary amine, such as pyridine or triethylamine, together with an alkylating agent such as benzyl chloride or diethyl sulphate.

As examples of quaternary ammonium salts we would mention cetyl trimethyl ammonium bromide, dicetyldimethyl ammonium chloride, octyl tributyl ammonium bromide, tetrabutyl ammonium bromide, trioctyl methyl ammonium chloride, benzyl dimethyl lauryl ammonium chloride, benzyl tri-n-butylammonium chloride, dilauryl dimethyl ammonium chloride tetrabutyl ammonium sulphate, and dieicosyl dimethyl ammonium chloride.

Quaternary phosphonium salts of similar formula to the above quaternary ammonium salts, with the N atom replaced by P, may also be used. An example is cetyl tripropyl phosphonium bromide.

Other phase transfer catalysts which may be used are, for example, crown ethers (macrocyclic polyethers) which are described in the "Journal of the American Chemical Society : 89, 7017 (1967)" by C. J. Pederson.

When the process of the invention is carried out in aqueous medium it may be advantageous to add a water-immiscible solvent, for example, toluene, xylene, chlorobenzene, o-nitrotoluene, octanol, benzyl alcohol, methyl isobutyl ketone, ethyl acetate, ethyl benzoate, cyclohexanol or cyclohexanone. Particularly useful are anisole, acetophenone and nitrobenzene. The solvent need not be present in amount sufficient to dissolve completely the dye but only in catalytic quantity which serves to 'soften' or lower the melting point of the dye. After reaction the solvent may be separated from the aqueous suspension by, for example, steam distillation and allowed to separate from the distillate for re-use. The inclusion of a water-immiscible solvent often further increases the rate of reaction.

The aromatic radical A may be any such radical including heteroaromatic radicals. Of particular interest are azo dyes where A is a substituted phenyl radical.

But the process of the invention is also useful where A is, for example, a benzo isothiazolyl-1,2 or -2,1 radical, a naphthyl or quinolyl radical.

Dyes which can conveniently be prepared by the process of the invention have one of the following general formulae:

wherein T is hydrogen, lower alkyl, lower alkoxy, cyano, halogen, nitro lower alkyl sulphonyl, lower alkylsulphonamido or a radical of the formula

E is hydrogen, lower alkyl, lower alkoxy, lower alkyl carbonyl, lower alkoxy carbonyl, trifluoromethyl, acylamino, halogen, optionally substituted phenylazo, cyano or especially nitro; G is hydrogen or nitro; J is hydrogen or nitro; Y is hydrogen, lower alkyl, lower alkoxy, or halogen; Z is hydrogen, lower alkyl, lower alkoxy, halogen, and particularly acylamino especially acetylamino and propionylamino; K is hydrogen; or Z and K together with the carbon atoms to which they are attached form a benzene ring which bears a sulphonic acid group or alkali metal salt thereof; R1 is lower alkyl, hydroxy lower alkyl, lower alkoxy lower alkyl, lower alkoxy carbonyl lower alkyl, cyano lower alkyl, and phenyl lower alkyl, cyclohexyl or phenyl; R2 is hydrogen, lower alkyl, hydroxy lower alkyl, lower alkoxy lower alkyl, lower alkoxy carbonyl lower alkyl or lower alkyl carrying a pyridinium salt; and, in particular, either or both R1 and R2 are

wherein R8 and R9 are independently methyl or hydrogen and R10 is lower alkyl or (CH2)n COOT" wherein n is 2 to 4 and R is lower alkyl, provided that if two substituents R8 are present in the same molecule, at least one of them is hydrogen; or R, and Y together with their linking carbon atoms and nitrogen atom form a fused piperidine ring; R3 is hydrogen, lower alkyl, phenyl, lower alkylphenyl, halophenyl, lower alkoxyphenyl or dihalophenyl; and either R4 is lower alkyl and R5 is lower alkyl or lower alkoxycarbonyl or R4 and R5 together with the carbon atoms to which they are attached form a benzene ring which may bear lower alkyl or lower alkoxy substituents.

wherein Y, Z, R1 and R2 have the meanings hereinbefore defined;

wherein Hal is halogen and Y, Z, R, and R2 have the meanings hereinbefore defined: or

wherein Y, Z, R1 and R2 have the meanings hereinbefore defined.

By the terms "lower alkyl" and "lower alkoxy" we mean alkyl and alkoxy radicals respectively containing from 1 to 4 carbon atoms.

As examples of dyestuffs which can be prepared by the process of the invention we mention, in particular, the dyestuffs of formula (a) wherein T and E are nitro, Y, K, G & J are hydrogen, Z is acetylamino and R1 and R2 are both ethyl; the dyestuff of formula (a) wherein T, Y, K, G, J and Z are all hydrogen, E is nitro and R, and R2 are both p-acetoxyethyl; and the dyestuffs of formula (a) wherein T is cyano, E is nitro, Y, K, G & J are hydrogen, Z is acetylamino and R1 and R2 are both ethyl.

Dyestuffs of the formula (a) wherein T is cyano can be prepared from the equivalent dihalo dyestuff by the process of the invention.

The exchange of cyanide for halogen becomes progressively more difficult from the iodo through to the chloro dyestuff. Exchange of cyanide for iodide is especially favourable and rapid but the starting dyes are of course expensive.

Exchange of cyanide for chloride is markedly slower and unless partial conversion only is required, it is preferable to use elevated reaction temperatures. The use of a nitrogenous base with the phase transfer catalyst may be advantageous in this case.

In general, the reaction rate is not sensitive to other substituents, although it is rather slower if the radical B contains an alkyl group ortho to the azo link. It is especially rapid, however, if the radical B contains an acylamino group in the ortho position to the azo link.

Preferably the copper compound is a copper (I) compound, including cuprous cyanide. However, copper (II) compounds may also be used since in the presence of an alkali metal or alkaline earth metal cyanide they are readily reduced to the cuprous state forming copper cyanide complexes.

The process of the invention is simply carried out by stirring the dye which is to be converted to the cyano derivative in a solvent, or in aqueous medium optionally in the presence of a water-immiscible solvent, together with an alkali metal or alkaline earth metal cyanide, a catalytic amount of a copper compound, and a phase transfer catalyst at a temperature of from 15"C to 1000C. However, if desired, temperatures of up to 150"C may be used to further increase the reaction rate. Agitation is continued for any time between 0.25 to 20 hours, usually between 1 to 5 hours, but again this will depend on the structure of the particular product involved.When the reaction is carried out in aqueous suspension the agitation is preferably vigorous, and since the rate of reaction will depend inter alia on the particle size of the reactants it is sometimes advantageous to subject the reactants to mild grinding during reaction for instance by agitating the reaction mixture in the presence of glass beads. A water-immiscible solvent may be used in addition to or instead of the grinding process.

The amount alkali metal or alkaline earth metal cyanide used may be varied between from 1 to 5 equivalents of each halogen atom to be replaced but usually between 1 and 2 equivalents is satisfactory. If, however, it is required to produce a mixture of dyes of a required shade, which may be achieved by replacing only part of the replaceable halogens by cyano, then less than one equivalent of the alkali metal or alkaline earth metal cyanide will be used.

A refinement of our process is to add the alkali metal or alkaline earth metal cyanide, preferably in aqueous solution, gradually as the reaction progresses. This minimises any degradation of the azo dyestuff by high concentrations of the metal cyanide.

The phase transfer catalyst is preferably present in the quantity of from 0.1 to 25% of the weight of the dye, more preferably from 1 to 12%.

In UK Patent No. 1529528 a process is claimed for the production of an azo dyestuff which in the diazo component, contains at least one cyano group in the ortho position relative to the azo bridge, comprising reacting a corresponding ortho-halogeno- azo dyestuff with a metal cyanide optionally in the form of a complex, which may be a copper cyanide complex, in an aqueous or aqueousorganic medium in the presence of a phase transfer catalyst.

By way of explanation, when we refer herein to a catalytic amount of a copper compound, we mean that there is insufficient copper provided to form a copper cyanide complex with all the cyanide required to displace the halogen on the halogen-containing dye. Normally however, there will be present at least 0.005 atoms of copper/atom of replaceable halogen.

It has also been found that the process of the invention can be used in dyeing textile materials.

Thus according to yet a further embodiment of the present invention we provide a process for dyeing textile materials which comprises applying to a textile material an azo dye having the formula: D-A-N = N-B wherein A is an aromatic radical, B is an optionally substituted benzenoid ring carrying a substituted nitrogen atom in the para position to the azo link and D is an iodine, bromine or chlorine atom ortho to the azo group, in the presence of an alkali metal or alkaline earth metal cyanide, a catalytic amount of a copper compound, and a phase transfer catalyst.

This embodiment of our invention is particularly useful for dyeing synthetic textile materials especially aromatic polyester textile materials with one or more disperse dyes devoid of water solubilising groups and containing a cyano group, the cyano derivative being obtained from the equivalent iodine, bromine or chlorine atom-containing dye during the dyeing process.

Apart from using this in situ dyeing process, the dyes manufactured by the process of the invention can, of course, be applied to the textile materials by any conventional method. Thus disperse dyes in the form of aqueous dispersions can be applied by dyeing, padding or printing processes using the conditions and other additives which are conventionally used, that is at temperatures of from 1 l00C to 140"C for 0.5 to 2. hours optionally in the presence of dispersing agents.

Alternatively the dyes can be applied by solvent methods, for example by applying to the material a solution or dispersion of the dye in a suitable solvent optionally containing a minor amount of water at elevated temperature.

The process of the invention provides inter alia an improvement in the process of obtaining certain azo dyes containing cyano groups from the equivalent halogencontaining azo dye in terms of faster reaction rates. It is surprising that a phase transfer catalyst should have this effect where other surfactants are apparently ineffective especially since cuprous cyanide is a neutral species and not anionic.

This is not to say that conventional surfactants cannot be used in addition to the phase transfer catalyst. Care must be taken, however, in choosing suitable surfactants for clearly they should not deactivate the phase transfer catalyst by complexing with it.

The invention is illustrated but not limited by the following examples in which parts and percentages are by weight.

Example 1

To an aqueous filter paste comprising 4.79 parts of the dyestuff of formula I and 10.8 parts of water is added 19.2 parts of water, 0.1 parts of cuprous cyanide, 0.5 parts of cetyl trimethyl ammonium bromide and 6 parts of anisole, and the mixture is stirred and boiled under reflux at 970C. A solution of 0.49 parts of sodium cyanide in 10 parts of water is then added dropwise by means of a peristaltic pump evenly during 3.5 hours. After addition is complete stirring and heating are continued for a further period of 3.5 hrs. Steam is then passed through the mixture and the anisole, which separates from the condensed distillate, is recovered for reuse. The aqueous residue from the distillation is cooled and stirred for 10 hrs. with 2 parts of ammonium persulphate and the cyano dyestuff of formula II is collected, washed with water and dried.The yield is 94% of theoretical and the dyestuff is found to contain only 0.15% of copper by weight.

Similar results are obtained if the cetyl trimethyl ammonium bromide used in this example is replaced by an equal weight of octyl tributyl ammonium bromide, or by an equal weight of tetrabutyl ammonium bromide or by an equal weight of tetrabutyl ammonium sulphate, or by an equal weight of cetyl tripropyl phosphonium bromide or by an equal weight of benzyl dimethyl lauryl ammonium chloride or by an equal weight of cetyl pyridinium bromide.

In like manner the following dyestuffs may be prepared, each from the corresponding dyestuff containing a bromo group in place of the cyano group ortho to the azo link. After each is shown the shade of the dyestuff in dimethyl formamide solution.

Example Dyestuff Shade

Reddish-blue Blue Reddish-blue Reddish-blue Blue Greenish-blue Blue Example Dyestuff Shade

Reddish-blue Grenish-blue Bluish-red Reddish-blue Bluish-red Greenish-blue Blue Example Dyestuff Shade

Yellowish-red Yellowish-red Red Yellowish-red Bluish-red Ruby Red Example Dyestuff Shade

Blue Blue Violet Blue Greenish-blue Greenish-blue Example Dyestuff Shade

Reddish-blue Blue Red Violet Red Blue-green Example Dyestuff Shade

Greenish-blue Blue Reddish-blue Blue Blue Example Dyestuff Shade

Violet Blue Blue-green Violet Example 44.

12.38 parts of a filter paste comprising 5.98 parts of the yellow dyestuff of formula III, in which T and L are both bromo, and 6.4 parts of water, is mixed with 0.30 parts of cuprous cyanide, 0.50 parts of octyl tributyl ammonium bromide, 3.0 parts of acetophenone and 25 parts of water and the mixture is stirred and heated to the boil under reflux. A solution of sodium cyanide (1.08 parts) in 20 parts of water is then added dropwise evenly during 8 hours. Stirring and heating under reflux is continued for I hour after addition is complete and then the mixture is steam distilled and the acetophenone is recovered by separation from the distillate. The residual aqueous dyestuff suspension is then cooled and stirred for 15 hours with 2.5 parts of ammonium persulphate.The dyestuff of formula IX in which T and L are both cyano is collected by filtration and is found after drying to contain 0.18% of copper. The yield is 94% of theoretical. The dyestuff gives attractive bright red shades of good light fastness on polyester fabrics.

If in this preparation the addition of sodium cyanide solution is stopped when 9 parts have been added the dyestuff consists essentially of the orange dyestuff of formula IX in which T is bromo and L is cyano.

Very similar results are obtained if in this example the octyl tributyl ammonium bromide is replaced by an equal weight of tetrabutyl ammonium bromide, or of cetyl trimethyl ammonium bromide or of benzyl lauryl dimethyl ammonium chloride, or of trioctyl methyl ammonium bromide.

A marked catalytic effect, quite suitable if only one bromo group is to be replaced, but slower than those above is observed if the octyl tributyl ammonium bromide is replaced by an equal weight of benzyl tri-n-butyl ammonium chloride, or of dilauryl dimethyl ammonium chloride or of dicetyl dimethyl ammonium chloride or of dieicosyl dimethyl ammonium chloride.

Further examples of dyestuffs containing two cyano groups in positions ortho to the azo group, which may be prepared from the corresponding dyestuffs containing bromo groups are listed in the following Table. After each is shown the shade of its solution in dimethyl formamide.

Example Dyestuff Shade

red blue violet reddish-blue greenish-blue bluish-red Example Dyestuff Shade

violet bluish-red violet blue blue

Claims

WHAT WE CLAIM IS:

1. A process for the manufacture of azo dyes of the formula: D-A-N = N-B wherein A is an aromatic radical, B is an optionally substituted benzenoid ring carring a substituted nitrogen atom in the para position to the azo link and D is a cyano radical ortho to the azo group which comprises reacting an azo dye ot the same formula except that D is an iodine, bromine or chlorine atom in the presence of a phase transfer catalyst (as herein defined) with an alkali metal or alkaline earth metal cyanide in the presence of a catalytic amount of a copper compound.

2. A process as claimed in claim 1 in which the reaction is carried out in aqueous medium.

3. A process as claimed in claim 2 in which the azo dye is free from watersolubilising groups.

4. A process as claimed in any one of the preceding claims in which the phase transfer catalyst is a quaternary ammonium or phosphonium salt having the respective formulae:

wherein R, R', R" and R"', which may be the same or different, are alkyl, hydroxyalkyl, aryl, aralkyl or cycloalkenyl groups, or any two of R, R', R", R"' may together form a ring system containing 5-7 carbon atoms, and X is an anion.

5. A process as claimed in claim 4 in which the quaternary ammonium or phosphonium salt contains more than 10 but not more than 70 carbon atoms per positively charged atom in each molecule.

6. A process as claimed in claim 4 in which the quaternary ammonium or phosphonium salt contains between 16 and 40 carbon atoms per positively charged atom in each molecule.

7. A process as claimed in any one of claims 2 to 6 in which there is added a water-immiscible solvent.

8. A process as claimed in claim 7 in which the solvent is anisole, acetophenone or nitrobenzene.

9. A process as claimed in any one of the preceding claims in which the radical A is a phenyl radical.

10. A process as claimed in any one of claims I to 8 in which the radical A is a benzoisothiazolyl- 1,2 or 2,1 radical.

11. A process as claimed in any one of claims 1 to 8 in which the radical A is a naphthyl or quinolyl radical.

12. A process as claimed in any one of claims I to 8 in which the manufactured azo dye has the formula:

wherein T is hydrogen, lower alkyl, lower alkoxy, cyano, halogen, nitro, lower alkyl sulphonyl, lower alkylsulphonamido or a radical of the formula:

E is hydrogen, lower alkyl, lower alkoxy, lower alkyl carbonyl, cyano, lower alkoxy carbonyl, trifluoromethyl, acylamino, halogen, -optionally substituted phenylazo or nitro; G is hydrogen or nitro; J is hydrogen or nitro; Y is hydrogen, lower alkyl, lower alkoxy, or halogen; Z is hydrogen, lower alkyl, lower alkoxy, halogen, or acylamino: K is hydrogen; or Z and K together with the carbon atoms to which they are attached form a benzene ring which bears a sulphonic acid group or alkali metal salt thereof; R, is lower alkyl, hydroxy lower alkyl, lower alkoxy lower alkyl, lower alkoxy carbonyl lower alkyl, cyano lower alkyl, and phenyl lower alkyl, cyclohexyl or phenyl; R2 is hydrogen, lower alkyl, hydroxy lower alkyl, lower alkoxy lower alkyl, lower alkoxy carbonyl lower alkyl or lower alkyl carrying a pyridinium salt; or either or both R, and R2 are

wherein R8 and R9 are independently methyl or hydrogen and R10 is lower alkyl or (CH2)n COOT11 wherein n is 2 to 4 and Rt, is lower alkyl, provided that if two substitutents R8 are present in the same molecule, at least one of them is hydrogen; or R1 and Y together with their linking carbon atoms and nitrogen atom form a fused piperidine ring; R3 is hydrogen, lower alkyl, phenyl, lower alkylphenyl, halophenyl, lower alkoxyphenyl or dihalophenyl; and either R4 is lower alkyl and R5 is lower alkyl or lower alkoxycarbonyl or R4 and R5 together with the carbon atoms to which they are attached form a benzene ring which may bear lower alkyl or lower alkoxy substituents.

13. A process as claimed in any one of claims 1 to 8 in which the manufactured azo dye has the formula:

wherein Y, Z, R, and R2 have the meanings defined in claim 12.

14. A process as claimed in any one of claims I to 8 in which the manufactured azo dye has one of the formulae:

wherein Hal is halogen and Y, Z, R, and R2 have the meanings defined in claim 12.

15. A process as claimed in any one of claims 12 to 14 wherein E is nitro; T is hydrogen, nitro or cyano; Z is acylamino; and R, and R2 are both lower alkyl-or lower alkoxy carbonyl lower alkyl.

16. A process as claimed in any one of the preceding claims in which the reaction is carried out at a temperature of from 15 to l()00C.

17. A process as claimed in any one of the preceding claims in which the amount of alkali metal or alkaline earth metal cyanide used is between from 1 to 5 equivalents of each halogen atom to be replaced.

18. A process as claimed in any one of claims I to 16 in which the amount of alkali metal or alkaline earth metal cyanide used is between from I to 2 equivalents of each halogen atom to be replaced.

19. A process as claimed in any one of claims I to 16 in which a mixture of reacted and unreacted dyes is produced by replacing less than all of the replaceable halogen atoms with cyano by using less than I equivalent of an alkali metal or alkaline earth metal cyanide for each halogen atom initially present.

20. A process as claimed in any one of the preceding claims in which the copper compound is a copper (I) compound.

21, A process as claimed in any one of the preceding claims in which the alkali metal or alkaline earth metal cyanide is added gradually as the reaction progresses.

22. A process as claimed in claim 21 in which the metal cyanide is added as an aqueous solution.

23. A process as claimed in any one of the preceding claims in which the phase transfer catalyst is present in the quantity of from 0.1 to 25% of the weight of the dye.

24. A process as claimed in any one of claims 1 to 22 in which the phase transfer catalyst is present in the quantity of from 1 to 12% of the weight of the dye.

25. A process as claimed in claim 1 substantially as herein described with reference to any one of Examples 1 to 55.

26. Dyestuffs whenever produced by a process as claimed in any one of claims 1 to 25.

27. A process for dyeing textile materials which comprises applying a dyestuff as claimed in claim 26 to a textile material by any conventional dyeing method.

28. A process for dyeing textile materials which comprises applying to a textile material an azo dye having the formula: D-A-N = NB N-B wherein A is an aromatic radical, B is an optionally substituted benzenoid ring carrying a substituted nitrogen atom in the para position to the azo link and D is an iodine, bromine or chlorine atom ortho to the azo group in the presence of an alkali metal or alkaline earth metal cyanide, a catalytic amount of a copper compound, and a phase transfer catalyst.

29. A process as claimed in claim 28 in which the textile material is synthetic and the azo dye is devoid of water solubilising groups.

30. A process as claimed in claim 29 in which the synthetic textile material is an aromatic polyester material.

31. Textile materials whenever dyed by a process as claimed in any one of claims 28 to 30.