GB2075042A

GB2075042A - Chromogenic Material

Info

Publication number: GB2075042A
Application number: GB8113113A
Authority: GB
Original assignee: Yamamoto Chemicals Inc
Current assignee: Yamamoto Chemicals Inc
Priority date: 1980-04-28
Filing date: 1981-04-28
Publication date: 1981-11-11
Also published as: IT1211030B; DE3116815A1; IT8121413A0; CH657367A5; BE888596A; GB2075042B; JPS56151597A; FR2481286B1; FR2481286A1; DE3116815C2

Abstract

Azaphthalide chromogenic materials for use in pressure and heat sensitive record materials have the general formula (I> <IMAGE> wherein R1 is an alkyl group (C1-12) or benzyl and R2 is alkyl (C1-4), R3 is H, alkyl or alkoxy (C1-4), R4 is alkyl (C1-4) or benzyl and R5 is alkyl (C1-4), benzyl or phenyl, or R4 and R5, together with the nitrogen atom to which they are attached, are a saturated 5-6 6- membered ring, or R4, together with the nitrogen atom to which it is attached and the C4 and C3 atoms, is a 6-membered ring system and either R5 is hydrogen or alkyl (C1-4) or, together with the nitrogen atom to which it is attached and the C4 and C5 atoms, is also a 6-membered ring system, which is substantially free from its corresponding 7-azaphthalide isomer of formula (II> <IMAGE> wherein R1 R2 R3 R4 and R5 are as above, provided that, when R4 and R5 are ethyl, R3 is ethoxy and R2 is methyl, R1 is not methyl or ethyl, and that, when R1 R2 R3 R4 and R5 are each methyl, R3 is not hydrogen.

Description

SPECIFICATION Chromogenic Material This invention relates to azaphthalide chromogenic materials, a method for their preparation, a microencapsulated chromogenic solution and record material containing them.

The colour forming system used in a record material of the pressure sensitive type generally employs a substantially colourless chromogenic material, a colour developer capable of reacting with the chromogenic material to generate a colour, and a solvent in which the colour forming reaction can take place. The reactive components of the colour forming system are kept apart until the time of use and this may be achieved by microencapsulating a chromogenic composition comprising a solvent solution of the chromogenic material. At the time of use, the application of pressure causes rupture of those microcapsules that are subject to such pressure. This leads to a release of the chromogenic material and its solvent. In this way both colour forming components are brought into contact and generate an image corresponding to the pattern of applied pressure.Pressure sensitive record material can be used to provide copies without the need for carbon paper.

In the case of heat sensitive record material the chromogenic material and colour developing agent are coated onto paper as a mixture in a binder. When heat is applied the chromogenic material or the colour developer melts and reacts with the other to produce an image corresponding to the pattern of applied heat.

In a self contained pressure sensitive copying system the record material comprises a sheet coated with, or having dispersed within, a mixture of colour developer and microcapsules containing chromogenic material and solvent.

In a transfer record system at least two record materials are employed. One comprises a sheet having a coating of microencapsulated chromogenic solution (the CB sheet) and the other comprises a sheet having a coating of colour developer (the CF sheet). The sheets are assembled together as a manifold set with their coatings in contiguous relationship so that transfer of the chromogenic solution can take place from the CB sheet to the CF sheet. If further copies are required the manifold set may additionally include a third record material which comprises a sheet having on one side a coating of the microencapsulated chromogenic solution and on the other side a coating of colour developer (the CFB sheet). One or more CFB sheets are placed between the CF and CB sheets with each microcapsule coating in contiguous relationship with a colour developer coating.

This invention relates in particular to the chromogenic materials used in these record materials. A number of such materials are often used in combination in order to engender a print with the desired physical properties and hue-usually blue or black. One of the most important is a blue chromogenic material which is nearly always !Crystal violet lactone (3,3-bis-(4-dimethylaminophenyl)-6- dimethylaminophthalide). However, a print produced from Crystal violet lactone fades quite quickly on exposure to light, and attempts to find a suitable replacement have so far failed.

One such attempt related to the use of an isomeric mixture of 4- and 7-azaphathalides having aminophenyl and an indolyl substituents (Japanese patent publications Nos. 16807/1976 and 38243/1 976). Whilst chromogenic materials of this kind produce a satisfactory blue print which has a much better resistance to fade than a print produced from Crystal violet lactone, they unfortunately suffer from the problem of self-colouration, i.e. premature development into the coloured form, which manifests itself during the manufacture of the record material. As a result, in the case of pressuresensitive record material, the capsules are coloured, and, in the case of heat-sensitive record material, the coating is coloured. In either case, such chromogenic materials are clearly not suitable replacements for Crystal violet lactone.

It has now been found that the problem of self-colouration is due to the relatively high proportion of the 7-azanaphthalide isomer in the isomeric mixture and that, if the chromogenic material comprises the 4-azanaphthalide isomer in a form substantially free from the 7-azaphthalide isomer, then the problem of self-colouration does not occur. The resulting material is accordingly eminently suitable as a replacement for Crystal violet lactone, having many advantages over it.

The present invention therefore provides a chromogenic material comprising a 4-azaphthalide of formula (I),

wherein R1 is an alkyl group having from 1 to 20 carbon atoms or a benzyl group, R2 is an alkyl group having from 1 to 4 carbon atoms, R3 is hydrogen, an alkyl or alkoxy group having from 1 to 4 carbon atoms, R4 is an alkyl group having from 1 to 4 carbon atoms or a benzyl group and R5 is an alkyl group having from 1 to 4 carbon atoms, a benzyl group or a phenyl group, or R4 and R5, together with the nitrogen atom to which they are attached, are a saturated 5- to 8-membered ring system, or R4, together with the nitrogen atom to which it is attached and the C4 and C3 atoms, is a 6-membered ring system and either R5 is hydrogen or an alkyl group having from 1 to 4 carbon atoms or, together with the nitrogen atom to which it is attached and the C4 and C5 atoms, is also a 6-membered ring system, which is substantially free from its corresponding 7-azaphthalide isomer of formula (it),

wherein R1, R2, R3 R4 and R5 are as defined above, provided that, when R4 and R5 are ethyl, R3 is ethoxy and R2 is methyl, R1 is not methyl or ethyl and that when R1, R2, R4and R5are each methyl, R3 is not hydrogen.

The chromogenic materials of the present invention are usually colourless or faintly coloured substances, but they produce an immediate and intense blue colour upon contact with a colour developer, such as an acidic clay or resin (in the case of pressure-sensitive record material) and bisphenol A (in the case of heat-sensitive record material). The resulting colour not only has excellent fade resistance but also has a satisfactory stability against plasticizers etc.

Preferably, the 7-azaphthalide of formula (II) is present in an amount of less than 10% based on the combined weight of both isomers. It is more preferred that the amount is less than 5% or even 2%.

Falling within the above-definition for the chromogenic materials of the present invention are those materials wherein the aminophenyl substituent having the groups R3, R4 and Ras is of formula (III) or (IV),

The aminophenyl substituents of formulae (III) and (IV) are commonly referred to as kairolyl and julolidinyl substituents respectively.

In the production of the isomeric mixture of the 4- and 7-azaphthalides in the prior art, quinolinic acid anhydride is reacted with an indole to give an isomeric mixture of keto-acids which are then reacted with an aromatic amine. The occurrence of an isomeric mixture as the end-product is therefore due to the intermediate production of an isomeric mixture which in turn is due to the alternative sites on the anhydride molecule which can react with the indole. Accordingly, in order to obtain a chromogenic material in which the 4-azaphthalide is substantially free from its corresponding 7azaphthalide isomer, it is necessary to use the keto acid, which gives the 4-azaphthalide isomer, substantially free from the other keto acid, which gives the 7-azaphthalide isomer.

The present invention therefore provides a method for the preparation of a chromogenic material comprising a 4-azaphthalide of formula (I), as hereinbefore defined, substantially free from its corresponding 7-azaphthalide isomer of formula (II), as hereinbefore defined, which method comprises reacting in the presence of a dehydrating agent a keto acid of formula (V),

wherein R1 and R2 are as defined hereinbefore, which is substantially free from the corresponding ketoacid isomer of formula (VI),

with an aromatic amine of formula (VII),

wherein R3, R4 and Rs are as hereinbefore defined.

Preferably, the keto-acid isomer of formula (VI) is present in an amount of less than 10% based on the combined weight of the keto acid isomers of formula (V) and (VI). It is even more preferred that the amount is less than 5% or even 2%.

The dehydrating agent is preferably an acid anhydride, such as acetic anhydride.

In order to obtain the keto acid of formula (V) in a form which is substantially free from its corresponding keto-acid isomer of formula (VI), the keto-acid isomeric mixture is prepared conventionally by reacting quinolinic acid anhydride with an indole, and then purifying the resulting mixture in favour of the desired isomer of formula (V). Such purification can be easily accomplished by recrystallization since the keto-acid isomers have considerably different solubilities. Alternatively or additionally the preparation of the keto-acid isomers can be carried out in one of a number of certain solvents which favours the production of the desired keto-acid isomer. Such solvents include benzene, toluene, chlorobenzene, alcohols, and acetonitrile.

The chromogenic material of the present invention may be used on its own or in combination with other known chromogenic materials, for example known phthalides, fluorans or spiropyrans. As examples of such known materials, there are mentioned 3,7-bis(dimethylamino)-1 0-benzoyl- phenothiazine (Benzoyl leuco methylene blue, BLMB); 3,3-bis (dimethylamino phenyl)-6dimethylaminophthalide (Crystal violet lactone, CVL); 2'-anilino-6'-diethylamino-3'-methylfluoran (N 102); 3,3-bis(1-ethyl-2-methylindol-3-yl) phthalide (indolyl red); 3,3-bis(1-butyl-2-methylindol-3-yl) phthalide; spiro-7-chloro-2,6-dimethyl-3-ethyl-aminoxanthene-9,2-(2H)-naphthol (1,8-bc) furan; 7chloro-6-methyl-3-diethylaminofluoran; 3-diethylaminobenzo (b) fluoran; 3-(4-diethylamino-2ethoxy)-3-(2-methyl-1 -ethylindol-3-yl)phthal ide; 3-(4-diethylamino-2-butoxy)-3-(2-methyl- 1 - ethylindol-3-yl) phthalide; and 3,7-bis (diethylamino)- 1 0-benzoyl-benzoxazine.

The chromogenic material of the present invention, alone or in combination with other known materials, is normally dissolved in a suitable organic solvent prior to microencapsulation. Examples of such solvents include dialkyl phthalates in which the alkyl groups have from 4 to 13 carbon atoms, such as dibutyl, dioctyl, dinonyl and ditridecyl phthalates; 2,2,4-trimethyl-1,3-pentanediol di-i-butyrate (TXIB, U.S. patent 4027065); ethyldiphenylmethane (U.S. patent 3996405); alkyl biphenyls, such as mono-i-propylbiphenyl (U.S patent 3627581); C10-C14 alkyl benzenes, such as dodecyl benzene; diaryl ethers, such as diphenyl ether, di(aralkyl) ether, such as dibenzyl ether, and aryl aralkyl ethers, such as phenyl benzyl ether; liquid dialkyl ethers having at least eight carbon atoms; liquid alkyl ketones having at least nine carbon atoms; alkyl or aralkyl benzoates, such as benzyl benzoate; alkylated naphthalenes; and partially hydrogenated terphenyls.

These solvents, which are all substantially odourless, may be used alone or in combination. They may also be used with a diluent in order to reduce the cost of the chromogenic solution. Of course, the diluent must not be chemically reactive with either the solvent or any other component of the solution and must be at least partially miscible with the solvent so as to give a single phase. The diluent is used in an amount sufficient to achieve a cost benefit but without impairing the solubility of the chromogenic material. Diluents are already known in the art and a preferred example thereof is Magnaflux oil, which is a mixture of saturated aliphatic hydrocarbon oils having a distillation temperature in the range of from 320 to 5500F.

The present invention additionally provides a microencapsulatjed chromogenic solution in which the chromogenic materials is in accordance with the present invention. Microencapsulation of the chromogenic solution can be carried out in accordance with the known encapsulation processes, such as those disclosed in U.S. Patents 2 800457,3041 289,3 533 958,3 755 190,4001140 and 4100103.

The colour developer of use with the present invention is an acidic material of any kind which falls within the definition of a Lewis acid, i.e. an electron acceptor. Such acidic materials include clays, e.g.

attapulgite, bentonite and montmorillonite, treated clays, e.g. silton clay as disclosed in U.S. patents 3 622 364 and 3 753 761, silica gel, talc, feldspar, magnesium trisilicate, pyrophyllite, zinc sulphate, zinc sulphide, calcium sulphate, calcium citrate, calcium phosphate, calcium fluoride and barium sulphate, aromatic carboxylic acids such as salicylic acid, derivatives of aromatic carboxylic acids and metal salts thereof as disclosed in U.S. patent 4 022 936 and acidic polymeric material such as phenol-formaldehyde polymers, metal-modified phenolic resins as disclosed in US patent 3 732 120, phenol-acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylene-maleic anhydride copolymers, carboxy polymethylene and wholly or partially hydrolysed vinyl methyl ether maleic anhydride copolymers and mixtures thereof as disclosed in U.S. patent 3 672 935.

The present invention further provides pressurn-or heat-sensitive record material which contains a chromogenic material, as herein defined. Generally, for heat-sensitive record material it is preferred to use the chromogenic material of the present invention in a form in which the 7azaphthalide isomer is present in an amount of less than 2% of the combined weight of both isomers.

Whereas for pressure-sensitive record material, it is preferred to use the chromogenic material of the present invention in a form in which the 7-azaphthalide isomer is present in an amount of less than 10% of the combined weight of both isomers.

Coating formulations and processes for the preparation of pressure-sensitive record material are generally known in the art, for example US patents 3 627 581,3 775 424 and 3 353 869.

Coating formulations and processes for the preparation of heat sensitive record material are also generally known in the art, for example US patents 3 539 375, 3 674 535 and 3 746 675.

The present invention will now be described with reference to a number of examples thereof.

Example 1 Preparation of 2-(1-ethyl-2-methylindol-3-ylcarbonyl)nicotinic acid (Va)

A mixture of 14.9 g quinolinic acid anhydride, 1 5.9 g of 1 -ethyl-2-methylindole, and 30 cm3 of acetonitrile was stirred at 25-300C for 1 5 hours. The resulting precipitate was filtered off, washed with acetonitrile and then dried to give a 70.8% yield (21.8 g) of 2-(1 -ethyl-2-methylindol-3- ylcarbonyl)-nicotinic acid in a form substantially free from its isomer. It was obtained as a pale brown powder and had a melting point of 181 to 1 820C.

Example 2 Preparation of 3-(l-ethyl-l -methylindol-3-yl)-3-l2-ethoxy-4-pyrrolidinylphenyl)-4-azaphthalide (la)

A mixture of 3.08 g of the keto acid of formula (Va), 1.91 g of m-pyrrolidinylphenetole and 5 g of acetic anhydride was reacted together at 60--65 OC for one hour. The reaction product was then neutralised with dilute ammonium hydroxide and extracted with toluene. The toluene solution was then concentrated to give a 79.0% yield of 3-(1 -ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4 pyrrolidinylphenyl)-4-azaphthalide obtained as a white powder with a melting point of 1 8 1--1 82 OC.

Example 3 Preparation of 3-(1 -ethyl-2-methylindol-3-yl)-3-{2-ethoxy-4piperidinylphenyl)-4Sazaphthalide (Ib)

The procedure described in Example 2 was repeated using 2.05 g of m-piperidinylphenetole instead of m-pyrrolidinylphenetole to give 3-( I -ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4- piperidinylphenyl)-A-azaphthalide (Ib) in a 69.7% yield with a melting point of 163 to 1 64oC.

Example 4 Preparation of 3-(1-ethyl-2-methylindol-3-yl)-3-kairolylXazaphthalide (Ic)

The procedure described in Example 2 was repeated using 1.47 g of kairoline in place of mpyrrolidinyl phenetole to give 3-(1-ethyl-2-methylindol-3-yl)-3-kairolyl-4-azaphthalide (Ic) in a 83.5% yield with a melting point of 177-1 780C.

Example 5 Preparation of 3- ethyl-2-methylindol-3-yl)-3julolidiffll-4-azaphthalide (Id)

The procedure described in Example 2 was repeated using 1.73 g of julolilidine in place of mpyrrolidlnylphenetole to give 3-(1-ethyl-2-methylindol-3-yl)-3julolidinyl-4-azaphthalide (Id) in a 75.8% yield with a melting point of 212--2130C.

Example 6 Preparation of 3-( I -ethyl-2-methylindol-3-yl carbonyl)picolinic acid (Vla)

The mother liquor remaining after the keto acid (Va) had been removed by filtration in Example I was concentrated and the resulting product extracted with dilute and the resulting product extracted with dilute ammonia water and filtered. The filtrate was acidified with dilute hydrochloric acid and the resulting precipitate removed by filtration, washed with water and dried. The product thus obtained in 26.6% yield (8.2 g) was a mixture of the keto acids (Va) and (Vla), the main constituent being 3-(1ethyl-2-methylindol-3-yl-carbonyl) picolinic acid (Vla) which was a pale pink powder with a melting point of 1 10c1 150C.

Example 7 Preparation of 3-(1-ethyl-2-methylindole-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide (Ila)

The procedure described in Example 2 was repeated using 3.08 g of keto acid (Vla) in place of keto acid (Va) to give 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide in a 58.2% yield as a white powder with a melting point of 221-2230C.

Example 8 Preparation of Microcapsules Containing the 4azaphthalide Isomer (la) 0.3 g of 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-4-azaphthalide in a substantially pure form were dissolved in 12 g of SAS-296 (as sold by Nippon Sekiyu Kagaku) and emulsified with 25 cm3 of water containing 3.25 g of gum arabic at 500 C. 3.25 g of gelatin in 25 cm3 of water were then added and the pH was adjusted to 4 with dilute acetic acid. A further 50 cm3 of water were then added and the resulting solution cooled to below 1 00C. 1 cm3 of formalin was then added, and the pH adjusted to between 9 and 10 by the addition of dilute sodium hydroxide. The resulting suspension of minute capsules containing the chromogenic material was then restored to room temperature.

This method was also used to encapsulate 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4- piperidinylphenyl)-4-azaphthalide (Ib); 3-(1-ethyl-2-methylindol-3-yl)-3-kairolyl-4-azaphthalide (Ic); 3 (1-ethyl-2-methylindol-3-yl)-3-julolidinyl-4-azaphthalide (Id), all in a substantially pure form; 3-(1 ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide (IIa); and a mixture of 3-(1 ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-4-azaphthalide (Ia) and 3-( 1 -ethyl-2- methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide (ill) in which.the 7-azaphthalide isomer is present in an amount of less than 10% by weight of the combined amount of isomers.

Example 9 Preparation of Pressure-sensitive Copy Paper The microcapsules obtained in Example 8 were coated onto paper to produce pressure-sensitive transfer (CB) sheets.

When these sheets were placed face to face with underlying receiving sheets (CF sheets with a coating of a colour developer) and pressure was applied an intense blue image was produced which corresponded to the pattern of applied pressure.

There was no tendency at all to self colouration when any of the substantially pure 4azaphthalide isomers (la), (lb), (Ic) or (Id) were used as the chromogenic material. Moreover, even when a mixture containing both the 4-azaphthalide isomer and the 7-azaphthalide isomer in which the latter isomer is present in an amount of less than 10% of the combined weight of both isomers, was used, a slight self colouration was apparent but importantly the pressure-sensitive copy paper produced was still acceptable.

However when the 7-azaphthalide compound was encapsulated and coated onto paper as above, self-colouration was apparent manifesting itself as a purple colouration of the capsules.

Example 10 Preparation of Heat-sensitive Copy Paper 3.5 g of 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-4-azaphthalide (la), 15 g of a 10% aqueous solution of polyvinyl alcohol and 6.5 g of water were mixed together with grinding to produce solution A.

35 g of bisphenol A, 1 50 g of a 10% aqueous solution of polyvinyl alcohol and 65 g of water were mixed together with grinding to produce solution B.

3 g of solution A were then mixed with 30 g of solution B to form a dispersion which was coated onto paper and dried.

This method was repeated for 3-(1 -ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-piperidinylphenyl)4-azaphthalide ill); 3-( 1 ethyl-2-methylindol-3-yl)-3-kairnlyl-4-azaphthalide (Ic); 3-(1-ethyl-2 methylindol-3-yl)-3julolidinyl-4-azaphthalide, (Id), all in a substantially pure form; 3-(1 -ethyl-2 methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide (ill); and a mixture of 3-(1-ethyl-2 methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-4-azaphthalide (la) and 3-(1 -ethyl-2-methylindol- 3-yl)-3-(2-ethoxy-4-pyrrolidinylphenyl)-7-azaphthalide (ill) in which the 7-azaphthalide is present in an amount of less than 2% of the combined weight of the isomers.

When heat was applied to the paper coated with the chromogenic composition described above an intense blue image was produced which corresponded to the pattern of applied heat.

There was no tendency for self colouration to occur when the substantially pure 4-azaphthalide isomers (la), (Ib), (Ic) and (Id) were used as the chromogenic material. Moreover, even when a mixture containing both the 4-azaphthalide isomer and the 7-azaphthalide isomer in which the latter isomer is present in amount of less than 10% of the combined weight of both isomers was used, a slight self colouration was apparent but importantly the heat-sensitive copy paper thus produced was still acceptable.

However when the 7-azaphthalide isomer was used, self-colouration was apparent manifesting itself as a purple'colouration of the paper coating.

Claims

1. A chrnmogenic material comprising a 4-azaphthalide of formula (I),

wherein R, is an alkyl group having from 1 to 12 carbon atoms or a benzyl group, R2 is an alkyl group having from 1 to 4 carbon atoms, R3 is hydrogen, an alkyl or alkoxy group having from 1 to 4 carbon atoms, R4 is an alkyl group having from 1 to 4 carbon atoms or a benzyl group and R5 is an alkyl group having from 1 to 4 carbon atoms, a benzyl group or a phenyl group, or R4 and R5, together with the nitrogen atom to which they are attached, are a saturated 5- to 8-membered ring system, or R4, together with the nitrogen atom to which it is attached and the C4 and C3 atoms, is a 6-membered ring system and either R5 is hydrogen or an alkyl group having from 1 to 4 carbon atoms or, together with the nitrogen atom to which it is attached and the C4 and C5 atoms, is also a 6-membered ring system, which is substantially free from its corresponding 7-azaphthalide isomer of formula (II),

wherein R" R1,R2,R3, and Re are as defined above, provided that, when R4 and R5 are ethyl, R3 is ethoxy and R2 is methyl, R1 is not methyl or ethyl, and that, when R1, R2, R4 and Re are each methyl, R3 is not hydrogen.

2. A chromogenic material according to claim 1, wherein the corresponding 7-azaphthalide isomer of formula (II) is present in an amount of less than 10% based on the combined weight of the 4and 7-azaphthalide isomers of formulae (I) and (II).

3. A chromogenic material according to claim 2, wherein the corresponding 7-azaphthalide isomer of formula (II) is present in an amount of less than 5% based on the combined weight of the 4and 7-azaphthalide isomers of formulae (I) and (II).

4. A chromogenic material according to claim 3, wherein the corresponding 7-azaphthalide isomer of formula (II) is present in an amount of less than 2% based on the combined weight of the 4and 7-azaphthalide isomers of formulae (I) and (II).

5. A chromogenic material according to any one of the preceding claims, wherein R1 is ethyl, R2 is methyl. R3 is ethoxy. and R4 and R, together with the nitrogen atom to which they are attached, are a pyrrolidinyl group.

6. A chromogenic material according to any one of the preceding claims, wherein R1 is ethyl, R2 is methyl, R3 is ethoxy, and R4 and Re, together with the nitrogen atom to which they are attached, are a piperidinyl group.

7. A chromogenic material according to any one of claims 1 to 4, wherein R1 is ethyl, R2 is methyl and the aminophenyl substituent having the groups R3, R4 and R8 is of formula (III),

8. A chromogenic material according to any one of claims 1 to 4, wherein R1 is ethyl, R2 is methyl and the aminophenyl substituent having the groups R3, R4, R5is of formula (IV),

9.A method for the preparation of a chromogenic material as defined in claim 1, which comprises reacting in the presence of a dehydrating agent a keto acid of formula (V),

wherein R1 and R2 are as defined in claim 1, which is substantially free from the corresponding keto- acid isomer of formula (VI),

with an aromatic amine of formula (ill),

wherein R3 and R4 and R5 are as defined in claim 1.

1 0. A method according to claim 9, wherein the keto-acid isomer of formula (Vl) is present in an amount of less than 10% based on the combined weight of the keto-acid isomers of formulae (V) and (VI).

11. A method according to claim 10, wherein the keto-acid isomer of formula (VI) is present in an amount of less than 5% based on the combined weight of the keto-acid isomers of formulae (V) and (Vi).

1 2. A method according to claim 11, wherein the keto acid isomer of formula (Vl) is present in an amount of less than 2% based on the combined weight of the keto-acid isomers of formulae (V) and (Vl).

1 3. A method according to any one of claims 9 to 12, wherein the dehydrating agent is an acid anhydride.

1 4. A method according to claim 13, wherein the acid anhydride is acetic anhydride.

1 5. A microencapsulated chromogenic solution which contains a chromogenic material as defined in any one of claims 1 to 8.

1 6. Pressure-sensitive record material which contains a chromogenic material as defined in any one of claims 1 to 8.

1 7. Heat-sensitive record material which contains a chromogenic material as defined in any one of claims 1 to 8.

1 8. A chromogenic material substantially as hereinbefore described with reference to examples 2, 3, 4, 5, and 7.

1 9. A method of preparing chromogenic material substantially as hereinbefore described with reference to Examples 2, 3, 4, 5 and 7.

20. A microencapsulated chromogenic solution substantially as hereinbefore described with reference to Example 8.

21. Pressure sensitive record material substantially as hereinbefore described with reference to Example 9.

22. Heat sensitive record material substantially as hereinbefore described with reference to Example 10.