FR2481286A1 - CHROMOGENIC MATERIAL OF THE AZAPHTALIDE CLASS, PROCESS FOR PREPARING THE SAME, CHROMOGENIC SOLUTION AND RECORDING MEDIUM CONTAINING THE SAME - Google Patents

Abstract

THE INVENTION CONCERNS CHROMOGENOUS MATERIALS OF THE AZAPHTHALIDE TYPE. THE CHROMOGENOUS MATERIALS OF THE INVENTION ARE 4-AZAPHTHALIDES OF THE FORMULA: (CF DRAWING IN BOPI) (IN WHICH THE RAR VARIABLES ARE ORGANIC RADICALS, R AND R MAY ALSO REPRESENT HYDROGEN) SENSITIVELY FREE OF ISOMERE 7 -AZAPHTALIDE CORRESPONDENT. THE CHROMOGENOUS MATERIALS OF THE INVENTION MAY BE USED IN PRESSURE AND HEAT SENSITIVE RECORDING MEDIA. THEY ARE CAPABLE OF PRODUCING INTENSE COLORS BY REACTION WITH RESIN OR CLAY TYPE COLOR DEVELOPERS, THE COLOR BEING SENSITIVELY RESISTANT TO ALTERATION AND SELF-COLORATION.

Description

1 2481286

  The present invention relates to chromogenic materials of the class of azaphthalides, a process

  to obtain them, a micro-chromogenic solution

  encapsulated and a recording medium containing them.

  The system used in a pressure sensitive type recording medium to form a color generally contains a virtually colorless color material, a color developer capable of reacting with the color former to generate a color and a solvent in which color formation reaction can take place. The reactive components of the color-forming system are kept separate until the moment of use and this separation can be achieved by micro-encapsulation of a chromogenic composition comprising a solution of the

  chromogenic material in a solvent. At the time of use

  tion, the application of pressure causes the rupture of the microcapsules which are sensitive to this pressure. This results in release of the chromogenic material and its solvent. In this way, the two color-forming components are brought into contact and generate an image that corresponds to the configuration in which the pressure is applied. A pressure-sensitive recording medium can be used for producing copies without

require carbon paper.

  In the case of a thermosensitive recording medium, the color former and the color revealing agent are layered on paper in the form of a mixture in a binder. When heat is applied, the color material or color developer melts and reacts with the other producing an image that

  corresponds to the model of the application of heat.

  In a pressure-sensitive autocopier system, the recording medium comprises a coated, or dispersion-containing, sheet of a mixture of a color developer and microcapsules.

  containing a chromogenic substance and a solvent.

  In a transfer recording system, at least two recording media are used. Mon

2 2481286

  of them comprises a sheet bearing a coating of microencapsulated chromogenic solution (CB sheet) and the other comprises a sheet which bears a coating of the color developer (CF sheet). The sheets are assembled into a bundle, their coatings turned towards each other, so that the transfer of the chromogenic solution can be made from the CB sheet to the CF sheet. If other copies are desired, the package may further comprise a third recording medium which comprises a sheet bearing on one side a coating of the microencapsulated chromogenic solution and on the other side a coating of the color developer ( CFB sheet). One or more CFB sheets are interposed between the CF and CB sheets, each microcapsule coating being contiguous with a developer coating.

color.

  The invention is particularly directed to

  chromogenic materials used in these recording media

  tration. Many of these materials are often used in combination to create an impression having the desired physical properties and the desired hue, usually blue or black. One of the most important chromogenic materials is a blue chromogenic material that is almost always the violet lactone

  crystallized (3,3-bis (4-dimethylaminophenyl) -6-dimethyl

  aminophthalide). However, an impression produced by the crystallized violet lactone fades very rapidly on exposure to light, and attempts to find a suitable substitute have

so far failed.

  One of these attempts was the use of an isomeric mixture of 4- and 7-azaphthalides bearing aminophenyl substituents and an indolyl substituent (see Japanese Patent Publication Nos. 16807/1976 and 38243/1976). While such chromogenic materials give a satisfactory blue impression which is much more resistant to discolouration than an impression produced by crystallized violet lactone, they exhibit

  unfortunately the disadvantage of a self-coloring is

  that is to say of a premature revelation of the colored form, which is manifested during the manufacture of the recording medium. Accordingly, in the case of a pressure-sensitive recording medium, the capsules are colored and, in the case of a thermosensitive recording medium, the coating is colored. In either case, these chromogenic materials are not, of course, suitable substitutes for

the lactone of crystallized violet.

  It has been discovered that the problem of autocoloration is due to the relatively high proportion of 7-azaphthalide in the isomeric mixture and that, if the chromogenic mixture contains the 4-azaphthalide isomer in a form substantially free of the isomer 7 -azaphthalide, the problem of autocoloration does not appear. The resulting material is therefore very suitable as a replacement for crystallized violet lactone, with many advantages over the latter. The present invention therefore provides a chromogenic material comprising a 4-azaphthalide of formula (I): wherein R 1 is an alkyl group having 1 to 12 carbon atoms or a benzyl group, R 2 is an alkyl group having 1 to 4 carbon atoms R3 is hydrogen, an alkyl or alkoxy group having 1 to 4 carbon atoms, R4 is an alkyl group having 1 to 4 carbon atoms or a benzyl group and R5 is an alkyl group having 1 to 4 carbon atoms, a benzyl group or a phenyl group, or else R4 and R5 form

2 48 128 6

  with the nitrogen atom to which they are attached an 8-membered saturated ring, or R4 forms a hexagonal ring with the nitrogen atom to which it is attached and the carbon atoms C4 and C3, and R5 is hydrogen or an alkyl group having 1 to 4 carbon atoms or also forms a hexagonal ring with the nitrogen atom to which it is bonded and the C4 and

  C5, which is substantially free of its corresponding isomer.

  which is 7-azaphthalide of formula (II)

/ 8

I

  wherein R 1, R 2, R 3, R 4 and R 5 are as defined above, with the proviso that when R 4 and R 5 are ethyl, R 3 is ethoxy and R 2 is methyl, R 1 is not methyl group and ethyl and that when R1, R2, R4 and R5 are each a methyl group,

  R3 is not a hydrogen atom.

  The chromogenic materials of the present invention are usually colorless or slightly colored substances, but they produce an immediate and intense blue color by contact with a color developer such as a clay or an acidic resin (in the case of a carrier). pressure-sensitive recording) and bisphenol A (in the case of a heat-sensitive recording medium). The resulting color not only has excellent resistance to weakening, but also has satisfactory stability to plasticizers, etc. Preferably, the 7-azaphthalide of formula (II) is present in a proportion of less than 10% relative to the total weight of the two isomers. It is more advantageous than the

  proportion is less than 5% or even 2%.

  The definition given above for the chromogenic materials of the present invention covers materials in which the aminophenyl substituent bearing the groups R3, R4 and R5 has the formula (III) or (IV) - C Ha (III) (IV) The aminophenyl substituents of formulas (III) and (IV) are usually called, respectively,

  kairolyl substituent and julolidinyl substituent.

  In the production, according to the prior art, of the isomeric mixture of 4- and 7-azaphthalides, the quinolinic acid anhydride is reacted with an indole to form an isomeric mixture of keto acids which is then reacted. with an aromatic amine. The appearance of an isomeric mixture as the final product is therefore due to the intermediate production of an isomeric mixture which, in turn, is due to other sites of the anhydride molecule that can react with the indole. Accordingly, to obtain a chromogenic material in which 4azaphthalide is

  almost devoid of its corresponding isomer, namely 7-

  azaphthalide, it is necessary to use the keto acid which gives the 4-azaphthalic isomer substantially free of

  the other keto acid which gives the 7-azaphthalide isomer.

  The present invention therefore provides a process for preparing a chromogenic material comprising a 4-azaphthalide of formula (I), as defined above, substantially free of its corresponding isomer, namely 7-azaphthalide of formula (II) as defined above, which process consists in reacting in the presence of a dehydrating agent a keto acid of formula (V): ## STR2 ## in which R1 and R2 have the definitions given above ,

  which is substantially free of the isomeric keto acid corresponding to

laying down of formula (VI):

1 5. CO., H

I Ca

(VI)

  with an aromatic amine of formula (VII):

R4

\\ Re VII

  in which R3, R4 and R5 have the definitions given below.

  above. Preferably, the isomeric keto acid of formula (VI) is present in an amount of less than 10% based on the total weight of the isomeric ketoacids of formulas (V) and (VI). It is even more advantageous that the proportion be

less than 5% or even 2%.

  The desiccant is preferably a

  acid anhydride such as acetic anhydride.

  To obtain the keto acid of formula (V) in a form which is substantially free of its corresponding isomeric keto acid of formula (VI), the isomeric mixture of keto acids is prepared in a conventional manner by reaction of the anhydride of quinolinic acid with an indole, and then purifying the resulting mixture in favor of the desired isomer of formula (V). This purification can be easily accomplished by recrystallization, since the ketoacids

  isomers have considerably different solubilities.

  Alternatively or additionally, the preparation of the isomeric keto-acids may be carried out in one of a variety of solvents which promotes the production of the desired iso-keto acid. These

  solvents include benzene, toluene, chlorinated

  benzene, alcohols and acetonitrile.

  The chromogenic material of the present invention may be used as such or in combination with other known color formers, for example phthalides, fluoranes or known spiropyrans. As

  examples of these known materials, mention is made of 3,7-bis-

  (dimethylamino) -10-benzoylphenothiazine (leucobase)

  Benzoyl Methylene Blue, BLMB); 3,3-bis-

  (dimethylaminophenyl) -6-dimethylaminophthalide (lactone

  crystallized violet, CVL); 2'-anilino-6'-diethylamino-3'-

  methylfluorane (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-ethylamino-xanthene-9,2- (2H) -naphtol- (1,8-bc) -furan; the

  7-chloro-6-methyl-3-diethylaminofluoran; 3-diethyl-

  aminobenzo- (b) -fluorane; 3- (4-diethylamino-2-ethoxy) -3-

  (2-methyl-1-éthylindol-3-yl) -phthalide; 3- (4-diethyl)

  amino-2-butoxy) -3- (2-methyl-1-éthylindol-3-yl) -phthalide; and

  3,7-bis (diethylamino) -10-benzoylbenzoxazine.

  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 formation of microcapsules. Examples of such solvents include dialkyl phthalates whose alkyl groups have 4 to 13 carbon atoms, such as

  dibutyl, dioctyl, dinonyl phthalates and

  decyl; 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB, U.S. Patent No. 4,027,065); ethyldiphenylmethane (U.S. Patent No. 3,996,405); alkylbiphenyls such as mono-isopropylbiphenyl (U.S. Patent No. 3,627,581); C10-C14 alkylbenzenes such as dodecylbenzene; diaryl ethers such as diphenyl ether, di- (aralkyl) ether such as dibenzyl ether and aryl and aralkyl ethers such as phenyl benzyl ether; liquid dialkyl ethers having at least 8 carbon atoms; liquid alkyl ketones having at least 9 carbon atoms; alkyl or aralkyl benzoates such as benzyl benzoate; alkylated naphthalenes; and terphenyls

partially hydrogenated.

  These solvents, all of which are substantially odorless, can be used alone or as a mixture. They can also be used with a diluent in order to lower the cost price of the chromogenic solution. Of course, the diluent must not be able to react chemically with the solvent or any other component of the solution and it must be at least partially miscible with the solvent to form a single phase. The diluent is used in an amount sufficient to lower the cost, but without impairing the solubility of the color material. Diluents are already known in the prior art and a preferred example is the "Magnaflux" oil which consists of a mixture of saturated aliphatic hydrocarbon oils having

  a distillation temperature of about 160 to 288 C.

  The present invention also provides a solution

  microencapsulated chromogen in which the chromo-

  The gene is in accordance with the present invention. The mic-

  encapsulation of the chromogenic solution may be carried out in accordance with known microencapsulation methods, such as those described in U.S. Patent Nos. 2,800,457, 3,041,289, 3,533,958,

  N 3 755 190, N 4 001 140 and N 4 100 103.

  The color developer used in the present invention is an acidic material of any kind meeting the definition of a Lewis acid, i.e., an electron acceptor. These acidic materials include clays, eg attapulgite, bentonite and montmorillonite, treated clays such as "silton" clay described in US Pat. Nos. 3,622,364 and 3,503,761. , silica gel, talc, feldspar, magnesium trisilicate, pyrophyllite, zinc sulphate, zinc sulphide, calcium sulphate, calcium citrate, calcium phosphate, calcium fluoride and barium sulfate, aromatic carboxylic acids such as salicylic acid, aromatic carboxylic acid derivatives and their metal salts as described in U.S. Patent No. 4,022,936 and an acid polymeric material such as phenol-formaldehyde polymers, phenolic resins

  modified by a metal as described in the US Pat.

  United States No. 3,732,120, phenolic polymers

  acetylene, maleic acid-rosin resins, styrene-maleic anhydride copolymers and partially or fully hydrolyzed ethylene-maleic anhydride copolymers, carboxypolymethylene and partially or fully hydrolysed vinyl and methyl vinyl ether and maleic anhydride copolymers and mixtures thereof, as described in US Pat.

  U.S. Patent No. 3,672,935.

  The present invention further provides a pressure or heat sensitive recording medium which contains a chromogenic material as defined herein.

  memory. In general, for a thermal recording medium

  Sensitively, it is preferable to use the chromogenic material of the present invention in a form in which the 7-azaphthalide isomer is present in a proportion of less than 2% of the total weight of the two isomers. While for a pressure-sensitive recording medium, it is preferable to use the chromogenic material of the

  present invention in a form in which the isomer 7-

  azaphthalide is present in a proportion of less than 10% of the total weight of the two isomers. Coating formulations and methods of preparing the pressure-sensitive recording medium are generally known in the prior art, for example in U.S. Patents Nos. 3,627,581, 3,775,424 and 3,853,869. Coating formulations and methods for preparing a thermosensitive recording medium are also generally known in the prior art, for example by US patents.

  No. 3,539,375, Nos. 3,674,535 and 3,746,675.

  Other details of the present invention

from the following examples.

EXAMPLE 1

  Preparation of 2- (1-ethyl-2-methylindol-3-yl) acid

  carbonyl) -nicotinic (Va) CA C C H3 Va A mixture is stirred at 25-30 C for 15 hours

  14.9 g of quinolinic acid anhydride, 15.9 g of

  ethyl-2-methylindole and 30 cm3 of acetonitrile. We separate by

  filtration the resulting precipitate, it is washed with

  nitrile, and then dried to obtain 21.8 g (yield

  70.8%) of 2- (1-ethyl-2-methylindol-3-ylcarbonyl) -

  nicotine in a form substantially free of its isomer. It is obtained in the form of a pale brown powder and

  its melting point is 181-182 C.

EXAMPLE 2

  Preparation of 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy)

  4-pyrrolidinylphenyl) -4-azaphthalide (Ia) I (]: a) 6065 ° C. for 1 hour is reacted with

  mixture of 3.08 g of the keto acid of formula (Va), 1.91 g of m-

  pyrrolidinylphenetol and 5 g of acetic anhydride. The reaction product is then neutralized with dilute ammonium hydroxide and extracted with toluene. The toluene solution is then concentrated to yield

  of 79.0% 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-)

  pyrrolidinylphenyl) -4-azaphthalide obtained in the form of a

  white powder having a melting point of 181-182 C.

EXAMPLE 3

  Preparation of 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-)

  piper idinylphenyl) -4-azaphthalide (Ib)

X -

"/

  CH3 (Ib) I1 The procedure of Example 2 is repeated in

  using 2.05 g of m-piperidinylphenol instead of n

  pyrrolidinylphenetol to give 3- (1-ethyl-2-methyl)

  indol-3-yl) -3- (2-ethoxy-4-piperidinylphenyl) -4-azaphthalide (Ib) in a yield of 69.7%, this compound having a

fusion of 163-164 C.

EXAMPLE 4

  Preparation of 3- (1-ethyl-2-methylindol-3-yl) -3-

kairolyl-4-azaphthalide (Ic) 7

X A- CH%

  9 N <3 X (Ic) The procedure of Example 2 is repeated,

  using 1.47 g kairoline instead of m-pyrrolidinyl-

  phenetole to obtain 3- (1-ethyl-2-methylindol-3-yl) -3-

  kairolyl-4-azaphthalide (Ic) in a yield of 83.5% and

  having a melting point of 177-178 ° C.

EXAMPLE 5

  Preparation of 3- (1-ethyl-2-methylindol-3-yl) -3-

julolidinyl-4-azaphthalide (Id)

I -

NO

Xt (Id)

CJiH -

  The procedure of Example 2 is repeated,

  using 1.73 g of julolidine in place of m-pyrrolidinyl-

  pheneterol, to obtain in a yield of 75.8% the 3- (1-

  ethyl-2-methylindol-3-yl) -3-julolidinyl-4-azaphthalide (Id) having a melting point of 212-213 ° C.

EXAMPLE 6

  Preparation of 3-1-ethyl-2-methylindol-3-yl

  The mother liquor remaining after the keto acid (Va) was filtered off in Example 1 is concentrated and the resulting product is extracted with a dilute aqueous solution (carbonyl) -picolinic (VIa). ammonia and filtered. The filtrate is acidified with dilute hydrochloric acid and the precipitate

  The resultant is separated by filtration, washed with water and dried.

  The product thus obtained in a yield of 26.6% (8.2 g) consists of a mixture of keto acids (Va) and (VIa), the

  main constituent being 3- (1-ethyl-2-methyl)

  indol-3-ylcarbonyl) -picolinic (VIa) which is a pale pink powder having a melting point of 110-115 Co

EXAMPLE 7

  Preparation of 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy)

  4-pyrrolidinylphenyl) -7-azaphthalide (IIa) W (IIa) CH c'OHis

14 2481286

  The procedure of Example 2 is repeated, using 3.08 g of the keto acid (VIa) in place of the keto acid

  (Va) to give 3- (1-ethyl-2-methylindol-3-yl) -3- (2-

  ethoxy-4-pyrrolidinylphenyl) -7-azaphthalide in a yield of 58.2%, in the form of a white powder having a point

melting point of 221-223 C.

EXAMPLE 8

  Preparation of microcapsules containing the 4-azaphthalide isomer (Ia)

  0.3 g of 3- (1-ethyl-2-methylindol-3

  yl) -3- (2-ethoxy-4-pyrrolidinylphenyl) -4-azaphthalide in a substantially pure form in 12 g of "SAS-296" (sold by the firm Nippon Sekiyu Kagaku) and the solution is emulsified

  with 25 cm3 of water containing 3.25 g of gum arabic at 50 ° C.

  3.25 g of gelatin are then added in 25 cm 3 of water and

  adjust the pH to 4 by addition of dilute acetic acid.

  Then another 50 cm3 of water is added and the resulting solution is cooled to below 10 ° C. Then 1 cm3 of formalin is added and the pH is adjusted to between 9 and 10 by the addition of dilute sodium hydroxide. The suspension obtained from small capsules containing the chromogenic material is

  then brought back to room temperature.

  This method is also used to encapsulate

  3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-piperidinyl)

  phenyl) -4-azaphthalide (Ib); 3- (1-ethyl-2-methylindol-3-

  yl) -3-kairolyl-4-azaphthalide (Ic); 3- (1-ethyl-2-methyl)

  indol-3-yl) -3-julolidinyl-4-azaphthalide (Id); all under one

  practically 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-pyrrolidinylphényl) -7-aza-

  phthalide (IIa) in which the 7-azaphthalide isomer is present in a proportion of less than 10% by weight of the

total amount of isomers.

EXAMPLE 9

  Preparation of pressure-sensitive copying paper The microcapsules obtained in Example 8 are layered on paper to produce sheets

  (CB) transfer pressure sensitive.

  When these sheets are placed face to face with underlying receiver sheets (CF sheets coated with a color developer) and pressure is applied, an intense blue image is produced, this image corresponding to the pattern of application of pressure. There is no tendency for autocoloration when any of the substantially pure isomeric 4-azaphthalides (Ia), (Ib), (Ic) or (Id) is used as the chromogenic substance. In addition, even if a mixture containing both the 4-azaphthalide isomer and the 7azaphthalide isomer in which the latter isomer is present in a proportion of less than 10% of the total weight of the two isomers is used, a slight autocoloration appears, but the important fact is that the pressure-sensitive copying paper obtained is

still acceptable.

  However, when the 7-azaphthalide compound is encapsulated and applied to the paper as above, autocoloration appears which manifests itself as

  a purple color of the capsules.

EXAMPLE 10

  Preparation of a thermosensitive copy paper

  3.5 g of 3- (1-ethyl-2-

  methylindol-3-yl) -3- (2-ethoxy-4-pyrrolidinylphényl) -4-aza-

  phthalide (Ia), 15 g of a 10% aqueous solution of polyvinyl alcohol and 6.5 g of water by grinding to produce a solution A. 35 g of bisphenol A, 150 g of a solution are mixed together. aqueous solution containing 10% of polyvinyl alcohol and 65 g of water by grinding to produce a solution B. 3 g of solution A are then mixed with 30 g of solution B to form a dispersion which is applied in

  layer on paper and dry.

  This procedure is repeated for 3- (1-ethyl)

  2-methylindole-3-yl) -3- (2-ethoxy-4-pipéridinylphényl) -4-aza-

  phthalide (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 form

16 2 4 2481286

  substantially pure; 3- (1-ethyl-2-methylindol-3-yl) -3- (2-

  ethoxy-4-pyrrolidinylphenyl) -7-azaphthalide (IIa); and one

  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-aza-phthalide (IIa) wherein 7-azaphthalide is present in

  a proportion of less than 2% of the total weight of the isomers.

  When heat is applied to the paper

  bearing the chromogenic composition layer described above

  above, the intense blue image corresponding to the model

  of heat application is produced.

  There is no tendency to autostain when the substantially pure isomeric 4-azaphthalides (Ia), (Ib), (Ic) and (Id) are used as the chromogenic material. In

  additionally, when a mixture containing both isomer 4-

  azaphthalide and the 7-azaphthalide isomer wherein the latter isomer is present in a proportion of less than 10% by weight

  total of the two isomers is used, a slight

  coloring appears but the important thing is that the paper

  To thermosensitive copy so produced is still acceptable.

  However, when using the isomer 7-

  azaphthalide, autocoloration appears, manifesting itself

  a purple coloring of the paper coating.

Claims (10)

  1. Chromogenic material, characterized in that it comprises a 4azaphthalide of formula (I): in which RI is an alkyl group having 1 to 12 carbon atoms or a benzyl group, R2 is an alkyl group having 1 to 4 carbon atoms. carbon, R3 is hydrogen, an alkyl or alkoxy group having 1 to 4 carbon atoms, R4 is an alkyl group having 1 to 4 carbon atoms or a benzyl group and R5 is an alkyl group having 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 form a saturated 8-membered ring, or R4 form a hexagonal ring with the nitrogen atom to which it is bonded and the carbon atoms C4 and C3, and R5 is hydrogen or an alkyl group having 1 to 4 carbon atoms or also forms a hexagonal ring with the nitrogen atom to which it is bonded and the C4 atoms and   C5, which is substantially free of its corresponding isomer.   which is 7-azaphthalide of formula (II) o (II) A, wherein R 1, R 2, R 3, R 4 and R 5 are as defined above, provided that when R 4 and R 5 are ethyl groups, R3 is ethoxy and R2 is methyl, R1 is not methyl or ethyl and when R1, R2, R4 and R5 are each methyl,   R3 is not a hydrogen atom.   2. Chromogenic material according to claim   1, characterized in that the corresponding 7-azaphthalide isomer   of formula (II) is present in an amount of less than 10%, preferably less than 5% and especially less than 2% on the basis of the total weight of the   4- and 7-azaphthalide isomers of formulas (I) and (II).   3. Chromogenic material according to one of the   Claims 1 and 2, characterized in that R1 is a   ethyl group, R2 is a methyl group, R3 is an ethoxy group and R4 and R5 form with the nitrogen atom to which they   a pyrrolidinyl group or a piperidinyl group are attached.   4. Chromogenic material according to one of the   Claims 1 and 2, characterized in that R1 is a   ethyl group, R2 is a methyl group and the aminophenyl substituent carrying the groups R3, R4, R5 is a substituent of formula: - N C% III or IV 19 2 2481286   5. Process for producing a color forming material according to claim 1, characterized in that it consists in reacting in the presence of a dehydrating agent a keto acid of formula (V): IC - q '   wherein R1 and R2 are as defined in claim 1, which is substantially free of the corresponding isomeric keto acid of formula (VI): ## STR2 ## wherein an aromatic amine of formula (VII): R3, R4 and R5 have the definitions given in claim 1.   6. Process according to Claim 5, characterized in that the isomeric keto acid of formula (VI) is present in a proportion of less than 10%, preferably less than 5% and especially less than 2%, based on the total weight of the keto isomeric acids of formulas (V) and (VI). 2 2481286   7. Method according to one of claims 5 and   6, characterized in that the desiccant is a   acid anhydride, preferably acetic anhydride.   8. Microencapsulated chromogenic solution, characterized in that it contains a chromogenic material   according to any one of claims 1 to 4.   Pressure-sensitive recording medium, characterized in that it encloses a material   color former according to one of claims 1 to 4.   10. Heat-sensitive recording medium, characterized in that it contains a chromogenic material   according to any one of claims I to 4.