Chromogenic compounds

The chromogenic azaphthalide compounds of the invention are of the formula: ##STR1## wherein A is a pyridine ring; R.sub.1 is hydrogen atom or alkyl radicals of from one to 4 carbon atoms; X is hydrogen atom, alkyl radicals of from one to 2 carbon atoms or alkoxy radicals of from one to 2 carbon atoms; R.sub.2 is alkyl radicals of from one to 2 carbon atoms or phenyl radical; R.sub.3 is hydrogen atom or alkyl radicals of from one to 8 carbon atoms. These compounds are particularly suitable for use in providing high quality pressure- or heat-sensitive copying sheets.

This invention relates to novel chromogenic azaphthalide compounds 
available as color former in copying (recording) materials. 
The novel chromogenic compounds according to the present invention are 
defined by the following general formula: 
##STR2## 
wherein A is pyridine ring; R.sub.1 is hydrogen atom or alkyl radicals of 
from one to 4 carbon atoms; X is hydrogen atom, alkyl radicals of from one 
to 2 carbon atoms or alkoxy radicals of from one to 2 carbon atoms; 
R.sub.2 is alkyl radicals of from one to 2 carbon atoms or phenyl radical; 
R.sub.3 is hydrogen atom or alkyl radicals of from one to 8 carbon atoms. 
The azaphthalide compounds of the general formula (I) (hereinafter referred 
to as the present compounds) are substantially colorless in themselves. 
They, however, have a property such that when they are brought into 
intimate contact with electron-accepting substances such as active clay 
substances, for example, acid clay, attapalgite clay, silton clay, 
bentonite, kaoline and acidic organopolymers, for example, phenol 
formaline resin, phenol acetylene resin, salicyclic acid formaline resin 
and Bis-Phenol A, they give rise to colors of the blue group or bluish 
purple group. 
As the chromogenic compounds of prior art which are capable of giving rise 
to blue to bluish purple colors, leuco-auramine compounds, phthalide 
compounds, leuco-methylene blue compounds and the like have been known. 
However, they have various disadvantages. That is, Michler's hydrol, one 
of the leuco-auramine compounds, is very poor in its stability before 
color forming and its color forming property exhibited upon application to 
sheets coated with an acidic organopolymer is poor, particularly with its 
colored image of poor light-resistivity. Crystal violet lactone, one of 
the phthalide compounds, has been usually used because of its initial 
colored image of dark bluish purple, however, its colored image shows 
extremely low resistivity to light and humidity. In benzoyl 
leuco-methylene blue, one of the leuco-methylene blue compounds, its 
colored image shows extremely high resistivity to light, but its color 
forming is very slow and its color forming property exhibited upon 
application to sheets coated with an acidic organopolymer is very poor. 
The chromogenic compounds which have improved the disadvantages and possess 
structure formulas similar to that of FORMULA (I) include 
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-7-azaphth 
alide, 
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphth 
alide and the like. However, their spontaneous color forming property is 
remarkable. 
In a first aspect of the present invention, there is provided a chromogenic 
compound of the general formula: 
##STR3## 
wherein A is a pyridine ring of a 4- or 7-azaphthalide group; R.sub.1 is 
hydrogen atom or alkyl radicals of from one to 4 carbon atoms; X is 
hydrogen atom, alkyl radicals of from one to 2 carbon atoms or alkoxy 
radicals of from one to 2 carbon atoms; R.sub.2 is alkyl radicals of from 
one to 2 carbon atoms or phenyl radical; R.sub.3 is hydrogen atom or alkyl 
radicals of from one to 8 carbon atoms. 
In a second aspect of the present invention, there is provided a process 
for the preparation of a chromogenic compound of the formula (I): 
##STR4## 
wherein A is a pyridine ring; R.sub.1 is hydrogen atom or alkyl radicals 
of from one to 4 carbon atoms; X is hydrogen atom, alkyl radicals of from 
one to 2 carbon atoms or alkoxy radicals of from one to 2 carbon atoms; 
R.sub.2 is alkyl radicals of from one to 2 carbon atoms or phenyl radical; 
R.sub.3 is hydrogen atom or alkyl radicals of from one 8 carbon atoms, 
comprising condensing a pyridinecarboxylic acid derivative of the formula 
(II): 
##STR5## 
wherein A, R.sub.2 and R.sub.3 are defined above, and an alkylaniline 
derivative of the general formula (III): 
##STR6## 
wherein X and R.sub.1 are defined above, in the presence of a condensing 
agent. 
In a third aspect of the present invention, there is provided a process for 
the preparation of a chromogenic compound of the formula (I): 
##STR7## 
wherein A is a pyridine ring; R.sub.1 is hydrogen atom or alkyl radicals 
of from one to 4 carbon atoms; X is hydrogen atom, alkyl radicals of from 
one to 2 carbon atoms or alkoxy radicals of from one to 2 carbon atoms; 
R.sub.2 is alkyl radicals of from one to 2 carbon atoms or phenyl radical; 
R.sub.3 is hydrogen atom or alkyl radicals of from one to 8 carbon atoms, 
comprising condensing an indole derivative of the formula (IV): 
##STR8## 
wherein R.sub.2 and R.sub.3 are defined above, and a pyridinecarboxylic 
acid derivative of the formula (V): 
##STR9## 
wherein A, X and R.sub.1 are defined above, in the presence of a 
condensing agent. 
The present compounds notably excellent in a light-resistivity of colored 
image and in a resistivity to a spontaneous color forming property, which 
retain the excellent properties of the known azaphthalide compounds 
without the disadvantage mentioned above. These compounds, therefore, are 
fully practicable as color former for pressure-sensitive and 
heat-sensitive copying sheets. 
The present compounds are synthesized by methods to be described below. 
A pyridinecarboxylic acid derivative (II) and an alkylaniline derivative 
(III) are condensed in the presence of a condensing agent such as 
concentrated aqueous sulfuric acid solution, acetic anhydride and 
polyphosphoric acid as shown schematically below. 
##STR10## 
(wherein A, R.sub.1, R.sub.2, R.sub.3 and X are defined previously). 
Alternatively, the present compounds are synthesized by condensing a 
pyridinecarboxylic acid derivative (V) and an indole derivative (IV) in 
the presence of the condensing agent mentioned above as shown 
schematically below. 
##STR11## 
(wherein A, R.sub.1, R.sub.2, R.sub.3 and X are defined previously). 
The reaction temperature is 40.degree. to 100.degree. C., preferably 
50.degree. to 60.degree. C. The reaction time is 4 to 10 hours, preferably 
6 to 8 hours. 
The pyridinecarboxylic acid derivative (II) is obtained by bringing indole 
derivative (IV) and quinolinic acid anhydride into reaction in an inert 
organic solvent such as tetrachloroethane, benzene, chlorobenzene, 
nitrobenzene and the like, or using a Friedel-Crafts catalyst such as 
aluminum chloride, zinc chloride, phosphorus chloride and the like. And, 
the pyridinecarboxylic acid derivative (V) is obtained by bringing 
alkoxyaniline derivative (III) and quinolinic acid anhydride into reaction 
as above. 
The present compound may be singly used or may be used by mixing one or 
more color formers. The color former which can be used in combination with 
the present compound is, for example, crystal violet lactone, benzoyl 
leucomethylene blue, di-substituted fluorane compounds disclosed in the 
specifications of British Pat. No. 1,182,743, Belgian Pat. Nos. 815,291, 
815,294, and 3,7-bisindolyl phthalide disclosed in the specification of 
DT-AS No. 22 59 711. 
Effective use of the present compounds in pressure-sensitive copying sheets 
can be accomplished by following any one of the methods described in the 
specification of U.S. Pat. Nos. 2,800,458, 2,806,457 and so on. 
Application of the present compounds to heat-sensitive recording materials 
can be effected by any one of the methods described in Japanese Patent 
Publication No. 14039/1970 and so on. 
The followings are the more detailed explanation of the present invention 
while referring to examples, however, it should be understood that the 
scope of the present invention is never restricted to examples shown as 
follows.

EXAMPLES OF SYNTHESIS 
1. Synthesis of 
3-(4-N-methyl-cyclohexylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3- 
yl)-4-azaphthalide 
##STR12## 
Into 60 ml of acetic anhydride, 6 g of 1-ethyl-2-methylindol-3-yl 
3-carboxypyridin-2-yl ketone and 4 g of N-methyl-N-cyclohexyl-3-anisidine 
are dissolved and brought into reaction at 50.degree. to 60.degree. C. for 
6 hours. After the reaction mixture is cooled to room temperature, it was 
poured into 500 ml of ice water to hydrolyse acetic anhyride and 
thereafter the resultant solution is adjusted to pH at 11 to 12 by 
addition of dilute aqueous solution of sodium hydroxide. Subsequently 100 
ml of toluene is added and stirred to separate the toluene layer. The 
solid substance is obtained by distillating off toluene. The solid 
substance is washed with 100 ml of methanol, then filtered and dried to 
afford 6 g of a pale bluish green and crystalline substance having a 
melting point of 117.5.degree. to 122.5.degree. C. The compound is 
identified to be the titled compound. 
2. Synthesis of 
3-(4-N-methyl-cyclohexylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3- 
yl)-7-azaphthalide 
##STR13## 
When the procedure of Synthesis 1 is repeated by using 6 g of 
1-ethyl-2-methylindol-3-yl 2-carboxypyridin-3-yl ketone as a 
pyridinecarboxylic acid derivative and 4 g of 
N-methyl-N-cyclohexyl-3-anisidine as an alkylaniline derivative, there is 
obtained 5 g of a colorless crystalline substance having a melting point 
of 226.5.degree. to 227.5.degree. C. The compound is identified to be the 
titled compound. 
3. Synthesis of 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-y 
l)-4-azaphthalide 
##STR14## 
When the procedure of Synthesis 1 is repeated by using 6 g of 
1-ethyl-2-methylindol-3-yl 3-carboxypyridin-2-yl ketone as a 
pyridinecarboxylic acid derivative and 4.2 g of 
N-methyl-N-cyclohexyl-3-phenetidine as an alkylaniline derivative, there 
is obtained 5.5 g of a colorless crystalline substance having a melting 
point of 141.degree. to 146.degree. C. The compound is identified to be 
the titled compound. 
4. Synthesis of 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-y 
l)-7-azaphthalide 
##STR15## 
When the procedure of Synthesis 1 is repeated by using 6 g of 
1-ethyl-2-methylindol-3-yl 2-carboxypyridin-3-yl ketone as a 
pyridinecarboxylic acid derivative and 4.2 g of 
N-methyl-N-cyclohexyl-3-phenetidine as an alkylaniline derivative, there 
is obtained 4.8 g of a pale brown crystalline substance having a melting 
point of 158.5.degree. to 160.5.degree. C. The compound is identified to 
be the titled compound. 
5. Synthesis of 
3-(4-N-ethyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl 
)-4-azaphthalide 
##STR16## 
Into 60 ml of acetic anhydride, 6 g of 1-ethyl-2-methylindol-3-yl 
3-carboxypyridin-2-yl ketone and 4.5 g of 
N-ethyl-N-cyclohexyl-3-phenetidine are dissolved and brought into reaction 
at 50.degree. to 60.degree. C. for 8 hours. After the reaction mixture is 
cooled to room temperature, it is treated by the same procedure as in 
Synthesis 1 to afford 4.0 g of a colorless crystalline substance having a 
melting point of 140.5.degree. to 144.5.degree. C. The compound is 
identified to be the titled compound. 
6. Synthesis of 
3-(4-N-ethyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl 
)-7-azaphthalide 
##STR17## 
When the procedure of Synthesis 5 is repeated by using 6 g of 
1-ethyl-2-methylindol-3-yl 2-carboxypyridin-3-yl ketone as a 
pyridinecarboxylic acid derivative and 4.5 g of 
N-ethyl-N-cyclohexyl-3-phenetidine as an alkylaniline derivative, there is 
obtained 4.5 g of a colorless crystalline substance having a melting point 
of 143.degree. to 146.degree. C. The compound is identified to be the 
titled compound. 
7. Synthesis of 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-methyl-2-phenylindol-3- 
yl)-7-azaphthalide 
##STR18## 
When the procedure of Synthesis 1 is repeated by using 6 g of 
1-methyl-2-phenylindol-3-yl 2-carboxypyridin-3-yl ketone as a 
pyridinecarboxylic acid derivative and 4 g of 
N-methyl-N-cyclohexyl-3-phenetidine as an alkylaniline derivative, there 
is obtained 6.5 g of colorless crystalline substance having a melting 
point of 177.5.degree. to 179.5.degree. C. The compound is identified to 
be the titled compound. 
As shown in the subsequent table, the present compounds synthesized 
according to the above-mentioned method rapidly form colors of indicated 
hues upon contact with acid clay. 
______________________________________ 
##STR19## 
or 
##STR20## 
R.sub.1 
X R.sub.2 R.sub.3 Hue 
______________________________________ 
H H CH.sub.3 H reddish purple 
CH.sub.3 
H CH.sub.3 CH.sub.3 
blue 
CH.sub.3 
H CH.sub.3 H blue 
CH.sub.3 
H 
##STR21## H blue 
CH.sub.3 
H 
##STR22## CH.sub.3 
blue 
CH.sub.3 
CH.sub.3 CH.sub.3 CH.sub.3 
blue 
CH.sub.3 
OCH.sub.3 
CH.sub.3 C.sub.2 H.sub.5 
bluish purple 
CH.sub.3 
OC.sub.2 H.sub.5 
CH.sub.3 C.sub.2 H.sub.5 
bluish purple 
C.sub.2 H.sub.5 
OC.sub.2 H.sub.5 
CH.sub.3 C.sub.2 H.sub.5 
bluish purple 
CH.sub.3 
OCH.sub.3 
CH.sub.3 CH.sub.3 
bluish purple 
CH.sub.3 
OCH.sub.3 
##STR23## H purple 
CH.sub.3 
OCH.sub.3 
CH.sub.3 H bluish purple 
CH.sub.3 
OCH.sub.3 
CH.sub.3 n-C.sub.8 H.sub.17 
bluish purple 
CH.sub.3 
OCH.sub.3 
CH.sub.3 n-C.sub.6 H.sub.13 
bluish purple 
CH.sub.3 
OCH.sub.3 
##STR24## C.sub.2 H.sub.5 
bluish purple 
CH.sub.3 
OCH.sub.3 
##STR25## CH.sub.3 
bluish purple 
______________________________________ 
EXAMPLES OF COMATIVE TEST 
The present compounds and compounds of prior art were subjected to a 
comparative test with respect to the following characteristics, a through 
c. Specimens used in this comparative test: 
A; Crystal Violet Lactone of the structural formula shown below (known 
compound) 
##STR26## 
B; 
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-7-azaphth 
alide of the structural formula shown below (known compound) 
##STR27## 
C; 
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-methyl-2-phenylindol-3-yl)-7-azapht 
halide of the structural formula shown below (known compound) 
##STR28## 
D; 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-y 
l)-7-azaphthalide of the structural formula shown below (present compound) 
##STR29## 
E; 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-methyl-2-phenylindol-3- 
yl)-7-azaphthalide of the structural formula shown below (present compound) 
##STR30## 
a. Light-resistivity of colored image: 
A 3% KMC-113 (a solvent made by Kureha Kagaku K.K.) solution of each 
specimen was applied to a sheet coated with an acid clay at a rate of 1 
g/m.sup.2. Then the sheet thus prepared was tested for color-forming 
concentration by means of Macbeth Reflection Densitometer using WRATTEN 
filter #25 with the light exposure time varied. 
The results are shown in Table 1 below. 
TABLE 1 
______________________________________ 
Light Exposure Time (hr) 
Specimen 0 1 2 3 
______________________________________ 
A (known compound) 
1.15 0.90 0.73 0.60 
D (present compound) 
1.10 0.90 0.81 0.72 
______________________________________ 
Further, the above procedure was repeated by using a sheet coated with 
phenol formaline resin in place of the acid clay. 
The results are shown in Table 2 below. 
TABLE 2 
______________________________________ 
Light Exposure Time (hr) 
Specimen 0 1 2 3 
______________________________________ 
A (known compound) 
1.02 0.60 0.36 0.30 
D (known compound) 
1.02 0.89 0.79 0.76 
______________________________________ 
It is clear from tables that sheets applied with the present compound 
exhibit less discoloration due to exposure to light than those applied 
with compound of prior art. This fact indicates that pressure- or 
heat-sensitive sheets produced by using the present compounds are 
excellent in color forming property and resistivity to light. 
b. Spontaneous color forming property in dilute aqueous acid solution: 
A 2% toluene solution of each specimen (10 ml) and an aqueous 15% acetic 
acid solution (15 ml) were shaken vigorously for one minute and the 
resultant mixture was left to stand at rest. The colored aqueous solution 
of acetic acid was tested colorimetrically with Shimadzu 
spectrophotometer. 
The results are shown in Table 3 below. 
TABLE 3 
______________________________________ 
Maximum Absorption 
Specimen Wavelength (m.mu.) 
Absorbency 
______________________________________ 
B (known compound) 
581 1.864* 
C (known compound) 
588 0.586 
D (known compound) 
581 0.546 
E (known compound) 
588 0.079 
______________________________________ 
*The colored aqueous solution of acetic acid was diluted 5 times by an 
aqueous 15% acetic acid solution and tested. 
The results indicate that the present compounds have very low degree of 
solubility in dilute acids as compared with compounds of prior art. This 
fact implicates that when an aqueous solution of gelatin is coagulated 
with a dilute acid in the preparation of microcapsules for use in the 
pressure-sensitive copying sheets, the present compound has little 
possibility of coloring the solution. 
c. Spontaneous color forming property exhibited upon application to sheets 
of filter paper: 
A 2% toluene solution of each specimen (25 .mu.l) was dropped onto a filter 
paper (Toyo Filter Paper No.2) followed by air-drying. Then the paper thus 
prepared was tested for color density by means of Macbeth Reflection 
Densitometer using WRATTEN filter #25. 
The results are shown in Table 4 below. 
TABLE 4 
______________________________________ 
Specimen Color Density 
______________________________________ 
B (known compound) 
0.14 
C (known compound) 
0.11 
D (known compound) 
0.10 
E (present compound) 
0.08 
______________________________________ 
It is clear from table that the present compounds are very low in the color 
density exhibited upon application to the sheets of filter paper as 
compared with compounds of prior art. This fact implicates that when the 
compound is finely divided and mixed such as with Bis-Phenol A to prepare 
a coating material for application to heat-sensitive sheets or 
heat-sensitive recording sheets, the heat-sensitive sheets or 
heat-sensitive recording sheets produced by using the present compounds 
experience little coloration of texture and are free from spontaneous 
coloration. 
EXAMPLES OF APPLICATION 
Example 1 
In 100 ml of monoisopropyl biphenyl was dissolved 3 parts of 
3-(4-N-methyl-cyclohexylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3- 
yl)-4-azaphthalide. The resultant solution was emulsified by addition of a 
solution of 20 parts of gum arabic in 160 parts of water. The emulsion was 
stirred with 20 parts of acid-treated gelatin and 160 parts of water added 
thereto, with the resultant mixture adjusted to pH 5 by addition of acetic 
acid. Subsequently, the mixture was subjected to coacervation in the 
presence of 500 parts of added water, with the result that a thick 
gelatin-gum arabic dope deposited in the form of coating film around the 
oil droplets of the color-forming compound dissolved in the solvent. The 
mixture was then adjusted to pH 4.4 and then mixed with 3.8 parts of an 
aqueous 37% formalin solution to solidify the liquid film mentioned above. 
It was then cooled to 10.degree. C., adjusted to pH 9 by addition of an 
aqueous sodium hydroxide solution and left to stand at rest for five to 
six hours so as to enable the capsulation to proceed to perfection. The 
capsulated liquid thus obtained was applied to a sheet and dried. This 
sheet was brought into tight contact with a sheet coated with acid clay as 
an acidic electron-accepting adsorbent. When the paired sheets were 
exposed to the pressure applied by the tip of a ball-point pen or to the 
impact exerted by the types of a typewriter, an image of a bluish purple 
color appeared on the acid clay surface. The colored image showed high 
resistivity to light. 
Example 2 
With 150 parts of an aqueous 10% polyvinyl alcohol solution and 65 parts of 
water, 30 parts of 
3-(4-N-methyl-cyclohexylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-y 
l)-4-azaphthalide was mixed and disintegrated to form "Component A". After 
this disintegration, this azaphthalide was found to have a particle 
diameter of 1 to 3 microns. Similarly, 35 parts of Bis-Phenol A, 150 parts 
of an aqueous 10% polyvinyl alcohol solution and 65 parts of water were 
mixed and disintegrated for one hour, to produce "Component B". After the 
disintegration, Bis-Phenol A was found to have a particle diameter of 1 to 
3 microns. 
Subsequently, 3 parts of Component A and 67 parts of Component B were 
mixed. The resultant mixture was spread on a sheet of paper and dried to 
produce a heat-sensitive recording sheet. The mixture in this case was 
applied at a rate of about 5 g/m.sup.2. When the heat-sensitive recording 
sheet thus obtained was exposed to heat applied by a heat pen, it 
instaneously formed a bluish purple color. The colored image showed high 
resistivity to light.