Electrochromic marking systems

3-(N-R.sup.2 -N-Acylamino)-7-(N-R.sup.3 -N-R.sup.4 -amino)-10-acylphenothiazines and phenoxazines useful as color formers, particularly in electrochromic recording systems, are prepared by the interaction of the corresponding 3-(N-R.sup.2 -amino)-7-(N-R.sup.3 -N-R.sup.4 -amino)phenothiazinium or phenoxazinium halide with a reducing agent to obtain the corresponding leuco compound and subsequently interacting the leuco compound with at least two molecular proportions of an acylating agent.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to novel compounds classified in the field of 
organic chemistry as phenothiazines and phenoxazines, useful as 
color-forming substances, particularly in the art of electrochromic 
recording; to electrochromic recording systems containing said compounds; 
and to processes for preparing said compounds. 
(b) Information Disclosure Statement 
Several classes of organic compounds of widely diverse structural types are 
known to be useful as colorless precursors for electrochromic recording. 
Among the more important classes, there may be named leuco-type dyestuffs 
such as: phthalides, for example, crystal violet lactone, Malachite green 
lactone; fluorans, for example, 3-diethylamino-5,7-dimethylfluoran; and 
indolinobenzospiropyrans, for example, 
1,3,3-trimethyl-6'-chloro-8'-methoxyindolinobenzospiropyrans. Also 
utilized as colorless precursors for electrochromic recording, either 
alone or in admixture with the leuco compounds indicated above, are 
substances known as redox indicators. The redox indicator which becomes 
colored in situ in the electrochromic recording process also is generally 
a leuco compound. Among the types of compounds which are applicable as 
redox indicators are phenothiazines, for example, leuco methylene blue and 
benzoyl leuco methylene blue. Other specific indicators are Leucoethyl 
Nile Blue, Leucomethyl Capyrl Blue and Leucosafranine T. Typical of the 
many such electrochromic recording systems taught in the prior art are 
those described in U.S. Pat. Nos. 3,726,769, 3,871,972, 3,864,684, 
4,017,366, 4,133,933, and Reissue Patent Re. 29,427 which issued Apr. 10, 
1973, Mar. 18, 1975, Feb. 4, 1975, Apr. 12, 1977, Jan. 9, 1979, and Oct. 
4, 1977, respectively. The methods for electrochromic recording taught in 
the prior art have many variations. Basically, a sheet of paper is coated 
or treated on one or both sides with a coating formulation containing at 
least one colorless color-forming (leuco) compound. Electrical current is 
then selectively applied to the coated side of the paper by some means, 
for example, a stylus or a printing head to which an electrical potential 
can be applied. The application of the current causes an electrochromic 
reaction involving the leuco compound to produce a visible image 
corresponding to the design traced by the stylus or that of the printing 
head. 
The following items to date appear to constitute the most relevant prior 
art with regard to the instant invention. 
U.S. Pat. No. 2,909.520, issued Oct. 20, 1959, discloses compounds having 
the formula 
##STR1## 
in which R is a phenyl or naphthyl moiety substituted with one or more of 
the following moieties: alkyl, alkoxy, halo, nitro, haloalkyl, 
alkoxycabonyl, phenyl, and phenylalkoxy. These compounds are disclosed as 
being useful as blue color formers in carbonless carbon papers, i.e., 
carbonless duplicating systems. 
Mariga and Oda in Kogyo Kagaku Zasshi 67 (7), 1050-4 (1964) (C.A. 62 2852b) 
describe the preparation and properties of acylated methylene blue having 
the structural formula 
##STR2## 
in which R represents an alkyl or a substituted phenyl moiety. The 
compounds are disclosed as being useful in pressure-sensitive carbonless 
duplicating systems. 
U.S. Pat. No. 4,309,255, issued Jan. 5, 1982, discloses and claims a 
phenothiazine having the structural formula 
##STR3## 
which is disclosed as being useful as a blue color former in 
electrochromic recording paper. 
Smets and Simionescu in Makromolecular Chemistry 1977 178(9), 2719-23 (C.A. 
87 186052t) disclose as a monomer for a colored polymer 
N-acryloyl-N,N',N'-trimethylthionine having the formula 
##STR4## 
Japanese Patent Publication No. 80,040,798, published Mar. 22, 1980, 
discloses thionines having the structural formula 
##STR5## 
in which R.sub.1 and R.sub.2 represent hydrogen or methyl; R and X 
represent halogen; Z represents (CH.sub.2).sub.3 to 12; n represents zero 
or one; m represents one or two; and m+n equals two. The compounds are 
disclosed as being monomers for reaction with polyethyleneimine to obtain 
a green-blue solid which is swellable by water and N,N-dimethylformamide. 
SUMMARY OF THE INVENTION 
In its composition of matter aspect, the invention relates to certain 
3-(N-R.sup.2 -N-acylamino)-7-(N-R.sup.3 -N-R.sup.4 
-amino)-10-acyl-phenothiazines and phenoxazines useful as colorless 
precursors in electrochromic recording systems. 
The present invention provides in its article of manufacture aspect, a 
substrate for use in electrochromic recording systems comprising a support 
sheet containing as a color-forming substance 3-(N-R.sup.2 
-N-acylamino)-7-(N-R.sup.3 -N-R.sup.4 -amino)-10-acyl-phenothiazines and 
phenoxazines. 
In its process aspect, the invention relates to a process for producing 
3-(N-R.sup.2 -N-acylamino)-7-(N-R.sup.3 -N-R.sup.4 
-amino)-10-acyl-phenothiazines and phenoxazines which comprises 
interacting the corresponding 3-(N-R.sup.2 -amino)-7-(N-R.sup.3 -N-R.sup.4 
-amino)phenothiazinium or phenoxazinium halide with a reducing agent to 
obtain the corresponding leuco compound and subsequently interacting the 
leuco compound with at least two molecular proportions of an acylating 
agent. 
DETAILED DESCRIPTION INCLUSIVE OF THE PREFERRED EMBODIMENTS 
More specifically, this invention in its composition of matter aspect 
resides in the novel compounds having the structural formula 
##STR6## 
wherein R and R.sup.5 independently represent non-tertiary C.sub.1 to 
C.sub.4 alkyl, non-tertiary C.sub.1 to C.sub.4 alkoxy, halogen or nitro; 
R.sup.1 represents hydrogen, non-tertiary C.sub.1 to C.sub.12 alkyl, 
C.sub.4 to C.sub.8 cycloalkyl, non-tertiary C.sub.1 to C.sub.12 alkyl 
substituted by halogen, non-tertiary C.sub.1 to C.sub.4 alkoxy or 
non-tertiary C.sub.1 to C.sub.4 alkoxycarbonyl, phenyl, phenyl substituted 
by one to three of non-tertiary C.sub.1 to C.sub.4 alkyl, non-tertiary 
C.sub.1 to C.sub.4 alkoxy, nitro, halo, phenyl, cyano or trihalomethyl; 
R.sup.2 represents hydrogen, non-tertiary C.sub.1 to C.sub.4 alkyl, 
phenyl, phenyl substituted by one or two of halo, nitro, non-tertiary 
C.sub.1 to C.sub.4 alkyl or non-tertiary C.sub.1 to C.sub.4 alkoxy, benzyl 
or benzyl substituted in the benzene ring by one or two of halo, nitro, 
non-tertiary C.sub.1 to C.sub.4 alkyl or non-tertiary C.sub.1 to C.sub.4 
alkoxy; R.sup.3 and R.sup.4 represent hydrogen, non-tertiary C.sub.1 to 
C.sub.4 alkyl, phenyl, phenyl substituted by one or two of halo, nitro, 
non-tertiary C.sub.1 to C.sub.4 alkyl or non-tertiary C.sub.1 to C.sub.4 
alkoxy, benzyl or benzyl substituted in the benzene ring by one or two of 
halo, nitro, non-tertiary C.sub.1 to C.sub.4 alkyl or non-tertiary 
C.sub.1 to C.sub.4 alkoxy; and X represents S or O. 
Particular embodiments within the ambit of the composition of matter aspect 
are the novel 1/2-R-3-[N(R.sup.1 -CO)-N-R.sup.2 -amino]-7-(N-R.sup.3 
-N-R.sup.4 -amino)-8/9-R.sup.5 -10-(R.sup.1 -CO)-phenothiazines of Formula 
I wherein X is S having the formula 
##STR7## 
in which R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 have the same 
respective meanings given in Formula I. 
Other particular embodiments with the ambit of the composition of matter 
aspect are the novel 1/2-R-3-[N-(R.sup.1 -CO)-N-R.sup.2 
-amino]-7-(N-R.sup.3 -N-R.sup.4 -amino)-8/9-R.sup.5 -10-(R.sup.1 
-CO)-phenoxazines of Formula I wherein X is O having the structural 
formula 
##STR8## 
in which R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 have the same 
respective meanings given in Formula I. 
In its process aspect, the invention sought to be patented resides in the 
process for preparing a compound according to Formula I having the 
structural formula 
##STR9## 
which comprises in the first step interacting a compound having the 
structural formula 
##STR10## 
with a reducing agent to obtain the corresponding leuco compound having 
the structural formula 
##STR11## 
and in a second step, interacting the leuco compound with at least two 
molecular proportions of an acylating agent having the structural formula 
EQU R.sup.1 --CO--Z Formula VI 
in which Z represents halo or R.sup.1 COO and R, R.sup.1, R.sup.2, R.sup.3, 
R.sup.4 and R.sup.5 have the same respective meanings given in Formula I. 
In its article of manufacture aspect, the invention sought to be patented 
resides in a substrate for use in electrochromic recording comprising a 
support sheet containing as a color-forming substance a phenothiazine or 
phenoxazine having the structure of Formula I. 
A particular embodiment within the ambit of the article of manufacture 
aspect in the substrate for use in electrochromic recording comprising a 
support sheet containing as a color-forming substance a 
1/2-R-3-[N-(R.sup.1 -CO)-N-R.sup.2 -amino]-7-(N-R.sup.3 -N-R.sup.4 
-amino)-8/9-R.sup.5 -10-(R.sup.1 -CO)-phenothiazine of Formula II wherein 
R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 have the same respective 
meanings given in Formula II. 
In a second particular embodiment within the ambit of its article of 
manufacture aspect is the substrate for use in electrochromic recording 
comprising a support sheet containing as a color-forming substance a 
1/2-R-3-[N-(R.sup.1 -CO)-N-R.sup.2 -amino]-7-(N-R.sup.3 -N-R.sup.4 
-amino)-8/9-R.sup.5 -10-(R.sup.1 -CO)-phenoxazine of Formula III wherein 
R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 have the same respective 
meanings given in Formula III. 
As used herein the terms "non-tertiary C.sub.1 to C.sub.4 alkyl" and 
"non-tertiary C.sub.1 to C.sub.12 alkyl" denote saturated monovalent 
straight or branched aliphatic hydrocarbon radicals including methyl, 
ethyl, propyl, isopropyl, butyl, isobutyl, amyl, 1-methylbutyl, 
3-methylbutyl, hexyl, isohexyl, heptyl, isoheptyl, octyl, isooctyl, 
2-ethylhexyl, nonyl, 3-ethylheptyl, n-decyl, n-undecyl, n-dodecyl and the 
like. 
The term "non-tertiary C.sub.1 to C.sub.4 alkoxy" includes saturated 
acyclic, straight or branched-chain groups such as methoxy, ethoxy, 
propoxy, isopropoxy, butoxy, sec-butoxy and isobutoxy. 
As used herein the terms "halo" and "halogen" include chloro, fluoro, bromo 
and iodo. Chloro is the preferred halo substituent because of the 
relatively low cost and ease of preparation of the required 
chloro-substituted intermediates and because the other halogens offer no 
particular advantages over chloro. However, the other above-named halo 
substituents are also satisfactory. 
As used herein the term "C.sub.4 to C.sub.8 cycloalkyl" denotes saturated 
monovalent cyclic aliphatic hydrocarbon radicals including cyclobutyl, 
cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and the like. 
The phenothiazinium and phenoxazinium dyes which are used as intermediates 
or starting materials for the compounds of Formula I are generally known 
dyestuffs readily prepared by procedures well known in the dyestuff art. 
Four references to the preparation of the phenothiazine and phenoxazine 
dyestuffs are: (a) Journal of the Society of Dyers and Colourists 4, 39 
(1888); (b) Liebig's Annalen der Chemie 251, 1 (1889); (c) Chemische 
Berichte 25, 3128 (1892); (d) FIAT Final Report No. 1313 and PB Report 
85172, Vol. II, p. 372. 
The acylating agents of Formula VI may be either aliphatic acid anhydrides 
(Z=R.sup.1 COO) or acid halides (Z=halo, preferably chloro), both of which 
constitute well known classes of compounds many of which are commercially 
available or are readily obtained by conventional synthesis well known in 
the art. The following list exemplifies aliphatic acid anhydrides and acid 
halides useful in carrying out the processes of this invention. Acetic 
anhydride, chloroacetic anhydride, dichloroacetic anhydride, 
trifluoroacetic anhydride, propionic anhydride, butyric anhydride, 
isobutyric anhydride, valeric anhydride, hexanoic anhydride, hepanoic 
anhydride, acetyl bromide, acetyl chloride, acetyl fluoride, bromoacetyl 
bromide, bromoacetyl chloride, chloroacetyl chloride, methoxyacetyl 
chloride, propionyl chloride, 2-bromopropionyl chloride, 3-bromopropionyl 
chloride, 2-chloropropionyl chloride, 3-chloropropionyl chloride, butyryl 
chloride, 4-chlorobutyryl chloride, 2-ethylbutyryl chloride, isobutyryl 
chloride, valeryl chloride, 5-chlorovaleryl chloride, isovaleryl chloride, 
4-methylvaleryl chloride, hexanoyl chloride, 6-bromohexanoyl chloride, 
heptanoyl chloride, octanoyl chloride, nonanoyl chloride, decanoyl 
chloride, 10-undecanoyl chloride, palmitoyl chloride, myristoyl chloride, 
lauroyl chloride, cyclopropyl carboxylic acid chloride, cyclobutane 
carboxylic acid chloride, cyclohexyl carboxylic acid chloride, m-anisoyl 
chloride, p-anisoyl chloride, benzoyl bromide, benzoyl chloride, benzoyl 
fluoride, 4-biphenylcarbonyl chloride, 2-bromobenzoyl chloride, 
4-bromobenzoyl chloride, 4-butoxybenzoyl chloride, 4-butylbenzoyl 
chloride, 2-chlorobenzoyl chloride, 3-chlorobenzoyl chloride, 
4-chlorobenzoyl chloride, 4-cyanobenzoyl chloride, 2,4-dichlorobenzoyl 
chloride, 2,6-dichlorobenzoyl chloride, 3,4-dichlorobenzoyl chloride, 
3,5-dimethoxybenzoyl chloride, 3,4-dimethoxybenzoyl chloride, 
3,5-dinitrobenzoyl chloride, 2-fluorobenzoyl chloride, 3-fluorobenzoyl 
chloride, 4-fluorobenzoyl chloride, 3-nitrobenzoyl chloride, 
4-nitrobenzoyl chloride, 2-methoxybenzoyl chloride, 3-methylbenzoyl 
chloride, 4-methylbenzoyl chloride, 2-iodobenzyl chloride, 4-iodobenzoyl 
chloride and 4-trifluoromethylbenzoyl chloride. 
The compounds of Formula I hereinabove are essentially colorless in the 
depicted form. When contacted with an electric current from an applied 
voltage stylus of the type ordinarily employed in electrochromic recording 
systems, the compounds of Formula I develop green, green-black, black and 
blue-black-colored images. These developed images are very insensitive to 
light, that is, once the color is developed, it remains unchanged when 
subjected to light exposure. The developed images also possess excellent 
xerographic reproducibility. 
The compounds of this invention may be incorporated in any of the 
commercially-accepted systems known in the electrochromic recording art. 
Typical techniques for the application of the color formers to paper are 
well known and are described in numerous patents, for example, U.S. Pat. 
Nos. Re. 29,427; 3,726,769; 3,864,684; 3,871,972; 3,951,757; 4,017,366; 
and 4,133,933. The usual paper coatings consist of the color-forming 
component, an organic metal salt, a binder and some type of conductor, 
either an inorganic salt or a conductive polymer. This mixture is milled 
together optionally in the presence of a non-ionic surface active agent 
until the desired particle size is obtained and then the mixture is coated 
on paper and dried. Optionally, the color-forming substance can be milled 
in the presence of a binder and the remaining components milled also in 
the presence of a binder and the two mixtures combined together prior to 
coating on paper. Normally the surface of the coated paper is wet with a 
conductive solution containing an inorganic alkaline metal or alkaline 
earth metal salt, for example, potassium chloride, calcium chloride, 
sodium chloride, sodium bromide, potassium bromide, potassium nitrate or 
sodium sulfate immediately prior to the printing with the applied voltage 
stylus. For a quick qualitative test, it has been determined that the 
color-forming component can be dissolved in a suitable volatile organic 
solvent, coated on paper and the coated paper dried to obtain a paper 
sheet coated with the color-forming component. This coated sheet can then 
be wet with a conductive salt solution and an image traced with an applied 
voltage stylus to develop the colored image. 
The compounds of Formula I can be used alone as color-forming components in 
electrochromic recording paper or can be used in admixture with one or 
more other color-forming compounds from the classes consisting of 
phthalides, for example, Crystal Violet Lactone; fluorans, for example, 
3-diethylamino-5,7-dimethylfluoran; redox indicators, for example, 
phenothiazines such as benzoyl leuco methylene blue and various other 
types of color-forming components currently employed in 
commercially-accepted electrochromic recording systems. 
The best mode contemplated by the inventors of carrying out this invention 
will now be described so as to enable any person skilled in the art to 
which it pertains to make and use the same. 
In accordance with the aforementioned process aspects of this invention, 
the compounds of Formula I are obtained by reacting one molecular 
proportion of a leuco compound of Formula V with at least two molecular 
proportions of an acylating agent of Formula VI. When using an anhydride 
as the acylating agent, the reaction is conveniently carried out in an 
excess of the acylating agent which is utilized as both the reaction 
medium and as the reactant. Optionally a small amount of an organic base, 
for example, pyridine may be used as a catalyst. The reaction is 
conveniently carried out at a temperature in the range of 90.degree. C. to 
reflux of the mixture for periods of approximately thirty minutes to 
approximately four hours. The compounds of Formula I thus obtained are 
isolated by pouring the reaction mixture into ice water and extracting the 
desired products into a suitable water immiscible organic liquid, for 
example, toluene. The organic liquid layer containing the product is 
subsequently washed with water to remove inorganic salts and water-soluble 
organics and then treated with decolorizing charcoal, if desired. The 
resulting organic liquid solution of the product is then concentrated by 
conventional means such as evaporation or distillation. 
Alternatively, the compounds of Formula I can be obtained also by reacting 
approximately one molecular proportion of a leuco compound of Formula V 
with about two molecular proportions of an acyl halide of Formula VI 
(Z=halo). A solution of the leuco compound dissolved in an organic liquid 
is cooled to a temperature in the range of 60.degree. to 80.degree. C. and 
disodium phosphate and acyl halide, dissolved in the same organic liquid, 
is added. The reaction is conveniently carried out at the reflux 
temperature of the mixture for periods of approximately fifteen minutes to 
approximately nineteen hours. Water and additional disodium phosphate are 
added to the reaction mixture and the resulting mixture is heated at 
reflux temperature for a period of approximately thirty minutes to 
approximately one hour. The organic liquid solution containing the desired 
product is separated from the water layer, washed with water and 
concentrated by conventional means such as evaporation or distillation. 
The isolated product can be purified by conventional means such as 
recrystallization or reslurrying with a suitable organic liquid and then 
collected by filtration. Purification can also be effected by column 
chromatography. The material to be purified is dissolved in a suitable 
organic liquid and the solution is passed through a chromatography column 
which has been packed with a suitable substrate, for example, silica gel, 
cellulose, alumina and the like. Numerous fractions are collected and 
analyzed to determine fraction(s) containing the desired product. The 
fraction(s) which contain the desired product are then combined (if more 
than one) and concentrated to obtain the product. The leuco compound of 
Formula V is conveniently prepared by reducing the corresponding 
phenothiazinium or phenoxazinium halide dyestuff of Formula IV with a 
reducing agent, for example, zinc dust. This reaction is conveniently 
carried out in an excess of the alkanoic anhydride acylating agent thus 
resulting in no need for an inert organic liquid reaction medium. 
Alternatively, the leuco compound of Formula V is conveniently prepared by 
reducing the corresponding phenolthiazinium halide or phenoxazinium halide 
of Formula IV with a reducing agent, for example, an alkaline 
hydrosulfite. The reaction in which the leuco compound is prepared is 
conveniently carried out in a mixture of water and a suitable water 
immiscible organic liquid, for example, toluene or xylene in an inert 
atmosphere, for example, nitrogen. The reaction is carried out in the 
presence of an alkaline substance, for example, sodium carbonate or 
disodium phosphate using, as the reducing agent, an alkali hydrosulfite, 
for example, sodium hydrosulfite. The reaction is conveniently carried out 
at ambient temperature for a period of approximately fifteen minutes to 
approximately two hours. The organic liquid solution which contains the 
leuco compound is separated from the water layer. Additional alkali 
hydrosulfite is added to the organic liquid solution and the resulting 
mixture is azeotroped to remove the remaining trace of water. The 
resulting solution can be used directly in the acylating step of the 
process. 
The molecular structures of the compounds were assigned on the basis of the 
modes of synthesis and a study of their infrared, nuclear magnetic 
resonance and mass spectra.