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Description  |
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FIELD OF THE INVENTION
The present invention relates to a silver halide photographic
light-sensitive material and, particularly, pertains to a silver halide
photographic light-sensitive material with which highly preservable
picture images are formed, which permits rapid processing and, further,
which is excellent in the processing stability.
BACKGROUND OF THE INVENTION
Of late, in this art, it is desired to provide a silver halide photographic
material which permits rapid processing, and produces highly preservable
picture images and shows high processing stability and is available at low
cost, and, particularly, permits rapid processing.
Thus subjecting a silver halide photographic material to running treatment
with an automatic developing machine installed at each developing shop is
practiced, but as one means of improvement in service to users, there has
been a call for making development and returning the material to the user
within the very day on which the request for development is received and,
further, even returning the developed material in several hours after the
request has been made is desired; as a consequence, need for rapid
processing has been all the more enhanced. Further, reduction in the
treatment time will lead to improvement in productivity efficiency, thus
enabling cost reduction, and to attain this, alacrity in developing rapid
processing is urgent.
For attainment of rapid processing, approaches from two phases of photo
graphic materials and processing solutions have been taken. With regard to
color developing, use of a higher temperature, higher pH, higher
concentration of color developing agent, etc., have been tried and,
further, use of such additives as development accelerators are known.
Mentioned as the aforementioned development accelerators,
1-phenyl-3-pyrazolidone disclosed in British patent No. 811,185,
N-methyl-p-aminophenol disclosed in U.S. Pat. No. 2,417,514 and
N,N,N',N'-tetramethyl-p-phenylene diamine disclosed in Japanese patent OPI
publication No. 15554/1975, etc. may be cited.
However, these methods can not achieve adequate rapidity and their effect
is often accompanied by performance degradation such as greater fogging.
On the other hand, it is known that the configuration, size and composition
of the silver halide grains of the silver halide emulsion used in
photographic materials have a large bearing on the speed of development,
etc.; particularly, the effect of halogen composition is large; especially
notably high rate of development is known to be achieved by use of high
chlorine content silver halide.
On the other hand, the formation of dye image using silver halide color
photographic material is made usually by oxidation of aromatic primary
amine color developing agent itself, as it reduces the silver halide
grains in the exposed silver halide photographic material, and subsequent
formation of dye by reaction of this oxidized product with the couplers
contained beforehand in the silver halide color photographic material. And
for the couplers, usually, a three layer couplers which form three dyes of
yellow, magenta and cyan for making reproduction by way of subtractive
color process.
The dye image obtained with silver halide color photographic material is
sometimes preserved for a long period under exposure to light or long kept
in a dark place under short exposure to light and it is known that a
discoloring or fading of the dye image notably, depends on the states of
its preservation. Generally, the discoloring or fading of the former is
called light discoloring of fading or light fading and discoloring or
fading of the latter is called dark discoloring or fading or dark fading.
When the color photographic material is kept semipermanently on record,
the degree of such light fading or dark fading has to be suppressed to be
as small as possible.
Mentioned as basic properties required of couplers are that first, their
solubility in high boiling organic solvents, etc., shall be large, that
they shall not readily crystalize in silver halide emulsion, their
dispersibility and dispersion stability in silver halide emulsions being
high, that they shall enable achieving excellent photographic
characteristics and that the dye picture images obtained with them shall
be fast to light, heat, moisture, etc. Especially, with regard to cyan
couplers, attainment of improvement in resistance to heat and moisture,
dark fading property, has recently been taken up as an important theme.
Hereto generally used cyan couplers, for example, those disclosed in
Japanese patent publication open to public inspection (hereinafter
referred to as Japanese patent O.P.I. publication) Nos. 37425/1972, 10135,
25228, 112038, 117422 and 130441/1975 and U.S. Pat. Nos. 2369929, 2423730,
2434272, 2474293 and 2698794 are unsatisfactory, being poor either in
light or dark fading, particularly, in the latter.
For this reason, various cyan couplers have been examined in an effort to
achieve improvement in the dark fading. As a result, for example,
2,5-diacyl amino type cyan couplers which are disclosed in U.S. Pat. No.
2895826 and Japanese patent O.P.I. publication Nos. 112038/1975,
109630/1978 and 163537/1980 and phenol type cyan couplers having an alkyl
group with 2 or more carbon atoms at the fifth position which are
disclosed in U.S. Pat. Nos. 3772002 and 4443536 have been found out to be
cyan couplers excellent in the dark fading.
Generally, processing of silver halide photographic high-sensitive material
is continuously run, while replenishing the processing solutions at
various developing shops such as photographic laboratories, etc. In this
situation, it is impossible to maintain the compositions of the processing
solutions constant between the initial period and the latter half period
of running and change in the compositions of the processing solutions
brings about fluctuations in the photographic characteristics,
particularly, graduation variation. This problem is growing more serious
with diminishing replenishment of processing solutions in recent years.
It has become clear that when a cyan coupler represented by the general
formula [I] is used in a high chloride content silver halide layer, the
photographic characteristics are greatly altered by change in the
compositions of the processing solutions and variation of conditions,
resulting in failure to obtain stable photographic performance, and thus
the problem of low processing stability.
What is called processing stability means the degree of fluctuation in
sensitometic characteristics of the photographic material relative to
fluctuations in the compositions of the treating solutions, pH and
temperature and the amounts of compounds other than the components of the
processing solutions mixed into it.
Complete prevention of mixing of bleach fixer into developer, of all these
events, is nearly impossible, even when the setting of strict replenishing
rate, prevention of evaporation and elimination of eluate from the
photographic material are implemented; particularly, in roller conveyor or
automatic developing machine, the amount of bleaching-fixer mixed into the
developer will notably vary with varying amounts treated and depending on
the squeezing method and in actual practice, if the replenishing rate of
the treating solution has dropped, its replenishment cycle rate will
lower, resulting in further difference in the mixing-in rate.
Further, the color developer is held at a high pH, but under the influence
of the amount of the solution replenished, oxidation by air, etc., during
the continuous operation, fluctuation in pH of color developer is
unavoidable.
Variations in photographic performances, in many cases, increase of fogging
and graduation change, due to such mixing of bleach-fixer into color
developer or fluctuation in pH pose large obstacles to attainment of
stable and proper color and gradation reproduction.
Because of the extreme difficulty in preventing the mixing-in of
bleach-fixer and the pH fluctuation themselves for reasons
above-described, there is a call for development of silver halide
photographic materials which give only small changes in photographic
properties, even when the mixing-in of bleach-fixer or pH fluctuation
occurs, that is, those excellent in the so-called BF (bleach-fixer)
mixing-in resistance and pH fluctuation resistance.
With the silver halide color photosensitive materials, dye image is formed
by subjecting them to the color developing-etc. after exposure, but with
silver halide color photographic materials using high chloride content
silver halide emulsion containing coupler which is suitable for rapid
processing, the rate of formation of the oxidized product of the color
developing agent is often rapider than the reaction of forming dye through
the coupling reaction between the aforementioned oxidized product and the
coupler. For this reason, the oxidized product of the developing agent
exists in large amount; this causes oxidation of the latent image uncleus
formed by exposure, thereby inducing bleaching of the latent image; the
larger degree of this latent image bleaching seems to be cause for
increasing processing fluctuation of the high silver chloride content
photosensitive materials.
Particularly, the high chloride content silver halide provides high speed
development, but is known to generally have low resistance to the latent
image bleaching by the oxidized product of the developing agent which is
formed in excess.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide a silver halide color
photosensitive material which enables rapid processing and which further
excels in image preservability, and it is a second object to provide a
silver halide photosensitive material which enables rapid treatment and
which further excels in the BF mixing-in and pH-fluctuation resistance.
The above-described objects of this invention have been achieved by a
silver halide photographic light-sensitive material comprising a support
having thereon photographic component layers comprising a blue-sensitive
silver halide emulsion layer, a green-sensitive silver halide emulsion
layer and a red-sensitive silver halide emulsion layer, wherein said
red-sensitive silver halide emulsion layer contains silver halide grains
comprising not less than 90 mol % of silver chloride, a compound
represented by the following formula [S] and a cyan coupler represented by
the following formula [I]:
##STR2##
wherein Ar is an arylene group or a cycloalkylene group; R.sub.A is an
alkyl group, an alkoxy group, a carboxyl group or its salt, a sulfo group
or its salt, a hydroxyl group, an amino group, an acylamino group, a
##STR3##
group, an --NHSO.sub.2 R' group or an group, R' and R" being a hydrogen
atom an alkyl group or an aryl group, respectively, and M is a hydrogen
atom, an alkali metal atom or an ammonium group; wherein R.sup.1 is an
alkyl group or an aryl group; R.sup.2 is an alkyl group, a cycloalkyl
group, an aryl group or a heterocyclic group; R.sup.3 is a hydrogen atom,
a halogen atom, an alkyl group or a alkoxy group, R.sup.3 and R.sup.1
being allowed to form a ring by coupling with R.sup.1 ; Z represent a
hydrogen atom or a group capable of being splitted off upon reaction with
the oxidized product of an aromatic primary amine color developing agent.
DETAILED DESCRIPTION OF THE INVENTION
In the silver halide photographic material of the invention, a compound
represented by the general formula [S] is contained in a red sensitive
silver halide layer.
In the general formula [S] mentioned as an arylene group denoted by Ar is,
e.g., phenylene, naphthylene group, etc.; or as a cycloalkylene group,
e.g., cyclohexylene group, etc.
Mentioned as an alkyl groups given by R.sub.A is, e.g., methyl, ethyl
groups, etc.; as alkoxy groups, e.g., methoxy, propoxy groups, etc.; as
acyl amino groups, e.g., acetyl amino, hexanoyl amino, benzoyl amino
groups, etc.; as
##STR4##
e.g., N-methyl carbamoyl, and N-phenyl carbamoyl groups, etc.; as
--NHSO.sub.2 R', e.g., methyl sulfonyl amino and benzene sulfonamide
groups, etc., or as
##STR5##
e.g., ureido, N-methyl rueido, N-ethyl rueido, N,N-dimethyl rueido,
N,N-diethyl rueido, N-phenyl rueido, etc. Groups represented by R.sub.A
further include those having substituents. Mentioned as an alkali metal
atom represented by M is, e.g., a sodium atom or potassium atom, etc.
In the following, typical examples of compounds represented by the general
formula [S] are given, but this invention is not restricted thereto:
______________________________________
General formula
##STR6##
Example
No. ArR.sub.A M
______________________________________
S-1
##STR7## H
S-2
##STR8## H
S-3
##STR9## H
S-4
##STR10## H
S-5
##STR11## H
S-6
##STR12## H
S-7
##STR13## Na
S-8
##STR14## K
S-9
##STR15## H
S-10
##STR16## Na
S-11
##STR17## K
S-12
##STR18## H
S-13
##STR19## H
S-14
##STR20## H
S-15
##STR21## H
S-16
##STR22## H
S-17
##STR23## H
S-18
##STR24## H
S-19
##STR25## H
S-20
##STR26## H
S-21
##STR27## H
S-22
##STR28## H
S-23
##STR29## H
S-24
##STR30## H
S-25
##STR31## H
S-26
##STR32## H
S-27
##STR33## H
S-28
##STR34## H
______________________________________
Compounds represented by the aforementioned formula [S] may be synthesized
in accordance with the methods which appear in, e.g., U.S. Pat. No.
3259976 and Japanese patent O.P.I. publication Nos. 14836 and 167023/1982,
95728/1983 and 68732/1984, etc.
For having the compound represented by the general formula [S], hereinafter
called compound [S], contained in the silver halide emulsion layers of
this invention, it should be added after dissolving it in water or some
organic solvent (e.g., methanol, ethanol, etc.) which is arbitrarily mixed
with water. The compound [S] may be used single or in combination with
other compounds represented by the general formula [S] or any of
stabilizers or fogging restrainers other than those represented by the
general formula [S].
Suitable time for adding the compound [S] may be any arbitrary time before
forming the silver halide grains, while forming the silver halide grains,
after completion of the silver halide grain forming but before starting
chemical ripening, during the chemical ripening, at the time when the
chemical ripening has completed or after accomplishing the chemical
ripening but before coating. Preferably, it should be added during
chemical ripening, at the time when the chemical ripening has completed or
after accomplishing the chemical ripening but before coating. The adding
of all amount may be done at a time or at several steps.
With regard to where it is to be added, it may be directly added to silver
halide emulsion or to the coating solution of silver halide emulsion or it
may be added to the coating solution for non-light-sensitive hydrophilic
colloidal layers located adjacent thereto so that it is to be contained in
the silver halide emulsion layers of this invention by its diffusion
thereinto at the time of coating multilayers.
Its amount added is not particularly limited, but normally, it is from
1.times.10.sup.-6 mol to 1.times.10.sup.-1 mol, or preferably, from
1.times.10.sup.-5 mol to 1.times.10.sup.-2 mol per mol of silver halide.
Some of the compounds [S] of the invention are compounds known in this as
stabilizers or fog inhibitors. For example, they are disclosed in British
patent No. 1273030, Japanese patent publication Nos. 9936/1983, 27010/1985
and Japanese patent O.P.I. publication Nos. 102639/1976, 22416/1978, 59463
and 79436/1980, and 232342/1984, etc. In the aforementioned well-known
literatures, descriptions on fogging inhibition and stabilization of
emulsion appear, but the effect of the invention or the fact that it is
effective against processing fluctuation which occurs when subjecting to a
color development the silver halide color photographic material containing
high silver chloride content silver halide grains and a specified cyan
coupler has heretofore been quite unknown.
And the compounds (S) are generally known as compounds which show such
actions as fogging restriction, etc., while accompanying desensitization
and inhibited development, descriptions appear in "Fundamentals of
Photographic Engineering, Silver Salt Photography", compiled by
Photographic Society of Japan Corona Company, 1979, p.195, etc., but the
fact that the treatment stability is improved by making use of these
compounds in the system of this invention was a quite unexpected effect.
The reasons why this effect which seems singular does arise have yet to be
elucidated, but a discussion on its mechanism may be dared as follows:
The color developing, as hereabove-described, consists of the so-called
"silver development" process in which the exposed silver halide is reduced
to silver by the color developing agent and the so-called "color forming"
process in which the oxidized product of the color developing agent formed
by the aforementioned reaction and a dye forming coupler make a coupling
reaction, yielding a dye. The system of this invention having combined the
high silver chloride content silver halide emulsion and the dye forming
coupler is a system in which the "silver development" process is very
rapid, but the "color forming" process is slow. Accordingly, on the
perimeter of the silver halide grains, there exists a high concentration
of the oxidized product of the color developing agent which is formed by
the "silver development". In this state, a phenomenon of the so-called
"latent image bleaching" may take place in which the oxidized product of
the color developing agent which exists in a large amount conversely
bleaches the "latent image" produced by exposure on the silver halide
grains, thereby turning it into an undeveloped state, resulting in reduced
color density. By this reasoning, the fact that the improvement in color
formation can not be achieved as expected mereby by using the high silver
chloride content emulsion may be interpreted and the effect of this
invention will be understood by assuming that the "latent image" is
strengthened against bleaching by the use of the compound [S].
The silver halide grains, according to this invention, desirably contain
0.5 to 5 mol % of silver bromide, rather than pure silver chloride, and
this very small amount of silver bromide may have some part in the "latent
image reinforcement".
The aforementioned discussion is in anyway a supposition; the real facts
are still indistinct.
In the red-sensitive silver halide emulsion layer of the silver halide
photographic material of this invention, silver halide grains with silver
chloride content not less than 90 mol % are contained.
The silver halide grains of this invention have a silver chloride content
not less than 90 mol %, and preferably have a silver bromide content not
more than 10 mol % and silver iodide content not more than 0.5 mol %. More
preferably, they are silver chlorobromide having silver bromide content
0.1 1 mol %.
The silver halide grains of this invention may be used singly or in
combination with other silver halide grains different in composition
therefrom. Or they may be used in mixture with silver halide grains having
silver chloride contents more than 10 mol %.
In the silver halide emulsion layer containing silver halide grains having
silver chloride content not less than 90 mol % of this invention, the
proportion of the silver halide grains with silver chloride content not
less than 90 mol % in proportion to the total silver halide grains
contained in the aforementioned emulsion layer is not less than 60% by
weight, preferably, not less than 80% by weight.
The composition of the silver halide grains of this invention may be
uniform from the interior to the exterior of the grain or its composition
may be different between its interior and exterior. And when the
composition of a grain is different between its interior and exterior, the
composition may be continuously altered or may be discrete.
The grain size or diameter of the silver halide grains of this invention,
which is not particularly limited, is preferably from 0.2 to 1.6 .mu.m, or
more preferably, in the range of from 0.25 to 1.2 .mu.m, taking account of
other photographic performances, etc., such as rapid treatability,
sensitivity, etc. The aforementioned grain size may be measured by various
methods which are generally utilized in the pertinent technical field.
Representative methods appear in Lapland's "Grain Size Analyzing Method"
(A.S.T.M. Symposium on Light Microscopy, 1955, pp. 94-122) or "Theory of
Photographic Process" (Chapter 2, coauthered by Meese and James, 3-rd
Edition, issued by MacMillan Company (1966)).
The grain size may be measured from the projected area of grain or
approximate value of its size. If the grains have substantially uniform
shape, the grain size distribution may be appreciably correctly given by
their sizes or projected areas.
The distribution of the sizes of the silver halide grains may be
polydispersive or monodispersive. Preferably, they are monodispersed
silver halide grains with variation coefficient 0.22 or lower, more
preferably, 0.15 or less in the grain diameter distribution of silver
halide grains. Here, the variation coefficient is a coefficient for giving
the spread of the grain size distribution, which is defined by the
undermentioned formula:
##EQU1##
Where ri designates grain size of individual grains, and ni their number.
The grain diameter represents the diameter of silver halide grain, if it
is spherical, but the diameter of the image of the circle having the same
area as its projected image, if it cubic or a grain of a shape other than
sphere.
The silver halide grains used for the emulsion of this invention may be
obtained by whichever of acid, neutral or ammonia process. The grains may
be grown at once or grown after forming the seed grains. The method of
forming the seed grains and growing method may be same or different.
As the system of reacting soluble silver salt with soluble halide,
whichever of the normal precipitation method, reverse precipitation method
or double jet precipitation method or their combinations is applicable,
but products obtained by the simultaneous mixing method is favorable. As
one form of double jet precipitation method, pAg-controlled double jet
method which appears in Japanese patent O.P.I. publication No. 48521/1979
may be employed.
Further, if need be, use of such solvent for silver halide as thioether,
etc., is permissible.
Any arbitrary shape of silver halide grain of this invention is usable, A
preferable example is a cube having {100} face as a crystal surface.
Besides, grains having such shapes as octahedron, tetradecahedron and
dedecahedrons, etc., may be formed by the methods which appear in
specifications of U.S. Pat. Nos. 4183756 and 4225666 and Japanese patent
O.P.I. publication No. 26589/1980, Japanese patent publication No.
42737/1980, etc., and in such literatures as The Journal of Photographic
Science, 21, 39 (1973), etc., and use may be made of them. Further, grains
having twin face may be used.
Into the interior and/or the surface of the silver halide grains used in
the emulsion of this invention, either one of ions of undermentioned
metals may be added, using salts of cadmium, zinc, lead, thallium, salts
or complexes of indium, rhodium or iron in the process of forming the
grains and/or the process of growing them, for it to be contained therein,
or reduction sensitizer nuclei may be provided in the interior and/or the
surface of the grains by placing them in an appropriate reducing
atmosphere.
From the emulsion containing the silver halide grains of this invention,
hereinafter referred to as this invention's emulsion, unnecessary soluble
salts may be removed, after accomplishing the growth of silver halide
grains, or they may be left contained therein. The removal of such salts
may be made, based on the method which appears in Research Disclosure No.
17643.
The silver halide grains used in the emulsion of this invention may be
mainly grains wherein latent image nuclei being formed on the surface or
those in the interior of grains, but the former is preferable.
The emulsion of this invention may be chemically sensitized by conventional
methods: Thus the sulfur sensitizing method making use of compounds
containing sulfur which reacts with silver ion or active gelatin, selenium
sensitizing method making use of selenium compounds, reduction sensitizing
method making use of reducing materials and noble metal sensitizing method
making use of gold and other noble metal compounds may be used singly or
in combination.
According to the invention, for example, chalcogen sensitizer may be used
as the chemical sensitizer. Chalcogen sensitizer is a generic name of
sulfur, selenium and tellurium sensitizers, but for photography, sulfur
and selenium sensitizers are preferable. Mentioned as the sulfur
sensitizers are, e.g., thiosulfuric acid allylthiocarbazide, thiourea,
allyl isothiocyanate, cystine, p-toluene thiosulfonate and rhodanine.
Besides, the usable are sulfur sensitizers which appear in U.S. Pat. Nos.
1574944, 2410689, 2278947, 2728668, 3501313 and 3656955, West German
O.L.S. patent No. 1422869 and Japanese patent O.P.I. publication Nos.
24937/1981 and 45016/1980. The amount of the sulfur sensitizer added may
vary over a substantial range, depending on various factors as pH,
temperature, size of silver halide grains, but preferably, fall within a
range of from about 10.sup.-7 mol to 10.sup.-1 mol per mol silver halide.
Instead of the sulfur sensitizers, selenium sensitizers may be employed.
Usable selenium sensitizers include aliphatic isoselenocyanates such as
allyl isoselenocyanate, selenourea compounds, selenoketones, selenoamides,
selenocarboxylic acid salts and esters, selenophosphates, selenides such
as diethyl selenide, diethyl diselenide, etc. Their particular examples
appear in U.S. Pat. Nos. 1574944, 1602592 and 1623499.
Further, the reduction sensitization may be jointly applied. Such reducing
agents, which are not particularly limited, may include stannous chloride,
thiourea dioxide, hydrazine, polyamine, etc.
Besides, compounds of noble metals other than gold, for example, paradium
compounds, etc., may be jointly used.
The silver halide grains of this invention may include gold compounds. As
the gold compounds used, its valences may be either mono- or tri-valent;
thus various gold compounds may be utilized. Representative examples
include chloroaurate, potassium chloroaurate, auric trichloride, potassium
auric thiocyanate, potassium iodoaurate, tetracyano-auric azide, ammonium
aurothiocyanate, pyridyl trichlorogold, gold sulfide, gold selenide, etc.
The gold compounds may be used in such a way as to sensitize silver halide
grains or not to substantially contribute to their sensitization.
The amount of gold compound added, which may vary depending on various
conditions, is within a range from 10.sup.-8 to 10.sup.-1 mol as a guide
line, and preferably, from 10.sup.-7 to 10.sup.-2 mol per mol of silver
halide. The time for adding such gold compound may be in whichever
process, either at the time of forming grains of silver halide or at the
time of physical or chemical digestion or after accomplishing the chemical
digestion.
The emulsion of this invention may be spectrally sensitized over any
desired wavelength range, using dyes known as sensitizing dyes in
photographic art. The sensitizing dyes may be used singly or in
combination of two or more of them.
Some super-sensitizer which strengthens the sensitizing effect of the
sensitizing dye, being a dye which itself has no spectral sensitizing
action or a compound which does not substantially absorb visible light,
may be contained in the emulsion, together with the sensitizing dye.
In the following, the cyan couplers represented by the aforementioned
general formula [I] of the invention are described:
According to this invention, the alkyl groups designated by R.sup.1 in the
general formula [I] are either of straight chained or branched chained,
which include, e.g., methyl, ethyl, iso-propyl, butyl, pentyl, octyl,
nonyl and tridecyl groups, etc.; and the aryl groups include, e.g., phenyl
and naphthyl groups, etc. The groups represented by R.sup.1 include those
having single or a plurality of substituents. The representative
substituents introduced into the phenyl group are, e.g., halogen atoms
(e.g., atoms such as fluorine, chlorine, bromine, etc.), groups of alkyl
(e.g., methyl, ethyl, propyl, butyl and dodecyl, etc.), hydroxyl, cyano,
nitro, alkoxy (e.g., methoxy and ethoxy), alkyl sulfonamido (e.g., methyl
sulfonamido and octyl sulfonamido, etc.), aryl sulfonamido (e.g., phenyl
sulfonamido and naphthyl sulfonamido, etc.), alkyl sulfamoyl (e.g., phenyl
sulfamoyl, etc.), alkyl oxycarbonyl (e.g., methyl oxycarbonyl, etc.),
aryloxycarbonyl (e.g., phenyl oxycarbonyl, etc.), aminosulfonamido (e.g.,
N,N-dimethyl amino-sulfonamide, etc.), acyl amino, carbamoyl, sulfonyl,
sulfinyl, sulfoxy, sulfo, aryloxy, alkoxy, carboxyl, alkyl carbonyl and
arylcarbonyl, etc.
More than of these groups may be introduced in the phenyl group.
The halogen atoms represented by R.sup.3 include, e.g., atoms of fluorine,
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