JP2012167243A - Oxazine and thiazine compounds - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dye composition having features of high clearness and coloration, and being excellent in the fastness such as heat resistance, wet heat resistance and water resistance.SOLUTION: There are provided oxazine and thiazine compounds represented by formula (1), and an oily or aqueous dye composition containing the compounds. In the formula, Rto Rare each independently a hydrogen atom, a 1-6C alkyl group or an aryl group: Rto Rare each independently a hydrogen atom or a substituent; and Y denotes an oxygen atom or a sulfur atom.

Description

  The present invention relates to novel oxazine and thiazine compounds.

  Oxazine and thiazine dyes are very clear and have high color developability. They are used in a wide range of applications such as various paints, water-based inks, oil-based inks, inkjet inks, and color filter inks as violet, blue or green colorants. in use. In general, the characteristics required for the color material include that the hue is clear and has high color developability, and that the colored material is highly resistant to light, heat, etc. However, these oxazine and thiazine dyes are excellent in color developability, but have the disadvantages of fastness such as light resistance, heat resistance, moist heat resistance and water resistance, and poor solubility in organic solvents. Since many useful coloring compositions are composed of organic compounds, the use of cationic dyes with poor solvent solubility is naturally limited.

  For this reason, there is a demand for dyes that have the sharpness and color developability of oxazine and thiazine dyes, and are highly durable and soluble in organic solvents. Patent Documents 1 and 2 describe oxazine dyes having a bistrifluoromethanesulfonylimide anion. Although these oxazine dyes have improved solubility in organic solvents, they have light resistance, heat resistance, and moisture resistance. Fastness such as heat resistance and water resistance is insufficient.

JP-A-8-253705 Special table 2007-503477

  As described above, the present invention has a novel and soluble oxazin and thiazine dyes, has excellent fastness such as light resistance, heat resistance, moist heat resistance and water resistance, and is soluble in organic solvents. An object is to provide an oxazine, a thiazine compound, and a dye composition using the compound.

  As a result of intensive studies to solve the above problems, the present inventors have found that a salt compound of a cationic oxazine or thiazine compound and a specific anion maintains the sharpness and color development of an oxazine or thiazine dye. In addition, the present inventors have found that heat resistance is drastically improved as compared with the prior art and have completed the present invention.

（式（１）において、Ｒ_１乃至Ｒ_４はそれぞれ独立に水素原子、炭素数１〜６のアルキル基またはアリール基を表し、Ｒ_５乃至Ｒ_１０はそれぞれ独立に水素原子、置換基を表し、Ｙは酸素原子または硫黄原子を表す。）、
（２）（１）に記載の化合物と少なくとも１種類の油溶性有機溶媒を含有する油性染料組成物、
（３）（１）に記載の化合物及び水性媒体を含有する水性染料組成物、
に関する。 That is, the present invention
(1) Compound represented by general formula (1)

(In the formula (1), R _{1 to} R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group, R _{5 to} R ₁₀ each independently represents a hydrogen atom, a substituent, Y represents an oxygen atom or a sulfur atom).
(2) an oil-based dye composition containing the compound according to (1) and at least one oil-soluble organic solvent,
(3) an aqueous dye composition containing the compound according to (1) and an aqueous medium,
About.

  As described above, the compound of the present invention is excellent in sharpness and color development, and when it is processed into a dyed colored body by forming an oily or aqueous dye composition, it exhibits characteristics excellent in fastness compared to conventional products. That is, the compound of the present invention can be used in dye-colored bodies and can be applied to a wide range of uses such as color filter inks and inkjet inks.

  The compound of the present invention is represented by the formula (1). In addition to the iminium, the cation moiety of the compound of the present invention includes all those in which any of the conjugated atoms in the heterocyclic skeleton is a cation.

  In formula (1), Y represents an oxygen atom or a sulfur atom.

In Formula (1), R _{1 to} R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group.

In R _{1 to} R ₄ in the formula (1), examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, an isobutyl group, a pentyl group, a cyclopentyl group, a hexyl group, and a cyclohexyl group. And an alkyl group such as a group. These alkyl groups may have a substituent. Examples of the substituent include a hydroxyethyl group, a hydroxypropyl group, a hydroxybutyl group, a 2-sulfoethyl group, a carboxyethyl group, a cyanoethyl group, a methoxyethyl group, and an ethoxy group. Examples include an ethyl group, a butoxyethyl group, a trifluoromethyl group, a pentafluoroethyl group, and a phenylmethyl group.

As the aryl group in R _{1 to} R ₄ in the formula (1), for example, an aromatic hydrocarbon residue such as a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, a benzopyrenyl group; a pyridyl group, a pyrazyl group, Examples thereof include an aromatic heterocyclic residue such as a pyrimidyl group, a quinolyl group, an isoquinolyl group, a pyrrolyl group, an indolenyl group, an imidazolyl group, a carbazolyl group, a thienyl group, and a furyl group.

The aryl group in R _{1 to} R ₄ in the formula (1) may further have a substituent. Examples of the substituent include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, t- (C1-C5) alkyl groups such as butyl group and pentyl group; halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom; sulfonic acid group, methoxy group, ethoxy group, propoxy group, butoxy group, t -(C1-C6) alkoxy groups such as butoxy group and hexyloxy group; hydroxy (C1-C5) alkyl groups such as hydroxyethyl group and hydroxypropyl group; methoxyethyl group, ethoxyethyl group and ethoxypropyl group , (C1-C5) alkoxy (C1-C5) alkyl group such as butoxyethyl group; hydroxy (C1-C1) such as 2-hydroxyethoxy group ) Alkoxy group; (C1-C5) alkoxy (C1-C5) alkoxy group such as 2-methoxyethoxy group, 2-ethoxyethoxy group; 2-sulfoethyl group, carboxyethyl group, cyanoethyl group, etc. .

R _{5 to} R ₁₀ in the formula (1) each independently represent a hydrogen atom or a substituent.

  Examples of the substituent include an aliphatic hydrocarbon group, aryl group, hetero group, acyl group, acyloxy group, acylamino group, aliphatic oxy group, aryloxy group, heterocyclic oxy group, aliphatic oxycarbonyl group, aryloxy Carbonyl group, heterocyclic oxycarbonyl group, carbamoyl group, aliphatic sulfonyl group, arylsulfonyl group, heterocyclic sulfonyl group, aliphatic sulfonyloxy group, arylsulfonyloxy group, heterocyclic sulfonyloxy group, sulfamoyl group, aliphatic sulfonamide Group, arylsulfonamido group, heterocyclic sulfonamido group, amino group, aliphatic amino group, arylamino group, heterocyclic amino group, aliphatic oxycarbonylamino group, aryloxycarbonylamino group, heterocyclic oxycarbonylamino group, Aliphatic fu Finyl group, arylsulfinyl group, aliphatic thio group, arylthio group, hydroxy group, cyano group, sulfo group, carboxyl group, aliphatic oxyamino group, aryloxyamino group, carbamoylamino group, sulfamoylamino group, halogen atom , Sulfamoylcarbamoyl group, carbamoylsulfamoyl group, dialiphatic oxyphosphinyl group, diaryloxyphosphinyl group, and the like.

  The compound of the present invention can be obtained, for example, by a known synthesis method described in Yutaka Hosoda “Theoretical Manufacturing Dye Chemistry” (pages 382 to 384) published by Gihodo Co., Ltd. Can be synthesized by adding the corresponding salt or acid and exchanging the salt.

  In the case of synthesizing the compound of the present invention by salt exchange, a compound in which the anion moiety is a chlorine anion is reacted with a reaction solvent (for example, water, methanol, ethanol, isopropanol, acetone, N, N-dimethylformamide (hereinafter abbreviated as DMF)). And water-soluble polar solvents such as N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), and these solvents may be used alone or in combination. About 5 to 3 equivalents are added, stirred at a predetermined temperature (for example, 0 to 100 ° C.), can be easily synthesized, and the precipitated crystals are obtained by filtration.

  Although the specific example of a compound represented by Formula (1) is shown to the following Table 1-1 and Table 1-2, this invention is not limited to these.

表１−２

表１−１及び表１−２中、Ｍｅはメチル基を、Ｅｔはエチル基を、それぞれ表す。 Table 1-1

Table 1-2

In Table 1-1 and Table 1-2, Me represents a methyl group, and Et represents an ethyl group.

  The compound of the present invention is used as an oil-based dye composition or an aqueous dye composition in coloring compositions such as various paints, water-based inks, oil-based inks, ink-jet inks, and color filter inks. The oil-based dye composition and the aqueous dye composition are used for materials to be colored such as plain paper, coated paper, plastic film, and plastic substrate. Examples of a method for applying the dye composition of the present invention to a material to be colored include various printing methods such as offset printing, letterpress printing, flexographic printing, and ink jet printing, and coating methods using a spin coater, a roll coater, and the like.

  The oily or aqueous dye composition of the present invention contains the compound of the present invention and an oil-soluble organic solvent in the case of an oily dye composition and an aqueous medium in the case of an aqueous dye. In the oily or aqueous dye composition of the present invention, the compound of the present invention is preferably contained in an amount of 0.2 to 40% by mass, and more preferably 0.5 to 20% by mass. In the oily or aqueous dye composition of the present invention, a colorant other than the formula (1) may be added as necessary for the purpose of adjusting the hue. Examples of colorants that can be added include water-soluble dyes such as acid dyes, reactive dyes, direct dyes, cationic dyes, and basic dyes, oil-soluble dyes such as disperse dyes and solvent dyes, organic pigments, and carbon black. And added in a dissolved or dispersed state in a solvent.

  The aqueous dye composition of the present invention can be prepared by dispersing the compound of the formula (1) in an aqueous medium. Examples of the aqueous medium include water or a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, benzyl alcohol; ethylene ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene Polyhydric alcohols such as glycol, polypropylene glycol, glycerin, trimethylolpropane, 1,3-pentanediol, 1,5-pentanediol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, Triethylene glycol monoethyl ether, triethylene glycol monobutyl Ether, glycol derivatives such as dipropylene glycol monomethyl ether; ethanolamine, diethanolamine, triethanolamine, amines such as morpholine; 2-pyrrolidone, NMP, 1,3-dimethyl - imidazolidinone.

  The oil-based dye composition of the present invention can be prepared by dissolving or dispersing the compound of the above formula (1) in at least one oil-soluble organic solvent. Examples of the oil-soluble organic solvent used include alcohols such as ethanol, pentanol, octanol, cyclohexanol, benzyl alcohol, and tetrafluoropropanol; ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol mono Glycol derivatives such as ethyl ether, dipropylene glycol monomonomethyl ether, dipropylene glycol monomonoethyl ether, triethylene glycol monoethyl ether, ethylene glycol diacetate, ethylene glycol diacetate, propylene glycol diacetate; ketones such as methyl ethyl ketone and cyclohexanone Butyl phenyl ether, benzyl ether Ethers such as hexyl ether, esters such as ethyl acetate, butyl acetate, ethyl benzoate, butyl benzoate, ethyl laurate, butyl laurate; polarities such as acetonitrile, DMF, dimethyl sulfoxide, sulfolane, NMP, 2-pyrrolidone, etc. An organic solvent etc. are mentioned. These solvents may be used alone or in combination of two or more.

  Dispersants used in oil dye compositions include sodium dodecylbenzenesulfonate, sodium laurate, formalin condensate of naphthalene sulfonic acid, formalin condensate of alkyl naphthalene sulfonic acid, formalin condensate of creosote oil sulfonic acid, poly Known anionic surfactants such as ammonium salts of oxyethylene alkyl ether sulfates, ammonium of polyoxyethylene alkyl phenyl ether sulfates, polyoxyalkyl ether phosphate esters, vinyl naphthalene derivatives, fats of α, β-ethylenically unsaturated carboxylic acids Aromatic alcohol esters, etc., styrene, styrene derivatives, acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, maleic acid, maleic acid derivatives, maleic anhydride, maleic anhydride A block copolymer consisting of at least two monomers selected from inic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, etc., or a random copolymer, or a high salt thereof. Examples thereof include molecular dispersants, and it is preferably used in an amount of 10 to 100% by mass with respect to the dye compound in which one or more of these are dispersed. In addition to these dispersants, known nonionic surfactants such as polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, copolymers of ethylene oxide and propylene oxide, and silicones A known acetylene-based antifoaming agent can be added at the time of pigment dispersion and / or after the pigment dispersion.

  Examples of the method for dispersing the pigment into the fine particles include a method using a sand mill (bead mill), a roll mill, a ball mill, a paint shaker, an ultrasonic disperser, a microfluidizer, and the like. Among these, a sand mill (bead mill) is preferable. In the grinding of pigments in sand mills (bead mills), it is preferable to use beads with small diameters and to treat them under conditions that increase the grinding efficiency by increasing the filling rate of beads. It is preferable to remove the elementary particles by separation or the like. The dye composition of the present invention may contain a surface adjusting agent, an antiseptic, an antifungal agent, a pH adjusting agent and the like as other additives. As surface conditioning agents, polysiloxane or polydimethylsiloxane surfactants, and as antiseptic / antifungal agents, sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, zinc pyridinethione-1-oxide 1,2-benzisothiazolin-3-one, amine salts of 1-benzisothiazolin-3-one, etc., as pH adjusters, alkali hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, Tertiary amines such as triethanolamine, diethanolamine, dimethylethanolamine, diethylethanolamine and the like can be mentioned, and each can be added as necessary.

  In addition, in the oily or aqueous dye composition of the present invention, for the purpose of improving the fixability of the pigment to the object to be colored, a polyamide system, a polyurethane system, or a polyester that is compatible with the medium in the composition within a necessary range. It is preferable to contain an epoxy resin, an epoxy resin, or a polyacrylic resin. Further, for the purpose of improving the fixability, a monomer, oligomer, polymerization initiator or the like having an ethylenically unsaturated group may be contained within a necessary range. The oily or aqueous dye composition of the present invention can be prepared by dissolving or dispersing and mixing the above components in a solvent.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In Examples, “part” means “part by mass” unless otherwise specified. Compound Nos. Obtained in the Examples 2 and no. The heat resistance evaluation method No. 6 is as follows.

Heat resistance test The dyed colored product obtained in the following examples was left in a constant temperature hot air dryer at 230 ° C. for 3 hours. The dyed colored body before and after the test was measured with a UV-3150 spectrophotometer manufactured by Shimadzu Corporation, and the chromaticity (L value, a value, b value) of the dyed colored body was measured as a C light source with a 2 degree viewing angle. The color was measured and the color difference was calculated from the following formula. In addition, it shows that it is excellent because there is little change of a hue, so that a color difference is small.
Color difference = [(L value before test−L value after test) ² + (a value before test−a value after test) ² + (b value before test−b value after test) ² ] ^1/2

Example 1 (Synthesis of Compound No. 2 in Table 1)
A 300 ml beaker was charged with 1 part of Basic Blue 3 (manufactured by Hodogaya Chemical Co., Ltd.) and 50 parts of water, and stirred at room temperature for 30 minutes. A solution prepared by dissolving 1.3 parts of a potassium salt of tristrifluoromethanesulfonium methide (manufactured by Central Glass) in 4.5 parts of DMF was added dropwise thereto and stirred for 3 hours. The precipitated dye was collected by filtration, washed with water, and dried to obtain 0.9 part of a dye (oxazine compound of the present invention). Maximum absorption wavelength: 653 nm (cyclohexanone)

Example 2 (Preparation of oil-based dye composition and dyed colored body)
In a 500 ml four-necked flask, 160 parts of propylene glycol monomethyl ether acetate, 6.6 parts of methacrylic acid, 30 parts of cyclohexyl methacrylate, 6 parts of 2-hydroxyethyl methacrylate, 2 parts of α, α′-azobis (isobutyronitrile) Nitrogen gas was poured into the flask for 30 minutes while charging and stirring, and then the temperature was raised to 80 ° C. as it was. The mixture was stirred at 80 to 85 ° C. for 4 hours. After completion of the reaction, the mixture was cooled to room temperature to obtain a colorless transparent and uniform liquid, that is, a copolymer solution. The polystyrene-reduced weight average molecular weight was 12000, and the acid value was 100. Compound No. 1 obtained in Example 1 was added to 0.8 part of the copolymer obtained and 1 part of cyclohexanone. 2,0.025 part was dissolved and the oil-based dye composition was created. The obtained oily dye composition was spin-coated on a glass substrate and dried at 200 ° C. for 20 minutes to prepare a dye-colored product.

Compound No. Table 2 to Table 4 below show the color measurement values and color differences in the heat resistance test No. 2. In addition, the comparative example 1 in the following Table 3 uses a imide salt compound of the following formula (100) and similarly produces a dye-colored body.

Compound No. The color measurement results of 2 are shown in Table 2 below.
(Table 2)
L value a value b value before test 80.15 -29.46 -27.69
After the test 79.89-25.73-25.95
Difference before and after test 0.26 -3.73 -1.74

The color measurement results of Comparative Example 1 are shown in Table 3 below.
(Table 3)
L value a value b value Before test 73.06 -31.61 -38.24
After the test 78.44 -4.40 -12.02
Difference before and after test -5.38 -27.21 -26.22

From Table 2 and Table 3 above, Compound No. Table 4 shows the results of the color difference between 2 and Comparative Example 1.
(Table 4)
Color difference compound no. 2 4.2
Comparative Example 1 38.2

  As is apparent from the results in Table 4, the color difference before and after the test of the dye-colored product of Comparative Example 1 showed a very large value of 38.2, whereas the dye-colored product of the present invention had an extremely large color difference of 4.2. A small value is shown, indicating that the heat resistance is extremely excellent.

Example 3 (Synthesis of Compound No. 6 in Table 1)
A 500 ml beaker was charged with 2 parts of methylene blue hydrate (manufactured by Tokyo Chemical Industry Co., Ltd.) and 250 parts of water, and stirred at room temperature for 30 minutes. To this, a solution prepared by dissolving 2.8 parts of a potassium salt of tristrifluoromethanesulfonium methide in 3.1 parts of DMF was added dropwise and stirred for 2 hours. The precipitated dye was collected by filtration, washed with water, and dried to obtain 3.4 parts of a dye (thiazine compound of the present invention). Maximum absorption wavelength: 663 nm (cyclohexanone)

Example 4 (Preparation of oil-based dye composition and dyed colored body)
In a 500 ml four-necked flask, 160 parts of propylene glycol monomethyl ether acetate, 6.6 parts of methacrylic acid, 30 parts of cyclohexyl methacrylate, 6 parts of 2-hydroxyethyl methacrylate, 2 parts of α, α′-azobis (isobutyronitrile) Nitrogen gas was poured into the flask for 30 minutes while charging and stirring, and then the temperature was raised to 80 ° C. as it was. The mixture was stirred at 80 to 85 ° C. for 4 hours. After completion of the reaction, the mixture was cooled to room temperature to obtain a colorless transparent and uniform liquid, that is, a copolymer solution. The polystyrene-reduced weight average molecular weight was 12000, and the acid value was 100. Compound No. 1 obtained in Example 4 was added to 0.8 part of the copolymer obtained by adding 1 part of cyclohexanone. 6, 0.025 part was dissolved to prepare an oily dye composition. The obtained oily dye composition was spin-coated on a glass substrate and dried at 200 ° C. for 20 minutes to prepare a dye-colored product.

Compound No. Table 5 to Table 7 below show the color measurement values and color differences in the heat resistance test No. 6. In addition, the comparative example 2 in the following Table 6 uses a imide salt compound of the following formula (101) and similarly produces a dye-colored body.

Compound No. The color measurement results of 6 are shown in Table 5 below.
(Table 5)
L value a value b value Before test 78.78 -15.94 -27.16
After the test 78.10-11.66-22.23
Difference before and after test 0.68 -4.28 -4.93

The color measurement results of Comparative Example 2 are shown in Table 6 below.
(Table 6)
L value a value b value Before test 71.46-12.27-38.30
After the test 80.25 -1.78 -12.02
Difference before and after test −8.79 −10.49 −26.28

From Table 5 and Table 6 above, Compound No. Table 7 below shows the results of the color difference between 6 and Comparative Example 2.
(Table 7)
Color difference compound no. 6 6.6
Comparative Example 2 29.6

  As is clear from the results in Table 7, the color difference before and after the test of the dye-colored product of Comparative Example 2 showed a very large value of 29.6, whereas the dye-colored product of the present invention had a small color difference of 6.6. The value is shown and it is understood that the heat resistance is extremely excellent.

Example 5 (Synthesis of Compound No. 9 in Table 1)
In a 500 ml beaker, 2 parts of Basic Blue 24 (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 parts of water were charged and stirred at 40 ° C. for 60 minutes. A solution prepared by dissolving 2.7 parts of a potassium salt of tristrifluoromethanesulfonium methide in 4 parts of DMF was added dropwise thereto and stirred for 3 hours. The precipitated dye was collected by filtration, washed with water and dried to obtain 3.0 parts of the dye (thiazine compound of the present invention). Maximum absorption wavelength: 632 nm (cyclohexanone)

Example 6 (Synthesis of Compound No. 10 in Table 1)
A 500 ml beaker was charged with 1.5 parts of Basic Green 5 (manufactured by Tokyo Chemical Industry Co., Ltd.) and 250 parts of water, and stirred at 35 ° C. for 30 minutes. A solution prepared by dissolving 2 parts of a potassium salt of tristrifluoromethanesulfonium methide in 4 parts of DMF was added dropwise thereto and stirred for 3 hours. The precipitated dye was collected by filtration, washed with water and dried to obtain 2.1 parts of the dye (thiazine compound of the present invention). Maximum absorption wavelength: 628 nm (cyclohexanone)

Example 7 (Synthesis of Compound No. 11 in Table 1)
In a 1000 ml beaker, 5 parts of Basic Blue 17 (manufactured by Tokyo Chemical Industry Co., Ltd.) and 800 parts of water were charged and stirred at 40 ° C. for 60 minutes. A solution in which 7.7 parts of a potassium salt of tristrifluoromethanesulfonium methide was dissolved in 9 parts of DMF was added dropwise thereto and stirred for 3 hours. The precipitated dye was collected by filtration, washed with water and dried to obtain 7.7 parts of a dye (thiazine compound of the present invention). Maximum absorption wavelength: 629 nm (cyclohexanone)

Example 8 (solvent solubility test)
Compound No. obtained above. 2 and no. 0.01 part of 6 was easily dissolved in 0.2 part of methyl ethyl ketone.

  Patent Document 1 discloses that 0.01 part of the dye of the above formula (101) is dissolved in 0.2 part of methyl ethyl ketone. 2 and no. 6 was also found to have equivalent solvent solubility.

Claims (3)

Compound represented by general formula (1)

(In the formula (1), R _{1 to} R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group, R _{5 to} R ₁₀ each independently represents a hydrogen atom, a substituent, Y represents an oxygen atom or a sulfur atom.) An oil-based dye composition comprising the compound according to claim 1 and at least one oil-soluble organic solvent. An aqueous dye composition comprising the compound according to claim 1 and an aqueous medium.