CN109232397B

CN109232397B - Alkaline precise pH test paper capable of being repeatedly utilized through washing and preparation method and application thereof

Info

Publication number: CN109232397B
Application number: CN201811094853.0A
Authority: CN
Inventors: 郝京诚; 董川
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2018-09-19
Filing date: 2018-09-19
Publication date: 2020-04-28
Anticipated expiration: 2038-09-19
Also published as: CN109232397A

Abstract

The invention relates to alkaline precise pH test paper capable of being repeatedly utilized by washing, a preparation method and application thereof, belongs to the technical field of colorimetric analysis and detection, and providesA compound shown as a formula I, 4 '-p-hydroxyazophenyl-2, 2', 6 '2' -terpyridine,

the preparation method of the compound shown in the formula I comprises the steps of firstly preparing 4 '-nitro-2, 2': 6 '2' -terpyridine, then preparing 4 '-amino-2, 2': 6 '2' -terpyridine, and then reacting with phenol to obtain 4 '-p-hydroxyazophenyl-2, 2': 6 '2' -terpyridine, wherein the compound shown in the formula I is used as a probe molecule to prepare alkaline precise pH test paper which can detect the change of the pH value of an aqueous phase within the range of 11-14.

Description

Alkaline precise pH test paper capable of being repeatedly utilized through washing and preparation method and application thereof

Technical Field

The invention belongs to the technical field of colorimetric analysis and detection, and particularly relates to alkaline precise pH test paper capable of being repeatedly utilized by washing, and a preparation method and application thereof.

Background

pH is an important basic concept in electrochemistry and also a very widely used indicator of solution chemistry. Since the definition includes single ion activity, thermodynamic method can only measure the average activity of electrolyte (i.e. the average activity of positive and negative ions), it is not a physical quantity that can be directly measured. In solution chemistry, as an important index for detecting the pH value of a solution, the pH value often needs a fixed detection standard and a galvanic cell electrode support based on potential analysis. And the appearance of the pH test paper provides a more convenient and visual thought for pH detection. In the 17 th century, Robertboyle, a British chemist, enlightens from the phenomenon that violet petals turn red when encountering acid, and after experiments are carried out by utilizing various plants, litmus paper which can turn blue when encountering acid and alkali is invented, and the litmus paper is also a prototype of the current pH paper. In the next three hundred years, it becomes an indispensable necessity in chemical experiments.

The pH indicator paper used today generally contains three indicators, methyl red, bromocresol green and thymol blue, which change color in a regular manner in solutions with different pH ranges. Although the test paper method is convenient and rapid in pH detection, the commonly used pH test paper still has the defects of incapability of recycling, easiness in being influenced by the gas atmosphere in a laboratory and the like.

Disclosure of Invention

In view of the problems of the prior art as described above, it is a first object of the present invention to provide a compound of formula (I). Provide a novel toolA compound having a color-developing action, a compound of formula (I) and OH^-The color of the product is changed by the action of the ionic salt, and the product is reacted with OH^-After the action, the compound can be re-protonated under the action of excessive water molecules to generate the compound shown in the formula (I).

In order to solve the technical problems, the technical scheme of the invention is as follows:

a compound of formula I, 4 '-p-hydroxyazophenyl-2, 2', 6 '2' -terpyridine, of the formula:

the second object of the present invention is to provide a process for preparing the compound represented by the above formula (I), which comprises the following steps:

1) synthesis of 4 '-nitro-2, 2', 6 ', 2' -terpyridine

Mixing 2-acetylpyridine and 4-nitrobenzaldehyde to obtain a solution A, adding a potassium hydroxide aqueous solution and concentrated ammonia water to react to obtain a solid, washing, extracting, drying, rotary steaming, recrystallizing, filtering and drying to obtain 4 '-nitro-2, 2', 6 ', 2' -terpyridine;

2) synthesis of 4 '-amino-2, 2', 6 ', 2' -terpyridine

Suspending the 4 '-nitro-2, 2', 6 ', 2' -terpyridine obtained in the step 1) and stannous chloride in concentrated hydrochloric acid for heating reaction, cooling, adding a sodium bicarbonate aqueous solution, filtering to obtain a solid, and purifying by column chromatography to obtain 4 '-amino-2, 2', 6 ', 2' -terpyridine;

3) synthesis of 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine

Dissolving the 4 '-amino-2, 2', 6 ', 2' -terpyridine obtained in the step 2) in concentrated hydrochloric acid, placing in an ice bath, dropwise adding a sodium nitrite aqueous solution, adding a mixed aqueous solution B of sodium hydroxide and phenol, carrying out suction filtration, washing and drying to obtain the 4 '-p-hydroxyazophenyl-2, 2', 6 ', 2' -terpyridine.

Preferably, the solvent of the solution A in the step 1) is methanol; violently stirring the mixture of the 2-acetylpyridine and the 4-nitrobenzaldehyde, wherein the reaction condition of the solution A, the potassium hydroxide and the ammonia water is room temperature, and the reaction time is 2-4d, preferably 3 d; preferably, the washing process in the step 1) is washing with distilled water and cold methanol respectively; preferably, the extraction process in step 1) is to dissolve the washed solid in ethyl acetate, and then add sodium bicarbonate aqueous solution; preferably, drying is performed using anhydrous sodium sulfate in step 1).

Preferably, the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in the concentrated hydrochloric acid in the step 2) is 70-90 ℃, and the temperature is cooled to room temperature after the reaction, preferably 80 ℃; preferably, after the solid powder in the step 2) is added into the sodium bicarbonate solution, the pH is adjusted to 12-13; preferably, the solid filtered in the step 2) is subjected to chromatographic separation by an alkaline alumina column, and the eluent is a mixture of ethyl acetate and petroleum ether; further preferably, the ratio of ethyl acetate to petroleum ether in the eluent in the step 2) is 1: 1-2: 1, preferably 1: 1.

preferably, the 4 '-amino-2, 2', 6 ', 2' -terpyridine in the step 3) is ultrasonically stirred in the process of dissolving in concentrated hydrochloric acid; preferably, after the sodium nitrite aqueous solution is dropped in the step 3), the reaction is carried out for 0.9 to 1.2 hours, preferably for 1 hour in an ice bath; preferably, the mixed aqueous solution B is added dropwise in the step 3), and after the mixed aqueous solution B is added, the mixture reacts in an ice bath for 0.9 to 1.2 hours and then at room temperature for 11 to 13 hours, preferably after the mixture reacts in the ice bath for 1 hour and then at room temperature for 12 hours.

Preferably, the mass fraction of the KOH aqueous solution in the step 1) is 15 percent, and the concentration of the strong ammonia water is 25 to 28 percent; preferably, the ratio of the 2-acetylpyridine to the 4-nitrobenzaldehyde to the aqueous solution of potassium hydroxide to the concentrated ammonia water to the methanol in the step 1) is 1g:0.6-0.7g:2-4mL:32-36mL:30-38mL, preferably 1g:0.634g:3mL:34mL:34 mL; preferably, NaHCO is used in step 1)₃The mass concentration of the aqueous solution was 1%.

Preferably, the 4 '-nitro-2, 2', 6 '2' -terpyridine and SnCl in the step 2)₂The ratio of concentrated HCl was 1g: 3-4 g: 24-28mL, preferably 1g: 3.3 g: 26 mL; preferably, the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in the concentrated hydrochloric acid in the step 2) is 70-90 ℃ and the reaction time is 7-9h, and preferablyThe reaction temperature is 80 ℃, and the reaction time is 8 h; preferably, NaHCO is added in step 2)₃Adjusting pH to 12-13.

Preferably, the 4 '-amino-2, 2', 6 '2' -terpyridine in the step 3), concentrated hydrochloric acid and NaNO₂And distilled water: NaOH: the ratio of phenol was 380-420 mg: 1mL of: 85-87 mg: 4mL of: 320-360 mg: 110-120mg, preferably 400 mg: 1mL of: 85.18 mg: 4mL of: 340 mg: 116.2 mg; preferably, the mass concentration of the mixed aqueous solution B is 16-18mg/ml of NaOH, 5.6-6.0ml/ml of phenol, preferably 17 mg/ml: 5.81 mg/ml.

The third purpose of the invention is to provide the application of the 4 '-p-hydroxyazophenyl-2, 2', 6 ', 2' -terpyridine as a probe molecule in pH test paper.

The fourth purpose of the invention is to provide the alkaline precise pH test paper which can be repeatedly utilized by washing, wherein the 4 '-p-hydroxyazophenyl-2, 2': 6 '2' -terpyridine is used as a probe molecule, and the probe molecule is loaded on slow-speed qualitative filter paper to obtain the alkaline precise pH test paper.

The test paper prepared by the application is accurate pH test paper for detecting the change of the pH value of a water phase within the range of 11-14, can be repeatedly used by washing, drying and drying, has strong tolerance to the change of an environmental atmosphere, and has good contrast and reproducibility and uniform and obvious color development. The defects that the existing pH test paper cannot be reused and has certain requirements on the temperature of the use environment can be effectively overcome, and higher stability and convenience are provided for pH detection.

The preparation method of the alkaline precise pH test paper capable of being repeatedly utilized by washing comprises the following specific steps:

dissolving 4 '-p-hydroxyazophenyl-2, 2', 6 '2' -terpyridine probe molecule in organic solvent to obtain mixed solution C, adding qualitative filter paper, and drying to obtain the alkaline precise pH test paper.

Preferably, the concentration of the mixed solution C is 0.015-0.020 mol/L; preferably, the organic solvent is dimethyl sulfoxide (DMSO) or N, N-dimethylformamide; preferably, the qualitative filter paper is placed into the mixed solution C for soaking for 15-30min at 20-30 ℃.

The invention has the beneficial effects that:

1) the phenol group at the end group position of the 4 '-p-hydroxyazophenyl-2, 2' 6 '2' -terpyridine of the invention can be reacted with OH in solution^-Deprotonation of the interaction and development of color; the ionic probe molecules can be re-protonated in the excess water to restore the color development capability.

2) The probe molecule separated from the liquid environment is loaded on qualitative filter paper, and the 4 '-p-hydroxyazophenyl-2, 2': 6 '2' -terpyridine molecule used as test paper (light yellow) can still be mixed with OH in the solution^-The color change occurs through interaction, so that the response is generated to the aqueous solution with the pH value of 11-14, and the test effect is visual and reliable;

3) the pH test paper disclosed by the invention is simple in preparation method, low in preparation cost, convenient and effective in measurement mode and strong in anti-interference capability.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

FIG. 1 is a graph of the mode of action of the 4 ' -p-hydroxyazophenyl-2, 2 ', 6 ', 2 "-terpyridine probe molecule with hydroxide ion and nuclear magnetic and mass spectrometric characterization of the probe molecule itself, as in example 1.

FIG. 2 is a photograph of UV-visible absorption spectrum and color development of the response ability of the organic solution of the probe molecule in example 1 to aqueous solutions of different pH.

FIG. 3 is a photograph of UV-visible absorption spectra and color development of organic solutions of probe molecules of example 1 in response to different solutions of Brewster's base salt.

FIG. 4 is the UV-VIS absorption spectrum and color development photographs of the probe molecule in different solvent systems in example 1, and the chart data is tabulated.

FIG. 5 is a photograph showing the color standard cardboard of the test paper loaded with probe molecules in example 1 under the action of solutions of different pH values and the detection of the solutions of different pH values by the circulation after water washing.

FIG. 6 is a photograph of a traceless writing paper and an inkless writing paper prepared by utilizing the color developing ability of the probe molecules in example 1.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The invention will be further illustrated by the following examples

Example 1

First, 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine was synthesized to 170ml of CH₃5g 2-acetylpyridine and 3.17g p-nitrobenzaldehyde were added to OH, and 15% KOH aqueous solution (15 ml) and 160ml NH were added thereto with stirring₄OH, the system is stirred for 3 days at room temperature. The dark red precipitate is obtained by suction filtration and washed three times respectively with distilled water and cold methanol. The solid obtained by filtration was dissolved in ethyl acetate and mixed with 1% NaHCO₃Extracting the aqueous solution for 1 time, and using anhydrous NaSO for the obtained organic phase₄Drying, CH₃CH₂OH is recrystallized to obtain 4 '-nitro-2, 2', 6 ', 2' -terpyridine molecules with the yield of 34 percent.

0.46g of the 4 '-nitro-2, 2', 6 '2' -terpyridine synthesized by the above method and SnCl₂1.536g was added to 12ml of concentrated HCl and heated at 80 ℃ for 8 hours. Cooling to room temperature, vacuum filtering to obtain residual solid powder, dissolving in ice water, and separating with NaHCO₃Adjusting pH to 12-13. Filtering to obtain solid, separating and purifying target molecule with basic alumina chromatographic column, and eluting with acetic acidEthyl ester: petroleum ether 1:1, 4 '-amino-2, 2', 6 '2' -terpyridine molecule yield 62%.

200mg of the 4 '-amino-2, 2', 6 ', 2' -terpyridine molecule is dissolved in 0.5ml of concentrated HCl, and ultrasonic stirring is carried out to assist dissolution. After complete dissolution, the solution was placed in an ice bath at 0 ℃ and stirred vigorously. Adding NaNO₂42.59mg were added to 2ml of distilled water and slowly dropped into the above solution system, and the whole process was controlled by means of a starch KI test paper. After the system became clear, the reaction was continued for 1 hour with stirring while maintaining the ice bath. Subsequently, a mixed aqueous solution of 170mg of NaOH and 58.1mg of phenol was added dropwise to the above system, and the reaction was stirred vigorously for 1 hour, and then removed from the ice bath and allowed to react at room temperature for 12 hours. And (3) carrying out suction filtration to obtain a residual solid, washing with ice brine and ice water for three times respectively, and drying to obtain 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine molecules with the yield of 81%.

Subjecting the resulting molecule to H₁And (2) nuclear magnetism and mass spectrum detection, as shown in figure 1, a is the action principle of the probe molecule, b is the nuclear magnetism spectrogram of the probe molecule, c is the mass spectrogram, the end group of the probe molecule is phenolic hydroxyl, corresponds to a wide peak at 10.5ppm of nuclear magnetism, and can be combined with OH in a solution in an organic-water mixed system^-And (3) acting to dissociate hydrogen ions, so that the molecules form ionic salts. The probe molecules in the form of ionic salts can interact with excessive water and are re-protonated into molecular states.

Example 2

The probe developed a color change to alkalinity.

The 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine synthesized in example 1 (10.84 mg) was dissolved in 20ml of DMSO, and after the solution was homogeneous and stable, 1ml of the solution was removed and diluted to 50ml to obtain a pale yellow probe mother solution.

Preparing 250ml of 0.1mol/L NaOH aqueous solution, diluting the NaOH aqueous solution one time by one time, preparing standard NaOH aqueous solution with pH of 7-13 by means of a pH meter, transferring 4ml of probe mother solution into a plurality of glass vials respectively, transferring 67ul of standard solution with different pH values to be mixed with the probe mother solution, measuring the ultraviolet-visible absorption curve of the detection solution under the action of different pH values, and taking pictures and recording the color change in different vials.

From the UV-Vis absorption curve of a in FIG. 2, it can be seen that^-The absorption peak of the interacted probe molecules is red-shifted from 372nm to 523nm and respectively corresponds to the probe molecules and OH^-The two states before and after the action change, with the increase of the pH value of the solution, the absorbance of the absorption peak at 523nm is gradually enhanced, the absorbance of the absorption peak of the original molecule at 372nm is gradually reduced, and the color of the system is changed from light yellow to deep red, as shown in b in figure 2, the color is gradually deepened from pH 7 to transparent light yellow, pH8-9 to slightly light red, pH11 to obviously light red, and pH12-14 is gradually changed from light red to deep red.

Example 3

The probe stock solution was prepared in the same manner as in example 2.

Respectively preparing NaBr, NaF, NaCl and NaH with the concentration of 0.012mol/L₂PO₄，Na₂HPO₄，Na₃PO₄，Na₂SO₄And (3) transferring the aqueous solution, mixing 67ul of different salt solutions with the mother solution, measuring the ultraviolet-visible absorption curves of different detection solutions, and photographing and recording the color change in different vials.

As can be seen from the UV-Vis absorption curve in a of FIG. 3, the probe molecules can also respond to different aqueous Brewster bases which dissociate to form hydroxide ions, with the absorption peak of the molecule red-shifted from 372nm to 523 nm. The shade of the color change in the visible range is related to the dissociation constant of the salt solution, i.e., the pH of the solution, where pka₃Greater Na₃PO₄The solution is most alkaline and the color change of the solution is most obvious. And several other alkaline salt solutions such as Na₂HPO₄，NaF，Na₂SO₄Etc. can also cause the probe solution to change color to different degrees, as shown in b in fig. 3. NaBr, NaCl, NaH₂PO₄The color change is not obvious, and the color is light yellow like that of a blank group, NaF and Na₂SO₄、NaH₂PO₄Light red, Na₃PO₄The color was dark red.

Example 4

Screening of organic solvent for preparing test paper

The probe stock solution was prepared in the same manner as in example 2.

The 4 ' -p-hydroxyazophenyl-2, 2 ': 6 ' 2 "-terpyridine prepared in example 1 (10.84 mg) was dissolved in 20ml of 1, 3-dimethyl-2-imidazolidinone (DMI), Tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N, N-Dimethylformamide (DMF), acetonitrile and acetone, respectively, and after the solution was homogeneous and stable, 1ml of the above solution was removed and diluted to 50ml to obtain probe stock solutions of different solvents.

0.012mol/L of Na was added₃PO₄Transferring 67ul of the aqueous solution into the different probe mother solutions respectively, measuring the ultraviolet-visible absorption curve of the detection solution after color development, and removing H from the probe molecules in different solvents⁺The red shift ranges of the front and rear peaks were tabulated.

In the solid chart on the upper right side in FIG. 4, Na added to the probe mother liquor and Na added to the probe mother liquor are shown₃PO₄The color development result of the aqueous solution shows that the color of the two glass bottles of the DMI is not obviously changed; the right sides of two glass bottles of DMF are light red, and the left sides are not discolored; no significant discoloration of the two glass bottles of THF; the right sides of two glass bottles of DMSO showed light red, and the left sides did not change color; the right sides of the two acetonitrile glass bottles are yellow, and the left sides of the two acetonitrile glass bottles are not discolored; the right sides of the two glass bottles of acetone appeared yellow and the left side did not change color.

In FIG. 4, a at the upper left side represents DMI, b represents THF, c represents acetonitrile, d represents DMF, and e represents DMSO; the probe molecules in DMI and THF did not undergo significant peak position changes, limited by the solubility of the probe molecules. In the remaining four organic solvents, the molecular absorption red-shift range gradually increases with increasing solvent polarity, which is caused by the π π transition of the intramolecular chromophore. Wherein the red shift range of the probe molecules in DMSO and DMF is the largest, and the color development effect is the most obvious.

Example 5

Dissolving the 4 '-p-hydroxyazophenyl-2, 2': 6 '2' -terpyridine probe synthesized in example 1 in DMSO to prepare a light yellow precursor solution with the concentration of 0.015mol/L, then soaking slow qualitative filter paper in the prepared precursor solution, standing and coloring for 15 minutes after the filter paper is completely immersed, taking out and drying to obtain the light yellow pH test paper with uniform coloring. Then, the prepared pH test paper is cut into rectangular fragments with integral size, and NaOH standard aqueous solution with pH of 7-14 is dripped on the test paper. After the test paper is quickly developed, the color change is recorded by photographing, and the color change is used as a standard color comparison card as shown in a in fig. 5. And then, repeatedly detecting standard solutions with the pH values of 12, 12.5, 13, 13.5 and 14 by using the same test paper, flushing the test paper by using water after each color development is finished to restore the original color, recording the color change of the test paper before and after repeated tests, and photographing and comparing the color change as shown in a b in the figure 5.

In fig. 5, a is a uniformly colored pale yellow pH test paper on the left side, a NaOH standard aqueous solution with pH 7 to 14 is added dropwise on the test paper on the right side for color development reaction, the color is gradually deepened from left to right, the color is gradually deepened from pH 7 to light yellow, from pH8 to 11, from pH11 to 11, to dark yellow, from pH 11.4 to 13, to dark brown, from pH 13.5 to 14, to dark brown, and from left to right.

In FIG. 5, b is replaced by the primary color (yellow) of the test paper and the color development (dark brown) of different pH responses from left to right, and the color development gradually deepens with the increase of pH to the deepest pH 14.

Through comparing with standard card paper, the test paper can remain accurate measuring capacity under washing reuse's prerequisite, and in the whole testing process, under the damaged prerequisite of test paper itself is not considered, development speed and accurate degree are not influenced by cycle number basically.

Example 6

The probe stock solution was prepared in the same manner as in example 3.

The test paper itself was also used as a special paper for writing without marks or inks, and the standard solution of pH 13 was prepared in the same manner as in example 5. The standard aqueous solution having a pH of 13 was used as an ink, and characters were written on the filter paper. Standing for a period of time until the solvent is completely volatilized, soaking the filter paper written with characters in the probe mother liquor, and photographing to record the color change of the sample. Meanwhile, the dyed test paper can be used as a substrate, a standard aqueous solution with the pH value of 13 is used as ink, the test paper is repeatedly drawn and written, then the test paper is washed by water, and the color change of the whole circulation process is recorded by photographing.

As shown in fig. 6, the right side of a in fig. 6 is white filter paper, the middle is filter paper before writing, and the filter paper after writing on the right side is put into the light yellow probe mother liquor, and the color development font is dark brown; in fig. 6, b is the replacement of the filter paper with the first to the last probe mother liquor and the written filter paper with the probe mother liquor, and the written filter paper is washed with water to obtain new filter paper, and the color development pattern is dark brown.

As shown in FIG. 6, the probe molecule can be used as a developer for traceless writing and a paper for inkless writing, and the written writing can be removed by washing with water and recycled, thereby having excellent reproducibility.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A compound of formula i, wherein: the structural formula is as follows:

2. a process for the preparation of a compound of formula i as claimed in claim 1, characterized in that:

1) synthesis of 4 '-nitro-2, 2', 6 ', 2' -terpyridine

2) synthesis of 4 '-amino-2, 2', 6 ', 2' -terpyridine

Suspending the 4 '-nitro-2, 2', 6 ', 2' -terpyridine obtained in the step 1) and stannous chloride in concentrated hydrochloric acid for reaction, cooling, performing suction filtration to obtain residual solid powder, adding a sodium bicarbonate aqueous solution, filtering to obtain a solid, and performing column chromatography purification to obtain 4 '-amino-2, 2', 6 ', 2' -terpyridine;

3) synthesis of 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine

Dissolving the 4 '-amino-2, 2', 6 '2' -terpyridine obtained in the step 2) in concentrated hydrochloric acid, placing in an ice bath, and adding NaNO₂Adding into distilled water, dripping into sodium nitrite water solution, adding into mixed water solution B of sodium hydroxide and phenol, filtering, washing, and oven drying to obtain 4 '-p-hydroxyazophenyl-2, 2' -6 '2' -terpyridine.

3. The method of claim 2, wherein: the solvent of the solution A in the step 1) is methanol; the mixture of 2-acetylpyridine and 4-nitrobenzaldehyde is stirred vigorously, and the reaction condition of solution A, potassium hydroxide and ammonia water is room temperature for 3 days.

4. The method of claim 2, wherein: the washing process in the step 1) is to wash with distilled water and cold methanol respectively.

5. The method of claim 2, wherein: the extraction process in the step 1) is to dissolve the washed solid in ethyl acetate and then add sodium bicarbonate water solution.

6. The method of claim 2, wherein: in step 1), drying is performed by using anhydrous sodium sulfate.

7. The method of claim 2, wherein: in the step 2), the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in concentrated hydrochloric acid is 70-90 ℃, and the temperature is cooled to room temperature after the reaction;

adding the solid powder in the step 2) into a sodium bicarbonate solution, and adjusting the pH value to 12-13;

and (3) performing column chromatography on the solid filtered in the step 2) through alkaline alumina, wherein the eluent is a mixture of ethyl acetate and petroleum ether.

8. The method of claim 7, wherein: in the step 2), the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in concentrated hydrochloric acid is 80 ℃.

9. The method of claim 7, wherein: the proportion of ethyl acetate and petroleum ether in the eluent in the step 2) is 1: 1-2: 1.

10. the method of claim 9, wherein: the proportion of ethyl acetate and petroleum ether in the eluent in the step 2) is 1: 1.

11. the method of claim 2, wherein: in the step 3), the 4 '-amino-2, 2', 6 ', 2' -terpyridine is ultrasonically stirred in the process of dissolving in concentrated hydrochloric acid;

dropwise adding a sodium nitrite aqueous solution in the step 3), and reacting in an ice bath for 0.9-1.2 h;

and 3) dropwise adding the mixed aqueous solution B into the mixture in the step 3), reacting in an ice bath for 0.9-1.2h, and reacting at room temperature for 11-13 h.

12. The method of claim 11, wherein: and 3) dropwise adding a sodium nitrite aqueous solution in the step 3), and reacting in an ice bath for 1 h.

13. The method of claim 11, wherein: after the mixed aqueous solution B was added, the mixture was reacted in an ice bath for 1 hour and then at room temperature for 12 hours.

14. The method of claim 2, wherein: in the step 1), the mass fraction of the KOH aqueous solution is 15 percent, and the concentration of the strong ammonia water is 25 to 28 percent;

in the step 1), the ratio of 2-acetylpyridine to 4-nitrobenzaldehyde to the aqueous solution of potassium hydroxide to concentrated ammonia water to methanol is 1g:0.6-0.7g:2-4mL:32-36mL:30-38 mL.

15. The method of claim 14, wherein: the ratio of 2-acetylpyridine, 4-nitrobenzaldehyde, potassium hydroxide aqueous solution, concentrated ammonia water and methanol in the step 1) is 1g:0.634g:3mL:34mL:34 mL.

16. The method of claim 2, wherein: NaHCO in step 2)₃The mass concentration of the aqueous solution was 1%.

17. The method of claim 2, wherein: in the step 2), 4 '-nitro-2, 2', 6 '2' -terpyridine and SnCl₂The ratio of concentrated HCl was 1g: 3-4 g: 24-28 mL;

in the step 2), the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in concentrated hydrochloric acid is 70-90 ℃ for 7-9 h;

adding NaHCO into the step 2)₃Adjusting pH to 12-13.

18. The method of claim 17, wherein: in the step 2), 4 '-nitro-2, 2', 6 '2' -terpyridine and SnCl₂The ratio of concentrated HCl was 1g: 3.3 g: 26 mL.

19. The method of claim 17, wherein: in the step 2), the reaction temperature of the 4 '-nitro-2, 2', 6 '2' -terpyridine and stannous chloride in concentrated hydrochloric acid is 80 ℃ and the time is 8 hours.

20. The method of claim 2, wherein: in the step 3), 4 '-amino-2, 2', 6 '2' -terpyridine, concentrated hydrochloric acid and NaNO are added₂And distilled water: NaOH: the ratio of phenol was 380-420 mg: 1mL of: 85-87 mg: 4mL of: 320-360 mg: 110-120 mg.

21. The method of claim 20, wherein: in the step 3), 4 '-amino-2, 2', 6 '2' -terpyridine, concentrated hydrochloric acid and NaNO are added₂And distilled water: NaOH: the ratio of phenol was 400 g: 1mL of: 85.18 mg: 4mL of: 340 mg: 116.2 mg.

22. The use of 4 ' -p-hydroxyazophenyl-2, 2 ' -6 ' 2 "-terpyridine as probe molecule in pH paper as set forth in claim 1.

23. The alkaline precise pH test paper capable of being repeatedly used by washing is characterized in that: the alkaline precision pH test paper is obtained by using the 4 '-p-hydroxyazophenyl-2, 2' 6 '2' -terpyridine as the probe molecule in the claim 1 and loading the probe molecule onto qualitative filter paper.

24. The method of preparing alkaline precision pH paper according to claim 23, characterized in that: dissolving 4 '-p-hydroxyazophenyl-2, 2', 6 '2' -terpyridine probe molecule in organic solvent to obtain mixed solution C, adding qualitative filter paper, and drying to obtain the alkaline precise pH test paper.

25. The method of preparing an alkaline precision pH paper according to claim 24, characterized in that:

the concentration of the mixed solution C is 0.015-0.020 mol/L;

the organic solvent is dimethyl sulfoxide or N, N-dimethylformamide;

soaking qualitative filter paper in the mixed solution C for 15-30min at 20-30 deg.C.