, also known as tetrabromofluorescein, is a common acid-base indicator with sensitive acid-base reaction characteristics. Belonging to organic dyes, the molecular formula is C15H9Br4NO5S, CAS 115-39-9. The chemical structure includes a benzene ring, four bromine atoms, a sulfonic acid group, and a hydroxyl group. Bromophenol blue pH indicator is a dark blue crystal with a high melting point and relative molecular weight. Different colors will appear at different pH values. Under acidic conditions (pH 3.8-5.4), it appears yellow; Under neutral or weakly alkaline conditions (pH 6.5-8.3), it appears green; Under strong alkaline conditions (pH 9-11), it appears dark blue. This color change is the basis for bromo blue as an acid-base indicator. It is a typical acid-base indicator that can react with acid or base to change color.

(: https://www.bloomtechz.com/chemical-reagent/laboratory-reagent/bromophenol-blue-solution-cas-115-39-9.html )

Method 1:

Step 1: Prepare ferrous ion solution. Add an appropriate amount of iron filings or nails to dilute hydrochloric acid, stir until dissolved, and obtain a ferrous ion solution. The chemical equation for this reaction is:

Fe + 2HCl → FeCl₂ + H₂ ↑.

Step 2: Prepare cyanide solution. Add an appropriate amount of sodium cyanide or potassium cyanide to water, stir until dissolved, and obtain a cyanide solution.

Step 3: Prepare Prussian blue. Mix the ferrous ion solution prepared in step one with the cyanide solution prepared in step two and stir evenly. Then add an appropriate amount of dilute sulfuric acid to promote the reaction. The chemical equation for the reaction is:

₂ + 4NaCN + 2H₂₄₆^- + 2NaCl + 4NaHSO₄

Step 4: Post processing. Filter the Prussian blue solution to remove unreacted solid substances. Then rinse the Prussian blue precipitate with a large amount of water to remove excess cyanide and sulfate. Finally, dry the Prussian blue precipitate to obtain the Bromophenol Blue finished product.

Method 2:

Step 1: Prepare a phenol solution. Add an appropriate amount of phenol to water and stir until dissolved to obtain a phenol solution.

Step 2: Prepare a bromine solution. Add an appropriate amount of bromine to water and stir until dissolved to obtain a bromine solution.

Step 3: Prepare Bromophenol Blue. Mix the phenol solution prepared in step one and the bromine solution prepared in step two together and stir evenly. Then add an appropriate amount of sodium hydroxide solution and adjust the pH value of the solution to neutral. The chemical equation for the reaction is:

C₆H₅OH + Br₂ → C₆H₄₂

Step 4: Post processing. Filter the Bromophenol Blue solution to remove unreacted solid substances. Then rinse the Bromophenol Blue precipitate with a large amount of water to remove excess bromine and sodium hydroxide. Finally, dry the Bromophenol Blue precipitate to obtain the finished product.

Method 3:

Step 1: Prepare a phenol solution. Add an appropriate amount of phenol to water and stir until dissolved to obtain a phenol solution.

Step 2: Prepare a bromine solution. Add an appropriate amount of bromine to water and stir until dissolved to obtain a bromine solution.

Step 3: Prepare Bromophenol Blue. Mix the phenol solution prepared in step one and the bromine solution prepared in step two together and stir evenly. Then add an appropriate amount of acid (such as hydrochloric acid or sulfuric acid) and adjust the pH of the solution to neutral.

₆H₅OH + Br₂ → C₆H₄₂.

Step 4: Post processing. Filter the Bromophenol Blue solution to remove unreacted solid substances. Then rinse the Bromophenol Blue precipitate with a large amount of water to remove excess bromine and acid. Finally, dry the Bromophenol Blue precipitate to obtain the finished product.

Method 4:

Step 1: Prepare a phenol solution. Add an appropriate amount of phenol to water and stir until dissolved to obtain a phenol solution.

Step 2: Prepare an oxidant solution. Choose appropriate oxidants, such as potassium chlorate, sodium nitrate, etc. Add an appropriate amount of oxidant to water and stir until dissolved to obtain an oxidant solution.

Step 3: Oxidize phenol. Add the phenol solution prepared in step one to the oxidant solution prepared in step two and stir evenly. React for a certain time at a certain temperature to oxidize phenol into iron (III) ions. The chemical equation for this reaction is:

C₆H₅OH + O₂₃

Step 4: Prepare cyanide solution. Add an appropriate amount of sodium cyanide or potassium cyanide to water, stir until dissolved, and obtain a cyanide solution.

Step 5: Prepare Bromophenol Blue. Mix the iron (III) ion solution generated in step three with the cyanide solution prepared in step four and stir evenly. Then add an appropriate amount of dilute sulfuric acid to promote the reaction. The chemical equation for the reaction is:

₆]₃^- + 2Fe(OH)₃ + 4H⁺₆^4- + 2Fe³⁺ + 4H₂O

Step 6: Post processing. Filter the Bromophenol Blue solution to remove unreacted solid substances. Then rinse the Bromophenol Blue precipitate with a large amount of water to remove excess cyanide and sulfate. Finally, dry the Bromophenol Blue precipitate to obtain the finished product.

Method 5:

Step 1: Prepare a mixed solution of phenol and ferric chloride. Mix an appropriate amount of phenol and ferric chloride together to form a mixed solution.

Step 2: Prepare cyanide solution. Add an appropriate amount of sodium cyanide or potassium cyanide to water, stir until dissolved, and obtain a cyanide solution.

Step 3: Prepare Bromophenol Blue. Mix the mixed solution prepared in step one and the cyanide solution prepared in step two together and stir evenly. Then add an appropriate amount of dilute sulfuric acid to promote the reaction. The chemical equation of the reaction is: [Fe(CN)₆]₃^- + 2Fe(OH)₃ + 4H⁺₆^4- + 2Fe³⁺ + 4H₂

Step 4: Post processing. Filter the Bromophenol Blue solution to remove unreacted solid substances. Then rinse the Bromophenol Blue precipitate with a large amount of water to remove excess cyanide and sulfate. Finally, dry the Bromophenol Blue precipitate to obtain the finished product.