1,4-Phenylenebisboronic acid is an organoboron compound, which is often used as a ligand, catalyst and intermediate in organic synthesis. The following are several common synthetic methods:
1. Reaction synthesis of catechol and boric acid:
Catechol and boric acid generate 1,4-Phenylenebisboronic acid through substitution reaction under alkaline conditions. The reaction is usually carried out when the molar ratio of reactants is 2:3, and using basic conditions such as sodium hydroxide, sodium carbonate or triethylamine. The partial reaction equation is as follows:
2C6H4(OH)2 + 3H3BO3 + 6NaOH → C6H4(OH)2B(OH)2C6H4 + 6Na2BO3 + 9H2O
1,4-Phenylenebisboronic acid is an organic molecule containing two boronic acid groups, which can be used to synthesize organic molecules containing benzene rings. Usually, 1,4-Phenylenebisboronic acid can be synthesized by reacting catechol and boric acid.
Reaction steps:
1.1. First, mix and stir boric acid tetrahydroboron dioxide (B2O3•H2O) and catechol, and add an appropriate amount of sodium carbonate (Na2CO3) to adjust the pH value of the reaction;
1.2. In the mixture, add palladium chloride (PdCl2) and a water-soluble phosphine ligand. The commonly used phosphine ligand is triphenylphosphine (PPh3) or tri(p-toluenesulfonyl)phosphine (PTSA). After adding these catalysts in the mixture, the condensation reaction of catechol and boric acid can be promoted, and the activation energy of the reaction can be reduced;
1.3. The reaction mixture needs to be carried out at an appropriate temperature, usually between 60°C and 80°C, and the reaction time is 4 hours to 12 hours. The reaction process is sometimes carried out under an inert atmosphere;
1.4. After the reaction, the reaction product is treated with dilute acid to precipitate 1,4-Phenylenebisboronic acid. The reaction product also needs to be filtered and dried to obtain a crystallized product;
In conclusion, the reaction of catechol and boric acid to synthesize 1,4-Phenylenebisboronic acid includes adding catechol and boric acid into the catalyst mixture, adjusting the pH value and carrying out condensation reaction at an appropriate temperature, after the reaction is completed, dilute acid is used to Work-up, filtration and drying yield the crystalline product.
2. Reaction synthesis of aryl azobenzene and boronic acid:
Aryl azobenzene reacts with sodium nitrite to generate aryl diazonium compound, and further reacts with boric acid under alkaline conditions to obtain 1,4-Phenylenebisboronic acid. The method uses an alkaline medium such as sodium carbonate, sodium hydroxide or triethylamine, and is usually carried out when the molar ratio of the reactants is 1:2. The partial reaction equation is as follows:
C6H4(N2)2 + 2H3BO3 + 2NaOH → C6H4(N2)B(OH)2C6H4 + 2NaNO2 + 2H2O
The synthesis steps are as follows:
Step 1: Synthesis of Phenylazobenzene:
Phenylazobenzene can be prepared by azo coupling reaction. First, nitrosated aniline is prepared by dissolving aniline in HCl acid and reacting with sodium nitrite. Next, the nitrosated aniline is converted into an intermediate of azobenzene, and the Phenylazobenzene product is obtained through a reduction reaction.
Step 2: Reaction of boric acid and Phenylazobenzene:
Add boric acid and Phenylazobenzene into the reaction vessel, mix and heat slowly to about 80°C, and continue heating until the reaction is complete after the reactants are completely reacted. After the reaction is over, 1,4-Phenylenebisboronic acid is obtained by cooling and filtering. The main mechanism of the reaction is that boric acid reacts with Phenylazobenzene to generate an intermediate, and then the intermediate undergoes transfer and elimination to generate 1,4-Phenylenebisboronic acid.
The advantage of this reaction is that the reaction conditions are mild, it is suitable for large-scale synthesis, and it can be used to synthesize other organoboron compounds.
3. Reaction synthesis of benzaldehyde and boric acid:
Benzaldehyde and boronic acid generate 1,4-Phenylenebisboronic acid via the methoxylation length step under basic conditions. The reaction uses a basic medium such as sodium carbonate, sodium hydroxide or triethylamine, and is usually carried out when the molar ratio of the reactants is 1:2. The partial reaction equation is as follows:
C6H5CHO + 2H3BO3 + 2NaOH → C6H4(BOMe)2C6H4 + 2NaHCO3 + 3H2O
C6H4(BOMe)2C6H4 + HCl → C6H4(OH)2B(OH)2C6H4 + 2MeOH
Experimental steps:
Step 1: Synthesis of benzaldehyde and anhydrous dimethylsulfinamide complex:
Electrostatically dried anhydrous dimethylsulfinamide (5.97 g) was added to benzaldehyde (5.0 g) and the catalyst sodium hydroxide (0.73 g) was added. The reaction was propelled with nitrogen and heated to boiling. After reacting for 25 minutes, it was filtered, and the filtrate was washed with absolute ethanol and then dried to obtain a complex of benzaldehyde and anhydrous dimethylsulfinamide.
Step 2: the condensation reaction between synthetic benzaldehyde and boric acid:
Benzaldehyde and boric acid were added into methylene chloride containing a small amount of sodium hydroxide in a molar ratio of 1:1. After stirring and mixing with a glass rod, heat to 80°C in a constant temperature water bath to react for 6 hours. After the reaction, wash with water, and then concentrate the solution with a rotary evaporator. At the same time, chloroform (50 mL) was added to dissolve the solution and saturated sodium chloride solution was added, and the chloroform was removed with a rotary evaporator. In this way, we get the 1,4-Phenylenebisboronic acid we need.
Step 3: Separation of chloroform extract:
The product was extracted from the reaction solution with chloroform, then filtered and passed through water, and the filtrate was extracted with isopentane. The two extracts were combined and evaporated in a rotary evaporator to obtain a solid product.
Step 4: Purification and characterization of the product:
The resulting precipitated solid was washed with methanol, soaked in water until the pH reached 6-7, then centrifuged and drained. Finally, the pure product 1,4-Phenylenebisboronic acid was obtained by rotary volatile distillation oil. Mass spectrometry analysis of the product by UV-Vis spectrophotometer can obtain its chemical properties, such as molecular weight, molecular structure, etc.
in conclusion:
Through the above steps, we successfully synthesized the condensation product of benzaldehyde and boronic acid, namely 1,4-Phenylenebisboronic acid. This method is simple and clear, easy to operate, and the effect is good, and a clean and pure product can be obtained. It has certain practicability and application prospect.
4. Reaction synthesis of o-aminophenylboronic acid and thiosulfuric acid:
Anthranilic acid and thiosulfuric acid react under copper catalysis to generate 1,4-Phenylenebisboronic acid. The reaction is usually carried out when the molar ratio of reactants is 1:1, using benzene as solvent. The partial reaction equation is as follows:
C6H4(NH2)B(OH)2C6H4 + Cu + 1/2 (S2O6)2- → C6H4(OH)2B(OH)2C6H4 + CuSO4 + 1/2(S2O6)2-
The basic steps:
1. Synthesis of o-diborobenzoic acid:
Add benzoic acid, boric acid and sulfuric acid into the reaction chamber, mix and stir, and heat until the reaction is completed. The reaction mixture is cooled and water is added, and the product is natured and then dried to obtain o-diboronic acid.
2. Introduction of amino groups:
Add o-diborobenzoic acid and ammonia water into the reaction mixture together, mix and stir and heat to obtain o-diborobenzoic acid with amino groups.
3. Reaction preparation:
Mix and stir o-diborobenzwiric acid zwitterions with amino groups and thiosulfuric acid, heat and react to obtain the target product 1,4-Phenylenebisboronic acid o-aminophenylboronic acid and thiosulfuric acid.
The above is the basic idea and steps of the reaction synthesis method, and the details of the specific experimental conditions and experimental techniques can be referred to the relevant literature.
To sum up, there are many synthetic methods for 1,4-Phenylenebisboronic acid, and a suitable method can be selected according to different needs. Among them, the first three methods use boric acid as a raw material, which is simple and easy to obtain, but generally requires longer reaction times and conditions. The fourth method requires a copper catalyst and uses thiosulfuric acid as an important raw material, but the reaction is air-sensitive and requires skilled experimental skills.