2,5-Dihydroxybenzaldehyde is an organic compound with the molecular formula C7H6O3 and CAS 1194-98-5. It is a light yellow crystalline form, usually present in powder or crystal form, with a special aldehyde taste, similar to the odor of bitter almonds. During the melting process, it will gradually turn yellow and sublimate at high temperatures. It can be soluble in water, but its solubility is not high. It is also slightly soluble in organic solvents such as alcohols and ethers. This compound consists of a benzene ring, an aldehyde group, and a hydroxyl group. Among them, the aldehyde group is located at the adjacent position of the benzene ring, and both hydroxyl groups are located at the intermediate position of the benzene ring. It is a reducing compound that can react with alkali to generate corresponding phenolic salts. It can undergo benzoin condensation reaction with acetaldehyde under acidic conditions, producing benzoic acid.
Method 1:
Preparation by phenol oxidation: Phenol can be oxidized to benzoquinone under alkaline conditions, and then undergoes Diels Alder reaction with ethyl acetate to obtain 2,5-dihydroxybenzoate ethyl ester. Finally, 2,5-Dihydroxybenzaldehyde is obtained through acidic hydrolysis.
The detailed steps for preparing 2,5-Dihydroxybenzaldehyde through phenol oxidation are as follows:
1. Add phenol and ethyl acetate to a round bottomed flask, stir and slowly add potassium permanganate, and add sulfuric acid dropwise. At this time, the temperature inside the flask will rise. Potassium permanganate reacts with phenol to produce potassium benzoate and manganese dioxide.
2. Add an appropriate amount of sodium hydroxide solution to neutralize excess potassium permanganate and sulfuric acid, so that the pH value of the solution reaches neutrality.
3. Cool the reaction solution to room temperature, then filter to remove the generated manganese dioxide precipitate.
4. Wash the upper organic layer with ethyl acetate in a separating funnel to remove unreacted phenol and ethyl acetate, then add an appropriate amount of hydrochloric acid to make the solution pH acidic.
5. Heat the reaction solution to reflux state, allowing the generated ethyl benzoate to undergo hydrolysis reaction under the action of hydrochloric acid to produce 2,5-dihydroxyethyl benzoate.
6. Cool the reaction solution to room temperature, then filter to remove the generated sodium chloride precipitate.
7. Wash the upper organic layer with ethyl acetate in a separating funnel to remove unreacted hydrochloric acid, and then perform column chromatography to separate and purify the product 2,5-Dihydroxybenzaldehyde.
C6H5OH + KMnO4 + H24 → C6H5COOK + MnSO4 + H2O
C6H5COOK + NaOH → C6H5COONa + KOH
C6H5COONa + HCl → C6H5COOH + NaCl
C6H5COOH + CH32H5 → C6H53 + H2O
C6H53 + H2O → C6H53 + HCl
C6H53 → C6H5(OH)CHO + CH3
C6H5(OH)CHO + H2O → C6H5(OH)COOH + HCl
In the above synthesis method, the first step is to generate potassium benzoate through the oxidation reaction of phenol and potassium permanganate under the action of sulfuric acid; The second step is to neutralize excess potassium permanganate and sulfuric acid by adding sodium hydroxide solution; The third step is to hydrolyze the generated ethyl benzoate by adding hydrochloric acid; The fourth step is to separate and purify the product 2,5-Dihydroxybenzaldehyde through column chromatography.
Method 2:
Preparation through condensation reaction of phenol and formaldehyde: Phenol and formaldehyde can undergo condensation reaction to form phenolic resin under alkaline conditions. By controlling the reaction conditions and the use of catalysts, high-purity 2,5-Dihydroxybenzaldehyde can be prepared.
The detailed steps for preparing 2,5-Dihydroxybenzaldehyde through the condensation reaction of phenol and formaldehyde are as follows:
1. Add phenol and formaldehyde to a round bottomed flask, then add an appropriate amount of sodium hydroxide solution, stir and slowly heat the reaction solution to reflux state. At this time, phenol and formaldehyde undergo condensation reaction under alkaline conditions to produce 2,5-dihydroxybenzaldehyde.
2. After the reaction is completed, cool the reaction solution to room temperature, and then add an appropriate amount of concentrated hydrochloric acid to make the pH value of the solution acidic.
3. Wash the upper organic layer with sodium carbonate solution in a separating funnel to remove unreacted phenol and formaldehyde, and then perform column chromatography to separate and purify the product 2,5-Dihydroxybenzaldehyde.
C6H5OH + HCHO → C6H5
C6H5(OH)CHO + HCl → C6H5(OH)COOH + HCl
In the above synthesis method, the first step is to generate 2,5-dihydroxybenzaldehyde through a condensation reaction between phenol and formaldehyde under alkaline conditions; The second step is to undergo an acidolysis reaction of the generated 2,5-dihydroxybenzaldehyde by adding concentrated hydrochloric acid to generate 2,5-dihydroxybenzaldehyde.
Method 3:
Preparation through condensation reaction of formic acid and phenol: Under acidic conditions, formic acid and phenol can undergo condensation reaction to produce benzoic acid. Then benzoic acid can be reduced to obtain 2,5-dihydroxybenzyl alcohol. Finally, 2,5-dihydroxybenzyl alcohol is oxidized to 2,5-dihydroxybenzaldehyde through an oxidation reaction.
1. Reaction preparation: Add an appropriate amount of formic acid and phenol to a round bottomed flask and ensure that they have good solubility in the solvent. Suitable solvents, such as ethanol or ether, can be selected to fully dissolve the reactants.
2. Condensation reaction: Slowly add an appropriate amount of sodium hydroxide solution while stirring. At this point, formic acid and phenol undergo condensation reaction under alkaline conditions. As this reaction is an exothermic reaction, it is necessary to control the reaction temperature to avoid local overheating. Keep the reaction solution at an appropriate temperature for condensation reaction until the reaction is complete.
3. Acid hydrolysis: After the condensation reaction is completed, cool the reaction solution to room temperature. Then slowly add an appropriate amount of concentrated hydrochloric acid to make the pH of the solution acidic. Under acidic conditions, the generated 2,5-dihydroxybenzoic acid undergoes a hydrolysis reaction, producing 2,5-dihydroxybenzaldehyde. Keep the reaction solution under acidic conditions for hydrolysis reaction until the reaction is complete.
4. Separation and purification: After the hydrolysis reaction is completed, cool the reaction solution to room temperature. Then, column chromatography was performed to separate and purify the product 2,5-Dihydroxybenzaldehyde. The specific chromatographic separation steps may vary depending on experimental conditions, but typically include pouring the reaction solution into a column chromatography device, selecting a suitable eluent for elution, collecting the eluent and evaporating it for concentration.
5. Post treatment: The concentrated solution is vacuum evaporated using a rotary evaporator or other evaporation equipment to obtain high-purity 2,5-Dihydroxybenzaldehyde. If further purification is required, column chromatography can be performed again or other purification methods can be used.
Formic acid and phenol undergo condensation reaction under alkaline conditions to produce 2,5-dihydroxybenzoic acid:
HCOOH + C6H56H5 + H2O
Under acidic conditions, 2,5-dihydroxybenzoic acid undergoes a hydrolysis reaction to produce 2,5-Dihydroxybenzaldehyde and water:
6H5 + HCl → C6H5(OH)CHO + HCl