P-Hydroxybenzaldehyde CAS 123-08-0

It is also divided into Reimer Tiemann reaction; Gattermann reaction; Phenol Trichloroacetaldehyde route; Phenol glyoxylic acid route; Phenol formaldehyde route and other synthetic processes. The phenol process is characterized by easy availability of raw materials, simple manufacturing process, low yield and high cost.

(1) Reimer Tiemann reaction: phenol and chloroform are heated in alkaline aqueous solution, and hydroxybenzaldehyde and o-hydroxybenzaldehyde (commonly known as salicylaldehyde) are generated at the same time. The total yield is about 50%, and the highest yield of hydroxybenzaldehyde is only 17%.

This process is mainly used to synthesize salicylaldehyde and hydroxybenzaldehyde as a by-product, but it is one of the main production methods. The conversion rate of raw materials and product yield of this process are very low, and a large amount of tar is produced. Chloroform must be excessive, unreacted phenol is not easy to recover, and product separation and purification are difficult. Therefore, we must vigorously develop new and efficient catalysts, improve the selectivity of the reaction, and develop simple and efficient product separation and purification methods to reduce the cost and improve the product yield.

(2) Gattermann reacts phenol and HCN. In the presence of AlCl3, dry HCl is introduced to carry out the catalytic reaction, which is decomposed in ice water to obtain hydroxybenzaldehyde. The product yield is high. If zinc cyanide is used instead of HCN, the yield is almost theoretical.

The product selectivity of this process is high, but the disadvantages are as follows: the cyanide is toxic and the operation technology is high; Difficult. Determination 2: due to the use of anhydrous operation, the requirements for reaction equipment are strict; High cost. Disadvantage 3: a small amount of salicylaldehyde is produced, which makes it difficult to separate and purify the product, thus restricting large-scale production.

The process of hydroxybenzaldehyde production by p-nitrotoluene method is divided into oxidation and reduction; Diazotization and hydrolysis were carried out in three steps.

(1) P-nitrotoluene was oxidized and reduced simultaneously with p-nitrotoluene by sodium polysulfide to obtain p-aminobenzaldehyde. The conversion and yield were above 90%. Sodium polysulfide can be sodium hydrosulfide; Caustic soda and sulfur as raw materials.

(2) Diazotization and hydrolysis: treat p-aminobenzaldehyde with sulfuric acid, add sodium nitrite solution, and decompose excess sodium nitrite with a small amount of urea to obtain p-aminobenzaldehyde diazonium salt solution. This solution is hydrolyzed in the presence of sulfuric acid. The product was extracted; Purification; The yield of hydroxybenzaldehyde was over 90%.

The advantages of this process are that the raw materials are cheap, but the disadvantages are that the process route is long, the equipment is huge, the intermediate product is toxic to p-aminobenzaldehyde, the reaction temperature is low, and the freezing conditions are high. At present, the domestic Qixian fine chemical plant uses this process to produce hydroxybenzaldehyde.

The process is to directly oxidize p-cresol with air or oxygen under the action of catalyst to synthesize hydroxybenzaldehyde.

1980s, Japan; U.S.A; Germany and other countries have conducted in-depth research and reported on this process route.

In the late 1980s and early 1990s, Jiangsu Province; Shanghai; Several research and production units in Dalian and other places have also carried out research and development on this process and applied it to industrial production.

The specific process flow is as follows: p-cresol; Sodium hydroxide; Methanol is added to the stainless steel pressure kettle, and after stirring until it is completely dissolved, cobalt acetate is added to seal the reaction kettle, oxygen is introduced into the kettle after heating, and the temperature in the kettle is kept at about 60 ℃. At the end of the reaction, the material is put into the primary autoclave, the solvent methanol is evaporated for recycling, and hydrochloric acid is added for salting out after water is added for dissolution. The solid-liquid material is filtered by a centrifuge, and the obtained solid is put into a vacuum oven and dried at about 60 ℃ for 3-5h to obtain p-hydroxybenzaldehyde with a content of more than 98%.