CN102795976A - Method for preparing diethoxymethane by using active carbon supported solid acid catalyst - Google Patents

Abstract

The invention relates to a method for preparing diethoxymethane with an activated carbon-supported acid catalyst, which is characterized in that formaldehyde and ethanol are used as raw materials, and the reaction pressure is carried out under the action of a solid acid catalyst, the reaction temperature is 70-100°C, and the reflux ratio is controlled to be 1: 1 ~ 4: 1, collect the 74 ~ 76 ℃ distillate at the top of the tower to obtain diethoxymethane product; after filtering out the aqueous solution of the tower kettle, the solid acid catalyst is left in the kettle for recycling; the formaldehyde and ethanol The molar ratio is 1:2 to 1:5, the raw material formaldehyde is formaldehyde solution with a concentration greater than 37% by weight, the raw material ethanol is absolute ethanol or an ethanol solution with a concentration of 75 to 95% by weight; the solid acid catalyst is activated carbon immobilized acid Catalyst, the active component acid is sulfuric acid, the acid solid loading is 15-25% by mass; the amount of the solid acid catalyst is 0.3-10% of the total mass of reactants. The invention has the advantages of economical catalyst preparation, easy separation from products, low corrosion to equipment, and easy recovery and treatment of spent catalysts.

Description

Method for preparing diethoxymethane with an activated carbon immobilized acid catalyst

technical field

The invention relates to a method for preparing diethoxymethane with an activated carbon-supported acid catalyst; diethoxymethane is also called formaldehyde diethyl acetal, and its structural formula is: CH ₃ CH ₂ OCH ₂ O CH ₂ CH ₃ ; it belongs to the technical field of organic chemical industry .

Background technique

Diethoxymethane is a colorless and transparent liquid with a molecular formula of C ₅ H ₁₂ O ₂ , a molecular weight of 104.15, a pure product with a boiling point of 88°C, a melting point of -66.50°C, and a solubility in water of 9% (wt) at 20°C. It can be used in organic synthesis and extraction, dilution, recrystallization and other solvents.

As a solvent in organic synthesis, diethoxymethane is an aprotic solvent with a low affinity for water, which is insoluble in water and non-hygroscopic, so it can be directly used in some water-sensitive solvents without further drying. Sensitive reactions such as organometallic reactions; diethoxymethane has low viscosity, and it can be used in low-temperature reactions and other high-viscosity reactions to simplify post-reaction treatment. For example, in the reduction reaction of lithium aluminum hydride, use diethoxymethane Diethoxymethane is used as a solvent, the post-treatment is simple, and the product has high purity; diethoxymethane is stable to alkali and can be used in different reactions under strong alkali conditions. Other familiar reactions can use diethoxymethane as a solvent, such as alkylation, acylation, organolithium reaction, Grignard reaction and oxidation reaction.

Diethoxymethane is used as fuel and other additives and reaction reagents. As an ethoxymethylation reagent, an equivalent of formaldehyde, a substrate for carbonylation reactions, for the preparation of phenylglycine derivatives and other amino acids, as a source of ethanol for the preparation of ethers and esters, etc.

The main preparation methods of diethoxymethane are: dichloromethane method, dimethyl sulfoxide method, calcium chloride method, acetal method of formaldehyde and ethanol, chloramphenicol by-product method, etc.

The dichloromethane method is an earlier method for the synthesis of diethoxymethane. The reaction not only requires sodium ethoxide as a reagent, but also requires anhydrous operation. In addition, the yield is low, so it is a method that has been eliminated.

Dimethyl sulfoxide is unstable to acid and decomposed by heating to generate formaldehyde, which undergoes addition reaction with ethanol to obtain diethoxymethane. This reaction produces SO ₂ as a by-product, which pollutes the environment and is not conducive to large-scale production.

The acetal method is formed by the reaction of formaldehyde and ethanol under the action of an acid catalyst. The operation is simple, the reaction time is short, and the yield is high. It is an ideal preparation method and is also the method that researchers are most concerned about at present.

In the production process of chloramphenicol, it is generated from the urotropine solution of p-nitro-2-bromoacetophenone, and the ethanol solution of hydrochloric acid is added to this solution to obtain the by-product diethoxymethane, many chlorine Mycin manufacturers use this method to obtain diethoxymethane.

At present, the relatively mature aldol condensation method generally adopts three operation modes of intermittent, continuous and catalytic distillation. The classic aldol condensation reaction uses inorganic acid (such as H ₂ SO ₄ , HF, H ₃ PO ₄ , p-toluenesulfonic acid, etc.) and Lewis acid (such as A1C1 ₃ , FeC1 _{3 ,} etc.) catalysts, which have good catalytic activity , but there are disadvantages such as difficulty in separation and recovery, and serious corrosion of equipment. For this reason, people develop solid acid catalysts, such as cation exchange resins, crystalline aluminosilicates, HZSM-5, H ₄ SiW ₁₂ O ₄₀ /SiO ₂ heteropolyacid catalysts, etc. to replace liquid acids, thus establishing an industrial production A new process of reactive distillation of methylal. In the method of using the catalyst, the catalyst particles can be loosely packed, or the catalyst can be dispersed in the container or reaction tower in the form of slurry, and the catalyst is also filled together with the Raschig ring, and some people put the catalyst in a cloth bag or use stainless steel. Wrapped in silk screen and filled for use.

Contents of the invention

The purpose of the present invention is to provide a method for preparing diethoxymethane which is economical in reaction, easy to separate the catalyst from the product, less corrosive to equipment, and clean.

The technical content of the present invention is: a method for preparing diethoxymethane with an activated carbon immobilized acid catalyst, which is characterized in that formaldehyde and ethanol are used as raw materials in a reaction kettle with a stirrer and a rectifying tower, Under normal reaction pressure, the reaction temperature is 70-100°C, the reflux ratio is controlled at 1:1-4:1, and the fraction at 74-76°C is collected at the top of the tower to obtain the diethoxymethane product; filter out the tower kettle After the aqueous solution, the catalyst is left in the kettle for recycling; the molar ratio of formaldehyde to ethanol is 1:2 to 1:5, the solid acid catalyst is activated carbon immobilized acid catalyst, and the active component acid of activated carbon immobilized acid catalyst is sulfuric acid , the acid solid loading is 15-25% by mass; the amount of solid acid catalyst is 0.3-10% of the total mass of reactants.

Diethoxymethane obtained in the present invention is a crude product, the content of diethoxymethane is about 60% to 70%, and the rest is mainly ethanol and water; wherein diethoxymethane and water can form an azeotrope, and the content of the azeotrope The boiling point is 75.2°C, the water mass content is 10%, diethoxymethane and ethanol can form an azeotrope, the boiling point of the azeotrope is 74.2°C, and the ethanol mass content is 32%. The crude product is refined to remove ethanol and water, and a product with a purity greater than 99% can be obtained.

The invention develops an active carbon immobilized acid catalyst system. The preparation process of this type of catalyst is simple and easy, and the sulfuric acid is converted into an insoluble solid acid through the action of the carbon base. Although this type of catalyst also plays a catalytic role through the proton acid site (-SO ₃ H) on it, but because -SO ₃ H forms a covalent bond with the C bond, it is a hydrophobic material, which can effectively absorb organic molecules without Absorbs water. When water exists, it avoids the problem that proton acid sites are prone to hydration and reduces catalytic activity, and facilitates the contact between reactants and acid sites to promote the reaction.

In the above-mentioned preparation method of diethoxymethane, the activated carbon-immobilized acid catalyst is based on activated carbon and sulfuric acid as a solid load. The preparation process: wash the activated carbon with distilled water, dry it, and activate it at 115-125 ° C for 2 ~ 4 h, weigh a certain amount of pretreated activated carbon and immerse in 25 ~ 30 times the mass concentration of 60 ~ 98% by mass sulfuric acid solution, stir and reflux at 100 ~ 140 ℃ for 3 ~ 5 h, suction filter, wash to medium properties, dried in an oven at 115-125 °C to constant weight, and cooled to obtain an activated carbon-supported acid catalyst. The catalyst has good temperature resistance and is less corrosive to equipment. After the reaction, it can be separated from the product by filtration, and can be recycled to realize clean production.

In the above-mentioned preparation method of diethoxymethane, the suitable reaction temperature for the normal pressure reaction is 70-100°C, the reflux ratio increases correspondingly with the increase of the reaction temperature, and the suitable tower top temperature is 74-76°C; after the reaction is completed, filter, The aqueous solution in the tower kettle is discharged, and the solid acid catalyst is left in the reactor for recycling; the suitable molar ratio of formaldehyde and ethanol is 1:2.2 to 1:4; the suitable molar ratio of formaldehyde and ethanol is 1:2.5 to 1:3; Increasing the amount of ethanol can increase the conversion rate of formaldehyde, thereby increasing the yield of diethoxymethane, but too much ethanol will cause the separation of ethanol and diethoxymethane products; raw ethanol can be absolute ethanol with a concentration of 75 ~95% by mass ethanol solution or 75% to 95% by mass ethanol solution recovered after purification of diethoxymethane; raw formaldehyde can be paraformaldehyde, industrial-grade formaldehyde solution with a concentration greater than 37% by mass, or their compound Formaldehyde with a concentration greater than 37% by mass dissolves.

In the above method for preparing diethoxymethane, the suitable catalyst dosage is 0.5-5% of the total mass of the reactants, and the most suitable catalyst dosage is 1-3% of the total mass of the reactants.

The advantages of the present invention are: using active carbon solid-carrying acid catalyst to synthesize industrial grade diethoxymethane, the solid acid catalyst active carbon carrier is cheap and easy to obtain, the catalyst is economical to prepare, easy to separate from the product, less corrosive to equipment, and waste catalyst It is easy to recycle and handle, and it is a new type of high-efficiency, green and environmentally friendly production method.

specific embodiment

The present invention is further described below by way of examples, but is not limited to the examples given.

The raw materials used in the present invention are industrial grade, and the activated carbon immobilized acid catalyst is self-made. The purity and ethanol content of the product diethoxymethane were analyzed by gas chromatography.

Example 1

Preparation of activated carbon-supported acid catalyst: Wash 50 g of activated carbon with distilled water, dry it, and activate it at 120 ° C for 2 h, weigh 30 g of pretreated activated carbon and immerse it in 20 times the mass concentration of 60 mass % sulfuric acid, and impregnate it at 120 ° C under stirring After 4 hours, filter with suction, wash until neutral, dry in an oven at 120°C to constant weight, and after cooling, obtain 30 g of activated carbon-supported acid catalyst with an acid-fixed capacity of 15% by mass, and set aside.

Example 2

Preparation of activated carbon-supported acid catalyst: Wash 50g of activated carbon with distilled water, dry it, activate it at 120°C for 2h, weigh 40g of pretreated activated carbon and immerse it in 20 times the mass concentration of 98% sulfuric acid, and impregnate it at 120°C under stirring After 4 hours, filter with suction, wash until neutral, dry in an oven at 120°C to constant weight, and obtain 40 g of activated carbon-supported acid catalyst with an acid-fixed capacity of 22% by mass after cooling, and set aside.

Example 3

In a 500ml three-neck flask equipped with a thermometer, a magnetic stirrer, a φ20×700 packed tower and a rectifying head, add 60g of formaldehyde solution with a concentration of 37% by mass, 136g of absolute ethanol, and the activated carbon immobilized _H2SO4 prepared in Example ₁ With 15.7g of catalyst, stir and raise the temperature until the bottom of the tower is in a boiling state. Totally reflux until the temperature at the top of the tower is stable at 74°C. Adjust the reflux ratio to 1:1 to collect fractions with a top temperature of 74-76°C; Increase the reflux ratio, when the top temperature reaches 76°C, increase the reflux ratio to 4:1; when the top temperature is greater than 76°C, control the reflux ratio to 1:1, switch to collect fractions with a top temperature less than 80°C, the reaction is completed, and the temperature is lowered . Collect 99g of diethoxymethane fraction, gas chromatography analysis diethoxymethane purity 57.8%, ethanol content 38.5%; collect ethanol fraction 48.1g, gas chromatography analysis diethoxymethane content 20.4%, ethanol content 79.0% . Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Example 4

In a 500ml three-necked flask equipped with a thermometer, a magnetic stirrer, a φ20×700 packed tower, and a rectifying head, respectively add 40 g of formaldehyde solution with a concentration of 60% by mass, and 154.9 g of ethanol with a concentration of 95% by mass. The activated carbon prepared in Example 2 is immobilized H ₂ SO ₄ catalyst 3.9g, stir and raise the temperature until the bottom of the tower is in a boiling state, fully reflux until the temperature at the top of the tower is stable at 74°C, adjust the reflux ratio to 1:1, collect the fraction with a top temperature of 74-76°C; As the temperature rises, gradually increase the reflux ratio. When the top temperature reaches 76°C, the reflux ratio increases to 4:1; After the reaction is over, the temperature is lowered. 103.6g of diethoxymethane fraction was collected, and the purity of diethoxymethane was analyzed by gas chromatography to be 62.1%, and the ethanol content was 37.6%. %. Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Example 5

In a 500ml three-necked flask equipped with a thermometer, a magnetic stirrer, a φ20×700 packed tower, and a rectifying head, add a concentration of 50% by mass formaldehyde solution 60g, a concentration of 95% by mass ethanol 121g, and the activated carbon immobilized H prepared in Example 2. ₂ SO ₄ catalyst 7.2g, stir and raise the temperature until the bottom of the tower is in a boiling state, total reflux until the top temperature is stable at 74°C, adjust the reflux ratio to 1:1, collect the fraction with a top temperature of 74-76°C; When the top temperature reaches 76°C, the reflux ratio is increased to 4:1; when the top temperature is greater than 76°C, the reflux ratio is controlled to 1:1, and the fraction with a top temperature less than 80°C is collected by switching to react. End, cool down. Diethoxymethane fraction 124.4g was collected, gas chromatography analysis of diethoxymethane purity 69.1%, ethanol content 30.6%; ethanol fraction collection 3.8g, gas chromatography analysis diethoxymethane content 31.1%, ethanol content 68.5% %. Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Example 6

In a 500ml three-necked flask equipped with a thermometer, a magnetic stirrer, a φ20×700 packed tower, and a rectifying head, 70g of formaldehyde solution with a concentration of 37% by mass, 119g of absolute ethanol, and activated carbon immobilized _H2SO4 prepared in Example ₂ were respectively added. Catalyst 9.4g, stir and heat up until the tower kettle is in a boiling state, total reflux until the tower top temperature is stable at 74°C, adjust the reflux ratio to 1:1, collect the fraction with a top temperature of 74-76°C; Increase the reflux ratio, when the top temperature reaches 76°C, increase the reflux ratio to 4:1; when the top temperature is greater than 76°C, control the reflux ratio to 1:1, switch to collect fractions with a top temperature less than 80°C, the reaction is completed, and the temperature is lowered . 108.7g of diethoxymethane fractions were collected, gas chromatography analysis of diethoxymethane purity 72.3%, ethanol content 26.5%; collection of ethanol fraction 16.5g, gas chromatography analysis of diethoxymethane content 46.2%, ethanol content 53.3% %. Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Example 7

In a 500ml three-necked flask equipped with a thermometer, a magnetic stirrer, a φ20×700 packed tower and a rectifying head, add 22g of paraformaldehyde and 170.9g of ethanol at a concentration of 75% by mass. The activated carbon prepared in Example 2 is immobilized with H ₂ SO ₄ Catalyst 11.6g, stir and heat up until the tower kettle is in a boiling state, total reflux until the tower top temperature is stable at 74°C, adjust the reflux ratio to 1:1, collect the fraction with a top temperature of 74-76°C; Increase the reflux ratio, when the top temperature reaches 76°C, increase the reflux ratio to 4:1; when the top temperature is greater than 76°C, control the reflux ratio to 1:1, switch to collect fractions with a top temperature less than 80°C, the reaction is completed, and the temperature is lowered . Collect 94g of diethoxymethane fraction, gas chromatography analysis diethoxymethane purity 60.8%, ethanol content 38.6%; collect ethanol fraction 50.5g, gas chromatography analysis diethoxymethane content 19.3%, ethanol content 80.5% . Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Example 8

After the reaction of Example 5, the remaining water in the three-necked flask was separated (activated carbon immobilized _H2SO4 catalyst was left in the bottle), and then 22 g of paraformaldehyde was added, with a concentration of 75% by _mass and 170.9 g of ethanol. Stir and heat up until the tower kettle was boiling When the total reflux reaches the top temperature at 74°C, adjust the reflux ratio to 1:1, and collect fractions with a top temperature of 74-76°C; gradually increase the reflux ratio as the top temperature rises, and when the top temperature reaches 76°C , the reflux ratio is increased to 4:1; when the top temperature is greater than 76°C, control the reflux ratio to 1:1, switch to collect fractions with a top temperature less than 80°C, the reaction is over, and the temperature is lowered. Collect 70.8g of diethoxymethane fraction, gas chromatography analysis diethoxymethane purity 62.8%, ethanol content 36.8%; collect ethanol fraction 74g, gas chromatography analysis diethoxymethane content 29.1%, ethanol content 70.8% . Diethoxymethane with a purity greater than 99% can be obtained by rectifying the crude product.

Claims (4)

1. A method for preparing diethoxymethane with an activated carbon-supported acid catalyst is characterized in that in a reactor with a stirrer and a rectifying tower, formaldehyde and ethanol are raw materials, and the normal reaction pressure is carried out under the action of a solid acid catalyst. , the reaction temperature is 70-100°C, the reflux ratio is controlled at 1:1-4:1, and the fraction at 74-76°C is collected at the top of the tower to obtain diethoxymethane; the molar ratio of formaldehyde to ethanol is 1 : 2～1:5, the raw material formaldehyde is a formaldehyde solution with a concentration greater than 37% by mass, the raw material ethanol is anhydrous ethanol or an ethanol solution with a concentration of 75～95% by mass; the solid acid catalyst is an activated carbon-supported acid catalyst, and the active component The acid is sulfuric acid, and the acid solid loading is 15-25% by mass; the amount of the solid acid catalyst is 0.3-10% of the total mass of the reactants. 2. The method for preparing diethoxymethane according to claim 1, characterized in that the preparation method of the activated carbon-supported acid catalyst is: wash the activated carbon with distilled water, dry it, and activate it at 115-125 °C For 2-4 hours, weigh a certain amount of pretreated activated carbon and immerse it in a sulfuric acid solution with a mass concentration of 25-30 times of 60-98% by mass, reflux and impregnate at 100-140 °C for 3-5 hours under stirring, filter with suction, and wash until Neutral, dry in an oven at 115-125 ℃ to constant weight, and get activated carbon-supported acid catalyst after cooling. 3. The method for preparing diethoxymethane according to claim 1, characterized in that the molar ratio of formaldehyde to ethanol is 1:2.3 to 1:4, and the amount of solid acid catalyst is the total mass of reactants 0.5 to 5% of that. 4. The method for preparing diethoxymethane according to claim 3, characterized in that the molar ratio of formaldehyde to ethanol is 1:2.5 to 1:3, and the amount of solid acid catalyst is the total mass of reactants 1 to 3% of that.