Background and overview[1][2][3]
Acetal, also known as acetal, reacts with an equal molecule of anhydrous alcohol under the catalysis of acid to form hemiacetal, which is then dehydrated with another molecule of alcohol to form a stable acetal. The general formula RCH(OR′)2. R and R’ are hydrocarbyl groups. Acetals usually have a pleasant aroma. The boiling point of dimethyl formal CH2(OCH3)2 is 42°C. Diethanol The boiling point of acetal CH3CH(OC2H5)2 is 104°C. Acetals can be regarded as ethers of diols with the same carbon atoms.
Its properties are similar to ether, very stable, not affected by alkali, stable to oxidants, and can be hydrolyzed by water in the presence of acid to return to the original aldehydes and alcohols. Therefore, in organic synthesis, the reaction of forming acetal is used to protect the aldehyde group from destruction in multi-step reactions. The aldehyde group is a very reactive group, especially sensitive to alkali, and is also easily oxidized. However, acetal is stable to oxidants and alkaline conditions, but unstable to acidic conditions. Therefore, in organic synthesis, the method of generating acetal is often used to protect the aldehyde group. A type of compound generated by aldol condensation, acetal in acid It is easily hydrolyzed into the original aldehydes and alcohols under the catalysis.
Acetal is stable to alkali. This property is often used in organic synthesis to protect the carbonyl group. After other reactions are completed, the original carbonyl group can be obtained by treating it with alkali. Hemiacetals are generally unstable and immediately decompose into the original aldehydes and alcohols when the solution is distilled. Some hemiacetals can exist stably, such as ethanol hemiacetal CCl3CH(OH)OC2H5, which has a melting point of 47.5°C and a boiling point of 110°C (741 mmHg). When the mixture of aldehydes and alcohols is catalyzed by acid, the water generated in the reaction is continuously removed to form acetal, which can exist stably and can be distilled.
Methyl is also known as formaldehyde dimethyl acetal. Colorless transparent liquid, molecular weight 76.10, melting point -104.8℃, boiling point 42.3℃, relative density 0.8593 (20/4℃), refractive index 1.3534, flash point -17℃, miscible with alcohol, ether and acetone at 16℃ The solubility in water is 32.3%, the solubility of water in methylal is 4.3%, and it has an odor similar to chloroform. Mainly used in the production of anion exchange resin. It is also used as a solvent and special fuel. It has strong ability to dissolve polytetrafluoroethylene wax powder. However, because its vapor has strong anesthetic properties, it is not suitable for use as a general solvent. Often used as a solvent for special occasions. It is produced by reacting methanol and formaldehyde in a synthesis tower under the catalysis of concentrated sulfuric acid.
Apply[4]
Methyl, also known as dimethoxymethane (DMM), is a colorless, transparent and volatile flammable liquid with a chloroform smell, which is irritating to mucous membranes and has an anesthetic effect. It is relatively stable to alkali and easily decomposes into formaldehyde and methanol when heated with dilute hydrochloric acid. Methyl is mainly derived from natural gas and coal chemical industry. Methyl has excellent physical and chemical properties, that is, good solubility, low boiling point, and good water solubility. It is widely used in cosmetics, medicines, household products, industrial automotive supplies, and pesticides. , leather polish, detergent, rubber industry, paint, ink and other products, it has strong oil staining ability, and its volatile characteristics can replace Freon and chlorine-containing solvents as environmentally friendly products.
1. Use functionalized acidic ionic liquid as a catalyst to react methylal and trimerformaldehyde to synthesize polymethoxymethylacetal under mild reaction conditions. The catalyst used in this method has high activity and high reaction conversion rate; it is easy to operate and has strong controllability; it has good product distribution and high raw material utilization rate.
2. Taking an electronically controlled high-pressure common rail diesel engine as the research object, the combustion characteristics of methylal diesel mixed fuel in four proportions were studied. Through the engine bench test, it was found that without changing the fuel supply system and combustion system of the diesel engine, at the same excess air coefficient and constant rotation speed, after adding methylal, the maximum pressure rise rate increased by 64.3% and the pressure peak advanced; the thermal efficiency increased, The peak heat release rate is advanced; the diffusion combustion period is shortened, the premixed combustion period does not increase significantly, and the combustion duration is shortened. Equivalent fuel consumption is reduced. Adding methylal improves the combustion characteristics of diesel engines;
3. A clean diesel additive polymethoxymethyl. Since the process uses the overhead steam of the dilute aldehyde concentration tower as the heat source for the reboiler of the light removal tower, the product tower uses a tower still reboiler and an intermediate The reboiler uses two different heat sources. It is precisely because of the use of high and low pressure thermal coupled distillation and intermediate reboiler technology that the process energy consumption is very low and the energy utilization is more reasonable; the raw material methanol consumption is low, and the DMM3 in the product -8 has high purity, and no highly toxic extraction agents are introduced in the process. The formaldehyde content in the wastewater complies with environmental emission standards and is suitable for large-scale industrial production.
4. Two Bronsted acidic ionic liquids, N-methyl-2-pyrrolidone hydrogen sulfate ([Hnmp]HSO4) and N-methyl-2-pyrrolidone-p-toluene sulfonate, have been synthesized. acid salt ([Hnmp]PTSA), the catalytic performance of the two ionic liquids in the condensation reaction of methylal and paraformaldehyde to prepare polyoxymethylene dimethyl ether (DMMn, n>1) was studied.
The results show that the acidity of ionic liquid determines its catalytic activity, and ionic liquid [Hnmp]HSO4 has higher catalytic activity; when the dosage of ionic liquid [Hnmp]HSO4 is 2.0wt%, When m methylal/m paraformaldehyde = 2.00, the reaction temperature is 110°C, and the reaction time is 6 hours, the conversion rate of methylal is 52.28%, and the selectivity of DMM3-8 is 49.18%. After the reaction, the ionic liquid [Hnmp]HSO4 and the product automatically separate into two phases with good stability. After being reused five times,Still has high catalytic activity.
5. Use macroporous strongly acidic cation exchange resin (CT175) as a catalyst to catalyze the reaction of methylal and trimerformaldehyde to obtain polyoxymethylene dimethyl ether (P-toluenesulfonic anhydride ODEn). The effects of catalyst type, temperature, time, pressure, catalyst dosage, and raw material ratio on the reaction were investigated, and the reusability performance of the catalyst was studied. When m (methylal): m (triformaldehyde) = 2.5:1, catalyst dosage 7.5wt%, temperature 90°C, time 0.5h, pressure 1.5MPa, the conversion rate of trimerformaldehyde reaches 89.0%, PODE3- The selectivity of 8 is 64.2%. After the catalyst was reused 20 times, there was no significant change in catalytic activity.
HMCM-22 molecular sieve was used to catalyze the synthesis of polymethoxydimethyl ether (DMMn), using methanol, methylal and trimerformaldehyde as raw materials. The effects of molecular sieve channel structure, crystal particle size, acidity and reaction system on the synthesis were investigated. Influenced by the reaction performance of polymethoxydimethyl ether, the selectivity of DMM2~8 is 65.1%; while for the binary reaction of methylal and trimerformaldehyde, the selectivity of DMM2~8 reaches 90.6%. This shows that the weak acidic sites are conducive to the depolymerization of trimerformaldehyde into formaldehyde, the medium and strong acidic sites promote the formation of long-chain molecules, and the strong acidic sites lead to DMM as the main product.
6. Methyl is an ideal fuel and raw material for synthetic diesel additives. Methyl and formaldehyde are used as raw materials, and p-toluenesulfonic acid-modified macroporous cationic resin is used as a catalyst. It is continuously passed through a fixed-bed reactor. The diesel additive polymethoxydimethyl ether was prepared using the feeding method. The reaction temperature, reaction pressure, gravity hourly space velocity, raw material ratio and the effects of different raw materials on the reaction were investigated using chemical titration and GC methods.
Under the conditions of reaction temperature 70°C, reaction pressure 1.5 MPa, gravity hourly space velocity 3 h-1, and raw material ratio n formaldehyde:n methylal=4:1, the conversion rate of DMMn 1 is 60.54%, and the poly The selectivity and yield of methoxydimethyl ether 3-5 were 33.92% and 20.54% respectively. Adding DMMn2 can improve the selectivity and yield of the target product DMMn 3-5.
Preparation[5]
A process for synthesizing methylal. The reaction for synthesizing methylal is carried out in a reactive distillation tower. Methanol vapor and formaldehyde solution enter the reactive distillation tower from the lower and upper parts of the reactive distillation tower respectively. The catalyst Placed on the tray, the formaldehyde solution and methanol vapor react in the reactive distillation tower to generate methylal. The mixed vapor of methylal and methanol enters the distillation tower for fractionation. The temperature at the top of the distillation tower is controlled at 42°C, and the fractionated The methanol solution refluxes to the lower layer of the reactive distillation tower and is heated and recycled. The fractionated methylal enters the condenser and is condensed to obtain the finished methylal product.
Main reference materials
[1] Encyclopedia of Chinese Adult Education·Chemistry·Chemical Engineering
[2] Handbook of Modern Pharmaceutical Terms
[3] Concise Dictionary of Fine Chemicals
[4] Zhou Xinjun. Research progress on the synthesis, purification and application of methylal[J]. Collection, 2017, 9: 003.
[5] Wang Lijun; Wang Jiansheng. A process for synthesizing methylal. CN201010190078.6, application date 2010-06-03
