CN109836424B - Method for preparing caffeine by methylation of environment-friendly theophylline sodium salt - Google Patents

Abstract

The present invention is an environment-friendly method for preparing caffeine by methylation of sodium salt of theophylline. The method comprises the following steps: adding theophylline sodium salt, DMC, and methanol to the reaction kettle, and reacting at 100-180° C. under stirring for 1-5 hours; after cooling, it is separated by rotary evaporation, and the obtained solid is crude caffeine . The invention greatly improves the reaction efficiency of the methylation reaction between theophylline sodium salt and DMC, and through simple purification steps, the obtained crude caffeine is purified; the maximum caffeine yield can reach 97.3%.

Description

Method for preparing caffeine by methylation of environment-friendly theophylline sodium salt

The technical field is as follows:

the invention relates to the field of organic synthesis, in particular to a method for synthesizing caffeine.

Background art:

caffeine is a xanthine alkaloid compound, which is 1,3, 7-trimethyl xanthine, white or slightly yellowish green in normal state, mercerized needle-like monohydrate crystal with molecular formula C₈H₁₀N₄O₂·(H₂O), molecular weight 212.2059. Sublimating monohydrated caffeine to obtain hexagonal prismatic anhydrous crystal with molecular formula of C₈H₁₀N₄O₂And the molecular weight is 194.19.

Caffeine is a central nerve stimulant, has a selective excitation effect on cerebral cortex, can temporarily drive drowsiness and restore energy, is clinically used for treating neurasthenia and coma resuscitation, and is also an important antipyretic analgesic.

The caffeine production method mainly includes extraction method, biological synthesis method and chemical synthesis method. Caffeine was first extracted from coffee at 1820 cadaver. butyl. Since the fischer chemical synthesis of caffeine in 1899, the preparation of caffeine by chemical synthesis has become the main source of caffeine.

At present, the synthetic routes of caffeine manufacturers are basically consistent, that is, cyanoacetic acid and dimethyl urea are used as initial raw materials and prepared by multiple reactions such as condensation, cyclization, nitrosation, reduction, phthalylation, methylation and the like, wherein the last step of caffeine synthesis, which is the most critical step, is the methylation reaction of theophylline sodium salt. This step also concerns whether the whole synthetic route has the characteristics of clean production or environmental protection production.

Typical methylating agents such as methyl iodide, dimethyl sulfate, methyl chloride, and the like are mostly limited in production and use due to their toxicity. However, in the prior art, the methylation reagent of caffeine is still dimethyl sulfate (DMS), the amount of wastewater generated by the reaction is large, the wastewater is subjected to very complicated post-treatment before being discharged, and the use of dimethyl sulfate and the carcinogenic byproduct of monomethyl sulfate generated after the reaction are not in line with the development trend of green chemistry and chemical engineering.

The invention content is as follows:

the invention aims to provide an environment-friendly method for preparing caffeine by methylation of theophylline sodium salt, aiming at the defects of the prior art. The method uses methanol as a solvent, does not use any catalyst, adopts a solid-liquid two-phase reaction process method, greatly improves the reaction efficiency of the methylation reaction of theophylline sodium salt and DMC, and purifies the prepared crude caffeine through simple purification steps.

The technical scheme of the invention is as follows:

an environment-friendly method for preparing caffeine by methylation of theophylline sodium salt comprises the following steps:

adding theophylline sodium salt, DMC and methanol into a reaction kettle, and reacting for 1-5 hours at the temperature of 100-180 ℃ under stirring; and cooling to room temperature, and performing rotary evaporation at 50-70 ℃ until the solvent is evaporated to dryness to obtain a solid, namely the crude caffeine.

Wherein the mol ratio is theophylline sodium salt: dimethyl carbonate (DMC) is 1: 1-20.

Wherein 5-30 ml of methanol is added into 0.01mol of theophylline sodium salt. The purification step of the crude caffeine comprises the following steps:

dissolving the obtained crude caffeine in ultrapure water, crystallizing at a low temperature of 0-10 ℃ for 1-3 hours, carrying out suction filtration while the caffeine is cold, putting the obtained solid in a vacuum oven, and carrying out vacuum drying at 60 ℃ for 2-4 hours;

wherein, the mass ratio of the coarse caffeine: the water accounts for 1: 1-10.

The invention has the substantive characteristics that:

in the prior related patents for preparing caffeine by methylation of theophylline sodium salt, catalysts are used, and a common solvent is water, so that the method is complex, difficult to separate and has more byproducts. The method does not use any catalyst, can finish the methylation reaction of theophylline sodium salt by only using organic phase methanol as a solvent, has relatively simple reaction system and method, simpler product separation and higher yield which reaches 97.3 percent.

The invention has the beneficial effects that:

1. the invention does not need any catalyst, thereby greatly reducing the production cost.

2. Both literature reports and actual production processes indicate that the product yield of the DMS process is about 90%. The DMC process of the present application has caffeine yield up to 97.3%, and obviously improves the utilization rate of raw material theophylline sodium salt.

3. The technology adopts a water washing cooling crystallization method to purify the caffeine, and avoids using limited products of chloroform and dichloromethane.

4. Compared with DMS technology, the technology adopts DMC methylation reaction system, and the generated byproduct sodium methoxide can be converted into methanol/water solution of sodium hydroxide in the purification process.

5. In conclusion, compared with the DMS process, the DMC methylation reaction process system has obvious energy-saving and emission-reducing effects.

The specific implementation mode is as follows:

the present invention will be described in detail with reference to examples, which should not be construed as limiting the scope of the invention.

The methylation reaction equation of theophylline sodium salt and DMC is as follows:

example 1

0.01mol of theophylline sodium salt, 0.1mol of DMC and 20ml of methanol are respectively added into a liner with a cover of a 100ml Hastelloy reaction kettle. The reaction was carried out at 160 ℃ for 3 hours under sealed conditions. Cooling to room temperature, and rotationally evaporating the mixture in the kettle at 60 ℃ until the solvent is evaporated to dryness to obtain crude caffeine. A certain amount of sample is taken to prepare a solution, and HPLC detection is used for obtaining the reaction yield of 90.9%.

Example 2

0.01mol of theophylline sodium salt, 0.1mol of DMC and 20ml of methanol are respectively added into a liner with a cover of a 100ml Hastelloy reaction kettle. The reaction was carried out at 160 ℃ for 4 hours under sealed conditions. Cooling, evaporating the solvent to obtain crude caffeine. A certain amount of sample is taken to prepare a solution, and HPLC detection is used for obtaining the reaction yield of 94.0%.

Example 3

0.01mol of theophylline sodium salt, 0.05mol of DMC and 20ml of methanol are respectively added into a liner with a cover of a 100ml Hastelloy reaction kettle. The reaction was carried out at 160 ℃ for 3 hours under sealed conditions. Cooling, evaporating the solvent to obtain crude caffeine. A certain amount of sample is taken to prepare a solution, and HPLC detection is used for obtaining that the reaction yield is 85.4%.

Example 4

0.01mol of theophylline sodium salt, 0.06mol of DMC and 10ml of methanol are respectively added into a liner with a cover of a 100ml Hastelloy reaction kettle. The reaction was carried out at 160 ℃ for 3 hours under sealed conditions. Cooling, evaporating the solvent to obtain crude caffeine. A certain amount of sample is taken to prepare a solution, and HPLC detection is used for obtaining the reaction yield of 97.3%.

Example 5

2g of the crude caffeine obtained in example 4 was put into a 100ml beaker, 20ml of ultrapure water at normal temperature was added, the beaker was put into a 5 ℃ refrigerator, crystallized at low temperature for 1 hour, filtered while cold, and the solid was put into a vacuum oven and vacuum-dried at 60 ℃ for 3 hours. A certain amount of sample is taken to prepare a solution, and the purity of the caffeine is 99.0% by HPLC detection.

The purification mechanism is that caffeine with higher purity is obtained by a method of adding a certain amount of water for cooling crystallization.

Because the crude caffeine contains a certain amount of sodium methoxide which is a byproduct in the process of reaction with water, methanol and sodium hydroxide can be generated, and the caffeine and the sodium hydroxide have different solubilities in water according to the data, the invention adds a certain amount of water into the crude caffeine to cool and crystallize the caffeine, and filters and purifies the caffeine while the caffeine is cold.

Wherein the mass ratio of the crude caffeine to the water is 1: 1-1: 10.

Solubility of pure caffeine and sodium hydroxide in water at various temperatures

The invention is not the best known technology.

Claims (2)

1. An environment-friendly method for preparing caffeine by methylation of theophylline sodium salt is characterized by comprising the following steps:

adding theophylline sodium salt, DMC and methanol into a Hastelloy reaction kettle, and reacting for 3 hours at 160 ℃ under stirring; cooling to room temperature, and performing rotary evaporation at 50-70 ℃ until the solvent is evaporated to dryness to obtain a solid, namely crude caffeine;

wherein the mol ratio is theophylline sodium salt: dimethyl carbonate (DMC) =1: 6; 10ml of methanol was added per 0.01 mole of theophylline sodium salt.

2. The process for preparing caffeine by methylation of sodium salt of theophylline under environment-friendly condition as claimed in claim 1, wherein the purification step of crude caffeine comprises:

dissolving the obtained crude caffeine in ultrapure water, crystallizing at a low temperature of 0-10 ℃ for 1-3 hours, carrying out suction filtration while the caffeine is cold, putting the obtained solid in a vacuum oven, and carrying out vacuum drying at 60 ℃ for 2-4 hours;

wherein, the mass ratio of the coarse caffeine: water =1: 1-10.