The invention relates to a method for recycling a byproduct, in particular to a method for directionally converting 2,3, 6-trichloro-5-trifluoromethylpyridine into 2-chloro-3-trifluoromethylpyridine.
Although the prior art has various methods for producing 2-chloro-3-trifluoromethylpyridine, the method for directionally converting 2,3, 6-trichloro-5-trifluoromethylpyridine into 2-chloro-3-trifluoromethylpyridine does not take 2,3, 6-trichloro-5-trifluoromethylpyridine as a raw material.
EP and WO still use 3-methylpyridine as raw material, and a series of products such as 2-chloro-3-trifluoromethylpyridine are synthesized by using aluminum fluoride as catalyst at the temperature of 200-400 ' and under the action of chlorine and hydrofluoric acid, and the general situation is similar to CN .
CN introduces a method for synthesizing 2-chloro-3-trifluoromethylpyridine at high temperature by using gaseous 3-methylpyridine and cobalt chloride as catalysts through chlorination of chlorine gas, fluorination of hydrofluoric acid and high temperature at 250 '. The method has high reaction temperature, high equipment requirement, no single product and poor selectivity, and the total yield of the useful products, namely the 2-chloro-3-trifluoromethylpyridine and the 2-chloro-5-trifluoromethylpyridine is about 80 percent.
IN describes a method for synthesizing 2-chloro-3-trifluoromethylpyridine by taking nicotinic acid as a raw material, chlorinating with phosphorus pentachloride, fluorinating with hydrofluoric acid to obtain 3-trifluoromethylpyridine, and carrying out a route like CN, WO and US /.
CN, WO and US/ describe processes for obtaining 2-chloro-5-trifluoromethylpyridine and 2-chloro-3-trifluoromethylpyridine from 3-trifluoromethylpyridine by treatment with oxides, phosphorus oxychloride or oxalyl chloride, triethylamine. The method uses peroxide, the extraction and extraction are not easy after the oxide of the 3-trifluoromethyl pyridine is generated, and the economic value of the 2-chloro-5-trifluoromethyl pyridine in the product obtained by the reaction is obviously inferior to that of the 2-chloro-3-trifluoromethyl pyridine.
CN introduces the process of chlorination, desolventizing, crystallization, centrifugation, fluorination and rectification of 2-chloro-3-methylpyridine, and 2-chloro-3-trifluoromethylpyridine is obtained with 84% yield. However, the price of the raw material 2-chloro-3-methylpyridine in the route is high, and the conditions of the fluorination process in the process route are harsh.
CN describes a method for obtaining 2-chloro-3-trifluoromethylpyridine by treating 3-trifluoromethyl-pyridine-2-carboxylic acid in dimethylformamide with azobisisobutyronitrile, triethylamine and sodium chloride, wherein the yield is 65%, the method has low yield, a large amount of solid waste is still generated, and the price of the raw material 3-trifluoromethyl-pyridine-2-carboxylic acid is not very expensive.
2-chloro-3-trifluoromethylpyridine is an important chemical intermediate, and is used for synthesizing herbicide flazasulfuron in the pesticide industry. The prior related production processes mainly comprise the following steps:
The 2,3, 6-trichloro-5-trifluoromethyl pyridine is a main byproduct obtained by over-chlorination in the production process of the 2, 3-dichloro-5-trifluoromethyl pyridine, and has no specific use value in production. In order to solve the solid waste in industrial production, realize resource utilization of the waste in the process of solving the waste and realize better economic benefit and social benefit, a directional conversion process is developed. The process can directionally convert the compound into 2-chloro-3-trifluoromethylpyridine which is an intermediate required in the production of herbicides.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a resource utilization scheme for directionally converting 2,3, 6-trichloro-5-trifluoromethylpyridine.
A process for producing 2-chloro-3-trifluoromethylpyridine from 2,3, 6-trichloro-5-trifluoromethylpyridine, comprising the steps of:
(1) in a lower aliphatic alcohol solvent, 2,3, 6-trichloro-5-trifluoromethylpyridine is converted into 2, 5-dichloro-3-trifluoromethylpyridine through selective reductive dechlorination;
(2)2, 5-dichloro-3-trifluoromethylpyridine reacts with lower fatty alcohol sodium to generate 2-alkoxy-5-chloro-3-trifluoromethylpyridine;
(3) 2-alkoxy-5-chloro-3-trifluoromethylpyridine is subjected to catalytic hydrogenation reduction to remove chlorine element, so as to obtain 2-alkoxy-3-trifluoromethylpyridine;
(4) 2-alkoxy-3-trifluoromethyl pyridine and hydrochloric acid with certain concentration are subjected to azeotropic reflux hydrolysis to obtain 2-hydroxy-3-trifluoromethyl pyridine;
(5) the 2-hydroxy-3-trifluoromethyl pyridine is chloridized to obtain the 2-chloro-3-trifluoromethyl pyridine.
Further, the lower aliphatic alcohol in the step (1) is selected from one or two or more of chain alcohol or cyclic alcohol containing 1-6 carbon atoms, and the using amount of the lower aliphatic alcohol is 1-4 times of the mass of the 2, 5-dichloro-3-trifluoromethylpyridine.
Further, the selective reduction method described in step (1) is divided into a direct method and an indirect method: wherein, the direct mode is that hydrogen gas released by the reaction of metal and acidic substances is utilized to reduce chlorine at the No. 2 position in the raw material 2,3, 6-trichloro-5-trifluoromethylpyridine to obtain 2, 5-dichloro-3-trifluoromethylpyridine; indirect way is to react 2,3, 6-trichloro-5-trifluoromethylpyridine with hydrazine in the presence of weak acid alkali metal salt, and then to obtain 2, 5-dichloro-3-trifluoromethylpyridine by sodium hypochlorite treatment under alkaline condition.
Further, in the selective reduction method described in step (1), the metals used in the direct method are mainly the cheap metals which are listed in the common metal activity order table and are listed in front of hydrogen and behind sodium, including but not limited to Mg, Al, Mn, Zn, Cr, Fe, Co, Ni, Sn, etc., and may be one kind, or two or more kinds, and the metals are preferably present in powder state; the acid used is mainly a common protonic acid, including but not limited to hydrochloric acid, sulfuric acid, acetic acid, propionic acid, phosphoric acid, nitric acid, p-toluenesulfonic acid and the like, and may be one or two or more, preferably acetic acid; wherein, the actual consumption molar equivalent number of the metal is 2-4 times of the theoretical consumption of the 2,3, 6-trichloro-5-trifluoromethyl pyridine which is used as the raw material and is determined by a reaction equation; the actual number of molar equivalents of acid consumed, which is 3 to 6 times the theoretical amount of consumption, is determined by the reaction equation, based on the total reaction of the starting 2,3, 6-trichloro-5-trifluoromethylpyridine.
Further, in the direct selective reduction method in the step (1), the reaction temperature is 20-65 ', preferably 35-55 '.
Further, in the indirect selective reduction method described in step (1), the weak acid alkali metal salt includes, but is not limited to, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium acetate, potassium acetate, etc., and may be one, or two or more, and the amount is 1.05 to 1.5 times, preferably 1.2 to 1.3 times, the theoretical consumption molar amount of the raw material 2,3, 6-trichloro-5-trifluoromethylpyridine; the hydrazine used may be an aqueous hydrazine, an anhydrous hydrazine, or a hydrochloride or sulfate salt of hydrazine, and when a hydrochloride or sulfate salt is used, the amount of the weak acid alkali metal salt to be used is adjusted in accordance with the molar equivalent in the neutralization reaction, and the number of molar equivalents of hydrazine to be used is 1.05 to 1.50 times, preferably 1.15 to 1.25 times that of 2,3, 6-trichloro-5-trifluoromethylpyridine.
Further, after the direct selective reduction in the step (1), filtering off redundant metal from the reaction solution, evaporating the solvent under normal pressure or reduced pressure for reuse, adding water for direct steam distillation to separate unreacted raw materials of 2,3, 6-trichloro-5-trifluoromethylpyridine and the intermediate 2, 5-dichloro-3-trifluoromethylpyridine, and reusing the raw materials.
Further, in the direct selective reduction reaction in the step (1), the reaction process is tracked, the raw material conversion rate is controlled to be 33% -40%, and too high raw material conversion rate brings too many byproducts.
Further, in the indirect selective reduction reaction in the step (1), when the 2-hydrazino-3, 6-dichloro-5-trifluoromethylpyridine is synthesized, hydrazine is dropwise added into the 2,3, 6-trichloro-5-trifluoromethylpyridine solution at 0-30 ', the temperature is gradually increased to 50-70 ', and the temperature is kept for 4-12 hours, so that the reaction is completely promoted.
Further, in the indirect selective reduction reaction in the step (1), after the synthesis of 2-hydrazino-3, 6-dichloro-5-trifluoromethylpyridine is completed, the solvent is distilled off, the temperature is reduced to 20-30 ', common halogenated aliphatic hydrocarbon is added as the solvent, the 2-hydrazino-3, 6-dichloro-5-trifluoromethylpyridine is stirred and dissolved, the filtrate is filtered, the residual acid substances and a small amount of salt are removed by washing, the filtrate is directly used as the reaction raw material to carry out the next step of oxidative hydrazine removal reaction to obtain the 2, 5-dichloro-3-trifluoromethylpyridine, preferably the halogenated aliphatic hydrocarbon dichloromethane and dichloroethane, the added solvent amount is 4-10 times of the theoretical mass of the 2-hydrazino-3, 6-dichloro-5-trifluoromethylpyridine, preferably 7-9 times.
Further, in the indirect selective reduction reaction and the hydrazine removal reaction in the step (1), under an alkaline condition, hypochlorite, preferably sodium hypochlorite, is used as an oxidant to remove hydrazino groups to obtain 2, 5-dichloro-3-trifluoromethylpyridine; the alkali used, mainly alkali metal hydroxide, preferably sodium hydroxide, is added in a concentration of 0.5-2mol/L, preferably 1.0mol/L, in a number of molar equivalents of 1.1-1.5 times, preferably 1.2-1.3 times; adding sodium hypochlorite with concentration of 10% effective chlorine, and adding molar equivalent amount of 1.05-1.2 times, preferably 1.05-1.10 times; the reaction temperature is 0-40 deg.C, preferably 15-30 deg.C.
Further, in the indirect selective reduction reaction in the step (1), after the hydrazine removal reaction is finished, adding common protonic acid, preferably hydrochloric acid, adjusting the pH value to 3-4, changing the dark brown color of the system into reddish brown, separating, concentrating, and distilling to obtain the 2, 5-dichloro-3-trifluoromethylpyridine.
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Further, the lower aliphatic alcohol in the step (2) is selected from one or two or more of chain alcohols or cyclic alcohols containing 1-6 carbon atoms, and the dosage of the lower aliphatic alcohol is 2-8 times, preferably 3-5 times, of the mass of the 2, 5-dichloro-3-trifluoromethylpyridine, and methanol and ethanol are preferred; the sodium alkoxide is generally added in a manner corresponding to the corresponding alcohol, and is used in an amount of 1.05 to 1.3 times, preferably 1.05 to 1.10 times, the molar amount of 2, 5-dichloro-3-trifluoromethylpyridine, and sodium methoxide and sodium ethoxide are preferred, and sodium alkoxide is preferably added in portions or dropwise to the alcohol solution thereof.
Further, the reaction temperature in the step (2) is 0-80 ', preferably 15-30 ', heat is released when the reaction is added, after the temperature is stable, the temperature is gradually increased to reflux, and the temperature is kept for 3-4 hours, so that the reaction is finished.
Further, after the reaction in the step (2) is completed, the solvent is removed, and the product is purified by steam distillation.
Further, the method for removing chlorine element by catalytic hydrogenation in the step (3) is mainly characterized in that under the existence of an acid binding agent, metal catalysts such as nickel, palladium, platinum, iridium, ruthenium and the like are used, and chlorine atoms on the 2-alkoxy-5-chlorine-3-trifluoromethyl pyridine are removed by catalytic reduction under certain hydrogen pressure.
Further, the catalytic hydrogenation catalyst in the step (3) is mainly nickel, palladium, platinum, iridium, ruthenium, etc., and may be one kind, or two or more kinds, and may be supported on an inert substrate, or may be a powdered active metal, preferably palladium, and preferably palladium supported on activated carbon.
The adopted load materials include but are not limited to activated carbon, diatomite, ZSM-5 molecular sieve, magnesia, titanium dioxide, alumina and other inert materials which do not participate in catalytic hydrogenation reaction;
the percentage of the loaded active ingredient is 0.1 to 10 percent, preferably 3.0 to 7.0 percent and more preferably 5 percent;
the water content of the supported catalyst is 1.0-70.0%;
further, the step (3) is characterized in that the reaction is carried out in a slurry bed reactor.
Further, the method is characterized in that the reaction conditions of the method are as follows: the reaction temperature is-10 ' to 65 ', the reaction pressure is 0.1MPa to 2.0MPa, the mass fraction of the added catalyst is 0.1 percent to 3.5 percent according to the weight of the 2-alkoxy-5-chloro-3-trifluoromethyl pyridine, the reaction time is 4 to 24 hours, preferably 45 to 60 ', the mass fraction of the catalyst is 1.0 to 2.0 percent, preferably 8 to 12 hours, and the preferred pressure is 0.1 to 0.2 MPa.
Further, the step (3) is characterized in that the acid-binding agent is one or more of sodium carbonate, potassium carbonate, triethylamine, sodium formate, ammonium formate, magnesium oxide, magnesium hydroxide and the like, preferably sodium carbonate and potassium carbonate; the solvent is one or more of methanol, ethanol, propanol, and isopropanol, preferably methanol and ethanol.
Further, in the step (3), the number of molar equivalents of sodium carbonate and potassium carbonate used as acid-binding agents is 1.2 to 3.0 times, preferably 1.4 to 1.6 times, relative to 2-alkoxy-5-chloro-3-trifluoromethylpyridine.
Further, in the step (3), the mass of methanol or ethanol to be used is 2 to 5 times, preferably 3 to 4 times, the mass of 2-alkoxy-5-chloro-3-trifluoromethylpyridine.
Further, the mass fraction of the hydrochloric acid in the step (4) is 30%, the number of the added molar equivalents is 2-3 times that of the 2-alkoxy-3-trifluoromethylpyridine, the reaction temperature is preferably weak reflux, and the reaction temperature is preferably 85-90 '.
Further, in the chlorination method described in the step (5), the chlorinating agent mainly used includes triphosgene, oxalyl chloride, phosphorus trichloride, phosphorus oxychloride, phosphorus pentachloride, silicon tetrachloride, tin tetrachloride, chlorine gas, and the like, and preferably, phosphorus oxychloride.
Further, the chlorination reaction temperature in the step (5) is 80-105 ', preferably 105 ' (reflux temperature).
The process of the present invention is further illustrated.
The resource utilization scheme of the 2,3, 6-trichloro-5-trifluoromethyl pyridine byproduct is characterized by comprising the following steps of:
(1) in a lower aliphatic alcohol solvent, 2,3, 6-trichloro-5-trifluoromethyl pyridine is converted into 2, 5-dichloro-3-trifluoromethyl pyridine through selective reduction dechlorination, and an intermediate product is purified through steam rectification;
(2) heating and refluxing 2, 5-dichloro-3-trifluoromethylpyridine in lower aliphatic alcohol to react with lower aliphatic alcohol sodium to generate 2-alkoxy-5-chloro-3-trifluoromethylpyridine, desolventizing, and purifying by steam distillation;
(3) 2-alkoxy-5-chloro-3-trifluoromethylpyridine is subjected to catalytic hydrogenation reduction to remove chlorine element, so as to obtain 2-alkoxy-3-trifluoromethylpyridine, and after the reaction is finished, the 2-alkoxy-3-trifluoromethylpyridine is filtered, desolventized, rectified and purified;
(4) 2-alkoxy-3-trifluoromethylpyridine and hydrochloric acid with certain concentration are subjected to azeotropic reflux hydrolysis to obtain 2-hydroxy-3-trifluoromethylpyridine, and after the reaction is finished, the hydrochloric acid is recovered by reduced pressure distillation to obtain white solid 2-hydroxy-3-trifluoromethylpyridine;
(5) heating, refluxing and chlorinating 2-hydroxy-3-trifluoromethylpyridine in phosphorus oxychloride, evaporating the phosphorus oxychloride after the reaction is finished, adding water and carrying out steam distillation to obtain the 2-chloro-3-trifluoromethylpyridine.
Step (1), in the direct reduction dechlorination, pyridine is used as an internal standard, dynamic changes of raw materials and products are detected and tracked by adopting liquid chromatography, the detection conditions are that the wavelength is 235nm, the flow is 0.8ml/min, and methanol: water 85: 15, adding 0.1% acetic acid into water, and separating by using a common C18 column with specification of 4.6 x 250mm and 5 um; depending on the molar response factors of 2, 5-dichloro-3-trifluoromethylpyridine and 2,3, 6-trichloro-5-trifluoromethylpyridine, it is also possible to simply obtain a ratio of the area of the front peak to the area of the rear peak of 1: 3, as the end point of the reaction control, the reaction selectivity was about 95%.
And (1) in the indirect reduction dechlorination, carrying out two reactions in front and back, and carrying out normalized tracking by using a gas chromatograph.
In the step (2), when sodium alkoxide is just added, the reaction releases more heat, the reaction is preferably carried out at a relatively low temperature, and the temperature can be increased for reflux in the later stage for accelerating the completion of the reaction.
In the step (3), the metal catalyst is used, and the effect is poor when the metal catalyst is reused, and a new catalyst is generally adopted.
In the step (4), 20% hydrochloric acid is added, after distillation under reduced pressure, hydrogen chloride can be introduced to 20% for continuous use, and during azeotropic reflux, the temperature is not too high, preferably weak reflux, or the internal temperature is controlled to be 85-90 '.
The invention has the advantages that: simple process, easy operation, contribution to industrial production, low production cost, high yield which is about 80 percent in total and 99 percent in purity.
The reaction principle is as follows:
physical properties of 2-chloro-3-trifluoromethylpyridine:
the molecular formula is as follows: C6H3ClF3N
Molecular weight: 181.54
Density: 1.416g/ml 25 deg.C
Boiling point: 166 ' 168-
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