CN112645796B - Method for preparing 2, 2-difluoroethanol - Google Patents
Method for preparing 2, 2-difluoroethanol Download PDFInfo
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- CN112645796B CN112645796B CN202011497405.2A CN202011497405A CN112645796B CN 112645796 B CN112645796 B CN 112645796B CN 202011497405 A CN202011497405 A CN 202011497405A CN 112645796 B CN112645796 B CN 112645796B
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Abstract
A process for the preparation of 2, 2-difluoroethanol. The present application provides a process for the preparation of 2, 2-difluoroethanol, the process comprising the steps of: step (i): 2, 2-Difluoroethyl acetate is transesterified in the presence of ethanol and optionally a base.
Description
Technical Field
The present application relates to a process for preparing 2, 2-difluoroethanol, in particular from 2, 2-difluoro-1-chloroethane (1-chloro-2, 2-difluoroethane).
Background
2, 2-difluoroethanol is an important intermediate in the synthesis of agrochemical and pharmaceutical active substances. Various methods are known for the preparation of fluorinated alcohols. Many of these processes are carried out by catalytic hydrogenation or by using reducing agents.
Henne et al, for example in j.am. Chem. Soc.1952,74,1426-1428, describe the reduction of lithium aluminum hydride to form difluoroacetyl chloride in situ, thereby producing difluoroethanol in 69% yield. It is economically disadvantageous to use the expensive hydrogen source in stoichiometric amounts.
Booth et al, tetrahedron 1990,46,2097-2110, describe the reduction of difluoroacetic acid with a boron-dimethylsulfide complex, whereby difluoroethanol is obtained in 55% yield.
EP1820789A1 describes the reduction of fluorinated carboxylic acids, carboxylic acid halides or carboxylic acid esters with hydrogen in the presence of a catalyst. The process described herein is particularly useful for the preparation of difluoroethanol (CF) 2 HCH 2 OH), wherein preference is given to starting from fluorinated esters, in particular from methyl difluoroacetate or ethyl difluoroacetate. The reaction is carried out at elevated pressure and iridium, rhodium or ruthenium on carbon is used as catalyst. The patent describes that the desired difluoroethanol is obtained in 74.4% yield after 18 hours at 40bar by catalytic hydrogenation using Rh/C catalyst starting from methyl difluoroacetate. The disadvantage of this process is that, on the one hand, expensive noble metal catalysts are used, and, on the other hand, the reaction is carried out at high pressure, which leads to the fact that the reaction has to be carried out in special high-pressure apparatuses.
WO2007/071841 for the preparation of difluoroethanol uses the compound CF 2 XC (O) X as starting material for (triple) catalytic hydrogenation, wherein Hal represents Cl, br or iodine (especially chlorodifluoroacetyl chloride). Ruthenium, rhodium, palladium, osmium, iridium and platinum applied to a support are used in particular as catalysts. The support should likewise have the function of a Lewis acid and in particular comprise aluminum ions (for example zeolites or montmorillonites). The reaction can be carried out in the gas phase, preferably at a temperature of from 200 to 300 ℃ and preferably at a hydrogen pressure of from 1 to 5 bar. The reaction can be carried out as wellIn the liquid phase, the reaction temperature is between 40 and 70 ℃ and the hydrogen pressure is preferably between 10 and 20 bar. The reaction in the gas phase proves to be advantageous because it provides better yields of difluoroethanol and higher conversions.
WO2009/040367 describes a process for preparing 2, 2-difluoroethanol. To this end, 1-bromo-2, 2-difluoroethane is prepared in a first stage starting from vinylidene fluoride. In the second stage, the compound is reacted with an oxygen-nucleophile, such as the sodium or potassium salt of acetic or formic acid. WO2009/040367 describes in addition the activation of the bromine atom in 1-bromo-2, 2-difluoroethane by reaction with magnesium, zinc, lithium or copper (especially NaI or KI) prior to reaction with an oxygen-nucleophile.
In particular, WO2009/040367 describes the preparation of difluoroethanol by reacting difluorobromoethane with sodium acetate (sodium salt of acetic acid) in stage 2 in the presence of potassium iodide by heating to 130 ℃ in DMF for 18h, followed by base-catalysed transesterification in the presence of methanol. The difluoroethyl acetate formed here can be first isolated by distillation in an intermediate step or converted directly into difluoroethanol. Starting from difluorobromoethane used, yields are between 56.8 and 87%. The process described herein is complex and relatively expensive and requires many intermediate steps to obtain the desired difluoroethanol. If only stage 2 is performed, expensive difluorobromoethane must be purchased.
Japanese publication JP62-273925A (= JP 1987-273925A) describes the preparation of 2, 2-difluoroethanol starting from 1-chloro-2, 2-difluoroethane with butyrolactone in the presence of water and potassium hydroxide. For this purpose, the reaction mixture was heated in an autoclave at 200 ℃ for 2.5h, whereby 2, 2-difluoroethanol was obtained in a yield of only 48.6% at a conversion of difluorochloroethane of 86%.
Therefore, none of the above-mentioned methods for producing 2, 2-difluoroethanol is optimal. Many of these processes use expensive catalysts and have to be operated under pressure, which is always associated with high complexity in the industry. Other processes (for example of WO 2009/040367) consist of a plurality of process steps, are carried out with expensive 1-bromo-difluoroethane, which must also be activated for a better reaction, or use inexpensive 1-chloro-2, 2-difluoroethane, whereby the yield and selectivity of 48.6% obtained at a conversion of difluorochloroethane of 86% is only very small, which can be attributed to the use of unreactive 1-chloro-2, 2-difluoroethane.
CN103687831B discloses a process for the preparation of 2, 2-difluoroethanol starting from 2, 2-difluoro-1-chloroethane (1-chloro-2, 2-difluoroethane), said process comprising the following two steps:
step (i): reacting 1-chloro-2, 2-difluoroethane with an alkali metal salt of formic acid or acetic acid in a suitable solvent to form the corresponding 2, 2-difluoroethyl formate or 2, 2-difluoroethyl acetate, characterised in that 1-chloro-2, 2-difluoroethane is slowly added to a mixture of the solvent and the alkali metal salt of formic acid or acetic acid heated to the desired reaction temperature.
Step (ii): (ii) the 2, 2-difluoroethyl formate or 2, 2-difluoroethyl acetate of step (i) is transesterified in the presence of an alcohol, preferably methanol, and optionally a base.
Although the above patent mentions alcohols (preferably methanol, butanol and pentanol, etc.) in step (ii), these alcohols have certain disadvantages. For example, methanol, butanol, etc. are toxic and harmful to the human body. The price of butanol and amyl alcohol is higher, thereby increasing the production cost. Ethanol is not mentioned in the above patent, mainly because the boiling points of ethanol (boiling point 78 ℃) and the transesterification product (ethyl acetate) (boiling point of ethyl acetate is 77 ℃) are close, and the product ethyl acetate cannot be easily removed during the transesterification reaction by distillation. The transesterification reaction is generally a reversible reaction, and the product is removed in the course of the reaction to promote the transesterification reaction to proceed unidirectionally, thereby improving the yield.
Therefore, there is a strong need in the art for a simple process for the preparation of 2, 2-difluoroethanol with higher yield, lower cost and lower environmental toxicity.
Disclosure of Invention
The inventors of the present application surprisingly found that transesterification can also be carried out with higher yields using ethanol instead of methanol or the like in the process described in CN 103687831B. Because ethanol is less toxic than methanol and less expensive than butanol, transesterification using ethanol instead of methanol can result in higher yields, lower costs, and lower environmental toxicity.
In one aspect, the present application provides a process for preparing 2, 2-difluoroethanol, the process comprising the steps of:
step (i): 2, 2-Difluoroethyl acetate is transesterified in the presence of ethanol and optionally a base.
In one example herein, the 2,2-difluoroethyl acetate can be obtained as follows:
step (a): reacting 1-chloro-2, 2-difluoroethane with an alkali metal salt of acetic acid in a solvent to form the corresponding 2, 2-difluoroethyl acetate, characterised in that 1-chloro-2, 2-difluoroethane is slowly added to a mixture of solvent and alkali metal salt of acetic acid heated to the desired reaction temperature.
In one example herein, the alkali metal salt of acetic acid is selected from sodium acetate or potassium acetate.
In one example of the present application, a purification step is further included to yield the 2,2-difluoroethyl acetate product.
In one example herein, the optional base is selected from the group consisting of alkali metal hydroxides, and alkali metal alkoxides in solid form, alkali metal carbonates, alkali metal acetates, alkali metal formates, and alkali metal phosphates.
In one example herein, the optional base is selected from potassium ethoxide and sodium ethoxide.
In one example herein, the step (i) is performed without adding a solvent.
In one embodiment of the present application, the molar ratio of ethanol to 2, 2-difluoroethyl acetate is preferably 1.0 or more, such as 1.0 to 4.0, more preferably 1.5 to 4.0, still more preferably 1.5 to 3.0.
In one example of the present application, the step (i) is performed at room temperature.
Detailed Description
In this context, percentages (%) or parts are percentages by weight or parts by weight relative to the composition, unless otherwise specified.
In this context, the individual components mentioned or their preferred components can be combined with one another to form new technical solutions, if not stated otherwise.
All embodiments and preferred embodiments mentioned herein can be combined with each other to form new solutions, if not specified otherwise.
In this context, all technical features mentioned herein as well as preferred features may be combined with each other to form new solutions, if not specified otherwise.
In this context, the sum of the contents of the individual components in the composition is 100%, if not stated to the contrary.
In this context, the sum of the parts of the components in the composition may be 100 parts by weight, if not stated to the contrary.
In this context, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers.
As used herein, unless otherwise noted, the range of integer values "a-b" represents an abbreviated representation of any combination of integers between a and b, where a and b are both integers. For example, the range of integer values "1-N" indicates 1, 2 \8230, 8230, N, where N is an integer.
In this context, unless otherwise stated, "combinations thereof" means multi-component mixtures of the individual elements mentioned, for example two, three, four and up to the maximum possible multi-component mixtures.
The terms "a" and "an" as used herein mean "at least one" if not otherwise specified.
All percentages (including weight percentages) stated herein are based on the total weight of the composition, unless otherwise specified.
The "ranges" disclosed herein are in the form of lower and upper limits. There may be one or more lower limits, and one or more upper limits, respectively. The given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this manner are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for particular parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.
In this context, all reactions are carried out at normal temperature and pressure unless otherwise stated. For example, all reactions were carried out at room temperature (25 ℃) and 1 atmosphere.
In this context, all reactions are carried out in solvents customary in the art, unless otherwise stated. For example, the solvent includes, but is not limited to, water.
In this context, all reaction steps are carried out sequentially, unless otherwise stated.
In this context, unless otherwise stated, the reagents used in the reaction are commercially available products (e.g., commercially available chemically pure products).
In one aspect, the present application provides a process for preparing 2, 2-difluoroethanol, the process comprising the steps of:
step (i): 2, 2-Difluoroethylacetate is transesterified in the presence of ethanol and optionally a base.
In this context, the 2, 2-difluoroethyl acetate is commercially available or can be prepared by the method disclosed in CN103687831B or by methods customary in the art.
In one example of the present application, the 2,2-difluoroethyl acetate can be obtained as follows:
a step (a): reacting 1-chloro-2, 2-difluoroethane with an alkali metal salt of acetic acid in a suitable solvent to form the corresponding 2, 2-difluoroethyl acetate, characterised in that 1-chloro-2, 2-difluoroethane is slowly added to a mixture of the solvent and the alkali metal salt of acetic acid heated to the desired reaction temperature.
Complete and simple conversion to the desired product is achieved by slow addition of 1-chloro-2, 2-difluoroethane to a heated mixture of an alkali metal salt of acetic acid and a solvent without having to operate under pressure and without having to use reaction auxiliaries (e.g. catalysts, additives). Likewise, the reaction time is relatively short. This has the advantage that the reaction can be carried out simply and at low cost, and furthermore it is environmentally friendly, since it does not require auxiliary chemicals.
According to the present application, the expression "slow addition" is understood to mean the addition of 1-chloro-2,2-difluoroethane portionwise or dropwise over a relatively long period of time. The length of this time depends on the amount of reaction charge and therefore on the amount of 1-chloro-2, 2-difluoroethane to be added and can be determined by the person skilled in the art by customary methods. It is decisive that the slowly added 1-chloro-2, 2-difluoroethane has sufficient time to react with the alkali metal salt of acetic acid. Thus, in the process of the present application, the reaction time is selected so as to ensure complete reaction of the 1-chloro-2, 2-difluoroethane. The reaction time may be in the range of 0.1 to 12 h. The reaction system is preferably adjusted such that the reaction time is in the range from 0.25 to 5h, and particularly preferably in the range from 0.5 to 2 or 3 h.
In step (a), sodium acetate or potassium acetate is preferably used, and potassium acetate is particularly preferably used.
The alkali metal salt of acetic acid used in the above step (a) is used in a molar excess of about 1-fold to about 10-fold, preferably in a molar excess of about 1-fold to about 2-fold, and particularly preferably in a molar excess of 1.1-fold to 1.5-fold, based on the 1-chloro-2, 2-difluoroethane used.
The solvent used in step (a) above is preferably used in such an amount that the reaction mixture is kept well stirred during the entire process. Advantageously, from 1 to 50 times the amount of solvent (v/v), preferably from 2 to 40 times the amount of solvent (v/v), particularly preferably from 2 to 20 times the amount of solvent (v/v), based on the 2, 2-difluoro-1-chloroethane used, is used.
The solvent in step (a) above is in particular an organic solvent (alone or as a mixture with other organic solvents) having a boiling point above 70 ℃ and being inert under the reaction conditions. Preferred solvents used in step (a) are dimethyl sulfoxide, tetramethylene sulfoxide, dipropyl sulfoxide, benzyl methyl sulfoxide, diisobutyl sulfoxide, dibutyl sulfoxide, diisoamyl sulfoxide; n, N-dimethylacetamide, N-methylformamide, N-dimethylformamide, N-dipropylformamide, N-dibutylformamide, N-methylpyrrolidone, N-methylcaprolactam and mixtures thereof, with particular preference being given to N, N-dimethylacetamide, N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide, tetramethylene sulfoxide and mixtures thereof, very particular preference being given to dimethyl sulfoxide or N-methylpyrrolidone and mixtures thereof.
The slow addition in step (a) according to the present application is carried out at the desired reaction temperature, wherein the reaction temperature is understood to be the internal temperature. The reaction temperature is generally in the range of 70 ℃ to 200 ℃, preferably in the range of 80 ℃ to 160 ℃, particularly preferably in the range of 90 ℃ to 150 ℃.
In principle, step (a) described above is carried out at normal pressure. Alternatively, however, it can also be carried out in a pressure-stable closed laboratory vessel (autoclave). The pressure during the reaction (i.e., the intrinsic pressure) depends on the reaction temperature used, the solvent used, and the amount of the raw material used. If a pressure increase is desired, an additional pressure increase may be made by adding an inert gas, such as nitrogen or argon.
In principle, step (a) above is carried out in the absence of reaction auxiliaries (e.g. catalysts or additives). From a chemical point of view, the reaction promoter/catalyst may be added to the mixture of alkali metal salt of acetic acid and solvent for the activation of 1-chloro-2, 2-difluoroethane. It is conceivable to use alkali metal iodides and alkali metal bromides (e.g. sodium iodide, potassium iodide, sodium bromide or potassium bromide). NR may also be used 4 + X - Quaternary ammonium salts of the form wherein R represents C 1-12 Alkyl and X represent Br or I (e.g., tetrabutylammonium bromide, tetrabutylammonium iodide and trioctylmethylammonium bromide). Possible concentrations of the catalyst are in the range from 0.001 to 0.1 equivalent, based on the 1-chloro-2.2-difluoroethane used。
The transesterification in step (i) of the process described herein is base-catalysed. In the case of the preparation of 2, 2-difluoroethyl acetate by the process disclosed in CN103687831B or by methods commonly used in the art, step (i) can be carried out directly with the reaction mixture of step (a), i.e. without isolation of the reaction mixture of 2, 2-difluoroethyl acetate produced in step (a), wherein it is not necessary to add a base to the reaction mixture, since it is already present in the reaction mixture (e.g. the alkali metal salt of acetic acid from step (a)).
Of course, in order to increase the yield of the product, it is preferred to use the isolated 2, 2-difluoroethyl acetate in step (i), since the solvent used in step (a) adversely affects the yield of 2, 2-difluoroethanol. For this purpose, the reaction mixture obtained after step (a) can be worked up and the 2, 2-difluoroethyl acetate isolated, or the commercially available 2, 2-difluoroethyl acetate product can be used. Furthermore, the esters can be separated by distillation. If the 2, 2-difluoroethyl acetate prepared in step (a) is to be isolated after step (a), it is necessary to add a base in step (i).
Step (i) is typically carried out in bulk, i.e. without addition of (further) solvent, wherein the ethanol used in step (i) acts as solvent.
The transesterification is carried out by adding an optional base and ethanol to the reaction mixture from step (a) or to the separated ester. Especially in the case of the use of isolated esters, no solvent addition is required. The mixture thus obtained is stirred at room temperature or under reflux conditions for 0.5-2h.
In step (i) of the present application, the molar ratio of ethanol to 2, 2-difluoroethyl acetate is preferably 1.0 or more, for example, 1.0 to 4.0, more preferably 1.5 to 3.0, still more preferably 1.5 to 2.8. The applicant of the present application has found that when the above molar ratio is equal to or greater than 1.5, a higher product yield can be obtained; when the above molar ratio is 2.8 or less, a higher product yield can be obtained.
Although step (i) may be performed at room temperature or under heating reflux, it is preferable to perform step (i) at room temperature (room temperature) in order to improve the yield of the product. The inventors of the present application have surprisingly found that when step (i) is carried out under heated conditions, the yield of the product is greatly reduced. Unlike the conventional transesterification reaction, the transesterification reaction of step (i) described herein can be carried out unidirectionally without removing the product, and the yield is also greatly improved.
Examples of bases according to the present application which are required in step (i) are alkali metal hydroxides, and in solid form or alkali metal alkoxides, alkali metal carbonates, alkali metal acetates, alkali metal formates and alkali metal phosphates. Preferred bases are alkali metal alkoxides (e.g., potassium ethoxide and sodium ethoxide). The amount of base added is from 0.001 to 0.1 equivalent based on the 2, 2-difluoroethyl formate or 2, 2-difluoroethyl acetate used.
The work-up (purification) of the 2, 2-difluoroethanol can be carried out by distillation.
The invention is further illustrated by the following examples, which should not be construed as limiting the invention.
Example 1: preparation of 2, 2-Difluoroethyl acetate
2, 2-Difluoroethyl acetate was prepared according to example 1 step (i) of CN 103687831B. The solvent dimethyl sulfoxide in the reaction product was removed by distillation.
Example 2: preparation of 2, 2-difluoroethanol
The catalyst was dissolved in ethanol to form a solution. The obtained ethanol solution and 2, 2-difluoroethyl acetate obtained in example 1 were directly charged into a flask, and the reaction was stirred at room temperature and monitored by gas chromatography (Fuliry analytical instruments, zhejiang). After the reaction, heating and distilling are carried out, the weight of the distillate is weighed, the concentration of the 2, 2-difluoroethanol in the distillate is analyzed, and the yield of the 2, 2-difluoroethanol is calculated.
The above catalyst, ethanol, 2-difluoroethyl acetate and their amounts, reaction time and temperature, yield of the product, etc. are shown in Table 1 below.
TABLE 1
Claims (7)
1. A process for preparing 2, 2-difluoroethanol, the process comprising the steps of:
step (i): 2, 2-difluoroethyl acetate in the presence of ethanol and optionally a base,
said step (i) is carried out without addition of a solvent,
said step (i) is carried out at room temperature,
the molar ratio of the ethanol to the 2, 2-difluoroethyl acetate is 1.5-4.0.
2. The process of claim 1, wherein the 2, 2-difluoroethyl acetate is obtained by:
step (a): reacting 1-chloro-2, 2-difluoroethane with an alkali metal salt of acetic acid in a solvent to form the corresponding 2, 2-difluoroethyl acetate, characterised in that 1-chloro-2, 2-difluoroethane is slowly added to a mixture of solvent and alkali metal salt of acetic acid heated to 70 ℃ to 200 ℃.
3. The method of claim 2, wherein the alkali metal salt of acetic acid is selected from sodium acetate or potassium acetate.
4. The process of claim 2, further comprising a purification step to obtain 2, 2-difluoroethyl acetate product.
5. The process of claim 1 or 2, wherein the optional base is selected from the group consisting of alkali metal hydroxides, and alkali metal alkoxides in solid form, alkali metal carbonates, alkali metal acetates, alkali metal formates, and alkali metal phosphates.
6. The method of claim 1 or 2, wherein the optional base is selected from the group consisting of potassium ethoxide and sodium ethoxide.
7. The process of claim 1 or 2, wherein the molar ratio of ethanol to 2, 2-difluoroethyl acetate is from 1.5 to 3.0.
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