|Title of Invention||
"A METHOD FOR PREPARING A TRIFLUORO ALKENONE ETHER"
|Abstract||Haloalkenone ethers can be produced by the attachment of carboxylic acid halides to a vinyl ether and by the expulsion of hydrogen halidc. The invention improves said method by carrying out the process without a base and/or in the presence or a stabiliser for the alkenone. Higher yields of the product can thus be obtained.|
The invention relates to a simplified process for the preparation of halogenated alkenone ethers.
Halogenated alkenone ethers, for example 4-ethoxy-1,1,1-trifluoro-3-buten-2-one, are building blocks in chemical synthesis, see for example EP-0 744 400. They can be prepared by reacting an acid-ehloride with a vinyl ether in the presence of a base, see the above-mentioned European publication; in that case, the base can also be used in excess as a solvent. It is for example known from N. D. Field and D. H. Lorenz, High Polymer, 1970, page 394, that the reaction of phosgene with vinyl ethers in the absence of a base results in polymerisation. It is an object of the present invention to devise a simplified process for the preparation of alkenones. This object is achieved by the process of the present invention.
The process according to the invention for the preparation of alkenones provides for the vinyl ether and carboxylic acid halide, preferably carboxylic acid chloride, to be reacted together in the absence of an acid scavenger and/or in the presence of a stabiliser for the alkenone. The term "acid scavengers" covers in particular bases, particularly nitrogen bases such as pyridine or secondary and tertiary amines and also onium salts, which are described in the international patent application having the application number PCT/EP 03/00913, which does not constitute a prior publication, no attempt at explanation being intended to be linked to this designation.
A process for the preparation of alkenones with halogen, in particular
fluorine and/or chlorine, substitution at the carboxylic acid radical is preferred. Very particularly preferably, alkenones of Formula (I) are prepared
wherein R1 stands for a C1-C4 alkyl group or for a C1-C4 alkyl group which is substituted by at least 1 halogen atom, or wherein R1 stands for CF3C(O)CH2, and wherein R2 stands for aryl, substituted aryl, a C1-C4 alkyl group or for a C1-C4 alkyl group which is substituted by at least 1 halogen atom, in that an acid halide of Formula (II)
wherein X stands for F, Cl or Br and R1 has the above meaning, is reacted with a vinyl ether of Formula (III)
wherein R2 has the above meaning, in the absence of an acid scavenger and/or in the presence of a stabiliser for the alkenone.
R1 preferably stands for methyl, ethyl, n-propyl or i-propyl, or methyl, ethyl, n-propyl or i-propyl substituted by at least 1 fluorine atom. Particularly preferably, R1 stands for methyl, ethyl, or methyl or ethyl substituted by at least 1 fluorine atom. Very particularly preferably, R1 stands for CF3, CF2H, CF2CI, C2F5, C3F7 or CF3C(0)CH2.
R2 may stand for aryl, for example phenyl or phenyl substituted [by] C1-C4 alkyl groups and/or halogen atoms. Preferably R2 is linear or branched C1-C4 alkyl. Very particularly preferably, R2 is methyl, ethyl, n-propyl or i-propyl.
The acid chloride is preferred as the acid halide. The invention will be
explained further with reference to this preferred embodiment.
The molar ratio of acid chloride and vinyl ether is expediently between 0.8:1 and 1:0.8, particularly between 0.8:1 and 1:1.
The process according to the invention is expediently carried out in two stages. In the 1st stage, the acid halide is added to the vinyl ether. The reaction may be exothermic, so the reaction mixture optionally has to be cooled or the reaction is carried out very slowly. If a low-boiling acid halide is used, it is advantageous to use a condenser attachment which condenses the acid halide and permits it to be returned into the reaction mixture. This stage is expediently carried out at -15°C to +50°C, preferably -15°C to +30°C. The 2nd stage comprises the elimination of hydrogen halide. It is expediently carried out at the temperature necessary for elimination and can readily be determined by observing the expulsion of the hydrogen halide. For the reaction of trifluoroacetyl chloride on ethyl vinyl ether, it is in the range of up to 150°C, preferably 30°C to 90°C.
Preferably no solvent is used in the reaction according to the invention between acid halide and vinyl ether. The advantage is that no solvent needs to be separated off (no recovery expense necessary, lower energy requirement).
The process according to the invention for the preparation of alkenones of Formula (I) can be carried out at elevated pressure. Ambient pressure or a slight partial vacuum (down to 0.5 bar) is advantageous, because resulting hydrogen halide can be removed better from the reaction mixture. It may be performed batchwise or partially continuously. Resulting hydrogen halide can be removed from the reaction mixture during or after the reaction e.g. by heating or partial vacuum, or both.
The process according to the invention comprises three variants: the reaction in the absence of an acid scavenger (this term also covers onium salts), the reaction in the presence of a stabiliser for the desired product (the alkenone), and finally the reaction with both features, namely in the absence of the acid scavenger and the presence of the stabiliser. Phenols substituted with several alkyl groups, e.g. phenol substituted by 2 t-butyl groups and one alkyl group with 1 to 3 C atoms, in particular 2,6-di-t-buty!-4-methylphenol, are e.g. suitable as stabilisers.
The reaction can also be performed in the presence of a stabiliser for the alkenone to be prepared in the presence of conventional acid scavengers such as amines, onium salts or corresponding solvents such as nitriles, sulphoxides or lactams. This variant represents an improvement to the known process, but the disadvantages are that salts are produced or that solvents have to be separated off.
The other two variants, reaction in the absence of an acid scavenger, and reaction in the absence of an acid scavenger and in the presence of a stabiliser for the alkenone to be prepared, are very much more advantageous than the process of the prior art, because the acid scavenger does not have to be separated off. These two variants are preferred and will be explained further.
One preferred variant provides for the reaction of the starting compounds generally in the absence of an acid scavenger for the alkenone. The term "acid scavenger" is defined further above.
The other of the two preferred variants provides for reacting the starting compounds in the absence of an acid scavenger, but in the presence of a stabiliser for the alkenone to be prepared. The phenols already mentioned above substituted with several alkyl groups, e.g. phenol substituted by 2
butyl groups and one alkyl group with 1 to 3 C atoms, in particular 2,6-di-t-butyl-4-methylphenol, are for example [suitable] as stabilisers.
The latter two variants, which each have as a feature the absence of an acid scavenger, are, as stated, preferred.
The reaction mixtures are worked up using conventional methods. For example, the desired alkenone of Formula (I) can be distilled out of the mixture.
The advantage of the process according to the invention is that in the absence of an acid scavenger working-up is made easier. The presence of a stabiliser for the alkenone already in the reaction mixture helps to increase the yield. The absence of an acid scavenger and the simultaneous presence of a stabiliser for the alkenone in the reaction mixture can be very beneficial to the yield.
The following examples are intended to explain the invention further, without limiting its scope.
Reaction of ethyl vinyl ether and trifluoroacetyl chloride to form 4-ethoxy-1,1,1 -trifluoro-3-buten-2-one ("ETFBO") in the absence of an acid scavenger and in the presence of a stabiliser for the alkenone to be prepared.
0.25 g (1.13 mmol) 2,6-di-t-butyl-4-methylphenol ("BHT")
12.9 g (99%, 0.18 mol) ethyl vinyl ether ("EVE") 21.0 g (0.16 mol) trifluoroacetyl chloride ("TFAC")
BHT and EVE were mixed together. The TFAC was then introduced in an ice bath under dry-ice reflux cooling and in so doing the temperature of the reaction mixture was kept below 26°C. Then the reaction mixture was thermolysed at 80°C. After the thermolysis, the reaction mixture still weighed 28.5 g. It was then distilled at 9 mbar.
24.1 g = 83.0% of theory.
Repeating with 0.25 g BHT, 13.8 g EVE and 19.7 g TFAC produced a yield of 87.6% of theory.
Preparation of ETFBO without stabiliser Batch:
13.0 g (99%, 0.19 mol) EVE
19.0 g (0.14 mol) TFAC
The EVE was introduced into the vessel and the TFAC was added at room temperature with dry-ice cooling. Then it was thermolysed at 80°C. The thermolysed mixture was then distilled at 7 mbar.
22.8 g = 90.4% of theory.
1. A method for preparing a trifiuoro alkenone ether, corresponding to Formula (I) :
R1 represents CF3,
R2 represents aryl, substituted aryl, a C1-C4 alkyl group or a C1-C4 alkyl group,
which is substituted by at least one halogen atom ;
said method comprising reacting a carboxylic acid halide with a vinyl ether in an addition
reaction in a first step, and subsequently eliminating hydrogen halide in a second step to
form the alkenone, wherein the reaction is carried out in the absence of an acid scavenger
for the resulting hydrogen halide and the second step is carried out at a temperature in the
range from 30°C to 90°C,
wherein the acid halide corresponds to Formula (II) :
X represents fluorine, chlorine or bromine, and
R1 has the meaning given above,
and the vinyl ether corresponds to Formula (III):
in which R as the meaning given above.
2. A method as claimed in claim 1, wherein R2 represents methyl, ethyl, n-propyl or
3. A method as claimed in claim 1, wherein the first step is carried out at a temperature in the range from -15°C to +30°C.
4. A method as claimed in claim 1, wherein the molar ratio of vinyl ether to carboxylic acid chloride ranges from 0.8 : 1 to 1 : 0.8.
5. A method according to claim 4, wherein the carboxylic acid chloride is used in a less than stoichiometric amount.
6. A method as claimed in claim 1, wherein the reaction is carried out optionally in the presence of a stabilizer for the resulting alkenone.
7. A method as claimed in claim 6, wherein said stabilizer comprises a phenol substituted by at least one C1-C5 alkyl group.
8. A method as claimed in claim 7, wherein said stabilizer comprises 2,6-di-t-butyl-4-
|Indian Patent Application Number||69/DELNP/2006|
|PG Journal Number||29/2010|
|Date of Filing||04-Jan-2006|
|Name of Patentee||SOLVAY FLUOR GMBH,|
|Applicant Address||HANS-BOCKLER-ALLEE 20,30173 HANNOVER, GERMANY.|
|PCT International Classification Number||C07C 45/45|
|PCT International Application Number||PCT/EP2004/005466|
|PCT International Filing date||2004-05-21|