WO2007074148A1

WO2007074148A1 - Purification of alkenone ethers

Info

Publication number: WO2007074148A1
Application number: PCT/EP2006/070191
Authority: WO
Inventors: Wolfgang Wiesenhöfer; Wolfgang Kalbreyer; Johannes Eicher
Original assignee: Solvay Fluor Gmbh
Priority date: 2005-12-29
Filing date: 2006-12-22
Publication date: 2007-07-05
Also published as: EP1803703A1

Abstract

Alkenone ethers, especially haloalkenone ethers are intermediates in chemical synthesis. By-products are formed during storage and these can be removed by freezing-out.

Description

Purification of alkenone ethers

The invention relates to a method of purifying alkenone ethers, especially halogenated alkenone ethers.

Halogenated alkenone ethers, for example 4-ethoxy- l,l,l-trifluoro-3-buten-2-one ("ETFBO"), are building blocks in chemical synthesis; see, for example, EP-O 744 400. They can be prepared by reacting an acid chloride with a vinyl ether in the presence of a base; see the abovementioned European first publication. Here, the base can also be used in excess as solvent.

WO 03/080562 discloses a process for preparing halogenated alkenone ethers from acid chlorides and vinyl ethers in the presence of onium salts. WO 2004/108647 discloses the preparation from acid chlorides and vinyl ethers in the absence of bases or onium salts or in the presence of stabilizers. A. Colla et al. describe in Synthesis, June 1999, pages 483 to 486, the preparation of trihaloacetylated enol ethers (= alkenone ethers) by reacting trichloroacetyl chloride or trifluoroacetic anhydride and enol ethers at 0⁰C in the presence of pyridine. Pyridine salts which form are removed, and the resulting raw product is washed with hydrochloric acid. The pure trihaloacetylated enol ethers are stored at 4 to 8 ⁰C; allegedly, no deterioration occurs for months. It has been found, according to NMR and GC (gas-chromatographic) studies, that impurities are formed especially in halogen-containing acyl- substituted alkenone ethers on standing; these are possibly dimers which are formed in a hetero-Diels- Alder reaction. For example, ETFBO is not insensitive to moisture in the surrounding air with which ETFBO can come into contact during packaging or transfer or during inappropriate storage. The products of this hydrolysis reaction include aldehydes and alcohols; the latter in turn react with the halogenated alkenone ethers in an addition reaction. The aldehyde or aldehydes formed oligomerize(s) in various ways, e.g. in an Aldol reaction, to form many by-products. It was an object of the present invention to provide a simple method by means of which impurities can be separated off, especially of such impurities which form during packaging, transferring or storage. This object is achieved by the method of the present invention. The novel method of purifying acetylated alkenone ethers, especially halogen-substituted acylated alkenone ethers provides for the alkenone ethers to be cooled so that a solid phase which represents the purified alkenone ether or the purified halogenated alkenone ethers and a liquid phase are formed, the solid phase to be separated off from the liquid phase and the purified alkenone ether to be obtained in this way.

The term "halogenated alkenone ether" denotes compounds which are substituted by at least one chlorine atom, at least one bromine atom, or, preferably, at least one fluorine atom in the ether group or, preferably, in the carboxyl group.

Preference is given to a method of purifying alkenone ethers having fluorine and/or chlorine substituents on the carboxylic acid radical. Very particular preference is given to purifying alkenone ethers of the formula (I) R^C(O)-C(H)=C(H)-OR² (I), where R¹ is a Cl-C4-alkyl group or a Cl-C4-alkyl group which is substituted by at least 1 halogen atom or R¹ is CF₃C(O)CH₂ and R² is aryl; substituted aryl, for example, aryl substituted by 1 or more halogen atoms, a nitro group or a nitrile group; a Cl-C4-alkyl group; or a Cl-C4-alkyl group which is substituted by at least 1 halogen atom. Such compounds can, according to the teachings of WO 03/080562 or WO 2004/108647, be prepared by reacting an acid halide of the formula (II)

R^C(O)X (II), where X is F, Cl or Br and R¹ is as defined above, with a vinyl ether of the formula (III)

CH₂ = C(H)-OR² (III), where R² is as defined above. This can, as is known from the prior art, occur in the presence of a base, in the presence of an onium salt or the absence of an acid scavenger and/or in the presence of a stabilizer for the alkenone ether.

R¹ is preferably methyl, ethyl, n-propyl or i-propyl or methyl, ethyl, n-propyl or i-propyl substituted by at least 1 fluorine atom. R¹ is particularly preferably methyl, ethyl or methyl or ethyl substituted by at least 1 fluorine atom. R¹ is very particularly preferably CF₃, CF₂H, CF₂Cl, C₂F₅, C₃F₇ or CF₃C(O)CH₂. R² can be aryl, for example phenyl, or Cl-C4-alkyl groups and/or halogen-substituted phenyl. R² is preferably linear or branched Cl-C4-alkyl. R² is very particularly preferably methyl, ethyl, n-propyl or i-propyl.

The alkenone ether compounds can be present as cis or trans isomers or as mixtures of cis and trans isomers and can be purified according to the invention.

The alkenone ether compound to be purified is cooled to a temperature which depends on the type and degree of contamination. It is below the solidification point of the alkenone ether compound. Depending on the compound, cooling to a temperature below -10⁰C is preferred. The lower limit is determined by the solidification point of the impurities. Cooling to a temperature in the range from -25 to -80⁰C is usually suitable, a temperature in the range from -30 to -45°C is very suitable and a temperature of from -33 to -37°C is particularly suitable in order to allow impurities to be separated off. The latter mentioned range is for example very suitable for trifiuoro-, difiuoro- and difiuorochloroacetyl alkenone ethers, especially for trifiuoroalkyl alkenone ethers.

The process according to the present invention is generally applicable to alkenone ethers which are essentially free from solvents or other diluents or constituents. The term "essentially free" denotes that the alkenone ethers comprise less than 5 % by weight, preferably less than 3 % by weight, very preferably less than 2 % by weight of solvents, diluents or other components which are neither alkenone ether nor impurities in the form of reaction products thereof. Such solvents or diluents may, for example, have been introduced into the alkenone ether during its preparation or purification.

It is also preferred that no impurities are comprised in the alkenone ether which may crystallize together with the pure alkenone ether which crystallizes out in the process of the present invention. For example, essentially no hydrochlorides of amine bases resulting from the preparation of the alkenone ether should be present. Here, the term "essentially" denotes a content of less than 5 % by weight, preferably less than 3 % by weight, very preferably less than 1 % by weight of such salts are present. It is especially preferred that no such hydrochloride is present. That is for example the case if the process of the present invention is applied to alkenone ethers which are produced in the absence of amines. In principle, the process of the present invention can be applied to any alkenone ethers. The expert can easily check if an alkenone ether can be purified, simply by cooling the compound, separating any crystallized product, and verify, e.g. by gas chromatography, if a purification is observed. The present invention is preferably applied to alkenone ethers which already have undergone a purification step, and in which, after that purification, impurities have formed, for example, caused by contact with air or moisture during package, transfer from one container to the other, or during storage for, e.g., one week, one month or longer, for example, by inherent instability of the molecules.

Further above, a possible explanation is given how and what impurities may form. It has to be noted that the invention is not intended to be limited by that explanation. The invention is also preferably applied to, but not intended to be limited to the removal of impurities which, according to the explanation given above, may form.

The solid formed can be separated off from the liquid by decantation or filtration; here, apparatuses which can likewise be cooled can be advantageous. The liquid which has been separated off and contains the impurities also contains relatively large proportions of the alkenone ether, so that it can be worthwhile not to discard the liquid but instead to work it up or reuse it, for example by adding it to a later batch and distilling.

An advantage of the method of the invention is that the removal of impurities can be effected by means of a simple operation - cooling and separation of solid and liquid. The following examples illustrate the invention without restricting its scope. Examples

Example : Purification of 4-ethoxy- 1,1,1 -trifluoro-3-buten-2-one (ETFBO) Procedure : 7.7 kg of "aged" ETFBO having an ETFBO content of 96.1 %

(cis + trans isomers) were stored at -35°C for 48 hours. During this time, a white solid crystallized out and a liquid remained. The solid was separated from the liquid by simple decantation. This gave two batches of ETFBO having different purities. The batch which was liquid at -35°C (3.6 kg) had an ETFBO content of 91.6 % (cis + trans). The batch which was solid at -35°C (4.1 kg) had an ETFBO content of 99.0 % (cis + trans). The results are summarized in Table 1 : Table 1

Sample , ^~. _n . Liquid batch Solid batch beiore freezing _

Amount 7.7 kg 3.6 kg 4.1 kg

GC content of trans-ETFBO 94.5 % 90.4 % 97.7 %

GC content of cis-ETFBO 1.6 % 1.2 % 1.2 %

GC content of DE-ETFBO 2.0 3.7 0.5

GC content of dimer 0.4 1.2 0.2

Number of signals in GC 30 21 11

Total cis + trans 96.1 % 91.6 % 99.0 %

Example 2 Example : Purification of 4-ethoxy- 1,1,1 -trifluoro-3-buten-2-one (ETFBO) Procedure :

4.2 kg of ETFBO having an ETFBO content of 96.6 % (cis + trans isomer) were purified in a manner analogous to Example 1. The results are summarized in Table 2. Table 2 _c i "aged" ETFBO . . , , , .. . , , Sample , Z _r ■ Liquid batch Solid batch beiore freezing _

Amount 4.2 kg 1.6 2.6

GC content of trans-ETFBO 95.1 93.9 97.0

GC content of cis-ETFBO 1.7 1.8 1.5

GC content of DE-ETFBO 0.9 0.8 0.8

GC content of dimer 0.1 0.4 < 0.1

Number of signals in GC 18 16 15

Total cis + trans 9^6 95/7 98.5

The two examples demonstrate that very effective purification of ETFBO can be achieved by simple freezing-out.

Claims

C L A I M S

1. Method of preparing purified alkenone ethers, wherein the alkenone ethers are cooled so that the alkenone ether precipitates and contaminating constituents remain liquid and the impurities are separated off from the alkenone ether.

2. Method according to Claim 1, characterized in that an alkenone of the formula (I)

R^C(O)-C(H)=C(H)-OR² (I)

where R¹ is a Cl-C4-alkyl group or a Cl-C4-alkyl group which is substituted by at least one halogen atom or R¹ is CF₃C(O)CH₂ and R² is aryl, substituted aryl, a Cl-C4-alkyl group or a Cl-C4-alkyl group which is substituted by at least one halogen atom, is purified.

3. Method according to Claim 1, characterized in that R¹ is methyl, ethyl or propyl or methyl, ethyl or propyl substituted by at least 1 fluorine atom.

4. Method according to Claim 1, characterized in that R¹ is CF₃, CF₂H,

CF₂Cl, C₂F₅, C₃F₇ or CF₃C(O)CH₂.

5. Method according to Claim 1, characterized in that R² is methyl, ethyl, n-propyl or isopropyl.

6. Method according to Claim 1, characterized in that the alkenone ether to be purified is cooled to a temperature of from -25 to -80⁰C.

7. Method according to Claim 6, characterized in that the alkenone ether to be purified is cooled to a temperature of from -30 to -45°C.

8. Method according to Claim 1, characterized in that the alkenone ether to be purified is cooled to a temperature of from -33 to -37°C, in particular to a temperature of -35°C.