Process for preparing 1,3-dioxoles

Abstract: A process for preparing 1,3-dioxoles of formula: in which X₁ and X₃, like or different from each other, are F or H, X₅ and x₆ , like or different from each other, are F or CF₃, by dehalogenation reaction of the corresponding 4,5-dihalodioxolanes in the presence of a dehalogenation agent at a temperature ranging from + 30° to + 130°C. The starting dioxolanes are essentially in the isomeric form anti.

Description: The present invention relates to a process for preparing 1,3-dioxoles by dehalogenation of the corresponding 4,5-dihalodioxolanes. More in particular, the present invention relates to a process for preparing fluorinated 1,3-dioxoles having formula: in which: X₁ and X₃, the same or different from each other, are F or H, X₅ and X₆ the same or different from each other, are F or CF₃. The growing demand for fluorodioxoles for the use thereof as monomers in the preparation of fluoropolymers justifies the interest in perfecting the processes for preparing them. It is known how to prepare dioxoles by dehalogenation of 4,5-dihalo-1,3-dioxolanes in the presence of a metal such as magnesium or zinc. U.S. patents 3,865,845 and 3,978,030 describe a process for the dehalogenation of fluorinated dioxolanes in an organic solvent in the presence of magnesium with a yield of 58% by mols. Furthermore, there is illustrated the debromination reaction with metallic zinc of perfluoro-2,2-dimethyl-4,5-dibromo-1,3-dioxolane, prepared by treating perfluoro-2,2-dimethyl-1,3-dioxole with bromine, in order to obtain the starting dioxole with a yield of 18% by mols. The yields of this process, besides being low, are little reproducible. U.S. patent 4,393,227 describes an improved dechlorination process with magnesium, mercury metal or a mercury salt, iodine and tetrahydrofuran, by means of which the reproduceability of the yields is improved. However, the drawback of this process is that the molar ratios of the metals to one another must be exact and defined, since even slight variations result in a drastic reduction in the dioxole yield. Lastly, U.S. patent 4,908,461 describes a method of dechlorinating 1,3-dioxolanes in the presence of LiAlH₄ and TiCl₃ or TiCl₄ in tetrahydrofuran. However, the utilized methodology is quite complex and the molar ratios of the dehalogenating agents to each other and to the starting dioxolane must be within defined ranges. From an examination of the prior art it results that there is the need for having available an easy industrial process which permits to prepare 1,3-dioxoles through dehalogenation of the corresponding 4,5-dihalodioxolanes with high yields and a high reproduceability. So far, any afforts have been essentially directed to the improvement of the dehalogenating agent. It has now surprisingly found by the Applicant that, irrespectively of the utilized dehalogenating agent,the dehalogenation reaction of 4,5-dihalodioxolanes exhibits high yields when the two halogen atoms,which are extracted,are in anti position. Thus, it is an object of the present invention to provide a process for preparing dioxoles of formula: wherein: X₁ and X₃, the same or different from each other, are F or H, X₅ and X₆, the same or different from each other, are F or CF₃, which comprises reacting a dioxolane of formula: wherein: X₁ and X₄ the same or different from each other, are Cl or Br, X₁, X₃, X₅ and X₆ have the same meaning as defined before, with at least a dehalogenating agent the dioxolane (II) having a proportion of anti isomer of at least 60%, and subsequently separating the dioxole(I)from the reaction products. The reaction is conducted at a temperature ranging from +30° to +130°C, preferably from +50° to +100°C. It has now surprisingly been found that, if the preparation of dioxolane (II) is effected according to the process described in EP-A-0 460 948, said dioxolane exhibits an anti/syn isomeric ratio, which is higher than the trans/cis ratio of the starting reagents. According to this process, dioxolane (II) is obtained from the reaction of a bis(fluoroxy)perfluoroalkane of formula C(OF)₂X₅X₆ with a halogenated olefin of formula CX₁X₂=CX₃X₄, where X₁, X₂, X₃, X₄, X₅ and X₆ have the meaning defined hereinbefore. The temperature of said reaction is generally in a range from -140° to +60°C, preferably from -100° to +30°C. According to page 3, line 13 to page 4, line 17 said EP-A-0 460 948 reads as follows: In a preferred embodiment of the invention, a flow of a bls(fluoroxy)perfluoroalkane, preferably in the presence of an inert diluting gas, and optionally also a gaseous or liquid stream consisting of a halogenated olefin, are fed into a liquid phase consisting of a halogenated olefin and of a solvent, if any, maintained at the above-cited reaction temperature. As an alternative, the halogenated olefin and the bis(fluoroxy)perfluoroalkane are simultaneously fed into a vessel containing optional solvent. At the end of the reaction time, feeding of the reagents is stopped and the reaction products are separated from the solvent, if any, and from the unreacted olefin, if present, preferably by fractionated distillation. The reaction can be conducted also in a thoroughly continuous manner by continuously withdrawing a liquid phase portion from the reactor, from this phase the reaction products are separated and recovered, while the optional solvent and the unreacted olefin are recycled. The total pressure in the reaction environment preferably ranges from 1 to 10 kg/cm² abs. More usually, it is operated at about the atmospheric pressure. The inert diluting gas of bis(fluoroxy)perfluoroalkane when it is utilized, is selected for example from nitrogen, argon, helium, CF₄ and C₂F₆. A further embodiment of the present invention consists in a particular discontinuous process for preparing halogena ted 1,3-di oxolanes of formula (I), wherein: X₁, X₂, X₃ and X₄, like or different from one another, represent F, Cl, Br, I, CF₂OSO₂F, SO₂F, C(O)F, H, perhaloalkyl or oxyperhaloalkyl radicals containing from 1 to 5 carbon atoms. X₅ and X₆, like or different from one another, represent F or CF₃, characterized in that a bis(fluoroxy)perfluoroalkane of formula C(OF)₂X₅X₆ is reacted, at a temperature ranging from -140°C to +60°C, with a halogenated olefin of formula CX₁X₂=CX₃X₄, X₁, X₂, X₃, X₄, X₅ and X₆ being the same as defined hereinbefore, on condition that at least one from among X₁, X₂, X₃ and X₄ is F. In the discontinuous method the reagents are condensed at a temperature not exceeding -140°C in the reaction vessel, preferably along with a solvent. The abovesaid condensation is preferably conducted at a temperature of -196°C. The reaction vessel so charged is usually allowed to reach the desired reaction temperature and is maintained at this temperature for a time ranging from 1 hour to 24 hours. the reaction products are purified by vacuum distillation by causing the vapours to flow through cooled traps. It must be pointed out that the temperature at which the reagents are condensed in the reaction vessel is not the actual reaction temperature, but only a convenient experimental procedure for charging the reagents in a discontinuous and exact manner without letting them react or to minimise any reaction until the desired reaction temperature is reached. In the discontinuous method the pressure preferably ranges from 0.5 to 20 kg/cm² abs. In both processes the reaction can be conducted in a condensed phase or in a gas phase. The synthesis of bis(fluoroxy)perfluoroalkanes of formula: wherein X is F or CF₃, is described in JACS (1967), 2263 and in U.S. patent 3,420,866. Among the utilized bis(fluoroxy) perfluoroalkanes, bis(fluoroxy) difluoromethane (BDM) is particularly preferred. The synthesis of BDM is described in JACS (1967). 1809-10. The halogenated olefins utilized in the present invention preferably contain from 2 to 6 carbon atoms. Particularly preferred olefins are, for example; CFCl=CFCl, CFBr=CFBr, CF₂=CFBr, CF₂=CH-CF₃, CF₂=CF-SO₂F, CF₂=CF-CF₂-OSO₂F, CF₂=CF-C(O)F, CF₂=CF-CF₃, CF₂=CF-O-CF₂-CF₃. The reaction temperature for both processes is usually in the range from -140° to +60°C; preferably it ranges from -100° to +30°C. The solvent, when it is utilized, is preferably selected from straight and cyclic fluorocarbons, chlorofluorocarbons, perfluoroamines and perfluorinated ethers. Examples of suitable fluorocarbons and chlorofluorocarbons are: perfluorocyclobutane, perfluorocyclohexane, 1-chloropentafluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane, 1,2-dichlorotetrafluoroethane and 1,1,1-trifluorotrichloroethane. Examples of suitable perfluoroamines are the perfluoroaminic Fluorinert® produced by 3M Co. Examples of suitable perfluorinated ethers are the perfluoropolyethers having a boiling point lower than 250°C, such as the Galden® produced by Montefluos. The halogenated olefin concentration in the liquid phase generally ranges from 0.01 to 10 moles/liter and above, i.e. up to the molar concentrations of the haloolefins in the pure state". Using said process of EP-A- 0 460 948, the proportion of anti isomer in the dioxolane is usually of at least 60% and more commonly of at least 80%. Preferably, the reatio between trans isomer and cis isomer in the starting halogenated olefin is of at least 1:1. In the dioxolanes of formula (II), X₁, X₃, X₅ and X₆ are preferably F. Particularly preferred are 4,5-dichloro-tetrafluoro-1,3-dioxolane and 4,5-dibromo-tetrafluoro-1,3-dioxolane. Starting from the abovesaid preferred dioxolanes, the obtained product is perfluoro-1,3-dioxole. As concerns the dehalogenation reaction , the dehalogenating agent/dioxolane molar ratio can vary over a relatively wide range. Usually it is higher than 1, preferably it ranges from 1.5 to 3.0. The dehalogenating agent is selected from the ones of the art. Preferably, it is a metal selected from the class comprising Zn, Mg, Hg, Cu, Fe, Sn. Particularly preferred is zinc. In a preferred embodiment, the starting dioxolane is fed to the reaction vessel maintained at the reaction temperature, which vessel contains the dehalogenating agent along with an optional solvent and, preferably, with little amounts of sodium or potassium iodide and of sodium or potassium carbonate (usually up to about 1% by weight in respect of the dehalogenating agent) On conclusion of the reaction, the reaction products are collected in a trap maintained at a lower temperature than the boiling temperature of said products. In order to favour this operation, a gaseous nitrogen flow should be preferably provided in the reaction vessel. The solvent, if it is used, shall be inert under the reaction conditions, and it is preferably selected from amides (such as dimethylformamide), ethers (such as dioxane) and sulphoxides (such as dimethylsulphoxide). Usually it is operated at about atmospheric pressure. However, it is possible to use both reduced pressures and pressures higher than 1,01325 bar (1 atmosphere). The reaction time is not a critical parameter; usually the reaction is concluded in a few minutes. The resulting dioxoles can be utilized as monomers for preparing copolymers and homopolymers, as is described e. g. in published European application No. 80,187 and in U.S. patents 4,535,175 and 3,978,030. The abovesaid polymers are utilizable,e.g., as anticorrosive coating material or as sneaths for optical fibres. For purposes of promoting a better understanding of the possibilities of carring out the present invention, ---> illustrative examples are given hereunder; it will nevertheless be understood that no limitation of the scope of the invention is thereby intended. EXAMPLE 1 Preparation of 4,5-dichloro-tetrafluoro-1,3-dioxolane Into a 5-neck glass reactor having a 100 ml volume, maintained at a temperature of -78°C, equipped with mechanical stirrer, reflux cooler, thermocouple and inner plunging pipe for letting in the gases, there were introduced 10 g of 1,2-dichloroperfluoro-ethylene (mixture of 50% cis and 50% trans) and 75 ml of dichlorodifluoromethane, maintaining the reactor at a temperature of -65°C. To the reactor so charged and maintained at a temperature of -65°C there were fed 0.851 litres of bis(fluoroxy) difluoromethane (BDM),at a flowrate of 0.4 l/h, diluted with N₂ (0.5 l/h). From the reaction rough product, after stripping of most of the solvent, the reaction products were separated by fractionated distillation in a tray column at atmospheric pressure. The fraction with boiling point at 47°C consisting of 7.25 g of 4,5-dichloro-tetrafluoro-1,3-dioxolane with a purity degree of 99.2% was collected; the impurity consisted of 1,1,2-trichloro-1,2,2-trifluoroethane. The isolated dioxolane was composed of a mixture of of syn isomer (20%) and anti isomer (80%). The reaction by-product 1,2-dichlorotetrafluoroethane formed in an equimolar amount with respect to the dioxolane and was prevailingly collected in the distillation fraction having a boiling point in the range of from 3°C to 4°C. The distillation column contained 800 mg of CF₂Cl CFClCFCl CF₂Cl. The dioxolane yield, defined as the ratio between mols of obtained dioxolane and mols of utilized BDM, was of 88%. EXAMPLE 2 Preparation of 4,5-dichloro-tetrafluoro-1,3-dioxolane To a multineck glass reactor having a 50 ml volume, equipped with a magnetic entrainment mechanical stirrer, reflux cooler, thermocouple, inner plunging pipe, and immersed in a bath cooled at -80°C, there were fed - after having introduced 35.3 g of 1,2-dichloro-1,2-difluoroethylene (mixture of 50% cis and 50% trans) - 0.6 l of bis(fluoroxy)difluoromethane at a flowrate of 0.4 l/h, diluted with N₂ (0.5 l/h). The reaction rough product was distilled in a Spaltrohr-Fisher tray column at atmospheric pressure, thereby obtaining the following products: 2.3 g of CF₂Cl-CF₂Cl, 28.3 g of CFCl=CFCl, 4.5 g of 4,5-dichloro-tetrafluoro-1,3-dioxolane and 2.1 g of CF₂Cl(CFCl)₂CF₂Cl. The isolated dioxolane was composed of a mixture of syn (20%) and anti (80%) isomers. The dioxolane yield, calculated as in example 1, was of 78%. EXAMPLE 3 Preparation of 4,5-dibromo-tetrafluoro-1,3-dioxolane Into a multineck glass reactor having a 100 ml volume, equipped with magnetic entrainment mechanical stirrer, reflux cooler, thermocouple, inner plunging pipe, immersed in a bath cooled at -80°C, there were introduced 75 ml of CF₂Cl₂ and 10 g of 1,2-dibromo-1,2-difluoroethylene (mixture of 22% cis and 78% trans). To the reactor so charged and maintained at a temperature of -80°C, 0.5 l of bis(fluoroxy)difluoromethane diluted with N₂ (0.5 l/h) were fed at a flowrate of 0.4 l/h. On conclusion of the reaction, after having distilled off the solvent, there were recovered 12.2 g of a mixture consisting of: CF₂Br₂ (3.8%), CF₂BrCF₂Br (37.8%), 4,5-dibromo-tetrafluoro-1,3-dioxolane (49.4%) and CFBr₂CF₂Br (8.8%); said mixture was analyzed by means of gas chromatography in a column sp. 1000 at a temperature gradient from 50°C up to 200°C (10°C/min.). From such mixture, distilled in a Spaltrohr-Fisher tray column at atmospheric pressure, 5.4 g of a dioxolane having a boiling point from 69° to 72°C were recovered. The dioxolane was composed of a mixture of syn (10%) and anti (90%) isomers. The dioxolane yield, defined as in example 1, was of 79.6%. EXAMPLE 4 Dehalogenation of 4,5-dichloro-tetrafluoro-1,3-dioxolane Operating in a nitrogen atmosphere, Zn (4.4 g), KI (180 mg), K₂CO₃ (300 mg) and dimethylformamide (DMF) (7 ml) were introduced into a 50 ml flask, equipped with thermometer, dropping funnel, distillation column and magnetic stirrer. Then, after having brought the mixture to 60°C, there were dropped thereinto, very slowly (1 hour),2.75 g of 4,5-dichloro-tetrafluoro-1,3-dioxolane (synthesized according to the method described in example 1) dissolved in 2.5 ml of DMF. During dropping, the mixture was heated up to 100°C and perfluoro-1,3-dioxole was removed by distillation as it formed. In the collection flask there were condensed 1.76 g of a distillate which, analyzed by means of gas chromatography (column sp. 1000, from 50°C to 180°C, 10°C/min.), resulted to be composed of: perfluoro-1,3-dioxole(82.2%), 4-chloro-2,2,4,5-tetrafluoro-1,3-dioxolane (3%) and 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (15%). The mixture was then distilled in a conventional vacuum line trhough four traps respectively cooled at -80°C, -130°C, -150°C and -196°C. 1,370 g of perfluoro-1,3-dioxole were collected in the trap cooled at -150°C. The isolated perfluoro-1,3-dioxole yield, calculated on the converted dioxolane, was of 82%. EXAMPLE 5 The preceding example was repeated following the same modalities and using the same ratio between the reagents, with the only exception that the mixture of isomers of 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (2.3 g) was composed for 86.3% of anti isomer and for 13.7% of syn isomer. From the mixture collected during the reaction there were recovered by successive distillation, as in example 1, 1.250 g of perfluoro-1,3-dioxoleand 110 mg of unreacted 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane. The perfluoro-1,3-dioxole yield, calculated as in exaample 1, was of 85%. EXAMPLE 6 The preceding example was repeated, using 2 g of a mixture of isomers of 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane, which mixture was composed for 65% of anti isomer and for 35% of syn isomer. 842 mg of perfluoro-1,3-dioxole and 150 mg of unreacted 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane were recovered from the reaction. The perfluoro-1,3-dioxole yield, calculated as in the preceding examples, was of 68%.

Claims: A process for preparing 1,3-dioxoles of formula: wherein: X₁ and X₃, the same or different from each other, are F or H, X₅ and X₆, the same or different from each other, are F or CF₃, which comprises reacting a dioxolane of formula: wherein: X₂ and X₄, the same or different from each other, are Cl or Br, X₁, X₃, X₅ and X₆ have the meaning defined hereinbefore, with a dehalogenating agent at a temperature ranging from +30° to +130°C, the dioxolane (II) having a proportion of anti isomer of at least 60 %, and subsequently separating the dioxole (I) from the reaction products. The process of claim 1, wherein the proportion of anti isomer in the dioxolane (II) is of at least 80 %. The process of claim 1 or 2, characterized in that the dioxolane (II) is obtained from the reaction of a bis(fluoroxy)perfluoroalkane of formula C(OF)₂X₅X₆ with a halogenated olefin of formula CX₁X₂=CX₃X₄ at a temperature ranging from -140° to +60°C, X₁, X₂, X₃, X₄, X₅ and X₆ having the meaning defined hereinbefore. The process of one or more of the preceding claims, characterized in that the reaction of the dioxolane with at least a dehalogenating agent is conducted at a temperature ranging from +50° to +100°C. The process of one or more of the preceding claims, characterized in that the dehalogenating agent is a metal selected from the class comprising Zn, Mg, Hg, Cu, Fe and Sn. The process of claim 5, characterized in that the dehalogenating agent is metallic Zn. The process of one or more of the preceding claims, characterized in that the reaction of the dioxolane with at least a dehalogenating agent is conducted in the presence of sodium or potassium iodide and of sodium or potassium carbonate. The process of one or more of the preceding claims, characterized in that the reaction of the dioxolane with at least a dehalogenating agent is conducted in a solvent, which is inert under the reaction conditions. The process of claim 8, characterized in that the solvent is selected from amides, ethers and sulphoxides. The process of one or more of the preceding claims, characterized in that X₁ and X₃ are F. The process of one or more of the preceding claims, characterized in that X₅ and X₆ are F.

Inventors: FONTANA SIMONETTA, NAVARRINI WALTER, FONTANA, SIMONETTA, NAVARRINI, WALTER
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1992
Main classification: C07D317
IPC codes: C07D317