IE64724B1

IE64724B1 - Synthesis of perfluoroalkyl bromides

Info

Publication number: IE64724B1
Application number: IE921621A
Authority: IE
Inventors: Gilles Drivon
Original assignee: Atochem Elf Sa
Priority date: 1991-05-21
Filing date: 1992-07-01
Publication date: 1995-08-23
Also published as: HU207506B; AU642350B2; IE921621A1; FI922293A0; CN1032306C; IL101772A; FI922293A; HUT60987A; NO921992L; CN1067239A; EP0515258A1; AU1703892A; EP0515258B1; CA2069018A1; NO177636C; ES2057968T3; DK0515258T3; IL101772A0; NO921992D0; KR920021478A

Abstract

Preparation of perfluoroalkyl bromides RF-Br, RF denoting a linear or branched perfluoroalkyl radical containing from 2 to 12 carbon atoms. The continuous process according to the invention consists in reacting bromine and a perfluoroalkyl iodide RF-I in the gas phase at a temperature of between 200 and 600 DEG C, it being possible for the Br2/RFI molar ratio to range from 0.1 to 2. The selectivity for RF-Br is virtually complete.

Description

The present invention relates to the preparation of perfluoroalkyl bromides or bromoperfluoroalkanes RF-Br, RF * denoting a linear or branched perfluoroalkyl radical CnF2rHl, containing from 2 to 12 carbon atoms. * These known compounds are employed in many fields, in particular in medicine as radioopacifiers (X-ray contrast agents) or as oxygen carriers in blood substitutes. A compound more particularly investigated in this field is nperfluorooctyl bromide C8F17Br.

Among the known methods for preparing these compounds there may be mentioned in particular: the action of bromine on a compound RfSF5 at 500 "C in the presence of nickel (US Patent 3,456,024); J - the gas phase photolysis of a compound RFH with 15 Br-Cl or Br-F (J.L. Adcock et al., CA 100. 34092 e) or with Br2 (French Patent FR 1,512,068).

The poor yields obtained and/or the use of fluorine derivatives which are not available industrially mean that economical production of the RFBr compounds on an industrial scale is not possible.

European patent EP 0,298,870 and European patent application EP 90403118.4 describe processes for the manufacture of RFBr compounds from the corresponding perfluoroalkane-sulphonyl chlorides RFSO2C1 which are reacted * either with gaseous HBr in the presence of a catalyst (EP 0,298,870), or with a quaternary ammonium or phosphonium bromide (EP 90403118.4). The yields obtained are generally high but the sulphochloride RFSO2C1, employed as starting material, is very complex to produce, since its synthesis from the corresponding iodide RFI requires two reaction stages, according to the equation: ( Zn 2C12 RfI + 2 S02 -> (RFSO2)2n —-> 2 RFSO2Cl + ZnCl2 The most direct route for obtaining the compounds RFBr would comprise radical bromination of the corresponding iodides RFI, the latter being products which are available in industrial quantities.

International Journal of Chemical Kinetics, vol. II, 273-285 (1975), E.N. Okafo et E. Whittle, describes the kinetics of thermal bromination of CF3I in a photochemical reactor between 173 and 321‘C, with a view to determining the dissociation energy of the C-I bond.

J. Chem. Soc. 1953, 3761-8, R.N. Haszeldine, describes a photochemical process for reacting RFI with bromine, the operation being carried out in a sealed tube with an excess of bromine (10 %) and while irradiating with a UV light for seven days. The reaction temperature and the purity obtained are not stated; it is merely indicated that the yield is higher than or equal to 90 %, depending on the length of the perfluorinated chain RF.

In examples of Japanese Application Kokai 85-184,033, which describes the reaction of RFI with Br2 in the presence of a chemical radical initiator, the yields indicated do not exceed 42 %.

The poor yields obtained and/or the slow kinetics of these techniques do not make it possible to envisage their * industrial exploitation.

According to the present invention, there is provided a continuous process for the preparation of a perfluoroalkyl bromide Rf-Br (wherein RF represents a linear or branched perfluoroalkyl radical containing from 2 to 12 carbon atoms) which process comprises reacting in gaseous phase bromine with the corresponding perfluoroalkyl iodide Rf-I (wherein RF represents a linear or branched perfluoroalkyl radical as defined above).

» The process of the present invention permits continuous production of perfluoroalkyl bromides RFBr containing from 2 to 12, preferably 6 to 10, carbon atoms, from the corresponding RFI, with very high selectivity for RFBr. The process according to the invention is characterised in that an RFI and bromine are reacted continuously in gaseous phase.

The reaction can be carried out in a tubular reactor at a temperature ranging from 200 to 600*0, but is advantageously operated at a temperature of between 300 and 500’C, preferably between 350 and 500C. The reactor can be t. a hollow tube, but it may optionally contain an inert solid substrate (for example glass or quartz) to facilitate the contact between the two gases (Br2 and RFI). The operation may also be carried out in the presence of an inert gaseous diluent, for example nitrogen, although this is not essential. t Since the reaction of bromine with RFI in gaseous phase is very fast, the contact time, that is to say the residence time of the reactants in the reactor, is not a critical parameter and may vary within wide limits. A contact time of from 1 second to 2 minutes is generally suitable but, on an industrial scale, it is preferred to operate with a contact time ranging from 5 to 30 seconds.

On an industrial scale it is preferred to work at atmospheric pressure, but working at a pressure above atmospheric pressure would not constitute a departure from the scope of the present invention, provided that the reaction system remains in the gaseous state.

To recover the RFBr formed and optionally unconverted RFI the gases leaving the reactor may be cooled, and the mixture is then distilled directly or after treatment with a reducing agent.

The process according to the invention may be implemented by operating with an excess or a deficiency of bromine in relation to the theoretical quantity (0.5 mol of Br2 per mol of RFI) . The Br2/RFI molar ratio may therefore * vary within wide limits, generally between 0.1 and 2.

However, for process economy, the operation is advantageously * carried out at a Br2/RFI molar ratio of between 0.3 and 1.

When the operation is carried out with an excess of bromine, and whatever the temperature and the contact time, the reaction takes place according to the scheme: RfI + Br2 ·* RFBr + Brl (1) Depending on the operating conditions used, it is then possible to obtain substantially complete conversion of the RFI, and this makes it easier to recover the RFBr in a very pure state merely by distillation. However, because of the thermodynamic equilibrium: Brl Br2 + h I2 a mixture containing bromine and iodine is inevitably found at the reactor exit.

When the operation is carried out with a deficiency of bromine and depending on the operating conditions (molar ratio, temperature, contact time), the reaction takes place either according to the scheme (1) above, or according to the scheme (2): RfI + Br2 -* 2 RFBr + I2 (2) Bearing in mind the deficiency of bromine, only partial conversion of the RFI will be obtained. However, it is possible to combine the operating conditions such as to permit a substantially complete conversion of the bromine (equation 2), and this simplifies the recovery and the upgrading of the iodine obtained as a by-product in its oxidised or reduced form. After separation of the iodine, the RFBr/RFI mixture can be distilled to separate off the unconverted RfI and to recycle it to the reactor. It is also possible to add supplemental bromine to the RFBr/RFI mixture and to complete the reaction in a second reactor.

The bromine and the RFI may be introduced into the reactor separately. However, since bromine is partially soluble in the RFI, it is advantageously possible, when working at a molar ratio below the solubility limit, to introduce both reactants by starting with a homogeneous mixture of these two compounds; this then makes it possible to operate with a single feed pump and thus to ensure a constant molar ratio.

The process according to the invention applies both to the preparation of a specific RFBr (for example C6F13Br, C8F17Br, C10F21Br, etc.) and to that of a mixture of different RFBr'compounds from a mixture of the corresponding RfI compounds.

In the following Examples, which further illustrate the invention, the degree of conversion (DC) of the RfI is calculated using the relationship: RfI moles input - RfI moles output DC 100 x RfI moles input δ and the selectivity (S) for RFBr using the relationship: S = 100 - (% of miscellaneous output - % of impurities input) EXAMPLE 1 : SYNTHESIS OF PERFLUOROOCTYL BROMIDE A glass tubular reactor (internal diameter: 30 mm; height: 300 mm) is employed, with 1/5 of it packed with rings to ensure good gas mixing, equipped with a thermometer sheath for checking the temperature and with a dip tube for introducing the reactants.

Test No. 1 This reactor is fed simultaneously and continuously for 2 hours, with the aid of two metering pumps, with 0.261 mol of bromine and 0.560 mol of perfluorooctyl iodide (purity: 99.3 %), together with 2 1/h of nitrogen.

The operating conditions are the following: temperature = 300’C contact time «30 seconds Br2/C8F 17I molar ratio = 0.47 The gases leaving the reactor are collected in an excess of aqueous solution of sodium sulphite. After settling, two phases are obtained: an upper aqueous phase which is analysed -, quantitatively by argentimetry to determine the content of bromide and iodide which are present (1' = 0.374 eq. and Br' = 0.150 eg.); - a lower organic phase which weighs 283.5 g and whose analysis by gas phase chromatography with a Varian 3300 *1 apparatus (catharometer detector; 30 m macrobore DB 1 » column:) gives the following composition by weight: C8F17Br = θ2·55 % C8F17I = 36.80 % miscellaneous = 0.65 % which corresponds to a degree of conversion of C8F17I of 66 % and a. selectivity for C8F17Br of 100 %.

Tests No. 2 to 26 These tests, carried out in the same apparatus and operating in the same way as in the case of Test No. 1, show the influence of the various parameters on the degree of conversion and the selectivity.

The operating conditions, the quantities employed and the results obtained in these tests are summarised in Tables I to V, which follow.

TABLE I EFFECT OF THE REACTION TEMPERATURE Contact time s 30 ± 2 seconds Br2/C8F17I molar ratio : 1 1 0.1 Purity of the starting C8F17I : 99.3 % Duration of a test : approximately 2 hours TEST Operating conditions Quantities used REACTOR EXIT Organic phase Agueou β phase No. Temperature •c . Br2/C8F17I molar ratio Br2 mol CeP17I mol Weight (9) CeF„Br mol c8f17i mol DC % Misc. % S % I’ eq. Br eq. 2 250 1.07 0.423 0.396 200.8 0.153 0.228 42.5 0.64 100 0.155 0.716 3 300 1 0.92 0.340 0.368 179.2 0.294 0.058 84 0.70 100 0.312 0.419 4 350 0.99 0.342 0.344 167.6 0.334 0.001 99.7 0.66 100 0.356 0.357 5 400 0.94 0.303 0.322 156.6 0.314 c #100 0.66 100 0.336 0.312 6 450 0.91 0.269 0.297 145.3 0.290 € #100 0.72 100 0.312 0.266 7 500 1.09 0.300 0.276 133.4 |0.264 e #100 1.42 99.3 0.287 0.343 ..

TABLE II EFFECT OF THE Br,/C.F,7I MOLAR RATIO AT 300 °C Contact time : 30 ± 2 seconds Purity of the starting CeFnI : 99.3 % Duration of a test : approximately 2 hours TEST NO. Br2/CaF jjl molar ratio Quantities usee REACTOR EXIT Organic phase Agueous phase Br2 mol CeFxjI mol Weight (9) CeF„Br mol c8f17i mol DC % Misc. % s % 1' eq. Br eq. 8 0.30 0.200 0.669 344.5 0.311 0.344 48.5 0.70 100 0.316 0.072 9 0.32 0.199 0.621 319.2 0.315 0.293 53 0.8 99.9 0.328 0.060 io 0.36 0.225 0.621 315.4 0.345 0.256 59 0.95 99.75 0.354 0.090 1 0.47 0.261 0.560 283.5 0.356 0.191 66 0.65 100 0.374 0.150 11 0.52 0.326 0.621 313.4 0.420 0.187 70 0.70 100 0.432 . 0.208 3 0.92 0.340 0.368 179.2 0.294 0.058 84 0.70 I 100 0.312 0.419 TABLE III EFFECT OF THE Br,/C.F.,I MOLAR RATIO AT 350*C Contact time : 30 i 2 seconds Purity of the starting C8F1?I : 99.3 % Duration of a test : approximately 2 hours TEST No. Br2/CaF17I molar ratio Quantities used REACTOR EXIT Organic phase Agueous phase Br2 mol CeFi,I mol Height (g) CeF nBr mol CeFnI mol DC % Mlsc. % S % I' eq. Br‘ eq. 12 0.30 0.182 0.606 310.7 0.341 0.255 58 0.4 100 0.334 e 13 0.385 0.216 0.562 271.8 0.405 0.123 78 0.9 99.8 0.404 0.014 14 0.54 0.279 0.513 251.8 0.471 0.028 94.5 0.6 100 0.494 0.066 4 0.99 0.342 0.344 167.6 0.334 0.001 99.7 0.66 100 0.356 0.357 -x' TABLE IV EFFECT OF THE Br,/C.F,,I MOLAR RATIO AT 400*C Contact time : 30 ί 2 seconds Purity of the starting C8F17I : 99.3 % Duration of a test : approximately 2 hours — TEST Br2/C8F17I Quantities used REACTOR EXIT Organic phase Agueou s phase No. molar ratio Br2 mol c8f»i mol Weight (9) C8F17Br mol cbf17i mol DC % Miec. % S % I* eq. Br' eq. 15 0.30 0.161 0.533 283.8 0.300 0.231 56.5 0.60 100 0.304 t 16 0.36 0.171 0.478 236.7 0.337 0.123 74 0.70 100 0.348 t 17 0.37 0.178 0.478 240.2 0.355 0.112 76.5 0.90 99.8 0.364 t 18 0.52 0.250 0.478 234.1 0.447 0.017 96.5 0.70 100 0.478 0.040 19 0.52 0.248 0.478 237.1 0.454 0.016 96.5 0.70 100 0.486 0.032 20 0.59 0.285 0.478 232.5 0.463 e 100 0.60 100 0.491 0.087 5 0.94 0.303 0.322 156.6 0.314 e 100 0.66 100 0.336 0.312 TABLE V Contact time : 10 ί 1 seconds Purity of the starting C8F17I : 99.1 % Duration of a test : approximately 1 hour Nitrogen flow rate : 2.2 to 4.3 1/h TEST Operating conditions Quantities used REACTOR EXIT Organic phase Aqueous phase No. Temperature •c Br2/C8F17I molar ratio Br2 mol CeF17I mol Weight (9) CeFx7Br mol c8f17i mol DC % Misc. % S % I* eq. Br' eq. 21 300 0.30 0.329 1.100 563.1 0.511 0.554 49.5 1.0 99.9 0.518 0.114 22 350 0.30 0.300 0.996 513.6 0.569 0.412 58.5 0.9 100 0.564 0.018 23 400 0.30 0.278 0.927 475.5 0.553 0.356 61.5 1.0 99.9 0.536 c 24 300 0.98 0.660 0.670 330 0.562 0.085 87.5 0.9 100 0.560 0.750 25 350 0.89 0.539 0.608 293.2 0.574 0.008 98.5 0.9 100 0.605 0.430 26 400 0.84 0.469 0.558 270.8 0.530 0.007 98.5 0.9 100 0.565 0.350 EXAMPLE 2 : SYNTHESIS OF PERFLUOROHEXYL BROMIDE Test No. 27 g (0.444 mol) of bromine and 180 g (0.404 mol) of perfluorohexyl iodide (purity: 99.5 %) are introduced over 40 minutes simultaneously and continuously, in the presence of 8.4 1/h of nitrogen, into the same apparatus as in Example 1, under the following operating conditions: temperature : 350°C - contact time : 8.6 seconds Br2/C6F13I molar ratio : 1.1 At the reactor exit, after neutralisation in an aqueous solution of sodium sulphite and settling, an organic phase is recovered, containing 98.8 % by weight of C6F13Br and 0.65 % of C6F13I, which corresponds to a selectivity for C6F13Br close to 100 %.

Test No. 28 The starting material is a homogeneous mixture of 441.7 g (0.99 mol) of C6F13I and of 67.2 g (0.42 mol) of bromine, which is introduced over 168 minutes with the aid of a single metering pump into the same reactor as in Example 1, in the absence of nitrogen, under the following operating conditions: temperature : 350°C - contact time : 28 seconds - Br2/C6F13I molar ratio : 0.42 After reduction with sulphite and settling, an organic phase is recovered at the reactor exit, containing, on a weight basis, 77.7 % of C6F13Br and 21.8 % of C6F13I corresponds to a selectivity for C6F13Br of 100 %. which

Claims

1. A continuous process for the preparation of a perfluoroalkyl bromide R F -Br (wherein R F represents a linear or branched perfluoroalkyl radical containing from 2 to 12 carbon atoms) which process comprises reacting in gaseous phase bromine with the corresponding perfluoroalkyl iodide R f -I (wherein R F represents a linear or branched perfluoroalkyl radical as defined above).

2. A process according to claim 1, in which the reaction is carried out at a temperature of 200 to 600°C.

3. A process according to claim 1, in which the reaction is carried out at a temperature between 350 and 500°C.

4. A process according to any preceding claim, in which the Br 2 /R F I molar ratio is between 0.1 and 2.

5. A process according to any of claims 1 to 3, in which the Br 2 /R F I molar ratio is between 0.3 and 1.

6. A process according to any preceding claim in which the reaction is carried out in the presence of an inert diluent.

7. A process according to claim 6, in which the inert diluent is nitrogen.

8. A process according to any preceding claim in which the contact time is from 1 second to 2 minutes.

9. A process according to any of claims 1 to 7, in which the contact time is from 5 to 30 seconds.

10. A process according to any preceding claim in which the reaction is carried out at atmospheric pressure.

11. A process according to any preceding claim in which a homogeneous mixture of bromine and R F I is introduced into the reactor.

12. A process according to any preceding claim in which the reaction is carried out with a Br 2 /R F I molar ratio below 0.5, and the iodine is then separated from the reaction mixture to obtain a R F Br/R F I mixture which is either distilled and the R F I is recycled, or to which supplemental bromine is added and the reaction is completed in a second reactor.

13. A process according to any preceding claim for the preparation of perfluorooctyl bromide.

14. A process according to any one of claims 1 to 12 for the preparation of perfluorohexyl bromide.

15. A process according to any one of claims 1 to 12 for the preparation of perfluorodecyl bromide.

16. A process according to any one of claims 1 to 12 for the preparation of a mixture of perfluoroalkyl bromides.

17. A process according to claim 1 substantially as described in Example l or 2.

18. A perfluoroalkyl bromide prepared by the process claimed in any preceding claim.