Synthesis of N,N-bis(trifluoromethyl)amino difluoromethylene trifluorovinyl ether

Journal of Fluorine Chemistry 132 (2011) 1194–1197

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Synthesis of N,N-bis(trifluoromethyl)amino difluoromethylene trifluorovinyl ether Darryl D. DesMarteau *, Changqing Lu Department of Chemistry, Clemson University, Clemson, SC 29634, USA

A R T I C L E I N F O

A B S T R A C T

Article history: Received 18 April 2011 Received in revised form 7 June 2011 Accepted 9 June 2011 Available online 1 July 2011

The first N-containing trifluorovinyl ether monomer (CF3)2NCF2OCF5 5CF2 was synthesized. The starting 5CF2 was converted to the perfluoroalkyl amine (CF3)2NH by HF. The amine perfluoroalkyl imine CF3–N5 was converted into the carbamoyl fluoride (CF3)2NC(O)F via reaction with carbonyl fluoride COF2 in the presence of NaF. The carbamoyl fluoride was subjected to catalytic fluorination with molecular F2 in the 5CFCl to presence of CsF to afford the hypofluorite (CF3)2NCF2(OF). The hypofluorite was added to CFCl5 provide a saturated halocarbon ether. Dechlorination of the ether with zinc in DMSO resulted in the title monomer. The new vinyl ether monomer readily copolymerizes with TFE. ß 2011 Elsevier B.V. All rights reserved.

Keywords: Fluorocarbon-nitrogen hypofluorite Trifluorovinyl ether monomer Fluoropolymer

1. Introduction Fluoropolymers have found increasing applications in petrochemical industries, microelectronics, aerospace, automotive, optics, and many others due to their thermostability, chemical inertness, surface energy, and dielectric constant [1]. The importance of fluorinated vinyl ethers in fluoropolymer technology is well known. For example, fluoroelastomers are synthesized from the radical copolymerization of fluoroalkenes (VDF, HFP, TFE, etc.) with perfluoroalkyl or perfluoroalkoxyalkyl trifluorovinyl ethers (PAVE) [2–9]. Copolymerization of perfluoroalkyl trifluorovinyl ethers CF25 5CFOCnF2n+1 (n = 1, 2, 3) with VDF led to fluoroelastomers with low glass transition temperatures [10]. Recently, perfluorovinylether monomers, CF25 5CFOCF2OCF2CF3 and CF25 5CFOCF2OCF2CF2OCF3, were prepared starting from CF2(OF)2. These highly reactive vinylethers are characterized by the OCF2O group directly bonded to the unsaturation. For this reason, they are excellent candidates for the preparation of very low Tg perfluororubbers [11]. The preparation of a variety of OCF2O group containing fluorovinylether monomers and the polymers obtainable there from were also reported [12,13]. Among these perfluoroalkoxyalkyl trifluorovinyl ether monomers, one with considerable interest is CF3OCF2OCF5 5CF2, whose copolymers have been used to formulate novel fluoroelastomers with very low glass transition temperatures [14,15]. Although a variety of functionalized trifluorovinyl ethers have been prepared, no fluorocarbon nitrogen functionalization appears

* Corresponding author. Tel.: +1 864 656 1251; fax: +1 864 656 2545. E-mail address: fl[email protected] (D.D. DesMarteau). 0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2011.06.012

to be known. This research describes the synthesis of a new fluorocarbon–nitrogen hypofluorite (CF3)2NCF2OF which can be used to prepare a functional vinyl ether (CF3)2NCF2OCF5 5CF2. The new vinyl ether monomer readily copolymerizes with TFE and may provide useful fluoropolymers. 2. Results and discussion (Trifluoromethyl)-carbonimidic difluoride was used as the starting material [16]. As shown in Scheme 1, by reacting with anhydrous HF, the starting material was converted into N,Nbis(trifluoromethyl)amine (1) in high yield. As shown in Scheme 2, the elimination of HF between (CF3)2NH (1) and carbonyl difluoride in the presence of NaF afforded N,Nbis(trifluoromethyl) carbamoyl fluoride (2). Carbamoyl fluoride (2) is a known compound and was obtained by electrochemical fluorination decades ago [17]. Carbamoyl fluoride (2) was directly fluorinated with excess molecular F2 in the presence of dry CsF at low temperature as shown in Scheme 3. The excess fluorine was removed at 196 8C. The crude product was fractionated to give the desired N,Nbis(trifluoromethyl)amino difluoromethylene hypofluorite (3) (CAUTION! hypofluorite (3) could be explosive and should be handled at low temperature and used immediately). Hypofluorite (3) was characterized by IR and 19F NMR spectroscopy. The wavelength for the characteristic IR absorption of O–F bond is 878 cm 1. The characteristic 19F NMR chemical shift for O–F is 168 ppm. The splitting patterns of 19F NMR peaks (triplet, triplet, and octet) match the structure of hypofluorite (3). The hypofluorites containing OCF2O unit are reactive species. The addition of these hypofluorites to halogenated olefins has been

D.D. DesMarteau, C. Lu / Journal of Fluorine Chemistry 132 (2011) 1194–1197

F3C-N=CF2

HF

70 oC, 24 h 95.6%

N,N-bis(trifluoromethyl)amino difluoromethylene trifluorovinyl ether readily copolymerizes with TFE in the presence of a radical initiator. Due to the limited amount of (CF3)2NCF2OCF5 5CF2 monomer and the un-optimized solution polymerization conditions, the TGA in Fig. 2 may not reflect the optimal polymers between monomer (CF3)2NCF2OCF5 5CF2 and TFE.

(CF3)2NH 1

Scheme 1. Addition of HF to imine moiety of starting material.

extensively studied [11,18]. The applications of these hypofluorites in industries to make fluoromonomers have also been well established [19]. Hypofluorite (3) contains NCF2O unit and could be used to synthesize a corresponding trifluorovinylether monomer via the well established halogenated olefin addition–elimination methodology [20]. Hypofluorite (3) was added to 1,2-dichloro-difluoroethene (a mixture of E- and Z-isomers) at low temperature as shown in Scheme 4. After the fractionation of the reaction mixture, the saturated halocarbon ether intermediate (4) was obtained. The intermediate (4) was dechlorinated with zinc in DMSO as shown in Scheme 5. The final product N,N-bis(trifluoromethyl)amino difluoromethylene trifluorovinyl ether (5) was obtained after the fractionation of the reaction mixture. The monomer (CF3)2NCF2OCF5 5CF2 (5) was characterized by IR and 19F NMR spectroscopy. The characteristic IR absorption of the C5 5C bond is 1839 cm 1. Monomer (5) was copolymerized with TFE in the presence of a radical initiator as shown in Scheme 6. The IR and TGA characterization of the copolymer are shown in Figs. 1 and 2. IR spectrum in Fig. 1 shows three new peaks at 1359, 992, and 732 cm 1 compared to that of PTFE. TGA characterization also supports the copolymerization between monomer (5) and TFE. The copolymerization was not optimized and the TGA suggests the presence of some low-molecular weight species. In summary, the new monomer N,N-bis(trifluoromethyl)amino difluoromethylene trifluorovinyl ether has been synthesized by the addition of N,N-bis(trifluoromethyl)amino difluoromethylene hypofluorite to 1,2-dichloro-difluoroethene followed by zinc dechlorination in DMSO. N,N-bis(trifluoromethyl)amino difluoromethylene hypofluorite was obtained by catalytic fluorination of N,N-bis(trifluoromethyl) carbamoyl fluoride.

(CF3)2NH

COF2

1195

3. Experimental procedures 3.1. Instruments 19

F NMR spectra were obtained on a JEOL ECX 300 NMR at 282.78 MHz. CFCl3 was used as the reference. Infrared spectra were recorded on a PerkinElmer 2000 FTIR. IR spectroscopy for a single compound was measured in gas phase at 5 Torr in a 10 cm glass cell with AgCl windows. IR spectroscopy for polymer was measured in a mixture with KBr. TGA were obtained with Perkin Elmer TGA-7. 3.2. Preparation of N,N-bis(trifluoromethyl)amine (1) [21] HF (0.270 g, 13.50 mmol) and CF3–N5 5CF2 (783 Torr, 0.32 L, 13.49 mmol) were condensed into a 50 mL Monel reactor and heated at 70 8C for 24 h. The reaction mixture was monitored by IR and NMR spectroscopy. After trap-to-trap fractionation at 70 8C, 120 8C, 160 8C, and 196 8C, (CF3)2NH (1) (749 Torr, 0.32 L, 12.91 mmol, 95.6%) was obtained at 120 8C trap. 19F NMR (282 MHz, CDCl3): d (ppm) 56.5 (s, 6F). IR (gas phase, 5 Torr): n (cm 1) 3464(m, nN–H), 1501(s), 1353(s), 1264(s), 1204(s), 1145(m), 950(m), 681(m). 3.3. Preparation of N,N-bis(trifluoromethyl) carbamoyl fluoride (2) [18] (CF3)2NH (1) (749 Torr, 0.32 L, 12.91 mmol) and COF2 (1683 Torr, 0.32 L, 28.95 mmol) were condensed into a 150 ml Monel reactor containing 5 g of dry NaF. The reactor was heated at 40 8C for 48 h. The reaction mixture was then subjected to trap-totrap fractionation at 70 8C, 110 8C, 150 8C, and 196 8C. The excess of COF2 was recovered at 196 8C trap. The desired product (CF3)2NC(O)F (2) was obtained at 70 8C and 110 8C traps

40 oC, 48 h

NaF

89.0%

1

NaHF2

(CF3)2NC(O)F 2

Scheme 2. Formation of N,N-bis(trifluoromethyl) carbamoyl fluoride.

(CF3)2NC(O)F 2

F2

CsF o

80 C, overnight 83.1%

(CF3)2NCF2(OF) 3

Scheme 3. Catalytic fluorination of carbamoyl fluoride with molecular F2.

(CF3)2NCF2(OF) 3

CFCl=CFCl

80 oC overnight 86.2%

F

F

(CF3)2NCF2O

Scheme 4. Addition of hypofluorite (3) to 1,2-dichloro-difluoroethene.

Cl 4

F Cl

D.D. DesMarteau, C. Lu / Journal of Fluorine Chemistry 132 (2011) 1194–1197

1196

F

F

(CF3)2NCF2O Cl 4

F Cl

F

F

(CF3)2NCF2O

F

Zn / DMSO 50 oC, 48 h 88.3%

5

Scheme 5. Dechlorination of intermediate (4) with zinc.

(667 Torr, 0.32 L, 11.49 mmol, 89.0%). 19F NMR (282 MHz, CDCl3): d (ppm) 5.62 (sept, 4J = 16.3 Hz, 1F), 55.8 (d, 4J = 16.3 Hz, 6F). IR (gas phase, 5 Torr): n (cm 1) 1884(s, nC5 5O), 1375(s), 1316(s), 1238(s), 1187(m), 1034(m), 999(s), 758(w), 732(m), 711(m). 3.4. Preparation of N,N-bis(trifluoromethyl)amino difluoromethylene hypofluorite (3) (CF3)2NC(O)F (2) (100 Torr, 0.32 L, 1.72 mmol) and F2 (5.21 mmol) were condensed into a 150 ml Monel reactor containing 15 g of dry CsF. The reactor was kept at 80 8C overnight. The excess of fluorine was removed at 196 8C. The crude product was then subjected to trap-to-trap fractionation at 80 8C, 120 8C, 160 8C, and 196 8C. The hypofluorite (CF3)2NCF2(OF) (3) was obtained at 80 8C trap (83 Torr, 0.32 L, 1.43 mmol, 83.1%) [CAUTION! hypofluorite (3) could be explosive and should be handled at low temperature and used immediately]. 19 F NMR (282 MHz, CCl4, 45 8C): d (ppm) 168 (t, 3J = 12.1 Hz, 1F),

(CF3)2NCF2OCF=CF2

CF2=CF2

5 0.396 mmol

TFE 1.98 mmol

54.8 (t, 4J = 12.8 Hz, 6F), 72.4 (dsept, 3J = 12.1 Hz, 4J = 12.8 Hz, 2F). IR (gas phase, 5 Torr): n (cm 1) 1363(s), 1232(s), 998(s), 979(m), 878(w, nO–F), 757(w), 734(w). 3.5. Addition of N,N-bis(trifluoromethyl)amino difluoromethylene hypofluorite to 1,2-dichloro-difluoroethene (CF3)2NCF2(OF) (3) (80 Torr, 0.32 L, 1.38 mmol) was transferred into a 50 ml Monel reactor with liq. N2 cooling. CFCl5 5CFCl (E/Z mixture from SynQuest) (80 Torr, 0.32 L, 1.38 mmol) was then condensed through vacuum line into the reactor. The reactor was kept at 80 8C overnight, then slowly warmed up to room temperature over 5 h. Trap-to-trap fractionation at 60 8C, 120 8C and 196 8C was then carried out. In 60 8C trap, the desired compound (CF3)2NCF2OCFCl–CF2Cl (4) was obtained (69 Torr, 0.32 L, 1.19 mmol, 86.2%). 19F NMR (282 MHz, CDCl3): d (ppm) 55.1 (t, 4J = 12.8 Hz, 6F), 57.6 (m, 2F), 71.1 (m, 2F), 78.3 (m, F). IR (gas phase, 5 Torr): n (cm 1) 1360(s), 1295(s), 1230(s), 1186(s), 1150(s), 1123(s), 1037(s), 995(s), 847(m), 738(w), 637(w). 3.6. Dechlorination of (CF3)2NCF2OCFCl–CF2Cl (4) with Zn in DMSO In a dry box, Zn (0.50 g, 7.69 mmol) was added into a 100 ml Ace thread reactor. Under N2 protection, 25 ml of dry DMSO was added.

1.28 mol% [(CF3)2CFC(O)O]2 F-113, 56 oC, 24 h

(CF3)2NCF2

O

F

F

F

F

C C F

F

C C

Scheme 6. Copolymerization of monomer (5) with TFE.

Fig. 1. IR spectroscopy of copolymer of monomer (5) with TFE.

m

F

n

D.D. DesMarteau, C. Lu / Journal of Fluorine Chemistry 132 (2011) 1194–1197

1197

Fig. 2. TGA of copolymer of monomer (5) with TFE.

(CF3)2NCF2OCFCl–CF2Cl (4) (60 Torr, 0.32 L, 1.03 mmol) was transferred through vacuum line into the reactor cooled with liq. N2. The reaction mixture was stirred and heated at 50 8C for 48 h. Trap-to-trap fractionation was conducted at 50 8C, 100 8C, 150 8C, and 196 8C. In 100 8C trap, the desired product (CF3)2NCF2OCF5 5CF2 (5) (53 Torr, 0.32 L, 0.91 mmol, 88.3%) was obtained. 19F NMR (282 MHz, CDCl3): d (ppm) 55.2 (t, 4 J = 16.3 Hz, 6F), 60.0 (m, 4J = 12.1 Hz, 4J = 12.8 Hz, 2F), 113.7 (dd, 3J = 12.1 Hz, 3J = 12.8 Hz, 1F), 121.7 (dd, 3J = 12.1 Hz, 2 J = 12.8 Hz, 1F), 137.0 (dd, 3J = 12.1 Hz, 2J = 12.8 Hz, 1F). IR (gas phase, 5 Torr): n (cm 1) 1839(w, nC5 5C), 1359(s), 1277(s), 1230(s), 1169(s), 1126(s), 1096(w), 993(s), 758(m), 732(m). 3.7. Copolymerization of monomer (5) with TFE Into a 50 ml stainless steel reactor containing glass beads for mixing, F-113 (2 ml) and perfluorinated initiator [(CF3)2CFC(O)O]2 (0.0304 mmol in 0.15 ml of F-113, 1.28% in molar ratio of the total monomers) were added. The system was cooled at 196 8C and the air inside the reactor was evacuated. After the process of warming up with ice water, cooling down with liq. N2, and removing air under vacuum was repeated once, two monomers, (CF3)2NCF2OCF5 5CF2 (5) (23 Torr, 0.32 L, 0.396 mmol) and TFE (CF25 5CF2) (115 Torr, 0.32 L, 1.98 mmol), were introduced into the reactor through vacuum line. The reactor was then allowed to warm up to room temperature slowly, shaken and heated with a heat tape at 56 8C for 24 h. The copolymerization solution was poured into a flask, and the solvent was evaporated. The residue was heated at 80 8C under vacuum overnight to yield a white solid copolymer (0.263 g, 83.2%).

Acknowledgement We gratefully acknowledge the partial financial support of this research by Solvay Solexis.

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