Received: September, 2012

Fluorine Notes, 2012, 84, 5-6

Method for the synthesis of pure (E)-3-(perfluoroalkyl)-allylic alcohols

Peter Ivanko, Csongor Szíjjártó, Dénes Szabó and József Rábai*

Institute of Chemistry, Eotvos Lorand University, P. O. Box 32, H-1518, Budapest 112, Hungary

e-mail: rabai@elte.hu

Abstract:Simple method for the preparation of (E)-3-(perfluoroalkyl)-allylic alcohols (1) is suggested.

Keywords: (E)-3-(perfluoroalkyl)-allylic alcohols, 3-perfluoroalkyl-2-iodo-1-propanols, lethargic dehydrohalogenation.

Perfluoroalkylpropenols have been prepared by the dehydrohalogenation of appropriate perfluoroalkyl-halohydrins and used as precursors for the synthesis of low surface energy materials. Their syntheses usually afford technical grade mixtures of the (E)-:(Z)-isomers, along with 2-perfluoroalkylmethyl-oxirane type side products. These methods call for simple inorganic bases such as NaOH, KOH, NaHCO₃, Na₂CO₃, alkoxides, or the bicyclic amidine type bases like DBU or DBN and use alcohol type solvents (MeOH, EtOH, and i-PrOH) at 15 to 100В°C reaction temperatures for 1-14 h treatments [1-3].

Perfluoroalkylpropenols [(E)-I/(Z)-I] could be made as disclosed in a US Patent in a 93:6 ratio of (E)-:(Z)-I with 69-91% yields using N-methylpirrilidone as solvent and Me₄NHCO₃ base for dehydrohalogenation of the starting halohydrins [4].

We have found that further increase of the (E)-:(Z)-isomeric ratio of F-alkyl-allylic alcohols (1a-e) was possible with the selective but rather slow dehydroiodination reaction of the easily accessible 3-perfluoroalkyl-2-iodo-1-propanols (2a-e, "fluorous-iodohydrins" [5]) with diethylamine as a base in ether at room temperature. The title compounds were obtained in high yields and purity after 11 to 44 days of reaction time. Any attempts to increase the rate of this type of reaction by using forcing conditions resulted in significant drop of yields and isomeric purities (cf. with the definition of "Lethargic reaction", [6]).
It should be noted that these iodohydrins (2a-e) could be involved in three different types of HI elimination reaction, either leading to the title Rfn-allylic alcohols (1a-e), fluorous-oxiranes (R_fnCH₂CHCH₂O) or -aldehydes (R_fnCH₂CH₂CH=O) [7].

The products obtained here were characterized by ¹H-, ¹³C and ¹⁹F-NMR spectra and GC. Their GC analyses indicate 95-97% presence of the trans-isomer, while that of the minor impurities at shorter retention times never exceeds 4%.

Experimental

The starting perfluoroalkyl-iodohydrins 2a-e were prepared by the reaction of perfluoroalkyl iodides 3a-e and allylic alcohol as reported [5]. ¹H-, ¹³C- and ¹⁹F-NMR spectra were recorded on Bruker Avance 250 instrument using a 5 mm inverse ¹H/¹³C/³¹P/¹⁹F probe head at room temperature. Chemical shifts (δ) are given in parts per million (ppm) units relatively to the internal standard TMS (δ=0.00 for 1H,δ=0.00 for 13C) and to CFCl₃ as external standard (δ=0.00 for ¹⁹F). В Melting points were determined on a Boetius micro-melting point apparatus and are uncorrected. The reactions were monitored by gas chromatography (Hewlett-Packard 5890 Series II, PONA [crosslinked methylsilicone gum] 50 m x 0.2mm x 0.5 mm column, H₂ carrier gas, FID detection; Program: 120 В°C, 5 min, 10 В°C/min, 250 В°C, 5 min; Inj.: 250В°C, Det: 280В°C).

General Procedure (GP). A solution of the iodohydrin (250mmol) in diethyl ether (2mL for 1g iodohydrin) was mixed with diethyl amine (750mmol) at room temperature. The reaction vessel was flushed with argon, closed and wrapped with an aluminum foil to protect from sunlight. The mixture was kept in the dark at room temperature until 99+% conversions were reached.The solid Et₂NH*HI salt was filtered off, washed with ether, and dried. Then the В filtrate was washed with 5% HCl-H₂O and water and dried (Na₂SO₄). The products were isolated by fractional distillation using a short Vigreaux column.

(E)-4,4,5,5,6,6,7,7,7-nonafluoro-hept-2-ene-1-ol (1a). The C₄F₉-iodohydrin (2a, 100 g, 248 mmol, GC assay 96%) was reacted according to the GP for 11 days and worked up to yield 57.05 g (83%) colorless oil, bp 85-86 В°C/20 mm Hg, with GC purity of 95.8%. ¹H NMR (CDCl₃) Оґ: 6.52 (hd, 1H, J= 15.8, 2.2 Hz, RfnCH); 5.95 (qa, 1H, J= 15.6 Hz, CHCH₂); 4.32 (m, 2H, J= 3.8, 2.2, 1.6 Hz, CH₂OH); 2.93 (s, br, 1H, OH); ¹³C NMR (CDCl₃) Оґ: 61.3 (C1); 116.4 (t, C2, J= 23.4 Hz); 141.6 (t, C3, J= 8.7 Hz); ¹⁹F NMR (CDCl₃) Оґ: -81.95 (tt, 3F, J= 9.9, 3.0 Hz, CF₃); -112.58 (~t, 2F, J= 12.0 Hz, CH₂CF₂); -125.05 (m, 2F, J= 10.1, 6.9 Hz); -126.59 (m, 2F, J= 6.9, 5.2 Hz).

(E)-4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-non-2-ene-1-ol (1b). The C₆F₁₃-iodohydrin (2b, 200 g, 397mmol, GC assay 96%) was reacted according to the GP for 14 days and worked up to yield 123 g (82%) colorless oil, bp 103 В°C/20 mm Hg, with GC purity of 96.1%. ¹H NMR (CDCl₃) Оґ: 6.52 (hd, 1H, J= 15.8, 2.2 Hz, R_fnCH); 5.95 (qa, 1H, J= 15.0 Hz, CHCH₂); 4.33 (m, br, 2H, CH₂OH); 2.66 (s, br, 1H, OH); ¹³C NMR (CDCl₃) Оґ: 61.5 (C1); 116.6 (t, C2, J= 23.4 Hz); 141.4 (t, C3, J= 8.5 Hz); ¹⁹F NMR (CDCl₃) Оґ: -81.77 (tt, 3F, J= 9.9, 2.6 Hz, CF₃); -112.43 (tt, 2F, J= 13.4, 3.4 Hz, CH₂CF₂);
-122.46 (br, 2F); -123.73 (br, 2F); -124.17 (m, br, 2F); -127.04 (m, 2F)

(E)-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoro-undec-2-ene-1-ol (1c). The C₈F₁₇-iodohydrin (2c, 200 g, 331mmol, GC assay 97%) was reacted according to the GP for 19 days and worked up to yield 140 g (89%) colorless oil, bp 126-127В°C/16 mmHg, with GC purity of 95.5%. ¹H NMR (CDCl₃) Оґ: 6.52 (hd, 1H, J= 15.8, 2.2 Hz, R_fnCH); 5.96 (qa, 1H, J= 15.2 Hz, CHCH₂); 4.33 (m, br, 2H, CH₂OH); 2.48 (s, br, 1H, OH); ¹³C NMR (CDCl₃) Оґ: 61.5 (C1); 116.6 (t, C2, J= 23.4 Hz); 141.4 (t, C3, J= 8.5 Hz); ¹⁹F NMR (CDCl₃) Оґ: -81.75 (~t, 3F, J= 9.9 Hz, CF₃); -112.40 (~t, 2F, J= 12.9 Hz, CH₂CF₂); -122.25 (m, br, 2F); -122.75 (m, br, 4F); -123.55 (m, br, 2F); -124.12 (m, br, 2F); -127.00 (m, br, 2F)

(E)-4,4,5,5,6,6,7,7,8,8,9,9,10,11,11,11-hexadecafluoro-10-trifluormethyl-undec-2-ene-1-ol (1d). The iso-C₉F₁₉-iodohydrin (2d, 48.3 g, 73.9mmol) was reacted according to the GP for 9 days and worked up to yield 27.7 g (71%) colorless oil, bp 142-144В°C/17 mmHg, with GC purity of 94.4%. ¹H NMR (CDCl₃) Оґ: 6.52 (hd, 1H, J= 15.8, 2.2 Hz, R_fnCH); 5.96 (qa, 1H, J= 14.7 Hz, CHCH₂); 4.34 (m, br, 2H, CH₂OH); 2.24 (s, br, 1H, OH); ¹³C NMR (CDCl₃) Оґ: 61.6 (C1); 116.6 (t, C2, J= 23.4 Hz); 141.5 (t, C3, J= 8.7 Hz) ¹⁹F NMR (CDCl₃) Оґ: -72.62 (m, 6F, CF₃); -112.31 (m, 2F, CH₂CF₂); -115.70 (s, br, 2F); -121.46 (s, br, 2F); -122.14 (m, br, 4F); -124.02 (m, br, 2F); -186.80 (m, br, 1F).

(E)-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,13-heneicosafluoro-tridec-2-ene-1-ol (1e). The C₁₀F₂₁-iodohydrin (2e, 25.0 g, 41.4mmol) was reacted according to the GP for 44 days and worked up to yield 16.9 g (71%) colorless melt, bp 108-110В°C/0.1 mm Hg, mp 54-56 В°C/isooctane, with GC purity of 94.4%. ¹H NMR (CDCl₃) Оґ: 6.71 (hd, 1H, J= 15.6, 2.4 Hz, R_fnCH); 6.06 (qa, 1H, J= 15.2 Hz, CHCH₂); 4.33 (s, br, 2H, CH₂OH); 2.94 (s, br, 1H, OH); ¹³C NMR (CDCl₃) Оґ: 61.5 (C1); 115.4 (t, C2, J= 23.4 Hz); 141.5 (t, C3, J= 8.5 Hz); ¹⁹F NMR (CDCl₃) Оґ: -81.74 (t, 3F, J= 10.4 Hz, CF₃); -112.41 (t, 2F, J= 12.9 Hz, CH₂CF₂); -122.21 (s, br, 2F); -122.60 (s, br, 8F); -123.51 (s, br, 2F); -124.13 (s, br, 2F); -126.99 (m, br, 2F)

Acknowledgement. This study was supported by the Hungarian Scientific Research Foundation (OTKA K 062191 "Sustainable fluorous chemistry"): The European Union and the European Social Fund have provided financial support to the project under the grant agreement no.TÁMOP_4.2.1./B-09/1/KMR-2010-0003

References

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3. US4278552, I. Hisamoto, et al. (Daikin Kogyo, Co.,Ltd) Patent filed: April 12, 1979. (et al. = N. Enjo, C. Maeda, T. Esaka, Y. Omure, T. Iida, H. Aomi)
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Recommended for publication by S. Igoumnov

Fluorine Notes, 2012, 84, 5-6