D.A. Wiebe, D.J. Burton / Journal of Fluorine Chemistry 139 (2012) 4–11
11
removed by distillation, and the residual liquid was distilled
through a 6 in. Vigreux column from 20 ml conc. H2SO4 to yield
2.7 g (0.009 mol) of 25, 51%, bp 92–95 8C, nD20 = 1.3144. IR:
before the addition of 10 ml conc. H2SO4. Distillation of the acid
mixture afforded 1.7 g (0.0004 mol), 67% of 29, mp 60–61 8C. The
product crystallized throughout the distillation apparatus and
required the use of a 150 W sunlamp to melt the product for
1768 cmꢀ1 (CHO). 19F NMR:
d
ꢀ78.6 (m, 6F), non-equivalent CF2
groups (AB pattern) at ꢀ110.6 and ꢀ112.8 respectively,
collection. IR: (Nujol) 1735 cmꢀ1
.
19F NMR:
d
ꢀ80.6 (m, 6F), the
(JFa,Fb = 284.7 Hz); 1H NMR:
d
9.57 (m, 1H). GC–MS, m/z (relative
non-equivalent CF2 groups at ꢀ109.29 and ꢀ111.10, respectively,
intensity): M+ not observed, 268 (C537ClF9+, 3.8), 266, (C535ClF9
13.5), 199 (C437ClF6+, 12.2), 197 (C435ClF6+, 37.8), 149 (C337ClF4
,
,
JFa,Fb = 282.6 Hz, ꢀ124.6 (m, 4F); 1H NMR:
d
4.53 (m, 1H), 8.67 (m,
+
1H). GC–MS, m/z (relative intensity): M+, not observed, 313
(C7HF12+, 4.2), 213 (C5HF8+, 39), 169 (C3F7+, 74), 163 (C4HF6+, 27),
119 (C2F5+, 22), 113 (C3HF4+, 35), 69 (CF3+, 100), 44 (54).
+
10.9), 147 (C335ClF4+, 37.2), 119 (C2F5+, 40), 69 (CF3+, 71), 29 (100).
3.14.5. Preparation of 2-chloro-2-heptafluoropropyl-3,3,4,4,5,5,5-
heptafluoropentanal, 26
4. Conclusions
Similar to Section 3.14.1, 4.1 g (0.011 mol) of 12, 15 ml glacial
acetic acid, and excess chlorine were stirred for 10 h at RT. The
reaction mixture was combined with 25 ml conc. H2SO4 and flash
distilled. The flash distillate was combined with 5 ml conc. H2SO4
and distilled through a 6 in. Vigreux column to afford 3.6 g
(0.009 mol), 80%, bp 75–78 8C (85 mm), nD20 = 1.3118. IR
2-Hydroaldehydes, containing one or more
a-perfluoroalkyl
groups are readily prepared via conversion of perfluoroalkyl
ketones to the corresponding vinyl ethers, which, on acid
hydrolysis, give the titled 2-hydroaldehydes. The 2-hydroalde-
hydes can be chemoselectively converted to the corresponding
a-
1770 cmꢀ1 (CHO). 19F NMR:
d
ꢀ81.1 (m, 6F), ꢀ107.0 (m, 4F),
hydroacyl halides via free-radical halogenation. The perfluoroalkyl
group deactivates halogenation at the 2-hydro site, and halogena-
tion occurs exclusively at the formyl hydrogen site. Halogenation
of the 2-hydroaldehyes with halogen in glacial acetic acid
chemoselectively occurs at the 2-hydro site to give exclusively
the corresponding 2-haloaldehydes. Hydrolysis of the 2-hydro-
perfluoroacyl halides gives the corresponding 2-hydro-branched
perfluorocarboxylic acids, potential perfluoro ketene precursors.
and the non-equivalent CF2 groups (AB pattern) at ꢀ118.81 and
ꢀ122.00 respectively (JFa,Fb = 287.6 Hz). GC–MS, m/z (relative
intensity): M+ not observed, 368 (C737ClF13
,
0.3), 366
+
(C735ClF13+, 1.1), 249 (C537ClF8+, 4.3), 247 (C535ClF8+, 12.9), 169
(C3F7+, 60), 119 (C2F5+, 21), 69 (CF3+, 100), 29 (50).
3.15. Preparation of polyfluorinated carboxylic acids
3.15.1. Preparation of 2-trifluoromethyl-3,3,3-trifluoropropanioc
acid, 27
Acknowledgments
A 100 ml flask equipped with a Teflon coated stir bar, water
cooled reflex condenser and a septum covered opening was
charged with 40.9 g (0.189 mol) of 14 and 50 ml tetrahydrofuran.
The reaction mixture was cooled to 10 8C with an ice bath before
the addition of 3 ml H2O was syringed into the mixture to ensure
complete reaction. The resultant mixture was stirred 4 h at RT. The
reaction mixture was combined with an equal volume of conc.
H2SO4. Distillation of the mixture through a 6 in. Vigreux column
afforded 33.4 g (0.170 mol) of 27, 90%, mp 50 8C. Reported for 27,
The authors thank Dr. D. Naae for the authentic sample of
CF3CCl2CF3, and DAW thanks the University of Iowa for financial
support.
References
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mp 49–50 8C [14]. IR: 1753 cmꢀ1
3JHF = 7.5 Hz), 1H NMR:
.
19F NMR:
d
ꢀ65.2 (d,
3
d
3.95 (heptet, JHF = 7.5 Hz, 1H), 10.55
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(C3HF5+, 65), 113 (C3HF4+, 72), 94 (C3HF3+, 23.0), 82 (C2HF3+, 38), 69
(CF3+, 62), 63 (C2HF2+, 17), 44 (100). 27 was also prepared in 40%
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3.15.2. Preparation of 2-pentafluoroethyl-3,3,3-pentafluorobutanoic
acid, 28
Similar to Section 3.15.1, 2.9 g (0.013 mol) of 17, 15 ml THF, and
5 ml H2O gave an exothermic reaction. The resultant mixture was
stirred 1 h at RT, before the addition of 35 ml conc. H2SO4.
Distillation of the reaction mixture afforded 1.6 g (0.008 mol) of 28,
60%, bp 133 8C (micro), nD20 = 1.3034, IR: 1760 cmꢀ1 19F NMR:
. d
ꢀ84.01 (m, 6F) and the non-equivalent CF2 groups (AB pattern) at
ꢀ113.72 and ꢀ115.76, respectively, JFa,Fb = 287.9 Hz; 1H NMR:
d
4.00 (m, 1H), 10.37 (s, 1H). GC–MS, m/z (relative intensity): M+, not
observed, 232 (C5HF9+, 0.3), 213 (C5HF8+, 22), 163 (C4HF6+, 96), 119
(C2F5+, 94), 113 (C3HF4+, 8), 69 (CF3+, 55), 44 (100).
Chem. Abstr. 59 (1963) 11266c.
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Ser. Khim. 8 (1965) 1478.
3.15.3. Preparation of 2-heptafluoropropyl-3,3,4,4,5,5,5-
heptafluoropentanoic acid, 29
Similar to Section 3.15.1, a 20 ml flask equipped with a Teflon
coated stir bar, distillation head, 150 8C immersion thermometer,
vacuum take off, and a 10 ml receiving flask was charged with 2.6 g
(0.006 mol) of 18, 5 ml THF and 1 ml H2O, which resulted in an
exothermic reaction. The resultant mixture was stirred for 1 h
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