Photochemical activation of extremely weak nucleophiles: Highly fluorinated urethanes and polyurethanes from polyfluoro alcohols

Article abstract of DOI:10.1021/jo5005789

An efficient and environmentally friendly photoreaction between phenyl isocyanate or pentafluorophenyl isocyanate and polyfluorinated alcohols and diols is described for the first time. New highly fluorinated urethanes and diurethanes, derived from aromat

Full text of DOI:10.1021/jo5005789

Article
pubs.acs.org/joc
Photochemical Activation of Extremely Weak Nucleophiles: Highly
Fluorinated Urethanes and Polyurethanes from Polyfluoro Alcohols
Marc Soto, Rosa María Sebastian,* and Jordi Marquet*
́
̀
Departament de Química, Universitat Autonoma de Barcelona, Bellaterra 08193, Barcelona, Spain
S
* Supporting Information
ABSTRACT: An efficient and environmentally friendly photoreaction between phenyl isocyanate or pentafluorophenyl
isocyanate and polyfluorinated alcohols and diols is described for the first time. New highly fluorinated urethanes and
diurethanes, derived from aromatic isocyanates, are produced in good yields in a photoreaction that is apparently governed by the
acidic properties of the polyfluoro alcohols and diols. The wettability properties of the new polyfluorinated diurethanes have been
tested, some of them showing significantly high values of hydrophobicity and oleophobicity. This new photoreaction has also
been tested in the production of a model polyfluorinated polyurethane, establishing the influence of the irradiation power in the
outcome of the process, and directly achieving a molecular weight distribution corresponding to a number-average DPn = 12 and
a highest DPn = 20 after 4 h of irradiation (DPn: “number-average degree of polymerization”).
with alkyl isocyanates and react very slowly with aromatic
isocyanates at room temperature, not very “green conditions”
such as catalysis with amines11 or with dibutyltin derivatives,12
or highly electrophilic carbamates (aroxysulfonylcarbamates),13
being necessary, with very few exceptions,8b for the reactions to
proceed at a synthetically useful rate. Alternative approaches
include the catalyzed reaction of fluorinated carbonates with
amines14 or the electrochemically induced Hofmann rearrange-
ment.15 Most of the mechanistic schemes proposed for the
reactions of isocyanates and alcohols include the intermediacy
of “complexes” of the ion-pair, and solvent stabilized ion-pair,
type, that evolve efficiently to the final carbamate.10,16
However, this evolution does not take place easily when acidic
weak nucleophiles such as polyfluoro alcohols are used.
Very recently, we have reported a new radical mechanism for
the reaction of polyfluorinated alcohols and phenyl isocya-
nate.17 Acidity of polyfluoro alcohols seems to be responsible
for the new reactivity, and evidence from kinetic studies,
electron paramagnetic resonance and cyclic voltammetry,
suggest that polyfluoroalkoxy radical is the key intermediate
in the chain. In the present work, we worked to develop this
reaction from the preparative point of view, finding that it is
INTRODUCTION
■
A lot of attention has been given to the synthesis of fluorinated
organic materials.1 Polyfluorinated organic compounds have
very interesting properties,2 their applications having special
significance in the fields of pharmaceutics, catalysis and
materials science.3,4 For instance, fluorinated polyurethanes5
combine some virtues of polyurethane and fluorinated
polymers, such as high thermal and oxidative stability, good
chemical resistance, high oxygen permeability, low water
absorptivity and attractive surface properties, excellence
resistance to ultraviolet radiation and nuclear radiation,
excellent flexibility, high weatherability, and good compatibility
with blood in biomedical applications.6,7 Also recently,
polyfluorinated oligourethanes with special applications as
alternatives to polydimethylsiloxane in fouling-releasing coat-
ings,8 and in microfluidic device fabrication,9 have been
described. However, polyfluorocarbamates derivatives have
not yet developed all their potential, among other reasons,
due to the general very low reactivity of fluorine substituted
alcohols, the main organofluorine building blocks involved in
their synthesis.
The standard approach to produce carbamates consists of the
reaction between an isocyanate and an alcohol.10 However,
polyfluorinated alcohols show a very low nucleophilicity in
polar reactions. Thus, polyfluorinated alcohols do not react
Received: March 11, 2014
Published: May 13, 2014
© 2014 American Chemical Society
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Table 1. Ground-State Reactions of Phenyl Isocyanate with Polyfluorinated Alcohols
a
b
Reported in ref 17. Described in this work. Reaction conditions: 0.50 mmol of PhNCO, 1 mmol of fluorinated diol, dry DMF (50 mL), rt under
c
d
nitrogen (procedure A). In acetonitrile, recovery of starting materials. No reaction observed, recovery of materials.
very sensitive to solvent and concentration, and that diols are
only reactive at one end, all together hampering its practical
use. However, we succeeded in photochemically stimulating the
reaction, and these results constitute the main body of the
article.
strict concentration conditions as described in ref 17. Under
these conditions, a radical chain mechanism seem to be
operating (Scheme 1)17 with the polyfluoroalkoxy radical as key
intermediate.19
In order to advance toward the aim of producing oligo- and
In this paper, we describe the novel photochemical reaction
of aromatic isocyanates and polyfluoro alcohols and polyfluoro
diols to produce arylcarbamate derivatives. In this way, a series
of polyfluoromonoaryl carbamates and dicarbamates with high
fluorine content have been synthesized, and their surface
properties (hydrophobicity and oleophobicity) tested. This new
photochemical procedure constitutes an environmental friendly
access to small molecules with a high content of fluorine18 that
could, in principle, have application as stain, grease, and water-
repelling chemicals. It also constitutes a new tool for the
synthesis of highly fluorinated polyurethanes as we describe in
the article.
polyurethanes, we explored the reactions of phenylisocyanate
Scheme 1. Mechanism Proposed in ref 17 for the Ground-
State Reaction of Phenyl Isocyanate and Polyfluorinated
Alcohols in DMF
RESULTS AND DISCUSSION
■
Phenyl isocyanate 1 does not react with 2,2,2-trifluoroethanol
2a, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro-1-octanol 2b,
and 1,1,1,3,3,3-hexafluoro-2-propanol 2c at room temperature
in acetonitrile (Table 1, entries 1, 3, and 5), being the reaction
only possible (Table 1, entries 2, 4,and 6) in DMF and under
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with polyfluorodiols, in the same conditions (Table 1, entries
7−10). To our surprise, a rather efficient reaction was observed
in three cases (no reaction could be achieved with 2g), but only
clean monocondensation took place (products 3d−f), with not
even traces of the dicondensation products being detected. We
were unable to attain a reaction at the second hydroxyl group.
The lack of reactivity of the hydroxyl group when a carbamate
group is already present in the structure was confirmed by
attempting the reaction of the monocondensated products
(3d−f), previously isolated, with phenyl isocyanate, under the
same conditions, that failed completely.
This, in principle, strange behavior could be understood in
the framework of the mechanistic proposal described in
Scheme 1. A crucial event in the mechanism seems to be the
protonation (or hydrogen bond formation) of the isocyanate
group by the relatively acidic polyfluoro alcohol. Simple
theoretical calculations (Scheme 2, AM1 method, implemented
described. Thus, upon irradiation of the solution with a 125 W
medium pressure Hg lamp (pyrex filter), the corresponding
carbamates were obtained in fair to good yields. It is remarkable
that under these new conditions the reaction proceeded in
acetonitrile, a useless solvent in the ground state reactions
described in Table 1.
In order to obtain some mechanistic insight in this new
photoreaction, we have compared the reactivity of trifluor-
oethanol with that of ethanol. It is remarkable the fact that the
reaction with a standard non fluorinated alcohol such as ethanol
does not show stimulation by UV irradiation. Thus, the
reaction of ethanol with phenylisocyanate (acetonitrile, r.t.)
does not show a significant difference in the absence or in the
presence of irradiation (25% yield after 15 min in both cases).
Comparison of this result with the described in Tables 1 and 2
for trifluoroethanol (acetonitrile), suggests the existence of
important differences between the preferred reactivity channels
of the two alcohols. This was confirmed by a competition
experiment. Thus, when the photoreaction of phenyl isocyanate
was carried out with a mixture 1:1 of trifluoroethanol and
ethanol, no reaction was observed for ethanol after 15 min,
while the trifluoroalkoxycarbamate 3a was produced in 75%
yield as the only product, indicating that under irradiation 2,2,2-
trifluoroethanol reacts fast enough to make the reaction of
ethanol neglectible.
Scheme 2. Mulliken Charges (AM1) and Preferred
Protonation Positions in Carbamates and Isocyanates
(Chem3d, ChemBioOffice 2010)
Having in mind the mechanistic proposal described in
Scheme 1 for the ground-state reaction, one question was if we
were in the presence of a photoinduced radical-chain process.
This was investigated by carrying out the photoreaction
between phenyl isocyanate and trifluoroethanol in the presence
of different radical scavengers and radical-interacting species
such as TEMPO, 1-octene, and acrylonitrile. In no case was any
effect observed, thus ruling out the existence of free radicals out
of the solvent cage in the photochemical mechanism.
in Chem3D) indicate that the electronic density in the
carbamate group is higher than in the isocyanate group.
Thus, the presence of a preformed carbamate in the structure
would produce a distraction of the proton from the isocyanate
and, hence, the quenching of the reaction. The mechanisms
probably have short chains and therefore need multiple
initiations.
To overcome this obstacle, we turned to photochemistry,
expecting that under irradiation the reaction would become
more efficient. In Table 2, the photoreactions of simple
polyfluoro alcohols with phenyl isocyanate in acetonitrile are
In Scheme 3, an interpretation for these mechanistic
experiments is proposed. It is well accepted that in the
Scheme 3. Proposed Mechanisms for the Reaction of Phenyl
Isocyanate with 2,2,2-Trifluoroethanol or Ethanol
Table 2. Photochemical Reactions of Phenyl Isocyanate with
a
Fluorinated Monoalcohols
reactions of nonfluorinated alcohols with isocyanates, the
nucleophilic center of the alcohol is first added to the
electrophilic carbon of the isocyanate group, and then hydrogen
atom is transferred to the nitrogen.10 This would correspond to
the reactivity of ethanol with phenyl isocyanate (steps 3 and 4
in Scheme 3). However, 2,2,2-trifluoroethanol is much less
nucleophilic but much more acidic than ethanol (ethanol pKa =
29.8 and 2,2,2-trifluoroethanol pKa = 23.5 in DMSO),20 and
therefore, the standard order of events seem not to be followed
in this case. What we propose here is an opposite order of
a
Reaction conditions: 0.5 mmol of PhNCO, 1.0 mmol of fluorinated
alcohol, dry CH3CN, under nitrogen, 60 min irradiation with mercury
high pressure lamp Philips HPK 125W (procedure B).
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events: trifluoroethanol would produce a strong hydrogen bond
complex with the isocyanate that upon irradiation would
undergo proton transfer followed by nucleophilic addition
(steps 1 and 2 in Scheme 3). These hydrogen-bonding
complexes between alcohols and isocyanates have been
previously proposed in the literature as intermediates in some
cases for urethane formation.16 The results from the
competition experiment indicate that the photochemical step
is fast (k2 ≫ k−1) and that the step 1 is not an equilibrium in
the presence of irradiation. These results also indicate that k1 ≫
k3, as expected since step 1 is a fast hydrogen-bond formation
process, while step 3 is a slower covalent bond formation.
Next we explored the viability of the new photoreaction, with
polyfluorodiols, and the results were remarkable in the
photoreactions with phenyl isocyanate (Table 3). Hence, now
the dicondensation products 4a−d could be obtained in good
yields (63−77%), thus overcoming the strong limitation found
in the ground-state reaction.
compounds. The contact angle on a flat surface is referred
normally as the “intrinsic contact angle” of the surface.
Typically, when the intrinsic contact angle is large enough, a
roughening of the surface will result in an increase of the value,
that in the ideal situation can give rise to a superhydrophobic
and superoleophobic surfaces.23 We have measured the intrinsic
contact angles of water and hexadecane (HD) on surfaces of
the products collected in Tables 3 and 4, prepared by spin-
coating on glass, and compared the values with the
corresponding ones for PTFE (Teflon) measured in the same
conditions. The results are gathered in Table 5.
Water sessile drop contact angle measurements (Table 5)
gave values over 80° for all compounds except 6c and 6d. In
this case, the already hydrophobic nature of compounds 4a−d
seems not to be significantly altered by the presence of the
perfluorinated phenyl rings. Even on the contrary, the average
water sessile drop contact angle for bis(pentafluorophenyl-
carbamates) 6a−d is smaller (74°) than the measured average
for the nonfluorinated bis(phenylcarbamates) 4a−d (83°).
A more defined effect is observed in the hexadecane sessile
drop contact angle measurements, where a loose relationship
can be observed between the contact angle values and the
fluorine content in the molecule. Hence, bis(pentafluoro-
phenylcarbamates) 6a−d show a significantly higher average
contact angle value (50°) than the bis(phenylcarbamates) 4a−d
(24°), confirming the effect of the fluorine content on the
lipophobicity of a particular molecule.
Table 3. Photochemical Reaction of Phenyl Isocyanate with
a
Polyfluorinated Diols
Remarkable is the behavior of the product 6a (Table 5, entry
5), containing a short polyfluorodiol moiety, and the
pentafluorophenylcarbamate moiety (Figure 1). In this case,
the water sessile drop contact angle is 96° and the
corresponding hexadecane value is 58° (117° and 48°,
respectively, for PTFE in the same conditions), significant
values for a nonbranched small molecule.24 Here, it is worth
mentioning the prominence that small molecules with a high
content of fluorine are gaining recently due to strong
environmental concerns over persistent long-chain perfluor-
oalkyl compounds.18
Finally, and in order to establish the scope of this simple
photochemical procedure, we tested the viability of producing
polyurethanes using polyfluorodiol 4a as a model. Hence, the
photoreaction of 2,2,3,3-tetrafluorobutane-1,4-diol, 4a, with
MDI (4,4′-methylenediphenyl diisocyanate)25 under the stand-
ard conditions (125 W mediumpressure Hg lamp, 4 h)
produces a distribution of oligourethanes (Figure 2a, n = 0, 1, 2,
and 3), with alcohol termination (no isocyanate group
absorption was detected by IR). Irradiation for 4 h with a
400 W lamp results in an increase in the average degree of
polymerization of the oligomer up to n = 6 in Figure 2a
representation (DPn = 12, IUPAC definition for “average
number degree of polymerization”, DPn, implies DPn = 2n, with
“n” being the repeating units as indicated in Figure 2a). In
Figure 2b, comparison of Gel permeation chromatography
(GPC) chromatograms for the two cases is shown. A
displacement toward higher molecular weights was observed
when a more powerful lamp was used, and in both cases, the
limit for the used conditions seems to be around n = 10−11
(5000 Da molecular weight, DPn = 20−22).
a
Reaction conditions: 0.5 mmol of PhNCO, 0.5 mmol of fluorinated
diol, dry CH3CN, under nitrogen, 4 h irradiation with mercury high
pressure lamp Philips HPK 125W (procedure C).
One of our aims was to build molecules with a high content
of fluorine, and therefore, the corresponding photoreactions
between the polyfluorodiols and pentafluorophenylisocyanate,
5, were also tested. The addition products 6a−d were obtained
in good yields (up to 85%, Table 4). It is worth noting that the
blank reactions (acetonitrile), in the absence of irradiation,
failed completely in all the cases.
Our hypothesis was that this new family of products could
show interesting wettability properties. Highly fluorinated
compounds normally show hydrophobic and oleophobic
properties21 that give rise to many potential applications. The
wettability of a surface is determined by two factors, the
chemical composition and the topographic structure.22 The
standard measurement of wettability is the “contact angle” of a
droplet of a standard liquid (water and hexadecane in our case)
on a surface modified by spin coating with the tested
The evolution of the photopolymerization with time is
described in Figure 2c using 19F{1H} NMR for the photo-
reaction with 400 W lamp. Distinct absorptions correspond to
fluorine atoms in the monomeric diol and in the polymer, and
for the polymer the absorptions are distinct depending if the
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a
Table 4. Photochemical Reaction of Pentafluorophenyl Isocyanate with Polyfluorinated Diols
a
Reaction conditions: 0.5 mmol of PhNCO, 0.5 mmol of fluorinated diol, dry CH3CN, under nitrogen, 4 h irradiation with mercury high-pressure
lamp Philips HPK 125W (procedure C).
Table 5. Contact Angle Measurements
a
contact angle (deg)
entry
compd
%
F
H2O
n-C16H32
wt
1
2
3
4
5
6
7
8
9
4a
19.0
25.3
47.5
28.6
45.8
48.2
58.1
48.0
76.0
86
81
24
19
11
41
58
47
53
40
48
4b
4c
84
4d
6a
82
96
85
6b
6c
44
6d
PTFE
72
117
a
Sessile drop contact angle measurement of the corresponding
dicarbamate (dissolved in acetone) deposited by spin coating (6.000
rpm) over a 1 × 1 cm surface of cleaned glass.
fluorine atoms are at the end part of the polymer (terminal
fluorine atoms) or in the inner part of the chain (inner fluorine
atoms). The different 19F chemical shifts are indicated in Figure
2a. The use of 19F NMR allows also establishment of the
number-average degree of polymerization through “end group
analysis” and complements GPC analysis. Thus, after 1 h of
irradiation, the spectrum indicates the presence of monomeric
diol 4a and that 30% of polyfluorodiol had reacted by one end
but significant poly reaction had not yet occurred. In the
spectrum taken after 2 h, there were approximately two
Figure 1. Photographs of sessile drops of water and hexadecane in a
surface spin coating modified with 6a and PTFE. Contact angle
measurements comparison.
terminal fragments for each inner part, this corresponding to n
= 1 in the structure of Figure 2a (DPn = 2). Finally after 4 h, the
polyfluorodiol had reacted completely, and three inner parts
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Figure 2. (a) Structure of the polymer and 19F{1H} NMR chemical shifts in acetone-d6. (b) Effect of the irradiation source. Comparison of the GPC
chromatograms of photoreaction using a 125 W lamp (1.8 × 1019 photon/s) vs a 400 W lamp (5.0 × 1019 photon/s) (irradiation time 4 h). (c)
19F{1H} NMR spectra at different reaction times using a 400 W UV−vis light source.
ppm relative to δ(TMS) = 0 for 1H and 13C and δ(CFCl3) = 0 for 19F.
formed for each terminal fragment, which corresponds to n = 6
13C and 19F NMR spectra were recorded by broadband proton spin
as an average for the structure depicted in Figure 2a (DPn =
decoupling.
12). This result agrees with the molecular weight distribution
obtained from GPC analysis (Figure 2b).
Infrared spectra were recorded with a spectrophotometer fitted with
a universal ATR (attenuated total reflectance) sampling accessory.
High resolution mass spectra (HRMS) were carried out using
MicroTOF-Q with electrospray ionization (ESI).
Solvents were dried and purified using standard procedures from ref
29.
CONCLUSION
■
We conclude that the attempt to extend the reported ground-
state reaction between polyfluoro alcohols and phenyl
isocyanate to polyfluoro diols, using the previously described
conditions,17 was not successful. However, a novel photo-
chemical version of the reaction has been successfully tested,
allowing the synthesis in good yields of polyfluorinated
diurethane small molecules, derived from aromatic isocyanates,
with high fluorine content and very interesting wettability
properties.
Purifications by flash chromatography were done using silica gel
0.04−0.06 mm, 230−400 mesh eluted using hexanes/ethyl acetate
with the appropriate polarity.
Gas chromatography was performed in a chromatograph equipped
with column Agilent HP-5 (30 m × 0,320 mm × 0,25 μm) and a FID
detector. The standard method used is T0 = 75 °C, 0.5 min; v = 25
°C/min; T1 = 240 °C.
Melting points have been recorded in a Reichert Kofler block
without further correction or alternatively measured using differential
scanning calorimetry (DSC) calibrated with indium (Tm = 429.75 K,
ΔHm = 3267 kJ/mol).
Gel permeation chromatography was performed in an equipment
with one column PL Mixed gel C, 5 μm, and another column PL gel, 5
μm, 10.000A, using THF as solvent and a refractive index detector.
The method used injects 40 μL of sample, elutes at a flow of 1 mL/
min at an isothermal temperature of 30 °C and was calibrated using
polystyrene standards.
Experimental Procedures and Characterization Data for
Products. General Procedure A. In a 100 mL Schlenk flask fitted with
a magnetic stirring bar under inert atmosphere, phenyl isocyanate (55
μL; 0.50 mmol) was dissolved in dried DMF (50 mL). Note: Special
caution should be employed when handling PhNCO to avoid its
tearing vapors. After addition of fluorinated alcohol (1.0 mmol), the
mixture was allowed to react for 60 min. After that reaction time, water
(20 mL) was added to hydrolyze the remaining isocyanate. The
Reactivity studies (comparison with the reactivity of ethanol,
radical scavenging, and competence experiments) suggest the
operation of a mechanism in the solvent cage, governed by the
acidic properties of the polyfluoro alcohols.
This new photochemical reaction has also been preliminary
tested successfully in the production of polyfluorinated
polyurethanes, this achievement opening a new environ-
mentally friendly avenue for the synthesis of this type of
polymers with highly non-nucleophilic alcohols.
EXPERIMENTAL SECTION
■
General Experimental Methods. Nuclear magnetic resonance:
1H NMR, 13C NMR, and 19F NMR were recorded at ambient
temperature using a 250 MHz spectrometer (250 MHz 1H NMR; 62.5
MHz 13C NMR; 235.2 MHz 19F NMR) or a 360 MHz spectrometer
1
(360 MHz H NMR; 90.5 MHz 13C NMR). Chemical shifts are in
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mixture DMF/water was extracted with ethyl acetate (3 × 20 mL) and
the organic phase washed with diluted hydrochloric acid (1 M; 3 × 20
mL) and water (20 mL). The organic phase was dried with anhydrous
magnesium sulfate and evaporated in the rotary evaporator. The
product after purification by a flash chromatography (initial eluent
hexanes/ethyl acetate 5:1) was obtained in yields reported in the
description in each case.
m/z calcd for C11H12F4NO3 [M + H]+ 282.0748, found 282.0786;
calcd for C11H12F4NNaO3 [M + Na]+ 304.0567, found 304.0577.
2,2,3,3,4,4-Hexafluoro-5-hydroxypentyl Phenylcarbamate, 3e.
White solid. Yield: A, 94 mg, 57%. IR (ATR): 3331 (NH, OH st),
1719 (CO st), 1536 (NH δ), 1501, 1445, 1226 (NCOO st as),
1185, 1153 (CF st), 1091, 750, 689. 1H NMR (360 MHz, acetone-d6):
δ 4.11 (dt, 3JHF = 15.1 Hz, 3JHH = 6.7 Hz, 2H), 4.79 (t, 3JHF = 14.9 Hz,
2H), 5.08 (t, 3JHH = 6.9 Hz, 1H), 7.09 (t, 3JHH = 7.5 Hz, 1H), 7.34 (t,
General Procedure B. Dry acetonitrile (50 mL) was degassed by
three cycles of freeze−pump−thaw and placed in a photochemical
reactor equipped with a magnetic stirring, a glass stopper, a stopcock,
and a water-flow cooled Pyrex immersion well under nitrogen
atmosphere. Phenyl isocyanate (54 μL, 0.5 mmol) was added and
the mixture stirred for 5 min. Fluorinated alcohol (1.0 mmol) was
added and the mixture stirred for a further 5 min to homogenize the
solution. Then, the UV−vis irradiation source, a mercury high-pressure
lamp Philips HPK 125 W, was turned on. After 60 min of reaction, the
lamp was switched off and the solvent and the alcohol were evaporated
in vacuo. The yellowish residue was purified by flash column
chromatography using initially hexanes/ethyl acetate 5:1 and then
with increasing polarity. Yields are reported in the description in each
case.
3
3JHH = 7.5 Hz, 2H), 7.60 (d, JHH = 7.5 Hz, 2H), 9.11 (s, 1H). 13C
NMR (90.5 MHz, acetone-d6): 59.5 (m,), 59.7 (m,), 111−119
(complex absorption), 118.5 (s), 123.2 (s), 128.8 (s), 138.6 (s), 152.0
(s). 19F{1H} NMR (235.2 MHz, acetone-d6): δ −127.25 (s, 2F),
−123,14 (s, 2F), −121.31 (s, 2F). HRMS-ESI+: m/z calcd. for
C12H11F6NNaO3 [M + Na]+ 354.0535, found 354.0575.
2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11-Icosafluoro-12-hydroxy-
dodecyl Phenylcarbamate, 3f. White-yellowish solid. Yield: A, 208
mg, 61%. 1H NMR (360 MHz, acetone-d6): δ 3.91 (dt, 3JHF = 14.3 Hz,
3JHH = 6.1 Hz, 2H), 4.59 (t, 3JHF = 15.4 Hz, 2H), 4.87 (t, 3JHH 6.7 Hz,
1H), 6.93 (t, 3JHH = 7.3 Hz, 1H), 7.19 (t, 3JHH = 7.3 Hz, 2H), 7.45 (d,
3JHH = 7.3 Hz, 2H), 8.87 (s, 1H). 13C NMR (90.5 MHz, acetone-d6):
60.0 (m), 60.6 (m), 111−119 (complex weak absorption), 119.6 (s),
124.3 (s), 129.8 (s), 139.4 (s), 152.7 (s). 19F{1H} NMR (235.2 MHz,
acetone-d6): δ −124.44 (bs, 4F), −123,00 (bs, 4F), −122.81 (bs, 6F),
−122.76 (bs, 4F), −122.71 (bs, 2F). HRMS-ESI+: m/z calcd for
C19H12F20NO3 [M + H]+ 682.0531, found 682.0492.
General Procedure C. Dry acetonitrile (45 mL) was degassed by
three cycles of freeze−pump−thaw and placed under inert atmosphere
in a photochemical reactor equipped with a magnetic stirring, a glass
stopper, a stopcock, and a water-flow cooled pyrex immersion well.
Aromatic isocyanate (1.0 mmol) was added and the mixture stirred for
5 min.
Afterward, a solution of fluorinated diol (0.5 mmol) in dried and
degassed acetonitrile (5 mL) was added and stirred for a further 5 min
to homogenize the solution. Then, the irradiation source (Philips HPK
125W) was turned on. After 4 h of reaction the lamp was switched off
and the solvent and the alcohol were evaporated in vacuo. After flash
column chromatography using initially hexanes/ethyl acetate 5:1 the
product was obtained with the yield in the description.
2,2,3,3-Tetrafluorobutane-1,4-diyl Bis(phenylcarbamate), 4a.
White solid. Yield: C, 141 mg, 71%. Mp (°C): 178.1 (DSC). IR
(ATR): 3350 (NH st), 3052 (arom CH st), 2968 (CH st), 1721 (C
O st), 1598 (arom CC), 1532 (NH δ), 1228 (NCOO st as), 1179,
1143 (CF st), 1091, 952, 934, 749 (CF δ) cm−1. 1H NMR (250 MHz,
2,2,2-Trifluoroethyl Phenylcarbamate, 3a.26 Crystalline white
solid. Yield: A, 104 mg, 93%; B, 95 mg, 87%. Mp (°C): 57−58. IR
(ATR): 3327 (NH st), 2969 (CH st), 1716 (CO st), 1538 (NH δ),
1226 (NCOO st as), 1160 (C−F st), 1079 cm−1. 1H NMR (250 MHz,
acetone-d6): δ 4.74 (q, 3JHF = 9.3 Hz, 2H), 7.09 (t, 3JHH = 7.5 Hz, 1H),
7.35 (t, 3JHH = 7.5 Hz, 2H), 7.59 (d, 3JHH = 7.9 Hz, 2H), 9.07 (s, 1H).
2
13C NMR (90.5 MHz, acetone-d6): δ 60.1 (q, JCF = 35.9 Hz), 118.6
1
(s), 123.3 (s), 123.7 (q, JCF = 276.9 Hz), 128.9 (s), 138.5 (s), 151.7
3
(s). 19F NMR (235.2 MHz, acetone-d6): δ −75.36 (t, JFH = 9.3 Hz,
3F). HRMS-ESI+: m/z calcd for C9H9F3NO2 [M + H]+ 220.0580,
found 220.0579; calcd for C9H8F3NNaO2 [M + Na]+ 242.0399, found
242.0395.
2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecafluorooctyl Phenyl-
carbamate, 3b. White solid. Yield: A, 151 mg, 58%; B, 93 mg,
36%. IR (ATR): 3354 (NH st), 2958, 2935 (CH st), 1728 (CO st),
1
1539, 1201 (NCOO st as), 1147, 1101 (CF). H NMR (250 MHz,
acetone-d6): δ 4.90 (t, 3JHF = 15 Hz, 1H), 7.10 (t, 3JHH = 7.5 Hz, 1H),
7.35 (t, 3JHH = 7.5 Hz, 2H), 7.60 (d, 3JHH = 7.5 Hz, 2H), 9.13 (bs, 1H).
2
13C NMR (90.5 MHz, acetone-d6): δ 59.3 (t, JCF = 26.7 Hz), 106−
120 (undefined) 118.6 (s), 123.4 (s), 128.8 (s), 138.4 (s), 151.7 (s).
19F NMR (235 MHz, acetone-d6): δ −127.18 (bs, 2F), −124.27 (bs,
2F), −123.71 (bs, 2F), −122.98 (bs, 4F), −120.70 (bs, 2F), −82.14 (t,
3JFF = 9.4 Hz, 3F). HRMS-ESI+: m/z calcd for C15H9F15NO2 [M +
H]+ 520.0388, found 520.0393; calcd for C15H8F15NNaO2 [M + Na]+
542.0208, found 542.0220.
3
3
acetone-d6): δ 4.77 (t, JHF = 15.0 Hz, 4H), 7.09 (t, JHH = 7.5, 2H),
7.34 (t, 3JHH = 7.5 Hz, 4H), 7.58 (d, 3JHH = 7.5 Hz, 4H), 9.06 (bs, 2H).
13C NMR (90.5 MHz, acetone-d6): δ 59.6 (t, JCF = 26.0 Hz), 115.4
2
1
2
(tt, JCF = 252.0 Hz, JCF = 31.0 Hz), 118.6 (s), 123.2 (s, 4C), 128.8
(s), 138.6 (s), 152.0 (s). 19F NMR (235.2 MHz, acetone-d6): δ
−122.88 (t, 3JHF = 15 Hz). HRMS-ESI+: m/z calcd for C18H17F4N2O4
[M + H]+ 401.1119, found 401.1126; calcd for C18H16F4N2NaO4 [M
+ Na]+ 423.0938, found 423.0958; calcd for C18H16F4KN2O4 [M +
K]+ 439.0678, found 439.0680.
1,1,1,3,3,3-Hexafluoropropan-2-yl Phenylcarbamate, 3c.27 White
solid. Yield: A, 115 mg, 80%; B, 95 mg, 66%. Mp (°C): 104−105. IR
(ATR): 3296 (NH st), 2978 (CH st), 1731 (CO st), 1537, 1224
1
(N-CO-O st as), 1193 (C−F st), 1104 cm−1. H NMR (250 MHz,
acetone-d6): δ 6.30 (septet, 3JHF = 6.7 Hz, 1H), 7.16 (t, 3JHH = 7.5 Hz,
3
3
2,2,3,3,4,4-Hexafluoropentane-1,5-diyl Bis(phenylcarbamate),
4b. Yield C: 0.139 g, 63%. Mp (°C): 134.5−135.1. IR (ATR): 3336
(NH st), 1705 (CO st), 1600 (arom CC), 1540 (NH δ), 1448,
1315, 1240 (NCOO st as), 1201, 1150 (CF st), 1088, 963, 937, 885,
763 (C−F δ), 686, 637 cm−1. 1H NMR (250 MHz, acetone-d6): δ 4.83
(t, 3JHF = 7.5 Hz, 4H), 7.07 (t, 3JHH = 7.5 Hz, 2H), 7.35 (t, 3JHH = 7.5
1H), 7.39 (t, JHH = 7.5 Hz, 2H), 7.61 (d, JHH = 10.0 Hz, 2H), 9.54
(bs, 1H). 13C NMR (90.5 MHz, acetone-d6): δ 67.0 (septet, JCF
=
2
1
34.0 Hz), 118.9 (s), 121.2 (q, JCF = 285.0 Hz), 124.1 (s), 129.0 (s),
137.6 (s), 149.8 (s). 19F NMR (235 MHz, acetone-d6): δ −74.76 (d,
3JHF = 6.7 Hz). HRMS-ESI+: m/z calcd for C10H8F6NO2 [M + H]+
288.0454, found 288.0462.
3
Hz, 4H), 7.60 (d, JHH = 7.5 Hz, 4H), 9.12 (s, 2H). 13C NMR (90.5
2,2,3,3-Tetrafluoro-4-hydroxybutyl Phenylcarbamate, 3d. White
solid. Yield: A, 104 mg, 74%. Mp (°C): 79.3−79.9. IR (ATR): 3323
(NH, OH st), 2955 (CH st), 1721 (CO st), 1602 (arCC), 1541
MHz, CD32OD): δ 59.5 (t, 2JCF = 28.0 Hz), 111.3 (m), 115.0 (tt, 1JCF
=
257.0 Hz, JCF = 30.0 Hz), 118.6 (s), 123.1 (s), 128.5 (s), 138.2 (s),
152.5 (s). 19F{1H} NMR (235.2 MHz, acetone-d6): δ −127.31 (s, 2F),
−121.15 (s, 4F). HRMS-ESI+: m/z calcd for C19H17F6N2O4 [M + H]+
451.1087, found 451.1102; calcd for C19H16F6N2NaO4 [M + Na]+
473.0906, found 473.0912; calcd for C19H16F6KN2O4 [M + K]+
489.0646, found 489.0621.
1
(NH δ), 1449, 1264 (NCOO st as), 1116 (CF st), 1101, 930. H
3
3
NMR (250 MHz, acetone-d6): δ 4.05 (dt, JHF = 14.3 Hz, JHH = 6.3
Hz, 2H), 4.74 (t, 3JHF = 15.2 Hz, 2H), 5.01 (t, 3JHH = 6.3 Hz, 1H), 7.08
(t, 3JHH = 7.5 Hz, 1H), 7.34 (t, 3JHH = 7.5 Hz, 2H), 7.59 (d, 3JHH = 7.5
Hz, 2H), 9.01 (s, 1H). 13C NMR (90.5 MHz, CD3OD): 59.9 (t, 2JCF
27 Hz), 60.6 (t, JCF = 25 Hz), 112−123 complex absorption), 118.9
(s), 123.6 (s), 129.2 (s), 139.1 (s), 152.6 (s). 19F{1H} NMR (235.2
MHz, acetone-d6): δ −125.14 (s, 2F), −123.63 (s, 2F). HRMS-ESI+:
=
2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11-Icosafluorododecan-
1,12-diyl Bis(phenylcarbamate), 4c. Yield C: 0.272 g, 68%. Mp (°C):
146.4 (DSC). IR (ATR): 3351 (NH st), 1722 (CO st), 1599 (arom
CC), 1536 (NH δ), 1447, 1274 (NCOO st as), 1143 (CF st), 988,
2
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1
953, 806, 759 (CF δ), 689, 622 cm−1. H NMR (360 MHz, acetone-
2,2,4,4,5,5,7,7-Octafluoro-3,6-dioxaoctane-1,8-diyl Bis-
(pentafluorocarbamate), 6d. Yield: C, 0.303 g, 85%. IR (ATR):
3290 (NH st), 1725(CO st), 1601 (arom C−C), 1536 (NH δ),
1500, 1449, 1402, 1271 (N-CO-O st as), 1147 (C−F st), 1001, 941,
792, 759 (C−F δ), 689, 624 cm−1. 1H NMR (360 MHz, acetone-d6): δ
d6): δ 4.90 (t, 3JHF = 10.8 Hz, 4H), 7.09 (t, 3JHH = 7.2 Hz, 2H), 7.34 (t,
3JHH = 7.2 Hz, 4H), 7.59 (d, JHH = 7.2 Hz, 4H), 9.15 (s, 2H). 13C
3
2
NMR (90.5 MHz, acetone-d6): δ 59.4 (t, JCF = 27.2 Hz), 107−123
(undefined), 118.6 (s), 123.4 (s), 128.9 (s), 138.4 (s), 151.7 (s). 19F
NMR (235.2 MHz, acetone-d6): δ −124.28 (m, 4F), −122.73 (m,
12F), −120.69 (m, 4F). HRMS-ESI+: m/z calcd for C26H17F20N2O4
[M + H]+ 801.0863, found 801.0889; calcd for C26H16F20N2NaO4 [M
+ Na]+ 823.0683, found 823.0705; calcd for C26H16F20KN2O4 [M +
K]+ 839.0422, found 839.0439.
3
4.79 (t, JHF = 10.8 Hz, 4H), 9.12 (bs, 2H). 13C NMR (90.5 MHz,
2
acetone-d6): 62.4 (t, JCF = 33.5 Hz), 112−122 (undefined), 112.5 (t,
2JCF = 22.0 Hz), 121.7 (t, 1JCF = 278 Hz), 137.2 (dm, 1JCF = 251 Hz),
139.8 (dm, 1JCF = 251 Hz), 143.6 (dm, 1JCF = 249 Hz), 152.1 (s). 19F
3
NMR (235.2 MHz, acetone-d6): δ −165.74 (t, JFF = 18.7 Hz, 4F),
3
3
−159.74 (t, JFF = 19.6 Hz, 2F), −148.42 (d, JFF = 19.3 Hz, 4F),
−89.92 (t, 3JFF = 11.7 Hz, 4F), −78.88 (t, 3JFF = 12.9 Hz, 4F). HRMS-
ESI+: m/z calcd for C20H7F18N2O6 [M + H]+ 713.0011, found
713.0042; calcd for C20H10F18N3O6 [M + NH4]+ 730.0277, found
730.0304; calcd for C20H6F18N2NaO6 [M + Na]+ 734.9831, found
734.9869; calcd for C20H6F18KN2O6 [M + K]+ 750.9570, found
750.9589.
Reaction of MDI with 2,2,3,3-Tetrafluorobutan-1,4-diol, 2d. Dry
acetonitrile (45 mL) was degassed by three cycles of freeze−pump−
thaw and placed under inert atmosphere in a photochemical reactor
equipped with a magnetic stirring, a glass stopper, a stopcock, and a
water-flow cooled Pyrex immersion well. 4,4′-Methylene diphenyl
diisocyanate MDI (63 mg, 0.25 mmol) was added. It was dissolved
using vigorous stirring and ultrasound until the solution became clear.
Afterward, a solution of 2,2,3,3-tetrafluorobutan-1,4-diol (41 mg, 0.25
mmol) in dried and degassed acetonitrile (5 mL) was added. The
mixture was stirred for 5 min to homogenize the solution before the
irradiation source was turned on. After 4 h, the lamp was stopped and
the solvent evaporated in vacuo to obtain a white-yellowish solid. To
perform GPC analysis, 10 mg was solved in 1 mL of THF and filtered
with a nylon syringe filter.
Radical Trapping in the Reaction of 2,2,2-Trifluoroethanol 2a
with Phenyl Isocyanate 1. Dry acetonitrile (50 mL) was degassed by
three cycles of freeze−pump−thaw and placed under inert atmosphere
in a photochemical reactor equipped with a magnetic stirring, a glass
stopper, a stopcock, and a water-flow cooled Pyrex immersion well.
Phenyl isocyanate (55 μL, 0.5 mmol) was introduced. Afterward,
2,2,2-trifluoroethanol (76 μL, 1 mmol) and 1 mmol of the
corresponding additive were added. Immediately, the irradiation
source (Philips HPK 125W) was turned on. Additives used:
TEMPO (147 mg, 0.94 mmol); 1-octene (156 μL, 1 mmol);
acrylonitrile (66 μL, 1 mmol).
2,2,4,4,5,5,7,7-Octafluoro-3,6-dioxaoctane-1,8-diyl Bis(phenyl-
carbamate), 4d. Yield C: 0.205 g, 77%. IR (ATR): 3349 (NH st),
1721 (CO st), 1603 (arom CC), 1538 (NH δ), 1449, 1401, 1276
(NCOO st as), 1151 (C−F st), 1080, 986, 940, 760, 736 (CF δ), 691
1
3
cm−1. H NMR (250 MHz, acetone-d6): δ 4.73 (t, JHF = 10.0 Hz,
4H), 7.09 (t, 3JHH = 7.5 Hz, 2H), 7.34 (t, 3JHH = 7.5 Hz, 4H), 7.59 (d,
3JHH = 7.5 Hz, 4H), 9.11 (s, 2H). 13C NMR (62.5 MHz, acetone-d6): δ
2
61.8 (t, JCF = 32.7 Hz), 119.1 (s), 112−127 (undefined), 123.7 (s),
129.2 (s), 138.8 (s), 152.1 (s). 19F NMR (235.2 MHz, acetone-d6):
3
3
−89.81 (t, JFF = 13.4 Hz), −78.66 (t, JFF = 13.4 Hz). HRMS-ESI+:
m/z calcd for C20H17F8N2O6 [M + H]+ 533.0953, found 533.0967;
calcd for C20H20F8N3O6 [M + NH4]+ 550.1219, found 550.1222; calcd
for C20H16F8N2NaO6 [M + Na]+ 555.0773, found 555.0798; calcd for
C20H16F8KN2O6 [M + Na]+ 571.0512, found 571.0529.
2,2,3,3-Tetrafluorobutane-1,4-diyl bis(pentafluorophenyl-
carbamate), 6a. Yield C: 0.229 g, 79%. IR (ATR): 3350 (NH st),
1723 (CO st), 1599 (arom CC), 1535 (NH δ), 1500, 1448, 1274
(NCOO st as), 1144 (CF st), 980, 824, 759 (CF δ), 689, 624 cm−1.
1H NMR (250 MHz, acetone-d6): δ 4.81 (t, 3JHF = 13.9 Hz, 2H), 9.03
(bs, 2H). 13C NMR (90.5 MHz, acetone-d6): 60.6 (t, 2JCF = 26.7 Hz),
2
1
2
112.7 (t, JCF = 16 Hz), 116.3 (tt, JCF = 253.0 Hz, JCF = 32 Hz),
1
1
137.7 (dm, JCF = 249.0 Hz), 139.3 (dm, JCF = 251 Hz), 143.6 (dm,
1JCF = 249.0 Hz), 152.4 (s). 19F NMR (235.2 MHz, acetone-d6): δ
3
3
−165.78 (t, JFF = 18.8 Hz, 4F), −159.83 (t, JFF = 19.7 Hz, 2F),
3
3
−148.37 (d, JFF = 17.1 Hz, 4F), −123.01 (t, JHF = 13.9 Hz, 4F).
HRMS-ESI+: m/z calcd for C18H7F14N2O4 [M + H]+ 581.0177, found
581.0212; calcd for C18H10F14N3O4 [M + NH4]+ 598.0442, found
598.0462; calcd for C18H6F14N2NaO4 [M + Na]+ 602.9996, found
603.0031; calcd for C18H6F14KN2O4 [M + K]+ 618.9736, found
618.9751.
2,2,3,3,4,4-Hexafluoropentane-1,5-diyl Bis(pentafluorophenyl-
carbamate), 6b. Yield C: 0.144 g, 45%. IR (ATR): 3349 (NH st),
1722 (CO st), 1601 (arom CC), 1536 (NH δ), 1448, 1400, 1274
(NCOO st as), 1145 (CF st), 1118, 987, 940, 759 (CF δ), 735, 690,
625 cm−1. 1H NMR (250 MHz, acetone-d6): δ 4.88 (t, 3JHF = 15.0 Hz,
In the case of using TEMPO as additive, following the evolution of
the reaction of phenyl isocyanate with 2,2,2-trifluoroethanol by GC did
not show any appreciable slowing.
In the reactions with 1-octene or acrylonitrile as additive, after 1 h
of reaction no polymers or oligomers derived from 1-octene or
acrylonitrile were observed by GPC. Moreover signals corresponding
to the starting alkenes were observed in 1H NMR spectra of the
reaction mixture at that time.
4H), 9.11 (bs, 2H). 13C NMR (90.5 MHz, acetone-d6): 60.7 (t, 2JCF
=
26.8 Hz), 108−112 (undefined, central), 112.6 (t, 2JCF = 16 Hz), 115.0
1
2
1
(tt, JCF = 256 Hz, JCF = 32 Hz), 137.8 (dm, JCF = 250 Hz), 140.1
(dm, JCF = 251 Hz), 143.6 (dm, JCF = 248 Hz), 152.4 (s). 19F{1H}
1
1
3
NMR (235.2 MHz, acetone-d6): δ −165.71 (apparent t, JFF = 18.8
Effect of Light in the Reaction of Phenyl Isocyanate 1 with
Ethanol: This reaction was studied under two conditions: irradiated
with UV light and under ground-state conditions.
Hz, 4F), −159.70 (t, JFF = 19.0 Hz, 2F), −148.38 (d, 3JFF = 16.9 Hz,
3
4F), −127.08 (s, 2F), −121.22 (s, 4F). HRMS-ESI+: m/z calcd for
C19H6F16N2NaO4 [M + H]+ 652.9964, found 652.9969.
Irradiated with UV: Dry acetonitrile (50 mL) was degassed by three
cycles of freeze−pump−thaw and placed under inert atmosphere in a
photochemical reactor equipped with a magnetic stirring, a glass
stopper, a stopcock, and a water-flow cooled Pyrex immersion well.
Phenyl isocyanate (55 mL, 0.5 mmol) was added, and afterward, dry
ethanol (58 mL, 1 mmol) was introduced. Immediately the irradiation
source (Philips HPK 125W) was turned on. Ground state: dry
acetonitrile (50 mL) was degassed by three cycles of freeze−pump−
thaw and placed under inert atmosphere in a Schlenk flask equipped
with a magnetic stirring and protected of light with foil. Phenyl
isocyanate (55 mL, 0.5 mmol) was added, and afterward, dry ethanol
(58 mL, 1 mmol) was introduced. The evolution of both reactions was
followed by GC (phenyl isocyanate, tR = 1.52 min; ethyl phenyl-
carbamate, tR = 3.67 min) without observing any significant difference.
Ethyl Phenylcarbamate:28 1H NMR (360 MHz, CDCl3): δ 1.32 (t,
3JHH = 7.2 Hz, 3H), 4.24 (q, 3JHH = 7.2 Hz, 2H), 6.89 (bs, 1H), 7.07 (t,
2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11-Icosafluorododecan-
1,12-diyl Bis(pentafluorophenylcarbamate), 6c. Yield: C, 0.265 g,
54%. IR (ATR): 3349 (NH st), 1722 (CO st), 1602 (arom CC),
1536 (NH δ), 1448, 1273 (NCOO st as), 1146 (CF st), 940, 759 (CF
δ), 735, 690 cm−1. 1H NMR (250 MHz, acetone-d6): δ 4.95 (t, 3JHF
=
13.8 Hz, 4H), 9.09 (bs, 2H). 13C NMR (90.5 MHz, acetone-d6): 60.5
2
2
(t, JCF = 26.7 Hz), 105−120 (complex absorption), 112.6 (t, JCF
=
1
1
14.0 Hz), 138.0 (dm, JCF = 250 Hz), 139.7 (dm, JCF = 251 Hz),
143.6 (dm, JCF = 249 Hz), 152.2 (s). 19F{1H} NMR (235.2 MHz,
1
3
acetone-d6): δ −165.77 (apparent t, JFF = 21.1 Hz, 4F), −159.67 (t,
3JFF = 16.0 Hz, 2F), −148.44 (d, 3JFF = 16.5 Hz, 4F), −124.38 (bs, 4F),
−122.35 (bs, F), −120.38 (bs, 4F). HRMS-ESI+: m/z calcd for
C26H7F30N2O4 [M + H]+ 980.9921, found 980.9909; calcd for
C26H10F30N3O4 [M + NH4]+ 998.0187, found 998.0184; calcd for
C26H6F30N2NaO4 [M + Na]+ 1002.9741, found 1002.9739; calcd for
C26H6F30KN2O4 [M + K]+ 1018.9480, found 1018.9477.
3JHH = 7.2 Hz, 1H), 7.31 (t, 3JHH = 7.2 Hz, 2H), 7.42 (d, 3JHH = 7.2 Hz,
5026
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Article
2H). 13C NMR (90.5 MHz, CDCl3): δ 14.6, 61.2, 118.9, 123.3, 129.0,
138.1, 153.8.
Callow, M. E.; Callow, J. A.; DeSimone, J. M. Macromolecules 2009, 42,
6999.
Photochemical Competitive Reaction of PhNCO 1 with 2,2,2-
Trifluoroethanol 2a and Ethanol. Dry acetonitrile (50 mL) was
degassed by three cycles of freeze−pump−thaw and placed under inert
atmosphere in a photochemical reactor equipped with a magnetic
stirring, a glass stopper, a stopcock, and a water-flow cooled Pyrex
immersion well. Phenyl isocyanate (109 mL, 1 mmol) was introduced,
and the concentration checked by GC. Afterward, dry ethanol (58 mL,
1 mmol) and 2,2,2-trifluoroethanol (76 mL, 1 mmol) were added.
Immediately the irradiation source (Philips HPK 125W) was turned
on. After 15 min of irradiation, an aliquot was analyzed by GC: 2,2,2-
trifluoroethyl phenylcarbamate (tR = 3.45 min), 76% conversion; ethyl
phenylcarbamate (tR = 3.67 min), no signal was observed.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Compound characterization spectra (1H, 13C, 19F NMR, IR,
HRMS, and in some cases, DSC thermograms). This material is
available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
́
V.; Vidal-Gancedo, J.; Sebastian, R. M.; Marquet, J. Tetrahedron Lett.
Corresponding Authors
2013, 54, 6310.
*E-mail: rosamaria.sebastian@uab.es.
*E-mail: jordi.marquet@uab.es.
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Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We acknowledge financial support from the Spanish Govern-
ment (CTQ2009-07469, CTQ2011-22649, Consolider IN-
GENIO 2010: CSD2007-00006), Generalitat de Catalunya
(2009 SGR 1441 and 2009 SGR 1084), and UAB for a
scholarship to M.S.
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