Exploring reversible reactions between CO2 and amines

Article abstract of DOI:10.1016/j.tet.2003.09.096

The 'old' chemistry between CO₂ and primary alkylamines has been revisited. Amines 1 and 2, with appended aromatic fluorophores, reversibly reacted with CO₂ in polar aprotic solvent (e.g. DMSO, DMF) with the formation of carbamic acids 3 and 4. As a result, strong fluorescence occurred, thus directly reporting on the CO₂ entrapment. Carbamic acids were studied by ¹H and ¹³C NMR spectroscopy in DMSO-d ₆. The carbamate bond, despite being covalent, is reversible and can be broken upon heating or simply flashing solutions with inert gases. Synthesis and evaluation of a CO₂-sensing amino acid-α-naphthylglycine 7 is also reported for potential CO₂ monitoring under biorelevant conditions in aqueous solutions.

Full text of DOI:10.1016/j.tet.2003.09.096

Tetrahedron 59 (2003) 9619–9625
Exploring reversible reactions between CO and amines
2
*
Erin M. Hampe and Dmitry M. Rudkevich
Department of Chemistry and Biochemistry, University of Texas at Arlington, Box 19065, Arlington, TX 76019-0065, USA
Received 14 August 2003; revised 29 September 2003; accepted 29 September 2003
Abstract—The ‘old’ chemistry between CO
fluorophores, reversibly reacted with CO in polar aprotic solvent (e.g. DMSO, DMF) with the formation of carbamic acids 3 and 4. As a
result, strong fluorescence occurred, thus directly reporting on the CO entrapment. Carbamic acids were studied by H and C NMR
2
and primary alkylamines has been revisited. Amines 1 and 2, with appended aromatic
2
1
13
2
spectroscopy in DMSO-d
solutions with inert gases. Synthesis and evaluation of a CO
monitoring under biorelevant conditions in aqueous solutions.
6
. The carbamate bond, despite being covalent, is reversible and can be broken upon heating or simply flashing
-sensing amino acid-a-naphthylglycine 7 is also reported for potential CO
2
2
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
natural processes can absorb this gas. The CO levels in the
2
atmosphere have risen by 31% over the last 250 years and
these concentrations may double or even triple in the next
century. Extensive CO circulation in atmosphere, biologi-
1
Carbon dioxide (CO ) is the major greenhouse gas. It
2
constantly circulates in the environment through a variety of
processes known as the carbon cycle. Both volcanic
eruptions and the decay of plants and animals release CO2
into the atmosphere.
2
cal systems, industry and agriculture necessitates the
development of novel methods of CO monitoring. Another
2
important and still unresolved issue is chemical fixation of
2
CO2.
,3
Oceans, lakes, and rivers absorb CO from the atmosphere.
2
Through photosynthesis, plants collect CO and use it to
2
CO2 is generally an unreactive molecule, but it does
combine rapidly with amines at ordinary temperatures and
pressures to form carbamates. The chemistry between CO
make their own food, in the process incorporating carbon
into new plant tissues and releasing oxygen to the
environment as a byproduct. Upon burning of fossil fuels,
oil, coal, and natural gas, and wood, huge amounts of CO2
are released into the air. As a result of these activities, CO2
in the atmosphere is accumulating faster than the Earth’s
2
4
and amines is essentially an acid–base equilibrium (Fig. 1).
Two molecules of an amine, in presence of CO , react to
2
form a carbamic salt, presumably by way of the correspond-
ing carbamic acid. Carbamate anions can be further
2
Figure 1. Reversible covalent chemistry between CO and amines.
Keywords: amines; amino acids; carbon dioxide fixation; fluorescence.
*
Corresponding author. Tel.: þ1-817-272-5245; fax: þ1-817-272-3808; e-mail: rudkevich@uta.edu
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.09.096

9620
E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
5
converted to isocyanates or may react with alkyl halides to
4
1 or 1-(aminomethyl)pyrene 2 in polar aprotic solvents such
as DMSO and DMF did not affect their UV–vis character-
istics, but resulted in dramatic changes in their fluorescence
,6,7
yield urethanes, thus providing an alternative synthetic
equivalent to highly toxic phosgene. Furthermore, carba-
mates are thermally unstable and release CO upon heating.
2
emissions. Specifically, upon excitation of 1 at l ¼282 nm,
ex
This can be useful under several circumstances. Polymer-
bound amines are employed in industry as reusable ‘CO
the fluorescence emission at l ¼334 nm in DMF increased
em
by more than 10 times (Fig. 2A). The fluorescence at
l ¼408 nm of pyrene derivative 2 in DMF increased
em
2
,9
8
scrubbers,’ removing CO from industrial exhaust streams.
2
By reacting with amino groups, CO2 is absorbed into
1
similarly, at l ¼341 nm (Fig. 2B).
ex
0
solutions of an amine or an amine-containing ionic liquid.
This method has also been extended to use of multiple
We found, that the species responsible for the observed
fluorescence are the corresponding carbamic acids 3 and 4.
Free amines 1 and 2 only weakly emit fluorescence under
ambient conditions. This is due to photo-induced electron
transfer (PET) quenching of the excited fluorophore by the
intramolecular amino group lone pair. Upon reaction of
1
1
amine-containing dendrimers. Exposure of solutions of
some long-chain alkyl amines to CO results in the
reversible formation of organogels. Thermally reversible
carbamate chemistry has been recently employed for
2
1
2
1
3
molecular imprinting of polymers.
dissolved CO with amines 1 and 2, carbamic acids 3 and 4
2
Chemical reactions between CO and amines have also been
1
are formed. PET quenching no longer takes place: the lone
pair of electrons on the nitrogen atom is now involved in a
conjugation with the carbonyl oxygen. This leads to an
overall increase in observed fluorescence. PET of this type
2
4–16
employed for the gas sensing.
Although CO sensing and environmental monitoring is
This is for a good reason.
2
1
7,18
well documented,
many significant problems remain.
1
5
16
19
One of them is a direct detection. Others and we recently
demonstrated the ability of some amines to function as
direct and reusable, fluorescent CO sensors (Fig. 1). In this
is known and has been exploited for pH sensing. In
fluorescent pH sensors, protonation of the amine in acidic
solutions prevents intramolecular PET from occurring.
Bubbling N through solutions of 3 and 4 resulted in loss
2
paper, we disclose the chemistry behind these processes and
identify the corresponding carbamic acids as the species
causing the fluorescence. We provide NMR spectroscopic
evidence of the formation of free (!) carbamic acid as an
observable intermediate in carbamate formation. Finally,
2
of fluorescence.
2.2. NMR spectroscopy
we report on the synthesis and evaluation of CO -sensing
2
Reactions, involving amines 1, 2, and CO , were then
2
amino acids for potential use in biocompatible environ-
ments. Taken together, our results open more possibilities to
detect and chemically utilize CO2.
monitored in the NMR tube in DMSO-d . The solvent was
6
first purged with dried N before addition of amines. In the
2
presence of dissolved CO (10–15 equiv.), 1 and 2 cleanly
2
and quantitatively reacted to form the corresponding
carbamic acids 3 and 4. These appeared to be reasonably
1
13
2
. Results and discussion
stable and can be studied by H and C NMR spectroscopy
Figs. 3 and 4).
(
2
.1. UV–vis and fluorescent spectroscopy
Specifically, prior to CO exposure, benzylic protons of 1
2
Primary amines 1 and 2, used in this work, possess
naphthalene and pyrene fluorophores, respectively, separ-
ated from the NH group by a methylene unit. Bubbling CO
and 2 were seen as singlets at 4.19 and 4.46 ppm,
respectively. After CO bubbling, these were transformed
2
into doublets (J¼6.0 Hz) at 4.63 and 4.91 ppm, respect-
2
2
for 1–2 h through solutions of 1-(aminomethyl)naphthalene
ively. In both cases, a very broad signal appeared at
Figure 2. Fluorescence measurements (DMF, 295^1 K) before and after saturation with CO
2
with: (A) aminomethylnaphthalene 1, lex¼282 nm;
26
(
B) aminomethylpyrene 2, lex¼341 nm. All solutions were deoxygenated with N prior measurements. [1]¼[2]¼10 M.
2

E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
9621
1
Figure 3. CO
NMR spectra (500 MHz, DMSO-d
with CO ; formation of carbamic acid 3; (C) independently prepared
carbamate salt 5. The NH and benzylic CH
solutions were deoxygenated with dried N
2
induced spectral changes of aminomethylnaphthalene 1. H
6
, 295 K) of: (A) 1; (B) 1 after saturation
2
2
signals are marked. The initial
prior measurements.
2
,
10.6 ppm, which was assigned to the C(O)OH. The
carbamate NH signals also emerged as triplets (J¼6.0 Hz) at
7
.37 and 7.54 ppm, respectively. Furthermore, resonances at
1
1
3
2
Figure 4. CO induced spectral changes of aminomethylpyrene 2. H NMR
,158 ppm in the C NMR spectra of 3 and 4 identified the
carbamic (CvO) carbon atom.
spectra (500 MHz, DMSO-d
CO ; formation of carbamic acid 4; (C) independently prepared carbamate
salt 6. The NH and benzylic CH
were deoxygenated with dried N
6
, 295 K) of: (A) 2; (B) 2 after saturation with
2
2
signals are marked. The initial solutions
2
prior measurements.
Bubbling N through these solutions resulted in loss of CO
2
2
from some carbamic acid molecules to form the free amines
or 2, which then quickly abstracted a proton from
remaining carbamic acid. Alkylammonium carbamic salts 5
and 6 partially precipitated from solution. Further CO loss
2
cannot be achieved by prolonged bubbling of N , but the
2
1
in the decomposition of carbamates, hydrolysis of iso-
cyanates, in the Hofmann and Curtius rearrangements.
There is little direct evidence, however, to support this. Up
to now, carbamic acids were thought to be highly unstable
and have only been observed by somewhat unconventional
carbamic salts can lose CO at elevated temperatures to
2
reform the amines 1 and 2, and this was in fact achieved by
brief reflux in toluene.
methods. Composite ices of NH
studied by IR, suggesting the formation of carbamic acid
, H O, and CO have been
3 2 2
2
0
upon irradiation with a 1 MeV proton source. Several
protonated carbamic acids have been characterized by Olah
The identities of the precipitated salts were confirmed by
comparison to separately prepared samples of the salts 5 and
2
1
and co-workers under superacidic conditions. In a
spectacular case, the solid-state structure of dibenzylamine
6
through solutions of 1 and 2 in a less polar solvent such as
(Fig. 5). These samples were prepared by bubbling CO2
2
2
carbamic acid was published. However in solution, prior
1
13
CHCl or MeCN. H NMR, C NMR, and CHN elemental
3
analysis confirmed the structure and composition of the salts
5
d as two separate signals in their H spectra: a singlet at
and 6. For instance, benzylic protons were seen in DMSO-
1
6
4
.22 and a doublet at 4.62 ppm (J¼5.5 Hz) for 5, and a
singlet at 4.48 and a doublet at 4.90 ppm (J¼5.5 Hz) for 6.
The carbamate NH signals were seen as triplets (J¼5.5 Hz)
at 7.32 and 7.53 ppm, respectively. A resonance at 158 ppm
1
3
in the C NMR spectrum of 5 identified the carbamic
CvO) carbon atom.
(
Carbamic acids, with NH C(O)OH as a simplest represen-
2
tative, have been the subject of considerable speculation and
are still elusive. These are often suggested as intermediates
Figure 5. Carbamic salts 5 and 6.

9622
E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
2
4
to our studies, no free carbamic acids had been observed.
Chemistry of carbamic acids is important, since they may
form in biological systems in presence of CO . Our results
indicate that facile atmospheric control can allow the
observation and study of carbamic acids using conventional
spectroscopic techniques such as NMR and fluorescence
spectroscopy.
Hosangadi and Dave. In short, reaction of 1-naphthalde-
hyde with (R)-2-amino-2-phenylethanol in CHCl , followed
3
by addition of trimethylsilylcyanide (TMSCN), generated
the intermediate 8 with a diastereomeric yield [(S,R)–(R,R)]
of 84:16, determined by integration of the a-methine proton
in the H NMR spectrum. The (S,R)-8 diastereomer was
further purified by successive recrystallizations from
2
1
EtOAc/hexanes, 1:4. This procedure provided (S,R)-8 with
1
2
.3. A CO -sensing amino acid
2
.98% diastereomeric purity by H NMR. After oxidative
cleavage of formaldehyde by Pb(OAc) , hydrolysis of the
4
2
4
For potential application in sensing, receptor molecules
must not only be preparatively available, but also readily
immobilizable on other (macro)molecules, solid supports,
or surfaces. Importantly, they should also be properly
configured to sufficiently respond to the presence of an
analyte. Existing literature protocols on synthesis of
naphthalenes and pyrenes, containing two or more
functional groups, typically require many steps and are
time-consuming. Aminomethyl naphthalenes and pyrenes
containing other functional fragments are not known.
Following the natural strategy to employ amino acids as
universal building blocks for a huge variety of proteins and
enzymes, we identified a-naphthylglycine 7 (Scheme 1) as
imine was attempted by stirring in 6 M HCl, as reported, at
rt for 1 h, followed by stirring at 908C for 1 h. The FTIR and
1
3
C NMR spectral analysis of the crude product revealed,
however, that the nitrile functional group still remains. A
carbon resonance at ,116 ppm was assigned for the nitrile,
and the resonance for a carboxylic acid was not found.
2
4
Accordingly, not acid 7, as reported earlier, but instead
nitrile 9 was formed under these conditions. This compound
1
was further unambiguously characterized by FTIR, H and
3
C NMR spectroscopy and CHN elemental analysis.
1
Obviously, while it is easy to cleave the imine, more effort is
needed to hydrolyze the nitrile group. After several
optimization experiments, we found that vigorous treatment
of 9 with concentrated HCl in a sealed vessel for 4 h at 908C
resulted in 70% formation of 1-naphthylglycine 7 as a
hydrochloric salt.
an immobilizible CO -sensing module. Indeed, similar to 1
2
and 2, structure 7 contains aminomethyl units attached to
the fluorescently active aromatic fragment. At the same
time, the carboxylic groups in 7 can be effectively used for
further attachments and/or incorporation into larger macro-
structures. For example, it can react with commercially
available polymeric supports such as chloromethyl,
hydroxymethyl or aminomethyl polystyrenes, or be
incorporated within the oligopeptide nanostructures.
Sensing experiments, similar to those for 1 and 2, were
performed for 7 in D O and DMSO-d , in the presence of
2
6
triethylamine (TEA). Addition of TEA effected neutraliz-
ation of the hydrochloric salt of 7, and as well prevented
protonation of the amino group. Control experiments
The simplest route to a-arylglycines is through the racemic
Strecker synthesis, known in the literature for over a
century. While racemic synthesis is both cost and time
efficient, it may prove useful for future biological
applications to acquire enantiomerically pure biocompatible
structures, particularly if they can be used to monitor
confirm that TEA does not react with CO and its presence
2
is innocuous. Upon exposure to CO , the fluorescent
2
2
3
response of 7 was similar to that of 1, showing an
enhancement of monomer emission by four to five times
2
5
in water or DMSO solution (Fig. 6).
1
enzyme–CO interactions. Modifications of the Strecker
2
When followed by H NMR spectroscopy in D O, the
2
procedure employ a chiral auxiliary to induce diastereo-
selectivity in an intermediate. The chiral auxiliary can be
further removed to yield the enantiomerically enriched
amino acid. Thus, the method chosen here reflects
consideration for experimental ease and a high yield of
enantio-enriched products.
a-methine signal of 7 was seen as a singlet at 5.04 ppm prior
to CO bubbling. After bubbling CO for 5 h, the methine
2
2
proton signal was shifted downfield to 5.52 ppm. In
addition, the aromatic region of the spectrum totally
changed (Fig. 7). These spectral data are in agreement
with observations recorded for amines 1 and 2, so at this
stage we conclude that the carbamate formation definitely
takes place with 7 in aqueous solution. The fate of the
corresponding carbamic acid is not clear and requires more
In the synthesis of 7 we initially followed the diastereo-
selective Strecker method (Scheme 1), recently reported by
Scheme 1. Diastereoselective Strecker synthesis of (S)-a-naphthylglycine 7: (a) R-2-amino-2-phenylethanol, CHCl
24 h, 76% (two steps). (c) Pb(OAc) , CH Cl /MeOH, 20 min. (d) 6 M HCl, rt, 1 h, 908C, 45 min, .95% (two steps). (e) 6 M HCl, 908C, 4 h, 70%.
3 3
, rt, 4 h. (b) TMSCN, CHCl /MeOH, rt,
4
2
2

E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
9623
the PET quenching effect. Free carbamic acids of amines
can be observed by NMR and fluorescence spectroscopy in
solution. The identification and evaluation of naphthyl-
glycine as a CO -sensitive module widens possibilities for
2
working in aqueous solution with an optical response and
also for immobilization and incorporation into natural
nanoscaffolds.
4. Experimental
4.1. General
Melting points were determined on a Mel-Temp apparatus
Laboratory Devices, Inc.) and a Buchi apparatus and are
(
1
13
uncorrected. H and C NMR spectra were recorded at
295^1 K, unless stated otherwise, on JEOL Eclipse
500 MHz spectrometer. Chemical shifts were measured
relative to residual non-deuterated solvent resonances. FTIR
spectra were recorded on a Bruker Vector 22 FTIR
spectrometer. UV–vis spectra were measured on a
JASCO V-530 spectrophotometer. Fluorescence studies
were performed on a Jobin Yvon Fluoromax 3 spectrometer.
Elemental analysis was performed on a Perkin–Elmer 2400
Figure 6. Fluorescence measurements with naphthylglycine 7 (4 equiv.
. lex¼282 nm;
TEA, H
[
2
O, 295^1 K) before and after saturation with CO
6
2
2
7]¼10 M.
CHN analyzer. For column chromatography, Silica Gel
˚
60 A (Sorbent Technologies, Inc.; 200–425 mesh) was
used. All experiments with moisture- or air-sensitive
compounds were run in freshly distilled, anhydrous solvents
under a dried nitrogen atmosphere.
1
4
.1.1. Aminomethylnaphthyl carbamic acid 3. H NMR
(
7
4
DMSO-d ): d¼10.60 (bs, 1H), 8.13 (d, J¼7.5 Hz, 1H),
6
.94 (d, J¼7.5 Hz, 1H), 7.83 (d, J¼7.5 Hz, 1H), 7.6–7.4 (m,
1
3
H), 7.37 (t, J¼6.0 Hz, 1H), 4.62 (d, J¼6.0 Hz, 2H);
C
NMR (DMSO-d ): d¼158.1 (CvO), 136.0, 133.8, 131.4,
6
1
29.1, 127.9, 126.7, 126.3, 126.0, 125.4, 124.0, 42.4.
4.1.2. Aminomethylpyrenyl carbamic acid 4. 1-(Amino-
methyl)-pyrene hydrochloride (0.268 g, 1 mmol) was
shaken in THF (15 mL) with 10% NaOH (15 mL) in a
separatory funnel. The organic layer was separated, dried
1
1
(Na SO ) and evaporated. H NMR (DMSO-d ): d¼8.5–
Figure 7. CO
spectra (500 MHz, D
saturation with CO ; (C) solution B after purging with N
2
induced spectral changes of naphthylglycine 7. H NMR
2
4
6
8.0 (m, 9H), 7.54 (t, J¼6.0 Hz, 1H), 4.91 (d, J¼6.0 Hz, 2H);
2
O, 4 equiv. TEA, 295 K) of: (A) 7; (B) 7 after
at 708C for 1 h.
1
3
2
2
C NMR (DMSO-d ): d¼158.1 (CvO), 134.0, 131.3,
6
1
1
30.8, 130.5, 128.3, 128.1, 127.9, 127.5, 126.9, 126.7,
25.8, 125.7, 125.3, 124.7, 124.5, 124.4, 123.6, 42.5.
detailed studies. The acidic proton is, most probably,
þ
transferred to a TEA molecule (pK (Et N H),10.75),
a
3
thus generating the corresponding carbamic anion (Fig. 6).
This is a well-known scenario for carbamate salts formation
4
.1.3. 1-(Aminomethyl)-naphthalene ammonium carba-
mate 5. CO2 gas was bubbled through a solution of
1-(aminomethyl)-naphthalene 1 (0.47 mL, 3.2 mmol) in
CHCl3 (10 mL) for 15 min. The white precipitate was
4
–14
in the presence of a base.
h did not reverse the process. The amino acid 7 was
however recovered by purging with N at 708C for 1 h
Subsequent bubbling of N for
2
3
2
filtered and dried in vacuo. Yield .95%; mp 1058C
1
(
Fig. 7).
(
decomp.); H NMR (DMSO-d ): d¼8.12 (t, J¼6.5 Hz,
6
2
7
4
H), 7.93 (d, J¼7.3 Hz, 2H), 7.81 (t, J¼7.3 Hz, 2H), 7.6–
These experiments confirm the capability of this unnatural
amino acid to form carbamates in the presence of dissolved
CO , and as such identify 7 as a possible CO sensor.
2
.4 (m, 8H), 7.32 (t, J¼5.5 Hz, 1H), 4.62 (d, J¼5.5 Hz, 2H),
13
.22 (s, 2H); C NMR (DMSO-d ): d 158.5 (CvO), 139.4,
6
2
6
2
136.3, 133.8, 131.5, 131.4, 129.0, 127.8, 127.4, 126.6,
1
1
26.5, 126.2, 126.14, 126.10, 126.0, 125.3, 125.0, 124.1,
24.0, 43.3, 42.4. Anal. calcd for C H N O ·0.2H O: C,
2
3
22
2
2
2
3
. Conclusions and outlook
76.30; H, 6.24; N, 7.74. Found: C, 76.20; H, 6.59; N, 7.76.
The simple chemistry between CO and amines can be used
2
to directly detect dissolved CO in polar solution through
2
4.1.4. 1-(Aminomethyl)-pyrene ammonium carbamate 6.
1-(Aminomethyl)-pyrene hydrochloride (0.268 g, 1 mmol)

9624
E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
2
3
was shaken in THF (15 mL) with 10% NaOH (15 mL) in a
separatory funnel. CO2 was then bubbled through the
organic layer for 15 min. The off-white precipitate was
(0.828 g, 70%): mp .2508C; [a] ¼þ155 (c¼1.0, 1 M
D
2
4
20
D
1
HCl) [lit. [a] ¼þ166 (c¼1.0, 1 M HCl)]; H NMR (D O,
2
Et N): d¼8.18 (d, J¼7.5 Hz, 1H), 8.9 (m, 2H), 8.55 (m,
3
1
filtered and dried in vacuo. Yield .95%; mp 80–958C
1
4H), 5.04 (s, 1H); H NMR ([D ]DMSO-d , Et N): d¼8.32
6
6
3
(
decomp.); H NMR (DMSO-d ): d¼8.5–8.0 (m, 18H),
(d, J¼8 Hz, 1H), 8.9 (m, 2H), 7.5–7.6 (m, 4H), 5.03 (s, 1H);
C NMR (D O, Et N): d 181.5, 138.6, 133.9, 130.9, 129.0,
2 3
6
1
3
7
Anal. calcd for C H N O : C, 82.98; H, 5.17; N, 5.53.
.53 (t, J¼5.5 Hz, 1H), 4.90 (d, J¼5.5 Hz, 2H), 4.48 (s, 2H).
128.1, 126.7, 126.1, 126.0, 123.7, 57.8; FTIR (KBr, 2 , HCl
salt): n¼3425, 2989, 1733, 1599, 1497. Anal. calcd for
C H NCl: C, 60.64; H, 5.09; N, 5.89. Found: C, 60.34; H,
1
3
5 26 2 2
Found: C, 83.03; H, 5.47; N, 5.35.
1
2 12
4
.1.5. (S,R)-2-[(2-Hydroxy-1-phenylethyl)amino]-2-(1-
naphthyl)ethanenitrile 8. A solution of 1-naphthaldehyde
1.36 mL, 10 mmol) and (R)-2-phenylglycinol (2.0 g,
5.30; N, 6.26.
(
4.2. Fluorescence measurements
1
4
5 mmol) in CHCl (35 mL) was stirred in presence of
3
˚
A molecular sieves at rt in air for 4 h. The solvent was
Fluorescence measurements were performed at 295^1 K
using solvents that had been previously degassed with
removed at reduced pressure to leave a pale-yellow oil,
which was then redissolved in CHCl (20 mL) and MeOH
dried N . All fluorescence spectra were recorded at
2
3
2
6
(
3 mL). The solution was cooled to 08C and trimethyl-
10 M concentration. The excimer emission was seen at
2
4
silylcyanide (2.8 mL, 20 mmol) was added slowly by
syringe. The mixture was then allowed to stir for 24 h at
rt. The solvents were removed at reduced pressure to afford
crude 8 as an yellow oil that crystallized upon standing. The
solids were recrystallized twice from EtOAc–hexanes, 1:4
.10 M. Solutions of 7 were prepared by dilution of a
22
2
3
stock solutions of 7 (10 M) and TEA (10 M).
Acknowledgements
(20 mL) and separated by vacuum filtration to give a shiny
1
off-white powder (2.29 g, 76%): mp 120–1228C; H NMR
Financial support is acknowledged from the University of
Texas at Arlington in the form of start-up funds and the
Faculty Research Enhancement Award. We also thank
Professor J.-L. Montchamp of the Texas Christian
University for the experimental advice. DMR is an A. P.
Sloan Research Fellow.
(
5
CDCl ): d¼8.85 (m, 3H), 8.7 (m, 1H), 8.4–8.6 (m, 8H),
3
.11 (s, 1H), 4.35 (dd, J¼9.5, 4.5 Hz, 1H), 3.84 (dd, J¼11,
.5 Hz, 1H), 3.68 (t, J¼10 Hz, 1H), 2.58 (br s, 1H), 1.77 (br
4
s, 1H); C NMR (CDCl ): d 138.1, 134.0, 130.7, 130.3,
1
3
3
1
1
30.2, 129.1, 129.0, 128.9, 128.3, 126.9, 126.3, 126.0,
25.4, 123.0, 118.9, 67.0, 63.8, 50.1. Anal. calcd for
C H N O: C, 79.44; H, 6.00; N, 9.26. Found: C, 79.34; H,
0 18 2
2
5
.94; N, 9.27.
References
4
5
.1.6. (S)-a-1-Naphthylglycine 7. A mixture of 8 (1.5 g,
mmol) in CH Cl (20 mL) and MeOH (10 mL) were
2
2
1. (a) Stigliani, W. M.; Spiro, T. G. Chemistry and the
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stirred to dissolve. After cooling to 08C, lead tetraacetate
2.22 g, 5 mmol) was added in one portion, darkening the
solution from pale yellow to orange. After stirring for
0 min, saturated aqueous NaHCO (50 mL) was added in
(
2
3
portions with swirling. Insoluble impurities were removed
by filtration over Celite and washed with CH Cl (50 mL).
2
2
The filtrate was extracted with CH Cl (2£10 mL), dried
2
2
over Na SO and evaporated at reduced pressure to leave a
2
4
yellow oil, which was subjected to hydrolysis without
purification. Several attempts to reproduce the published
2
2
procedure for the hydrolysis, employing 6 M HCl at rt for
h, and then at 908C for 45 min, resulted only in nitrile 9 as
1
a hydrochloric salt. Yield .95%; mp 1808C (decomp.); H
1
NMR (D O): d¼8.10 (m, 3H), 7.90 (d, J¼7 Hz, 1H), 7.7 (m,
2. (a) Xiaoding, X.; Moulijn, J. A. Energy Fuels 1996, 10,
305–325. (b) Batjes, N. H. Biol. Fertil. Soils 1998, 27,
230–235, Both physical and chemical properties of CO are
2
1
3
3
1
H), 6.52 (s, 1H); C NMR (D O): d¼133.8, 132.2, 129.5,
2
29.1, 128.3, 127.4, 127.3, 125.6, 124.0, 121.6, 115.6, 41.9;
2
2
1
FT-IR (oil mull, cm , HCl salt): n¼2364 (CN). Anal. calcd
currently utilized. The first category includes beverage
industry, fire extinguisher technology, refrigeration, enhanced
oil recovery and supercritical CO extraction and cleaning. In
for C H N Cl: C, 65.90; H, 5.03; N, 12.81. Found: C,
1
2 11 2
6
5.98; H, 5.35; N, 12.91.
2
2
the other category, CO is used as a reactant. In organic
In the modified procedure, a suspension of the oil in
concentrated HCl (10 mL) was stirred at 908C in a sealed
vessel. The solids dissolved at temperatures greater than
chemical industry, CO2 is employed in preparation of
carbonates, (amino) acids, esters, lactones, amino alcohols,
carbamates, urea derivatives, and various polymers or
copolymers—polyurethanes, polycarbonates, etc. In inorganic
chemical industry, it is used to manufacture Na CO or
8
08C and then began to precipitate as the amino acid salt
began to form after ,1 h. After 4 h of stirring, the mixture
was cooled to 08C and solids were filtered and washed with
small portions of cold H O, followed by cold ether to yield
2
3
NaHCO (the Solvay process), CaCO , and other carbonates.
3
3
2
CO2 is also used as an acid in water purification and
neutralization processes. The major applications of CO in
(
S)-a-1-naphthylglycine hydrochloride 7 as a white powder
2

E. M. Hampe, D. M. Rudkevich / Tetrahedron 59 (2003) 9619–9625
9625
USA, however, are nonchemical and are mostly in refriger-
ation and beverage industries. Totally, only 0.7–1.0% of the
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2
produced CO is used, and the consumption in chemical
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2
3
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(
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1
1
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6
2
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2
5
2
5. At concentrations .10 M, both monomer and excimer
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2
enhanced by presence of dissolved CO . Further investigations
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1
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8
68–874.