Studies on the solvent dependence of the carbamic acid formation from ω-(1-naphthyl)alkylamines and carbon dioxide

Article abstract of DOI:10.1016/j.tet.2004.10.033

Carbamic acid formation from amine and carbon dioxide in a variety of solvents was investigated by measuring NMR (¹H, ¹³C, HMBC) and IR spectra in situ. Bubbling of CO₂ through solutions of naphthylalkylamines 1-3 in DMSO, DMF or pyridine (protophilic, highly dipolar, aprotic solvent) resulted in complete conversion of the amines to the corresponding carbamic acids 4-6. In dioxane (protophilic, dipolar, aprotic solvent), the carbamic acid and a small amount of the ammonium carbamate were formed. By contrast, in MeCN (protophobic, dipolar, aprotic solvent), in benzene or CHCl₃ (apolar, aprotic solvent), or in 2-PrOH or MeOH (dipolar, amphiprotic solvent), ammonium carbamates 7-9 rather than 4-6 were formed, although the ammonium bicarbonates/carbonates were competitively formed in MeOH. The ammonium carbamates precipitated in many cases and hence they could be separated. The selective generation of the undissociated carbamic acids in preference to the ammonium carbamates in protophilic, dipolar, aprotic solvents (DMSO, DMF, pyridine, and dioxane) is rationalized by considering the acid-base equilibria between the amines 1-3 and the carbamic acids 4-6 in nonaqueous media. The obtained selectivity is likely due to the larger pK_a values for 4-6 than the amines 1-3 in these solvents. Interestingly, the fluorescence intensities for 1-3 were dramatically enhanced (4-50 times) in DMSO or DMF upon introduction of CO₂, while they were not altered very much in dioxane, MeCN, benzene, CHCl₃, 2-PrOH, and MeOH, except small to medium increases (1.3-3 times) for 1 in dioxane, MeCN, 2-PrOH and MeOH. As a whole, the solvent effects observed in these fluorescence studies are consistent with those observed in the above NMR and IR studies. Finally, methoxycarbonylation of amine 3 into the methyl carbamate was successfully accomplished by using (trimethylsilyl)diazomethane in the presence of CO ₂. Probably due to pK_a(6)>pK_a(3) in protophilic dipolar aprotic solvents, the conversion 3→6 is nearly complete while the formation of 9 is minimal.

Full text of DOI:10.1016/j.tet.2004.10.033

Tetrahedron 61 (2005) 213–229
Studies on the solvent dependence of the carbamic acid formation
from u-(1-naphthyl)alkylamines and carbon dioxide
*
Koji Masuda, Yoshikatsu Ito, Masahiro Horiguchi and Haruo Fujita
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Kyoto 615-8510, Japan
Received 26 August 2004; accepted 4 October 2004
Available online 5 November 2004
1
13
Abstract—Carbamic acid formation from amine and carbon dioxide in a variety of solvents was investigated by measuring NMR ( H, C,
2
HMBC) and IR spectra in situ. Bubbling of CO through solutions of naphthylalkylamines 1–3 in DMSO, DMF or pyridine (protophilic,
highly dipolar, aprotic solvent) resulted in complete conversion of the amines to the corresponding carbamic acids 4–6. In dioxane
(
(
protophilic, dipolar, aprotic solvent), the carbamic acid and a small amount of the ammonium carbamate were formed. By contrast, in MeCN
protophobic, dipolar, aprotic solvent), in benzene or CHCl (apolar, aprotic solvent), or in 2-PrOH or MeOH (dipolar, amphiprotic solvent),
3
ammonium carbamates 7–9 rather than 4–6 were formed, although the ammonium bicarbonates/carbonates were competitively formed in
MeOH. The ammonium carbamates precipitated in many cases and hence they could be separated. The selective generation of the
undissociated carbamic acids in preference to the ammonium carbamates in protophilic, dipolar, aprotic solvents (DMSO, DMF, pyridine,
and dioxane) is rationalized by considering the acid–base equilibria between the amines 1–3 and the carbamic acids 4–6 in nonaqueous
media. The obtained selectivity is likely due to the larger pK values for 4–6 than the amines 1–3 in these solvents. Interestingly, the
a
fluorescence intensities for 1–3 were dramatically enhanced (4–50 times) in DMSO or DMF upon introduction of CO , while they were not
2
altered very much in dioxane, MeCN, benzene, CHCl , 2-PrOH, and MeOH, except small to medium increases (1.3–3 times) for 1 in
3
dioxane, MeCN, 2-PrOH and MeOH. As a whole, the solvent effects observed in these fluorescence studies are consistent with those
observed in the above NMR and IR studies. Finally, methoxycarbonylation of amine 3 into the methyl carbamate was successfully
2
accomplished by using (trimethylsilyl)diazomethane in the presence of CO .
q 2004 Elsevier Ltd. All rights reserved.
0 0
ammonium carbamate salt [RR NCO ][ H NRR ].
2 2
K
C
1. Introduction
Thus, bubbling of CO2 gas through a solution of
suitable amine in a variety of solvents such as
chloroform (CHCl ), methylene chloride, acetonitrile
3
Suitable amines can reversibly trap carbon dioxide through
carbamic acids, which are important intermediates in view
of their synthetic, industrial and biological applications.
1
–5
(MeCN), benzene, toluene, ethyl ether, tetrahydrofuran
(THF), dioxane, and methanol (MeOH) (anhydrous),
generally results in precipitation of the corresponding
ammonium carbamate salt as a white solid. By contrast,
In an attempt to accomplish new methods for irreversible
fixation of carbon dioxide, we have been pursuing basic
research on the reactivity of carbon dioxide with amines
bearing an aromatic group as a chromophore and fluor-
ophore. Mechanistic studies of amine–CO2 reactions in
organic solvents are scarce unlike in aqueous solutions,
although carbamic acids have been known for a long time to
be readily generated from a primary or secondary aliphatic
6
7
we and others have recently found that in a particular
solvent like dimethyl sulfoxide (DMSO) and N,
N-dimethylformamide (DMF), where the carbamate
salts are well soluble, the carboxylation of a primary
aralkylamine into the carbamic acid RNHCO H
2
0
1–5
proceeds up to the complete (w100%) conversion. We
have already studied a number of primary aralkyla-
mines: for instance, u-(1-naphthyl)alkylamines (uZ1–3)
amine RR NH.
however, their isolation in the free acid form RR NCO H
Because of their transient nature,
0
2
†
is very difficult. They are usually obtained as an
1
–3, u-(9-anthryl)alkylamines (uZ1–3), u-phenyl-
6
alkylamines (uZ1 or 2), tryptamines, and catecholamines.
Their N-carboxylation in DMSO by CO2 bubbling
proceeded smoothly to w100% conversion. However,
arylamines such as aniline and its derivatives did not
undergo substantial N-carboxylation under similar
conditions, although indoline and p-anisidine were
N-carboxylated to a low conversion (22 and 11%,
Keywords: Carbon dioxide; Carbamic acid; Naphthylamines; Solvent
effect; Carbon dioxide fixation; Fluorescence.
*
Corresponding author. Tel./fax: C81 75 383 2718;
e-mail: yito@sbchem.kyoto-u.ac.jp
A successful isolation and the X-ray structure determination of N,N-
†
4
NCOOH was reported. However, we were
dibenzylcarbamic acid Bn
unable to reproduce its isolation. We obtained only the ammonium
2
K
C
2 2 2 2
carbamate [Bn NCO ][ H NBn ].
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.033

214
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
Chart 1. Carbamic acid formation from selected arylamines in DMSO-d
1
yield was estimated in situ by H NMR analysis.
6
through bubbling of CO
2
at room temperature. The conversion or the carbamic acid
‡
respectively: Chart 1).
The carboxylation experiments were carried out by passing
a large excess of CO gas through a solution of amine (0.13–
2
K5
0
.15 M for NMR and IR experiments and w6!10 M for
absorption and fluorescence measurements) at room tem-
perature for 0.5–1 h. Analyses for the products were
1
13
performed in situ by measurements of H and C NMR
including 2D NMR (COSY, NOESY, HMQC, and HMBC),
IR, and absorption and fluorescence spectra.
K1
0
0
RR NH CCO #RR NCO H
(1)
(2)
2
2
K2
0
0
0
K
0
C
RR NCO H CRR NH# ½RR NCO ꢀ½RR NH ꢀ
2
2
2
ðprecipitate in many solventsÞ
0
RZalkyl or aralkyl, R ZH, alkyl or aralkyl.
Since amine, carbamic acid, and ammonium carbamate are
rapidly equilibrated in the solution phase (Eqs. 1 and 2),
2. Results and discussion
2
,5,8
we assumed that in the dissolving solvents (DMSO and
DMF) all the free aralkylamine could finally be converted to
the carbamic acid by excess CO . We now report that the
The NMR measurements in situ after bubbling of CO2
through a solution of 3 in DMSO, DMF or Py revealed that
3-(1-naphthyl)propylcarbamic acid (6) was formed quanti-
tatively in complete conversion (e.g., see Fig. 1 for the
DMSO case; also see Fig. 2(a)–(c)). In dioxane, formation
of the predominant product 6 (see Fig. 2(d)) was
accompanied by precipitation of a small amount of
2
observed complete transformation of the amine into the
carbamic acid is not only due to the dissolving power of
the solvent, but also is a consequence of the solvent effect on
the acid–base equilibrium in Eq. 2. We investigated 1–3,
especially 3-(1-naphthyl)propylamine (3), because its
ammonium carbamate 9 has been found to have relatively
large solubility in various solvents, an advantageous
property for spectroscopic studies. The solvents employed
are (deuterated) DMSO, DMF, pyridine (Py), dioxane,
§
ammonium carbamate 9. The carboxy carbon of 6 appeared
at d 157–160 and the NH proton appeared as a broad triplet
at d 6.0–7.8 (d 6.9, 7.0, 7.8 and 6.0, respectively, in DMSO,
DMF, Py and dioxane). The a-methylene protons reso-
nanced as a quasi-quartet at d 3.1–3.6, considerably lower
than the corresponding signal of 3, which occurred as a
MeCN, benzene, CHCl , 2-propanol (2-PrOH), and MeOH.
3
‡
§
It is reported that the efficiency for carbamate formation in water is
controlled by both steric hindrance of the N-substituents and by electron
Like the dioxane solution of 3, 3-(9-anthryl)propylamine in THF solution
afforded, upon CO bubbling, its carbamic acid (solution phase) and a
2
little ammonium carbamate (precipitate and solution): Horiguchi, M.;
Ito, Y.; Masuda, K.; unpublished data.
9
densities on the nitrogen lone-pair. The details of these structural
effects, however, still remain to be elucidated.

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
215
1
13
6 2
Figure 1. The H and C NMR spectra of 3 in DMSO-d before and after CO bubbling.
K1
triplet at d 2.6–2.8 (Dd 0.40–0.81). The HMBC measure-
ments demonstrate that there is a cross peak between the
a-methylene proton and the carboxy carbon, unambigu-
ously proving the N–C bond formation between the amine
1575 cm in DMSO: this was more evident for the salts 7
and 8 dissolved in DMSO. Therefore, the carbamate salts
change to the original carbamic acids when dissolved in
DMSO or Py.
nitrogen and the CO carbon. In Figure 2(a)–(d), the HMBC
2
spectra in DMSO-d , DMF-d , Py-d and dioxane-d are
6
Although not precipitated from the solution, ammonium
carbamate 9 was formed also in CHCl or 2-PrOH, as was
demonstrated in situ by the NMR and IR analyses. Thus, six
7
5
8
displayed. The IR spectra for the solutions of 3 were
likewise measured after CO bubbling (Figs. 3 and 4). The
3
2
K1
1
methylene signals can be seen in the H NMR spectra,
spectra showed a strong band at 1700 cm
Fig. 4(a)) or Py (Fig. 3(b)) and at 1723 cm in dioxane
Fig. 4(b)). These bands can be assigned to the CO H group
of the carbamic acid 6. The IR measurement of the DMF
solution was useless because of the presence of the strong
absorption by DMF in this region.
in DMSO
K1
(
(
corresponding to a mixture of the carbamate anion and the
ammonium cation (Figs. 5 and 6). However, the reaction is
not quantitative. Considering the presence of a small
amount of the free amine which is undistinguishable from
the ammonium species, the yield of 9 was estimated as 82
and 98%, respectively. The carboxy carbon of the carbamate
2
2
Bubbling CO through a solution of 3 in MeCN or benzene
2
anion is slightly more deshielded (dw163) than that of 6
resulted in formation of 3-(1-naphthyl)propylammonium
3-(1-naphthyl)propylcarbamate (9) as a white precipitate. In
the filtrate, only a trace of the free amine was detectable (in
¶
d 157–160). As seen from the HMBC spectra in CDCl
(
and 2-PrOH-d (Fig. 2(e) and (f)), there is an expected cross
3
8
peak between the a-methylene proton and the carboxy
carbon. A strong support for the absence of the undisso-
ciated carboxy group is the IR spectrum. From inspection of
1
situ H NMR). The precipitate 9 was characterized by H
1
1
3
and C NMR (DMSO-d ), IR (KBr) and elemental
6
analysis. The NMR and elemental analyses revealed that a
half of the amine is N-carboxylated. The IR spectrum in a
KBr pellet (Fig. 3(e)) showed a broad band at about
Figure 3(d) (CHCl ) and Figure 4(c) (2-PrOH), the
3
K1
absorption around 1700 cm
is negligible. Instead, we
K1
K
1
575 cm , which is assignable to the NHCOO group of
the carbamate anion. It is to be noted that the IR spectrum of
dissolved in DMSO (Fig. 3 inset) or Py (Fig. 3(c)) showed
¶
The carbamyl carbon of butylammonium butylcarbamate is at d 162.6 in
10a
benzene-d
6
.
The NMR spectra of the carbamate anions of homo-
O containing
Their carbamyl carbons occurred further
downfield to d 163–165 (measured with reference to dioxane d 67.4).
9
veratrylamine, taurine, and various amino acids in D
K CO was measured.
2 3
2
K1
10b–d
a strong absorption at 1700 cm corresponding to the
carbamic acid 6. Almost no absorption is visible around

216
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
2
Figure 2. The HMBC spectra of 3 in a variety of solvents after CO bubbling.

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
217
exists in the CO -saturated MeOH solution of 3 is almost
2
doubtless a 3-(1-naphthyl)propylammonium bicarbonate or
carbonate. It is well established that the bicarbonate
formation is competitive with the carbamate formation in
5
,8
aqueous media, depending on pH. In the present paper, all
the experiments were done by using commercially available
solvents without special precaution for drying them.
Therefore, the bicarbonate could probably be formed by
reaction with the contaminant water. In the case of amine 1
which reacts with CO more rapidly than 2 or 3 (see Section
2
4), however, the corresponding ammonium carbamate 7 did
precipitate from the MeOH solution upon bubbling of CO ,
as expected from the previously published results.
2
1
f,1g
Scheme 1 summarizes the effect of solvent changes on the
reactions of 3 with CO . Virtually the same solvent
2
dependence was observed for the amines 1 and 2. As
described below, many of these results may be rationalized
by considering the acid–base reaction between amine and
the corresponding carbamic acid (Eq. 2) in nonaqueous
1
2–15
media.
and bases are affected by the Brønsted/Lewis acid–base
It is known that the pKa values of acids
properties of the solvent (e.g., empirical parameters a and b
or AN and DN), its dielectric constant (3 ), and its solvation
r
1
2–14
ability (Scheme 2).
pK values in Table 1, acetic acid AcOH is a stronger acid
As seen from consideration of the
1
2
a
C
than butylammonium ion BuNH3 in water or MeOH, that
is, dipolar amphiprotic solvent. In sharp contrast, the
opposite holds in DMSO, DMF or Py, that is, dipolar
aprotic solvent. If the solvent influence on the acidity of
s
carbamic acids is similar to that of carboxylic acids, this
contrasting difference suggests that the equilibrium reaction
6
C3%9 is in favor of carbamic acid 6 in DMSO, DMF or
Py, while it is in favor of ammonium carbamate 9 in MeOH.
As a result, since formation of the salt 9 is unfavorable in
dipolar aprotic solvents, most of the amine 3 may be
converted to 6 in the presence of CO , as was experimen-
2
*
*
tally found (Scheme 1).
Although MeCN is a dipolar aprotic solvent like DMSO,
DMF and Py, it is special in that (a) its hydrogen-bond
acceptor basicity (b) is relatively poor and (b) considerable
†
†
1
2,13,15
homoconjugation and heteroconjugation occur.
first point is reflected on the large pK values of AcOH and
The
a
BuNH measured in MeCN (Table 1). As for the second
2
point, since 9 precipitated from the MeCN solution (vide
supra), it is probable that the relevant anion and cation are
unusually stabilized in MeCN by the homo- and hetero-
conjugation and they eventually combine, leading to the
precipitation of 9. Although dioxane is not polar in terms of
Figure 2 (continued)
K1
can clearly observe a broad band around 1575 cm , being
similar to that of 9 in KBr (Fig. 3(e)). From these spectral
evidences, the carboxylated product is not the carbamic acid
the 3 scale (Table 1), it is classified as a dipolar aprotic
r
solvent due to its protophilicity. A common feature of
DMSO, DMF, Py, and dioxane is their high basicity and low
6
, but the carbamate anion.
†
†,12
In MeOH-d , the downfield shift of the a-methylene protons
4
by bubbling of CO was relatively small (Dd 0.29) and the
2
1
3
s
8b
The pK
a
for p-nitrophenylcarbamic acid is reported to be 4.2 in water,
C NMR signal in the carboxy region appeared at
61.5 ppm. However, their correlation peak could not be
observed in the HMBC spectrum (Fig. 2(g)). The IR
not very different from that of acetic acid (4.76) or benzoic acid (4.19).
1
**
As distinct from the small K
proposed here, the K value for another equilibrium 3CCO
2
value for the equilibrium 6C3%9 which is
%6 is
presumably large in protophilic dipolar aprotic solvents (DMSO, DMF
1
2
K1
spectrum showed strong bands at 1642 and 1310 cm
and Py), because 6 lasts pretty long in these solvents even under air
(
According to the Kolthoff’s review, DMSO, DMF and Py as well as
dioxane and THF are categorized as protophilic dipolar aprotic solvents,
while MeCN is a protophobic dipolar aprotic solvent.
(
NaHCO suspended in MeOH or for the bicarbonate salt of
DBU (Z1,8-diazabicyclo[5.4.0]undec-7-ene) in a KBr
pellet or MeOH solution. Accordingly, the species that
Fig. 4(d)). These bands were also observed for Na CO or
2 3
based on NMR in situ).
3
††
15
1
1

218
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
Figure 3. The IR spectra for (a) amine 3 in pyridine, (b) amine 3 in pyridine after CO
carbamate 9 dissolved in pyridine, (d) amine 3 in CHCl after CO bubbling, that is, ammonium carbamate 9 in CHCl
a KBr pellet (inset, solid ammonium carbamate 9 dissolved in DMSO). The backgrounds are pyridine for (a)–(c), CHCl
2
bubbling, that is, carbamic acid 6 in pyridine, (c) solid ammonium
, and (e) solid ammonium carbamate 9 in
for (d), and air for (e) and inset.
3
2
3
3
acidity (Table 1). Hence, it does not seem strange that 6 was
predominantly formed in dioxane. Also, it should be pointed
out that CO solubility in dioxane is relatively high (0.27 M,
2
of the ammonium carbamate was not visible in any solvent.
The absorption spectra under Ar were found to remain
unchanged by bubbling of CO . However, the intensity of
2
vide infra). The higher CO concentration renders the free
2
fluorescence is expected to be affected by CO , provided that
2
amine concentration lower and will shift the equilibrium of
Eq. 2 to the left side. In apolar solvents like benzene, the
ionic dissociation of acids is difficult but the salt formation
fluorescence quenching via intramolecular electron transfer
(IET) from the amino group to the naphthalene moiety is the
case. Table 1 (lines 7–9) shows the fluorescence intensity
1
2
with bases can nevertheless progress.
formation of 9 in benzene is also not surprising.
Therefore,
ratio between the CO -saturated solution and the Ar-
2
saturated solution I (CO )/I (Ar). Exciplex emission was
F
2
F
not observed in all cases. The fluorescence intensity for 1–3
in DMSO solutions saturated with CO was considerably
Methoxycarbonylation of amine 3 into the carbamic acid
methyl ester 10 was successfully accomplished by reaction
2
stronger than that saturated with Ar, that is, I (CO )/I (Ar)Z
F
2
F
with (trimethylsilyl)diazomethane in the presence of CO2
12.0 for 1, 9.4 for 2, and 3.6 for 3. The fluorescence intensity
for 1–3 in DMF solutions even more increased upon
saturation with CO : I (CO )/I (Ar)Z50.0, 15.3 and 8.2,
(
Eq. 3). TMSCHN is a well-known reagent for preparation
2
1
6
of methyl esters of carboxylic acids. The reaction was
virtually quantitative and complete in 20 min at room
temperature. Like the carbamic acid 6, the ester 10 showed
an HMBC cross peak between the a-methylene protons and
the carboxy carbon (Fig. 7). Solvent effects on this
esterification reaction as well as application of this
esterification method to other various amines are in progress.
2
F
2
F
respectively. A similar effect by CO was recently reported
7,18
2
for 1.
dioxane, MeCN, benzene, CHCl , 2-PrOH, and MeOH,
In contrast, the ratio was not altered very much in
3
except small to medium increases for 1 in dioxane, MeCN, 2-
PrOH and MeOH where I (CO )/I (Ar)Z1.3, 1.6, 1.9 and
F
2
F
2
.9, respectively (Table 1). Unfortunately, the fluorescence
spectra in Py could not be measured because the absorption
end of Py overshadowed the naphthyl group absorption.
The aforementioned remarkable increases in the fluor-
escence intensity upon saturation with CO (observed for 1–
2
(3)
3
MeOH) are completely unrelated with CO solubility: the
in DMSO and DMF and for 1 in MeCN, 2-PrOH and
2
concentration of CO is 0.13, 0.21, 0.15, 0.27, 0.32, 0.11,
2
0
benzene, CHCl , 1-PrOH and MeOH, respectively, at 25 8C
.14, 0.11 and 0.15 M in DMSO, DMF, Py, dioxane, MeCN,
3
1
9
and 1 atm. Instead, these increases may be ascribed to two
reactions: (a) the carbamic acid formation in DMSO, DMF,
MeCN, 2-PrOH and MeOH and (b) the bicarbonate/
carbonate formation in MeOH. This inference is reasonable,
because the lone pair on the nitrogen atom becomes hard to
use for the IET quenching when the amino group is
carboxylated or protonated. These situations are illustrated
Quenching of arene fluorescence by amine donors via
intramolecular electron transfer or exciplex formation is
well studied. Thus, we have measured the absorption and
1
7
emission spectra of naphthylalkylamines 1–3 in a variety of
solvents under Ar and CO2. Since the total amine
6
K5
concentrations are very low (w6!10 M), precipitation

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
219
2
Figure 4. The IR spectra of 3 in DMSO, dioxane, 2-PrOH, or MeOH before and after CO bubbling.
in Scheme 3. It is notable in Table 1 that the I (CO )/I (Ar)
F
comrared with the undissociated carboxyl group (COOH)
(s-metaZ0.37, s-paraZ0.45). Thereby, the IET quench-
ing by NHCOO may be much more efficient than by
NHCOOH, leading to the stronger fluorescence emission
from 4 than from 7.
2
F
values for 1 in DMSO (12) and DMF (50) are much larger
than those in MeCN, 2-PrOH and MeOH (1.6–2.9).
Probably, this difference partly originates in the fact that
carbamic acid 4 is formed in DMSO or DMF whereas
ammonium carbamate 7 is formed in MeCN, 2-PrOH or
MeOH (compare B(i) and B(iii) in Scheme 3). The electron
withdrawing property of the dissociated carboxyl
K
At this stage, it must be mentioned that, in those cases where
I (CO )/I (Ar)z1 as found for 2 and 3 in dioxane, MeCN,
F
2
F
K
group (COO ) (the Hammett substituent constants
s-metaZK0.1, s-paraZ0.0) should be much smaller as
benzene, CHCl , 2-PrOH and MeOH and for 1 in benzene
3
and CHCl (Table 1), the occurrence of the IET event is
3

220
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
1
13
3 2
Figure 5. The H and C NMR spectra of 3 in CDCl after CO bubbling.
‡
‡
probably negligible even under Ar. In order to fully
understand the fluorescence data in Table 1, quantitative
data about the K and K values (Eqs. 1 and 2) and about the
carbamic acids 4–6. In dioxane (protophilic, dipolar, aprotic
solvent), the carbamic acid and a minor amount of the
ammonium carbamate are formed. By contrast, in MeCN
(protophobic, dipolar, aprotic solvent), benzene or CHCl3
(apolar aprotic solvent), and 2-PrOH or MeOH (dipolar
amphiprotic solvent), the ammonium carbamates 7–9 are
formed rather than 4–6. It appears that these results can be
well understood by considering the solvent effect on the
acid–base reaction between amine (1–3) and carbamic acid
(4–6). For more complete understanding, however, further
information about K , K , the solubility of ammonium
1
2
IET quenching efficiencies in various solvents are required.
As a whole, however, the results of the present fluorescence
study are well in line with those obtained from the NMR and
IR studies, as schematically depicted in Scheme 3.
3. Conclusion
1
2
On the basis of the NMR and IR studies coupled with the
fluorescence study, we conclude that bubbling of CO2
through the solutions of naphthylalkylamines 1–3 in
protophilic, highly dipolar, aprotic solvent (DMSO, DMF
or pyridine) produces quantitatively the undissociated
carbamate, and the IET quenching efficiency will be
required. Carbamic acids are involved in various biological
phenomena, for example, the CO fixation by Rubisco or
2
2
0a,b
20c
biotin,
cycle,
the CO transport by hemoglobin,
2
and the neurotoxicity and chemical signaling.
the urea
2
0d
20e
Therefore, the question as to whether the carboxyl group in
the molecule is dissociated or undissociated will be
physiologically an important matter. Recent studies on
‡‡
On the basis of the Rehm–Weller equation, the estimated free energy for
electron transfer from propylamine to naphthalene singlet or exciplex
3
b,c
C
formation is 0.03 eV in MeCN, slightly endergonic (DGetZE(D /D)K
reversible organogels based on reversible uptake of CO2
K
E(A/A )KE0,0CDEcoulZ1.59K(K2.49)K3.99C(K0.06)Z
may as well take into account such a solvent effect.
Although the intermediacy of carbamic acid is not
demonstrated, dipolar aprotic solvents are solvent of choice
17a
0.03 eV). Therefore, the electron transfer will not be very efficient.
The IET efficiency depends not only on DGet but also on the solvent
polarity and the relative geometry (configuration and distance) between
2
1
17
in many CO -fixation reactions through amines. Aqueous
2
the donor (D) and the acceptor (A). As can be judged by the relative
(Ar) values (Table 1, lines 10–12), the quenching efficiency through
IET is higher for 1 as compared with 2 and 3, where I (Ar) is the
I
F
solutions of amino alcohols are often employed for
absorbing CO from industrial gases, usually as bicarbon-
F
2
fluorescence intensity of the Ar-saturated solution. This is expected,
since 1 is a D–A system connected by the shortest polymethylene chain
9,3a
ates rather than carbamates.
Therefore, the present paper
should be fundamental to these various aspects of mechan-
istic, biological and industrial interests.
(
more polar solvents but not in nonpolar solvents.
nZ1). For this kind of the system, IET is expected to occur in ethers and
17b

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
221
1
13
8 2
Figure 6. The H and C NMR spectra of 3 in 2-PrOH-d after CO bubbling.
Scheme 1.
4
. Experimental
2400PC spectrometers, respectively. Fluorescence spectra
were gathered with a SHIMADZU RF-5300PC spec-
trometer and excited at the absorption maximum (280–
4
.1. General
285 nm). Melting points were measured on a YANACO
MP-S3 microscopic hot-stage and are uncorrected.
1
13
H and C NMR spectra were measured on a JEOL EX-
2
2
70J, GSX-270, or AL-300 spectrometer. Measurements of
D NMR were carried out with JEOL JUM-A400. Mass, IR,
CO gas (99.99%) was purchased from Ekika Tansan Co.,
2
and absorption spectra were recorded on JEOL JMS-HX
10A, SHIMADZU FTIR-8400, and SHIMADZU UV-
Inc. All the solvents we employed (deuterated solvents,
spectroscopic grade solvents, and dehydrated or anhydrous
1

222
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
solvents. The amine concentrations are 0.13–0.15 M for
the NMR and IR measurements and 5.9–6.7!10 M for
K5
the absorption and fluorescence ones. The CO or Ar gas
2
was introduced into a solution of amine through a needle.
The bubbling was continued for 0.5–1 h at room tempera-
ture. After the bubbling, the tube or cell was tightly closed
and the spectra were measured.
The IR spectra were taken with the background of either air
or the respective solvent. In Figures 3 and 4, only the latter
spectra are shown, unless otherwise specified. The original
data of the fluorescence spectra are collected in
Figures 8–10.
12–14
Scheme 2. The acid–base equilibria in a solvent (SH)
.
solvents) are commercially available (from Aldrich, Sigma-
Aldrich, Wako, Dojin, or Nakarai Tesque) and were used as
received. The IR experiments were carried out by using
dehydrated or anhydrous solvents and the absorption and
fluorescence experiments by using spectroscopic grade
4.2. (1-Naphthyl)methylamine (1), 2-(1-naphthyl)-
ethylamine (2) and 3-(1-naphthyl)propylamine (3)
These are known compounds. Commercial amine 1 was
used. Amine 2 was prepared according to the literature
a
, basicity b and acidity a, solvent influence on the acidity constant K
b
for acetic acid and butylamine, and
Table 1. Values of solvent dielectric constant 3
r
a
c
solvent dependence of the fluorescence intensity ratio I
F
(CO )/I (Ar) and the relative fluorescence intensity I (Ar) for compounds 1–3
F
2
F
DMSO
DMF
Py
Dioxane
MeCN
Benzene
CHCl
3
2-PrOH
MeOH
2
H O
3
b
a
pK
pK
r
46.45
0.76
0.00
12.6
11.1
12.0
36.71
0.69
0.00
13.5
10.5
50.0
15.3
8.2
12.91
0.64
0.00
10.1
5.5
—
—
—
—
—
2.21
0.37
0.00
—
35.94
0.31
0.19
22.3
18.3
1.6
1.0
1.2
0.84
3.7
2.27
0.10
0.00
—
4.89
0.10
0.20
—
—
1.0
1.0
1.0
0.33
0.39
0.35
19.92
0.84
0.76
—
—
1.9
1.0
1.0
1.0
3.5
32.66
0.66
0.98
9.7
11.8
2.9
1.0
1.0
1.1
3.5
78.36
0.47
1.17
4.76
10.64
—
—
—
—
—
a
a
(AcOH)
(BuNH
2
)
—
1.3
—
ꢀ
d
e
I ðCO Þ
1
1.0
1.0
1.1
2.1
3.7
3.4
F
2
2
9
3
.4
.6
1.2
1.1
1.5
2.3
2.7
I ðArÞ
F
3
ꢀ
relative
1
0.24
0.041
0.20
0.45
2
0
1
.39
.00
IFðArÞ
3
f
—
2.9
3.2
3.5
—
a
A b scale is a measure of the solvent hydrogen-bond acceptor (HBA) basicity, while an a scale is a measure of the solvent hydrogen-bond donor (HBD)
14
1
4
acidity. The values for the related solvent scales, donor number (DN) and acceptor number (AN), respectively, can also be derived from the same source.
Ref. 12.
b
c
d
e
f
I
F
(Ar) and I
F 2 2
(CO ) are the fluorescence intensities for the Ar-saturated and the CO -saturated solutions, respectively.
O10 (Ref. 7).
1.5 (Ref. 18).
F
Relative I (Ar) for 3 in DMSOZ1.00 as the reference.
3
Figure 7. The HMBC spectrum for methyl 3-(1-naphthyl)propylcarbamate (10) in CDCl .

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
223
Scheme 3.
2
methods. The preparation method for amine 3 was
2
distilled pyridine (1: 3 v/v). Then, 1.71 g (0.0452 mol) of
NaBH was added by portions with stirring. After refluxing
modified as outlined in Scheme 4. The spectral data were
23b,24 25
3.
4
2
in accordance with those of the literatures: 11, 12,
3
for 2 h, the mixture was allowed to cool to room
temperature and then poured into 100 mL of 10% aqueous
HCl. The oily layer separated and it was taken up with
60 mL of ether. The ethereal layer was rotary-evaporated to
afford 4.54 g (0.0251 mol, 82% yield) of crude 3-(1-
4.2.1. Compound 2. Colorless oil, bp 136 8C (bath
temperature) at 0.6 mm Hg H NMR (270 MHz, DMSO-
1
d6) d 8.10 (1H, d, JZ7.9 Hz), 7.89 (1H, finely split d, JZ
1
7
.3 Hz), 7.75 (1H, d, JZ7.9 Hz), 7.56–7.33 (4H, m), 3.11
naphthyl)propionitrile (12) as a yellow oil. H NMR
(CDCl ) d 7.95–7.76 (3H, m), 7.57–7.33 (4H, m), 3.41
3
1
3
(
(
2H, t, JZ7.4 Hz), 2.84 (2H, t, JZ7.4 Hz); C NMR
67.8 MHz, DMSO-d ) d 136.39, 133.31, 131.48, 128.38,
(2H, t, JZ7.5 Hz), 2.73 (2H, t, JZ7.5 Hz).
6
1
3
26.32, 126.26, 125.70, 125.42, 125.36, 123.73, 43.28,
7.16; MS (EI) m/z 171 (M , 14), 142 (100), 141 (42), 115
C
A stirred solution containing 4.16 g (0.110 mol) of LiAlH
4
(
1
34); HRMS (EI) calcd for C H N 171.1048, found
1
71.1045.
in 50 mL of dry THF was cooled in an ice bath. To this
solution, a solution containing 4.54 g (0.0251 mol) of crude
2 13
12 in 20 mL of dry THF was added dropwise over a period
of 15 min. The stirring was continued at reflux for 2 h, then
at room temperature for 20 h. After quenching excess
LiAlH by careful addition of EtOH–water (1: 1 v/v), the
4
(
.2.2. Preparation of 3. A mixture of 1-naphthaldehyde
21.02 g, 0.136 mol), cyanoacetic acid (13.72 g, 0.161 mol)
and morpholine (14 mL, 0.161 mol) in 120 mL of DMF was
stirred at room temperature for 15 min. The stirring was
continued at reflux for 5 h. After being left overnight, the
reaction mixture was rotary-evaporated and the residue was
distilled at 135 8C (bath temperature)/0.5 mm Hg to afford
4
mixture was filtered and the residue was washed with ether.
The filtrate and the washings were combined and rotary-
evaporated to afford a yellow oil. This yellow oil was treated
with a mixture of 1 M aqueous HCl (100 mL) and EtOH
(30 mL) at 90 8C for 1 h and an insoluble part of the oil was
removed by extraction with ether (100 mL). The aqueous
layer was rotary-evaporated and the resultant solid was
washed with ether. 3-(1-Naphthyl)propylamine hydro-
chloride was obtained as a white solid: yield 1.38 g
(0.0062 mol, 25%).
1
0.80 g (0.0603 mol, 45% yield) of an E/Z mixture of 3-(1-
naphthyl)acrylonitrile (11) (E/Z ratioZ7:3 from NMR).
This mixture, which solidified on standing, was recrystal-
lized from MeOH to give 8.21 g (0.0458 mol, 34% yield) of
1
E)-11 as pale yellow needles: mp 72–75 8C. H NMR
270 MHz, CDCl ) d 8.24 (1H, d, JZ16.3 Hz), 8.07–7.85
3H, m), 7.69–7.47 (4H, m), 5.97 (1H, d, JZ16.4 Hz); MS
EI) m/z 179 (M , 100), 178 (73), 152 (30), 151 (26);
(
(
(
(
3
C
The above salt was dissolved in 150 mL of water and made
alkaline (pH 14) with 1 M aqueous NaOH. Extraction with
ether (40 mL!3), drying the ethereal layer with Na SO ,
HRMS (EI) calcd for C H N 179.0735, found 179.0734.
13 9
2
4
An E/Z mixture of 11 (5.47 g, 0.0305 mol) was dissolved in
6 mL of MeOH (predried with Molecular Sieves 3A)-
and rotary-evaporation, followed by distillation at 133 8C
(bath temperature)/0.5 mm Hg, afforded 0.404 g
5

224
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
Figure 8. The fluorescence spectra for the CO
2
-saturated and the Ar-saturated solutions of 3-(1-naphthyl)propylamine (3).

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
225
Figure 9. The fluorescence spectra for the CO
2
-saturated and the Ar-saturated solutions of 2-(1-naphthyl)ethylamine (2).

226
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
Figure 10. The fluorescence spectra for the CO
2
-saturated and the Ar-saturated solutions of (1-naphthyl)methylamine (1).

K. Masuda et al. / Tetrahedron 61 (2005) 213–229
227
4 4
Scheme 4. Reagents and conditions: (i) DMF, cyanoacetic acid, morpholine, reflux; (ii) MeOH, NaBH , pyridine; (iii) THF, LiAlH .
(0.0022 mol, 36%) of 3-(1-naphthyl)propylamine (3) as a
colorless oil. H NMR (270 MHz, DMSO-d ) d 8.08 (1H, d,
JZ7.9 Hz), 7.89 (1H, d, JZ7.3 Hz), 7.74 (1H, d, JZ
DMSO-d ) d 157.30, 137.92, 133.41, 131.28, 128.48,
6
1
126.28, 125.79, 125.50, 125.43, 123.60, 40.10, 30.77,
29.50; IR (DMSO) 3600–3200 (br, s), 1700 (s), 1545 (br,
6
K1
7
.9 Hz), 7.32–7.56 (m, 4H), 3.05 (2H, t, JZ7.8 Hz), 2.62
m), 1250 (br, s) cm
.
1
3
(2H, t, JZ6.8 Hz), 1.72 (2H, m); C NMR (67.8 MHz,
DMSO-d ) d 138.55, 133.44, 131.38, 128.52, 126.18,
6
4.4. Isolation of u-(1-naphthyl)alkylammonium
u-(1-naphthyl)alkylcarbamates 7–9
1
2
1
1
25.95, 125.79, 125.55, 125.45, 123.81, 41.53, 34.70,
9.71; MS (EI) m/z 185 (M , 40), 168 (100), 153 (87),
C
42 (54), 141 (54), 115 (41); HRMS (EI) calcd for C H N
85.1204, found 185.1204.
13 15
Pure ammonium carbamates 7, 8, and 9 precipitated as a
white solid upon bubbling of CO through the solutions of 1
2
(
in CHCl , MeCN, benzene, or 2-PrOH), 2 (in CHCl ,
3 3
Viscous oils of amines 1–3 reacted with CO in the air,
2
MeCN, or benzene), and 3 (in MeCN or benzene),
respectively. These were collected by filtration and were
dried in vacuo at room temperature.
changing into a white solid of the corresponding ammonium
carbamate, 7–9, respectively. The solidification was rapid
for 1 and was relatively slow for 2 and 3, indicating that 1
reacts with CO more efficiently.
2
1
.4.1. Compound 7. Mp 72.5–76 8C. H NMR (270 MHz,
4
DMSO-d ) d 8.11 (2H, br), 7.92 (2H, m), 7.79 (2H, d, JZ
6
4.3. Selected spectral data for u-(1-
naphthyl)alkylcarbamic acids 4–6
7.6 Hz), 7.57–7.43 (8H, m), 7.32 (1H, br t, JZ5.8 Hz,
carbamic NH), 4.61 (2H, d, JZ5.8 Hz, carbamic a-CH ),
2
1
.21 (2H, s, free amine a-CH2); C NMR (67.7 MHz,
3
4
DMSO-d ) d 157.60, 138.61, 135.50, 133.09, 130.73,
These carbamic acids were quantitatively generated by
bubbling of CO through the solutions of amines 1–3 in
6
2
1
1
4
28.29, 127.07, 126.74, 125.91, 125.78, 125.53, 125.45,
25.38, 125.26, 124.64, 124.27, 123.39, 123.33, 42.64,
1.83; IR (KBr) 3314 (m), 3100–2000 (br s), 1611 (s,
DMSO, DMF, or pyridine at room temperature for 0.5–1 h.
Without delay after the CO bubbling, their NMR, IR,
2
absorption, and fluorescence spectra were directly
measured. Evaporation of the solvent resulted in reversion
to the original amine. Selected spectral data for 4–6 are as
follows.
C
K
RNH ), 1577 (m, NCOO ), 1540 (m), 1499 (vs), 1465 (m),
3
K1
375 (br m), 1350 (s), 1286 (vs) cm . Anal. Calcd for
1
C H N O : C, 77.07; H, 6.19; N, 7.82%. Found: C, 77.22;
H, 6.26; N, 7.76%.
2
3 22 2 2
1
.3.1. (1-Naphthyl)methylcarbamic acid (4). H NMR
4
(
(
1
.4.2. Compound 8. Mp 74–77.5 8C. H NMR (270 MHz,
4
400 MHz, DMSO-d ) d 8.11 (1H, dd, JZ7.1, 2.0 Hz), 7.93
6
1H, dd, JZ10.4, 2.4 Hz), 7.82 (1H, d, JZ7.9 Hz), 7.58–
DMSO-d ) d 8.14 (2H, br), 7.90 (2H, m), 7.76 (2H, d, JZ
6
7
3
.8 Hz), 7.56–7.34 (8H, m), 6.82 (1H, br, carbamic NH),
.23–3.13 (6H, m), 2.88 (2H, br, free amine a-CH2);
7
6
1
1
.33 (4H, m), 7.35 (1H, t, JZ6.0 Hz), 4.61 (2H, d, JZ
1
3
13
.0 Hz); C NMR (100 MHz, DMSO-d ) d 157.18, 135.37,
C
) d 158.07, 135.80, 133.26,
31.41, 128.37, 126.43, 126.36, 125.78, 125.42, 125.39,
6
33.28, 130.78, 128.49, 127.33, 126.12, 125.72, 125.43,
24.84, 123.43, 41.77; IR (DMSO) 3500–3100 (br, s), 1700
NMR (67.8 MHz, DMSO-d
6
1
1
3
1
K1
23.62, 42.59, 41.61, 35.95, 33.41; IR (KBr) 3284 (m),
100–2000 (br s), 1642 (m), 1577 (s, NCOO ), 1469 (s),
(
s), 1545 (m), 1245 (br, s) cm
.
K
K1
433 (m), 1395 (m), 1353 (m), 1334 (s) cm . Anal. Calcd
1
.3.2. 2-(1-Naphthyl)ethylcarbamic acid (5). H NMR
4
for C H N O : C, 77.69; H, 6.78; N, 7.25%. Found: C,
25 26 2 2
(
400 MHz, DMSO-d ) d 8.15 (1H, d, JZ8.4 Hz), 7.90 (1H,
6
77.73; H, 6.76; N, 7.20%.
dd, JZ8.6, 1.5 Hz), 7.77 (1H, d, JZ8.1 Hz), 7.57–7.48 (2H,
m), 7.44–7.34 (2H, m), 6.85 (1H, br t, JZ6 Hz), 3.30–3.23
1
3
1
4.4.3. Compound 9. Mp 65–69 8C. H NMR (270 MHz,
(
2H, m), 3.21–3.14 (2H, m); C NMR (100 MHz, DMSO-
d6) d 157.11, 135.50, 133.42, 131.58, 128.52, 126.67,
26.52, 125.97, 125.55, 125.53, 123.62, 41.31, 33.09; IR
DMSO) 3500–3100 (br, s), 1702 (s), 1544 (m), 1246 (br,
DMSO-d ) d 8.10 (2H, br), 7.91 (2H, m), 7.76 (2H, d, JZ
6
1
(
7.7 Hz), 7.57–7.35 (8H, m), 6.83 (1H, br, carbamic NH),
3.05 (6H, br), 2.66 (2H, br t, JZ6.7 Hz, free amine a-CH ),
2
K1
13
1.78 (4H, br); C NMR (67.7 MHz, DMSO-d ) d 157.50,
m) cm
.
6
1
38.07, 137.78, 133.18, 131.08, 128.29, 126.03, 125.59,
1
.3.3. 3-(1-Naphthyl)propylcarbamic acid (6). H NMR
4
(
125.32, 125.24, 123.53, 40.99, 33.71, 30.81, 29.49; IR
(KBr) 3344 (w), 3100–2000 (br), 1642 (m), 1570 (s br,
NCOO ), 1448 (s br), 1387 (m), 1318 (s) cm . Anal.
Calcd for (9)1.0(H O)0.3: C, 77.22; H, 7.34; N, 6.67%.
2
Found: C, 77.31; H, 7.34; N, 6.67%.
400 MHz, DMSO-d ) d 8.06 (1H, d, JZ8.1 Hz), 7.89 (1H,
6
K
K1
dd, JZ7.7, 1.6 Hz), 7.75 (1H, d, JZ8.1 Hz), 7.55–7.47 (2H,
m), 7.42–7.35 (2H, m), 6.81 (1H, br t, JZ6 Hz), 3.08–3.00
1
3
(
4H, m), 1.79 (2H, quin, JZ7.3 Hz); C NMR (100 MHz,

228
K. Masuda et al. / Tetrahedron 61 (2005) 213–229
4
.4.4. Isolation of methyl 3-(1-naphthyl)propylcarba-
mate (10). Through a 5 mL methanolic benzene solution
benzene–MeOH 4:1 v/v) containing 73 mg (0.393 mmol)
complicated owing to, for instance, their pH dependency and
the hydrolysis equilibrium of CO . See, for example,
2
(
(a) Caplow, M. J. Am. Chem. Soc. 1968, 90, 6795–6803.
(b) Johnson, S. L.; Morrison, D. L. J. Am. Chem. Soc. 1972, 94,
1323–1334. (c) Ewing, S. P.; Lockshon, D.; Jencks, W. P.
J. Am. Chem. Soc. 1980, 102, 3072–3084. (d) Crooks, J. E.;
Donnellan, J. P. J. Chem. Soc., Perkin Trans. 2 1989, 331–333.
9. (a) Yoon, S. J.; Lee, H. Chem. Lett. 2003, 32, 344–345.
(b) Suda, T.; Zhang, Y.; Iwaki, T.; Nomura, M. Chem. Lett.
1998, 189–190. (c) Chakraborty, A. K.; Bischoff, K. B.;
Astarita, G.; Damewood, J. R. Jr. J. Am. Chem. Soc. 1988, 110,
6947–6954. (d) Sartori, G.; Savage, D. W. Ind. Eng. Chem.
Fundam. 1983, 22, 239–249.
of amine 3 was bubbled CO gas for 15 min. Into this
2
solution was added 0.5 mL (1.0 mmol) of (trimethylsilyl)-
diazomethane (Aldrich 2.0 M solution in hexanes) at room
temperature with both stirring and CO2 bubbling. The
yellow color of TMSCHN disappeared in 20 min. The
2
mixture was stirred for additional 2 h under CO bubbling.
2
Then, it was rotary-evaporated to afford 93 mg of a colorless
viscous oil, which was almost pure methyl 3-(1-naphthyl)-
propylcarbamate (10) containing only a trace of 3 from the
NMR analysis. Further purification was carried out by
preparative TLC on silica gel (CHCl –MeOH 20:1 v/v) to
3
10. (a) Nomura, R.; Hasegawa, Y.; Ishimoto, M.; Toyosaki, T.;
Matsuda, H. J. Org. Chem. 1992, 57, 7339–7342.
(b) Kumamoto, Y.; Ito, Y., Unpublished data (c) Sherry,
A. D.; Malloy, C. R.; Jeffrey, M. H.; Chavez, F.; Srere, H. K.
J. Magn. Reson. 1990, 89, 391–398. (d) Armarego, W. L. F.;
Milloy, B. A. J. Chem. Soc., Perkin Trans. 1 1974, 1905–1907.
11. Hori, Y.; Nagano, Y.; Fukuhara, T.; Teramoto, S.; Taniguchi,
H. Nippon Kagaku Kaishi 1987, 1408–1413.
1
give 93 mg (97% yield) of 10 as a colorless viscous oil: H
NMR (400 MHz, CDCl ) d 8.00 (1H, d, JZ8.2 Hz), 7.85
3
(
(
(
(
(
1H, dd, JZ8, 1.7 Hz), 7.71 (1H, d, JZ8.1 Hz), 7.53–7.44
2H, m), 7.38 (1H, t, JZ7.6 Hz), 7.31 (1H, d, JZ7 Hz), 4.74
1H, br s), 3.67 (3H, s), 3.28 (2H, quar, JZ6.5 Hz), 3.10
1
3
2H, t, JZ7.6 Hz), 1.96 (2H, quin, JZ7.6 Hz); C NMR
100 MHz, CDCl ) d 157.13, 137.44, 133.91, 131.72,
3
1
5
1
28.84, 126.83, 125.97, 125.88, 125.53, 125.52, 123.58,
2.06, 40.95, 30.88, 30.11; IR (neat) 3336 (m), 1705 (br, s),
538 (br, s), 1258 (s), 778 (s) cm ; MS (FAB ) m/z 244
12. (a) Izutsu, K. Acid–Base Dissociation Constants in Dipolar
Aprotic Solvents (IUPAC Chemical Data Series; No. 35);
Blackwell: Boston, 1990. (b) Izutsu, K. Electrochemistry in
Nonaqueous Solutions; Wiley: Weinheim, 2002; Chapter 3.
13. Zielinska, J.; Makowski, M.; Maj, K.; Liwo, A.; Chmurzynski,
L. Anal. Chim. Acta 1999, 401, 317–321.
K1
C
C
C
(
MH , 100), 243 (M , 58), 212 (13), 168 (21); HRMS
C
FAB ) calcd for C H NO 243.1259, found 243.1259.
(
1
5
17
2
1
4. (a) Reichardt, C. Solvents and Solvent Effects in Organic
Chemistry; Wiley: Weinheim, 2003. (b) Isaacs, N. S. Physical
Organic Chemistry, 2nd ed.; Longman Scientific and Techni-
cal: Essex, 1995; Chapter 5.
References and notes
1
5. Kolthoff, I. M. Anal. Chem. 1974, 46, 1992–2003.
1
. (a) Fichter, F.; Becker, B. Chem. Ber. 1911, 44, 3473–3480;
see also pp 3481–3485. (b) Werner, E. A. J. Chem. Soc. 1920,
16. Hashimoto, N.; Aoyama, T.; Shioiri, T. Chem. Pharm. Bull.
1981, 29, 1475–1478.
1
17, 1046–1053. (c) Hayashi, T. Bull. Inst. Phys. Chem. Res.
17. (a) Schneider, S.; Rehaber, H.; Sch u¨ ßlbauer, W.; Lewis, F. D.;
Yoon, B. A. J. Photochem. Photobiol. A: Chem. 1996, 99,
103–114. (b) Lewis, F. D.; Cohen, B. E. J. Phys. Chem. 1994,
98, 10591–10597. (c) Mataga, N.; Miyasaka, H. Adv. Chem.
Phys. 1999, 107, 431–496.
(
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