Strongly basic macrocyclic triamines, 1,5,9-triazacyclododecanes for solvent extraction of gold(I) cyanide

Article abstract of DOI:10.1016/S0040-4039(02)02322-5

Solvent extraction of gold(I) dicyanide anion from alkaline gold(I) cyanide solution using unusually basic amine extractants was conducted. 1,5,9-Triazacyclododecane (4) is known as an unusually basic macrocyclic amine having pK_a=12.3-12.7, and is thus a good candidate as a basic amine extractant. Three lipophilic derivatives of 4 expected to stay in the organic phase during gold solvent extraction were synthesized. N-Dodecyl-1,5,9-triazacyclododecane (3) was prepared from 1,5,9-triazacyclododecane-2,4-dione (1) by N-alkylation with n-dodecyl iodide and then reduction with BH₃-THF. N,N′-Didodecyl-1,5,9-triazacyclododecane (5) and N,N′,N′′-tridodecyl-1,5,9-triazacyclododecane (6) were efficiently synthesized by selective di-alkylation of 4 with n-dodecyl iodide, and by reductive alkylation of 4 with n-dodecanal, respectively. The extractants 3 and 6 showed pH₅₀=10.5, which is the minimum value required for practical application.

Full text of DOI:10.1016/S0040-4039(02)02322-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9385–9389
Strongly basic macrocyclic triamines, 1,5,9-triazacyclododecanes
for solvent extraction of gold(I) cyanide
a,
a
a
a
a
Heung-Jin Choi, * Yoon-Kyung Bae, Seok-Chan Kang, Yeon Sil Park, Joon Won Park,
a
b
Woong-Il Kim and Thomas W. Bell
a
Department of Industrial Chemistry, Kyungpook National University, Taegu 702-701, South Korea
b
Department of Chemistry, University of Nevada, Reno, NV, 89557, USA
Received 13 September 2002; accepted 11 October 2002
Abstract—Solvent extraction of gold(I) dicyanide anion from alkaline gold(I) cyanide solution using unusually basic amine
extractants was conducted. 1,5,9-Triazacyclododecane (4) is known as an unusually basic macrocyclic amine having pK =12.3–
a
1
2.7, and is thus a good candidate as a basic amine extractant. Three lipophilic derivatives of 4 expected to stay in the organic
phase during gold solvent extraction were synthesized. N-Dodecyl-1,5,9-triazacyclododecane (3) was prepared from 1,5,9-triazacy-
clododecane-2,4-dione (1) by N-alkylation with n-dodecyl iodide and then reduction with BH -THF. N,N%-Didodecyl-1,5,9-triaza-
3
cyclododecane (5) and N,N%,N%%-tridodecyl-1,5,9-triazacyclododecane (6) were efficiently synthesized by selective di-alkylation of 4
with n-dodecyl iodide, and by reductive alkylation of 4 with n-dodecanal, respectively. The extractants 3 and 6 showed
pH =10.5, which is the minimum value required for practical application. © 2002 Elsevier Science Ltd. All rights reserved.
50
Amines are an important class of extractants in solvent
metal extraction technology, and have been used indus-
trially for the recovery of uranium and copper.
The basicity of the lipophilic amine is a critical factor
for application in gold extraction and stripping pro-
1,2
−
cesses. Practical amine extractants for Au(CN)
have
2
not been reported with sufficiently high basicity
required in hydrocarbon extraction media.
Development of extractants for gold dicyanide anion,
−
3
Au(CN)2 is an active area of research. Of particular
significance are the extraction of gold from dilute,
alkaline cyanide solutions and the possible use of sol-
vent extraction for gold recovery in cyanidation pro-
1,5,9-Triazacyclododecane (4) is known to be an unusu-
ally basic azacrown compound which has pK =12.3–
a3
5,6
1
2.7, pK =7.3–8.0 and pK =2.4–3.3. The strong
a2 a1
3
basicity is attributable stabilization of a proton in the
monocation by hydrogen bonding with nitrogen atoms
in the fashion of a macrocyclic complex. To keep the
protonated amine in the organic phase, lipophilic dode-
cyl groups are attached to nitrogen atoms of 4. Synthe-
ses of the alkylated amines are shown in Scheme 1.
cesses. Solvent extraction and enriching processes are
performed in two stages: extraction of gold from dilute,
alkaline cyanide leach solutions into a hydrocarbon
medium containing a lipophilic extractant, and then
stripping the gold into a more basic solution, from
which the pure metal can be obtained by electro-
winning.
7
Many synthetic methods for azacrowns are known.
Representative methods for preparation of 4 are Weis-
man synthesis via a tricyclic orthoamide intermediate,
the Parker approach involving condensation of a mal-
onate ester and bis(3-aminopropyl)amine, and Rich-
man-Atkins cyclization of a bis-p-toluenesulfonamide
The pH of a typical alkaline gold cyanide leach solution
4
is about 10.5. Since the pK of HCN is 9.21, below pH
a
1
0 toxic HCN is evolved. Thus, the lipophilic amine
extractant must be protonated in the hydrocarbon
extraction medium at pH]10.5 to form an ion-pair
8
salt with a bis-tosylate. For efficient and selective
−
with Au(CN) , which is extracted to the organic phase.
2
mono-alkylation on one of three identical nitrogens of
1
, the Parker synthesis is most practical. Condensation
of bis(3-aminopropyl)amine with diethyl malonate in
the presence of a catalytic amount of sodium methoxide
in ethanol increased the yield of 1 to 22%, compared to
14% without sodium methoxide, as reported by Parker
Keywords: 1,5,9-triazacyclododecane; amine extractant; solvent
extraction; gold cyanide; gold leach solution; pH .
5
0
*
Corresponding author. Tel.: +82-53-950-5582; fax: +82-53-950-6594;
8a
e-mail: choihj@knu.ac.kr
et al.
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02322-5

9
386
H.-J. Choi et al. / Tetrahedron Letters 43 (2002) 9385–9389
phase ratio, keeping a 1:1 organic to aqueous volume
14
ratio.
The pH50 value is the pH at which 50% of the desired
metal has been extracted from the aqueous solution by
a particular amine. A higher value of pH50 is indicative
of an increase in base strengh of the amine. A pH50
value greater than or equal to 10.5 is desired for
3
practical application in gold cyanide extraction. The
percentage of gold extracted as a function of pH is
shown in Fig. 1 for azacrown extractants, 3, 5, and 6 as
well as for n-dodecylamine, di-n-dodecylamine, and
tri-n-dodecylamine.
Primary, secondary and tertiary aliphatic amines have
−
been examined for the extraction of Au(CN)2 from
alkaline gold cyanide solution. The pH50 value of these
3
amines were reported to be below 8. It is generally
Scheme 1. Reagents and conditions: (a) MeONa, EtOH,
reflux, 7 d, 22%; (b) n-dodecyl iodide, DMA, rt, overnight,
known that the basicities of alkylamines in polar sol-
vents increase in the order: secondary>primary>tertiary
amine, due to opposing inductive and solvation
6
0%; (c) BH ·THF, reflux, 24 h, 95%; (d) BH ·THF, reflux, 24
3
3
15
h, 99%; (e) n-dodecyl iodide, NaHCO3, DMA, 80°C,
overnight, 88%; (f) n-dodecanal, NaCNBH , H O/CH CN,
effects. The pH50 values for gold extraction with
amines increased as the amine concentration was
increased, but varying the gold concentration or
organic solvent type did not significantly change the
3
2
3
pH=4–5, rt, overnight, 90%.
3a
pH50 value. The pH50 values for 50 mM solutions of
commercial lipophilic primary, secondary and tertiary
amines in xylene were reported as 6.6, 7.2 and 5.7,
Acyclic by-products initially formed by intermolecular
oligomerization may be in equilibrium with the starting
materials in the presence of sodium methoxide in hot
ethanol. Heating the reaction mixture under reflux for a
prolonged period (7 days) gave 1 in 22% yield after
3b
respectively, which is parallel to the order of amine
basicity.
9
column chromatography. Alkylation of 1 with n-dode-
cyl iodide in DMA gave 2 in 60% yield after crystalliza-
1
0
tion from MeOH–CH Cl . Reduction of 2 with
2
2
11
BH ·THF gave 3 in 95% yield. Azacrown 4, prepared
3
8
a
by reduction of 1 using BH ·THF was treated with
3
excess n-dodecyl iodide in DMA in the presence of
NaHCO to give N,N%-didodecyl azacrown 5 in 80%
3
yield as the trihydrochloride salt after treatment with
12
HCl gas in THF. This selective alkylation of two of
the three equivalent nitrogens of 4 can be attributed to
the characteristic of its strong basicity. Under the reac-
tion conditions, product 5 is monoprotonated, appar-
ently reducing the nucleophilicity of the remaining
secondary amine nitrogen. Reductive amination of 4
13
with n-dodecanal gave 6 in 90% yield. The NMR
spectra of 3 and 6·3HCl demonstrated the expected
1
13
molecular symmetry. However, H and C NMR spec-
tra of 5·3HCl in DMSO-d6 did not show the C2v
symmetry expected from its structure even at 130°C,
suggesting the presence of cis and trans stereoisomeric
salts.
−
The equilibrium distributions of Au(CN)2 were deter-
mined after mixing the organic extractant phase con-
sisting of a toluene solution of the lipophilc amine with
the alkaline cyanide aqueous phase (pH 3–13). The pH
of the aqueous phase was adjusted, and continuously
monitored by means a glass pH electrode. After equi-
librium of the phases was established, samples of the
aqueous solution were taken. An equal amount of the
organic phase was also removed to maintain a fixed
−
Figure 1. Percent extraction of Au(CN)2 from alkaline gold
cyanide solution as a function of pH for amine extractants in
toluene. Aqueous phase: 0.05 mM KAu(CN)2 in 125 ppm
cyanide solution (10 ppm Au); Organic phase: 5 mM amine
extractant in toluene.

H.-J. Choi et al. / Tetrahedron Letters 43 (2002) 9385–9389
9387
Table 1. The pH50 values of amine extractants for gold solvent extraction under the given extraction conditions
Extraction conditiona
Amine extractants
Dib
Tric
6
3
5
1
5
5
5
mM amine/10 ppm Au
mM amine/10 ppm Au
mM amine/100 ppm Au
0 mM amine/100 ppm Au
–
–
9.6
10.5
9.8
10.5
\13
\13
5.2
5.8
6.9
4.0
4.2
5.4
a
b
c
The extraction was conducted in two phases; toluene containing amine/alkaline gold cyanide solution at rt.
Di-n-dodecylamine.
Tri-n-dodecylamine.
In the current study, the pH50 values of solutions of 5
mM di-n-dodecylamine and tri-n-dodecylamine in tolu-
ene were measured as 5.2 and 4.0, respectively, as
shown in Table 1. Increasing gold concentration by a
factor of ten did not affect the pH50 amine basicity, but
ten-fold increase of amine concentration enhanced the
pH50 values over one pH unit. Under these extraction−
conditions, n-dodecylamine did not extract Au(CN)2
anion from gold cyanide solution. It is apparent that
n-dodecylamine stays in the acidic aqueous phase at the
expected pH50 value. The extraction of gold with simple
alkylamine extractants is limited to acidic solutions.
Thus, polar modifiers such as tributyl phosphate or
dibutyl butyl phosphonate have been added to the
organic phase enhance the pH50 values up to 4 pH
In conclusion, the unusually basic lipophilic amine
extractants, 3, 5 and 6, based on 1,5,9-triazacyclodode-
cane (4) were synthesized and examined for solvent
extraction of gold from alkaline gold cyanide solution.
The pH50 values for 3 and 6 were measured to be 10.5.
These amines are the first efficient amine extractants
that can be used for solvent extraction of gold without
modifiers. We plan to further examine the applicability
of polyamines in this new structural class for extraction
of gold from alkaline gold cyanide leach solutions.
Acknowledgements
3
uints.
This work was supported by Korea Research Founda-
tion Grant (KRF-2001-015-200110211). We also thank
Dr. Maurice C. Fuerstenau, professor of Metallurgy,
University of Nevada, Reno, for helpful information
and advice concerning this project.
However, under the same extraction conditions, the
amine extractants 3 and 6 based on the highly basic
1,5,9-triazacyclododecane skeleton markedly shifted the
position of the percent extraction/pH curves to pH50
values of 10.5. Dialkylated analog 5 completely
extracted gold over the entire pH range tested, pH 5 to
References
13, and did not show the usual sigmoid extraction/pH
curve. Dilution of the amine concentration to 1 mM in
toluene slightly reduced the pH50 values to 9.6 and 9.8
for 3 and 6, respectively. However, 1 mM solutions of
any of the alkyamines were not able to extract gold
from 10 ppm gold cyanide solution. The results are
presented in Table 1.
1. (a) Coleman, C. F.; Brown, K. B.; Moore, J. G.; Crouse,
D. J. Ind. Eng. Chem. 1958, 50, 1756; (b) Moore, F. L.
Anal. Chem. 1960, 32, 1075; (c) Itzkovitch, I. J.; Rickel-
ton, W. A. Can. CA 157278, 1983; Chem. Abstr. 1984,
100, 160090.
2. (a) Virnig, M. J.; Mackenzie, J. M. US Patent 466166;
Chem. Abstr. 1997, 126, 110207; (b) Power, K. L. Solvent
Extr., Proc. Int. Solvent Extr. Conf. 1971, 2, 1409; Chem.
Abstr. 1975, 83, 182483.
3. (a) Miller, J. D.; Mooiman, M. B. Sep. Sci. Technol.
1984, 19, 895; (b) Mooiman, M. B.; Miller, J. D. Miner.
Metall. Process 1984, 1, 153; (c) Mooiman, M. B.; Miller,
J. D. Hydrometallurgy 1986, 16, 245; (d) Miller, J. D.;
Wan, R. Y.; Mooiman, M. B.; Sibrell, P. L. Sep. Sci.
Technol. 1987, 22, 487; (e) Riveros, P. A. Hydrometal-
lurgy 1990, 24, 135; (f) Kordosky, G. A.; Sierakoski, J.
M.; Virnig, M. J.; Mattison, P. L. Hydrometallurgy 1992,
30, 291; (g) Sastre, A. M.; Madi, A.; Alguacil, F. J.
Hydrometallurgy 2000, 54, 171.
It is not clear why dialkyl derivative 5 behaves as a
more basic amine under these extraction conditions
than the monoalkyl (3) and trialkyl (6) analogs. The
major factors affecting alkylamine basicity are the
1
5
inductive and solvation effects. If these effects deter-
mine the basicities of its derivatives, 3 bearing two
secondary amines and one tertiary amine should be
most basic than 5 and 6, which have one secondary
amine and none of secondary amine, respectively. How-
ever, for azacrown 4 and its derivatives, basicity is
influenced by specific hydrogen bonding interactions
between the nitrogens and the proton held in the cavity
of the macro ring. Extractant 5 may be too basic to be
applicable for gold solvent extraction because the strip-
ping process using basic hydroxide might be not
efficient. However, compounds 3 and 6 are novel
extractants, from which gold can be stripped at high
pH.
4. Perrin, D. D. Ionisation Constants of Inorganic Acids and
Bases in Aqueous Solution; 2nd Edn; Pergamon Press:
Oxford, 1982.
5. (a) Bell, T. W.; Choi, H.-J.; Harte, W. J. Am. Chem. Soc.
1986, 108, 7427; (b) Choi, H.-J. Ph.D. Dissertation, State
University of New York, Stony Brook, 1989.

9
388
H.-J. Choi et al. / Tetrahedron Letters 43 (2002) 9385–9389
6. (a) Reido, T. J.; Kaden, T. A. Chimia 1977, 31, 220; (b) oily product 3 (265 mg, 95%). The product was dissolved
Zompa, L. J. Inorg. Chem. 1978, 17, 2531; (c) Briellmann,
M.; Kaderli, S.; Meyer, C. J.; Zuberbuhler, A. D. Helv.
Chim. Acta 1987, 70, 680; (d) Geraldes, C. F. G. C.;
Sherry, A. D.; Marques, M. P. M.; Alpoim, M. C.;
Cortes, S. J. Chem. Soc., Perkin Trans. 1 1991, 137.
in THF (15 mL), and bubbled with HCl gas. The precip-
itate was collected by decanting off THF, washed with
hexane, and dried under high vacuum to afford 3·3HCl
1
salt (336 mg, 92%) as slightly yellow solid: For 3,
H
NMR (400 MHz, CDCl ) l 3.40 (br t, J=5.5 Hz, 2 H),
3
7
8
. Parker, D. In Macrocycle Synthesis
Approach; Parker, D., Ed.; Oxford University Press:
Oxford, 1996; pp. 1–23.
. (a) Helps, I. M.; Parker, D.; Jankowski, K. J.; Chapman,
J.; Nicholson, P. E. J. Chem. Soc., Perkin Trans. 1 1989,
A
Practical
2.95 (t, J=5.3 Hz, 4 H), 2.83 (t, J=5.3 Hz, 4 H), 2.59 (t,
J=5.7 Hz, 4 H), 2.44 (t, J=7.7 Hz, 2 H), 1.95 (quin.,
J=5.3 Hz, 2 H), 1.82 (quin., J=5.5 Hz, 4 H), 1.43 (quin.,
J=7.7 Hz, 2 H), 1.27 (m, 18 H), 0.88 (t, J=6.7 Hz, 3 H);
13
C NMR (100 MHz, CDCl ) l 52.5, 51.0, 49.8, 47.4,
3
2
079; (b) Hoye, R. C.; Richman, J. E.; Dantas, G. A.;
Lightbourne, M. F.; Shinneman, L. S. J. Org. Chem.
001, 66, 2722; (c) Richman, J. E.; Atkins, T. J. J. Am.
32.1, 29.88, 29.83, 29.80, 29.51, 27.8, 26.7, 24.6, 24.3,
24.0, 22.9, 14.3; MS (EI, relative intensity) m/z 340 (M+1,
+
2
16), 339 (M , 50), 171 (20), 170 (100).
Chem. Soc. 1974, 96, 2268; (d) Atkins, T. J.; Richman, J.
E.; Oettle, W. F. Org. Syn. 1978, 58, 86; (e) Alder, R. W.;
Mowlam, R. W.; Vachon, D. J.; Weisman, G. R. J.
Chem. Soc. Chem. Commun. 1992, 507.
. 1,5,9-Triazacyclododecane-2,4-dione, 1: A mixture of
diethyl malonate (8.03 g, 50 mmol), bis(3-
aminopropyl)amine (6.56 g, 50 mmol), sodium methoxide
12. 1,5-Didodecyl-1,5,9-triazacyclododecane, 5: A mixture of
4 (171 mg, 1 mmol), n-dodecyl iodide (2.96 g, 10 mmol),
NaHCO3 (0.84 g, 10 mmol) and DMA (20 mL) was
heated at 80°C overnight. The solvent was removed by
vacumm distillation at 80°C. The residue was basicified
with concd NaOH solution (15 mL), and extracted with
9
CH Cl2 (3×20 mL). The combined organic layer was
2
(270 mg, 5 mmol) and abs ethanol (600 mL) was heated
dried over Na SO , filtered, and concentrated under
2
4
at reflux for 7 days under nitrogen. The solvent was
removed under reduced pressure. The oily residue was
purified by a column chromatography on silica gel using
MeOH/CH Cl /NH OH (75:20:5) to afford the product
reduced pressure. The residue was loaded on a silica gel
column, and washed with hexane to elute out excess
n-dodecyl iodide. The product was eluted using MeOH/
CH Cl /NH OH (79:20:1) to afford the oily product 5
2
2
4
2
2
4
(
2.2 g, 22%) as a white solid, which can be crystallized
(447 mg, 88%). The dried oily product was dissolved in
THF, and filtered. The filtrate (20 mL) was bubbled with
HCl gas. The precipitate was collected by decanting off
the solvent, washed with hexane, and dried under high
vacuum to afford 5·3HCl salt (494 mg, 80%) as slightly
from MeOH-CH Cl to give plate-like crystals: mp 153-
1
2
2
8a
54°C (lit. 152–154°C ).
1
0. 9-Dodecyl-1,5,9-triazacyclododecane-2,4-dione, 2: A mix-
ture of 1 (1.00 g, 5.02 mmol), n-dodecyl iodide (4.50 g,
1
1
5.2 mmol) and DMA (50 mL) was stirred at room
yellow soild: For 5·3HCl, H NMR (400 MHz, DMSO-
temperature overnight. The solvent was removed by vac-
umm distillation at 80°C. The residue was washed with
hexane on a filter paper to remove excess dodecyl iodide.
d6, 130°C) l 3.33 (br t, J=7.8 Hz, 2 H), 3.11 (br t, J=8.2
Hz, 2 H), 2.42 (br t, J=5.0 Hz, 2 H), 2.33 (br t, J=7.0
Hz, 4 H), 1.72 (m, 2 H), 1.67 (m, 2 H), 1.58 (m, 2 H),
1.42 (br quin., J=6.8 Hz, 2 H), 1.38–1.20 (m, 44 H), 0.89
The solid was dissolved in CH Cl2 and washed with a
2
13
Na CO3 solution. The organic layer was dried over
(t, J=6.8Hz, 6 H); C NMR (100 MHz, DMSO-d6,
80°C) l 57.3, 54.9, 52.6, 50.3, 48.0, 31.0, 28.83, 28.74,
28.65, 28.62, 28.48, 28.40, 28.06, 26.9, 25.9, 25.5, 23.1,
21.8, 20.7, 19.2, 13.6 MS (EI, relative intensity) m/z 508
2
Na SO , filtered and concentrated under reduced pres-
2
4
sure. The residue was crystallized from MeOH–CH Cl2
2
to give needle shaped crystals (1.11 g, 60%): mp 134–
1
+
1
3
4
35°C; H NMR (400 MHz, CDCl ) l 7.40 (br s, 2 H),
(M+1, 12), 507 (M , 30), 214 (8), 213 (74), 212 (100), 211
3
.40 (q, J=5.5 Hz, 4 H), 3.18 (s, 2 H), 2.53 (t, J=5.5 Hz,
H), 2.38 (t, J=7.8 Hz, 2 H), 1.75 (quin., J=5.5 Hz, 4
(20), 210 (77).
13. 1,5,9-Tridodecyl-1,5,9-triazacyclododecane, 6: A mixture
of 1,5,9-triazacyclododecane (100 mg, 0.58 mmol), n-
H), 1.46 (quin., J=7.8 Hz, 2 H), 1.26 (m, 18 H), 0.88 (t,
13
J=6.8 Hz, 3 H); C NMR (100 MHz, CDCl ) l 167.3,
dodecanal (1.76 g, 9.5 mmol), NaCNBH (160 mg, 2.54
3
3
5
2
3.7, 53.3, 46.4, 40.0, 31.9, 29.67, 29.65, 29.62, 29.4, 27.6,
mmol), acetonitrile (10 mL) and water (3 mL) was aci-
dified to pH 4–5 with diluted HCl solution. The mixture
was stirred at room temperature overnight. The solvent
was removed under reduced pressure. The residue was
basicified with concd NaOH solution (3 M, 10 mL), and
extracted with CH Cl (3×15 mL). The combined organic
6.0, 24.6, 22.7, 14.1; MS (EI, relative intensity) m/z 369
+
(M+2, 2), 368 (M+1, 8), 367 (M , 15), 213 (47), 212 (100),
2
10 (31).
1. 9-Dodecyl-1,5,9-triazacyclododecane, 3: To a solution of
(300 mg, 0.82 mmol) in THF (15 mL) under nitrogen
1
2
2
2
was added a solution of BH ·THF (1 M, 6 mL) dropwise
layer was dried over MgSO , filtered, and concentrated
3
4
by a syringe. The mixture was heated at reflux for 24 h.
After cooling to room temperature in an ice bath was
slowly added methanol (5 mL), and then HCl solution (1
M, 0.5 mL). The mixture was stirred for 10 min, and
concentrated under reduced pressure. To the residue was
added HCl solution (6 M, 15 mL). The mixture was
heated at reflux for 3 h. After cooling to room tempera-
ture, the mixture was basicified to pH 13 with concd
NaOH solution, and extracted with CH Cl (3×15 mL).
under reduced pressure. The oily residue was distilled
under high vacuum to remove excess dodecanal. The
residue was loaded on a silica gel column, and washed
with CH Cl2 to elute out excess n-dodecanal. The
2
product was eluted using MeOH/CH Cl / NH OH
2
2
4
(79:20:1) to afford the oily product 6 (380 mg, 96%). The
oily product was dissolved in THF (10 mL), and filtered.
The filtrate was bubbled with HCl gas. The precipitate
was collected by filteration, washed with hexane, and
dried under high vacuum to afford 6·3HCl salt (410 mg,
2
2
The combined organic layer was dried over Na SO ,
2
4
1
filtered, and concentrated under reduced pressure to give
90%) as slightly yellow soild: H NMR of 6·3HCl salt

H.-J. Choi et al. / Tetrahedron Letters 43 (2002) 9385–9389
9389
(
(
400 MHz, DMSO-d at 130°C) l 2.93 (br s, 12 H), 2.74
br t, J=7.0 Hz, 6 H), 1.93 (br s, 6 H), 1.62 (br t, J=7.0
(50 mL) in a beaker was vigorously stirred using a mag-
netic stirrer for 5–10 min. The pH of the aqueous phase
was adjusted by small additions of concd 1 M H SO and
6
Hz, 6 H), 1.34–1.25 (m, 54 H), 0.90 (t, J=6.8 Hz, 9 H);
2
4
1
3
C NMR (100 MHz, DMSO-d , 80°C) l 53.8, 48.1, 31.3,
1 M (3 M or pellet) KOH, and was continuously moni-
tored by a pH electrode. After stirring, the mixture was
kept for 15 to 30 min to be separated, and samples, 2 mL
of the aqueous phase were removed. An equal amount of
the organic phase was also removed to maintain a fixed
phase ratio, thus the organic to aqueous phase ratio was
kept as 1:1. The aqueous phase samples were measured
by an atomic absorption spectrometer, Chem. Tech. Ana-
lytical-2000, to detemine gold concentration in range of
0–10 ppm Au, which was caliberated prior to measure.
15. Trotman-Dickenson, A. F. J. Chem. Soc. 1949, 1293–
1297.
6
2
9.03, 29.00, 28.92, 28.72, 26.5, 23.9, 22.1, 14.0; MS (EI,
+
relative intensity) m/z 676.7 (M+1, 2), 675.7 (M , 5),
6
74.7 (M−1, 4), 507.5 (42), 506.5 (100).
1
4. General procedure for solvent extraction of gold: Alka-
line gold cyanide solution, 10 ppm Au in 125 ppm
cyanide was prepared by adding AuCN (11.32 mg, 0.05
mmol) and KCN (312.8 mg) in a 1 L volumetric flask,
and by filling with water. 5 mM Extractant solution was
prepared by dissolving amine extractant (0.25 mmol) in
toluene (50 mL). Equal volume of mixture, the alkaline
gold cyanide solution (50 mL) and the extractant solution