7
352 Zhang et al.
Asian J. Chem.
1
Monoester (3b): White solid, m.p. 310-311 ºC; H NMR
EXPERIMENTAL
(
Hz, 2H), 3.34-3.51(m, 6H), 3.62(q, J = 20 Hz, 2H), 11. 73 (s,
400 MHz, CDCl
3
) δ: 1.25 (t, J = 14 Hz, 3H), 1.88(d, J = 31
1
All melting points are uncorrected. H NMR at 400 MHz
13
13
and C NMR at 100 MHz spectra were measured in CDCl
3
1H); C NMR (100 MHz, CDCl
42.1, 42.7, 43.8, 45.0, 48.8, 51.6, 58.2, 172.1, 185.3. HRMS
calcd. (%) for C13 234.0892, found (%) 234.0887.
Monoester (3c): White solid, m.p. 322-323 ºC; H NMR
(400 MHz, CDCl ) δ: 0.93 (t, J = 14 Hz, 3H), 1.67(d, J = 30
Hz, 2H), 1.84-1.91(m, 2H), 3.45-3.56 (m, 6H), 3.93(t, J = 13
3
) δ: 14.2, 29.3, 33.4, 36.8,
solutions using TMS as an internal standard. HRMS spectra
were recorded on an Agilent 6210 high-resolution mass spec-
trometer.
14 4
H O
1
General procedure: The diester (10 mmol) was dissolved
in 50 mL of hexane and a solution of p-TsOH (0.15 mmol in
3
1
3
5
mL of toluene) was added. The reaction mixture was
immersed in an ice-water bath and cooled to 0 ºC and 11 mmol
0.2 mL) of H O was added under ultrasonic irradiation until
Hz, 2H), 11.75 (s, 1H); C NMR (100 MHz, CDCl
3
) δ: 10.3,
22.0, 30.4, 32.8, 34.3, 42.0, 43.4, 44.7, 48.2, 48.5, 50.6, 60.2,
171.3, 186.1. HRMS calcd. (%) for C14
(%) 248.1045.
(
2
16 4
H O 248.1049, found
the initial consumption of the starting diester was observed by
thin-layer chromatography. The reaction proceeded at the same
temperature and the reaction mixture was cooled to -20 ºC for
purification. A fine white precipitate formed and was care-
fully filtered. The precipitate was washed with hexane and
dried under high vacuum to yield a stable white powder.
RESULTS AND DISCUSSION
In order to optimize the reaction conditions for the
monohydrolysis of polyhedral diesters the following
parameters were investigated i.e., catalytic activity, catalyst
quantity, ultrasound irradiation power, solvents and reaction
temperature.
1
Monoester (1a): White solid, m.p. 257-258 ºC; H NMR
(
3
400 MHz, CDCl ) δ: 1.71 (s, 2H), 1.82-1.92 (m, 8H), 2.07(s,
2
H), 2.20 (s, 2H), 3.40 (s, 3H), 11.63 (s, 1H). The spectroscopic
The catalytic activity of p-dodecylbenzene sulphonic acid
17
data matched that reported in the literature .
Monoester (1b): White solid, m.p. 269-270 ºC; H NMR
400 MHz, CDCl ) δ: 1.24 (t, J = 14 Hz, 3H), 1.69 (s, 2H),
.83-1.92 (m, 8H), 2.05 (s, 2H), 2.17 (s, 2H), 4.12 (q, J = 22
(
DBSA), trifluoromethanesulphonic acid (TfOH), H
and p-toluene sulphonic acid (p-TsOH) were studied first
Table-1). The monohydrolyzation of dimethyl 1,3-adamantane
dicarboxylate was performed in the absence of a catalyst using
O (0.2 mL), toluene (5 mL) and hexane (50 mL) as the
solvent mixture for 10 h in an ice bath as a control reaction
and no hydrolysis was observed (entry 1). DBSA, TfOH, H SO
2 4
SO , HCl
1
(
3
(
1
13
Hz, 2H), 11.66 (s, 1H). C NMR (100 MHz, CDCl ) δ: 14.2,
3
H
2
2
1
2
7.8, 35.3, 37.7, 37.9, 39.5, 40.7, 40.8, 60.3, 167.8, 176.7,
252.1362, found (%)
83.3. HRMS calcd. (%) for C14
52.1359.
H
20
O
4
2
4
and HCl were all inactive (entries 2-5) whereas p-TsOH
effectively catalyzed the hydrolysis (entry 6) and gave the
monoester in a yield of 76 %. The results may be a conse-
quence of the water forming small droplets in the nonpolar
solvent, hexane, which concentrates the catalytic species, the
proton, onto the surface of the droplets where the reaction
takes place. The p-TsOH serves as a phase transfer catalyst
and transfers protons from the water into the nonpolar solvent.
Because the monoester products are insoluble in the nonpolar
solvent, they migrate to the aqueous phase, which pushes the
equilibrium between the diesters and monoesters to the
monoester side and provides the high selectivity of the mono-
hydrolyzation. Furthermore, the white precipitate was very
clean and only the monoester 1a, was observed by thin-layer
chromatography; therefore, the isolation and purification were
straightforward (just filtration).
1
Monoester (1c): White solid, m.p. 281-282 ºC; H NMR
(400 MHz, CDCl ) δ: 0.94 (t, J = 15 Hz, 3H), 1.62-1.69 (m,
3
4
1
1
1
2
H), 1.83-1.89 (m, 8H), 2.05 (s, 2H), 2.17 (s, 2H), 4.03 (t, J =
13
3 Hz, 2H), 11.78 (s, 1H). C NMR (100 MHz, CDCl
3
) δ:
0.4, 22.0, 27.8, 35.3, 37.7, 37.9, 39.5, 41.8, 42.9, 65.9, 176.7,
83.2. HRMS calcd. (%) for C15
66.1513.
H
22
O
4
266.1518, found (%)
1
Monoester (2a): White solid, m.p. 182-183 ºC; H NMR
(
400 MHz, CDCl ) δ: 3.72 (s, 3H), 4.26-4.29 (m, 3H), 4.32-
3
4
.34 (m, 3H), 11.64 (s, 1H). The spectroscopic data matched
18
that reported in the literature .
Monoester (2b): White solid, m.p. 302-303 ºC; H NMR
400 MHz, CDCl ) δ: 1.31 (t, J=14 Hz, 3H), 4.20 (q, J = 21
Hz, 2H), 4.26-4.31 (m, 3H), 4.32-4.35(m, 3H), 11.67(s, 1H);
1
(
3
1
3
C NMR (100 MHz, CDCl
0.8, 171.5, 183.3. HRMS calcd for C12
%) 202.0735.
3
) δ: 14.3, 41.7, 46.9, 47.1, 55.9,
6
H O
12 4
202.0736, found
The effect of the quantity of the catalyst is also shown in
Table-1. It was apparent that 0.01 equivalents were insufficient
to completely catalyze the hydrolysis reaction (entry 6) and
(
1
Monoester (2c): White solid, m.p. 314-315 ºC; H NMR
(400 MHz, CDCl ) δ: 1.12 (t, J = 14 Hz, 3H), 1.66-1.70 (m,
3
0
.02 and 0.025 equivalents of p-TsOH did not completely
dissolve in the mixed solvent system, while adding an extra
mL of toluene into the system would dissolve the resulting
2
3
4
H), 4.08 (t, J = 14 Hz, 2H), 4.25-4.27(m, 3H), 4.32-4.35 (m,
13
H), 11.58 (s, 1H), C NMR (100 MHz, CDCl
1.6, 46.9, 55.9, 47.2, 66.0, 171.5, 183.2. HRMS calcd. (%)
234.0892, found (%) 234.0890.
Monoester (3a): White solid, m.p. 299-300 ºC; H NMR
400 MHz, CDCl ) δ: 1.68 (d, J = 30 Hz, 2H), 3.24-3.48 (m,
H), 3.54 (s, 3H), 11.72 (s, 1H), C NMR (100 MHz, CDCl
δ: 30.2, 33.1, 36.5, 41.5, 42.7, 43.9, 48.9, 49.1, 51.6, 57.7,
72.2, 185.9. HRMS calcd. (%) for C12 220.0736, found
%) 220.0732.
3
) δ:10.2, 22.1,
5
monocarboxylic acids and reduce the yields (entries 8-9). The
best yield was obtained with 0.015 equiv. of p-TsOH.
for C13
14 4
H O
1
2
The effect of the quantity of H O on the monohydrolysis
(
3
of dimethyl 1,3-adamantane dicarboxylate when using p-TsOH
as the catalyst was also investigated. The results are summa-
13
6
3
)
rized in Table-2 and it was apparent that 0.1 mL of H
insufficient to maximize the yield (entry 1), whereas 0.3 and
.4 mL of H O were found to be excessive for the monohydrolysis
2
O was
1
12 4
H O
(
0
2