924
Can. J. Chem. Vol. 77, 1999
was added and the mixture was heated under reflux for 2 h.
The solvent was removed by evaporation and the residue
was dissolved in dichloromethane (50 mL), washed with wa-
ter (50 mL), dried with MgSO4, and evaporated. The result-
ing yellow crystals were decolorized with activated charcoal
and recrystallized twice from hexane to give the ester
(0.65 g, 34%) as white crystals: mp 86–87°C; 1H NMR
(200 MHz) δ: 8.00 (2H, d, J = 9 Hz, Ar), 6.98 (3H, m, Ar),
6.92 (2H, d, J = 9 Hz, Ar), 3.87 (3H, s, OCH3), 2.44 (6H, s,
(CH3)2Ar), 2.00 (6H, s, (CH3)2).
volysis products. Aqueous solutions containing sodium azide
were adjusted to pH ≈ 7 with concentrated HClO4 before use.
The products of the reactions of Me-1-(4-methoxyben-
zoate) ([S] = 2 mM) in the absence of azide ion were ana-
lyzed after 2–30 halftimes for reaction of the substrate and
were shown to be stable during this time. For reactions in
the presence of azide ion the products were analyzed after
30–40 halftimes, because the substrate and the azide ion
adduct Me-1-N3 coeluted from the HPLC column. At these
long reaction times there was slight (≤ 5%) breakdown of
Me-1-N3 that resulted in significant increases in the rela-
tively small fractional yields of the solvent adducts Me-1-
OSolv. For the reactions in the presence of 0.05 M azide ion
and increasing concentrations of acetate ion the solutions
were buffered with acetate, 95% anion. UV spectroscopy
showed that under these conditions more than 97% of the
azide is in the anionic form. In all cases the HPLC peak area
for the elimination product Me-3 was corrected for the 7.0%
of this alkene that was present as a contaminant of the sub-
strate.
2-(2,4,6-Trimethylphenyl)-2-propyl 4-methoxybenzoate
Me-1-(4-methoxybenzoate) was prepared from 2-(2,4,6-
trimethylphenyl)-2-propyl alcohol by the procedure de-
scribed above for 2-(2,6-dimethylphenyl)-2-propyl 4-
methoxybenzoate. Recrystallization from hexane gave the
1
ester in 50% yield: mp 106–107°C; H NMR (200 MHz) δ:
8.00 (2H, d, J = 9 Hz, Ar), 6.92 (2H, d, J = 9 Hz, Ar), 6.80
(2H, s, Ar), 3.87 (3H, s, OCH3), 2.41 (6H, s, (CH3)2Ar),
2.21 (3H, s, CH3Ar), 1.99 (6H, s, (CH3)2).
The products of the reactions of Me-1-(4-nitrobenzoate)
([S] = 1 mM) were analyzed after 5–20 halftimes for reac-
tion of the substrate and were shown to be stable during this
time.
2-(4-Methoxy-2,6-dimethylphenyl)-2-propyl 4-
methoxybenzoate
MeO-1-(4-methoxybenzoate) was prepared from 2-(4-
methoxy-2,6-dimethylphenyl)-2-propyl alcohol by the proce-
dure described above for 2-(2,6-dimethylphenyl)-2-propyl 4-
methoxybenzoate. Purification by column chromatography
on silica gel, eluting with 1:1 ethyl acetate – hexanes, fol-
lowed by recrystallization from hexane gave the ester in
Product studies for the relatively fast reactions of MeO-1-
(4-methoxybenzoate) ([S] = 0.1–0.5 mM) were carried out at
room temperature, 22 ± 2°C. It has been shown in previous
work that there is no detectable difference between product
ratios determined at room temperature and at 25°C (1, 14).
For reactions in the absence of azide ion the products were
analyzed after 20–70 halftimes for reaction of the substrate
and were shown to be stable during this time. For reactions
in the presence of azide ion the substrate concentration was
at least 10-fold smaller than that of azide ion, in order to
1
22% yield as plates: mp 86–87°C; H NMR (400 MHz) δ:
7.99 (2H, d, J = 9 Hz, Ar), 6.91 (2H, d, J = 9 Hz, Ar), 6.52
(2H, s, Ar), 3.86 (3H, s, OCH3), 3.74 (3H, s, OCH3), 2.43
(6H, s, (CH3)2Ar), 1.98 (6H, s, (CH3)2).
2-(2,4,6-Trimethylphenyl)-2-propyl 4-nitrobenzoate
–
maintain pseudo-first-order conditions. For reactions at [N3 ]
Me-1-(4-nitrobenzoate) was prepared from 2-(2,4,6-
trimethylphenyl)-2-propyl alcohol and 4-nitrobenzoyl chlo-
ride by the procedure described above for 2-(2,6-
dimethylphenyl)-2-propyl 4-methoxybenzoate. Recrystallization
from ether gave the ester in 18% yield as needles: mp 232–
= 1–5 mM the azide ion adduct MeO-1-N3 was unstable and
the products were analyzed within the first 3 halftimes for
reaction of the substrate, during which breakdown of MeO-
–
1-N3 is insignificant. For reactions at [N3 ] ≥0.05 M, the
azide ion adduct Me-1-N3 was stabilized by a common ion
effect and the products were analyzed after 10–20 halftimes
for reaction of the substrate. The substrate and the trifluoro-
ethyl ether solvolysis product MeO-1-OCH2CF3 coeluted
from the HPLC column. Therefore, for reactions that were
analyzed before complete disappearance of the substrate, the
total HPLC peak area for the solvent adducts was calculated
with the assumption that the ratio of the HPLC peak areas
for the solvolysis products MeO-1-OH and MeO-1-
OCH2CF3 is the same as that determined in the absence of
azide ion. In all cases, the HPLC peak area for the elimina-
tion product MeO-3 was corrected for the 1.6% of this
alkene that was present as a contaminant of the substrate.
1
233°C (sl. dec.); H NMR (400 MHz) δ: 8.28 (2H, d, J =
9 Hz, Ar), 8.20 (2H, d, J = 10 Hz, Ar), 6.81 (2H, s, Ar), 2.39
(6H, s, (CH3)2Ar), 2.22 (3H, s, CH3Ar), 2.03 (6H, s, (CH3)2).
2-(4-Methoxy-2,6-dimethylphenyl)propene
MeO-3 was prepared by dehydration of 2-(4-methoxy-2,6-
dimethylphenyl)-2-propyl alcohol by the literature procedure
(11) for the preparation of 2-(2,4,6-trimethylphenyl)propene.
Purification by distillation gave the alkene in 96% yield: bp
1
82°C (1 Torr (= 133.3 Pa)); H NMR (400 MHz) δ: 6.60
(2H, s, Ar), 5.27 (1H, broad, CH2), 4.75 (1H, br, CH2), 3.78
(3H, s, OCH3), 2.25 (6H, s, (CH3)2Ar), 1.94 (3H, s, CH3).
Product studies
HPLC analyses
Unless stated otherwise, product studies were carried out
in 50:50 (v:v) trifluoroethanol–water at 25°C and I = 0.50
(NaClO4). Reactions were initiated by making a 100-fold di-
lution of a solution of substrate in acetonitrile into the ap-
propriate reaction mixture and product distributions were
determined by HPLC analysis. For reactions at [N3 ] ≤0.05 M
the solutions were buffered with 25 mM cacodylate, 80%
anion, which prevented acid-catalyzed breakdown of the sol-
Unless noted otherwise, the products of the reactions of
X-1-Y were cleanly separated by reverse-phase HPLC as de-
scribed previously (14, 15), with peak detection by a Waters
996 diode array detector. The products were detected by
their UV absorbance at 280 nm for MeO-1-Y and at 269 nm
for Me-1-Y and H-1-Y. These wavelengths are λmax for the
corresponding alcohols X-1-OH. The products of solvolysis
–
© 1999 NRC Canada