Elimination Reactions of (E)-2,4-Dinitrobenzaldehyde O-aryloximes
J . Org. Chem., Vol. 63, No. 9, 1998 3009
pK
a
value of 19.18 for EtOH in EtOH22 and the K
value.
1
It is conceivable that a strong electron-withdrawing
â-aryl substituent may decrease the energy of the car-
banion intermediate lower than that of the E2 transition
state to induce a change in the reaction mechanism.
However, no change in the reaction mechanism has been
K
1
EtO- + ROH y z EtOH + RO-
(2)
K
2
5
-
realized by the 2,4-dinitro substituents, despite 5 × 10
EtO + p-O NC H CH CN y z EtOH + p-O NC H Ch HCN
2
6
4
2
2
6
4
fold enhancement in rate. It appears that more stabili-
zation energy is obtained by forming the partial triple
bond than by delocalizing the negative charge at the
â-carbon with the electron-withdrawing groups. Note-
worthy is the relative insensitivity of the nitrile-forming
transition state to the variation of the â-aryl substituent.
(3)
K
3
RO- + p-O NC H CH CN y z ROH + p-O NC H Ch HCN
2
6
4
2
2
6
4
(4)
-
-
K ) [RO ]/[EtO ][ROH]
(5)
1
-
K ) [p-O NC H Ch HCN]/[EtO ][p-O NC H CH CN] (6)
2
2
6
4
2
6
4
2
Exp er im en ta l Section
-
K ) [ROH][p-O NC H Ch HCN]/[RO ] ×
3
2
6
4
Ma ter ia ls. (E)-2,4-Dinitrobenzaldehyde O-aryloximes (1-
) were prepared by the reactions of 2,4-dinitrobenzaldehyde
[
p-O NC H CH CN]
2 6 4 2
(7)
(8)
3
with appropriately substituted O-arylhydroxylamines in the
presence of catalytic amount of HCl as described in the
pK (ROH) ) 19.18 - log K1
a
1
,12,13
literature.
compounds were consistent with the proposed structures. The
yield (%), melting point (°C), NMR (DMSO-d ), IR (KBr, CdN,
cm ), and combustion analysis data for the new compounds
are as follows. 2,4-(NO CHdNOC -4-NO (1): yield
0; mp 182-183; IR 1587; NMR δ 9.21 (s, 1H), 8.88 (s, 1H),
.65 (dd, 1H), 8.36 (d, 1H), 8.32 (d, 2H), 7.54 (d, 2H). Anal.
: C, 47.00; H, 2.43; N, 16.86. Found: C,
6.87; H, 2.37; N, 16.56. 2,4-(NO CHdNOC -2-Cl-4-
(2): yield 70; mp 154-155; IR 1582; NMR δ 9.31 (s, 1H),
The spectral and analytical data of the
P r od u ct Stu d ies. The products of the reactions between
-
-
1-3 and EtO , PhC(CH
3
)dNO /PhC(CH
3
)dNOH, and CF
3
-
6
-
1
-
CH
2
O /CF
3
CH
2
OH buffers in EtOH were identified by TLC
2
)
2
C
6
H
3
6
H
4
2
and GC-MS. The products were 2,4-dinitrobenzonitrile and
aryloxides, which were stable under the experimental condi-
tion. The products were also identified by periodically moni-
toring the UV absorption of the reaction mixtures under the
reaction condition. For all reactions the absorbance corre-
sponding to the reactants decreased at 310-330 nm, and those
for the products increased at 400-404 nm as the reactions
proceeded. The UV spectra of the products were identical to
those of the aryloxides. Clean isosbestic points were observed
at 357, 339, and 354 nm for the reactions of 1, 2, and 3,
respectively. The yields of the aryloxides determined by
comparing the UV absorptions of the infinity samples with
those for the authentic aryloxides were in the range of 90-
98%.
7
8
Calcd for C13
4
8 4 7
H N O
2
)
2
C
6
H
3
6 3
H
NO
2
8
1
1
.88 (d, 1H),8.66 (dd, 1H), 8.42 (d, 1H), 8.36 (d, 1H), 8.29 (dd,
H), 7.84 (d, 1H). Anal. Calcd for C13 ClN : C, 42.58; H,
.93; N, 15.28. Found: C, 42.66; H, 1.87; N, 14.93. 2,4-
CHdNOC -2,4-(NO (3): yield 72; mp 163-168;
IR 1601; NMR δ 9.36 (s, 1H), 8.89 (m, 2H), 8.70 (dd, 1H), 8.63
dd, 1H), 8.38 (d, 1H), 8.10 (d, 1H). Anal. Calcd for
: C, 41.39; H, 1.87; N, 18.57. Found: C, 41.20; H,
H
7
4 7
O
(NO
2
)
2
C
6
H
3
6
H
3
2 2
)
(
13 7 5 9
C H N O
1
.83; N, 18.60.
Ethanol was purified by reaction with magnesium and
Kin etic Stu d ies. Rates of the eliminations from 1-3
-
-
distillation. Solutions of EtONa-EtOH were prepared by
promoted by EtO -EtOH, PhC(CH
3
)dNO /PhC(CH
3
)dNOH,
-
adding clean pieces of sodium metal to anhydrous EtOH under
and CF
3
CH
2
O /CF
3
CH
2
OH buffers in EtOH were followed
-
nitrogen. The buffer solutions of PhC(CH
CH
3
)dNO /PhC-
using a stopped-flow spectrophotometer. Reactions were
monitored by the increase in the absorption of the aryloxides
at 400-404 nm under pseudo-first-order condition employing
at least 50-fold excess of base. In almost every case, plots of
-
-
(
(
3 3 2 3 2 6 4 6 4
)dNOH, CF CH O /CF CH OH, and YC H O /YC H OH
YdH, p-Cl, m-Cl, p-CN) were prepared by adding appropriate
amount of the conjugate acid to EtONa-EtOH. In all cases
the buffer ratio was maintained to be 1.0.
-ln(A
∞
- A
t
/A
∞
o
- A ) vs time were linear over at least two
half-lives. The slope was the pseudo-first-order rate constants.
Freshly prepared buffer solutions were used in all kinetic runs.
p K
CF CH
equilibrium constant K
using p-nitrobenzyl cyanide as an indicator. The K
a
Va lu es. The pK
a 3
values of the of PhC(CH )dNOH and
3
2
OH in ethanol were determined by measuring the
-
1
between ROH and EtO in ethanol
Con tr ol Exp er im en ts. The stability of 1-3 and their
solutions were determined by measuring the melting point and
periodical scanning of the solutions with the UV spectropho-
tometer. No change in melting point or UV spectrum was
detected for 1-3 during six months in the refrigerator. The
solutions of 1 and 2 in EtOH were stable for at least three
weeks when stored in the refrigerator.
1
4
2
value
-
4
was determined by adding 1.0 × 10 M of p-nitrobenzyl
-5
-
cyanide to a solution containing 2.0 × 10 M of EtO in EtOH.
The absorbance of the p-nitrobenzyl cyanide anion was mea-
sured at 530 nm and divided by its molar extinction coefficient
(
ꢀ ) 29400) to obtain the anion concentration. The equilibrium
constant K was calculated with eq 6 using the p-nitrobenzyl
cyanide anion concentration as described previously.
2
1
5
Ack n ow led gm en t. This research was supported by
Basic Science Research Institute Program, Ministry of
Education, 1996 (Project No. BSRI-96-3406).
-
2
To this solution was added (4.6-13) × 10 M of ROH in
small increments, and the absorbances at 530 nm were
2
measured. Utilizing the K value determined as above and
the p-nitrobenzyl cyanide anion concentration measured after
addition of the ROH, the [EtO ] was calculated with eq 6. The
-
Su p p or tin g In for m a tion Ava ila ble: Observed rate con-
stants for eliminations from (E)-2,4-dinitrobenzaldehyde O-
1
K values were calculated with eq 5 using the concentrations
-
-
-
-
aryloximes (1-3) promoted by EtO -EtOH, PhC(CH
3
)dNO /
OH buffers in ethanol
of [EtO ] calculated as above and [RO ] and [ROH] obtained
-
-
-
-
PhC(CH
3
)dNOH, and CF
3
CH
2
O /CF
3
CH
2
from the relationship [RO ] ) [EtO ]
0
- {[EtO ] + [p-O
2
-
-
-
at 25.0 °C (2 pages). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
NC
6
H
4
CHCN ]} and [ROH] ) [ROH]
0
- [RO ]. The pK
a
values of the ROH were then calculated with eq 8 using the
(
27) Rochester, C. H.; Rossal, B. Trans. Farady Soc. 1969, 65, 1004-
1
013.
J O972192V
Cho, Bong Rae
