372
PYUN
(s, 1H), 9.28 (s, 2H); 13C NMR
127.4, 148.4, 148.8, 150.5, 174.2.
Reagent grade acetonitrile and secondary amines
R1R2=Bz( ꢀPr)NH (benzylisopropylamine), ꢀBu2NH
(diisobutylamine), ꢀPr2NH (diisopropylamine), 2,6ꢀ
DMP (2,6ꢀdimethylpiperidine), were fractionally disꢀ
tilled over CaH2. The MeCN solution of amine was
prepared by adding appropriate amounts of amine to
MeCN.
δ
27.1, 38.4, 123.8,
k
obs, s–1
0.15
0.12
0.09
0.06
0.03
(
i
i
i
Kinetic studies. Reactions of
1 with R2NH in
MeCN were followed by monitoring the decrease in
the absorbance of the substrate at 268–280 nm with a
UVꢀvis spectrophotometer as described elsewhere [1–3].
On the other hand, the rates of the reactions of 1f were
too fast to follow to completion. Therefore, the rate
studies utilized a stoppedꢀflow spectrophotometer.
However, the kobs values calculated from the slopes of
0
0.01
0.02
ꢀPr2NH], M
0.03
[i
Fig. 1. Plot of
k
vs. base concentration for the reaction
obs
the plots were in excellent agreement (within 5%
)
of (E)ꢀ2,4,6ꢀ(NO ) C H CH=NOC(O)C(CH ) proꢀ
2 3
6
2
3 3
with the kobs calculated by using a UVꢀvis spectrophoꢀ
tometer. All rate constants were average from at least
three experiments.
moted by
iꢀPr NH in MeCN at 25 C.
°
2
EXPERIMENTAL
Materials. (E)ꢀBenzaldehyde Oꢀpivaloyloximes
Product studies. The products of the reactions of 1a and
1fwith iꢀBu2NH in MeCN were identified by GCꢀMS and
melting point. A solution of 0.30 g (1.47 mmol) of 1a and
an excess amount of base (15 ml) was stirred for 10 hrs
at room temperature. The solvent was removed
in vacuo, and the residue was extracted with CH2Cl2
and washed thoroughly with water until all of the
amine, ammomium salt, and benzoate were completely
1a–e were available from previous work. The comꢀ
pounds were again recrystallized from ethanol. Freshly
purified compounds were used in all kinetics runs. (E)ꢀ
2,4,6ꢀtrinitrobenzaldehyde Oꢀpivaloyloxime (1f) was
prepared in reasonable yield by adding the pivaloyl chloꢀ
ride (0.6 mmol) to the solution of (E)ꢀ2,4,6ꢀtrinitrobenꢀ
zaldoxime (0.14 g, 0.5 mmol) in aqueous NaOH soluꢀ
tion (0.4 M, 1.5 ml) at 0°C as described previously [1].
The solution was stirred for 20–30 min at 10°C and
poured into 10 ml of cold water. The products were
recrystallized from ethanol. HRMS and elemental
analysis results for 1f could not be performed because
they decomposed after several hours. However, the
NMR data of the compound was consistent with the proꢀ
removed. The yield of PhC
GC. The product studies of 1f with
was also carried out as described above. The product
was 2,4,6ꢀtrinitrobenzonitrile with mp 133–135
(mp 134–135 [10]). The yield of 2,4,6ꢀtrinitrobenꢀ
≡N
(94%) was determined by
iꢀBu2NH in MeCN
°
C
°
C
zonitrile was 92%.
Control experiments. The stabilities of
1 were
determined as reported [2]. The solutions of 1a–e in
MeCN were stable for at least 4 weeks, when stored in
the refrigerator. They were stable for a long time in the
solid state. However, MeCN solution of 1f was stable
for only several hours.
posed structure. The yield (%), melting point ( C), IR
°
(KBr, C=O, cm–1), 1H NMR (400 MHz, Acetoneꢀd6),
and 13C NMR (100 MHz, DMSOꢀd6) spectral data for
the new compounds are as follows. Yield 91%; mp
1
243°
C
; IR 1763 cm–1; H NMR
δ
2.05 (s, 9H), 9.15
RESULTS
The reactions of 1a and 1f with iꢀBu2NH in MeCN
Table 1. The firstꢀorder rate constants for elimination from (E)ꢀ
–5
–1
produced benzonitrile and 2,4,6ꢀtrinitrobenzonitrile,
respectively. The yields of products were 94 and 92%,
respectively. No trace of benzaldehyde oximes could
be detected by TLC.
2,4,6ꢀ(NO ) C H CH=NOC(O)C(CH ) (5.0 10 mol l )
×
2 3
6
2
3
promoted by
i
ꢀPr NH in MeCN at 25 C
°
2
102 [
i
ꢀPr NH], mole l–1
102 kobs, s–1 b, c
2
The kinetics of the elimination reaction for 1e and
1f measured from the disappearance of the substrate
absorption at 280 nm show excellent pseudoꢀfirst
order kinetic plots that covered at least two halfꢀlives.
However, the rates of the reactions of 1a–d were too
slow to follow to completion. Therefore, initial rate
method was employed [11].
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
2.0
3.0
1.17
2.10
3.12
3.95
4.82
5.81
6.81
7.03
8.73
12.7
The observed rate constants for eliminations from
1f are listed in Table 1. Plot of kobs for the reaction of 1f
KINETICS AND CATALYSIS Vol. 52
No. 3
2011