Chemistry Reference
In-Depth Information
SCHEME 4.5.
Solvolysis of
N
-
tert
-butyl-
N
-chloroanilines.
Gassman and coworkers examined the solvolysis of
N
-
tert
-butyl-
N
-chloroanilines
(Scheme 4.5) in methanol and ethanol starting in 1968.
60-64
In buffered ethanol
the solvolysis rate constants for
14
s
þ
with
r
þ
of
6.4.
62,64
The
14a-f
correlate with
major products are
15
and the anilines
16
. Unsubstituted
14c
also yields
16d
(11%
compared to 48% of
15c
). Only the most reactive compound,
14a
, yields a significant
amount (10%) of solvent-derived product,
17a
. The yield of
16
increases with
increasing electron withdrawing power of X from 1% for
. The
results were explained by ionization to yield a tight ion pair that underwent internal
return to form
14a
to 29% for
14f
are derived from a
triplet ion that is stabilized relative to the singlet by electron withdrawing substitu-
ents.
64
Only the ion derived from
15
. It was suggested that the reduction products
16
appeared to be stable enough to escape internal
return and react with solvent. In the more strongly ionizing and more nucleophilic
methanol containing silver trifluoroacetate more solvent-derived products were
observed:
14a
under these conditions.
60,61,63
18a
accounts for 70% of
14a
If X is
electron withdrawing the solvent-derived products are suppressed. Both
14e
and
.
63
Decomposition of aryl azides in aqueous acid was known to produce
para
-
aminophenols before Bamberger began his work on
N
-arylhydroxylamines.
65
Bam-
berger recognized that
N
-arylhydroxylamines and aryl azides produce identical
product mixtures when decomposed under the same conditions in aqueous acid. He
proposed a common mechanism involving an aryl nitrene.
66
In 1981, Takeuchi and
coworkers began reporting on the photolysis and thermolysis of phenyl azide under
acidic conditions.
67
In AcOH containing ethanol, phenyl azide gave products
consistent with competing nitrene and nitrenium pathways (Scheme 4.6). Photolysis
at 25
C led to a larger proportion of the nitrene-derived product
14g
yield only the rearranged products
15
and the reduction products
16
than did
thermolysis at 138
C, but both conditions gave rise to all products shown in
Scheme 4.6.
67
Because the
ortho
/
para
ratio
19
21
/
20
exceeds 1.0 under all conditions,
but
23
/
22
is less than 0.5, and the yield of (
22þ23)
is small compared to (
20þ21)
