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On the mechanism of the clay catalyzed reaction of benzylamine
Tetrahedron Letters. Vo1.32, No.3, pp 303-306, 1991 Printed in Great Britain
ON THE MECHANISM
OF THE CLAY CATALYZED
Shelton
Bank* and Rumara
Department State University
The
benzylamine
mechanism
of the aluminum
was studied with deuterium
dibenzylamine
and the recovered
process is thus unlikely
NY
reaction
ammonia.l-*
A proposed
the related
reactions
of primary
extensive
involving
involves
R-NH,
+
oxidation
Moreover
reduction
reactions.4
reduction
reactive
Indeed tertiary
amines.
processes
Such oxidation fact, in the production surfaces,
reaction.* depicted
is suggested An alternate
is observed.
An SN?
substitution
of the
of
reaction
similar to
no obvious applied
R’kH,R +NH,A R-NHR
+
the presence
as scavengers
of aniline totally
to the amine
derives reactions
amines from primary
inhibits
likely involve
of nitrocyclohexane
of oxidation
reaction. imines,
and in
An imine
to account
in the clay catalyzed
which can account for these observations
303
While
of
over nickel and palladium
as key intermediates.5
imines are observed
below.
reaction. reaction
with the importance
would
in many
for radical cations.
from a displacement
amines
more
intermediates
with a displacement
effect is compatible
explanation
and are possibly
are probable
amines are employed
6 Moreover
l-ii
should be considered
in the nickel boride reduction mechanism
A
R -AH,
that are incompatible
reaction
of secondary
of dicyclohexylamine.
of
insights into the mechanism
a proton-catalyzed
the imine and Schiff bases have been identified
intermediate formation
schemes
exchange
amines and the elimination
(from oxidation)
Such an inhibiting
whereas
that provide
-
mechanisms
there are some observations
aniline does not give the diamine normally
hydrogen
_
Laszlo has shown that radical cations
clay catalyzed
reaction
of the product
an imine is suggested.
A+-
R-NH,A
R-tit@?
However
catalyzed
From the analysis
and thiols.3
R.Npr*+ 2 +
likely.
Montmorillonite
benzylamine.
amines to give secondary
mechanism
of alcohols
12222
exchanged
We wish to report the results of experiments clay catalyzed
Jewett
of Chemistry
labelled
benzylamine
and a process
OF BENZYLAMlNE
of New York at Albany
Albany,
Summay
REACTION
involves
for the amine the steps
304
-
RCH=NH
+ RCH,NH,
-
NCH,R+
R-CH, -NH,
z
RCH=
Thus two mechanisms amines:
a substitution
approach
amine and starting
reaction
benzonitrile
and monitored
RCH=NH
of primary amines
sequence
involving
these by labelling
benzylamine-a,a-dn
and lithium aluminum
spectroscopy present.
reaction
+ NH3
RCH,NHCH,R+
for the reaction
and an oxidation between
RCH=NH RCH=NCH,R
imines.
experiments.
for loss of deuterium
to give seconds:y Our experimental
We reacted
benzylamine-
in the product dibenryl
material.
The compound
revealed
was prepared
deuteride
(98%d).
in 73% yield from the reaction
Analysis
this material
to be 97% deuterated,
bentylamine
(5.09
of
by proton and carbon-13
NMR
with both the dl and d0 benzylamine
(Table 1)
The deuterated Montmorillonite reaction
are candidates
seeks to differentiate
a,a -dz in a clay-catalyzed
OXID
RCH,NH,
mixture was extracted
removed
(rotovap)
with methylene
to give a quantitative
Gas chromatographic dibenzylamine
analysis
.37 hydrogens.
chloride
recovery
with a reflux condenser.
and filtered.
The methylene
The
chloride
was
of material.
of the material
and no other compounds
spectra of the mixture showed contained
0.47 mol) was heated with 1 .O g of Al exchanged
(SWy-1) at 1800 for 60 hours in a glass apparatus
showed
present in amounts
that the alpha position
72% benzylamine
and 28%
greater than 0.5%.
The proton NM9
(of both the starting material
Thus 30% of the deuteriums
had exchanged
and product)
for hydrogen
during the
reaction. The analysis
is further supported
and expanded
in the carbon spectra the alpha carbons and independent distinguished
analysis
is possible.
by both chemical
of isotopic substitution
deuteriums
In a control
reaction
for hydrogen. and involves
extensive
water and/or hydroxyl
and a control
The exchange protons available
to dibenzylamine have been
to debenzylamine
of alpha deuteriums
reaction.
5% of the in benzylamine
is
from either the amine protons or the
protons present on the catalyst.
The results of the exchange
reaction
process.
demand
Moreover
protons must occur with a source of hydrogens intermediate
to obtain the extent
Table I records the proton and ?31:
where 28% of the benzyl amine is converted
have exchanged
in a reversible
and it is possible
and product.
where there is no conversion
First
separated
are clearly
of the benzyl amine and the product dibenzylamine
by the clay catalyst
reasonable
differences,
amine, the products of reaction
catalyzed
an intermediate
amine are clearly
the d-2, d-l and d-0 materials
shift and coupling
The results in Table I indicate 30% of the alpha deuteriums exchanged.
Second,
in both the starting material
NMR results for the initial deuterated
by the results of the t3C NMR spectra.
for benzyl amine and dibentyl
for this reversible
lability of the alpha hydrogens the exchange
for example
exchange
of the bentyl
the NH or catalyst
is the imine.
and formation
deuteriums OH protons.
That this exchange
for A most
reaction
of
305
occurs on the same time scale as the dimerization is responsible
for both the exchange
The remarkable precedent.
formation
of secondary
In 1972 Richey and Erickson
amines from primary
amines.
are many important clay catalyzed
that this ” ...indicates We propose accounted
of the relevant
considered
Second,
in the clay catalyzed
of mechanism
(pK) differences
greatty moderated
at 2000C.
bases would contribute differences
requires
in an SN2 process by oxidation
between
Finally, only
(or base reaction)
hydrogenation
reactions However
The source of hydrogen transfer
reactions
reaction.7
but
for an SN2
a final hydrogenation
they
based on the small basicity reasons.
potential
The effectiveness
as well as basicity, than cyclohexane
Therefore
of a
and in this amine.
at 25oC would be
some fraction of the basicity differences
scheme
involves
between
the two
only small if any reactivity
conversion
of an imine to an amine.
of the Schiff base is catalyzed there is no traditional
there is an alternate in these reactions Moreover
bonds in the aluminum
reaction
in cross
reactivity
benzyl amine and cyclohexylamine
possibility
is depicted
in the Meerwein-Pondorff-Verley-Oppenauer
base catalyzed double
selectivity
the hydride transfer to imine is somewhat
this conversion
the clay and base catalyzed
Therefore
are the same.
for an SN2 process based on these considerations.
The final step in the proposed clay catalyzed
hydrogenation.
for imine generation.
catalyst.
directly to the rate differences.
would be expected
is similarly
by the thermodynamic
proceses
and therefore
since the imine scheme
is determined
the 1.3 pK difference
for
reaction.
for the clay catalyzed
regard, benzyl amine might prove to be a more potent nucleophile Additionally,
commen?
that is, benzyl imine is far more stable than
an imine intermediate
for the large selectivities
in an SN2 process
reaction
amines is then determined
(1.3pK units) of the amines is unlikely for the following
nucleophile
and acid
This selectivity
in the clay catalyzed
reasons. 2 First, they argue that the
of a hydrogenation
An explanation difference
between
for by basicity
process of the two amines. note the absence
selectivity
there
for a mixed product
Richey and Erickson
to that obtained
imine stabilities,
for several
can be accounted
Interestingly
the base catalyzed
selectivity
steps of both the acid and base catalyzed
rejected this mechanism reactions
identical
Selectivity
Purnell and Ballantyne
of secondary
imines.
roles played by the two amine molecules...“.
is virtually
imines which is independent
the product determining
between
with clays has
formation
involves
amine are reacted together.
for by the same relative imine.
they propose
among these is the enhanced
that the considerable
hexyl or cyclohexyl stability
the different
reaction
amines
a base catalyzed
in the results and conclusions
Foremost
when benzyl amine and an aliphatic the base catalyzed
infers that this same imine intermediate
amines from primary
discovered
The mechanism
parallels
reactions.
reaction
and the reaction.
the aluminum
isopropoxide
transition involving
problematical.
by the metal catalyst. metal
in catalysis
exchanged
clay.
similar to the hydrogen
A similar scheme
ion is involved
conversion
For
present for the final
the aluminum
below in a sequence reaction.
In the In
is proposed
of carbon
of oximes to carbonyls.8
for t?e
nitrogen
306
Acknowledaements Acknowledgement the American
Chemical
discussions
1.
Table
is made to the Donors of The Petroleum Society,
Deuterium
Content
at AIDha Positiona Dibenzvlamine
Material
d2
dl
d0
95.5
3.0
1.5
90.1
6.4
1.5
Product Mixture
67.8
5.2
Determined
b
The amine was heated with the unexchanged conditions
by tH and l3C
27.0
a
as the reaction
d2
dl
dO
66.0
33.5
2.4
NMR Spectroscopy. clay Montmorillonite
with the Al exchanged
clay.
(SWY-1)
The unexchanged
under identical
clay is inactive
for tne
dimerization.2
Reference% 1.
J. A. Ballantine,
H. Purnell, M. Rayanakorn,
J. M. Thomas and K. J. Williams,
J. Chem. Sot.
Chem. Comm. 9, (1981). 2.
J. H. Purnell and J. A. Ballantine,
3.
J. A. Ballantine,
J. Mol. Car. 27, 169 (1984).
H. Purnell, M. Rayanakorn,
J. M. Thomas
and K. J. Williams,
J. Chem. Sot.
Chem. Comm. 4, (1981). 4.
P. Laszlo, Act. Chem. Res. B,
5.
a) C. F. Winans, H. Adkins, J. Am. Chem. Sot., a,
6.
:,y
We thank Janet F. Bank for helpfu!
Ben7vlamine
Controtb
amine
Fund, administered
during the course of this work.
Compound
Starting
for the support of this research.
Research
121 (1966).
Christensen,
J. Am. Chem. Sot., 70, 1817 (1948).
Shimamura,
and S-l Murahashi,
J. 0. Osby and B. Ganem,
b) R. A. Clarke and B E.
c) N. Yoshimura,
I. Moritani,
J. Am. Chem. Sot. $& 3038 (1973).
Tetrahedron Lett., s,
7.
H. G. Richey, Jr. and W. F. Erickson,
8.
J. K. Sugden
6413 (1985).
Tetrahedron L&t. $J, 2807 (1972).
Chem. industry (London) 680 (1972).
(Received in USA 11 October 1990)
306 (1932).
T.
ON THE MECHANISM
OF THE CLAY CATALYZED
Shelton
Bank* and Rumara
Department State University
The
benzylamine
mechanism
of the aluminum
was studied with deuterium
dibenzylamine
and the recovered
process is thus unlikely
NY
reaction
ammonia.l-*
A proposed
the related
reactions
of primary
extensive
involving
involves
R-NH,
+
oxidation
Moreover
reduction
reactions.4
reduction
reactive
Indeed tertiary
amines.
processes
Such oxidation fact, in the production surfaces,
reaction.* depicted
is suggested An alternate
is observed.
An SN?
substitution
of the
of
reaction
similar to
no obvious applied
R’kH,R +NH,A R-NHR
+
the presence
as scavengers
of aniline totally
to the amine
derives reactions
amines from primary
inhibits
likely involve
of nitrocyclohexane
of oxidation
reaction. imines,
and in
An imine
to account
in the clay catalyzed
which can account for these observations
303
While
of
over nickel and palladium
as key intermediates.5
imines are observed
below.
reaction. reaction
with the importance
would
in many
for radical cations.
from a displacement
amines
more
intermediates
with a displacement
effect is compatible
explanation
and are possibly
are probable
amines are employed
6 Moreover
l-ii
should be considered
in the nickel boride reduction mechanism
A
R -AH,
that are incompatible
reaction
of secondary
of dicyclohexylamine.
of
insights into the mechanism
a proton-catalyzed
the imine and Schiff bases have been identified
intermediate formation
schemes
exchange
amines and the elimination
(from oxidation)
Such an inhibiting
whereas
that provide
-
mechanisms
there are some observations
aniline does not give the diamine normally
hydrogen
_
Laszlo has shown that radical cations
clay catalyzed
reaction
of the product
an imine is suggested.
A+-
R-NH,A
R-tit@?
However
catalyzed
From the analysis
and thiols.3
R.Npr*+ 2 +
likely.
Montmorillonite
benzylamine.
amines to give secondary
mechanism
of alcohols
12222
exchanged
We wish to report the results of experiments clay catalyzed
Jewett
of Chemistry
labelled
benzylamine
and a process
OF BENZYLAMlNE
of New York at Albany
Albany,
Summay
REACTION
involves
for the amine the steps
304
-
RCH=NH
+ RCH,NH,
-
NCH,R+
R-CH, -NH,
z
RCH=
Thus two mechanisms amines:
a substitution
approach
amine and starting
reaction
benzonitrile
and monitored
RCH=NH
of primary amines
sequence
involving
these by labelling
benzylamine-a,a-dn
and lithium aluminum
spectroscopy present.
reaction
+ NH3
RCH,NHCH,R+
for the reaction
and an oxidation between
RCH=NH RCH=NCH,R
imines.
experiments.
for loss of deuterium
to give seconds:y Our experimental
We reacted
benzylamine-
in the product dibenryl
material.
The compound
revealed
was prepared
deuteride
(98%d).
in 73% yield from the reaction
Analysis
this material
to be 97% deuterated,
bentylamine
(5.09
of
by proton and carbon-13
NMR
with both the dl and d0 benzylamine
(Table 1)
The deuterated Montmorillonite reaction
are candidates
seeks to differentiate
a,a -dz in a clay-catalyzed
OXID
RCH,NH,
mixture was extracted
removed
(rotovap)
with methylene
to give a quantitative
Gas chromatographic dibenzylamine
analysis
.37 hydrogens.
chloride
recovery
with a reflux condenser.
and filtered.
The methylene
The
chloride
was
of material.
of the material
and no other compounds
spectra of the mixture showed contained
0.47 mol) was heated with 1 .O g of Al exchanged
(SWy-1) at 1800 for 60 hours in a glass apparatus
showed
present in amounts
that the alpha position
72% benzylamine
and 28%
greater than 0.5%.
The proton NM9
(of both the starting material
Thus 30% of the deuteriums
had exchanged
and product)
for hydrogen
during the
reaction. The analysis
is further supported
and expanded
in the carbon spectra the alpha carbons and independent distinguished
analysis
is possible.
by both chemical
of isotopic substitution
deuteriums
In a control
reaction
for hydrogen. and involves
extensive
water and/or hydroxyl
and a control
The exchange protons available
to dibenzylamine have been
to debenzylamine
of alpha deuteriums
reaction.
5% of the in benzylamine
is
from either the amine protons or the
protons present on the catalyst.
The results of the exchange
reaction
process.
demand
Moreover
protons must occur with a source of hydrogens intermediate
to obtain the extent
Table I records the proton and ?31:
where 28% of the benzyl amine is converted
have exchanged
in a reversible
and it is possible
and product.
where there is no conversion
First
separated
are clearly
of the benzyl amine and the product dibenzylamine
by the clay catalyst
reasonable
differences,
amine, the products of reaction
catalyzed
an intermediate
amine are clearly
the d-2, d-l and d-0 materials
shift and coupling
The results in Table I indicate 30% of the alpha deuteriums exchanged.
Second,
in both the starting material
NMR results for the initial deuterated
by the results of the t3C NMR spectra.
for benzyl amine and dibentyl
for this reversible
lability of the alpha hydrogens the exchange
for example
exchange
of the bentyl
the NH or catalyst
is the imine.
and formation
deuteriums OH protons.
That this exchange
for A most
reaction
of
305
occurs on the same time scale as the dimerization is responsible
for both the exchange
The remarkable precedent.
formation
of secondary
In 1972 Richey and Erickson
amines from primary
amines.
are many important clay catalyzed
that this ” ...indicates We propose accounted
of the relevant
considered
Second,
in the clay catalyzed
of mechanism
(pK) differences
greatty moderated
at 2000C.
bases would contribute differences
requires
in an SN2 process by oxidation
between
Finally, only
(or base reaction)
hydrogenation
reactions However
The source of hydrogen transfer
reactions
reaction.7
but
for an SN2
a final hydrogenation
they
based on the small basicity reasons.
potential
The effectiveness
as well as basicity, than cyclohexane
Therefore
of a
and in this amine.
at 25oC would be
some fraction of the basicity differences
scheme
involves
between
the two
only small if any reactivity
conversion
of an imine to an amine.
of the Schiff base is catalyzed there is no traditional
there is an alternate in these reactions Moreover
bonds in the aluminum
reaction
in cross
reactivity
benzyl amine and cyclohexylamine
possibility
is depicted
in the Meerwein-Pondorff-Verley-Oppenauer
base catalyzed double
selectivity
the hydride transfer to imine is somewhat
this conversion
the clay and base catalyzed
Therefore
are the same.
for an SN2 process based on these considerations.
The final step in the proposed clay catalyzed
hydrogenation.
for imine generation.
catalyst.
directly to the rate differences.
would be expected
is similarly
by the thermodynamic
proceses
and therefore
since the imine scheme
is determined
the 1.3 pK difference
for
reaction.
for the clay catalyzed
regard, benzyl amine might prove to be a more potent nucleophile Additionally,
commen?
that is, benzyl imine is far more stable than
an imine intermediate
for the large selectivities
in an SN2 process
reaction
amines is then determined
(1.3pK units) of the amines is unlikely for the following
nucleophile
and acid
This selectivity
in the clay catalyzed
reasons. 2 First, they argue that the
of a hydrogenation
An explanation difference
between
for by basicity
process of the two amines. note the absence
selectivity
there
for a mixed product
Richey and Erickson
to that obtained
imine stabilities,
for several
can be accounted
Interestingly
the base catalyzed
selectivity
steps of both the acid and base catalyzed
rejected this mechanism reactions
identical
Selectivity
Purnell and Ballantyne
of secondary
imines.
roles played by the two amine molecules...“.
is virtually
imines which is independent
the product determining
between
with clays has
formation
involves
amine are reacted together.
for by the same relative imine.
they propose
among these is the enhanced
that the considerable
hexyl or cyclohexyl stability
the different
reaction
amines
a base catalyzed
in the results and conclusions
Foremost
when benzyl amine and an aliphatic the base catalyzed
infers that this same imine intermediate
amines from primary
discovered
The mechanism
parallels
reactions.
reaction
and the reaction.
the aluminum
isopropoxide
transition involving
problematical.
by the metal catalyst. metal
in catalysis
exchanged
clay.
similar to the hydrogen
A similar scheme
ion is involved
conversion
For
present for the final
the aluminum
below in a sequence reaction.
In the In
is proposed
of carbon
of oximes to carbonyls.8
for t?e
nitrogen
306
Acknowledaements Acknowledgement the American
Chemical
discussions
1.
Table
is made to the Donors of The Petroleum Society,
Deuterium
Content
at AIDha Positiona Dibenzvlamine
Material
d2
dl
d0
95.5
3.0
1.5
90.1
6.4
1.5
Product Mixture
67.8
5.2
Determined
b
The amine was heated with the unexchanged conditions
by tH and l3C
27.0
a
as the reaction
d2
dl
dO
66.0
33.5
2.4
NMR Spectroscopy. clay Montmorillonite
with the Al exchanged
clay.
(SWY-1)
The unexchanged
under identical
clay is inactive
for tne
dimerization.2
Reference% 1.
J. A. Ballantine,
H. Purnell, M. Rayanakorn,
J. M. Thomas and K. J. Williams,
J. Chem. Sot.
Chem. Comm. 9, (1981). 2.
J. H. Purnell and J. A. Ballantine,
3.
J. A. Ballantine,
J. Mol. Car. 27, 169 (1984).
H. Purnell, M. Rayanakorn,
J. M. Thomas
and K. J. Williams,
J. Chem. Sot.
Chem. Comm. 4, (1981). 4.
P. Laszlo, Act. Chem. Res. B,
5.
a) C. F. Winans, H. Adkins, J. Am. Chem. Sot., a,
6.
:,y
We thank Janet F. Bank for helpfu!
Ben7vlamine
Controtb
amine
Fund, administered
during the course of this work.
Compound
Starting
for the support of this research.
Research
121 (1966).
Christensen,
J. Am. Chem. Sot., 70, 1817 (1948).
Shimamura,
and S-l Murahashi,
J. 0. Osby and B. Ganem,
b) R. A. Clarke and B E.
c) N. Yoshimura,
I. Moritani,
J. Am. Chem. Sot. $& 3038 (1973).
Tetrahedron Lett., s,
7.
H. G. Richey, Jr. and W. F. Erickson,
8.
J. K. Sugden
6413 (1985).
Tetrahedron L&t. $J, 2807 (1972).
Chem. industry (London) 680 (1972).
(Received in USA 11 October 1990)
306 (1932).
T.