Note: Descriptions are shown in the official language in which they were submitted.
"` 9L~L%~74~
1 Case 4080-A
PRODUCTION OF 2,6-DIMETHYL ANILINE
FROM CYCLOHEXYL ~INES
This invention relates to the production of 2,6-
dimethyl aniline. More particularly the invention comprises
an improved process for generating this compound from cyclo-
hexyl amines. It is known to produce aromatic amines by
contacting a cyclohexyl amine with a Group VIII metal cata-
lyst preferably in the presence of ammonia and hydrogen.
However, when this technique is applied to producing 2,6-di-
methyl aniline, it is found that forma`tion of the desiredproduct is very slow. The present invention provides sub-
stantial improvement in the rate of formation. It comprises
heating a mixture of 2,6-dimethylcyclohexylamine and a phenol
in contact with a palladium catalyst, maintaining the reac-
- 15 tantsin a liquid phase and at an elevated temperature of
about 200 to 400 C.
Various methods have been used in the past to pre-
pare aromatic amines. According to one method, an aromatic
compound is nitrated to form a nitroaromatic which is then
hydrogenated to the corresponding aromatic amine. This
method is used commercially to make aniline from benzene.
Van Verth et al, U. S. 3,219,702, describes a pro-
cess in which a cyclohexanone îs reacted with ammonia in the
presence of a hydrogen acceptor (e.g. nitrobenzene) and a
dehydrogenation catalyst.
Wilder et al, U. S. 3,219,704, describes a similar
process in which the hydrogen acceptor is eliminated and the
- amount of cyclohexanone is at least equivalent to the amount
of ammonia used.
Barker, U. S. 3,272,865, describes the production
of anilines by reaction of phenols with ammonia in contact
with a silica-alumina, titania-alumina, zirconia-alumina,
phosphoric acid or tungsten oxide catalyst. The process is
similar to that described by Neuroessen, U. S. 1,935,209,
- 35 and Lowy et al, U. S. 1,449,423.
~2-~749
Barker, U. S. 3,361,818, describes the production
of aromatic amines by passing cyclohexyl amine through a
Group VIII metal catalyst. Preferably hydrogen and ammonia
are included.
Barker, U. S. 3,442,950, describes the reaction of
a cyclohexanol with an aminating agent (e.g. ammonia) in
contact with a metal catalyst to form the corresponding
aromatic amine. If cyclohexanone is present, hydrogen is
added initially in an amount at least equivalent to the
amount of cyclohexanone.
Wollensak, U. S. 3,931,298, describes the production
of aromatic amines by the reaction of a phenol with ammonia
in contact with a Group VIII metal catalyst and a promoter
amount of a cyclohexanone.
Other processes for making aromati~c amines are
taught by Ballard, U. S. 2,413,598; Vogt, U. S. 2,013,873;
Groggins, I'Unite Processes in Organic Synthesis," 5th Ed.;
and Houben-Weyl, "Methoden der Organische Chemi," Vol. 11/1,
pp. 117-122.
According to the present process, 2,6-dimethyl
aniline is formed from 2,6-dicyclohexyl amine by reaction
with a hydroxy aromatic at elevated temperatures, in contact
with a palladium catalyst. The 2,6-dimethylcyclohexyl amine
can be initially made by reacting 2,6-dimethylphenol with
hydrogen and ammonia either sequentially or concurrently in
contact with any of a variety of hydrogenation catalysts,
e.g. Ni.
A preferred embodiment o the invention is a pro-
cess for making 2,6-dimethyl aniline, said process comprising
heating a mixture of 1 to 10 mole parts of a 2,6-dimethyl-
cyclohexyl amine and 1 to 10 mole parts of a phenol at a
temperature of about 200 to 400 C. in contact with a palla-
dium catalyst and under sufficient pressure to maintain the
reactants in a liquid phase and recovering said aromatic
amine from the resultant mixture.
The phenol used in the process can be any phenol
.
~ 4 ~
which does not adversely affect the reaction. It is not
necessary that the phenol correspond in structure with the
cyclohexyl amine. The phenol may be unsubstituted or sub-
- stituted with such groups as alkyl, cycloalkyl, aryl, araIkyl,
haol, alkoxy and the like~ Some examples o~ such phenols
are:
phenol
~-cresol
o-cresol
2,6,-dimethylphenol
2,6-diethylphenol
2-methyl-6-isopropylphenol
2,6-diisopropylphenol
2-methyl-6-tert-butylphenol
2,6-di-tert-butylphenol
2-sec-butylphenol
2,6-di-sec-butylphenol
2,4-dimethylphenol
4-sec-octylphenol
2-sec-dodecyl-4-methylphenol
2-sec-eicosylphenol
4-cyclohexylphenol
4-phenylphenol
l-naphthol
2-naphthol
2-(a,a-dimethylbenzyl)phenol
2,6-di-(a-methylbenzyl)phenol
4-(a,a-dimethylbenzyl~phenol
2,4-di-(~,a-dimethylbenzyl)phenol
4-chlorophenol
2,4-dichlorophenol
2,4,6-trichlorophenol
4-bromophenol
2,6-dibromophenol
; 35 4-fluorophenol
4-iodophenol
~. ~
749
2,6-dichlorophenol
4-methyoxyphenol
2-ethyoxyphenol
~-dodecoxyphenol
and the like.
In a more preferred embodiment the phenol corres-
ponds in structure with the cyclohexyl amine. In other
words the preferred phenol is 2,6-dimethylphenol.
The reaction can be carried out by merely mixing
the 2,6-dimethylcyclohexyl amine with the phenol and
heating the mixture at about 200 to 400 C. in contact
with the catalyst. Preferably the palladium is on a
suitable catalyst support such a~s alumina, silica-alumina,
magnesia, zirconia, or the like. The preferred catalyst
support is charcoal. The amount of catalys* can vary over
a wide range. Reaction rate is dependent on the amount
of catalyst used. A useful range is from about 0.0001 to
0.01 mole parts of palladium excludi~g support per mole
part of reaction mixture. A preferred range is 0.0005 to
0.001 mole of palladium per mole of reaction mixture.
The amount of each reactant can vary over a wide
range. A useful range is from about 1 to 10 mole parts
of 2,6-dimethylcyclohexyl amine for each 1 to 10 mole
parts of phenolic reactant. More preferably, the process
is carried out with 1 to 2 mole parts of a 2,6-dimethyl-
cyclohexyl amine for each 1 to 2 mole parts of a phenol.
Most preferably equal mole amounts are used.
The reaction is effected by heating the mixture to
about 200 to 400 C. A more preferred temperature range is
about 225 to 300 C. The reaction is preferably carried
out at autogenous pressure in a closed vessel such as an
11Z~7~9
autoclave to maintain the reactants in the liquid phase.
The reaction is conducted for a time sufficient to convert
a substantial amount of the cyclohexyl amine to aromatic
amine. A useful reaction time is from about 30 minutes to
8 hours. Generally, good results are achieved in about 1
to 4 hours.
The reaction will proceed without the necessity
of adding hydrogen or ammonia to the autoclave. It is
highly preferred that the process be conducted without
adding hydrogen or ammonia. Preferably an inert atmosphere
such as nitrogen is placed over the reactants at the start
of the reaction.
The 2,6-dimethylcyclohexyl amine is believed to
be converted to the corresponding aromatic amine according
15 to the following equation: -
NH2 OH NH2 OH
H3C ~ CH3 ~ 3C` ~ ~ 3
.,
~`:
Some cyclohexanone forms. The aromatic amine can be readi-
ly recovered from the mixture by distillation. When 2,6-
dimethylphenol is used the 2,6-dimethylcyclohexanol and
cyclohexanone (referred to collectively herein as "reduced
` products") which form are not waste products but can be
recycled to the process after being converted to the cor-
responding 2,6-dimethylcyclohexyl amine. This can be
accomplished by known methods such as by reacting the re-
duced products with ammonia in the presence of a dehydration
catalyst such as activated alumina at temperatures of about
200 to 500 C. Alternatively, the reduced products can be
reacted with a mixture of hydrogen and ammonia in thepresence
of a hydrogenation catalyst at about 200 to 500 C. to form
2,6-dimethylcyclohexyl amine. The hydrogenation catalyst
need not be palladium but can be any of the metal catalysts
; , known to catalyze hydrogenation such as the transition
l~LZ~749
metal catalysts, especially the less costly catalysts made
from metals of the First Transition Series, viz., V, Cr, Mn,
Fe, Co, Ni, Cu, and the like. Preferably the hydrogenation
catalyst is a Group VIII metal catalyst. I~hen a metal hy-
drogenation catalyst is used to convert the reduced productsto 2,6-dimethylcyclohexyl amine it is preferably removed
from the cyclohexyl amine product and replaced with the
preferred palladium catalyst for the reaction of the 2,6-
dimethylcyclohexyl amine with the phenol in the manner pre-
viously described.
The method according to which the process is con-
ducted is illustrated by the following examples.
Example 1
In an autoclave was placed 60 grams of a mixture
consisting essentially fo 52 grams of 2,6-dimethylcyclo-
hexyl amine and 8 grams of 2,6-dimethyl aniline. To this
was added 13 grams of 5 percent palladium on charcoal
catalyst and 90 grams of 2,6-dimethylphenol. The autoclave
was sealed and heated to 250 C. and maintained at that
temperature for 2 hours. It was then cooled~and analyzed
by vapor phase chromatography (VPC). It contained 48.5
grams of 2,6-dimethyl aniline, recoverable by distillation.
Barker, U. S. 3,361,818, discloses a process for
converting cyclohexyl amines to anilines by merely heating
25 the cyclohexyl amine to 180 to 500 C. in contact with a
catalyst such as palladium. That process appears to work
well in converting cyclohexyl amine to aniline. However,
; it is not very effective in converting 2,6-dimethylcyclo-
hexylamine to 2,6-dimethylaniline.
Comparative tests were conducted which show the
significant effect of the phenol on the reaction of 2,6-
dimethylcyclohexylamine in contact with a palladium catalyst.
The first test was conducted by heating 2,6-dimethylcyclo-
hexylamine in contact with a palladium catalyst without
adding a phenol. The following example describes this
test.
112474~
Example 2
In an autoclave was placed 87 grams of 2,6-dimethyl-
cyclohexylamine and 14.6 grams of wet 5 percent Pd on char-
coal. The autoclave was flushed with hdyrogen. It was then
pressurized with hydrogen to 1,000 psig ~70.3 kg.'/sq. cm.) and
heated to 50 C. as a standard method of activatLng the Pd catalyst. The
autoclave was cooled and vented and 18 grams of ammonia was
added. It was sealed. and heated to 300 C. considered the
"start" of the reaction. It was necessary to vent 8 grams
of ammonia to keep the pressure within the limit of the
autoclave. The autoclave was maintained at 300 C. for
three hours with samples taken at the start and hourly. The
sampels analyzed as follows:
Area Percent VPC Analysis of Reaction Mixture
, . _
~5 ~ 2,6-dimethyl-
A B C D E aniline
initial 6.2 1.9 - 88.5 - 1.0
"start" 3.3 1.8 - 74.3 ~0.04 9.0
1 hour - 10.6 1.570.4 0.3 15.3
2 hours - 18.8 1.960.3 0.2 17.8
3 hours - 24.1 3.051.7 0.5 20.0
A = water; B = 2,6-dimethylcyclohexane; C = m-xylene;
D = 2,6-dimethylcyclohexylamine; E = 2,6-dimethylphenol.
In this experiment carried out without adding 2,6-
dimethylphenol, the formation of 2,6-dimethylaniline was
very slow. The major products after three hours were (B)
2,6-dimethylcyclohexane and (C) m-xylene.
The following example shows the effect of including
2,6-dimethylphenol in the above reaction.
Example 3
In an autoclave was placed 40 grams of 2,6-di-
methylcyclohexylamine, 38.5 grams 2,6-dimethylphenol and
13.4 grams wet 5 percent Pd on charcoal. The autoclave was
flushed with hydrogen and then pressurized with hydrogen to
1,000 psig (70.3 kg./sq. cm.) and heated to 50 ~. to
r,
112~74~
activate the catalyst. The autoclave was cooled and vented
and 9 grams of ammonia added. The autoclave was heated to
300 C., which was considered the "start" of the reaction.
Samples were taken at the start and hourly for VPC analysis.
The following table shows the results of the above reaction:
'
.
112-~749
~^
~o
~ rl
a~ ~ oo ~ D
~. . . . .
.,, ~ o ~ oo ~ oo
ra ~ U~ U~
a~
~ ~ .
X
~D
o ~ o o o o 11
~ ...
a) Oo ~ ~ u~ Q)
o .. ..
4~ o ~
o
C~
~ ~ ~ o X
~o ~o
~J ~ ~ C`J ~o
3 ~,
~, ~ ~ O 0
,. P
. ~, ~ .....
h c~
C~
~ , C~ ~ U~ ~ 11
Sl ~O
¢
~ C`~ ~ . _
FqIOOOOO
~ O
~1
I r~ -
¢ .
~ c~ ll
~- ~
a~ ~
h ~ td td
O O O ~
,,
, ':
'~ , ' ,':
,
li;i: ~749
The above results show that when the same reaction
as in Example 2 is carried out in the presence of 2,6-di-
methylphenol, the 2,6-dimethylaniline forms very rapidly
giving a reaction mixture analyzing over 50 percent 2,6-
dimethylaniline.
