Note: Descriptions are shown in the official language in which they were submitted.
BASF Aktiengesellschaft 930746 O.Z. 0050/44982
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Preparation of cyclic lactams
The present invention relates to a process for the preparation of
cyclic lactams by reacting an aminocarboxylic acid compound of
the general formula I
HaN - (CH2)m - COR1 I
where R1 is -OH, -0-C1-Clz-alkyl or -NRZR3 and Ra and R3, indepen-
dently of one another, are each hydrogen, Cl-Ci2-alkyl or r
C5-Cg-cycloalkyl and m is an integer from 3 to 12,
with water.
US 3,485,821 relates to the uncatalyzed conversion of amino-
caproic acid, aminocaproamide and alkyl-substituted derivatives
thereof into caprolactam or alkyl-substituted caprolactam by
carrying out the reaction in water at from 150 to 350°C, it being .
possible to add ammonium salts to the water. However, the convey- _.,
sions to caprolactam are not higher than 90
DE-A 2,535,689 describes a process for the preparation of capro
lactam by converting 6-aminocaproic acid dissolved in methanol or
ethanol, the solvent having an alcohol content of at least60 ~-
by volume and the reaction being carried out at from 170 to 200°C.
According to DE-A 2,535,689, higher temperatures, in particular
220°C or higher, lead to the increased formation of the comes-
ponding alkyl ester of 6-aminocaproic acid, which finally results
in increased oliqomer formation. According to this document,
water contents above 40 ~ by volume should lead to the formation. -
of open-chain polyamides. For commercial use, the addition of the
6-aminocaproic acid is a considerable disadvantage since the
aminocaproic acid should be completely dissolved before it is
converted into caprolactam, and hence 6-aminocaproic acid must be
constantly added-and its consumption monitored.
Ind. Eng. Chem. Process Des. Dev. ~(1) (1978), 9-16 (Mares et
al.) describes the conversion of 6-.aminocaproic acid, both in
water and in ethanol, into caprolactam without the addition of a
catalyst. The yield of caprolactam in water at a reaction
temperature of 211°C is only 65 ~, while yields of up to 98 ~ are _
said to be achievable in pure ethanol- Eiowever, the yields of
92 ~ or higher described by Mares et al. could not be_ repeated in
our own experiments. Rather, these high yields can be explained-
only by the fact that Mares et al. did not use a 10 ~ strength by
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weight solution of 6-aminocaproic acid but cyclized minimum -
6-aminocaproic acid concentrations to give caprolactam by contin-
uous addition of 6-aminocaproic acid to the ethanolic solution. -
Since caprolactam is-stable under the chosen reaction conditions,
it was possible to obtain the high yields (92 ~ and 98 ~) only by
virtue.of the fact that the concentration of caprolactam in-
creased during the reaction. This assumption is supported by
US 2,535,689 (with Mares as coinventor). Example 1 of this U.S.
patent indicates that a reaction of the 6-aminocaproic acid is to
be prevented before the 6-aminocaproic acid has completely dis- -_
solved. For this purpose, the 6-aminocaproic acid should be added- -
so slowly that no solid acid is present in the solvent but the
6-aminocaproic acid is dispersed virtually immediately in the hot
solvent and is completely dissolved or is dispersed during heat-
ing. Since the maximum solubility of 6-aminocaproic acid in both
cold and boiling ethanol (78°C) is only 1.3 g/I (= 0.13 ~ by
weight), it is clear that, in Mares et al.., 6-aminocaproic acid
could be added only gradually in order to obtain a solution
which, purely theoretically, contained 10 ~ by weight of 6-amino-
caproic acid. Otherwise, the technicalprocedure for such meter-
ing at 200°C and 80 bar entails very great difficulties as wellas __.
._
a long time.
In Mares et al. (Ind. Eng. Chem. Process Des. Dev. 1~(1) (1978), .
9-16), the conversion of ethyl 6-aminocaproate in ethanol into
caprolactam is also investigated. It is found that quantitative
cyclization is possible only at low temperatures and at high
dilution. According to Mares et al., in particular a caprolactam
yield of only 90 ~ is achievable from ethyl 6-aminocaproate at
200°C and in a reaction time of 10 hours. According to Mares et
al., the yield can be increased to not more than 95 ~ at 150°C,
but reaction times of 10 hours_or more are out of the question
for commercial use.
Mares et al. likewise describe the conversion of ethyl 6-amino- -
caproate in water into caprolactam at 200°C and in a reaction time
of five hours with a yield of not more than 62.5 ~. In the same -
publication, the conversion of 6-aminocaproamide into capro-
lactam, both in water and in ethanol, is investigated, and yields
of not more than 71 ~ in a reaction time of more than 70 minutes
can be obtained.
Tetrahedron Lett. ~, (1980), 2443 describes the cyclization of -
6-aminocaproic acid as a suspension in toluene in the presence of
alumina or silica gel with removal of the water of reaction. For
complete desorption of the caprolactam, the catalyst must be
washed with methylene chloride/methanol and polymers must be
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precipitated with diethyl ether. The yield of caprolactam is 82 ~
over alumina and 75 ~ over silica gel, but the reaction time is
20 hours in each case.
EP-A 271 815 describes the cyclization of 6-aminocaproates to _ _
give caprolactam, the esters being dissolved. in an aromatic
hydrocarbon and then cyclized at from 100 to 320°C with simulta- __
neous removal of the alcohol formed.
Disadvantages are the separation of the alcohol under super-
atmospheric pressure as well as the aromatic hydrocarbons, which
are expensive to remove since they are high-boiling, and the long
reaction times, for example 14 hours when the reaction is carried
out in o-xylene (140°C).
EP-A 376 122 describes the cyclization of 6-aminocaproates in the
presence of an aromatic hydrocarbon and water at from 230 to 350°C
to give caprolactam.
It is an object of the present invention to provide a process for
the preparation of cyclic lactams by reacting an aminocarboxylic
acid compound of the general formula I -
H2N - (CH3)m - COR1 I
where R1 is -OH, -O-C1-CZZ-alkyl-or -NRaR3-and Rz and R3, indepen-
dently of one another, are each hydrogen, C1-C1a-alkyl or
CS-C$-cycloalkyl and m is an integer from 3 to 12, with water,
which process does not have the disadvantages described above. _
We have found that this object is achieved by an improved process-
for the preparation of cyclic lactams by reacting an amino-
carboxylic acid compound of the general formula 1
H2N - (CH2)m - COR1 I
where RI is -OH, -0-C1-C12-alkyl or -NR~R3 and R2 and R3, indepen-
dently of one another, are each hydrogen, C1-Ciz-alkyl or -
CS-C8-cycloalkyl and m is an integer from 3 to 12, with water by
carrying out the reaction in the liquid phase using a hetero-
geneous catalyst.
The starting materials used in the novel process are amino-
carboxylic acid compounds, preferably those of the general
formula I
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HZN - (CH2)m - COR1 I
where R1 is -OH, -0-C1-Clz-alkyl or -NRZR3 and Rz and R3, indepen-
dently of one another, are each hydrogen, C1-C12-alkyl or
CS-Ca-cycloalkyl and m is 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. -
If the preferred starting compounds are those in which R1 is -OH
or -0-C1-C4-alkyl, such as -0-methyl, -0-ethyl, -O-n-propyl,
-0-isopropyl, -0-n-butyl, -0-sec-butyl, -0-tert-butyl or -0-iso-.
butyl, -NR2R3 is -NHa, -NHMe, -NHEt, -NMe1 or -NEtz and m is 5. _
6-Aminocaproic acid, methyl 6-aminocaproate, ethyl 6-amino-
caproate, 6-amino-N-methylcaproamide, 6-amino-N,N-dimethylcapro- - _
amide, 6-amino-N-ethylcaproamide, 6-amino-N,N-diethylcaproamide
and 6-aminocaproamide are very particularly preferred.
The starting compounds are commercially available or can be pre-
pared, for example, according to EP 234,295 and Ind. Eng. Chem.
Pracess Des.Dev. ~ (1978), 9-16.
In the novel process, the aminocarboxylic acid compounds
described above are reacted with water in the liquid phase using
a heterogeneous catalyst to give cyclic lactams. Whenamino- _.._ ._ -_
carboxylic acid compounds of the general formula I are used, the __>
corresponding cyclic lactams of the general formula II
(CHI ) n
I I
H-N - CO
where m has the abovementioned meanings, are obtained. Particu-
larly preferred lactams are those in which m is 4, 5 or 6, in
particular 5 (in the latter case, caprolactamis obtained). The __
reaction is carried out in the liquid phaseat in general from
140 to 320°C, preferably from 160 to 300°C; the pressure is
usual-
ly chosen to be from 0.5 to 25 MPa, but so that the reaction mix- ___
ture is liquid under the conditions used. The residence times are
as a rule from 5 to 120, preferably from 10 to 60, minutes.
Advantageously, the aminocarboxylic acid compound is used in the
form of a 1 - 50, preferably 5 - 50, particularly preferably 5 -
25, ~ strength by weight solution in water or in a water/solvent
mixture_ Examples of solvents aze alkanols, in particular
C1-C4-alkanols, such as methanol, ethanol, n-propanol, iso-
propanol, n-butanol, isobutanol, sec-butanol and tert-butanol,
BASF Aktienqesellschaft 930746 O.Z. 0050/44982 -
polyols, such as diethylene glycol and tetraethylene glycol,
lactams, such as pyrrolidone, caprolactam and alkyl-substituted
lactams, in particular N-CI-C~-alkyllactams, such as N-methyl-
pyrrolidone, N-methylcaprolactam or N-ethylcaprolactam. Ammonia,
5 too, may be present in the reaction. Mixtures of organic solvents
may of course also be used.
Heterogeneous catalysts which may be used are, for example:
acidic, basic or amphoteric oxides of the elements of the second,
third or fourth main group of the Periodic Table, such as boron
oxide, alumina or silica as silica-gel, kieselguhr, quartz or
mixtures thereof, and oxides of metals of the second to sixth
subgroups of the Periodic Table, such as titanium dioxide as
anatase or rutile, zirconium oxide or mixtures thereof. Oxides of -
the lanthanides or actinides, such as lanthanum oxide, cerium
oxide, thorium oxide, praseodymium oxide or neodymium oxide, or -
mixtures thereof with abovementioned oxides may also be used.
Further catalysts may be, for example:
vanadium oxide, niobium oxide, iron oxide, chromium oxide, molyb-
denum oxide, tungsten oxide and mixtures thereof_ Mixtures of
these oxides with one another are also possible.
The abovementioned oxides may be doped with compounds of main
groups I and VII of the Periodic Table or may contain these.
Zeolites, phosphates and heteropoly acids and acidic and alkaline
ion exchangers, for example Naphion~', are also examples of suit-
able catalysts.
If required, these catalysts may contain up to 50 ~ by weight in
each case of copper, tin, zinc, manganese, iron, cobalt, nickel,
ruthenium, palladium, platinum, silver or rhodium.
The amount of catalyst depends as a rule on the procedure: in a
batchwise procedure, the amount of catalyst is chosen to be from
0.1 to 50, preferably from 1 to 30, ~ by weight, based on the
aminocarboxylic acid compound of the general formula I;-in the
continuous procedure, the catalyst space velocity is chosen to be
from 0.1 to 5 kg per 1 per h, based on the aminocarboxylic acid
compound of the general formula I.
In the novel process, cyclic lactams, in particular caprolactam,
are obtained in high yield.
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Examples
Example 1
5 A solution of 6-aminocaproic acid in water was passed, at
100 bar, into a heated tube reactor which had a capacity of
100 ml, diameter of 9 mm and a length of 400 mm and was filled
with titanium dioxide (anatase) in the form of 1.5 mm extrudates.
The product stream leaving the reactor was analyzed by gas
10 chromatography and high-pressure liquid chromatography (HPLC).
AminocarboxylicWater Temperature Residence Yield
acid [$] [~C] time
[min]
15
10 90 220 15 66
10 I 90 I 220 I 30 I 76
Example 2
Similarly to the experiments described in Example 1, a solution
of aminocaproic acid in ethanol/water was pumped through a tube
reactor filled with titanium oxide extrudates.
AminocarboxylicWater Ethanol Temperature Residence Yield
acid [~] [~] (~C] time
[~]
[min]
10 40 50 220 15 98
10 40 50 220 30 90
Example 3
Similarly to the experiments described in Example 1, a solution
of ethyl aminocaproate in ethanol, in the presence of water, was
pumped through a tube reactor filled with titanium oxide extru-
dates.
Ethyl Water EthanolTemper- Residence Conver- Selec- Yield
amino- [~] f~] ature time sion tivity
caproate [~C] [min]
[~l
10 1.1 88.9 220 15 97 93 90
10 1.1 88.9 220 30 97 85 83
10 1.1 88.9 220 60 100 79 79
10 4.4 85.6 220 30 97 95 92
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Comparative example
In each case a 10 ~ strength by weight solution of 6-aminocaproic
acid in ethanol was heated to 200°C during different residence
times, according to Ind. Eng. Chem. Process Des. Dev. ,y2 (1978),
16. The results are listed in the table below.
Residence Temperature Conversion Selectivity Yield of
time [~C] [~] ['k] caprolactam
[min] _
10 200 90 80 72
200 87 93 80
200' 90 90 81
15 30 200 90 91 82
40 200 91 88 80
Yields
above
82
~
were
not
obtained.
25
35
45
