Note: Descriptions are shown in the official language in which they were submitted.
'7
.~
HOECHST AXTIENGESELLSCHAFT HOE 89/F 912 Dr.GL-nu
Werk Gendorf
Process for reducing the content of primary and secondary
amine in a tertiary amine
Description
The inven~ion relates to a process for reduaing the
content of primary and ~econdary amine in a tertiary
amine.
As is known, tertiary amines in general contain a larger
1~ or smaller amount of primary and secondary amine bscause
of their method of preparation. ~his particularly applies
to those tertiary amine products which have been prepared
by the very frequently used aminolysis process, tha~ is
to say by reaction of secondary amines with alcohols as
alkylating agents in the presence of dehydroge-
nation/hydrogenation catalysts, compare U.S. Patent
4,I38,437, in particular Example l, lines 46 to 48, and
British Patent 1,585,480, in particular column 1, lines
:~ :
54 to 59. ~he tertiary amine obtained by this process,
which is advantageous per se, as a rule has a content of
primary and/or secondary amine of up to about 2 parts by
weight in total per 100 parts ~y weight of tertiary
~` amine, the secondary amine representing the main pro-
portion in comparison with the primary amine (there are
usually mere}y traces of the primary amine). However,
precisely the secondary amines are a particularly unde-
sirable impurity, because nitrosamines are known to be
able to form from these amines. The~primary and secondary
amines, in particular in the form of the so-called
methylalkylæmines, often cannot be separated by distil-
lation because of the }ow difference in boiling point.
This particularly applies if the products are so-called
chain blends ~which is as a rule the case) in which the
boiling points of the mono- and dimethylalkylamines even
overlap.
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The object of the invention accordingly is to provide a
process with which a substantial to complete reduction in
the amount of impurities in question is possible, ~o that
a tertiary smine which is practically free from prLmary
and secondary amines can be achieved. It should further-
more be possible to carry out the novel proces~ easily
and with li~tle expenditure.
The process according to the in~ention for reducing the
content of primary and secondlary amine in a tertiary
amine comprises the tertiary amine to be treated bringing
into contact with an organic anhydride until the reduc-
tion sought in the content of primary and secondary amine
is achieved.
The chemical reaction on which the purification process -
according to the invention is based probably proceeds in
accordance with the equations below. The equations
contain acetic anhydride, succinic anhydride and phthalic
~; anhydride as the organic anhydride and dodecylamine and
methyldodecylamine as the primary and secondary amine
(that is to say the amines to be reacted):
,'.
~` CH3-CO O O
;~ ~ o + H2NC12H25 > CH3-C + CH3-C
CH3-CO OH NHC12H25 ~ `
.
CH3-CO CH3 // //
O ~ HN , j -~ CH3-C ~ CH3-C~
CH3-CO C12H25 OH N-CH3
cl2H25 .
O
CH2-CO CH2-C-OH
O + H2Ncl2H25 >
CH2 -c-NHcl2H2 5
CH2-CO \\
-- 3 --
// '
CH2-C ~CH3 1 2-C-OH
O + HN > O
2_~_/ C12H2S ~ :H,2-C-N-CH3
C12~I25 ::
+ NzNC12N25 ~ I~C-NHC12H25
~ O
~CO ~N3 C-OH
co C12H2 5 ~C-N-CH3
12H25 .
As the equations show, acid and acid amide or amide acid
(likewise called acid-amide below) are formed from the
undesirable primary and secondary amine and the anhydride -~
employed. The components now present in the tertiary
~ 5 amine, that is to say acid and~or acid amide, either can
-~ be removed, for example in the context of a distillation,
, or can remain in the tertiary amine since they result in -~
no noticeable disadvantages, which applies in particular `
to the acid amide.
Because of the high reactivity of the anhydrides, the
reaction according to the invention often also already
proceeds at low temperatures, so that merely brinqing the
tertiary amine to be treated into contact with the
anhydride alr~eady produces the conversion sought. On the
other hand, higher temperatures can also be used. A ~
:`
:
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higher temperature i8 appropriate if the tertiary amine
product to be ~reated has a relatively high melting point
and/or if a particularly short reaction time i~ desired.
The process according to the invention i6 accordingly as
a rule carried out at a temperature of 20 to 200C,
preferably at a temperature of 50 to 150~C. The reaction
tLme, which is the time required fox reaction o~ the
anhydride with the primary and/or secondary 2~mine, i8 as
a rule 0.3 to 3 hours. It clearly depends in particular
on the reaction temperature and on the degree of reaction
sought.
As regards the amount of anhydride, it has proved advan-
tageous to employ this in at least the equimolar ratio to
the primary and/or secondary amine present. ~he amount of
anhydride is thus preferably 1 to 2 mol, and in par-
ticular 1.05 to 1.5 mol, per mol of amine to be reacted.
; The amount of primary and secondary amine in the tertiary
amine to be treated can be determined, for example, from
the known reaction of the tertiary 2~nine product with
carbon disulfide and titration of the thioacids formed
from the primary and secondary amine.
: . .
The nature of the organic anhydrides to be employed
; according to the invention is not in itself critical. It
goes without saying that an anhydride which suits the
tertiary amine to be treated will be employed. Possible
anhydrides are thus aliphatic, cycloaliphatic or aromatic
acid anhydrides. The preferred acid anhydrides are those
of the following formula
Rl-CO
\
O
R2-CO
in which Rl and R2 are an alkyl radical having 1 to 18
carbon atoms, preferably 2 to 4 carbon atoms, or an
alkenyl radical having 2 to 18 carbon atoms, preferably
2 to 4 carbon atoms, or R1 and R2 together are an alkylene
s~
~2~ 7
radical having 1 to 10 carbon atoms, preferably 2 to 4
carbon atoms, which can also contain double bonds, or an
optionally substituted ortho-phenylene radical. Preferred
acid anhydrides are thus those of monocarboxylia acids,
preferably saturated (that is to say R1 and R2 are identi-
cal and are the alXyl radical mentioned), such as acetic
anhydride, propionic anhydride, butyric anhydride and the
like, and furthermore those of saturated or unsaturated
dicarboxylic acids (that is to say R1 and R2 together are
the divalent radical mentioned), such as malonic anhy-
dride, succinic anhydride, adipic anhydride, maleic
anhydride and the like, and phthalic anhydride. Par-
ticularly preferred acid anhydrides are, especially for
practica- reasons, acetic anhydride and phthalic anhy-
dride.
According to a preferred embodiment, the process accor-
ding to the invention is carried out by adding the acid
anhydride in at least the stoichiometric (equimolar)
amount, based on the primary and secondary amine present
(compare above equations), preferably in an amount of 1
to 2 mol, in particular l.OS to 1.5 mol, per mol of
primary and secondary amine, to the tertiary amine to be
treated, heating the mixture to a temperature of 20 to
200C, preferably 50 to 150C, while stirring, and
keeping the mixture at this temperature, likewise while
stirring, until the primary and secondary amine pre~ent
has reached the lower limit value sought or has been
converted completely. The reaction can be carried out
under normal pressure or under pressure. Removal of
excess acid anhydride and the components formed, that is
to say acid and acid amide, can be achieved, if desired,
for example, by distillation. The acid and acid anhydride
can also be separated off from the tertiary amine, for
example, by treating the reaction mixture with alkali
(solid or in the form of an aqueous solution) to convert
the acid and acid anhydride into the corresponding alkali
metal salts. The tertiary amine can now be obtained
without problems as the distillate from the mixture now
- 6 2~2~7
-
present, whereas the metal salts mentioned remain in the
bottom product. As already mentioned above, as a rule the
acid amide present results in no particular disadvantages
in the tertiary amine.
The tertiary amines in ~he context of the present inven-
tion are prefexably those of the following formula
R4
R3-N/
R5
in which R3 is an alkyl radical or an alkenyl radical
having 6 to 24 carbon atoms, preferably 8 to 22 carbon
atoms, and R4 and R5, which are preferably identical, are
an alkyl~radical having 1 to 4 carbon atoms, preferably
the methyl radical. Examples which may be mentioned for
R3 are octyl, dodecyl, tetradecyl, stearyl, oleyl, tallow
fat alkyl and coconut alkyl.
. :
The abovementioned aminolysis is also shown in the form
of an e~uation below, dodecyl alcohol (lauryl alcohol)
functioning as the alcohol and dimethylamine as the
amine:
` :
CH3 CH3
Cl2H2s-oH + H-N > C12H25-N + H2O
CH3 CH3
In addition to thisl main reaction, as is ~known a dig-
proportionation of the dimethylamine into, inter alia,
monomethylamine, which forms the secondary amine methyl-
dodecylamine with the alcohol present, takes place. The
undesirable slecondary amines in question accordingly in
general correspond to the formula R3-NH-R4, in which R3
and R4 have the meanings given.
The process according to the invention has a number of
2~3~
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advantages. It is a simple method which requires little
expenditure for partial to complete elimination of
primary and secondary amine in a ter~iary amine, it being
possible for a tertiary amine which is practically free
from the impurities mentioned to be obtained without
problems. The reagent used in the process according to
the invention, tha~ i8 to ~ay the acid anhydride, is in
general readily obtainable and highly reactive. A com-
plete conversion can in this way already be achieved
under relatively mild reaction conditions. The conversion
products formed in the reaction, if they are troublesome
at all, can as a rule be removed without problems, so
that a tertiary amine which is not only free from primary
and secondary amines but also free from other compounds
and therefore completely pure can be achieved.
The invention will now be illustrated in more detail by
examples.
Example 1
100 g of tertiary amine are to be treated, of the formula
Cl214-N(CH3)2, which contained 1.8 g (0.008 mol) of secon-
dary amine of the formula Cl2l4-NH-CH3, were introduced
into a reaction vessel equipped with a stirrer, reflux
condenser and thermometer, and 0.83 g (0.008 mol) of
acetic anh~dride was added. The mixture was heated to
100C, while stirring, and kept at this temperature for
1 hour. After the reaction mixture has been cooled, the
content of secondary amine was determined. It was only
0.3 parts by weight in 100 parts by weight of tertiary
amine.
Examples 2 to 8
These examples were carried out analogously to Example 1.
The tertiary amines to be treated (these are dimethyl-
alkylamines, as in Example 1) and their content of
secondary amine, the aci~ anhydride employed, the molar
J u~ ~ ~t3 ~
ratio of acid anhydride to secondary amine, the reaction
temperature, the reaction time and the reduction achieved
in the content of secondary amine are summarized in the
following table, which also contains Example 1 for
simplicity. The following is al~;o mentioned regarding the
table, by way of explanation: the alkyl radical of the
dimethylalkylamine is shown in column 2 and the values in
respect of the content of secondary amine in the third
and last column are percentages by weight, based on the
tertiary amine to be treated (crude amine).
As regards the examples, it should also be stated that in
those where phthalic anhydride is used as the reagent for
the secondary amine, the excess phthalic anhydride and
the phthalamido acid formed can be removed simply by
distillation of the reaction mixture, the phthalic
anhydride and the phthalamido acid remaining in the
bottom product, because of the boiling point differences,
whilst the top product is the pure tertiary amine sought.
In examples where acetic anhydride is used, the excess
anhydride and the acetic acid formed are removed in the
following manner: a 30~ strength by weight methanolic
sodium methylate solution was added to the reaction
mixture so that an amount of sodium methylate which
corresponds to the molar amount of acetic acid and acetic
anhydride present was introduced, after which the mixture
was stirred at 70C for 0.25 hours for complete conver-
sion of the acetic acid and acetic anhydride into the
corresponding sodium salts. Vacuum distillation gave the
(acetamide-containing) tertiary amine as the top product,
whilst the sodium salts mentioned remained in the bottom
product.
2~2~7
. _.
~ ,o,o,,,~
~'o-~O=
..._
'~U 0r~o
. . _
~ ,o ~ ~
~rl ~ ~ 11~ N _I ~ In U~ O ~:
~ W O ~
'1:) 'C1 ~ 'Cl h h h h
a
~:~ CO~ ~ ooo
._ . ~ .. . . ..
.~ ~ u u u u 5 u u
_ _ ._
E~ ~ ~ ~:
: . .
