Note: Descriptions are shown in the official language in which they were submitted.
~o537a3 -Z- 29,814
PROCESS FOR WORKING UP NITRATION MIXTURES
This invention relates to a process for working up reaction
mixtures obtained by nitration of aliphatic or cycloaliphatic ketones
with at least 95% w/w nitric acid in the presence o~ an inert organic
solvent.
The nitration of ketones with highly concentrated nitric acid
in inert organic solvents is highly advantageous. One advantage is
that the startin~ materlals are readily available, and another is
that by-products are not formed in stoichiometric amounts as in
other processes for the preparation of a-nitroketones. Doubly
nitrated ketones are not formed. Furthermore, such nitration may be
carried out continuously.
Suitable aliphatic or cycloaliphatic ketones are for example
acetone, butanone-2, pentanone-3, methyl isobutyl ketone and cyclo-
aliphatic ketones such as cyclopentanone, cycloheptanone, cyclo-
octanone, cyclodecanone and cyclododecanone and in particular cyclo-
hexanoneO If desired, nitratlon may be carried out in the presence
of the alcohols corresponding to the ketonesO Specific mention may
be made of the nitration of cyclohexanone/cyclohexanol mixtures.
Particularly suitable inert solvents are halogenated aliphatic
hydrocarbons, particularly CCl4, CCl3F and CCl3Br. Alternatively,
nitration may be carried out in the presence of other solvents which
are inert under the conditions o~ the reaction and which may be
polar solvents, for example nitro(cyclo)alkanes such as nitromethane
and nitrocyclohexane, nitroaromatics such as nitrobenzene, halogenated
aromatics such as chlorobenzene and o-dichlorobenzeneJ open-chain
or cyclic sulfones such as dimethylsulfone and diethylsulfone and
q~
10537C~3
and substituted tetrahydrothiophen~-l,l dioxlde, and other polar
solvents reslstant to HN0~ e.g. dimethoxyethane and cyclic ethers
such as dioxane and tetrahydrofuran, (cyclo)aliphatic hydrocarbons
such as pentane, hexane and cyclohexane, and also mixtures o~ these
solvents with the halohydrocarbons. The addition of lower hydro-
carbons such as pentane and hexane can racilitate isolation of the
resulting a-nitroketone from the reaction mixture.
The ratio of ketone to halohydrocarbon to be added is not fixed,
but in general the ratio by weight of halohydrocarbon to ketone is
rrom 100:1 to 1:10. The ratio of the solvents which are inert under
the conditions of the reaction to the halohydrocarbon may be from
10:1 to 1:10, although other ratios are possible.
The water content Or the nitric acid used for nitration is
generally less than 5~ and pre~erably less than 2% and more prefer-
ably less than 0.5%, by welght. The molar ratio of nitric acid to
ketone is generally about 1:1. In some cases it is desirable, to
accelerate the reaction, to use a stoichiometric excess of nitrlc
acid of for example 25% or in particular Or 50%, by weight.
Nitration should be carried out at a temperature of not more
than 90C and advantageously at below 50C. In the case of less
reactive ketones, particularly less reactive cyclic ketones, it may
be necessary to raise the reaction temperature to up to 70 C.
A suitable method of nitrating ketones to a-nitroketones with
substantially anhydrous nitric acid is described for example in
Canadian patent No. 996,57g.
It is an ob~ect of the invention to obviate the retention of
relatively large amounts o~ nitric acid in the organic solvent during
working up and at the same time to separate the unconverted nitric
acid in such a manner that it may be simply reconverted to anhydrous
~0 nitric acid. These objects are achieved by the present invention.
The invention relates to a process for working up a reaction
mixture obtained by nitration of aliphatic or cycloaliphatic ketones
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~537~3 . z. 29,814
in the presence or absence of the corresponding alcohols, wlth at
least 95% w/w nitric acid ln the presence of an inert organic sol-
vent for the organic compounds, wherein there is added to the reac-
tion mixture a nitric acid of a concentration such that the reaction
mixture contains 40~80% nitric acid prior to separation of the
organic phase.
It has been found that the concentration of nitric acid does
not fall sufficiently during nitration to make working up directly
possible, even though nitric acid is consumed in the reaction and
one mole equivalent of water is formed~ This is due to the fact that
under the condltlons stated, nitration is advantageously carried to
conversions of from 10 to 50% whilst giving high yields of a-nitro-
ketoneO When water-binding agents are used during nitration, the con-
centration of nitric acid drops even less of course.
The nitric acid to be added to the reaction mixture following
nitration generally has a strength of from 40 to 70~ and in particu-
lar of from 60 to 70%~ The amount and concentration of the nitric
acid required to dilute the reaction mixture may be determined by
simple experiment or by calculation~ It is an advantage when the
nitric acid contained in the reaction mixture ~ust prior to separation
of the organic phase has a concentration within the azeotropic ran~e,
i.e. a concentration of more than 68~ by weight.
The coefficient of partition of nitric acid between organic
and aqueous phases increases steeply with concentration. For example,
in the case of carbon tetrachloride and 25C it is 0.002 for 68% w/w
acid but 0.03 for anhydrous acid. Thus if working-up were carried
out in the presence of highly concentrated nitric acid, a certain
amount of the acid would remain in the organic phase.
Working up is advantageously carried out at a temperature of
less than 50C. To achieve good separation, it is recommended that
temperatures of between 0 and 30C be used, since the aforementioned
partition coefficient rises with temperature.
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~oS37~3 oO zo 29,814
Following the removal of unconverted nitric acid from the
organic phase by distillation in a solvent, the organic phase may
be separated into unconverted ketone and 2-nitroketone. In the case
of 2-nitrocyclohexanone, which serves as an intermediate in the
synthesis of ~-caprolactam, the distillation of the nitroketone may
be omitted.
If ammonia is passed through the organic phase at a temperature
of from -10 to 20C, the solid ammonium salt of nitrocyclohexanone
may be separated and then converted to ~-nitrocapronamide by heating
in organic solvents such as benzene or toluene, chlorinated hydro-
carbons such as chloroform or carbon tetrachloride or branched
alcohols such as t-butanol, or it may be hydrogenated to a-amino-
capronamide in ammoniacal medium. If the ammonia is passed through
at temperatures above 20C, in particular temperatures between 20C
and the bolling point of the solvent, ~-nitrocapronamide is isolated,
this being quantltatively precipitated from, say, carbon tetra-
chloride.
It has been found advantageous, after the addition Or nitric
acid and separation of the aqueous phase, to extract the latter once
or a number of times with a solvent, conveniently the same solvent
as that used in the nitration, in order to remove and, if desired,
recover organic materialO
It has also been found highly convenient to add magnesium nitrate
to the reaction m~xture following nitration, in order to diminish
further the residual concentration of organic material in the aqueous
nitric acid phase. Thls salt addition may be effected separately from,
or together with, the addition of nitric acid.
The process of the invention is distinguished by the fact that
working up of the nitric acid for re-use in the nitration reaction,
~0 if desired, is greatly facllitated. In general, the nitric acid is
further concentrated by treatment with sulfuric acid or the addition
of magneslum nitrate.
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10S3703 o o z . 29, 814
If, in working up according to the process of the invention,
dilution is effected such that a nitric acid concentration of only
68~ by weight or above is achieved, i,eO the azeotropic concentra-
tion, concentration of the acid to 100% is a very simple matter.
The above ad~ustment of the nitric acid concentration in the
reaction mixture prior to working up ensures that the proportion of
nitric acid in the organic phase is reducedO This means that when
the organic phase is worked up, the proportion of oxidation products,
e.gO adipic acid, which are otherwise formed in the reaction mixture
consisting of cyclohexanone and nitric acid is diminished to an
acceptable level.
In the following Examples the parts and percentages are by
weight O
EXAMPLE 1
In a 1 liter three-neck flask equipped with mechanical stirrer,
reflux condenser and dropping funnel, a well-stirred mixture of
640 parts of carbon tetrachloride and 21.6 parts of 100% nitric acid
is mixed with 25 parts of cyclohexanone added at ~0 + 1C over
6 minutes. The mixture is stirred for a further 15 minutes and then
cooled to O-5C, whereupon ~5 parts of 68~ nitric acid are added,
so that the aqueous phase contains 77% nitric acidO After a brief
period of stirring, the phases are separated~ The aqueous phase is
shaken three times with lOO parts of carbon tetrachloride each time.
The organic phase is found to contain, in addition to unreacted
cyclohexanone, 702 parts of 2-nitrocyclohexanone containing less
than 1.5~ of impuritiesO
EXAMPLE 2
Nitration is carried out as described in Example 1, after which
30 parts of 68~ nitric acid saturated with magnesium sulfate are
added to the reaction mixture. The phases are separated and the
organic phase is shaken wlth ~0 parts of water and is then found by
~0 gas-chromatographic analysis to contain 6.8 parts of 2-nitrocyclo-
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1053703 o . z. 29,814
hexanone containing less than 2~ of impurities.
For the purpose of isolating the 2~nitrocyclohexanone in the
form of -nitrocapronamideJ ammonia is passed through the organic
phase at 0C for 30 minutesO The precipitated solid ammonium salt
of nitrocyclohexanone is filtered off, suspended in isopropanol
and heated under reflux for 60 minutesO The reaction mixture is
then cooled and solld product ls filtered off and dried to give
7.15 parts of c-nitrocapronamide having a melting point of 108C.
The mixed melting point with an authentic sample shows no depression.
