Note: Descriptions are shown in the official language in which they were submitted.
1168262
TITLE
Treatment Of Dibasic Esters With Alkali Metal
Borohydrides, Permanganates Or Methylates
BACKGROUND OF THE INVENTION
-
Field of the Invention
The present invention relates to reducing
the color forming tendencies of c~rtain esters and,
more particularly, to the treatment of esters with an
alkali metal borohydride in the presence of water, an
alkali metal permanganate in the presence of water
and/or an alkali metal methylate.
Description of the Prior Art
Borohydrides are recognized as compounds
for the selective reduction of a wide range of
functional groups, e.g., aldehydes, ketones, imines,
esters and amides, etc. The use of borohydrides is
compiled in the publication entitled Process Stream
Purification, Bulletin No. BA-8UG, Ventron Corp.,
September, 1978. This publication lists 6 patents
relating to the purification of esters, but it does
not include any relating to the remo~al of color
formers from aliphatic dibasic esters.
U.S. Patent 2,957,023 issued on October 18,
1960 discloses a method for the stabilization of
alcohols contaminated with carbonyl and/or unsaturated
compounds such as olefins by adding a borohydride to
the alcohol during or before the esterification. The
patentees disclose that a solvent is preferred because
of the relative insolubility of the borohydride but
indicate that the choice of solvent is not critical
to their invention. Solvents which are disclosed
include water, isopropanol ether, low molecular
weight amines and the like.
The production of color free polyvinyl
PI-0280 35 alcohol is obtained according to the teachings of
~b
q~
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U.S. Patent 3,679,646 issued on July 25, 1972 by
pre-treating an alcohol solution of a polyvinyl
ester with from about 0.03 to about 3~ by weight
based upon the weight of the polyvinyl ester of an
alkali metal borohydride followed by alkaline
hydrolysis. The patentees prefer to use the
borohydride in a finely divided, e.g., powder form.
U.S. Patent 3,681,482 issued on August 1,
1972 discloses a process for improving the color of
phosphate esters by contacting the esters with 0.002
to 0.05 percent by weight of sodium or lithium
borohydride. The patentees disclose that the
borohydride is preferably in solid form but can
be in aqueous solution.
German Patent 2,556,258 issued on May 26,
1977 teaches the stabilization of polyhydroxy
carboxylate polymers by the addition of sodium
borohydride.
U.S. Patent 3,991,100 issued on November 9,
1976 discloses a process for the production of esters
of dibasic acids which exhibit a reduced color-
forming tendency under alkaline or transesterification
conditions. The process involves heating the esters
to remove water, oxides of nitrogen and nitric acid,
esterifying the thus heated product and finally
distilling off volatile materials in the presence
of a dry base such as sodium carbonate and calcium
hydroxide. It should be noted, however, that this
method does not completely eliminate the color-
forming tendencies of the esters during trans-
esterification.
The art discloses that under ordinary
conditions aliphatic nitro compounds are not reactive
with sodium borohydride and that for such a reaction
to occur to any significant extent transition metals,
1168262
their salts and complexes of ~ewis acids are required
(Sodium Borohydride, Ventron Corporation, December,
1979, pages 35-36).
U.S. Patent 2,831,883 issued on April 22,
1958 discloses the reduction of nitro impurities
in alpha, omega-alkanedioic acid esters prepared
from diacids via the nitric acid oxidation of organic
compounds. The patentees disclose several methods
for reduction of the nitro compounds including
reduction with a metal and an acid, e.g.,
zinc dust and an alcoholic solution of a mineral
acid; catalytic reduction with Raney nickel or with
reduced precipitated nickel and chemical reduction,
e.g., by catalytic reduction with palladium or
platinum.
U.S. Patent 3,991,100 issued on November 9,
1976 discloses a process for the production of esters
of dibasic acids which exhibit a reduced color forming
tendency under alkaline or transesterification
conditions. The process involves heating the esters
to remove water, oxides of nitrogen and nitric acid,
esterifying the thus heated product and finally
distilling off volatile materials in the presence of
a dry base such as sodium carbonate or calcium
hydroxide. The disclosed method does not completely
eliminate the color forming tendencies of the esters
during transesterification.
Belgium Patent 828,5Q8 issued on April 29,
1974 discloses a process for the removal of organic
nitrogen containing compounds from dodecanedioic acid
by treating the acid with potassium permanganate in
an alkali medium. There is no disclosure of treating
acids other than dodecandioic acids nor to the
treatment of esters of any acids.
A general method for oxidizing the salts of
1168262
mononitro compounds with neutral potassium
permanganate is disclosed in the article appearing in
J. Organic Chem. 27, page 3699 (1962). The process
disclosed involves converting the nitro compounds to
their potassium salts in an aqueous solution which
is then added to an aqueous solution of potassium
permanganate. The aldehyde and/or ketones that
are produced are steamed distilled out of the aqueous
reaction mixture.
U.S. Patent 3,642,871 issued on February
15, 1972 discloses the use of an alkali metal
alkoxide, e.g., sodium methylate necessarily
combined with phosphorus atoms, e.g., phosphoric
acid to improve the color stability of a wide
variety of organic esters including diesters of
aliphatic carboxylic acids, e.g., dimethyl adipate,
dibutyl sebacate and diisopropyl succinate.
SUMMARY OF THE INVENTION
A process for reducing the color forming
tendency of alkanedioic acid esters, e.g., those
esters derived from dicarboxylic acids having 4-12
carbon atoms which comprises contacting the esters
with alkali metal borohydride in the presence of
water, an alkali metal permanganate in the presence
of water and/or an alkali metal ~ethylate. It is
preferred to dissolve the borohydride and
permanganate in water before contact with the esters.
DETAILED DESCRIPTION OF THE INVENTION
The esters to which the present invention
is particularly applicable are those prepared from
the acids isolated as co-products from the air
oxidation of cyclic hydrocarbons to cyclic ketones
and alcohol followed by the oxidation of the ketones
and alcohols with nitric acid. The oxidation of
cyclohexane to cyclohexanol and cyclohexanone can
1 16826~
be conducted according to the teachings, for example,
of U.S. Patent 3,530,185 issued on September 22, 1970.
Cyclohexanol and cyclohexanone produced according
to the aforementioned patent are then oxidized with
nitric acid according to the teachings of U.S.
Patents 3,359,308 issued on December 19, 1967 and
3,365,490 issued on January 23, 1968. Illustrative
of the co-product acids that are produced along with
adipic acid in the aforementioned processes are
succinic acid and glutaric acid.
The preparation of alkane dicarboxylic
acids having from 8 to 12 carbon atoms by the nitric
acid oxidation of the corresponding alcohols and
ketones is disclosed in U.S. Patent 3,758,564
issued on September 11, 1973. Illustrative of the
co-product acids produced in this process are pimelic
acid, suberic acid, azelaic acid, sebacic acid and
undecanedioic acid.
The principal acids produced in the above
described processes, i.e., adipic acid and dodecane-
dioic acid are commonly separated from the co-product
acids by crystallization and the co-product acids
then recovered from the mother liquor by known
methods. These co-product acids can be converted
to esters by known esterification processes. Even
after rigorous distillation, these esters still
exhibit a marked tendency to turn yellow when
subjected to alkaline conditions or when heated to
temperatures for which the esters are eventually
3Q employed, e.g., for the preparation of other esters
and polyesters by transesterification.
The color-forming tendency of esters which
are treated according to the process of the present
invention is believed due to the presence of small
amounts of aliphatic nitro compounds which form
1168262
during the nitric acid oxidation of the ketones or
alcohols andtor during acid catalyzed esterification
in the presence of residual nitrate ion. These
impurities co-distill with the esters; are not
adsorbed to any significant extent on activated
carbon and are not amenable to bleaching, e.g.,
with peroxides or aqueous hypochlorites.
The borohydrides which are operable in the
present invention include sodium, potassium and
lithium borohydride and mixtures of the foregoing.
Sodium borohydride is the preferred borohydride.
The methylates which are operable in the
present invention include sodium, potassium and
lithium methylate and mixtures of the foregoing.
Sodium methylate is preferred.
The permanganates which are operable in
the present invention include sodium, potassium and
lithium permanganate and mixtures of the foregoing.
Potassium permanganate is preferred.
The method for contacting the above
described additives with the esters is not critical
to the present invention provided water is present
during contact in the case of the permanganate and
borohydride. Low shear stirring at ambient
temperature has been found completely satisfactory
for mixing, but as one skilled in the art can
appreciate, higher shear mixing and/or elevated
temperatures will accelerate the reaction. The
contacting may be conducted at temperatures in the
range of 0-100C and preferably 20-75C for times
varying from about 0.5-2 hours. Time can be
decreased as the agitat~on and/or temperature is
increased. The borohydride and/or permanganate and
water may be introduced separately into the esters
but preferably, they are dissolved in water before
~168262
introduction. In the case of the borohydride the
minimum amount of water required for formation of
the solution depends on the solubility of the
borohydride at the temperature of the water, but
the amount of water can be up to twice the weight
of the borohydride or more~ In any event, it is
desirable to ir,troduce only the minimum amount of
water necessary and thereby minimize the drying
required after reaction. The presence of water
markedly reduces the effectiveness of the methylate
and it is preferred to maintain water at the lowest
practical level, e.g., less than 0.1% by weight
based upon the weight of the esters.
Since the borohydrides decompose rapidly
in the presence of acid, the esters should be neutral
or slightly basic for optimum utili~ation of the
hydride and for color reduction. This also applies
to treatment with the methylate. Usually a
precipitate is formed during the contact of the
ester and the methylate which can if desired be
removed by known methods, e.g., filtration before
further processing of the treated esters.
The amount of additive required will,
of course, depend upon the amount of color-formers
present which is dictated by the conditions used in
preparing the acids and/or the esters. It has been
determined that two parts by weight of borohydride
per 1000 parts by weight of ester is usually
sufficient for complete reduction in color. However,
in many instances less than one part of borohydride
per 1000 parts of ester can accomplish complete color
reduction. Generally, 0.05-5% and prefera~ly about
0.1-0.3% by weight of borohydride based upon the
weight of the ester is employed. It has been
determined that 2-25 and usually about 5 parts by
1 16~26.~ ,
weight of methylate per 1000 parts by weight of ester
is usually sufficient for complete reduction in color.
In many instances less than one part of methylate
per 1000 parts of ester can accomplish complete
color reduction. It has been determined that 6.6
parts by weight of permanganate per 1000 parts by
weight of ester is usually sufficient for complete
reduction in color. However, in many instances
less than 6.6 parts of permanganate per 1000 parts
of ester can accomplish complete color reduction.
Generally, 0.1-2% and preferably about 0.4-0.8~
by weight of permanganate based upon the weight
of the ester is employed. In any event, the amount
of additive required is readily determined by
increasing or decreasing the amount until the
desired le~el of color is obtained. Excess additive
can be employed to assure an essentially complete
reduction in color forming tendency.
The following eY~amples are presented to
illustrate but not to restrict the present invention.
Parts and percentages are by weight unless otherwise
specified. The color forming tendencies of the
esters treated according to the process of the
present invention were determined by adding two
drops of a 40% by weight solution of benzyltrimethyl
ammonium-hydroxide in methanol to 5 ml of esters,
followed by shaking the solution. All esters reported
in the Examples were treated in this manner before
determining the color. The polyesters were not
treated before determining the color. Color was
judged usin~ a Hellige* Color Comparator equipped
with a Gardner color disc ~color system of the
Institute of Paint and Varnish Research). This
technique measures the yellowness of samples on a
* denotes trade mark
..... .. ................. .... ... . ........ .... .. . .
1168262
g
scale from 1 (very light yellow~ to 10 (dark yellow).
A colorless sample exhibits a Gardner color of less
than 1.
EXAMPLE I
S To a 12 liter flask fitted with a simple
distillation head and suitable heating equipment was
added 10 kilograms of the mixed methyl esters of
succinic, glutaric and adipic acid, having the
analysis set forth in Table I and a Gardner color
of 6.
TABLE I
Dimethyl succinate 2%
Dimethyl glutarate 71~
Dimethyl adipate 27%
This ester mixture was prepared as described
hereinabove by esterification of the acids obtained
by the nitric acid oxidation of a mixture of cyclo-
hexanol and cyclohexanone followed by removal of
the majority of adipic acid by crystallization.
Approximately 10 grams of sodium borohydride
was dissolved in 20 grams of water and the resultant
solution introduced into the fla~k. After standing
overnight at room temperature (about 16 hours at 20C),
the ester had a Gardner number less than 1. This
ester was then distilled under 25 mm Hg vacuum. A
small foreshot was removed and 9.5 kilograms of
distillate at a boiling point in the range of
110-118C was collected, The distillate also
exhibited a Gardner color of less than 1 and when a
polyester was made from this material by trans-
esterification with ethylene glycol in the presence
of n-butyl stannoic acid, a polyester having a
Gardner color of less than 1 was obtained.
-Comparative A
Example I was repeated except that 10 grams
116~262
of powdered sodium borohydride (no water) were
thoroughly mixed with the esters. The Gardner color
of the distillate was 4 indicating that only a small
amount of color-formers were removed in the absence
of water.
Comparative B
Example I was repeated except that 40 grams
of sodium borohydride (no water) were employed. A
polyester prepared from this ester had a Gardner
color of 6.
The foregoing illustrates that even a
substantial excess of sodium borohydride does not
provide satisfactory color reduction in the absence
of water.
EXA~LE II
To a 12 liter flask fitted with a simple
distillation head and suitable heating equipment was
added 8153 grams of the mixed methyl esters of
succinic, glutaric and adipic acid, having the
analysis set forth in Table I of Example I and a
Gardner color of 6.
This ester mixture was prepared as described
in Example I.
Approximately 57 grams of potassium
permanganate was dissolved in 323 grams of water at
85C and the resultant solution introduced into the
flask and the mixture was maintained at 77-93C for
65 minutes. The mixture was then distilled under
25 mm Hg vacuum. A small foreshot containing water
was removed and 7264 grams of distillate at a
boiling point in the range of 110-115C was collected.
The distillate exhibited a Gardner color of less than
1 and when a polyester was made from this material
by transesterification with ethylene glycol in the
presence of n-butyl stannoic acid, a polyester
lQ
1188262
11
having a Gardner color of less than 1 was obtained.
A similar polyester made from the untreated esters
was dark orange.
EXA~lPLE III
To a 500 ml flask fitted with a simple
distillation head and suitable heating equipment was
added 227 grams of the mixed methyl esters of
succinic, glutaric and adipic acid, having the
analysis set forth in Table I of Example I and a
Gardner color of 4.
This ester mixture was prepared as described
in Example I.
Approximately 3.5 grams of sodium methylate
was introduced into the flask. The resultant slurry
was heated with stirring at 75C for one hour
whereupon the contents of the flas~ turned yellow.
This ester was then distilled with essentially no
fractionation under 25 mm Hg vacuum. Approximately
215 grams of distillate having a ~ardner color of
~1 was collected.
EXAMPLE IV
.
A mixture of C7_12 straight chain dibasic
acids recovered from the nitric acid oxidation of
cyclododecanone and cyclododecanol as described
hereinabove were esterified with methanol using a
dodecylbenzene sulfonic acid catalyst. The resultant
esters were then distilled under 1 mm Hg pressure
and a distillate boiling in the range of 99-150C
and having a Gardner color of 7 was recovered. This
ester distillate had the composition given in Table II.
TABLE II
Dimethyl pimelate 0.5% Dimethyl sebacate 7.0%
Dimethyl suberate 2.4% Dimethyl undecandioate 47.6%
Dimethyl azelate 3.3% Dimethyl dodecandioate 39.2%
To 150 parts of this ester distillate was
ll~8262
added 6 parts of a 25% by weight aqueous solution of
sodium borohydride. The mixture was then stirred at
room temperature for 1 hour and then re-distilled
under the above described conditions. A small
foreshot boiling below 99C was taken and discarded.
A product was collected at a boiling range of
99-155C which had a Gardner color of less than 1.
EXAMPLE V
To 124 parts of the ester distillate
as described in Example IV and having a Gardner
color of 9 was added 1.6 parts of potassium
permanganate dissolved in 4.8 parts of hot water
(85C) with mild agitation at room temperature.
The mixture was then distilled at Cl mm Hg pressure.
After a small foreshot containing water was
discarded, 87 parts of treated esters were collected
which had a Gardner color of less than 1.
EXAMPLE VI
To 124 parts of the ester distillate of
Example V was added 2 parts of sodium methylate with
mild agitation at room temperature. The mixture was
then distilled at ~1 mm Hg pressure. After a small
foreshot which was discarded, 104 parts of treated
esters were collected which had a Gardner color of
less than 1.
