U.S. patent application number 10/575100 was filed with the patent office on 2007-03-15 for method for producing benzoic acid esters.
This patent application is currently assigned to OXENO OLEFINCHEMIE BMBH. Invention is credited to Michael Grass, Dietmar Gubisch, Michael Woelk-Fahrmann.
Application Number | 20070060768 10/575100 |
Document ID | / |
Family ID | 34399517 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070060768 |
Kind Code |
A1 |
Grass; Michael ; et
al. |
March 15, 2007 |
Method for producing benzoic acid esters
Abstract
A process for preparing benzoic esters whose alkoxy groups have
from 7 to 13 carbon atoms by reacting benzoic acid with at least
one alcohol having from 7 to 13 carbon atoms, the water of reaction
formed being removed during the esterification reaction by
distillation, and the alcohol not converted in the esterification
reaction being removed after the esterification reaction, in which
the reaction takes place in the presence of a tin(II) compound as
catalyst and, without treatment with a base, the catalyst and/or
its derivatives is/are separated off by filtering or by
centrifuging from the reaction mixture which remains after the
unconverted alcohol has been separated off.
Inventors: |
Grass; Michael; (Haltern am
See, DE) ; Gubisch; Dietmar; (Marl, DE) ;
Woelk-Fahrmann; Michael; (Marl, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
OXENO OLEFINCHEMIE BMBH
MARL
DE
|
Family ID: |
34399517 |
Appl. No.: |
10/575100 |
Filed: |
August 20, 2004 |
PCT Filed: |
August 20, 2004 |
PCT NO: |
PCT/EP04/51854 |
371 Date: |
April 10, 2006 |
Current U.S.
Class: |
560/103 |
Current CPC
Class: |
C07C 67/08 20130101;
C08K 5/101 20130101; C07C 69/78 20130101; C08L 27/06 20130101; C07C
67/08 20130101; C07C 67/48 20130101; C07C 69/78 20130101; C07C
67/48 20130101 |
Class at
Publication: |
560/103 |
International
Class: |
C07C 69/76 20060101
C07C069/76 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2003 |
DE |
103 47 863.9 |
Claims
1. A process for preparing benzoic esters whose alkoxy groups have
from 7 to 13 carbon atoms by reacting benzoic acid with at least
one alcohol having from 7 to 13 carbon atoms, the water of reaction
formed being removed from the reaction mixture during the
esterification reaction by distillation with the alcohol used in
excess, and the alcohol not converted in the esterification
reaction being removed after the esterification reaction,
characterized in that the reaction takes place in the presence of a
tin(II) compound as catalyst at a temperature of 160 to 250.degree.
C. and in that, without treatment with a base, the catalyst and/or
its tin-containing derivatives are removed by filtering or by
centrifuging from the reaction mixture which remains after the
unconverted alcohol has been separated off, to an extent such that
the tin content of the end product (filtrate) is below 1 mg/kg
(ppm) and in that alcohols used are heptanols, 1-octanol,
2-octanol, 2-ethylhexanol, nonanols and/or tridecanols.
2. The process of claim 1, characterized in that a mixture of
alcohols with the same or different number of carbon atoms is
used.
3. The process of claim 1, characterized in that the unconverted
alcohol is removed by stripping, distilling or steam-distillation
or by a combination of two or more of these methods.
4. The process of at least one of claim 1, characterized in that
the unconverted alcohol is separated off after the esterification
reaction by vacuum distillation and subsequent stripping with steam
or nitrogen.
5. The process of claim 1, characterized in that the catalyst is
separated off at a temperature below 160.degree. C.
6. The process of claim 1, characterized in that the catalyst
and/or derivative(s) thereof is/are separated off from the reaction
mixture, after the alcohol has been separated off and without base
treatment, by filtration at temperatures below 130.degree. C.
7. The process of claim 1, characterized in that the volume of
liquid removed from the reaction mixture during the esterification
by (azeotropic) distillation is made up in whole or in part with
the reactant alcohol or reactant alcohol mixture.
8. The process of claim 1, characterized in that the volume of
liquid removed from the reaction mixture during the esterification
by (azeotropic) distillation is partly recycled, by separation of
the liquid separated off into an aqueous phase and an organic
phase, and recycling of the organic phase into the esterification
reaction.
9. The process of claim 1, characterized in that the volume of
liquid removed from the reaction mixture during the esterification
by (azeotropic) distillation is made up in whole or in part, by
separation of the liquid separated off into an aqueous phase and an
organic phase and recycling the organic phase, additionally admixed
with fresh alcohol, into the esterification reaction.
10. The process of claim 1, characterized in that the volume of
liquid removed from the reaction during the esterification by
(azeotropic) distillation is made up in whole or in part with the
fresh alcohol.
11. The process of claim 1, characterized in that tin(II) salts of
monocarboxylic or dicarboxylic acids are used as catalyst.
12. The process of claim 1, characterized in that a molar ratio of
tin to benzoic acid of 10.sup.-5: 1 to 10.sup.-3: 1 is set at the
beginning of the reaction.
13. The process of claim 1, characterized in that a polymeric or
ceramic membrane, composite membrane or paper filter is used as
filter.
14. The process of claim 1, characterized in that the benzoic acid
is esterified to an acid number of <0.1 mg KOH/g, determined in
accordance with DIN EN ISO 2114.
15. A composition comprising benzoic ester(s) and isononyl
benzoate, prepared by a process of claim 1.
16. The composition of claim 15, characterized in that the tin
content of the product is below 1 mg/kg.
17. A method of using the composition of claim 15 in paints,
varnishes, adhesives or components of adhesives or as a viscosity
reducer and/or plasticizer for PVC.
Description
[0001] The present invention relates to a process for preparing
benzoic esters from benzoic acid and alcohols having 7 to 13 carbon
atoms.
[0002] Benzoic esters whose alkoxy groups have 7 to 13 carbon atoms
are used as film-forming auxiliaries in compositions such as
emulsion paints, mortars, renders, adhesives, and varnishes.
Additionally they can be used as plasticizers and/or viscosity
reducers in flexible (unplasticized) PVC applications, especially
in plastisols.
[0003] The preparation of carboxylic esters by reaction of
carboxylic acids with alcohols is known. This reaction can be
carried out autocatalytically or catalytically, by means of
Bronsted or Lewis acids, for example. Irrespective of the type of
catalysis selected, a temperature-dependent equilibrium is always
developed between the reactants (carboxylic acid and alcohol) and
the products (ester and water). In order to shift the equilibrium
in favor of the ester, many esterifications use an azeotrope
former, with whose aid the water of reaction is removed from the
reaction mixture. If one of the reactants (alcohols or carboxylic
acid) has a lower boiling point than the ester formed and forms a
miscibility gap with water, that reactant can be used as an
azeotrope former and, following removal of the water, can be
recycled to the batch. In the case of esterification of carboxylic
acids the alcohol employed is frequently used as an azeotrope
former.
[0004] Many end-use applications require the ester prepared by
esterifying a carboxylic acid to possess a low acid number--in
other words, the conversion of the carboxylic acid ought to be
virtually quantitative. Otherwise the yield is lessened and the
acid has to be separated off, by neutralization for example. This
is costly and inconvenient and can lead to by-products, which
require disposal. To maximize conversion of the carboxylic acid,
esterifications are generally carried out with an excess of
alcohol.
[0005] Esterification catalysts used can be acids, such as sulfuric
acid or p-toluenesulfonic acid, or metals and compounds thereof.
Suitable examples include tin, titanium, and zirconium, which can
be used as finely divided metals or, advantageously, in the form of
their salts, oxides or soluble organic compounds. In contrast to
protic acids, the metal catalysts are high-temperature catalysts,
achieving their full activity only at temperatures above
180.degree. C. In the art, however, they are used preferentially on
account of the fact that, in comparison to proton catalysis, the
level of by-products they form, such as olefins of the alcohol
employed, for example, is lower. Exemplary representatives of metal
catalysts are titanic esters such as tetraisopropyl orthotitanate
or tetrabutyl orthotitanate, and zirconium esters such as
tetrabutyl zirconate.
[0006] After the esterification has taken place, the excess
reactant alcohol, residues of acid, the catalyst and/or its
derivatives, and also other by-products, must be separated from the
desired carboxylic ester. The economics of an esterification
process are good only when both the technical complexity and the
time consumed for physical separation are low.
[0007] The esterification of carboxylic acids with tin compounds is
described in patents GB 2 098 211, EP 0 036 712, and EP 0 037 172.
In those cases, a portion of the tin compounds is put onto a metal
mesh, which is in contact with the reaction solution, while the
other portion of the tin compounds is in solution and/or suspension
in the reaction solution.
[0008] Esterification takes place with distillative removal of the
water of reaction. After the esterification, acids still present
are neutralized in a second vessel, and their salts, and tin
compounds, are separated off. This is accomplished by adding a
solid base to the crude ester and removing the precipitated solids
(base, salts, tin compounds) by filtration, or by extracting the
crude ester with an aqueous base. With these workup methods, the
result is either an aqueous phase containing organic and inorganic
compounds, or a solids mixture containing organic and inorganic
compounds. Disposing of these by-products occasions costs which in
certain circumstances are high.
[0009] U.S. Pat. No. 6,235,924 describes a process for preparing
benzoic esters by reacting benzoic acid with an alcohol in the
presence of a titanium catalyst. The esterification is carried out
with the water of reaction being separated off by distillation. The
benzoic ester is separated off from the ester mixture by means of
fractional distillation. A disadvantage of this process is the time
and energy consumed for the distillation.
[0010] The object was therefore to find a process for preparing
benzoic esters that does not have the disadvantages of the known
processes.
[0011] Surprisingly it has been found that benzoic esters of high
purity can be easily prepared by reacting benzoic acid with
alcohols having 7 to 13 carbon atoms in the presence of a tin(II)
compound if the esterification takes place with distillative
removal of the water of reaction, the esterification is followed by
removal of the excess alcohol present in the reaction mixture by
means of distillation and stripping with a gas or steam, and,
without treatment with a base, the resultant crude ester is
filtered. The filtration allows the tin catalyst and/or its
tin-containing derivatives to be separated off to an extent such
that the tin content of the end product (filtrate) is well below 1
mg/kg (ppm).
[0012] The present invention accordingly provides a process for
preparing benzoic esters whose alkoxy groups have from 7 to 13
carbon atoms by reacting benzoic acid with at least one alcohol
having from 7 to 13 carbon atoms, the water of reaction formed
being removed from the reaction mixture during the esterification
reaction by distillation with the alcohol used in excess, and the
alcohol not converted in the esterification reaction being removed
after the esterification reaction, which is characterized in that
the reaction takes place in the presence of a tin(II) compound as
catalyst at a temperature of 160 to 250.degree. C. and in that,
without treatment with a base, the catalyst and/or its derivatives
are removed by filtering or by centrifuging from the reaction
mixture which remains after the unconverted alcohol has been
separated off, virtually to completion.
[0013] Likewise provided by the present invention are compositions
comprising benzoic ester(s), obtainable by the process of the
invention, and also their use.
[0014] The process of the invention is notable for the following
advantages:
[0015] Workup, particularly the simple removal of the catalyst by
filtration, is less costly and inconvenient by comparison with
known methods.
[0016] With no base being added, neither salts of neutralization
nor waste waters loaded with organic and inorganic substances are
obtained.
[0017] The catalyst separated off, and/or its derivative(s), can be
easily worked up or disposed of.
[0018] Because no bases or other auxiliaries have to be added to
the reaction mixture, time and costs are saved and additional
contamination of the ester is avoided.
[0019] The process of the invention for preparing benzoic esters,
compositions prepared by the process, and uses thereof is/are
described below, without any intention that the invention should be
restricted to these embodiments.
[0020] The process of the invention for preparing benzoic esters
whose alkoxy groups have from 7 to 13 carbon atoms by reaction of
benzoic acid with one or more alcohols having from 7 to 13 carbon
atoms, the water of reaction formed being removed from the reaction
mixture during the esterification reaction by distillation with the
alcohol used in excess, and the alcohol not converted in the
esterification reaction being removed after the esterification
reaction, is notable for the fact that the reaction takes place in
the presence of a tin(II) compound as catalyst at a temperature of
160 to 250.degree. C. and in that, without treatment with a base,
the catalyst and/or its derivatives can be separated off almost
completely by filtering or by centrifuging from the reaction
mixture which remains after the unconverted alcohol has been
separated off, so that the tin content of the end product (the
filtrate) is below 1 mg/kg, (ppm), in particular well below 1
mg/kg, and preferably less than 0.1 mg/kg.
[0021] Throughout the esterification reaction and also the
subsequent removal of excess alcohol and catalyst, therefore, there
is no treatment with a base and no neutralization step.
[0022] In the process of the invention the benzoic acid is
esterified using branched or linear aliphatic alcohols or mixtures
of alcohols having 7 to 13 carbon atoms. The alcohols may be
monohydric or polyhydric, but are preferably monohydric. The
alcohols may be secondary or primary, linear or branched. The
alcohol used may comprise a mixture of alcohols having the same or
different number of carbon atoms. The alcohols can be employed as
an isomerically pure compound, as a mixture of isomeric compounds,
or as a mixture of isomeric or isomerically pure compounds with a
different number of carbon atoms.
[0023] The alcohols used may originate from a variety of sources.
Examples of suitable reactant alcohols include fatty alcohols,
alcohols from the Alfol process (oligomerization of ethylene in the
presence of aluminum alkyls with subsequent oxidation and
hydrolysis to the corresponding primary alcohols), or alcohols or
alcohol mixtures obtained by hydrogenating saturated or unsaturated
aldehydes, particularly those whose synthesis includes a step of
hydroformylation.
[0024] Alcohols which can be used with preference in the process of
the invention are, for example, heptanols, 1-octanol, 2-octanol,
2-ethylhexanol, nonanols, decyl alcohols and/or tridecanols.
Particularly preferred reactant alcohols are mixtures of isomeric
octanols, decanols, especially 2-propylheptanol, nonanols or
tridecanols, the latter obtainable from the corresponding butene
oligomers, especially oligomers of linear butenes, by
hydroformylation and subsequent hydrogenation. The butene oligomers
can be prepared in principle by three methods. Acid-catalyzed
oligomerization, for which, for example, zeolites or phosphoric
acid on supports are used industrially, yields the oligomers with
the greatest branching. Using linear butenes results in, for
example, a C.sub.8 fraction composed substantially of
dimethylhexenes (WO 92/13818). A method which is likewise
implemented worldwide is that of oligomerization with soluble Ni
complexes, known as the DIMERSOL process (B. Cornils, W. A.
Herrmann, Applied Homogeneous Catalysis with organometallic
Compounds, pages 261-3, Verlag Chemie 1996). The oligomerization
can also be implemented over fixed-bed nickel catalysts, as
described for the OCTOL process, for example (Hydrocarbon Process.,
Int. Ed. (1986) 65 (2. Sect. 1), pages 31-3).
[0025] Especially preferred reactants for the esterification of the
invention are mixtures of isomeric nonanols or mixtures of isomeric
tridecanols, prepared by oligomerizing linear butenes to C.sub.8
olefins and C.sub.12 olefins by the Octol process, with subsequent
hydroformylation and hydrogenation. Likewise of preferential
suitability as a reactant are decyl alcohol mixtures of which more
than 50% by mass comprises 2-propylheptanol. These mixtures are
prepared in general by hydroformylation of butenes, hydrogenation
to the corresponding pentanals, aldolization of the pentanals to
the corresponding decenals, and final hydrogenation to the
decanols.
[0026] The catalyst used in the process of the invention comprises
one or more divalent tin compounds or else tin compounds and/or
elemental tin able to react with the reactants to form divalent tin
compounds. As the catalyst it is possible to make use, for example,
of tin, tin(II) chloride, tin(II) sulfate, tin(II) alkoxides or
tin(II) salts of organic acids, especially of monocarboxylic and
dicarboxylic acids. Preferred tin catalysts are tin(II) oxalate
and/or tin(II) benzoate.
[0027] It has proven advantageous if a molar ratio of tin to
benzoic acid of preferably 10.sup.-5 to 10.sup.-3: 1, more
preferably of 10.sup.-4 to 10.sup.-3: 1, is set at the beginning of
the reaction.
[0028] The esterification is carried out in a reaction vessel
(reactor) in which the reaction batch can be mixed intensively with
the aid of a stirrer or circulation pump. The reactants and the
catalyst can be introduced into the reactor simultaneously or in
succession. Where the benzoic acid is in solid form at the
introduction temperature, it can be advantageous to introduce the
alcohol or alcohol mixture to start with. The benzoic acid can be
fed in as a powder, granules, crystallizate or melt. It is likewise
possible for the benzoic acid to be fed into the reactor in
solution in a solvent, preferably in an alcohol, and more
preferably in an alcohol likewise used as a reactant. In order to
shorten the batch time it is advantageous to commence heating
during the introduction procedure. The catalyst can be introduced
into the reactor in a pure form, as a suspension or as a solution,
preferably in alcohol or alcohol mixture employed, at the start or
not until after the reaction temperature has been attained. The
volume of catalyst to be employed can be added all at once or in
two or more portions.
[0029] The alcohol to be converted, which also serves as an
azeotrope former, is employed in a stoichiometric excess, with an
excess of preferably 5% to 50%, more preferably 10% to 30%, of the
amount required by stoichiometry.
[0030] In the process of the invention the reaction temperatures
are situated in the range from 160.degree. C. to 250.degree. C.,
preferably from 180.degree. C. to 230.degree. C., more preferably
from 190.degree. C. to 210.degree. C. The optimum temperatures
depend on the reactant alcohol(s), the progress of the reaction,
the type of catalyst, and the catalyst concentration. For each
specific case they can be determined readily by means of tests.
Higher temperatures raise the reaction rates and favor side
reactions, such as elimination of water from alcohols or formation
of colored by-products, for example. For the removal of the water
of reaction it is necessary for the alcoehol to be removable from
the reaction mixture by distillation. The desired temperature or
temperature range can be set via the pressure in the reaction
vessel (slight overpressure-atmospheric
pressure-underpressure).
[0031] In the case of the esterification of benzoic acid with a
mixture of isomeric nonanols, for example, it is particularly
preferred to operate in a temperature range from 190.degree. C. to
210.degree. C. in the pressure range from 1 bar to 100 mbar.
[0032] The water of reaction formed during the esterification
reaction is removed in the course of the ongoing esterification
reaction by means of distillation, in particular an azeotropic
distillation. This measure removes not only the water of reaction
but also a portion of the alcohol. It is possible to replace some
or all of the volume of liquid removed by the azeotropic
distillation, by separating the liquid separated off into an
organic phase, which besides the alcohol may also contain benzoic
ester(s), and into an aqueous phase, and recycling the organic
phase into the esterification reaction. As an option, fresh alcohol
can be added to the separated-off organic phase which is recycled
into the reaction.
[0033] The liquid removed from the reaction mixture by distillation
in the course of the removal of the water of reaction is preferably
replaced by a corresponding volume of liquid which is added again
to the reaction mixture. The volume of liquid to be recycled into
the reaction may be composed in part or in whole of the reactant
alcohol or reactant alcohol mixture. The volume of liquid removed
from the reaction mixture during the esterification by (azeotropic)
distillation can be at least partly made up, for example, by
separation of the liquid separated off into an aqueous phase and an
organic phase and recycling of the organic phase into the
esterification reaction. It is also possible for the reaction
mixture to be made up in whole or in part by the volume of liquid
removed from the reaction mixture during the esterification by
(azeotropic) distillation, by separation of the liquid separated
off into an aqueous phase and an organic phase and recycling of the
organic phase, additionally admixed with fresh alcohol, into the
esterification reaction. A further possibility is to replace some
or all of the volume of liquid removed from the reaction mixture by
(azeotropic) distillation by fresh alcohol, i.e., alcohol standing
ready in a stock vessel.
[0034] The alcohol/water mixture removed distillatively from the
reaction mixture in the course of the reaction, as an azeotrope or
with a virtually azeotropic composition, may where appropriate
additionally comprise benzoic ester(s). The vapors obtained leave
the reaction vessel, via, for example, a short column (internals or
structured packings; 1 to 5, preferably 1 to 3, theoretical
plates), and are condensed. In a phase separator or a coalescer,
for example, the condensate can be separated into an aqueous phase
and an organic phase. It can be advantageous to cool the
separated-off azeotrope to far below the condensation temperature
of the vapors, thereby achieving more effective phase separation.
The aqueous phase is separated off and, after workup where
appropriate, can be discarded or else used as stripping water for
the after treatment of the ester.
[0035] The organic phase obtained after separation of the
azeotropic distillate can be recycled partly or wholly into the
reaction vessel. In the art a level-controlled fill level
monitoring system in the reaction has been found appropriate for
supplying the alcohol; in such a system, when the amount of alcohol
or alcohol mixture obtained through distillation is insufficient,
the addition of fresh alcohol is advantageous.
[0036] For supplying the organic phase to the esterification
reaction there are a variety of possibilities. For example, the
organic phase can be fed to the column as a return flow. Another
possibility is to pump the organic phase, after heating where
appropriate, into the liquid reaction mixture. As a result of the
removal of the water of reaction, there is a fall in the reaction
volume in the apparatus. It is advantageous, however, as described
in DE 100 43 545.9 (shorter reaction time), to feed in
additionally, during the reaction, an amount of alcohol
corresponding to the volume of the removed distillate (water and,
where appropriate, alcohol), so that the fill level in the reaction
vessel remains constant. The increase in the excess of alcohol
shifts the equilibrium in favor of the benzoic ester(s).
[0037] After the end of the reaction the reaction mixture comprises
benzoic ester(s), excess alcohol(s), and catalyst and derivative(s)
thereof, and also any low-boiling and/or high-boiling by-products.
Preferably the reaction is carried out such that there is virtually
no free benzoic acid left in the reaction mixture--that is, the
benzoic acid has undergone virtually complete esterification. A
measure used for this purpose is the acid number to DIN EN ISO
2114. The product of the process of the invention has an acid
number of preferably <0.1 mg KOH/g, more preferably <0.07 mg
KOH/g, very preferably <0.04 mg KOH/g.
[0038] The unconverted alcohol can be removed by stripping,
distilling or steam-distillation or by a combination of two or more
of these methods. The unconverted alcohol is preferably separated
off after the esterification reaction by vacuum distillation and
subsequent stripping with steam or nitrogen.
[0039] The removal of the excess alcohol can be carried out, for
example, initially by vacuum distillation, optionally without
further supply of energy, selectively down to an alcohol
concentration below 10%, preferably below 5%, more preferably below
3%, very preferably below 1% in the reaction mixture. The
distillation conditions for this are, in terms of temperature,
preferably from 160 to 250.degree. C., more preferably from 180 to
230.degree. C.; the pressure is preferably from 5 mbar to 1 bar.
When preparing isononyl benzoate the vacuum distillation is carried
out, for example, at a preferred distillation temperature of 180 to
210.degree. C. and a preferred distillation pressure of 10 to 320
mbar.
[0040] After the vacuum distillation the remaining alcohol and any
residual low boilers present can be removed by stripping with an
inert gas, such as nitrogen, for example, or steam in the
temperature range from 130 to 240.degree. C. Stripping takes place
preferably with steam in the temperature range from 170 to
220.degree. C. under a pressure of 20 to 500 mbar, more preferably
from 20 to 150 mbar. Both for stripping and for vacuum
distillation, pressure and temperature are to be selected in each
case such that the ester remains in the liquid phase in the bottom
of the column, while the alcohol or alcohols, and any low boilers
present, are separated off in gas form.
[0041] In one particular embodiment of the process of the invention
it is also possible to dispense with the vacuum distillation and to
remove the entire excess of alcohol and low-boiling by-products by
stripping alone. Stripping can be carried out batchwise, in the
reaction vessel for example. Stripping can also be carried out,
optionally, continuously, in a packed column for example. The
amount of residual alcohol and low-boiling by-products can be
lowered in this way (by stripping alone) to below 500 ppm,
preferably below 300 ppm, more preferably below 200 ppm.
[0042] A feature of the process of the invention is that no base is
added before, during or after the removal of alcohol. After the
alcohol has been removed, the ester which remains is centrifuged or
filtered, optionally with the addition of a filter aid, in order to
remove the catalyst. The filter medium used may comprise customary
filters, such as paper filters, filter cloths, polymeric or ceramic
membranes, metal screens, composite membranes and/or the filter
cake itself. For centrifuging it is possible in principle to use
all commercially customary centrifuges. The catalyst is separated
off preferably at a temperature less than 160.degree. C.,
preferably in the temperature range from 20 to 150.degree. C., the
temperature of the mixture being more preferably from 80 to
130.degree. C. With particular preference the catalyst and/or
derivative(s) thereof is/are separated from the reaction mixture,
after the alcohol has been separated off and without base
treatment, by filtration at temperatures between 100 and
130.degree. C. Even at these relatively high temperatures, adequate
removal of the catalyst by filtration is possible. Only by means of
the process of the invention has it been possible to dispense with
lengthy cooling to ambient temperature prior to catalyst
removal.
[0043] The product which is obtained after the catalyst has been
separated off (benzoic ester or mixture of two or more benzoic
esters) can be obtained with a high purity. Depending on the purity
of the reactants, the benzoic ester purity is typically more than
99%, preferably more than 99.5%, more preferably more than 99.7%.
The amount of tin compounds, calculated as metallic tin, is below 1
mg/kg (ppm), preferably below 0.1 mg/kg. The acid number of the
product in accordance with DIN EN ISO 2114 is preferably below 0.1
mg KOH/g.
[0044] After the catalyst has been separated off by filtration, the
reaction mixture is obtainable with the purity described above.
Further purification for the purpose of separating off any
relatively high-boiling impurities that may be present, by means of
fractional vacuum distillation, is indeed an option, but is
generally unnecessary.
[0045] The process of the invention can be carried out in one
container or in a plurality of vessels in series, in each case
preferably stirred reactors. Thus, for example, the esterification
and the workup can take place in different vessels.
[0046] The alcohol separated off in the course of working up, which
where appropriate may contain benzoic ester(s) and/or by-products,
may be used for the subsequent batch, following removal of a
portion where appropriate.
[0047] By means of the process of the invention it is possible to
obtain compositions which comprise benzoic ester(s), and which in
particular may comprise isononyl benzoate. These compositions can
be used in paints, varnishes, adhesives or components of adhesive
or as plasticizers for plastics, preferably PVC, more preferably in
PVC plastisols.
[0048] The examples which follow are intended to elucidate the
invention in more detail without restricting the scope of
protection as provided by the description and the claims.
EXAMPLE 1
Preparation of Isononyl Benzoate with Tin Oxalate Catalyst
(Inventive)
[0049] The esterification of benzoic acid with isononanol was
carried out in a heatable 4-liter three-neck flask equipped with a
stirrer, internal thermometer, dip tube with sampling point, and
water separator with top-mounted condenser. The apparatus was
capable of evacuation via the water separator with condenser. The
water separator was filled with isononanol. The flask was charged
with 915 g of benzoic acid (DSM Fine Chemicals, purity >99.9%),
1296 g of isononanol (OXENO olefinchemie GmbH), and 0.55 g of tin
oxalate (Aldrich), and this initial charge was heated to
210.degree. C. with stirring. After it had reached 210.degree. C.,
the heating output was reduced, and temperature and reflux were
held constant via reduced pressure. The water obtained in the water
separator was separated off, while the alcohol obtained ran back
into the reaction flask. Where water was drained from the water
separator, the amount removed was replaced by addition of pure
alcohol, in order to maintain the fill level constant in the
reaction flask.
[0050] The progress of the esterification was monitored at regular
intervals via the acid number. Esterification was ended when the
acid number was less than 0.04 mg KOH/g. The esterification time
required for this, counted from the beginning of boiling, was
approximately 3 hours.
[0051] For the purpose of workup, a 10-cm Multifill column with
top-mounted Claisen bridge was attached in place of the water
separator, and the excess alcohol was distilled off at a
temperature of 180.degree. C. and a pressure of 10 mbar.
[0052] To purify the crude ester obtained in this way as the bottom
product, water was injected via the dip tube (8% by mass, based on
the amount of crude ester). The temperature at this stage was kept
constant at 180.degree. C.
[0053] After the end of the steam-distillation, the ester was
cooled to 100.degree. C. under reduced pressure and filtered under
reduced pressure via a suction filter with filter paper (Filtrak,
moderately wide-pored, type 389) via a filter cake 1.5 cm thick,
which was composed of Filterperl D14 filter aid (Perlite).
[0054] The resultant ester was colorless (APHA 19, Hazen color
number, in accordance with DIN ISO 6271) and clear and had a purity
of 99.96% by mass (determined by gas chromatography) and an acid
number of 0.01 mg KOH/g (determined in accordance with DIN EN ISO
2114). The residual alcohol content was 74 ppm, determined by gas
chromatography. The tin content was 10 .mu.g/kg (ppb, determined by
means of atomic spectrometry (ICP-OES) in accordance with DIN EN
ISO 11885). The ester remained clear even after cooling to room
temperature.
EXAMPLE 2
Preparation of Isononyl Benzoate with Tetrabutyl Titanate Catalyst
(without Neutralization, Comparative Example)
[0055] The esterification of benzoic acid with isononanol was
carried out in a heatable 4-liter three-neck flask equipped with a
stirrer, internal thermometer, dip tube with sampling point, and
water separator with top-mounted condenser. The apparatus was
capable of evacuation via the water separator with condenser. The
water separator was filled with isononanol (OXENO Olefinchemie
GmbH). The flask was charged with 915 g of benzoic acid (DSM Fine
Chemicals, purity >99.9%), 1296 g of isononanol and 0.55 g of
tetra-n-butyl titanate (Fluka), and this initial charge was heated
to 210.degree. C. with stirring. After it had reached 210.degree.
C., the heating output was reduced, and temperature and reflux were
held constant via reduced pressure. The water obtained in the water
separator was separated off, while the alcohol obtained ran back
into the reaction flask. Where water was drained from the water
separator, the amount removed was replaced by addition of pure
alcohol, in order to maintain the fill level constant in the
reaction flask.
[0056] The progress of the esterification was monitored at regular
intervals via the acid number. Esterification was ended when the
acid number was less than 0.04 mg KOH/g. The esterification time
required for this, counted from the beginning of boiling, was
approximately 2.5 hours.
[0057] For the purpose of workup, a 10-cm Multifill column with
top-mounted Claisen bridge was attached in place of the water
separator, and the excess alcohol was distilled off at a
temperature of 180.degree. C. and a pressure of 10 mbar.
[0058] To purify the crude ester obtained in this way, water was
injected via the dip tube (8% based on the amount of crude ester).
The temperature at this stage was kept constant at 180.degree.
C.
[0059] After the end of the steam-distillation, the ester was
cooled to 100.degree. C. under reduced pressure and filtered under
reduced pressure via a suction filter with filter paper (Filtrak,
moderately,wide-pored, type 389) via a filter cake 1.5 cm thick,
which was composed of Filterperl D14 filter aid (Perlite).
[0060] The resultant ester was colorless (APHA 19, Hazen color
number, in accordance with DIN ISO 6271) and clear and had a purity
of 99.96% (determined by gas chromatography) but a significantly
increased acid number of 0.12 mg KOH/g. The residual alcohol
content was 197 ppm, determined by gas chromatography. The titanium
content was 33 mg/kg (determined by means of atomic spectrometry
(ICP-OES) in accordance with DIN EN ISO 11885). After cooling to
room temperature the ester turned turbid. Only by means of
additional purification steps, such as washing, draining off the
wash water and drying by renewed heating, for example, was it
possible to obtain a product which had an acid number of <0.05
mg KOH/g and a titanium content of <0.1 mg/kg and which remained
clear even after cooling to room temperature.
EXAMPLE 3
Preparation of Isononyl Benzoate with Tetrabutyl Titanate Catalyst
(with Neutralization, Comparative Example)
[0061] The esterification of benzoic acid with isononanol (OXENO
Olefinchemie GmbH), was carried out in a heatable 4-liter
three-neck flask equipped with a stirrer, internal thermometer, dip
tube with sampling point, and water separator with top-mounted
condenser. The apparatus was capable of evacuation via the water
separator with condenser. The water separator was filled with
isononanol. The flask was charged with 915 g of benzoic acid (DSM
Fine Chemicals, purity >99.9%), 1296 g of isononanol and 0.55 g
of tetra-n-butyl titanate (Fluka), and this initial charge was
heated to 210.degree. C. with stirring. After it had reached
210.degree. C., the heating output was reduced, and temperature and
reflux were held constant via reduced pressure. The water obtained
in the water separator was separated off, while the alcohol
obtained ran back into the reaction flask. Where water was drained
from the water separator, the amount removed was replaced by
addition of pure alcohol, in order to maintain the fill level
constant in the reaction flask.
[0062] The progress of the esterification was monitored at regular
intervals via the acid number. Esterification was ended when the
acid number was less than 0.1 mg KOH/g. The esterification time
required for this, counted from the beginning of boiling, was
approximately 2 hours.
[0063] This was followed by cooling to 80.degree. C. and
neutralization using 6 times the stoichiometrically required amount
as determined from the acid number of aqueous sodium hydroxide
solution (5% by weight). After that, the mixture was stirred at
this temperature for approximately another 30 minutes.
[0064] For the purpose of workup, a 10-cm Multifill column with
top-mounted Claisen bridge was attached in place of the water
separator, the product was heated to 180.degree. C., and the excess
alcohol was distilled off at a temperature of 180.degree. C. and a
pressure of 10 mbar.
[0065] To purify the crude ester obtained in this way, water was
injected via the dip tube (8% based on the amount of crude ester).
The temperature at this stage was kept constant at 180.degree.
C.
[0066] After the end of the steam-distillation, the ester was
cooled to 100.degree. C. under reduced pressure and filtered under
reduced pressure via a suction filter with filter paper (Filtrak,
moderately wide-pored, type 389) via a filter cake 1.5 cm thick,
which was composed of Filterperl D14 filter aid (Perlite).
[0067] The resultant ester was colorless (APHA 14, Hazen color
number, in accordance with DIN ISO 6271) and initially clear and
had a purity of 99.98% (determined by gas chromatography) and an
acid number of 0.01 mg KOH/g. The residual alcohol content was 104
ppm, determined by gas chromatography.
[0068] After cooling to room temperature, however, a precipitate
was formed, necessitating further workup (filtration, for example).
The titanium content determined after working up was below the
detection limit of 0.1 mg/kg (determined by means of atomic
spectrometry (ICP-OES) in accordance with DIN EN ISO 11885).
[0069] As is readily apparent from Examples 1 to 3, the process of
the invention makes it possible in a simple way, without
neutralization and without an additional workup step, to prepare a
benzoic ester having a metal content of less 1 mg/kg.
EXAMPLE 4
Preparation of Isotridecyl Benzoate (Inventive)
[0070] The esterification of benzoic acid with isotridecanol was
carried out in a heatable 4-liter three-neck flask equipped with a
stirrer, internal thermometer, dip tube with sampling point, and
water separator with top-mounted condenser. The water separator was
filled with isotridecanol (OXENO Olefinchemie GmbH). The flask was
charged with 732 g of benzoic acid (DSM Fine Chemicals, purity
>99.9%), 1600 g of isotridecanol and 0.44 g of tin oxalate
(Aldrich), and this initial charge was heated to 210.degree. C.
with stirring. After it had reached 210.degree. C., the heating
output was reduced, and temperature and reflux were held constant
via addition of toluene. The water obtained in the water separator
was separated off, while the alcohol/toluene mixture obtained ran
back into the reaction flask. Where water was drained from the
water separator, the amount removed was replaced by addition of
pure alcohol. The progress of the esterification was monitored at
regular intervals via the acid number.
[0071] Esterification was ended when the acid number was less than
0.04 mg KOH/g. The esterification time required for this, counted
from the beginning of boiling, was 3 hours.
[0072] For the purpose of workup, a 10-cm Multifill column with
top-mounted Claisen bridge was attached in place of the water
separator, and the excess alcohol was distilled off at up to
210.degree. C., 10 mbar.
[0073] To purify the crude ester obtained in this way, water was
injected via the dip tube (8% based on the amount of crude ester).
The temperature at this stage was kept constant at 180.degree.
C.
[0074] After the end of the steam-distillation, the ester was
cooled to 100.degree. C. under reduced pressure and filtered under
reduced pressure via a suction filter with filter paper (Filtrak,
moderately wide-pored, type 389) via a filter cake 1.5 cm thick,
which was composed of Filterperl D14 filter aid (Perlite).
[0075] The resultant ester was clear and colorless (APHA=15, Hazen
color number, in accordance with DIN ISO 6271). The purity was
99.97% (determined by gas chromatography) with a residual alcohol
content of 280 ppm (determined by gas chromatography). The acid
number of the ester was 0.026 mg KOH/g. The tin content is below 1
mg/kg (determined by means of atomic spectrometry (ICP-OES) in
accordance with DIN EN ISO 11885).
* * * * *