Process for the preparation of halogenated carboxylic anhydrides
The present invention, which claims priority to European application No.
13170868.7, the whole content of this application being incorporated herein by
reference for all purposes, relates to a process for the preparation of halogenated
carboxylic anhydrides and, more particularly, to a process for the preparation of
5 halogenated carboxylic anhydrides by reacting a halogenated carboxylic acid
with sulfuric acid, oleum and/or disulfuric acid.
Halogenated carboxylic anhydrides like trifluoroacetic acid are valuable
reagents for the manufacture of various products in the pharmaceutical and
agrochemical industry.
10 It is known to prepare trifluoroacetic anhydride (Hudlicky, Chemistry of
Organic Fluorine Compounds, 1976, p. 726) by reaction of trifluoroacetic acid
with phosphoric anhydride. The method described therein is disadvantageous for
industrial production because phosphoric anhydride is a solid and tends to form
amalgams with the reactants and/or products.
15 Now therefore the invention makes available an improved process for the
production of halogenated carboxylic anhydrides. It is an object of the present
invention to provide a process for the production of halogenated carboxylic
anhydrides allowing for improved yields and/or purity of the products.
Furthermore, it is an object of the present invention to provide a process with a
20 more economical and/or more ecological waste and/or unwanted side product
profile, e.g. a process wherein the waste and/or side products are more easily
separated from the product of the process and/or wherein the waste and/or side
products are less toxic and/or less harmful to the environment. Furthermore, it is
an object of the present invention to provide a process starting from cheaper,
25 and/or more readily available reactants and/or reagents, as for example using
reactants with a lower degree of purity.
These and other objectives are achieved by the process of this invention.
Accordingly, the first embodiment of the present invention is a process for
the preparation of a compound of general structure (I) :
30 HalR2C(0)-0-C(0)CR2Hal wherein Hal is selected from the group consisting
of F, CI and Br ; and wherein R is independently selected from the group
consisting of H, F, CI, Br, alkyl and aryl ; which comprises reacting a compound
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of general structure (II): HalR2C(0)-OH wherein Hal and R are defined as
above, with sulfuric acid, oleum and/or disulfuric acid.
The term "sulfuric acid" is intended to denote pure sulfuric acid, H2S04,
as well as the aqueous solutions thereof. Preferably, the sulfuric acid used
5 according to this invention has a concentration of 70 wt % and above, more
preferably a concentration of 90 wt % and above, and most preferably
concentrated sulfuric acid is used, which has a concentration of about 98 wt %.
The term "oleum" is intended to denote mixtures of H2S04 and S03.
Concentrations of oleum are either expressed in terms of wt % S03
10 (called X % oleum) or as wt % H2S04. For example, 65 % oleum refers
to 114.6 wt % H2S04. The percentage of S03 in the oleum is also referred to as
the free S03. Thus, 65 % oleum contains 65 wt % free S03.
The term "disulfuric acid" is intended to denote H2S207.
The term "alkyl" is intended to denote an optionally substituted chain of
15 saturated hydrocarbon-based groups, such as, in particular, a C1-C6 alkyl. By
way of example, mention may be made of methyl, ethyl, propyl, isopropyl, butyl,
t-butyl, pentyl, isopentyl and hexyl.
The term "aryl" is intended to denote an optionally substituted group which
derives from an aromatic nucleus such as, in particular, a C6-C10 aromatic
20 nucleus, in particular phenyl or naphthyl.
In a preferred embodiment, Hal is fluorine. More preferably, the
compound of general structure (I) is trifluoroacetic anhydride and the compound
of general structure (II) is trifluoroacetic acid.
Another embodiment of the present invention is the reaction of acetic acid,
25 an acetate salt or a mixture thereof with sulfuric acid, oleum and/or disulfuric
acid to form acetic anhydride. Useful examples of the acetate salt include
sodium acetate, potassium acetate, calcium acetate, lithium acetate, magnesium
acetate, or any mixtures thereof. The acetate salt and/or the acetic acid can be
used in neat form or as a solution in a solvent, preferably as an aqueous solution.
30 In another preferred embodiment, the compound of general structure (II) is
reacted with oleum, preferably the oleum contains from 5 to 95 wt % free S03,
more preferably from 25 to 80 wt % free S03, most preferably from 50
to 70 wt % free S03, specifically 65 wt % free S03.
In another preferred embodiment, the halogenated carboxylic acid is
35 present in molar excess relative to the stoichiometry of the reaction. The total
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quantity of halogenated carboxylic acid is preferably from 1.05 to 2 times the
stoichiometry, more preferably 1.05 to 1.10 times the stoichiometry.
Suitably, the reaction is performed at elevated temperatures, wherein the
internal temperature of the reaction mixture is equal to or higher than the boiling
5 point of the product. Preferably, the reaction is performed at a temperature in the
reaction mixture from 50 to 150°C, preferably from 70 to 115°C. The
temperature of the reaction mixture refers to the internal temperature in the
reaction vessel.
In another preferred embodiment, the product is removed from the reaction
10 mixture by distillation, more preferably the distillation is performed using a
packing column. The packing column is suitably filled, e.g. with Raschig rings.
Also preferably, the distillation is performed using a reflux condenser for
controlling the rate at which the product is removed from the reaction mixture.
In another preferred embodiment, the reaction is performed in a reaction
15 vessel which is at least partially ceramic-lined and/or a glass-lined. Suitably, a
continuously-stirred Pfaundler vessel with a ceramic lining can be used. Also
preferably, the reaction is performed in a reaction vessel at least partially made
of an alloy containing nickel and/or molybdenum. Examples of suitable alloys
include Hastelloy B, Hastelloy B-2, or Hastelloy B-3.
20 A further advantage of the process according to the invention is that
halogenated carboxylic anhydride of high purity can be produced in high yields
even in case of reactants, i.e. the halogenated carboxylic acid, of lower purity are
employed. For example, tailing fractions containing unreacted halogenated
carboxylic acid and pollutants from previous reactions can be employed in the
25 process of the present invention. Thus, recycled halogenated carboxylic acid can
be used in the process of the invention. Accordingly, in a preferred embodiment,
the halogenated carboxylic acid employed in the reaction has a purity of equal to
or less than 98 %, more preferably a purity of less than 95 %, even more
preferably a purity of less than 90 %. Alternatively, the halogenated carboxylic
30 acid employed in the reaction has a purity from 50 % to 98 %, more preferably a
purity from 50 % to 95 %, even more preferably a purity of 50 % to 90 %. In
another preferred embodiment, the halogenated carboxylic acid used in the
process is comprised in a mixture also containing at least one product, at least
one reagent, at least one solvent and/or at least one side product from a previous
35 reaction step.
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Should the disclosure of any patents, patent applications, and publications
which are incorporated herein by reference conflict with the description of the
present application to the extent that it may render a term unclear, the present
description shall take precedence.
5 The invention will now be further described in examples without intending
to limit it.
Examples :
Production of trifluoroacetic anhydride
A 115 1 ceramic-lined Pfaundler stirred vessel equipped with a 2.5 m
10 packing column filled with 10 mm glass Raschig rings and equipped with a
condenser was filled with 70.5 kg trifluoroacetic acid followed by 19.1 1 65 %
oleum, i.e. oleum with 65 wt % free S03. Subsequently, the Pfaundler vessel
was heated by means of an oil bath to a temperature of 130 °C. The product was
removed by distillation at a rate of 7.4 kg/h and directed into PE-lined metal
15 drums. During the distillation the temperature of the reaction mixture changed
gradually from 78 °C to 96 °C. The yield of trifluoroacetic anhydride was
64.9 kg (99 %). The purity of the product was > 99.9 %. Additionally, 7.8 kg of
a tailing fraction was obtained that contained trifluoroacetic anhydride and
trifluoroacetic acid next to other not identified side products. This second
20 fraction can be submitted to the reaction mixture of a subsequent batch.
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CLAIMS
1. A process for the preparation of a compound of general structure (I)
HalR2C(0)-0-C(0)CR2Hal (I)
wherein Hal is selected from the group consisting of F, CI and Br ;
5 and wherein R is independently selected from the group consisting of H, F, CI,
Br, alkyl and aryl;
which comprises reacting a compound of general structure (II)
HalR2C(0)-OH (II)
wherein Hal and R are defined as above,
10 with sulfuric acid, oleum and/or disulfuric acid.
2. The process of claim 1 wherein Hal is fluorine.
3. The process of claim 2 wherein the compound of general structure (I)
is trifluoroacetic anhydride and the compound of general structure (II) is
trifluoroacetic acid.
15 4. The process of any one of claims 1 to 3 wherein the compound of
general structure (II) is reacted with oleum.
5. The process of claim 4 wherein the oleum contains from 5 to 95 wt %
free SO3, preferably from 25 to 80 wt % free SO3, more preferably from 50
to 70 wt % free SO3, most preferably 65 wt % free SO3.
20 6. The process of any one of the claims 1 to 5 wherein the halogenated
carboxylic acid is present in molar excess relative to the stoichiometry of the
reaction.
7. The process of any one of the claims 1 to 6 wherein the reaction is
performed at a temperature in the reaction mixture from 50 to 150°C, preferably
25 from 70 to 115°C.
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8. The process of any one of the claims 1 to 7 wherein the compound of
general structure (I) is removed from the reaction mixture by distillation.
9. The process of claim 8 wherein the distillation is performed using a
packing column.
5 10. The process of claim 8 or 9 wherein the distillation is performed using
a reflux condenser for controlling the rate at which the compound of general
structure (I) is removed from the reaction mixture.
11. The process of any one of the claims 1 to 10 wherein the reaction is
performed in a reaction vessel which is at least partially ceramic-lined and/or
10 glass-lined.
12. The process of any one of the claims 1 to 10 wherein the reaction is
performed in a reaction vessel at least partially made of an alloy containing
nickel and/or molybdenum.
13. The process of any one of the claims 1 to 12 wherein the compound of
15 general structure (II)
HalR2C(0)-OH (II)
employed in the process has a purity of equal to or less than 98 %, more
preferably a purity of less than 95 %, even more preferably a purity of less
than 90 %.
20 14. The process of any one of the claims 1 to 13 wherein the compound of
general structure (II)
HalR2C(0)-OH (II)
employed in the process is recycled material.
15. The process of any one of the claims 1 to 14 wherein the compound of
25 general structure (II)
HalR2C(0)-OH (II)
is employed comprised in a mixture also containing at least one product, one
reagent, one solvent and/or one side product from a previous reaction step.