Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2001-08-31
2003-04-29
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S020000, C560S106000, C560S203000, C560S204000
Reexamination Certificate
active
06555703
ABSTRACT:
BACKGROUND
The invention relates to a process for the preparation of carboxylic acid benzyl esters from dibenzyl ethers.
Benzyl acetate, the main component of jasmin oil, is an important fragrance for the preparation of scent compositions and starting material for the preparation of fruit ethers.
The preparation of benzyl acetate has already been widely reported. Thus, for example, the preparation of benzyl acetate by reacting benzyl alcohol with acetic acid has been known for a long time. Benzyl acetate can also be prepared by reacting benzyl chloride with alkali metal acetates, optionally in the presence of phase transfer reagents (Wang et al., Chem. Eng. Commun. 100, (1991), 135-147). A disadvantage is the formation of salts which have to be disposed of and thus reduce the costefficiency of this process.
DD-A5-286 577 describes the preparation of benzyl acetate by reacting dibenzyl ether with acetic anhydride. Disadvantages are the drastic reaction conditions (300° C./20 MPa) and the only moderate yields.
The object of the invention was therefore to provide a process for the preparation of dicarboxylic acid benzyl esters starting from dibenzyl ethers, which can be carried out under mild reaction conditions and leads to good yields.
Surprisingly, we have now found a process for the preparation of carboxylic acid benzyl esters and dibenzyl ethers which is characterized in that dibenzyl ethers are reacted with carboxylic acids in the presence of heteropolyacids as catalysts.
SUMMARY
The invention relates to a process comprising reacting a dibenzyl ether with a carboxylic acid in the presence of a heteropolyacid and forming a carboxylic acid benzyl ester. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DESCRIPTION
The invention relates to a process comprising reacting a dibenzyl ether with a carboxylic acid in the presence of a heteropolyacid and forming a carboxylic acid benzyl ester.
The dibenzyl ether used in the process according to the invention is an unsubstituted or substituted dibenzyl ether which can, for example, carry one or more substituents from the series branched or straight C
1
-C
6
-alkyl, C
1
-C
6
-alkoxy, CN, CO(C
1
-C
6
)-alkyl, NO
2
or halogen. Preferred substituents are methyl, methoxy or chlorine. Particular preference is given to using unsubstituted dibenzyl ether.
In the process according to the invention, dibenzyl ethers or dibenzyl ether/benzyl alcohol mixtures, as are produced, for example, during the preparation of benzyl alcohol from benzyl chloride, can be used. The content of dibenzyl ether in dibenzyl ether/benzyl alcohol mixtures may, for example, be from about 50 to about 100% by weight, preferably from about 60 to about 100% by weight, particularly preferably from about 70 to about 100% by weight.
The carboxylic acids used in the process according to the invention are straight-chain or branched alkyl-, aryl- or aralkylcarboxylic acids which are saturated or unsaturated and contain 1 to 50 carbon atoms, preferably 2 to 30 carbon atoms, particularly preferably 2 to 10 carbon atoms. In the process according to the invention, it is possible to use acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, caprylic acid, lauric acid, myristic acid, stearic acid, oleic acid, acrylic acid, cinnamic acid, phenylacetic acid, benzoic acid or salicylic acid. Very particularly preferred carboxylic acids are acetic acid and propionic acid.
The process according to the invention is preferably carried out with removal of water that forms during the process. It is appropriate to remove the water by distillation or by passing through an inert gas such as nitrogen. To remove the water formed, preference is given to using dehydrating agents such as zeolites, aluminium oxides or clay earths. Particular preference is given to removing the water formed by carrying out the reaction in the presence of the corresponding anhydride of the carboxylic acid used as dehydrating agent. Very particularly preferred anhydrides are acetic anhydride and propionic anhydride.
In the process according to the invention, from about 2 to about 50 equivalents of carboxylic acid, preferably from about 3 to about 30 equivalents, particularly preferably from about 4 to about 20 equivalents, based on dibenzyl ether, are used.
If the process according to the invention is carried out in the presence of the corresponding anhydride of the carboxylic acid used, then from about 0.1 to about 10 equivalents of anhydride, preferably from about 0.5 to about 7.5 equivalents, particularly preferably from about 1 to about 5 equivalents, based on dibenzyl ether, are preferably used. Since one molecule of anhydride used reacts with the uptake of water to give 2 molecules of carboxylic acid, it is possible to use smaller amounts of carboxylic acid in the process according to the invention. From about 1 to about 25 equivalents of carboxylic acid, preferably from about 1.5 to about 15 equivalents, particularly preferably from about 2 to about 10 equivalents of carboxylic acid, based on dibenzyl ether, are then preferably used.
In the process according to the invention, the heteropolyacids used are preferably those of the formula (I)
A
a
X
b
M
c
O
d
(I)
in which
A represents protons and/or metal cations
X is P, Si, B, Ge, As, I, Se or Te
M is W, Mo, V or Cr
a is 3, 4, 5 or 6, such that the heteropolyacids or salts thereof are electrically neutral
b is 1 or 2
c is 12 or 18 and
d is 40 or 62.
Suitable cations A which are to be mentioned are, for example, cations of the alkali metals, such as lithium, sodium, potassium, rubidium or caesium, or cations of the metals manganese, nickel, cobalt, copper or lanthanum or protons.
Preferred heteropolyacids are phosphomolybdic acid, phosphotungstic acid, phosphovanadic acid, silicomolybdic acid, silicotungstic acid, silicovanadic acid, and particularly preferred heteropolyacids are phosphomolybdic acid, phosphotungstic acid, silicomolybdic acid and silicotungstic acid.
Preferred heteropolyacids are also those of the Keggin type, i.e., compounds of the formula (I) in which b is 1, c is 12 and d is 40, and those of the Dawson type, i.e., compounds of the formula (I), in which b is 2, c is 18 and d is 62. Particularly preferred compounds are A
3
[PMo
12
O
40
], A
3
[PW
12
O
40
], A
3
[SiMo
12
O
40
] and A
3
[SiW
12
O
40
].
Methods for the preparation of the heteropolyacids are known and described, for example, in Römpp, Lexikon der Chemie volume 3, 10th edition, Stuttgart/New York 1997, p. 1741; Chemical Reviews 98, 1998, 1ff or Catal. Rev. Sci. Eng. 37, 1995, 311ff.
The heteropolyacids can also be used in the form of their hydrates. It is also possible to use mixtures of heteropolyacids in the process according to the invention.
In the process according to the invention, the heteropolyacids may be used or may be present as homogeneous catalysts or as heterogeneous catalysts. Whether the heteropolyacids are present as homogeneous or heterogeneous catalysts depends on the type and amount of the heteropolyacid used. Furthermore, the heteropolyacids can be used as heterogeneous catalysts applied to an inert support. Suitable support materials are, for example, activated carbon, silica gel, aluminium oxide, alumosilicates, such as zeolites, or phyllosilicates, clay earths, titanium oxides or zirconium oxides.
If supported heteropolyacids are used in the process according to the invention, then these are preferably used in dried form. The drying can be achieved by heat and/or reduced pressure. Furthermore, drying may take place by washing with hydrophilic liquids such as the carboxylic acid used in the process or the corresponding carboxylic anhydride, or by azeotropic distillation with organic solvents, e.g., toluene, xylene or methylene chloride.
The supported heteropolyacids can be used as powders or molded bodies, e.g., balls, cy
Ooms Pieter
Schenke Bernd-Ulrich
Akorli Godfried R.
Bayer Aktiengesellschaft
Eyl Diderico van
Richter Johann
Zucker Paul A.
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