Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-02-28
2003-05-06
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S484000, C568S485000
Reexamination Certificate
active
06559346
ABSTRACT:
The present invention relates to a process for the continuous preparation of glutaraldehyde by reaction of alkoxydihydropyrans of the formula I
where R is a straight-chain or branched C
1
-C
20
-alkyl, preferably C
1
-C
8
-alkyl, in particular a methyl group, with water at from 0° C. to 200° C., preferably from 40 to 150° C., and a pressure in the range from 0.01 bar to 16 bar, preferably from 0.1 to 5 bar.
Glutaraldehyde is used, for example, as a microbiocide or in tanning.
U.S. Pat. No. 4,244,876 and the associated U.S. Pat. No. 4,448,977 describe storage-stable compositions comprising glutaraldehyde acetals and an organic acid as catalyst from which an aqueous solution of glutaraldehyde can be prepared quickly when required by addition of water. This solution is used, in particular, as biocide for the control of sulfur bacteria in oil wells. For this purpose, separation of the reaction mixture into its pure components is not necessary and the unpurified hydrolysis product is used. A 2-alkoxy-3,4-dihydropyran is reacted with an alcohol or glycol in the presence of an acid catalyst, e.g. a strong acid ion exchanger, to give a mixture of 2,6-dialkoxytetrahydropyran, dialkoxypentanal and 1,1,5,5-tetraalkoxypentane. After the ion exchanger has been separated off, an organic acid is added to the mixture. The resulting mixture is storage-stable. At the point of use, e.g. a drilling site, it can be converted into a glutaraldehyde-containing aqueous solution by addition of water.
The European patent application EP 0 066 224 A1 describes a process for preparing an essentially water-free glutaraldehyde precursor from which glutaraldehyde can be liberated within a short time by addition of water. To prepare the storage-stable precursor, a 2-alkoxy-3,4-dihydropyran is reacted with water in a molar ratio of from 1:1 to 3:1 at from 30 to about 100° C. in the presence of an acid catalyst, e.g. an acid ion exchanger. This gives a mixture comprising 2-hydroxy-6-methoxytetrahydropyran as main component together with traces of 2,6-dimethoxytetrahydropyran and glutaraldehyde. After the acid catalyst has been separated off, e.g. by filtration, the mixture is storage-stable. Addition of water results in hydrolysis to form glutaraldehyde. No provision is made for purifying the glutaraldehyde.
JP 72 26 488 discloses a process for the continuous preparation of glutaraldehyde by hydrolysis of a 2-alkoxy-3,4-dihydropyran in the presence of an acid catalyst. For this purpose, a mixture of the 2-alkoxy-3,4-dihydropyran and water in a molar ratio of from 1:2 to 1:100 is heated to from 50 to 200° C. The process is carried out so that a concentration of from 0.5 to 10% by weight of the 2-alkoxy-3,4-dihydropyran is maintained in the system. No provision is made for further purification. The reaction product obtained is used as tanning agent for leather.
U.S. Pat. No. 2,546,018 describes the synthesis of glutaraldehyde and C-substituted glutaraldehydes starting from dihydropyrans. The hydrolysis of the dihydropyran can be carried out in the presence or absence of acid catalysts, with an uncatalyzed reaction being preferred because of the simpler work-up of the mixture after the reaction. The reaction can be carried out batchwise, and it is also proposed that the alcohol formed be removed continuously from the reaction mixture during the reaction. It is also proposed that the reaction be carried out continuously. For this purpose, the reaction mixture is said to be passed through a tubular reactor which is heated to an appropriate temperature. The flow rate is selected so that the desired conversion has taken place at the outlet of the reactor. After the reaction mixture has left the reactor, it can either be collected first and then distilled batchwise or, as an alternative, a continuous distillation with the desired fractions being separated off is proposed. In each of the examples in this patent, the hydrolysis of the dihydropyran is carried out in a first step and a fractional distillation is subsequently carried out in a second step. A disadvantage of this process is that an elaborate apparatus is necessary, with the hydrolysis being carried out in a first stage using a first apparatus and the desired product being separated off by fractional distillation in a second stage using a second apparatus. This is cumbersome and incurs costs.
It is an object of the present invention to provide a process by means of which glutaraldehyde or C-substituted glutaraldehydes can be prepared continuously in increased purity in a simple manner, with the outlay for apparatus being kept as small as possible in order to keep production costs low.
We have found that this object is achieved by a process for the continuous preparation of glutaraldehyde by reaction of an alkoxydihydropropan of the formula I with water at from 0° C. to 200° C. and a pressure in the range from 0.01 bar to 16 bar to form glutaraldehyde and the alcohol corresponding to the alkoxy group, wherein water and alkoxydihydropyran are fed continuously to a reaction column, preferably at a point between the top and the bottom outlet of the reaction column, and a distillate enriched in the alcohol corresponding to the alkoxy group is taken off at the top of the column and a product enriched in glutaraldehyde is taken off at the bottom.
The apparatus used for the reaction can be very compact since the hydrolysis of the alkoxydihydropyran is carried out in the column and it is therefore not necessary to provide a separate vessel for carrying out the hydrolysis reaction. The continuous reaction mode significantly reduces the dimensions of the plant for the same throughput per unit time compared to a batchwise reaction with the alcohol formed and the glutaraldehyde being distilled off separately. Selection of appropriate reaction parameters or appropriate dimensions of the plant makes it possible to achieve virtually complete conversion of the alkoxydihydropyran, so that an increased yield can be achieved and the glutaraldehyde formed has a higher purity than that obtained in processes known hitherto.
The reaction rate can be increased by carrying out the reaction in the presence of an acid catalyst. Suitable acids are organic acids such as saturated and unsaturated carboxylic acids having from 1 to 10 carbon atoms. It is also possible to use polyfunctional acids such as maleic acid. Preference is given to using inorganic acids such as phosphoric acid, boric acid, nitric acid, sulfuric acid or acid salts, e.g. NaH
2
PO
4
. If acids which are not readily volatile under the operating conditions of the reaction column are used, they are preferably added in the upper part of the reaction column. When using acids which are volatile under the operating conditions, they can also be added in the lower or middle part of the reaction column. The amount of acid should be such that an acid concentration in the range from 0.0001% by weight to 10% by weight, in particular from 0.01% by weight to 3% by weight, is obtained in the stream leaving the bottom of the column. The catalysts are preferably used as solutions. Suitable solvents are water, alcohol, the alkoxydihydropyran or glutaraldehyde/water mixtures.
In place of liquid acids, catalytically active packing comprising solid acids can also be installed in the reaction column. Such solid acids are, for example, ion exchangers such as Amberlyst® 15 or the bleaching earth catalysts mentioned in DE 44 29 262. The catalysts are generally arranged in the column so that intimate contact of the reaction solution with the catalyst is possible but the solid catalyst is kept in place in the column by means of screens or filters. An example of such an arrangement is KATAPAK® from Sulzer. Further solid catalysts which can be used are thin layer catalysts in the case of which a catalytically active composition has been applied directly to internals, ordered packing or random packing in the column, e.g. by impregnation and subsequent drying.
The reaction column preferably has at least 2, in particular at least 3, theoretical plates.
Oost Carsten
Therre Jörg
BASF - Aktiengesellschaft
Keil & Weinkauf
Richter Johann
Witherspoon Sikarl A.
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