DE2104206A1 - Process for the continuous production of alkyl orthoformate - Google Patents

Description

Troisdorf, January 27, 197t 71 002 (1870)

DYNAMIT NOBEL AKTIENGESELLSCHAFT Troisdorf, District Cologne

"Process for the continuous production of orthoaric acid alkyl ester"

The invention relates to a continuous process for the production of alkyl orthoformate by reacting chloroform with alkali metal alkoxides.

There are already numerous methods for the production of alkyl orthoformate known. A summary of the methods of preparation can be found in the "Organic Synthesis" Coll. VoI I, P. 253 ff »" Houben Weyl, Methods of Organic Chemistry ", 4. Edition, Volume 6, Part 3 (1965), pp. 300 to 308 and in "Organic Chemistry" Vol. 14 (1970), pp. 2 to 54, (Carboxylic Ortho Acid Derivatives by Robert H. De Wolfe).

These known processes are discontinuous and have considerable disadvantages: numerous by-products are formed which reduce the yield considerably and make the economic isolation of the pure ortho ester very difficult or impossible. The best yields that are obtained by the known processes are, according to German Patent 919.465, 87 % of unclean orthoformic acid trirae

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thylestei? with a boiling range of 95 to 102 ⁰ C based on the methylate used and 65 % unclean triethyl orthoformate (boiling range 135 to 142 ⁰ C) based on sodium ethylate.

In the patent mentioned, the poor yields of orthoformic acid esters of the known processes are reduced to the low ones Stability of the resulting orthoesters in relation to the reaction medium returned. In the method according to this patent specification is specified as a condition that the resulting Ester must be separated from the reaction mixture immediately after the reactants have been brought together.

The competing reactions that occur in the implementation of chloroform occur with an alcoholic solution of alkali alcoholates are outlined in "Organic Chemistry" Vol 14 (1970), p. 12. In addition to carbon monoxide and alkenes, the side reactions of the intermediate dichlorocarbene in the alcoholic alcoholate solution occur regarded as the main cause of the modest yields.

Another disadvantage of the known process is that the alkali metal chloride formed in the reaction is caused by the addition of Water is brought into solution and thus separated from the ester; this creates an additional technical one Expenditure.

It has now surprisingly been found that orthoformic acid esters from chloroform and alkali alcoholate

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let that one see the two reaction components in approximately stoichiometric amounts continuously at the same time to a reaction vessel, the reaction is carried out in the absence of water and as complete as possible exclusion of oxygen at temperatures between 40 and 120 ⁰ C and a pressure of 1 to 8 ata, the reaction products continuously withdraws and then the separation of the alkali metal chloride formed is carried out from the reaction solution with exclusion of water.

In this way of working it was surprisingly found that that the yields, especially in the case of trimethyl orthoformate, are largely independent of the reaction temperature and the reaction time and are much higher than in the known batch processes. That means that contrary to the known State of the art The orthoesters formed are resistant to the reaction medium. It is therefore not necessary to separate these immediately from the reaction mixture.

As a reactor, in particular a longer reaction tubes are suitable, m which are advantageously constructed such that settling of the Alkälichlorids which forms in the reaction, is prevented. However, other reaction vessels with stirrers can also be used and several reactors can be connected in series so that most of the reactants are converted in the first reactor and the reaction is completed in the downstream reactors, if necessary at elevated temperature and pressure.

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When using two or more reactors connected in series, it is advantageous to convert up to 80 % of the reactants in the first reactor and to complete the reaction in the reactors connected downstream. The alkali metal chloride is expediently separated off after the last reactor.

In the procedure according to the invention, it is important to ensure that that the two reaction components are present as a homogeneous mixture as quickly as possible. This can be done either by violent Mix the components using a high speed stirrer at a speed of about 100 to 1000 Revolutions / min, or the mixture is left at a speed of about 0.3 to 10 m / sec. through a pipe section flow.

The resulting considerable heat of reaction can be dissipated both by external cooling and by evaporative cooling. The temperature in the reactor should be about 40 to 120 ⁰ C. In general, it is preferred to keep the reaction temperatures as high as possible in order to increase the space-time yields. If you use temperatures above the boiling range, you need an apparatus that can withstand moderate pressures. Preferred temperatures are in the range of 60 to 10O ⁰ C.

Sodium and / or potassium alcoholates are preferred as alcoholates used. They are used as a solution in the appropriate alcohol. The concentration of the solution should be

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are preferably adjusted so that an almost saturated solution is present under the desired reaction conditions (pressure and temperature). In principle, however, it is also possible to carry out the reaction according to the invention with an alcoholate solution of a lower concentration of, for example, 10 % by weight or even lower.

The two reactants should be about stoichiometric Quantities are brought to implementation. A small excess of chloroform in the amount that the molar ratio of chloroform: alkali alcoholate is between 1.0: 3 and 1.2: 3.

The reaction conditions (residence time, temperature, pressure) are advantageously set so that the alkali metal chloride formed during the reaction contains 0 to a maximum of 1 % alkali metal alcoholate and the solution freed from the alkali metal chloride still contains about 0.5 to 2 % chloroform.

The work-up in the procedure according to the invention is continuous The reaction mixture obtained can be carried out in a simple manner using methods known per se. In general the alkali metal chloride formed is removed by centrifugation or filtration and / or evaporation of the reaction solution, and then the alcohol is separated from the orthoester by distillation.

If desired, the work-up can also be carried out batchwise be performed.

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For the method according to the invention, devices are made of stainless steel Steel is particularly suitable. The invention is illustrated by the following examples, in which all parts are parts by weight represent:

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21Ö420S

example Λ

The continuous production of trimethyl orthoformate was carried out under nitrogen in an apparatus which consisted of 2 reactors. The first reactor had a capacity of 20 liters and the second 30 liters. 1200 parts of chloroform per hour and 5100 parts / hour of a 32% strength by weight sodium methylate solution in methanol were introduced into the first reactor. The two reaction components were mixed well and then fed directly to the second reactor. The temperature of the reaction ^ j onsgemisches was maintained by external cooling to about 60 ⁰ C. The crude reaction product was continuously withdrawn from the second reactor, the liquid content in both reactors being kept constant over the entire duration of the experiment. The sodium chloride was continuously separated off by centrifugation from the reaction mixture withdrawn from the second reactor. The freed from NaCl solution was in a known manner by distillation aufgearbeitet..Aus column could hour 130 parts Orthoester (boiling point 102 ⁰ C) 96.abgezogen having a purity of 99.8 J. This corresponded to a yield of 97.3 % of theory, based on chloroform and 97 % of theory, based on sodium methylate.

Example 2

The same apparatus as in Example 1 was used for this experiment. In the reactor were 600 parts of chloroform / hour and a solution of sodium ethylate in ethanol with 20 wt.% Ethylate is fed in at a rate of 5100 parts / hour.

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leads. The reaction mixture was been deducted from the first reactor and continuously fed to the second reactor from which the reaction product was removed so that the contents of both the reaction vessels remained practically constant. The mixture was stirred well in each reaction vessel and kept at about 65 ° C. by external cooling. The sodium chloride was separated off and the reaction mixture was worked up by distillation as described in Example 1.

590 parts of ethyl orthoformate / hour were withdrawn from the column, which corresponded to a yield of about 79 % of theory. The boiling point of the orthoformate was 146 ° C.

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Claims (4)

2104 * 06 'claims 1. A process for the preparation of trialkyl orthoformate by reacting an alcoholic alkali metal alcoholate solution with chloroform, characterized in that the two reaction components are continuously used in approximately stoichiometric amounts. -.- borrowed a reaction vessel at the same time, the reaction in the absence of water and as complete as possible exclusion of oxygen at temperatures between 40 and 120 ° C and a pressure of 1 to 8 ata, the reaction pro (^ products are continuously withdrawn and then the alkali halides formed are separated off with the exclusion of water. 2. The method according to claim 1, characterized in that a molar ratio of chloroform: alkali metal alcoholate of 1.0 to 1.2: 3 selects and the excess chloroform after distillation Separation continuously fed back into the reactor. 3. Verfahrön according to claims 1 and 2, characterized in that the resulting after separation of the alkali metal halides reaction solution preferably contains 0 to 5%, 0.5 to 2% _t of chloroform. 4. Process according to Claims 1 to 3, characterized in that that the. Implementation takes place in the absence of air. Dr.Sk/Ko 209835/1187