DE2453284A1 - PROCESS FOR THE MANUFACTURING OF CHLOROCAR ACID ESTERS - Google Patents

Description

BACP Aktiengesellschaft

Our reference: O.Z. 30 968 mu / yes 6700 Ludwigshafen, November 7, 1974

Process for the production of chlorocarbonic acid esters

Addendum to patent. ... ... (patent application P 22 51.206.7-42)

Chlorocarbonic acid esters - also known as chloroformic acid esters or chlorocarbonates - are produced by converting alcoholic Compounds containing groups obtained with phosgene »The reaction can be catalyzed by Ansolvo acids or bases will; The hydrogen chloride formed during the reaction is also an effective catalyst, so that the reaction can take place externally without adding a catalyst.

Chlorinated esters, especially of polyhydric alcohols, are required in high purity; they are used e.g. for production organic polycarbonate. Since the later purification of the esters is hardly possible because of their sensitivity it is important that the production of the chlorocarbonic acid esters is as free of by-products as possible. more details are dealt with in the description of the main patent.

The invention according to the main patent relates to a process for producing highly pure Chlorkohlensäureester of mono- or polyhydric alcohols by continuously reacting essentially equivalent amounts of phosgene with an alcohol in the presence of excess phosgene and at a temperature below 5O ⁰ C and with a residence time of less than 60 minutes, continuously feeding phosgene and alcohol to a reaction vessel containing at least 20 wt the amount of the reaction mixture corresponding to the added amounts of alcohol and phosgene is deducted, this - if appropriate

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after passing through a post-reaction zone - freed from phosgene and hydrogen chloride and the phosgene, if appropriate together with at least part of the hydrogen chloride of the Reaction zone feeds back.

There are several reasons why this procedure still needs improvement: Mixtures with a high content of phosgene have a high dissolving power for hydrogen chloride, so that this is no longer released immediately after the reaction is gassed, but only after a delay; in technical operation this leads to uncontrolled development of gas bubbles Disturbances «

On the other hand, a high excess of phosgene is undesirable from the standpoint of economy, because it is known that the recovery of low-boiling substances must be bought at the cost of using expensive coolants. On the other hand, reducing the phosgene excess leads to an increased formation of carbonates, i.e. completely esterified products. This circumstance occurs especially with the esters of low molecular weight alcohols., Z ₀ B-. the methyl chlorocarbonic acid ester.

It has now been found that the procedure according to the main patent gives a very satisfactory result if it is modified somewhat; the invention therefore relates to a further embodiment of the invention according to the main patent ο ο "ο" ο ", (patent application P 22 51 206" 7-42) ₃ by choosing the time for the homogeneous mixing of the alcohol to be less than 1 second, whereby in equilibrium over time, a phosgene excess of only at least 2% by weight in the reaction mixture, a temperature of up to 70 ° C. and a residence time of up to 300 minutes can be maintained "

The invention is based on the knowledge ₉ that there is a much more extensive relationship between the required phosgene excess and the mixing time than was previously assumed

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be sufficient to ensure that there is no shortfall can occur - provided that a sufficiently short mixing time is achieved. Of course, this does not mean that from Apart from the economy - a larger excess of phosgene would be disadvantageous for the reaction.

In fact, the reaction of the first phosgene chlorine atom with the alcohol is a very rapid reaction; she is a few decimeters after passing through a test section (the flow velocity is around 10 cm / sec) practically ended after mixing, as can be easily established in the experiment.

According to a preferred procedure, the rapid mixing of the alcohol with the reaction mixture and the Fresh phosgene caused by a mixing nozzle, with - preferably coaxially - phosgene and alcohol the reaction mixture at a high speed, e.g., at least about 5, practically between about 5 to 100 m / sec. In practice, the supply of phosgene through the central bore, which is expediently a diameter of about 0.5 to 10 mm. In any case, these measures ensure a mixing time of less than 1, usually even less than 0.5 seconds. On the other hand, the end of the mixture can be recognized by the fact that the material jet from the mixing nozzle compared to the reaction mixture has come to rest, which is generally in 20 to 60 cm from the nozzle mouth of the Case is (to be observed in a glass apparatus). This is where the evolution of hydrogen chloride generally occurs and indicates an already well advanced reaction.

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example

To demonstrate the invention, 25 liters of methanol and 49 liters of phosgene are continuously fed into a closed tubular reactor with a capacity of 200 liters and filled with methylchlorocarbon ester, which at a reaction ^{temperature of 31 °} C. results in a steady phosgene excess - determined analytically at the reactor outlet - of 10 ₉ 7 % leads.

a) comparison

The reactor is initially equipped at the lowest point with a dip tube for phosgene feed and a tube that is blown out at the end and perforated on one side for the methanol feed. The circulation is brought about by the HCl gas evolved in the ascending part of the reactor. The mixing of alcohol and reaction mixture is partly due to the stirring action of the gas bubbles and ends after a distance of about 50 cm (mixture speed about 20 cm / sec). Carbonate content in the reaction product after phosgene and HCl have been removed about 2.3 %>

b) procedure according to the invention

The supply is through two concentric mixing tubes, the inside of which has a free cross section of 1.15 ram and the outside of which has a free cross section of 2.6 mm ₉ ; the phosgene is supplied through the inner pipe. The amount of phosgene and methanol fed in per hour is slightly increased compared to the comparison; 60 or 30 liters are implemented each time. The gas development zone begins at a distance of about 30 to 40 cm behind the mouth of the mixing tube. sec fraud. In an experiment lasting several months, the carbonate content fluctuates between about 0 _s 1 and 0 _s 4 %,

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Claims (1)

O.Z. 30 968 Claim Further development of the process for the production of chlorocarbonic acid esters of monohydric or polyhydric alcohols by continuously reacting essentially equivalent amounts of phosgene and an alcohol in the presence of excess phosgene and at a temperature of less than 50 ° C. and with a residence time of less than 60 minutes, according to patent. ... '.. (patent application P 22 51 206.7-42), being obtained continuously phosgene and a Reaktionsge alcohol-r mixed, the time in the balance at least 20 wt.% Of phosgene in the reaction mixture, feeding such that the time for the homogeneous mixing of the alcohol into the reaction mixture is less than 5 seconds, an amount of the reactant mixture corresponding to the added amounts of alcohol and phosgene is withdrawn, this is freed from phosgene and hydrogen chloride and the phosgene is returned to the reaction vessel, characterized in that the time for the homogeneous mixing of the alcohol chooses to less than one second, said mixture has a temperature of up to 70 ⁰ C and a residence time can be maintained up to 300 minutes in the time balance a phosgene excess of only at least 2 wt. # in the reaction *. BASF Aktiengesellschaft 609821/0950