DE2104911A1 - Process for the preparation of thiodipropionic acid compounds - Google Patents

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Process for the preparation of thiodipropionic acid compounds

The invention relates to a process for the preparation of thiodipropionic acid compounds by reacting Acrylonitrile or acrylic acid esters with hydrogen sulfide in the presence of a catalyst. It is known that starting from unsaturated alkyl nitriles or alkyl acid esters Produce thiodialkyl nitrile or thiodialkylic acid ester can by the unsaturated nitriles or the unsaturated acids themselves or their esters with an aqueous Phase of sodium hydrogen sulfide or sodium sulfide both in stoichiometric amounts or with an excess thereof Converts sulphides. You can use elevated temperatures. You can also use hydrogen sulfide as a gas phase give up and you can work under increased pressure. Sodium sulfide or sodium hydrogen sulfide as having an alkaline effect Substances are effective as catalysts. It is also known to have the same unsaturated compounds to react with hydrogen sulfide in the absence of water, substances with an alkaline effect are used as the catalyst, e.g. amines or alkali sulfides.

209837/1177

Bankhaus DelbrücK & Co, Cologne - Berliner Handels-Gesellschaft - Frankfurter Bank, Frankfurt a. M. · Deutsche Bank AG, Bensheim · Dresdner Bank AG., Darmstadt

German advance

9 1 Π / Q 1 1 Advance

£ I U H α J I Production GmbH

Sheet for writing from to

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Peroxides and UV light have also been proposed. It is common to all of these processes that a concentration occurs at the start of the reaction or in the course of the reaction present in non-remediated, unsaturated feedstock which can lead to undesired polymerization. This polymerization can take place so spontaneously that Explosive destruction of the system and thus corresponding hazards to the operation are possible.

It has now been found how the reaction can be carried out with absolute certainty. While in the majority of organic-chemical reactions the reaction speed decreases in line with the conversion, in most cases especially for the last 10 to 20 percent, and even asymptotically for the last 5 percent, this does not apply to the formation of thiodipropionitrile or thiodipropionic acid ester from the unsaturated acrylic compounds and hydrogen sulfide in the presence of a catalyst. It has surprisingly been found that the reaction proceeds equally quickly even in the presence of less than 1 percent acrylic compound if the desired end product, thiodipropionitrile or thiodipropionic acid ester, is used as the diluent. This makes it possible to design the process in a very simple and economical one-step continuous manner and to only have the acrylic compounds, which tend to spontaneously polymerize, in a concentration that eliminates any risk. The desired end product is immediately available in the form of the discharged solution. Solvents, which would otherwise have to be used in an uneconomically high excess, for example with a 95 % to 99% fraction, to achieve the same effect, are dispensed with.

209837/1177

German

1 Π / Q 1 1 advance

IU H a II Production GmbH

Sheet for writing from to

-3-

The end product used as a solvent is thereby pumped around in a circulatory system at great speed and at a suitable location, preferably on the level control vessel of the circuit, hydrogen sulfide is applied. In general, the reaction can be reduced Carry out normal pressure, but you can also drive with increased pressure. In this case, however, arise in addition to mentioned thiodi compounds also the corresponding ß-mercaptonitriles or esters in noticeable proportions.

At another suitable point in the circuit, the catalyst is metered in solid or in, for example, an aqueous solution. The unsaturated alkyl nitrile or the unsaturated alkyl acid ester is entered as raw material to the extent that that the rapid reaction in the presence of the catalyst reduces the concentration of unsaturated compounds never over $ 10, but preferably not over $ 1, lets come. From the level of the control container built into the circuit, the discharge valve can be controlled via a Control loop set and the running reaction solution either directly or after passing through a post-reaction section be freed from hydrogen sulfide in a manner known per se.

If the catalyst is in solid form, it is separated off by filtration, otherwise by separation in settling tanks or separators. The temperature in the circuit is kept between 30 and 100 C, preferably at k5 ° C.

example 1

A reaction tube with a diameter of 100 stroke and a length of 55 m, which is provided with cooling and heating sections, is followed by a circulation pump with an ^{output of 45 m J} / h, which with

209837/1177

German advance

Sheet for writing from to

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is connected to a level holding vessel with a capacity of 200 1 is placed at the beginning of the reaction tube. The circuit is filled with 450 l of thiodipropionitrile and 200 g of sodium hydrogen sulfide filled, the pump started and the mixture heated to 45 ° C. Then start with the dosage of 0.25 kg / h of a 20 $ aqueous solution of sodium hydrogen sulfide and hydrogen sulfide the surface of the solution in the level vessel or into the working solution flowing into it. 31 »3 kg acrylonitrile / h are metered on the suction side of the pump. The reaction starts immediately, the heat is transferred through the cooling jackets the reaction tube discharged and the temperature to 45.degree regulated. The specified amount of acrylonitrile consumes about 11.5 kg H "s / h. As the level rises the control circuit for the discharge begins to work and the discharge valve opens so far that the fill level remains approximately constant in the level holding vessel. The draining thiodipropionitrile contains even after the plant has been running Never more than $ 1 acrylonitrile for several weeks. The solution runs into the storage tank via an HS stripper.

Example 2

In the plant described, methyl acrylate is fed in instead of acrylonitrile and the procedure is the same. The consumption of hydrogen sulfide falls to 6.5 kg in accordance with the molecular weights. The process is analogous Example 1.

209837/1177

Claims (6)

German advance Sheet for writing from to Claims \ J Process for the production of thiodipropionic acid compounds by reacting hydrogen sulfide and acrylic compounds. in the presence of alkaline substances or peracids or UV light, characterized in that the reaction takes place continuously in highly dilute solution and the thiodipropionic acid compound formed is used or initially charged as a solvent. 2. The method according to claim 1, characterized in that the concentration of acrylic compounds on no more than 10 5 ^, but preferably not above $ 1. 3. The method according to claim 1 and 2, characterized in that the reaction is circulated and the acrylic compounds and the catalyst is fed in continuously and the thiodipropionic acid compound is continuously discharged will. H. Process according to claims 1-3 »characterized in that the hydrogen sulphide is pressurized or pressurized with a slight excess pressure and is replenished to the extent that it is consumed. 5. The method according to claims 1-4, characterized in that the ratio of the dispensed or added volumes to Circulation volume is 1: 5 to 1: 5O, preferably 1 ι 1O . 6. The method according to claims 1-5 »characterized in that that the reaction takes place in a reaction tube and the circulation rate of the circulation pump per hour is 10 to 150 times, preferably 90 to 100 times the volume of the liquid amounts to. 209837/1177