DD292239A5 - PROCESS FOR THE PREPARATION OF ALKALISALCES OF THE N-ALKYL SUBSITUTED AMINO ALKANSAURES - Google Patents

Abstract

The invention relates to a process for the preparation of alkali metal salts of N-alkylated Aminoalkansaeuren after the Strereckersynthese. It is based on the task of making this process more economically and environmentally friendly by modifying the starting materials. It has been found that N-alkyl-substituted Aminoalkansaeurenitrile can be prepared from a substituted amine, an aliphatic aldehyde and a 15 to 30% Alkalizyanidloesung that can be saponified without further addition of alkali metal hydroxides to the alkali metal salt of N-alkyl-substituted Aminoalkansäure. The aqueous solution of the salts, predominantly alkali salts, of the N-alkyl-substituted aminoalkanoic acids are used predominantly for the selective removal of hydrogen sulphide and carbon dioxide from industrial gases. {N-alkyl-substituted aminoalkanesaeurealkalisalt; Strecker synthesis; Environmental Protection; Alkalizyanidloesung; substituted amine; aliphatic aldehyde; N-alkyl-substituted aminoalkane acid nitrile; saponification; Production method}

Description

Field of application of the invention

The invention relates to a process for the preparation of alkali metal salts of N-alkyl-substituted aminoalkanoic acids according to the synthesis of stretchers. The aqueous solutions of these salts are used for the selective removal of hydrogen sulfide and carbon dioxide from industrial gases.

Characteristic of the known state of the art

It is known that the synthesis of alkali metal salts of N-alkyl-substituted aminoalkanoic acids takes place in two steps. In the first step, the alkyl-substituted amine, an aldehyde and hydrocyanic acid is prepared from the N-alkyl-substituted Aminoalkansäurenitril. The catalyst used is calcium cyanide (DRP 694808). It is also possible to dispense with the catalyst and metered konzemrierte hydrocyanic acid so that the concentration of free hydrocyanic acid in the reaction mixture is always below 0.1% (DE-OS 2,503,582). This synthesis is known in the literature as Strereckersynthese. In a second step, saponification to the corresponding alkali metal salt of the N-alkyl-substituted aminoalkanoic acid is carried out after addition of 30 to 50% strength alkali hydroxide by heating in stages.

Disadvantage of this method is the necessary production of highly concentrated hydrogen cyanide by reaction of an alkali metal cyanide with a mineral acid and subsequent distillation. This can cause hazards due to hydrocyanic acid. By incomplete reaction of the alkali metal cyanides with the mineral acid, portions of alkali cyanide enter the wastewater and lead to environmental damage, unless a costly detoxification takes place.

Other disadvantages are a high salt load of the wastewater, severe corrosion of the equipment used and a high use of energy for the distillation of hydrogen cyanide.

Another method for the preparation of aminonitriles is Knoevenagel / Bucherer called (B.37,4511,1904). By adding a carbonyl compound to an aqueous concentrated sodium bisulfite solution, an addition compound is prepared. By further addition of the amine and following a very concentrated Alkalizyanidlösung the aminonitrile is prepared.

Further processing is possible only after extractive isolation of the nitrile. Therefore, this method has not been industrially applied.

Object of the invention

The aim of the invention is to avoid the environmental impact of carrying out the stretching synthesis for the production of N-alkyl-substituted aminoalkanoic acids by free hydrocyanic acid or alkali metal cyanides in the atmosphere and wastewater or the cost of detoxification.

Explanation of the essence of the invention

The invention is based on the object, a process for the preparation of alkali metal salts of N-alkyl-substituted aminoalkanoic acids after the Strereckersynthese with a mono- or dialkyl-substituted amine having 1 to 4 carbon atoms in the substituents and an aldehyde having 1 to 4 carbon atoms as starting materials to develop via the intermediate N-alkyl-substituted Aminoalkansäurenitril and subsequent saponification without using free hydrogen cyanide. According to the invention, the object has been achieved in that, instead of the concentrated hydrocyanic acid, a 15 to 30% strength aqueous alkali metal cyanide solution of the alkali metal is used, which is reacted with the starting materials arnir; and aldehyde in a molar ratio at 5 to 15 ° C are reacted. The resulting intermediate N-alkyl-substituted Aminoalkansäurenitril can be saponified without addition of alkali by raising the temperature to about 9O ⁰ C to the salts of N-alkyl-substituted aminoalkanoic acid. This effect of the nitrile formation reaction with aqueous alkali metal cyanide was not to be expected, since in the literature the stretching synthesis is always carried out with concentrated hydrogen cyanide (Organikum, VEB Deutscher Verlag der Wissenschaften, Berlin 1977, 558; Methodicum Chimicum, Georg Thieme Verlag Stuttgart, 1974,! 3D 6,616) 1; H. Beyer, Lehrbuch der organischen Chemie, Hirzel Verlag, Leipzig, 1968,225).

By addition of alkaline substances, even the reaction should shift towards starting materials (Houben Weyl, Vol. VIII, 1952, 275).

It was thus more surprising that the synthesis of the N-alkyl-substituted aminoalkanesonitrile proceeds smoothly with yields up to

98% of theory, if the alkali metal cyanide is used as a 15 to 30% solution. In the first step of the reaction, the nitrile of the N-alkyl-substituted aminoalkanoic acid forms from the alkyl-substituted amine, an aliphatic aldehyde and alkali metal cyanide.

By heating the resulting reaction solution, the N-alkyl-substituted Aminoalkansäurenitril to alkali metal salt of

Saponified N-alkyl-substituted aminoalkanoic acid.

The N-alkyl-substituted Aminoalkansäurenitril is also extractable with conventional solvents.

By using aqueous alkali metal cyanide for synthesis, it is possible to avoid environmental damage. The economics of the process are improving considerably as plant parts, energies and chemicals have been saved.

The ratio of N-alkyl-substituted Aminoalkansäurenitril to alkali metal hydroxide in the saponification on its own.

Dosing errors are avoided.

embodiments

The invention will be explained in more detail below with reference to the following embodiments.

example 1

614 ml (5 mol) of dimethylamine 40% are added with stirring and cooling to 476 ml (5 mol) of formaldehyde 30% so that the temperature does not exceed 3O ⁰ C. It is then cooled to 10 ° C. Thereafter, at this temperature, 245 g (5 mol) of sodium cyanide, dissolved in 1000 ml of water, so metered that the temperature between 5 to 15 ° C moves. After a residence time of 1 hour at 15 ⁰ C, the reaction mixture is heated to 60 to 65 ⁰ C. After a further 2 hours, the reaction solution is heated to 105 ⁰ C, wherein distilled off an aqueous ammonia solution. After 8 hours saponification is complete

 There are obtained 612.5 g of the sodium salt of dimethylaminoacetic acid (98% of theory) in 1.51 aqueous solution.

Example 2

614 ml (5 mol) of dimethylamine 40% are added with stirring and cooling to 476 ml (5 mol) of formaldehyde 30%

Temperature does not exceed 30 ° C. It is then cooled to 1O ° C. Thereafter, at this temperature, 325g (5 moles)

Potassium cyanide, dissolved in 1200 ml of water, dosed so that the temperature between 5 to 15 ° C moves.

After a residence time of 1 hour at 15 ⁰ C, the reaction mixture is heated to 60 to 65 ° C. After a further 2 hours, the reaction solution is heated to 105 ⁰ C, wherein an aqueous ammonia solution distilled off. After 8 hours saponification is complete.

There are obtained 680 g of the potassium salt of Ν, Ν-dimethylsinoacetic acid (96.5% of theory) in 1.51 aqueous solution.

Example 3

365 g (5 mol) of n-butylamine are dissolved in 500 ml of water. While stirring and cooling 360 grams (5 moles) of butyraldehyde is added thereto so that the temperature does not exceed 3O ⁰ C. It is then cooled to 10 ⁰ C. Thereafter, at this temperature, 325 g (5 mol) of potassium cyanide, dissolved in 1200 ml of water, so metered that the temperature between 5 to 15 ⁰ C moves.

After a residence time of 1 hour at 15 ° C, the reaction mixture is heated to 60-65 ° C. After another 2 hours

the reaction mixture is heated to 105 ⁰ C, after which distilled off an aqueous ammonia solution. After 8 hours saponification is complete.

The conversion is 93% of the theoretical yield.

Claims (1)

A process for the preparation of alkali salts of N-alkyl-substituted aminoalkanoic acids after the streamer synthesis with a mono- or dialkyl-substituted amine having 1 to 4 carbon atoms in the substituents and an aliphatic aldehyde having 1 to 4 carbon atoms as starting material via the intermediate N-alkyl-substituted Aminoalkansäurenitril and subsequent saponification, characterized in that the reaction takes place to the N-alkyl-substituted Aminoalkansäurenitril with an aqueous 15 to 30% strength alkali metal cyanide solution in a molar ratio at a temperature of 5 to 15 ⁰ C.