CS201910B1 - Method for the continuous preparation of substituted symmetric urea - Google Patents

Description

The invention relates to a continuous process for the preparation of the substituted symmetrical ureas of the formula I

X-N-CO-N-X (I);

YX wherein X and Y are hydrogen, C 1 -C 4 alkyl or phenyl optionally substituted with one to two C 1 -C 4 alkyl, wherein when one of the symbols is a hydrogen atom, the other has a different meaning, by treating phosgene with the corresponding amine of formula II

HN-X 1 (II),

Y wherein X and Y have the same meaning as in Formula I, in the presence of an aqueous solution of a hydrogen chloride evolving agent such as hydroxide or sodium carbonate.

The compounds of formula I are important intermediates for further syntheses or even used as products themselves. E.g. this includes diethyldipheaylurea, which is used as a stabilizer for cellulose nitrate, for example in the manufacture of gunpowder; it also includes diphenylurea, which is an intermediate in the manufacture of dyes.

201 910

To date, these substances have been produced by introducing an appropriate amine into the reactor, to which an aqueous sodium hydroxide or carbonate solution is added, and phosgene is added to the mixture with stirring. The resulting reaction mixture is then treated after separation of the aqueous layer, for example, by adding sulfuric acid to the organic phase, which binds the unreacted starting amine, which is then removed together with the acid layer. By _ee gave a crude product which was PEK may be further purified, e.g. by crystallization or distillation under reduced pressure. Typically, hydrocarbon shear solvents or alcohols are used for crystallization.

The basic disadvantage of this process is that the reaction of the amine with phosgene is carried out in the non-continuous pH range, starting with a multiple excess of alkali at the start of the reaction, where the pH is about 12-14, to about 8 per reaction. Initial excess alkalinity deteriorates the synthesis process, breaks down the phosgene feed and eventually the urea formed, thereby reducing the plant performance and reaction yield, which is about 78% of the theory, calculated on the amine used.

This disadvantage is overcome by a process for the continuous preparation of the substituted symmetrical ureas of the formula I

XN-CO-NX, _T , 11 ^(I) '

YY where X and Y are hydrogen, alkyl of 1 to 4 carbon atoms, or phenyl optionally substituted with one to two alkyl of 1 to 4 carbon atoms, wherein when one of the symbols is a hydrogen atom, the other has a different meaning , by treating phosgene with the corresponding amine of formula II

ΗΤΓ - X l (ID,

Y where X μ Y have the same meaning as in formula I, in the presence of an aqueous solution of a hydrogen chloride evolving agent such as sodium hydroxide or carbonate according to the invention, characterized in that the amine of formula TI and gaseous phosgene are introduced into a stirred of the reactor while continuously adding an aqueous solution of a hydrogen chloride-releasing agent, such as sodium hydroxide or carbonate, at a rate of maintaining a pH of 8 to 9 in the reaction mixture, maintaining the temperature between 50 and 85 ° C. , which is further processed to the desired product by any of the known methods.

An advantage of the process according to the invention is, in particular, that higher yields of substituted symmetrical urea of the formula I are obtained, which are around 90% of the theoretical relative to the starting amine of the formula II, as indicated in the examples.

Since the process according to the invention is operated at a pH of 8-9, the decomposition rate of the phosgene in question is considerably reduced compared to the practice hitherto used. whereas so far the amine: phosgene ratio was 2: 1.1 to 1.2 molar.

In addition to these advantages, it is necessary to add the continuous production process itself, which is easy to carry out with the usual measuring and technical equipment.

In order that the invention may be more fully understood, the following non-limiting Examples are provided.

Example 1

110 kg of N-ethylaniline, calculated as 100% and 45 kg of phosgene gas per hour, corresponding to a molar ratio of 0.91: 0.455, are continuously fed into a 100 liter stirred reactor. Simultaneously, 30 to 35 kg of sodium hydroxide is dosed as 100% in the form of a 15% solution so that the resulting pH of the reaction mixture is maintained in the range of 8 to 9. The sodium hydroxide solution dosing can also be controlled automatically according to the pH-meter aqueous phase of the reaction mixture. The temperature is maintained by gentle non-cooling to 60-70 ° C during the reaction. The effluent mixture was separated into water and an organic phase in the separator. The unreacted amine is removed from the organic phase by extraction with sulfuric acid at a temperature of 100-110 ° C to give crude diethyldiphenyl-Ν, Ν'-urea having a solidification temperature of 71-72 ° C and a yield of 90% of theory starting from. ethylaniline may be subjected to further purification by crystallization from a hydrocarbon solvent.

Example 2

850 g of aniline (9.1 mol) per hour and 450 g of gaseous phosgene (4.55 mol) per hour are continuously fed into a 1 liter laboratory stirred reactor. In parallel, 350 g of NaOH, calculated as 100%, is added in the form of a 10% aqueous solution, so that the resulting pH of the mixture leaving the reactor is maintained between 8 and 9. The NaOH solution is dosed automatically according to the pH-meter draining the aqueous phase of the reaction mixture. The temperature is maintained at 60-85 ° C by gentle cooling during the reaction. The effluent mixture is a suspension of diphenylurea in water and the residues of the starting amine are freed from acidification with sulfuric acid while heating to boiling. The precipitated diphenylurea is subsequently purified by recrystallization from ethanol or a hydrocarbon type solvent. Diphenylurea is obtained in a yield of 90% of theory, calculated on the starting aniline.

Claims (1)

OBJECT OF THE INVENTION. A process for the continuous preparation of substituted symmetrical ureas of formula (I) X-N-CO-N-X (I); YY where X and Y are hydrogen, alkyl of 1 to 4 carbon atoms, or phenyl, optionally substituted with one to two alkyl of 1 to 4 carbon atoms, wherein when one of the symbols is a hydrogen atom, the other has a different meaning , by treating phosgene with the corresponding amine of formula II HN - X Y (TI) Me X and Y have the same meaning as in formula I, in the presence of an aqueous solution of a hydrogen chloride-releasing reagent such as sodium hydroxide or carbonate, and after separating the aqueous phase from the resulting reaction mixture by quenching the remaining organic phase, e.g. II by adding sulfuric acid and separating the acidic layer, and optionally purifying the crude product obtained, for example by crystallization or distillation under reduced pressure, characterized in that the amine of the formula II n phosgene is fed to a stirred reactor and simultaneously hydrogen chloride, such as sodium hydroxide or sodium carbonate, is released at a rate that maintains a pH of 8-9 in the reaction mixture, the temperature of which is maintained at 50-85 ° C, while the reactor does not flow out The reaction mixture is removed and further processed to the desired product by any of the known methods.