DE800414C - Process for the preparation of 1-alkoxy-2-amino-4-nitrobenzenes - Google Patents

Description

(WiGBl. P. 175)

ISSUED NOVEMBER 6, 1950

p 16290 IV c j 12q D

In the production of the ethers of 2-amino-4-nitrophenol, which are known to be characterized by a sweet taste, one starts from the o-alkyl derivatives of the 2,4-dinitrophenol and subjects partial reduction using suitable reducing agents such as sodium sulfide, sodium disulfide, Xsodium hydrosulphide, ammonium hydrosulphide or Ziniiehlorür. In this reduction, only one nitro group of the dinitrophenol derivative is formed reduced to the amino group, but this creates two isomeric compounds with the Amino groups in the 2- or 4-position, of which only the 2-amino compound has the character of a sweetener.

There are already several separation routes for the decomposition of the mixture of isomeric X'itranilinderivate known. For example, the amine mixture is extracted with an organic solvent, the solvent evaporated, the oil obtained inoculated and strongly cooled, taking it partially solidified in crystalline form. The sweetener which has crystallized out is then centrifuged still adhering proportions of i-alkoxy-2-nitro-4-aminobenzene freed.

It is also known to mix the amine mixture with one that acts selectively for the sweetener Extract solvent, completely evaporate the solvent and remove the residue recrystallize from a suitable solvent. The precipitated crystals the sweetener is separated off and the mother liquor is completely evaporated. The one here residue obtained is combined with the first extraction residue and thus do the same Operation of extraction and recrystallization repeated to a second and optionally also get a third fraction of sweetener crystals.

It is also already known that the amine mixture can be converted into salts by treatment with an acid and then to separate them based on their different solubilities. These are particularly suitable the hydrochloride as the hydrochloride

Claims (1)

the i-alkoxy-2-nitro-4-aminobenzenes in contrast to the hydrochloricls of i-alkoxy-2-amino-4-nitrobenzenes (sweeteners) are sparingly soluble in cold, dilute hydrochloric acid. The last method of separation described has the disadvantage that the separation of the two isomers Amines by fractional crystallization of the hydrochloride is not complete, so that in the subsequent treatment of the mother liquor with sodium hydroxide solution, not only the 2-amino compound (Sweetener), but also considerable amounts of the 4-amino compound precipitate. It is therefore necessary to recrystallize the precipitated raw sweetener from a solvent, to keep it completely free from the bitter tasting i-alkoxy-2-nitro-4-aminobenzenes to obtain. This method fails completely if the sweetener is not in solid form but rather separates out as an oil and cannot be purified by crystallization, as is the case with e.g. B. at the i-sec. Butoxy-2-amino-4-nitrobenzene is the case. It has now been found that a much better separation of the isomeric arning mixture can be achieved by the mixture of the salts, expediently the hydrochloride, in aqueous Solution subjected to hydrolysis. Here z. R. the Hydrochloric! of i-alkoxy-2-amino-4-nitrobenzenes (Sweeteners) hydrolytically split, while the Hydrochloric! of i-alkoxy-2-nitro-4-aminobenzenes is so stable that it can be recrystallized from hot water. The precipitated free i-alkoxy-2-amino-4-nitrobenzene will smell it of trapped hyd! or id to free it after cooling in added an organic solvent, the solution washed with water and the solvent evaporated after drying, leaving the sweetener in pure form as a solid residue or obtained as an oil. This way of working is advantageous in all cases because the Separation of the salts, e.g. B. the hydrochloride, no complete separation in hydrochloric acid solution of the hydrochloride of the bitter substance is achieved, while the separation of the salts by hydrolysis only the sweetener component is excreted. In those cases in which the both free isomeric amino compounds are liquid and not after separation Crystallization can be purified like it z. B. in the i-sec. Butoxyderivaten is the case, the separation of the isomeric amino compounds at all can only be carried out in the manner according to the invention. In these cases the known separation processes completely. The invention is based on the following Examples detailed. example 1 120 g i-sec. Butoxy-2, 4-dinitrobenzene (bp ₁ : 173 to 175 °) are in 1 1 absolute sec. ßutyl alcohol partially reduced at 40 ° by introducing a gas mixture of ammonia and hydrogen sulfide. After suctioning off the separated sulfur and the Atnnionschulfelverbindungen the sec. Butyl alcohol evaporated, the oily residue with sec. Butyl chloride, benzene or another water-immiscible solvent is boiled up and this solution is washed with water. After the solvent has evaporated, the oil is stirred hot with 300 ecm 10% hydrochloric acid. The mixture of hydrochlorides of the i-sec. Butoxy-2-amino-4-nitrobenzene and the i-sec. Butoxy-2-nitro-4-aminobenzene is sucked all over and washed with a little 2N hydrochloric acid. 130 g of hydrochloride mixture are obtained. This is taken up in ι 1 water and heated at 90 to 100 ° ι hour. This is where the i-sek is divided. Butoxy-2-amino-4-nitrobenzene (sweetener) as an oil, which is separated in a few seconds. Butyl chloride or benzene is added and washed with water. The yield is $ j g. Distillation in vacuo at bp ₁ : 167 to 169 ⁰ gives 50 g of the pure sweetener which is completely free of the bitter-tasting isomeric compound. Example 2 1.3 l of water are added to a mixture of 30 g of i-isopropoxy-2-amino-4-nitrobenzene hydrochloride and 30 g of i-isopropoxy-2-nitro-4-aminobenzene hydrochloride. This solution corresponds to an HCl content of 0.2N. It is hydrolyzed by heating to 90 to 100 'for one hour. After cooling, 16 g of i-isopropoxy ^ ^ -nitrobenzene -ainino separate in crystalline form with a melting point of 63 ^0. The substance is completely pure after one recrystallization from isopropanol. By blunting the mother liquor down to a pn value between 1 and 3, one obtains a additional amount of isopropoxy sweetener; the overall yield is about 65% of theory. By Reuse of the mother liquor for renewed hydrolytic cleavage of the isomer mixture is loss-free work is possible. You can also dissolve the salt mixture in less water, bring the solution to a pn value of 1 to 3. and then hydrolyze in the heat. Pa T F. N T Λ Χ PROBLEM: Process for the separation of the i-alkoxy-2-amino-4-nitrobenzenes of those in the partial reduction of i-alkoxy-2,4-dinitrobenzenes 1-alkoxy-2-nitro-4-aminobenzenes formed at the same time after conversion of the amino compounds in the salts, characterized in that the mixture of salts, expediently the hydrochloride, in water at increased Temperature is hydrolyzed. © 2400 10 5U