CH630336A5 - Process for the preparation of aromatic amines from alpha, beta-unsaturated cycloaliphatic ketoximes - Google Patents

Description

The invention thus relates to a process for the preparation of aromatic amines from the corresponding cyclohex-2-en-l-one oximes, which may carry inert substituents or are fused with cycloaliphatic or aromatic rings, by heating with water-releasing agents, which is characterized in that that the oximes are used in the form of the hydrochlorides.

Suitable starting materials are all cyclohex-2-en-1-one oximes, the possible substituents of which are stable under the reaction conditions and do not react undesirably with the water-releasing agent. Of course, the substituents on the cyclohexenone system must allow aromatization. Preferred cyclohex-2-en-1-one oximes are substituted by lower alkyl, unsubstituted or substituted by inert substituents, and also fused-on cycloaliphatic or aromatic rings, and in the case of fused-on aromatics the cyclohexene double bond can be part of an aromatic ring. Substituents which are stable and inert under the reaction conditions are, in particular, lower alkyl, lower alkoxy, nitro, trifluoromethyl or carbamoyl and sulfamoyl groups optionally substituted on nitrogen by lower alkyl groups, and halogen, in particular chlorine, atoms.

This increase in yield allows aromatic amines, which are difficult to access in other ways, to be produced economically. Because of the high yields, there are also no significant processing problems.

According to the invention, water-releasing agents are used in particular acetic anhydride or acetyl chloride or a mixture of the two substances. Sulfuric acid, hydrochloric acid or polyphosphoric acids are also possible, but they do not give very good yields.

The oxime hydrochloride is expediently introduced continuously or in portions into the water-releasing agent. The reaction is very exothermic. If you preheat the water-releasing agent, the rate of oxime hydrochloride introduction allows the reaction to be controlled well. The oxime hydrochloride can be introduced both in solid form and dissolved in a solvent. Glacial acetic acid is particularly suitable as a solvent. The oxime hydrochloride can also be prepared by reacting the α, β-unsaturated cycloaliphatic ketoximes in the solvent with the calculated amount of hydrogen chloride gas.

The reaction can preferably be carried out between 0 ° C and 200 ° C; A temperature between 20 ° C and 140 ° C, especially 80 ° C to 140 ° C, is particularly suitable. The reaction can be carried out under reflux or the heat of reaction can be used to distill off solvents or acetic acid formed. If the liquid reaction products and excess water-releasing agent are distilled off after the reaction has ended, the acetamino compound can be isolated as an intermediate product. In general, however, they will be processed immediately to the free amine.

Sometimes it can be advantageous to carry out the reaction in the presence of hydrogen chloride. However, it should be noted that the dosage of the same must be adapted to the respective oxime hydrochloride. In general, the yields decrease with increasing amounts of hydrogen chloride and are optimal when using pure oxime hydrochloride.

The amines produced by the process according to the invention are valuable intermediates, e.g. for the production of colorants.

In the following examples, percentages relate to the weight.

example 1

175 g of 3,5-dimethylcyclohex-2-en-1-onoxime hydrochloride are slowly introduced into 375 g of 80 ° C warm acetic anhydride. The temperature rises until the mixture boils. When all the oxime hydrochloride has been introduced, the acetic acid and the excess acetic anhydride are distilled off completely in a water jet vacuum, 350 ml of water and 340 g of 3 l% hydrochloric acid are added and the mixture is boiled under reflux for 2 hours. After the dark colored solution has been clarified, the mixture is adjusted to at least pH 10 with about 564 g of 33% sodium hydroxide solution and separated from the excreted sym. M-xylidine at room temperature. the aqueous phase is extracted.

104 g (86% of theory) of crude m-xylidine of Kpo.s 70-72 ° C. are obtained.

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630336

Example 2

125 g of 3-methylcyclohex-2-en-1-onoxime (1 mol) are dissolved in 250 g of acetic acid and 38 g of hydrogen chloride gas are introduced. A thick, white, easily stirrable suspension is formed

This solution is added to 350 g of acetic anhydride at room temperature and then gradually warmed to the boil of the mixture. The procedure is continued as indicated in Example 1. 87 g of m-toluidine, corresponding to 81% of the ion which is heated to 80 ° C., are obtained in order to obtain the 3-M theoretical yield obtained; Bp 203 ° C. Bring thylcyclohexenonoxime hydrochloride into solution.

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Claims (2)

630336 2 PATENT CLAIMS 1. A process for the preparation of aromatic amines from the corresponding cyclohex-2-en-1-one oximes, which may carry inert substituents or are condensed with cycloaliphatic or aromatic rings, by heating with water-releasing agents, characterized in that the oximes are in the form the hydrochloride starts. 2. The method according to claim 1, characterized in that one uses the oxime hydrochloride dissolved in a solvent. In the aromatization named after Semmler and Wolff, a, ß-unsaturated aliphatic keto-ximes, formally by elimination of water, give aromatic amines (Houben-Weyl: Methods of Organic Chemistry, Volume 10/4 (1968) 265, Krauch-Kunz , Reactions of organic chemistry, 5th ed., 585 and Org. React. 11,1). The older references do not mention yields, but the occurrence of by-products, partly to a significant extent, reports. According to Schroeter (Ber. 63, [1930] 1316), satisfactory yields are obtained in the conversion of tetra-hydronaphthalonoxime to a-naphthylamine. The oxime is reacted with acetic anhydride while passing HCl gas through it, giving 56% of theory. Th. A-naphthylamine hydrochloride. Hardy and Ward (J. former Soc. 1956, 1979-81) obtained yields in a similar amount when converting nitrotetra-hydronaphthalon-oxime to nitronaphthylamine (38-45% of theory). In the literature, conc. Sulfuric acid, 20% hydrochloric acid, polyphosphoric acid, acetic anhydride and acetyl chloride are described. The processes described above cannot be used for the rational, large-scale production of aromatic amines, among other things because the necessary treatment of the waste water causes great costs. It has now been found that when using the oxime hydrochlorides instead of the free oximes, the yields of aromatic amines can be increased considerably. So obtained from 3,5-dimethylcyclohexenonoxime hydrochloride and acetic anhydride the sym. M-xylidine in a yield of 86% of theory. Th., While using pure oxime only about 25% base is formed. It is very surprising that this modification of the long-known reaction causes such an increase in yield.