DK156428B - METHOD FOR PREPARING N-ALKYLED ANILINES BY REDUCED ALKYLING OF SUBSTITUTED ANILINES - Google Patents

Description

DK 156428 B

The present invention relates to a peculiar reductive alkylation reaction for the preparation of novel N-alkylated anilines which include can be used in the preparation of certain 2,6-dinitroaniline herbicides by the specific nitration method disclosed in DK Patent No. 152,751, which relates to a process for the preparation of herbicide-active N-alkylated and Ν, Ν-dialkylated 2, 6-dinitroaniline compounds of formula R1 R2 R2

0? N. i NO

2 2 il (I ·)

15 I

y where Y is C 1-4 alkyl, halogen or CF 3, Z represents hydrogen, halogen, C 1-4 alkoxy, C 1-4 alkyl optionally monosubstituted with halogen or C 1-4 alkoxy, R 1 represents 20 C 1-8 -alkyl (straight or preferably branched), C4-5 cycloalkyl, C1-4 alkyl substituted by halogen or C1-4 alkoxy, and means hydrogen or one of the groups R1, by nitration of the corresponding N- alkylated anilines.

The N-alkylated anilines prepared by the process of the invention have the formula V Rl 30 r./·. (IN)

'' • R

35 B

3 2

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wherein R betyder is C3gg-sec-alkyl, C4_6-cycloalkyl, C3_4-sec-alkyl monosubstituted with halogen or C ^alk ^alkoxy, R₂ means hydrogen, halogen, C_4-alkoxy or C_ Ci alkyl alkyl optionally monosubstituted with halogen or 0-4-4 alkoscy and R3 is C1-4 alkyl, trifluoromethyl or halogen.

The method of the present invention is peculiar to that of the characterizing part of claim 1.

With the process of the invention, it has become possible to avoid disadvantages associated with known methods for the preparation of N-alkylated anilines, e.g. as disclosed in U.S. Patent No. 3,541,153, from which it is known to alkylate anilines by reaction with a ketone, hydrogen and a noble metal catalyst in the presence of a C 1-4 monocarboxylic acid.

This known method is a high pressure method (pressure of 35-70 atm.) Carried out in the presence of 1-20% by weight of water and at a relatively high temperature (up to 120 ° C), just as the acid used has a pKa value which fails beyond the range required by the invention. In such high-pressure diluted acid systems there are serious corrosion problems. Furthermore, it is necessary to work at the upper limit of the pressure range (67-70 atm) if high yields are to be obtained.

In contrast, the temperature of the process according to the invention is preferably 60-70 ° C, the pressure is 2-5 atm, and the promoter acid has a pKa value of 0.3-2.0. The reduction of pressure and temperature is a clear economic benefit, and the pKa value of the promoter acid also causes less corrosion problems. Furthermore, it is noteworthy that the present process is carried out in the absence of water. It is shown in the exemplary embodiments below that the addition of water and / or the use of a promoter acid with a pKa value outside the specified range leads to a clearly poorer reaction, cf. Table I.

3

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Examples of halogen substituents in the compounds of formula (I) are fluorine, chlorine, bromine and iodine. Examples of C 1-4 alkyl substituents are methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl and sec-butyl. The cycloalkyl groups 5 include e.g. cyclobutyl and cyclohexyl.

Examples of C3_4 sec. -alkyl substituents are 2-propyl, and 2-butyl.

Examples of secondary monosubstituted alkyl substituents are 3-chloro-2-propyl, 4-methoxy-2-butyl, 3-bromo-2-butyl, 2-chloropropyl and 2-ethoxybutyl.

Examples of compounds of formula (I) which can be prepared by the process of the present invention are e.g. N-2-butyl-3,4-dimethylaniline, N-3-pentyl-3,4-dimethylaniline, N-2-propyl-3,4-dimethylaniline, N-2-butyl-3-methyl-4-tert. butylaniline, N-3-pentyl-3-methyl-4-chloroaniline, N-3-pentyl-3-methyl-4-trifluoromethylaniline, N-2-hexyl-3,4-dimethylaniline, N-3-pentyl -3-methoxymethyl-4-methylaniline, N-3-pentyl-3-methoxymethyl-4-trifluoromethylaniline, N-2-butyl-4-bromo-3-methylaniline, N-2-pentyl-4-bromo-3-methylaniline , N-2-hexyl-4-chloro-3-methylaniline, N-2-pentyl-3-ethoxy-4-methylaniline and N-2-butyl-3- (2-chloroethyl) -4-butylaniline.

The N-alkylated anilines are prepared by reacting the starting aniline of formula (II) with a suitable ketone, a noble metal catalyst and an acid having a pKa value in the range of 0.3-2.0, preferably 0.5-1.0. The pKa value is defined as the negative number logarithm of the first ionization constant of the acid in water.

The anilines used as starting material in this process have the formula 30 nh2 in '' (ÏI)

35; R

R3

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4 wherein R 2 and R 3 are as defined in formula (I).

Illustrative anilines are e.g. 3,4-xylidine, 3,4-diethylaniline, 3,4-di-n-butylaniline, 3-methyl 1 -4-ethylaniline, 3 3-methyl-4-trifluoromethylaniline, 3-methyl-4-chloroaniline, 3- ethyl 1 -4-bromaniline, 3-chloromethyl-4-methylaniline and 3-methoxymethyl-4-methylaniline.

Illustrative acids are e.g. 2-naphthalenesulfonic acid, p-toluenesulfonic acid, ethylbenzenesulfonic acid and trichloroacetic acid.

The ketone is selected according to the desired N-alkyl group.

For example, if if a 2-propyl substituent such as R 1 is desired, dimethyl ketone is preferably used.

More specifically, the ketones used herein may be represented by formulas (III) and (IV) listed below.

For the preparation of the N-alkylated aromatic amines of formula \ R1

V

20; In (I) R3 wherein R R is C C_5-sec-alkyl and R₂ and R3 have the meaning given in the above formula (I), it is preferred to use the following ketone:

30 O

4 11 «R4 - C - R5 (III) wherein R4 and R5 are C1-4 alkyl with the proviso that the total number of carbon atoms in R4 + R5 does not exceed 5 to ensure a carbon atom number in R1 of 3-6.

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When it is possible to prepare an N-alkylated aromatic amine of formula (I) wherein R 1 is monosubstituted O 3 -sec.-alkyl, wherein the substituent is halogen or C 1-4 alkoxy, and R 2 and R 3 have the compound of formula (I) meaning, it is preferred to use a ketone of the formula

ISLAND

, R6 - C - R7 (IV) where R6 and R7 are r a <* subject to the total number of carbon atoms in R6 + R7 not exceeding 3 and R6 or R7 being monosubstituted with a halogen group or a C 1-4 alkoxy group .

Examples of ketones for use in the process of this invention are acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, ethoxy-2-propanone and methyl isobutyl ketone.

The noble metal catalysts used are those conventionally used in hydrogenation reactions, i.e. group VIII members of the periodic table of the platinum and palladium families. They are preferably in finely divided form adsorbed in or supported on a suitable substrate. Platinum and palladium are preferred catalysts. Platinum on carbon is particularly preferred as it is readily available commercially and, when used, it prevents the ketone from being converted to the corresponding carbinol, which occasionally occurs when palladium is used. Thus, yields of 30% or more are obtained.

A typical process for carrying out the reductive alkylation of the present invention is described below.

A pressure reactor is fed with the aniline, the appropriate ketone, the acid promoter and the precious metal catalyst. Oxygen is removed from the reactor preferably by evacuation followed by rinsing with purified nitrogen. The reactor is then added hydrogen to a pressure of 2-5 kg / cm 2 and the reaction mixture heated to 6

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execution of the turnover. Temperatures in the range 40-150 ° C are generally appropriate, however temperatures in the range 60-125 ° C are preferred. Reaction times of 10 minutes to several hours during which the pressure in the reactor of 5 desirable is either maintained by the addition of hydrogen gas or allowed to drop are generally sufficient to ensure complete reaction. Then the reaction mixture is cooled, pressure is taken off the reactor and it is opened and the contents removed. The desired product is reprocessed in a conventional manner.

10 Satisfactory results can be obtained when the amount of acid used in the promoter system is as low as 0.1 mol per liter. 100 moles of the aniline. The upper acid limit is limited for practical reasons only. The most preferred amount of acid is in the range of 1-3 moles of acid per day. 100 moles of aniline.

Preferably, the precious metal catalyst is used in an amount of at least approx. 0.3 g of precious metal (preferably platinum) per moles of the aniline that is alkylated. If the catalyst is adsorbed on a substrate, the amount of material used must be adjusted so that there is at least approx. 0.3 g average per mole of 20 aniline, regardless of the amount of substrate on which it is adsorbed.

The amount of metal typically found in commercial catalysts is 1-50% by weight of the carrier material. A preferred commercial catalyst contains 5% platinum of 25 carbon which is used in an amount of approx. 5% of the aniline present in the reaction mixture.

The catalyst used in the process of the present invention may be recycled in a conventional manner, but it is preferred to enhance the spent catalyst with a sufficient amount of fresh catalyst to maintain its activity level. The amount of fresh catalyst added usually amounts to less than 10% of the amount initially used, preferably 2-5%.

The catalyst may be reduced in advance or the noble metal oxide may be used and reduced to the metal in the reaction mixture.

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7

The ketone and aniline are combined in molar ratios from 1.1: 1 to 10: 1. A single mole of hydrogen is consumed for the conversion of the aniline to the corresponding N-alkylated compound.

The preferred molar ratio of ketone to amine is approx. 1.1: 1-5 approx. 1.5: 1.

The hydrogen is usually used in an amount far in excess of the amount needed for conversion.

The N-alkylated anilines prepared by this process are useful as intermediates in the preparation of the corresponding 2,6-dinitroaniline herbicides.

Examples 1-28 describe the reductive alkylation of 3,4-xylidine compounds, but it should be understood that any aniline of formula (II) can be used instead.

All parts and percentages are by weight, unless otherwise stated.

Example 1 24.2 g (0.20 mole) of 3,4-xylidine, 38.4 g (0.44 mole) of diethyl ketone, 1.2 g of 5% palladium carbon and 0.90 g (2 20 mole percent of 2-naphthalenesulfonic acid is added to an autoclave which is sealed, evacuated and rinsed with nitrogen, then hydrogen gas is added to a pressure of 3.30 kg / cm 2. The temperature of the auto key is raised to 60 ° C and kept at 60-65 ° C for approx. 3/4 hour, after which the temperature is lowered to approx.

25 ° C. The pressure is taken out of an autoclave and it is opened, after which the contents are taken out and filtered to separate the catalyst. The lower layer of the filtrate is isolated in a separating funnel and the catalyst cake, filter flask and separating funnel are rinsed with 10 ml of diethyl ketone which is combined with organic phase 30 and evaporated to a constant weight of 38.2 g. The resulting product has a purity of 97.2% , which gives a conversion of 97.2% and a yield of 97.2% N- (3-pentyl) -3,4-xylidine.

Examples 2-19 35 The following examples illustrate the influence of various promoter acids on the conversion by a single passage 8

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as well as the yield of the resulting N-alkylated product. The general method used is the same as that described in Example 1. Mole percent acid per 100 moles of 3,4-xylidine, the relative amounts of ketone and catalyst, reaction conditions,% unreacted 3,4-xylidine,% 3,4-xylidine converted to the desired product,% of product obtained and% of theoretical yield are In the following Table I. In all cases, the starting materials are diethyl ketone and 3,4-xylidine.

Generally fresh 5% platinum-carbon is used, but in some cases the catalyst is recycled, and in several cases 10% platinum-carbon is used. The results show that when using acids which have mainly pKa values of 0 and those acids having pKa values above 2.0, such as phosphoric acid, acetic acid and benzoic acid, lower yields and conversions are obtained than using those acids whose pKa value is about the same as that of arylsulfonic acids.

DK 156428 B

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12

Examples 20-25

From the following examples it appears that 10% of platinum-β-carbon can be repeatedly recycled as a catalyst with p-toluenesulfonic acid as a promoter acid with excellent product conversions and yields. The general procedure used is the same as that described in Example 1, starting from diethyl ketone and 3f4-xylidine. The reaction conditions and results are given in the following Table II.

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14

Example 26

Preparation of N-3-pentyl-α, α.α-trifluoro-β-toluidine

To a pressure vessel is added 8.05 g (0.05 mole) of α, α, α-trifluoro-β-toluidine, 6.9 g (0.08 mole) of diethyl ketone, 0.3 g of 5% platinum carbon and 0.23 g of 2-naphthalenesulfonic acid.

The vessel is closed and the reaction mixture is heated to 55-60 ° C, whereupon hydrogen gas is introduced to a pressure of 3.1 - 3.5 kg / cm 2. The mixture is allowed to react until hydrogen uptake has ceased. It is then cooled to room temperature, 10 and the pressure is taken off the container. The mixture is removed from the vessel, filtered and the lower water layer is removed from the filtrate. The filtrate is evaporated in vacuo to give 11.2 g of the desired product in the form of an oil (97% of the theoretical). The identity of the product is confirmed by proton magnetic resonance spectroscopy and by elemental analysis which shows a nitrogen content of 5.92% corresponding to a theoretical value of 6.06%.

Example 27 Preparation of N-2-Butyl-3-chloro-p-toluidine 28.3 g (0.2 mole) of 3-chloro-p-toluidine, 23.0 g (0.32 mole) of methyl ethyl ketone, 1, 2 g of 5% platinum-on-carbon and 0.9 g of 2-naphthalenesulfonic acid are added to a 500 ml pressure reactor and the reactor is closed. The reactor is pressurized with hydrogen gas 25 to a pressure of approx. 3.6 kg / cm 2, and the temperature is raised from 40 ° C to 65 ° C and maintained until pressure drop indicates that the theoretical amount of hydrogen is used up. The system is then cooled to room temperature and the pressure is removed and the contents removed The lower water layer is discarded and the 30 pure layer is concentrated in vacuo to give the desired product as a raw material in 100% yield. Comparison of the raw material by IR and NMR spectroscopy with pure N- (2 -butyl) -3-chloro-p-toluidine confirms its structure and shows that it is contaminated with less than 5% methyl ethyl ketone and a small amount of 2-naphthalenesulfonic acid.

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15

Example 28 Comparative Example Example

The general procedure of Example 1 is repeated with various, strong inorganic acids and with acetic acid as an acid promoter. The acetic acid has been used both alone and with 16% by weight of water added (known from US Patent No. 3,541,153). The catalyst is 5% platinum-carbon. The results are shown in the following table: ill. It will be seen that the use of promoters with a pKa value outside the range of the invention (0.3-2.0): yields results in substantially higher yields.

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Claims (2)

A process for the preparation of N-alkylated anilines of the general formula 5 H R1 Ν "" R 2 S | (I), 10 k3 wherein R 1 is C 3 -6 sec-alkyl, C 1 H 3 -tycycloalkyl C 3 -4-sec. -rmalkyl monosubstituted with 'halogen or C1-4 alkoxy, 3R2 means hydrogen, halogen, C1-4 alkoxy or C1-4 alkyl; optionally monosubstituted with halogen or C4-4alkylxy and R3 means C 1-4 alkyl, trifluoromethyl or halo-cgene 2 - by which -a-haloim of the formula MO nh9 I z II (II) 25 k3 wherein R 2 and R 3 are as defined above are reacted with hydrogen, a noble metal catalyst, a promoter acid and a ketone, characterized in that a promoter acid having a pKa value of 0.3-2.0 is used, the reaction is carried out in autoclave under hydrogen gas at a pressure of 2-5 kg / cm 2 and in the absence of water that the molar ratio of ketone to starting compound is from 1.1: 1 to 10: 1, that the promoter acid is an aromatic sulfonic acid, that the amount of aromatic sulfonic acid is 0.1-10 mole percent, calculated and the molar ratio of the precious metal to the starting compound is 0.005: 1 - 0.25: 1. Process according to claim 1 for the preparation of N-sec-butyl-3,4-xylidine, characterized in that a starting mixture consisting of a mixture of 3,4-xylidine and methyl ethyl ketone, wherein the molar ratio of methyl ethyl ketone to 3.4 -xylidine is in the range of 1.1: 1 - 2.0: 1, reacted with hydrogen gas at a pressure of 2.1-3.5 kg / cm 2 and a temperature in the range of 60-70 ° C in the presence of a platinum catalyst adsorber -10 prepared on carbon and 1-3 mole percent 2-naphthalenesulfonic acid, calculated on 3,4-xylidine, until the reaction is complete, whereupon the platinum catalyst is isolated from the reaction mixture and N-sec-butyl-3,4-xylidine is recovered.