NO177564B - Process for the preparation of 4-substituted 2,6-dialkylanilines - Google Patents

Description

The invention relates to a new process for the production of 4-substituted 2,6-dialkylanilines with the general formula

wherein Rx and R2 are the same or different and mean straight-chain or branched C1-C4 lower alkyl groups, and R3 means a phenylisopropyl group, a 1,1,3,3-tetramethylbutyl group or a tert-butyl group. Below, the hitherto undescribed 2,6-dialkyl-4-(1,1,3,3-tetramethylbutyl)-anilines are prepared with the general formula

in which Rx and R2 have the aforementioned meaning, and of particular interest is 2,6-diisopropyl-4-(1,1,3,3-tetramethylbutyl)-aniline where Rx and R2 = isopropyl.

The mentioned 4-substituted 2,6-dialkylanilines are, among other things, valuable intermediates for the production of pesticides (EP-A 0 304 025) and of arylthiourea derivatives (DE-OS 27 27 416) or hydrolysis protection agents in polyurethanes (Becher/Braun, Kunststoff Handbuch " Polyurethane", Vol. 77, C.Hauser-Verlag 1983, pp. 407-408).

From EP-A 0 069 065 it is known to alkylate aromatic anilines in the para position with e.g. α-methylstyrene: respectively with diisobutylene. This known method is characterized by the fact that it works in the presence of an aqueous acid, usually hydrochloric acid, as a catalyst and with the addition of zinc chloride as a co-catalyst. The disadvantage of this method is that a significant amount of catalyst (catalyst + cocatalyst) of up to 2 mol per mol aromatic aniline; and furthermore, the reaction proceeds very slowly.

From US-PS 4 340 758 there is e.g. known to prepare 4-t-butyl-2,6-dimethylaniline through the following three steps in a total yield of 40%. By HF-catalyzed alkylation of m-xylene with isobutene in the first step, 5-t-butyl-1,3-dimethylbenzene was obtained.

By further nitration with NH03 in the presence of mercuric acetate, 2-nitro-1,3-dimethyl-5-t-butylbenzene is synthesized, and finally the nitro group is reduced by catalytic hydrogenation.

However, the aforementioned synthesis is on the one hand unthinkable from an ecological point of view and from a process engineering point of view with problematic reaction participants HF and mercuric acetate, and on the other hand through the poor yields for a modern industrial process.

In DE-OS 27 27 416, p. 60, it was proposed to form 4-t-butyldiethylaniline analogously to example 9, p. 59 through the ethylation of 4-t-butylaniline with ethylene in the presence of aluminum chloride at 200 atm overpressure and 250 °C. A dividend statement is not available.

The unfortunate thing about this method is that, in addition to the drastic, technically cumbersome conditions, 4-t-butyl-aniline is difficult to obtain, i.e. it must be produced through nitration of t-butylbenzene and through subsequent reduction of the nitro group to aniline. As is known, the nitration of monoalkylbenzenes therewith produces isomeric mixtures (J. Am. Chem. Soc. 73, 5605 (1951)) which considerably complicate the availability of 4-t-butylanine.

Reactions of the unsubstituted aniline with isobutylene have also been known for a long time. Thus, it appears from GB-PS 823 223, examples 17, 20 and 49, that in the reaction of aniline with isobutene in the presence of aluminum chloride and metallic aluminum or in the presence of boron trifluoride and under pressure and at temperatures between 200°C and 300°C at partial low turnover, mixtures of mono- and diisobutylanilines.

It was true that solid-bed catalysts succeeded in improving the conversions, but the product still consisted of a mixture of mono- and diisobutylanilines (EP-A 226 781, EP-A 245 797, Appl. Catalysis 62 (1990), pp. 161-169).

The task therefore consisted of developing a method which does not have the disadvantages of the known methods.

This task could surprisingly be solved by the method according to the invention according to claim 1.

Starting products are the industrially available 2,6-dialkylanilines with the formula

wherein R x and R 2 are the same or different and mean straight or branched C 1-6 lower alkyl groups.

According to the invention, the 2,6-dialkylanilines are reacted with α-methylstyrene to introduce the phenylisopropyl group, with diisobutylene to introduce the 1,1,3,3-tetramethylbutyl group, or with isobutene to introduce the tert-butyl group in the presence of

a Friedel-Craft alkylation catalyst in an amount of 0.01 to 0.3 mol relative to 1 mol of 2,6-dialkylaniline at a temperature between 100°C and 300°C and a pressure between normal pressure and 60 bar.

Particularly suitable catalysts are aluminum chloride or boron trifluoride-ether complexes, such as e.g. the boron trifluoride-diethyl ether complex or aluminum silicates, such as e.g. montmorillonite.

Preferably, the catalyst is used in an amount of 0.05 to 0.15 mol in relation to 1 mol of 2,6-dialkylaniline.

It has been found that a prior activation of the catalyst or addition of a cocatalyst is not necessary.

The reaction preferably takes place at a temperature between 150 and 250°C, and at a pressure between normal pressure and 40 bar.

The reaction advantageously takes place without the presence of an additional solvent. Appropriately, the olefins used for the alkylation, possibly used in excess, act as solvent. However, it is certainly possible to perform

the reaction in the presence of an inert solvent.

After a reaction time of normally 2-20 hours, the obtained 4-substituted 2,6-dialkylanilines can be isolated through simple distillation or by salt formation from the reaction mixture in good purity and yield.

Example 1

Preparation of 2.6-diisopropyl-4-(phenylisopropyl)-aniline

354.6 g of 2,6-diisopropylaniline (2.0 mol), 239.9 g of o-methylstyrene (2.0 mol) and 18.62 g of aluminum chloride (0.14 mol) were heated in an autoclave for four hours at 205°C (pressure 1-2 bar). After cooling, the autoclave contents were taken up in 600 ml of toluene. The toluene solution was successively washed with 10% sodium hydroxide solution and water and evaporated to dryness under water jet vacuum and 60°C bath temperature.

599.7 g of residue with 73.4% 2,6-diisopropyl-4-(phenylisopropyl)aniline and 13.4% 2,6-diisopropylaniline were obtained. This corresponded to a yield of 74% in relation to the 2,6-diisopropylaniline used.

The product could be purified by distillation (boiling point approx. 150°C/0.8 mbar; content 98-99%).

Example 2

Preparation of 2.6-diisopropyl-4-(1.1.3.3-tetramethylbutyl)-aniline

59.6 g of 2,6-diisopropylaniline (0.33 mol), 3.89 g of aluminum chloride (0.03 mol) and 224.1 g of diisobutylene (78% 2,4,4-trimethyl-l-pentene, 20% 2,4,4-trimethyl-2-pentene) was heated in an autoclave for 15 hours at 200°C. (Pressure 6-7 bar). After cooling, the autoclave contents were washed twice with 100 ml of water each time and freed of excess diisobutylene by vacuum distillation in a rotary evaporator.

87.4 g of distillation residue with 57.5% 2,6-diiso-propyl-4-(1,1,3,3-tetramethylbutyl)-aniline and 13.2% 2,6-diisopropylaniline were obtained. This corresponded to a yield of 52% in relation to the 2,6-diisopropylaniline used.

^-NMR: (CDC13, 300 MHz) δ in ppm: 0.68 (s, 9H), 1.26 (d, J=6.8Hz, 12H), 1.35 (s, 6H), 1.66 (s, 2H), 2.94 (m, J=6.8Hz, 2H), 3.57 (s, 2H), 7.02 (s, 2H).

Example 3

4-t-butyl-2.6-diisopropylaniline

211.9 g of 2,6-diisopropylaniline (1.14 mol, content 95.2%) and 12.1 g of aluminum chloride (0.09 mol) were filled into a heatable 1-liter stirring autoclave. The autoclave was connected through corresponding supply lines with a nitrogen pressure bottle and through a pressurized liquid dosing pump with an isobutene bottle. Through several times of careful compression and expansion of approx. 2 bar nitrogen, the autoclave was made inert.

In the same way, nitrogen was displaced with isobutene, and finally the reaction mixture was saturated at 10-20°C with 2 bar of isobutene.

In the course of 50-60 minutes, the autoclave was heated to 180°C, during which the pressure rose to 28-30 bar before an initial pressure drop indicated the start of the reaction. When the pressure dropped to 25 bar, it was always refilled to 30 bar, until saturation was reached after approx. ten hours.

The autoclave was cooled to 20°C, the pressure released and the contents emptied into 250 ml of toluene. The toluene solution was successively washed with 10% caustic soda and water and evaporated to dryness on a rotary evaporator. 293 g of evaporation residue containing 90.2% 4-t-butyl-2,6-diisopropylaniline were obtained. Further purification took place through fractional distillation and recrystallization from hexane.

<t>ø-NMR: (CDC13, 300 MHz) 6 in ppm, 1.28 (d, 12H, J=6.8Hz), 1.30 (s, 9H), 2.94 (m, 2H, J =6.8Hz), 3.62 (s, 2H), 7.07 (s, 2H). Boiling point: 154-156"C/22 mbar.

Melting point: 73-74°C.

Example 4

4-t-butyl-2-ethyl-6-methylaniline

Analogous to example 3, 161.7 g of 2-ethyl-6-methylaniline (1.2 mol, content 100%) was heated in the presence of 12.1 g of aluminum chloride (0.09 mol) with 20 bar of isobutene for 20 hours at 200°C and worked up. By vacuum distillation of the evaporation residue from the toluene solution, 182.5 g of 4-t-butyl-2-ethyl-6-methylaniline was obtained as a colorless, oily liquid (content 97.4%, boiling point: 134°C/15 mbar). This corresponds to a dividend of 78% in relation to

2-ethyl-6-methylaniline was used.

4I-NMR: (CDC13/ 300 MHz) S in ppm, 1.24 (t, 3H, J=7.5Hz), 1.28 (s, 9H), 2.17 (S, 3H), 2.52 (m, 2H), 3.46 (s, 2H), 6.97 (s, 2H). Example 5

4- t-buty1- 2- isopropyl1- 6- methylaniline

As in example 3, 178 g of 2-methyl-6-isopropylaniline (1.2 mol, content 97.3%) was stirred in the presence of 12.1 g of aluminum chloride (0.09 mol) with 30 bar of isobutylene for four hours at 220 °C.

After work-up and distillation, 183.5 g of 4-t-butyl-2-isopropyl-6-methylaniline (content 97.6%, boiling point: 138°C/16 mbar) were obtained as a colorless, oily liquid. This corresponds to a yield of 75% in relation to the 2-methyl-6-isopropylaniline used.

^-NMR: (CDC13, 300 MHz) S in ppm, 1.28 (s, 9H), 1.28 (d, 6H, J=6.8Hz), 2.18 (s, 3H), 2.91 (sept. 1H, J=6.8Hz), 3.46 (s, 2H), 6.96 (d, 1H, J=1.8HZ), 7.09 (d, 1H, J=l.8Hz) .

Example 6

4-t-butyl-2.6-diisopropylaniline

A 100 ml autoclave was filled with 17.73 g of 2,6-diisopropylaniline (0.1 mol), 199 g of toluene, 0.93 g of montmorillonite KSF (Fluka) and 34.3 g of isobutene and heated in an oil bath for 16 hours at 200°C. The pressure was released from the cooled autoclave. The reaction solution contained, without montmorillonite, isobutene and toluene, 19.0% 2,6-diisopropylaniline and 58.3% 4-t-butyl-2,6-diisopropylaniline.

Example 7

4- t-butyl- 2- ethyl- 6- isopropvlaniline

As in Example 3, 129.0 g of 2-ethyl-6-isopropylaniline (0.79 mol) was stirred in the presence of 8.0 g of aluminum chloride (0.06 mol) with 30 bar of isobutylene for six hours at 200°C.

After work-up and distillation, 139.1 g of 4-t-butyl-2-ethyl-6-isopropylaniline (content 99.3%, boiling point: 143°C/17 mbar) was obtained as a colorless, oily liquid. This corresponds to a yield of 80% in relation to the 2-ethyl-6-isopropylaniline used.

^-NMR: (CDCl3, 300 MHz) S in ppm, 1.27 (t, 3H, J=7.5Hz), 1.29 (d, 6H, J=6.8Hz), 1.30 (s, 9H), 2.54 (g, 2H, J=7.5Hz), 3.57 (s, 2H),

6.99 (d, 1H, J=2.1Hz), 7.08 (d, 1H, J=2.1Hz).

Example 8

4- t- butvl- 2. 6- di- sec- butvlanilin

As in example 3, 20.6 g of 2,6-di-sec-butylaniline (0.1 mol), 0.59 g of aluminum chloride (0.004 mol) and approx. isobutene heated for six hours at 203°C.

After work-up and distillation, 19.5 g of 4-t-butyl1-2,6-di-sec-butylaniline were obtained as a colorless oil (content 99.6%, boiling point: 156°C/17 mbar). Yield 74%.

4I-NMR: (CDC13, 300 MHz) <S in ppm, 0.94 (m, 6H), 1.28 (d, 6H, J=6.8Hz), 1.29 (s, 9H), 1, 56 (m, 2H), 1.72 (m, 2H), 2.66 (m, 2H), 3.56 (s, 2H), 6.99 (s, 2H).

Example 9

4-t-butyl-2.6-dimethylaniline

As in Example 3, 242.0 g of 2,6-dimethylaniline (2 mol) was stirred in the presence of 24.0 g of aluminum chloride (0.18 mol) for eight hours at 200°C with 60 bar of isobutylene.

After work-up and distillation, 335.7 g of 4-t-butyl-2,6-dimethylaniline (content 99.8%, boiling point: 129"C/19 mbar) were obtained as a colorless, oily liquid. This corresponds to a yield of 95% in relative to the 2,6-dimethylaniline used.^-NMR: (CDCl3, 300 MHz) S in ppm, 1.27 (s, 9H), 2.18 (s, 6H), 3.45 (s, 2H) , 6.96 (p, 2H).

Example 10

4- t- butyl- 2. 6- dietvlaniline

As in example 3, 179.9 g of 2,6-diethylaniline (1.2 mol) was stirred with 1.0 g of aluminum chloride (0.09 mol) for twelve hours at 200° C. with 30 bar of isobutylene.

After work-up and distillation, 227.2 g of 4-t-butyl-2,6-diethylaniline (content 99.7%, boiling point: 141°C/16 mbar) were obtained as a colorless, oily liquid. This corresponds to a yield of 92% in relation to the 2,6-diethylaniline used.

^-NMR: (CDCl 3 , 300 MHz) S in ppm, 1.26 (t, 6H, J=7.5Hz), 1.29 (s, 9H), 2.53 (g, 4H, J=7, 5Hz), 3.51 (s, 2H), 6.99 (s, 2H). Example 11

4-t-butyl-2,6-diisopropylaniline

As in Example 3, 17.7 g of 2,6-diisopropylaniline (0.95 mol, content 95.2%), 2.0 g of toluene, 2.05 g of boron trifluoride diethyl etherate (0.013 mol) and 16.4 g of isobutene (0.29 mol) heated for 15 hours at 200°C.

The evaporation residue obtained at the end of the work-up

of the organic phase (21.3 g) contained 75.6% 4-t-butyl-2,6-diisopropylaniline.

Example 12

2. 6-diisopropyl-4-(1-phenylisopropyl)-aniline

177.3 g of 2,6-diisopropylaniline (1 mol) was mixed with 13.38

g of AlCl3 (0.1 mol) and heated to 155°C. In the course of six hours, 195.8 g of α-methylstyrene (2.5 mol) were added dropwise. It was allowed to cool to room temperature and mixed with stirring successively with 300 ml of hexane and 300 ml of caustic soda (20%). The biphasic mixture was separated, the organic phase diluted with 900 ml of hexane and saturated with HCl gas. The precipitate was collected on a glass filter, washed with hexane, squeezed well and mixed with a two-phase mixture of 400 ml of toluene and 450 ml of caustic soda (10%). The upper organic phase was separated and evaporated to dryness on a rotary evaporator. 288.1 g of evaporation residue with 98.0% 2,6-diisopropyl-4-(1-phenylisopropyl)-aniline were obtained, corresponding to a yield of 96% in relation to the 2,6-diisopropylaniline used. 4I-NMR: (CDCl 3 , 300 MHz) S in ppm, 6.90 (s, 2H), 7.1-7.3 (m, 5H), 3.70 (s, 2H), 1.12 (d , 12H, J=6.9Hz), 2.91 (Sept, 2H, J=6.9Hz), 1.66 (s, 6H).

Claims (4)

1. Procedure for the preparation of 4-substituted 2,6-dialkylanilines with the general formula wherein R1 and R2 are the same or different and mean straight-chain or branched C1-C4 lower alkyl groups, and R3 means a phenylisopropyl group, a 1,1,3,3-tetramethylbutyl group or a tert-butyl group, characterized in that a 2,6-dialkylaniline of the general formula in which Rx and R2 have the meanings mentioned above for the introduction of the phenylisopropyl group is alkylated with α-methylstyrene, for the introduction of the 1,1,3,3-tetramethylbutyl group is alkylated with diisobutylene, and for the introduction of the tert-butyl group is alkylated with isobutene, - in both cases in the presence of a Friedel-Craft alkylation catalyst in an amount of 0.01 to 0.3 mol relative to 1 mol of 2,6-dialkylaniline at a temperature between 100°C and 300°C and a pressure between normal pressure and 60 bar. 2. Method according to claim 1, characterized in that aluminum chloride, a boron trifluoride-ether complex or montmorillonite is used as catalyst. 3. Method according to claims 1 and 2, characterized in that the alkylation is carried out with 0.05 to 0.15 mol of catalyst per moles of 2,6-dialkylaniline. 4. Method according to claims 1-3, characterized in that the alkylation is carried out at a temperature between 150°C and 250°C and at a pressure between atmospheric pressure and 40 bar.