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Reductive Alkylation of Ethanolamine and Methylamine

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Reductive Alkylation of Ethanolamine and Methylamine Indian Journal of Chemistry Vol.32A, February 1993, pp. 165-167 Reductive alkylation of ethanolamine and ml of benzene and 2.1g of the reduced catalyst were methylamine by carbonyl compounds over taken in an autoclave. After flushing with nitrogen, copper chromite: Deactivation of the the autoclave was pressurized with hydrogen to 50 atm and heated at 140°C with stirring for 1 hr. catalyst Hydrogen was admitted as required during the reaction to maintain the pressure at 50± 10 atm. At R B C PiIlai, K K Bhattacharyya & C N PiIlai* Department of Chemistry, Indian Institute of Technology, the end of 1hr the autoclave was rapidly cooled and Madras 600 036 the catalyst separated by centrifugation. The product Received 20 July 1992; accepted 24 August 1992 was analyzed by gas chromatography and the N-benzylethanolamine recovered by vacuum Ethanolamine and methylamine have been reductively distillation. alkylated by carbonyl compounds over copper chromite in Experiments under different conditions were done the presence of hydrogen. The catalyst is rapidly similarly. Experiments with other carbonyl deactivated during these reactions. Regeneration of the catalyst does not restore the original activity. compounds and ethanolamine were done in a similar manner and working up procedures modified as N-substituted 2-aminoalcohols are of particular required. interest as organic intermediates. Reductive Reaction of acetone with methylamine alkylation of ethanolamine and analogues is a ready In a typical experiment methylamine (40% WfW in method for their preparation. water)'0.32 mol, acetone, 1.3mol and reduced copper H2N - CH2 - CH2 - OR + R'R"CO H2,catalyst• chromite 4.2g were taken in an autoclave and R'R" CH - NH - CH2 - CH2 - OH + H20 hydrogenated as in the ethanolamine reactions. At Generally platinum catalyst is used for this processl. the end of the reaction time, the catalyst was removed Catalysts based on other metals like palladium, by centrifugation. The reaction mixture was nickel and copper are also useful for reductive transferred to a separatory funnel and the bluish alkylations in generaF. Copper chromite is especially aqueous layer was removed. After removal of useful for the reductive alkylation of aromatic solvents from the organic layer, the secondary amine amines, but is prone to rapid deactivation3•4. Details was recovered by distillation. of the use of copper chromite for the reductive Reactions with other carbonyl compounds were done in a similar manner. alkylation of aliphatic amines are not available. Aliphatic amines pose special problems because of Results and discussion their ability to form complexes with copper and Typical results of the reaction of ethanolamine thereby causing deactivation and oth~r problems. with benzaldehyde under reductive alkylation The present paper reports an investigation of the conditions are listed in Table 1. The optimum reductive benzylation of ethanolamine by temperature and pressure for the reaction were 140°C benzaldehyde and that of methylamine by acetone and 50 atm. Higher pressures did not make any and other related reactions over copper chromite. substantial increase in yield. Higher temperatures Special attention was paid to the deactivation of the adversely affected the yield. As in other copper catalyst in view of the earlier observations with the chromite catalyzed reactions, the reaction rate was aniline-acetone system3. very slow below 140°C. Reactions of ethanol-amine with acetophenone and benzophenone under similar Experimental conditions afforded the corresponding Catalyst aralkylethanolamine in 42 and 37% yield Commercial copper chromite Harshaw Cu 1184 re~~~ely .. was used. The powdered catalyst was heated in a Examination of the data in Table 1shows that the stream of hydrogen at 300°C for 4 hr before use. yield of N-benzylethanolamine increased when the Reaction of benzaldehyde with ethanolamine aldehyde to amine ratio increased (S.Nos. 3,6,7 and 8) In a typical experiment, 19.2 g (0.32 mol) of and also when the catalyst concentration increased ethanolamine, 33.3g (0.32 mol) of benzaldehyde, 100 (S.Nos. 1-4). More interesting was the observation .. 166 N-benzyl-Ethanol-timeethanol-dehydeCatalyst10Reaction(mol)0.320.640.961.28I59465I77884.55586Benzal-low0.320.3232I3IYield(g)theWt.catalystlby14187recoveredlossheatingof%TGA)onof(hr) INDIAN J CHEM, SEe. A, FEBRUARY 1993 amine o/" 4 6 amine273958(mol) aminebasedethanol-molon Reaction temperature: 140°C; Pressure: 50 atm; Solvent: Benzene, 100 ml I S.No. Table I-Reductive benzylation of ethanolamine by benzaldehyde over copper chromite that the yield decreased as the reaction time increased Table 2-Deactivation of copper chromite in the ethanolamine (S.Nos.3,5,9). A clue to the reason for this reaction phenomenon was obtained from the observation that Reaction Temperature: 14(\°C;Reaction time: I h ; Pressure: 50 the recovered catalyst upon heating to 51ooe (TGA) atm; [Ethanolamine] : 0.32 mol; [Benzaldehyde] : 0.32 mol; suffered a weight loss which depended upon the Copper chromite : 5g reaction time. The catalyst which was used in the Ihr S.No. Catalyst Yield of N-benzyl- Catalyst properties reaction suffered 7% weight loss, increasing to 14% history* ethanolamine (5 hr) and 18% (10 hr). The weight loss was obviously (mol % based on Surface area Pore volume due to the burning away of organic deposits on the ethanolamine) (cm2/g) (cc/g) catalyst formed during usage. The reduction in yield I I (Fresh) 86 82 0.19 coupledi with this observation suggested that the 2 2 69 product N-benzylethanolamine decomposed on 3 3 44 prolonged heating leaving an insoluble deposit on the 4 4 24 5 5 II 56 0.13 catalyst surface. It was independently verified that 6 Regene• 64 68 0.18 N-benzylethanolamine decomposed on heating at its rated boiling point (240°C) or below, leaving a tarry residue. *S.Nos.I-5 represent the use of the same lot of catalyst in successive 1 h experiments without regeneration. Deactivation of the catalyst The catalyst underwent rapid deactivation. The followed by a stream of hydrogen at 3000e for 4 hr. results listed in Table 2 pertain to the use of the same The activity of this regenerated catalyst (64%) sample Qf catalyst over and. over in five successive (S.No.6, Table 2) was significantly lower than that of experim~nts without regeneration. After each the fresh catalyst (86%) (S.No.l, Table 2). This experim~nt the catalyst was filtered and washed inability to regain the original activity was not thoroughly with benzene and used for the next observed in the case of the aniline-acetone experiment. As can be seen, the activity of the catalyst reactions3. rapidly decreased. This phenomenon was observed Part of the reason for the deactivation of the also in the reductive alkylation of aniline by acetone catalyst is the blocking of the active sites by the polar reported by us earlier3. The deactivation was more nitrogenous molecules. Such poisoning of the active rapid in the present case than in the aniline-acetone sites (believed to be coordinately unsaturated system. The catalyst after the fifth experiment was cuprous ion sites on the surface) by polar molecules regenerated in the following manner3. The used have been reported by others5. It is noteworthy that catalyst was dried at llOoe for 3 hr, heated in a stream copper chromite when used for the hydrogenation of of air at 3000e for 4 hr, then in nitrogen (30 min) acetone to isopropyl alcohol, for which it is an " "ll , I' NOTES 167 excellent catalyst, suffers no decativation. In a stuqy to verify this fact, a sample of copper chromite (5g) Table 3--Reductive alkylation of methylamine by acetone over copper chromite was used for the hydrogenation of acetone (79g) for 1 Reaction Temperature: 140°C; Reaction time: 2 h ; Pressure: 50 hr at 140·C/50 atm hydrogen pressure. The atm; [Methylamine]; 0.32 mol (40%jH20); [Acetone]: 1.3 mol; conversion of acetone to isopropyl alcohol was Copper chromite : 4.2 g 93.7%. The catalyst was recovered by centrifugation Yield of and reused without regeneration for another five S.No. Catalyst Catalyst properties history N-met• experiments. The conversion in all the experiments hylisopropyl• Surface Pore Wt. loss was 93-94%. Thus, the rapid deactivation of the amine based OJ' area volume of catalyst catalyst in a few hours of use isa feature of only the methylamine (m2jg) (ccjg) at 510°C (mol %) (TGA) reductive alkylation reaction. Physical examination % ofthefresh, used (5 x 1hr reactions) and regenerated catalysts are summarized in Table 2. The substantial I Regener-7thFresh0.190.100.1612.7NilCy-446183481033 loss in surface2 areaatedde·of the used catalyst is attributed3 to the blocking of the pores by the nitrogenous polymeric matter (which was also inferred by the TGA study). The reduced surface area of the regenerated catalyst suggests some degree of texture ·Catalyst was recovered after the first 2 h experiment, and reused change either during the reaction or during without regeneration, and this repeated for, 6 successive regeneration. It may be recalled that in the experiments. aniline-acetone reactions3, the regenerated catalyst had the same surface area and activity as the fresh surfa(;e complexes are probably formed. In the catalyst. It appeared that the aliphatic amine methylamine reactions the aqueous layer had a blue (ethanolamine) was more harmful to the catalyst than colour showing that some copper-amine complex aniline. had come into the solution. However the loss of In order to examine this question furthet;, the copper by such a process was negligible since reaction between acetone and methylamine under chemical analysis of the used catalyst showed no reductive alkylation conditions over copper significant change in composition. Much of the chromite was examined. In these reactions, a 40% complexes obviously remain on the surface as shown aqueous solution of methylamine was used.
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