Catalysts, design secondary amines

Amination of i-butanol to diisobutylamine was investigated on vanadium modified granulated Raney nickel catalyst in a fixed bed reactor. The addition of 0.5 wt.% V to Raney nickel improved the yield of amines and the stability of catalyst. Factorial experimental design was used to describe the conversion of alcohol, the yield and the selectivity of secondary amine as a function of strong parameters, i.e. the reaction temperature, space velocity and NHs/i-butanol molar ratio. Diisobutylamine was obtained with 72% yield at 92% conversion and reaction parameters P=13 bar, T=240°C, WHSV=1 g/g h, and molar ratios NH3/iBuOH= 1.7, H2/NH3= 1.9. 

The highest (iBu)2NH yield (72 %) was obtained a conversion level of 92% and at reaction parameters P=13 bar, T=240°C, WHSV=1.0 g/g h, NH3/iBuOH= 1.7, H2/NH3= 1.9. In conclusion, a secondary amine yield above 70 % can be was obtained in fixed bed reactor using vanadium promoted Raney nickel catalyst without recycling unconverted alcohol. In order to describe the conversion of alcohol, as well as the yield and selectivity of diisobutylamine in the function process parameters, experiments were carried out and results were evaluated according to orthogonal factorial design (6,7). 

Reductive alkylation is an efficient method to synthesize secondary amines from primary amines. The aim of this study is to optimize sulfur-promoted platinum catalysts for the reductive alkylation of p-aminodiphenylamine (ADPA) with methyl isobutyl ketone (MIBK) to improve the productivity of N-(l,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6-PPD). In this study, we focus on Pt loading, the amount of sulfur, and the pH as the variables. The reaction was conducted in the liquid phase under kinetically limited conditions in a continuously stirred tank reactor at a constant hydrogen pressure. Use of the two-factorial design minimized the number of experiments needed to arrive at the optimal solution. The activity and selectivity of the reaction was followed using the hydrogen-uptake and chromatographic analysis of products. The most optimal catalyst was identified to be l%Pt-0.1%S/C prepared at a pH of 6. 

The asymmetric catalytic reduction of ketones (R2C=0) and imines (R2C=NR) with certain organohydrosilanes and transition-metal catalysts is named hydrosilylation and has been recognized as a versatile method providing optically active secondary alcohols and primary or secondary amines (Scheme 1) [1]. In this decade, high enantioselectivity over 90% has been realized by several catalytic systems [2,3]. Therefore the hydrosilylation can achieve a sufficient level to be a preparative method for the asymmetric reduction of double bond substrates. In addition, the manipulative feasibility of the catalytic hydrosilylation has played a major role as a probe reaction of asymmetric catalysis, so that the potential of newly designed chiral ligands and catalysts can be continuously scrutinized. 

This catalyst design in which the stereochemical outcome of the reaction is controlled by hydrogen bonding interactions with an acidic site at the catalyst has been applied to other differently modified chiral secondary amines, generally consisting of a 2-substituted pyrrohdine motif. Some representatives are... 

Very intensive research in this field has led to the design of a wide number of different chiral secondary amine catalysts for carrying out this transformation in an efficient way (Figure 2.6). In this context, diamines such as 14a and 14d have performed well in this reaction, also allowing, in the case of 14a, the use of oc,a-disubstituted aldehydes, which led to the generation of quaternary stereocenters, although in moderate stereoselectivities. Alexakis has studied in detail the use of 2,2 -bipyrroline derivative 15a and its bimorpholine analogue... 

Figure 3.1 Factors to be considered when designing a chiral secondary amine catalyst to be used in Michael reactions under iminium activation.

Lately, Maruoka, et al. reported an organocatalytic Diels-Alder reaction of a-substimted a,p-unsaturated aldehydes with cyclopentadiene, Scheme 3.16 [29], Usually, the organocatalytic Diels-Alder reactions were not applicable to a-substi-tuted acroleins due to serious steric repulsion between the substituent of aldehyde and the secondary amine catalyst. A binaphthyl-based primary amine, catalyst 49, was designed for the reaction, and a plausible mechanism for the stereoselectivity reaction was presented. 

In an effort to increase the nucleoplrilicity of the amine catalyst, based on the a-heteroatom effect, quiral sulfonyl hydrazines 34 and 35 were designed as secondary amine catalysts [74]. However, the addition of carbamate based... 

A wide range of small organic molecules, mainly secondary amines such as proline derivatives, promote asymmetric aldol reactions through enamine catalysis [6]. List, Reymond, Gong, and others reported the first examples of peptidic catalysts for aldol reactions [7]. In their report, Reymond and coworkers [7a] developed two classes of peptides, following two different designs. In the first peptide class a primary amine is present as a side chain residue (similar to the natural type I aldolase) or as free N-terminus in the second a secondary amine or a proHne residue is present at the N-terminus of the peptide, which incorporated at least one free carboxyhc function (Figure 5.3). 

Figure 7.3 Designer chiral secondary amine catalysts.

In comparison with the widespread application of chiral secondary amines in organocatalytic Diels-Alder reactions, only a few successful examples have been reported with the use of chiral primary amines. In the case of a-substituted acroleins, it is difficult for chiral secondary amines to activate this type of substrates, probably because of poor generation of the corresponding iminium ions. To solve this problem, Ishihara and Nakano designed and synthesized a novel class of primary amine catalysts (55) [24]. Indeed, this type of less bulky ligand proved to be effective for enantioselective Diels-Alder reactions of a-acyloxyacroleins 51 or a-phthalimidoacroleins 53 to produce the desired cycloadducts 52 or 54 with quaternary stereocenters (Scheme 38.16). 

Palladium containing alumina supported catalysts were designed for hydrodechlorination of chlorobenezne and for conversion of 4-chloro-2-nitroaniline, in which both hydrodechlorination and reduction steps are involved. Best results were obtained on catalysts containing palladium in ionic form. For reductive amination of acetone a skeletal nickel catalyst and its tin modified version was designed. On these catalysts the ratio of primary to secondary amines could be controlled and the fonuation of isopropyl alcohol was strongly suppressed. 

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