Amines nitrile hydrogenation

Reductive alkylations and aminations requite pressure-rated reaction vessels and hiUy contained and blanketed support equipment. Nitrile hydrogenations are similar in thein requirements. Arylamine hydrogenations have historically required very high pressure vessel materials of constmction. A nominal breakpoint of 8 MPa (- 1200 psi) requites yet heavier wall constmction and correspondingly more expensive hydrogen pressurization. Heat transfer must be adequate, for the heat of reaction in arylamine ring reduction is - 50 kJ/mol (12 kcal/mol) (59). Solvents employed to maintain catalyst activity and improve heat-transfer efficiency reduce effective hydrogen partial pressures and requite fractionation from product and recycle to prove cost-effective. 

Reductions of Nitriles. In the reduction of nitriles, hydrogen is added progressively across the carbon—nitrogen triple bond, forming first the imine and then the amine. 

The above scheme to account for products of nitrile hydrogenation was proposed sixty years ago (80), and with minor variations 28,45,86] has withstood the test of time, It might be expected from the foregoing that, if a nitrile were reduced in the presence of an amine, unsymmetrical amines would result 48), and indeed the reaction provides an excellent way of preparing these amines 49,74). 

Since the hydrogenation is a metal-catalyzed reaction, it is appropriate to use an oxide support to enhance the dispersion. However, the support, like the metal, needs to be chosen with the desired selectivity in mind. The early view [5] that the selectivity in nitrile hydrogenation is determined largely by the behaviour of the partially-hydrogenated intermediate, the imine R-CH = NH, which can either accept two further hydrogens to form the primary amine or can react with an already-formed amine to start a sequence which... 

Teter et al. filed a series of patents aimed at the production of organic compounds containing nitrogerf or the production of nitriles and amines from ammonia and olefins by passing mixtures of olefin and NH3 over transition metals, mainly cobalt deposited on various supports at 250-370°C and 100-200 bar [27- 3]. With cobalt on asbestos, a mixture of amine, nitrile, olefin hydrogenation product, polymers, and cracking products is obtained (Eq. 4.1) [31]. 

The selectivity of RNH2 on M/A1203 and Raney catalysts decreased in the order Co Ni Ru>Rh>Pd>Pt. This order corresponds to the opposite sequence of reducibility of metal-oxides [8] and standard reduction potentials of metalions [9], The difference between Group VIII metals in selectivity to amines can probably been explained by the difference in the electronic properties of d-bands of metals [3], It is interacting to note that the formation of secondary amine, i.e. the nucleophilic addition of primary amine on the intermediate imine can also take place on the Group VIII metal itself. Therefore, the properties of the metal d-band could affect the reactivity of the imine and its interaction with the amine. One could expect that an electron enrichment of the metal d-band will decrease the electron donation from the unsaturated -C=NH system, and the nucleophilic attack at the C atom by the amine [3], Correlation between selectivity of metals in nitrile hydrogenation and their electronic properties will be published elsewhere. 

T. A. Johnson and D. P. Freyberger, Lithium Hydroxide Modified Sponge Catalysts for Control of Primary Amine Selectivity in Nitrile Hydrogenations, Chemical Industries (Dekker), 82 (Catal. Org. React.), 201-227 (2000). 

Isophorone diamine is synthesized traditionally by aminoreduction of iso-phoronenitrile. Raney cobalt was used for this process. More recently, a new two-step process was patented. The first step consists of synthesizing the imine and the second one of hydrogenating the latter. Ra-Ni was used as catalyst at 150°C and 60 bar hydrogen pressure. Under these conditions, the catalyst reduces the nitrile groups and is able to cleave the N-N bonds, too. Ammonia is required to promote primary amine formation during nitrile hydrogenation (Scheme 4.151).554... 

The heterogeneous catalytic hydrogenation of nitriles has been used in amine preparation for a long time. Generally the products are a mixture of primary, secondary and tertiary amines, the nature of which depends on the catalyst used as well as on reaction conditions (refs. 1,2). The selectivity of nitrile hydrogenation is of importance, particularly in the production of primary amines. In such reactions the catalysts most often proposed are Raney nickel catalysts (refs. 1-3). 

Lithium aluminum hydride is a convenient reagent for reduction of nitro compounds, nitriles, amides, azides, and oximes to primary amines. Catalytic hydrogenation works also. Aromatic nitro compounds are reduced best by reaction of a metal and aqueous acid or with ammonium or sodium polysulfides (see Section 23-12B). Reduction of /V-substituted amides leads to secondary amines. 

The Strecker reaction is a three-component reaction of an aldehyde (or ketone), ammonia (86, or another amine) and hydrogen cyanide (87, or equivalents) to give a-amino nitriles and, after hydrolysis, a-amino acids (Scheme 9.16). 

The acid-catalysed reaction of hydrogen azide with electrophiles, such as carbonyl compounds, tertiary alcohols or alkenes. After a rearrangement and extrusion of N2, amines, nitriles, amides or imines are produced. 

Although, at that time, the term supramolecular chemistry had not yet been coined, the practical potential for inclusion complexation for acetylene alcohol guests 1 and 2 was recognized back in 1968 [12], Spectroscopic studies showed that 1 and 2 formed molecular complexes with numerous hydrogen-bond donors and acceptors, i.e. ketones, aldehydes, esters, ethers, amides, amines nitriles, sulfoxides and sulfides. Additionally, 1 formed 1 1 complexes with several n-donors, such as derivatives of cyclohexene, phenylacetylene, benzene, toluene, etc. The complexation process investigated by IR spectrometry revealed the presence of OH absorption bands at lower frequencies than those for uncomplexed 1 and 2 [12], These data, followed by X-ray studies, confirmed that the formation of intermolecular hydrogen bonds is the driving force for the creation of complexes [13],... 

The choice of catalyst and variations of the temperature, pressure and concentration of ammonia can control the product mix of amines from hydrogenation of a nitrile. The reaction is shown in Eq. (14.8) ... 

An aliphatic dinitrile sebaconitrile has been converted to 1,10-decanediamine in 79-80% yields with addition of an 8 molar ratio of ammonia to the nitrile (7.20).34 In this hydrogenation, the presence of ammonia at least in 5 molar ratio to the nitrile was claimed to be necessary to minimize the formation of secondary amine. The hydrogenation of a number of dinitriles, including industrially important adiponitrile and m-... 

There have been many known cases where high yields of primary amines were obtained over cobalt catalysts in the hydrogenation of nitriles. Hydrogenation of 3,4-... 

An early example of a hydride with pronounced H donor character is [Cp2ZrHCl] , which attacks ketones, aldehydes, esters, epoxides, and even CO2, as shown in Scheme 1. Cp 2ScH is so active that it even attacks nitriles to give Cp Sc(N=CHR) the resulting imine complexes react with H2 to give amines, and the Sc complex is a nitrile hydrogenation catalyst. ... 

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