Improved Methodology for the Preparation of Chiral Amines

compared to the oil refinery industry which has the lowest E factor. Atom efficiency is
calculated by dividing the molecular weight of the desired product by the sum of the
molecular weights of all the substances produced in the stoichiometric equation.
3.4.2. Hydrogenation and Green Chemistry:
Catalytic hydrogenation–utilizing hydrogen gas and heterogeneous catalysts–can be
considered as the most important catalytic method in synthetic organic chemistry on both
laboratory and production scales. Hydrogen is, without doubt, the cleanest reducing agent and
the heterogeneous robust catalysts have been routinely employed. Catalytic hydrogenation
has distinctive advantages over other methodologies. Key advantages of this technique are: [67]
1. Broad scope, many functional groups can be hydrogenated with high selectivity.
2. High conversions are usually obtained under relatively mild conditions in the liquid phase.
3. The large body of experience with this technique makes it possible to predict the catalyst
of choice for a particular problem.
4. The process technology is well established and scale-up is therefore usually
straightforward.
The field of hydrogenation is also the area where catalysis was first widely applied in the fine
chemical industry. It is a key example of green technology, due to the low amounts of
catalysts required, in combination with the use of hydrogen (100% atom efficient!) as the
reductant. In general, if chirality is not required, heterogeneous supported catalysts can be
used in combination with hydrogen. Catalytic hydrogenation is considered as the green route
for the synthesis of different functional compounds as amines, alcohols, and amino acids.
Once selectivity and chirality is called for, homogeneous catalysts and biocatalysts are
applied. The use and the application of chiral Ru, Rh and Ir catalysts has become a well
developed technology. Homogenous catalytic hydrogenation gives access to a large variety of
asymmetric transformations: imines and functionalized ketones and alkenes can be converted
with high selectivity in most cases.
75