The document discusses homogeneous catalysis where the catalyst is in the same phase as the reactants. It provides examples of important homogeneous catalytic reactions like hydrogenation, hydroformylation, and hydrocyanation. Hydrogenation involves using metal catalysts like palladium, platinum, or nickel to reduce double and triple bonds. Hydroformylation uses cobalt or rhodium catalysts to add a formyl group and hydrogen to an alkene to produce an aldehyde. Hydrocyanation employs nickel phosphite catalysts to add hydrogen cyanide to an alkene to yield a nitrile, with an important application being the production of adiponitrile.

1. Homogeneous Catalysis

2. CONTENTS:
 Introduction
 Homogeneous Catalysis
 Hydrogenation Catalysis
 Hydroformylation
 Hydrocynation
 References.
2

3. Introduction
 It refers to catalytic reactions where the
catalyst is in the same phase as the reactants.
 It applies to the reactions in the gas and
liquids phase and even in solids.
 In homogeneous catalysis, all the reactants
and catalysts are present in a single fluid
phase and usually in the liquid phase.
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4. General features:
 Liquid phase reactions dominate the field.
 Industrially less relevant; but complex
organic or asymmetric transformations
possible!
 Reaction conditions milder than required for
heterogeneous reactions (-78 °C - ~200 °C).
 Investigation of reactions by spectroscopic
methods (NMR, MS, IR, UV-Vis) directly in
solution possible.
 Fine-tuning of catalyst properties using
different ligands/additives easy possible.
 Major challenge: Separation of products and
catalysts/additives.
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5. Advantages
Advantages of homogeneous processes can be
summarized as follows:
 In many reactions, homogeneous catalysts are
more active and/or selective compared to
heterogeneous catalysts.
 In homogeneous catalysis, the catalysts are
molecularly dispersed within the fluid. Hence,
pore diffusion limitations are absent. However,
bulk phase mass transfer limitation may occurs.
 Catalytic chemistry and mechanism for
homogeneous catalysis are better studied and
understood. Therefore, it is easier to control and
manipulate the process parameters.
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6. Acid Catalysis
 The proton is the most pervasive homogeneous
catalyst because water is the most common
solvent. Water forms protons by the process of
self-ionization of water. In an illustrative case
acid accelerate (catalyze) the hydrolysis of
esters:
 In the absence of acids, aqueous solutions of
most esters do not hydrolyze at practical rates.
 The most widely used industrial operations are
either Homogeneous or Heterogeneous Catalysts.6

7. Examples
 Many of the homogeneous catalysed
reactions have been studied in both gas and
liquid phases and some of the common
examples in gas phase are as follows.
 In the lead chamber process during the
manufacture of sulphuric acid, the presence
of nitric oxide gas helps in catalysing the
oxidation of sulphur dioxide.
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8.  During the decomposition of acetaldehyde,
the catalysis is carried out by iodine
vapours.
 The presence of nitric oxide as catalyst
during the combination of carbon monoxide
and oxygen also clarifies the homogeneous
catalysis.
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9.  Examples of homogeneous catalysis in liquid phase
are as follows:
 The decomposition of nitroso – tri-acetone-amine by
hydroxyl ion catalysis.
 The hydrolysis of nitrile is catalysed by H+ and OH-
ions as well.
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10. Hydrogenation Catalysis
 Hydrogenation – meaning, to treat with hydrogen
– is a chemical reaction between molecular
hydrogen and another compound or element,
usually in the presence of a catalyst such as
nickel, palladium or platinum. The process is
commonly employed to reduce or saturate
organic compounds
 Hydrogenation reduces double and triple bonds
in hydrocarbons.
 The Hydrogenation of alkenes to alkanes at low
pressure (1-4 atm) and moderate temperature
(0-100 C) contain nobel metals such as platinum,
palladium, or rhodium.
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11. Example
 Hydrogenation of alkenes is an exothermic
reaction.
 Mostly Hydrogenation reactions are having
high free energies of activation.
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12. Mechanism
Steps in the hydrogenation of a
C=C double bond at a catalyst
surface, for example Ni or Pt :
 (1) The reactants
are adsorbed on the catalyst
surface and Hydrogen
dissociates.
 (2) An H atom bonds to one C
atom. The other C atom is still
attached to the surface.
 (3) A second C atom bonds to
an H atom. The molecule
leaves the surface.
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13. Catalyst used in catalytic hydrogenation
reaction are following
 Palladium
 Adam's Catalyst
 Raney Nicke
 Copper Chromite
 Transfer Hydrogenation
 Rhodium
 Ruthenium
 Triethylamine
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14.  Palladium: An active form of palladium
obtained from palladium chloride.
 More commonly the palladium chloride
reduce in presence of charcoal or any other
solid support on which the metal is
deposited in a very finely divided state.
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15.  Adam's catalyst: Chloroplastinic acid is
fused with sodium nitrate to give a brown
platinum oxide which can be stored .
 When required, it is treated with hydrogen
to give a very finely divided black
suspension of the metal.
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16. Advantages & Disadvantages
Advantages:
 Relatively high specificity
 Relatively low reaction temperatures
 Far more easily studied from chemical &
mechanistic aspects
 Far more active
 Generally Far more selective for single
product.
Disadvantages:
 More difficult for achieving product/
catalyst separations.
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17. Applications
Hydrogenation
 Requires metal catalyst (Pd, Pt, or Ni)
 Used for converting polyunsaturated oils into
Margarine.
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18. 18

19.  Reduction of esters
 Reduction of amide
 Reduction of unhydride. 19

20. Hydroformylation
 Hydroformylation, also known as oxo
synthesis or oxo process, is an industrial
process for the production of aldehydes
from alkenes.
 This chemical reaction entails the net
addition of a formyl group (CHO) and a
hydrogen atom to a carbon-carbon double
bond(alkenes).
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21. Mechanism
 step 1-Mechanism of cobalt-catalyzed
hydroformylation. The process begins with
dissociation of CO from cobalt tetracarbonyl hydride
to give the 16-electron species.
 step 2-Subsequent binding of alkene gives an 18e
species.
 step 3- The olefin inserts to give the 16e alkyl
tricarbonyl.
 step 4-Coordination of another equivalent of CO give
alkyl tetracarbonyl .
 step 5-Migratory insertion of CO gives the 16e acyl .
 step 6- oxidative addition of hydrogen gives a
dihydrido complex,
 step 7-this dihydrido complex releases aldehyde by
reductive elimination.
 Step 8- is unproductive and reversible.
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22. 22

23. Examples of Catalyst:
 Cobalt tetracarbonyl hydride
 Tris(triphenylphosphine)rhodium carbonyl
hydride
Disadvantages:
 Catalyst losses due to its high Volatility
 Loss of alkene through Hydrogenation in a
reaction Competing with Hydroformylation
 Inherent difficulties in mechanic studies
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24. Hydrocyanation
 Hydrocyanation is, the process whereby H+
and –CN ions are added to a molecular
substrate.
 The substrate is an alkene and the product
is a nitrile.
 Cyanide is both a good σ–donor and π–
acceptor its presence accelerates the rate
of substitution of ligands
 A key step in hydrocyanation is the
oxidative addition of hydrogen cyanide to
low–valent metal complexes.
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25. Examples
Mechanism:
 Hydrocyanation is commonly performed on
alkenes catalyzed by nickel complexes of
phosphite (P(OR)3) ligands.
 A general reaction is shown:
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26.  The reaction proceeds via the oxidative
addition of HCN to Ni(0) to give a
hydridonickel(II) cyanide complex,
abbreviated Ni(H)(CN)L2.
 Subsequent binding of the alkene gives the
intermediate Ni(H)(CN)L(alkene), which
then undergoes migratory insertion to give
an alkylnickel(II) cyanide Ni(R)(CN)L2.
 The cycle is completed by the reductive
elimination of the nitrile.
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27. Applications of Hydrocyanation
 Hydrocyanation is important due to the
versatility of alkyl nitriles (RCN), which are
important intermediates for the syntheses
of amides, amines, carboxylic acids, and
esters.
 The most important industrial application is
the nickel-catalyzed synthesis of
adiponitrile (NC–(CH2)4–CN) synthesis from
1,3–butadiene (CH2=CH–CH=CH2).
 Adiponitrile is a precursor to
hexamethylenediamine (H2N–(CH2)6–NH2),
which is used for the production of certain
kinds of Nylon. 27

28. References:-
1. https://en.m.wikipedia.org/wiki/Homogen
eous_catalysis
2. https://chemistry.tutorvista.com/inorganic
-chemistry/homogeneous-
catalyst.html?view=simple
3. https://en.m.wikipedia.org/wiki/Hydrogen
ation
4. https://en.m.wikipedia.org/wiki/Hydrofor
mylation
5. https://en.m.wikipedia.org/wiki/Hydrocya
nation
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