Ziegler-Natta Catalysis Presented by: Mehrban ashiq Saad afzal Presented To: M.phil Inorganic- Analytical Chemistry 3 rd Semester Department of Chemistry, University of Gujrat, Pakistan. Course Title: Organo -Transition Chemistry Course code: CHEM-529 Instructor: Dr. Muhammad Ali Mohsin
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Ziegler-Natta Catalysis Presented by: Mehrban ashiq Saad afzal Presented To: M.phil Inorganic- Analytical Chemistry 3 rd Semester Department of Chemistry,
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Ziegler-Natta Catalysis
Presented by:
Mehrban ashiqSaad afzal
Presented To:
M.phil Inorganic- Analytical Chemistry 3rd Semester Department of Chemistry, University of Gujrat,
Introduction CatalysisActivation Energy Ziegler-Natta Olefin PolymerizationZiegler's DiscoveryMechanismNatta's DiscoveryPP StereochemistryDifferent Catalyst system and % yieldConclusion
Catalysis• Catalysts increase reaction rate without
themselves being changed• Can accelerate a reaction in both directions• Do not affect the state of equilibrium of reaction
– simply allow equilibrium to be reached faster
Activation energy• Molecules must be
activated before they can undergo a reaction– Reactants must absorb
enough energy from surroundings to destabilize chemical bonds (energy of activation)
• Transition state– Intermediate stage in
reaction where the reactant molecule is strained or distorted but the reaction has not yet occurred
Ziegler’s Discovery• 1953 K. Ziegler, E. Holzkamp, H. Breil & H. Martin• Angew. Chem. 67, 426, 541 (1955); 76, 545 (1964).
Al(Et)3 + NiCl2 Ni100 atm110 C
CH3CH2CH=CH2 + +AlCl(Et)2
TiCl4 1 atm20-70 C
Al(Et)3 + CH2CH2"linear"
Mw = 10,000 - 2,000,000
Problem
Idea:
Ziegler-Natta CatalystsZiegler-Natta Catalysts Combination of a transition metal compound of Combination of a transition metal compound of
an element from groups IV to VIII, and an an element from groups IV to VIII, and an organometallic compound of a metal from groups organometallic compound of a metal from groups I to III.I to III.
Catalyst Catalyst –– Transition metal Transition metal
Co-catalyst Co-catalyst –– Organometallic Compound, mainly Organometallic Compound, mainly alkyl or alkylhalides of aluminium and boron, or alkyl or alkylhalides of aluminium and boron, or methylaluminoxane.methylaluminoxane.
Ziegler-Natta Catalysis of Ziegler-Natta Catalysis of Alkene PolymerizationAlkene Polymerization
A typical Ziegler-Natta catalyst is a combination of A typical Ziegler-Natta catalyst is a combination of
TiClTiCl44 and (CH and (CH33CHCH22))22AlCl, AlCl,
or or
TiClTiCl33 and (CH and (CH33CHCH22))33Al.Al.
H2C CH2
Ziegler-Natta CatalystCH2 CH2 n
Polymerization Steps
1. Replacement of one Cl by alkyl group of Al alkyl
2. Bonding of Propylene to a vacant site
3. Insertion of propylene into Metal-alkyl bond- Initiation
4. Creation of vacant site for propylene adsorption
5. Repetition of steps 2,3 & 4 leading to chain growth/propagation
6. Catalyst configuration decides the configuration of added propylene
7. Termination of polymer chain with hydrogen- Termination
Conventional Ziegler-Natta Catalyst
• Catalyst components TiCl4 & AlEt3
• Organo aluminium compound reduces TiCl4 to generate TiCl3
• Active phase TiCl3
• Different crystalline forms- α , β, γ , & δ• β Chain structure; α , γ , & δ have layer structure• Activity & Isotacticity differs• α – Hexagonal Close packed – hcp of Cl ions• γ - Cubic close packed –ccp of Cl ions• Ti ions occupy Octahedral holes of Cl- matrix
Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization
InitiationInitiation
Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization
General Composition of Catalyst System and % Yield
Main Group Metal alkyl
Transition Metals Compounds % Yield of Polymer
Al2Et6 TiCl4 48
AlBu3 TiCl4 60
Al2Et6 TiCl*3 80-92
Al2Et6 VCl4 78
Al2Et6 VCl3 73
Al2Et6 CrCl3 36
Al2Et6 TiCl3 40-50
[Et2Be] n TiCl*3 94-96
[Et2Mg] n TiCl*3 78-85
Et2Zn TiCl*3 30-40
[AlClMe2] 2 TiCl*3 96-98
R.C.MEHROTRA,. A.SINGH. “Organometallic Chemistry” Revised Second Edition page(464)
Limitations
we can't make poly(vinyl chloride) by Ziegler-Natta polymerization. When the catalyst and cocatalyst come together to form the initiating complex, radicals are produced during intermediate steps of the reaction. These can initiate free radical polymerization of the vinyl chloride monomer.
Acrylates are out, too, because Ziegler-Natta catalysts often initiate anionic vinyl polymerization in those monomers.
Move forward
homogeneous polymerization catalyst
metallocene catalysis polymerization
Ziegler – Natta olefin polymerization
homogeneous polymerization catalyst:
Reactive intermediates such as A or B, alkyl olefin complexes, should be unsaturated