REAKSI POLIMERISASI PEMBUKAAN CINCIN ?-KAPROLAKTON, ASETALASI BENZALDEHIDA, DAN POLIMERISASI ?-PINEN MENGGUNAKAN KOMPLEKS Zr ?-DIKETONAT SEBAGAI KATALIS

• Main Author: Yusuf, Muhammad
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/32823
• Institution: Institut Teknologi Bandung

The decrement of fossil oil reserves and the rise of CO2 emission as the impact of dependence on fossil based energy, has led to intensified research aiming to producing bio-based chemicals as substitute to petroleum base chemicals with environmentally benign and sustainable materials. One of attractive biomasses to be explored is starch plants. It is a very promising feedstock for the production of bio-based chemicals. The C6 sugars for example d-fructose in starch plants are interesting precursors for a broad range of chemicals with high potential applications, such as ?-caprolactone. An other biomass material is cinnamon oil derived from cinnamon tree, which are interesting precursors for benzaldehyde. Turpentine oil from pine trees containing ?-pinene as its major component is also an important biomass sources. Ring opening polymerization (ROP) of ?-caprolactone (?-CL) has been an interesting topic for many researchers because of its capability in producing degradable polymers. Generally, early transition metal complexes are used as catalysts in ROP of ?-CL due to its Lewis acid property. Lewis acid catalysts are also employed in acetalization of benzaldehyde and polymerization of ?-pinene. Unfortunately, many early transition complexes have some drawbacks such as their instability in air and moisture, corrosive, and also have less electronic control towards Lewis acidity. In addition, current ROP of ?-CL and polymerization of ?-pinene gave polymers with low molecular weight and low melting point. In this research, zirconium ?-diketonates have been choosen as Lewis acid catalysts in ROP of ?-CL, acetalization of benzaldehyde, and polymerization of ?-pinene. NBO analysis was used to calculate the Lewis acidity of zirconium ?-diketonate complexes using a Gaussian-09 package with an NBO 3.1 program. Various ?-diketonates ligands were explored computationally to observe the effect of electron withdrawing (Phenyl, CF3) and electron donor (CH3) group in controlling the Lewis acidity at zirconium center. Relative Lewis acidity among zirconium ?-diketonates based on NBO results were used to find efficient catalysts for ROP of ?-CL, acetalization of benzaldehyde, and polymerization of ?-pinene. Plausible reaction mechanisms of ROP of ?-CL and ?-pinene polymerization using tris(acetylacetonato)zirconium(IV) chloride as a complex model were also explored computationally in this research. ROP of ?-CLs were successfully performed using four series of zirconium ?-diketonates, i.e. tris(acetylacetonato)zirconium(IV) chloride ([Zr(acac)3]Cl) (i), tris(benzoylacetonato)-zirconium(IV) chloride ([Zr(bzac)3]Cl) (ii), tris(dibenzoylmetanato)zirconium (IV) chloride ([Zr(dbzm)3]Cl) (iii), and tris(benzoyltrifluoroacetonato)zirconium (IV) chloride ([Zr(btfa)3]Cl) (iv) at 100 °C for 4 h. Complexes iv and ii showed comparably high activity in this polymerization (11.7 kg•mol-1•h-1 and 11.6 kg•mol-1•h-1) than that of i (10.7 kg•mol-1•h-1), and iii (7.7 kg•mol-1•h-1). The difference in catalytic activity is likely due to the difference in Lewis acidity. Acetalization of benzaldehyde were also successfully performed using i – iv at r.t for 1 h. Complexes iii and iv showed good catalytic activity (>99 %) compared to ii (86%) and i (70%) with the catalytic activity order of the following: iv, iii>ii>i. Zirconium ?-diketonate iii were also employed in ?-pinene polymerization. Polymerization of ?-pinene at r.t. for 24 h gave conversion of 11%. On the other hand, i, ii, and iv resulted in no reaction. The result of NBO calculations of zirconium ?-diketonates showed that the order of Lewis acidity based on NBO natural charge of Zr atom in the complexes was ii>iv>iii>>i. Although this order was derived from NBO natural charge at zirconium center, the value does not reflect the easy way of ?-CL, ?-pinene, and benzaldehyde to coordinate at Zr, as this may also involves a sterical factor of two phenyl rings (R1 = R2 = Ph) in complex iii. The peculiar behaviour of the trifluoromethyl group (R=CF3) in complex iv was predicted due to high reactivity of fluorine atoms which disturbed coordination of substrate to the metal center. Computational calculations employed at ROP of ?-CL and ?–pinene polymerization provided three possible reaction routes of the coordination of ?-CL and ?–pinene at zirconium. First, dissociation of one ?-diketonate ligand from the complex prior to the insertion of monomer (?-CL and ?-pinene). Second, direct insertion monomer into zirconium ?-diketonates. Third, dissociation of one oxygen of diketonate ligand. Based on the three possible reaction routes, the second route was the most possible route for ?-CL to coordinate with zirconium ?-diketonates complex due to its lowest energy. Whereas, the most possible reaction routes for ?-pinene to coordinate with zirconium ?-diketonates complex is the third route due to its lowest energy too (0,1 kJ/mol). Based on these results, zirconium ?-diketonates may be employed as potential catalysts in the ROP of ?-CL, and acetalization of benzaldehyde. In contrast, these catalyst is likely not suitable to proceed polymerization of ?-pinene. In overall, these catalysts have advantages such as higher stability towards moisture and air, non corrosive, and ease control of Lewis acidity.