Chemistry of Fullerenes - CHM 102 PDF

CHM 102 CHEMISTRY OF FULLERENES CHEMISTRY OF FULLERENES Introduction: Fullerenes, a unique form of carbon allotropes, have garnered significant interest across multiple scientific fields due to their diverse structural properties and potential applicati...

CHM 102 CHEMISTRY OF FULLERENES CHEMISTRY OF FULLERENES Introduction: Fullerenes, a unique form of carbon allotropes, have garnered significant interest across multiple scientific fields due to their diverse structural properties and potential applications. These molecules are characterized by their distinctive closed-cage formations, which include a variety of shapes such as hollow spheres, ellipsoids, and tubes. The structure of fullerenes is based on fused rings of carbon atoms, where each carbon atom is bonded to three others through single and double bonds, forming a mesh that includes hexagonal and pentagonal rings. This structural versatility results in a large number of isomers and homologous series with similar sizes and shapes. Definition: Fullerenes are a distinct class of carbon allotropes composed of carbon atoms connected by single and double bonds, forming fused rings of five to seven atoms. These structures create closed or partially closed mesh formations that can take on various shapes, such as hollow spheres, ellipsoids, and cylinders. Notably, when arranged in a cylindrical form, they are known as carbon nanotubes. Each carbon atom in a fullerene is typically bonded to three other carbon atoms, creating a stable, cage-like structure. The most well-known fullerene is the buckminsterfullerene (C₆₀), which resembles a soccer ball made up of 20 hexagonal and 12 pentagonal rings. Other forms of fullerenes include carbon nanotubes, which are cylindrical structures formed by arranging carbon molecules in a tube-like shape. These nanotubes exhibit remarkable mechanical, electrical, and thermal properties, making them valuable in various technological and industrial applications. Physical Properties of Fullerene i. Its behaviour and structure depend on the temperature. As the temperature is increased fullerene gets converted into the C70. CHM 102 CHEMISTRY OF FULLERENES ii. The structure of fullerenes can change under different pressures. iii. Fullerene has an ionization enthalpy of 7.61 electron volts (733.39Kj/mol). iv. Its electron affinity is 2.6-2.8 electrons volts (250.75-270.17Kj/mol). Chemical formula C60 Molar mass 720.66 g·mol−1 Appearance Dark needle-like crystals Density 1.65 g/cm3 Melting point sublimates at ~ 600 °C (1,112 °F; 873 K) Solubility in water insoluble in water Chemical Properties of Fullerene i. Fullerenes are stable, but not totally unreactive. ii. In chemical reactions, fullerene can act as an electrophile. e.g. cyclopropanation, amination and 1,3-Dipolar Cycloaddition. iii. It acts as an electron-accepting group and is characterized as an oxidizing agent. E.g. in reaction with sodium Naphthalenide, where the naphthalenide is oxidized back to naphthalene. iv. Fullerenes when doped or crystallized with alkali or alkaline earth metals showcases superconductivity properties. v. Fullerene is ferromagnetic. vi. Some fullerenes are inherently chiral. vii. It is soluble in organic solvents such as toluene, chlorobenzene, and 1,2,3- trichloropropane and 1,2-dichlorobenzene. By attaching polar groups, such as hydroxyl groups, to the fullerene structure, they can become soluble in water. Types of Fullerenes The primary types of fullerenes include nanotubes, megatubes, polymers, nano- onions, and buckminsterfullerene (C60). 1. Carbon Nanotubes Description: Cylindrical structures with hollow interiors, extremely small in diameter. CHM 102 CHEMISTRY OF FULLERENES Properties: Can have single or multiple walls. Applications: Widely used in electronics due to their exceptional electrical conductivity, high tensile strength, and thermal conductivity. 2. Megatubes Description: Larger in diameter than nanotubes, with walls of varying thickness. Properties: Can transport molecules of different sizes. Applications: Potential uses in nanotechnology and materials science. 3. Polymers Description: Formed under extreme temperature and pressure conditions, can be one-dimensional chains, two-dimensional sheets, or three-dimensional networks. Properties: Diverse structures with potential for various industrial applications. Applications: Used in advanced materials and composites. 4. Nano-Onions Description: Spherical structures composed of multiple concentric layers of carbon atoms with a buckyball core. Properties: Excellent lubricants due to their layered structure. Applications: Used in lubrication and other nanotechnological applications. 5. Buckminsterfullerene (C60) Description: Composed of 60 carbon atoms arranged in a structure similar to a soccer ball, with 12 pentagons and 20 hexagons. Properties: Highly symmetrical, stable, and can undergo various chemical modifications. Applications: Used in materials science, medicine, and electronics. 6. Buckyball Clusters CHM 102 CHEMISTRY OF FULLERENES Description: Smaller fullerenes, like C20, with structures similar to dodecahedra. Properties: Unsaturated versions of fullerene structures. Applications: Fundamental research and potential nanotechnology applications. 7. Linked Ball and Chain Dimer Description: Two buckyballs connected by a carbon chain. Properties: Unique structural features leading to specific chemical and physical properties. Applications: Research in molecular chemistry and potential nanotechnological uses. 8. Heterofullerenes Description: Fullerenes with heteroatoms (non-carbon atoms) substituting some carbon atoms in the cage or tube structures. Properties: Modified electronic and chemical properties. Applications: Advanced materials and chemical research. 9. Metallofullerenes Description: Fullerenes with a metal atom encapsulated inside the carbon cage. Properties: Exhibit unique magnetic, electronic, and catalytic properties. Applications: Catalysis, materials science, and electronics. Synthesis of Fullerenes Fullerenes have become valuable and versatile building blocks in organic chemistry. They were initially synthesized through a process of laser vaporization of carbon in an inert atmosphere, which produced only small quantities of fullerenes. Subsequent advancements led to more effective methods for fullerene synthesis. 1. Electric Arc Heating of Graphite CHM 102 CHEMISTRY OF FULLERENES This method involves creating an electric arc between graphite rods in an inert atmosphere. The process produces a fluffy condensate known as soot, which contains extractible fullerenes. Here is a step-by-step breakdown: 1. Electric Arc Creation: An electric arc is generated between graphite rods in an inert gas environment. 2. Formation of Soot: The electric arc vaporizes the graphite, forming a fluffy condensate (soot). 3. Extraction of Fullerenes: Fullerenes are extracted from the soot using toluene as a solvent. 4. Purification: The solvent is removed using a rotary evaporator, yielding primarily C60 fullerenes with small amounts of higher fullerenes. This process allows for the extraction and purification of C60 fullerenes from the soot. 2. Laser Irradiation of Polycyclic Aromatic Hydrocarbons (PAHs) This technique is used to produce new fullerene homologues that are difficult to obtain through uncontrolled graphite evaporation. The method involves the following steps: 1. Selection of PAHs: Polycyclic aromatic hydrocarbons (PAHs) with the necessary carbon frameworks are chosen. 2. Flash Vacuum Pyrolysis (FVP): PAH molecules undergo flash vacuum pyrolysis, where they are "rolled up" into fullerenes. 3. Laser Irradiation: PAHs are irradiated with a laser at a specific wavelength (e.g., 337 nm for C60 synthesis). 4. Formation of Fullerenes: The laser irradiation induces the formation of fullerene structures. This method allows for the direct production of fullerenes from PAHs, which already possess the required carbon skeletons. CHM 102 CHEMISTRY OF FULLERENES Applications of Fullerenes Fullerenes, due to their unique physical and chemical properties, have a wide range of applications across various fields such as medicine, photovoltaics, gas adsorption and storage, and materials science. Here are some key applications: Medical Applications Antiviral and Antibacterial/Antimicrobial Activity: Antiviral: Fullerene and its derivatives exhibit antiviral properties due to their distinctive molecular cage structure and antioxidant properties. Studies have shown that fullerene derivatives can inhibit HIV protease, making them potential treatments for HIV. Antibacterial/Antimicrobial: Functionalized fullerenes have been shown to effectively inactivate pathogenic germs through photocatalytic activities, making them useful in water purification and environmental. Photovoltaics and Energy Materials Photovoltaics: Fullerenes are used in organic photovoltaic devices (OPVs) and organic field- effect transistors (OFETs) due to their excellent electrochemical properties, improving the performance of polymer transistors and light detectors. Supercapacitors: Fullerenes are utilized in surface electrodes for supercapacitors. Their nanostructure enhances surface area, pore size distribution, electrolyte accessibility, and electrical conductivity, thereby improving capacitance. Lithium-Ion Batteries: Fullerene-based materials, particularly hydrogenated fullerenes, are investigated as high-performance anode materials for lithium-ion batteries. They enhance the reversible capacity and reduce the irreversible capacity of commercial graphite anodes. Superconductors: CHM 102 CHEMISTRY OF FULLERENES When alkali metals are inserted into fullerene C60, new composite materials with superconducting properties are formed. For example, the K3C60 composite exhibits high superconducting critical temperature, excellent 3-D superconductivity, current density, ductility, and stability. Fullerene-Based Polymeric Materials Fullerene-based polymers are created by directly attaching fullerene materials to polymers or by linking fullerenes with spacer groups. These materials have excellent electrical properties and are used in various applications, including electrode films and redox-active polymers. Water Purification and Environmental Protection Functionalized fullerenes can act as adsorbents for organic molecules and metal speciation, contributing to water purification. They produce reactive oxygen species (ROS) that are effective for water disinfection. Hydrogen Storage Fullerenes have a cage-like structure capable of storing hydrogen. Although they can only store up to 6.1% hydrogen, this makes them potentially useful for hydrogen storage in fuel cells for electric cars. The degree of hydrogenation can be determined by color changes in the material. Reinforced Composites Fullerene C60 is used to reinforce materials, such as Al-Mg alloy, enhancing their mechanical, thermal, and malleability properties. This makes fullerene- reinforced composites valuable for improving infrastructure materials.