What Is Trimethylaluminum?
Trimethylaluminum (TMA) is an organic aluminum compound with the chemical formula C6H18Al2. The molecular formula is (CH3)3Al, but it exists as a dimer connected via a methyl group. It has a molecular weight of 144.18, a melting point of 15°C, a boiling point of 125°C, and is a clear, colorless liquid with a density of 0.752 g/mL at room temperature.
TMA is miscible in organic solvents such as hexane, heptane, and other aliphatic saturated hydrocarbons, toluene, and xylene. It is a volatile substance, spontaneously combustible in air and water, with a low flash point of -18°C, igniting at room temperature.
Uses of Trimethylaluminum
Trimethylaluminum is used in various applications, including as a raw material for producing trimethylgallium (TMG), in MO-CVD processes, and for doping silicon semiconductors. These applications are crucial in the production of LEDs and semiconductors. TMA also serves as a precursor for high-purity aluminum oxide.
In synthetic organic chemistry, it is used to make Tebbe reagents, which convert carbonyls to exo-olefins, and as a Ziegler-Natta catalyst for olefin polymerization.
Principle of Trimethylaluminum
Below is an explanation of the chemical properties and applications of trimethylaluminum:
1. Chemical Properties of Trimethylaluminum
As a dimeric compound connected via a methyl group, trimethylaluminum is one of the most reactive alkylaluminums with a high heat of hydrolysis. It oxidizes and ignites immediately upon contact with water. It must be handled with care to avoid contact with acids, air, amines, flammable substances, carbon halides, halogens, and oxidizing agents, preferably in inert gas or hydrocarbon solvents.
2. Trimethylaluminum in Organometallic Chemistry
Trimethylaluminum is utilized to introduce methyl groups into metal halides, such as in the production of trimethylgallium by reacting with gallium (III) chloride. Its properties are also employed in activating titanium chloride in Ziegler-Natta catalysts for olefin polymerization and in Tebbe reagents for converting carbonyls to exo-olefins.
Types of Trimethylaluminum
There are various forms of trimethylaluminum, including reagents for research and development in synthetic organic chemistry, and industrial chemical products. Laboratory reagents are commonly handled in hexane or toluene solutions with concentrations like 1.0 mol/L, 1.4 mol/L, and 2.0 mol/L, available in 100 mL, 800 mL, and 1 L volumes.
These solution products are prone to hydrolysis and may precipitate upon contact with water. Thus, they must be handled with well-dried and nitrogen-filled syringes. For industrial purposes, pure trimethylaluminum is supplied in quantities of 25g, 100g, 300g, 600g, 100mL, etc., and is stored in special containers with desiccants due to their hazardous nature.