Trimethylaluminium
- C3H9Al
- C6H18Al2 (dimer)
Pyrophoric, colorless liquid
- 72.08 g · mol -1
- 144.18 g.mol -1 ( dimer)
Liquid
0.75 g · cm -3
15 ° C.
125 ° C
- Violent reaction with water
- Soluble in toluene, hexane and heptane
Risk
-136.4 KJ / mol
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Trimethylaluminum (TMA or TMAl ) is a pyrophoric colorless liquid and is one of the aluminum alkyls. TMA has a boiling point of 127 ° C and a very high vapor pressure. In air, it forms white smoke, spontaneously ignites and reacts explosively with water. Therefore, this compound should be stored and handled under argon or nitrogen. As a reagent as a solution in toluene, hexane or heptane, is often used.
Properties
Chemical Properties
Since the aluminum atom is surrounded by only three methyl groups, it has only six valence electrons. To satisfy the octet rule and to achieve a noble gas configuration, the dimer of TMA, in which the two aluminum nuclei are bridged by two methyl groups, is formed. The structure is similar to that of the diborane molecule, wherein the aluminum atoms to the boron atoms and the methyl groups correspond to the hydrogen atoms. As the hydrogen nuclei in the diborane form the bridging methylene groups, a two -electron three - center bond to each methylene group represents two electrons available. Although the carbon atoms of the bridging methylene groups are each surrounded by five neighbors, they only have eight electrons in the outermost shell. This situation causes an electron deficit, which makes TMA extremely reactive. TMA is a Lewis acid and to react with a variety of substances. It exchanged very rapidly from methyl groups to other groups or atoms (eg halogens ) which contain more electrons. This property makes TMA at an excellent methylating agent.
Use
TMA is used for the preparation of methylaluminoxane, a co-catalyst for the Ziegler-Natta polymerizations, as an activator and as a methylating agent. It also finds application in the semiconductor industry. TMA and the Tebbe reagent is prepared, which is used for the methylenation of esters and ketones. With titanium tetrachloride TMA reacts to Reetz reagent, with which it is possible to convert a ketone into a gem- dimethyl compound.
Safety
TMA is highly corrosive. The connection ignites spontaneously in air and reacts explosively with water. Therefore it must always be carried out in a dry inert gas atmosphere.