Redistribution (chemistry)
Encyclopedia
In chemistry, redistribution usually refers to the exchange of anionic ligands bonded to metal and metalloid centers. The conversion does not involve redox, in contrast to disproportionation
reactions. Redistribution reactions are usefully conducted at higher temperatures; upon cooling the mixture, the product mixture is kinetically frozen and the individual products can be separated. In cases where redistribution is rapid at mild temperatures, the reaction is less useful synthetically but still important mechanistically.
In another example, tetramethylsilane
is an undesirable product of the industrially important direct process
, but it can be converted (recycled) into more useful products by redistribution with silicon tetrachloride
:
In organotin chemistry, the mixed alkyl tin chlorides are produced by redistribution:
Many metal halide
s undergo redistribution reactions, usually to afford nearly statistical mixtures of products. For example, titanium tetrachloride
and titanium tetrabromide
redistribute their halide ligands, one of many reactions in this conversion is shown:
Disproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
reactions. Redistribution reactions are usefully conducted at higher temperatures; upon cooling the mixture, the product mixture is kinetically frozen and the individual products can be separated. In cases where redistribution is rapid at mild temperatures, the reaction is less useful synthetically but still important mechanistically.
Examples
Useful redistribution reactions are found in organoaluminium-, organoboron-, and organosilicon chemistry.- BCl3 + 2 B(C2H5)3 → 3 BCl(C2H5)2
In another example, tetramethylsilane
Tetramethylsilane
Tetramethylsilane is the chemical compound with the formula Si4. It is the simplest tetraorganosilane. Like all silanes, the TMS framework is tetrahedral...
is an undesirable product of the industrially important direct process
Direct process
The Direct Process, also called the Direct Synthesis, Rochow Process, and Müller-Rochow Process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and Richard Müller in the 1940s...
, but it can be converted (recycled) into more useful products by redistribution with silicon tetrachloride
Silicon tetrachloride
Silicon tetrachloride is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.-Preparation:...
:
- SiMe4 + SiCl4 → 2 SiMe2Cl2
In organotin chemistry, the mixed alkyl tin chlorides are produced by redistribution:
- 3 SnBu4 + SnCl4 → 4 SnBu3Cl
Many metal halide
Halide
A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
s undergo redistribution reactions, usually to afford nearly statistical mixtures of products. For example, titanium tetrachloride
Titanium tetrachloride
Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is an unusual example of a metal halide that is highly volatile...
and titanium tetrabromide
Titanium tetrabromide
Titanium tetrabromide is the chemical compound with the formula TiBr4. It is the most volatile transition metal bromide. The properties of TiBr4 are an average of TiCl4 and TiI4. Some key properties of these four-coordinated Ti species are their high Lewis acidity and their high solubility in...
redistribute their halide ligands, one of many reactions in this conversion is shown:
- TiCl4 + TiBr4 → 2 TiBr2Cl2