ALKYLATION

ALKYLATION

Alkylation is the introduction of an alkyl radical by substitution or addition into an organic compound. For example, the combining of an olefin to a hydrocarbon is an alkylation reaction. In the presence of an acid catalyst such as hydrogen fluoride or sulphuric acid, this reaction is used for the conversion of gaseous hydrocarbons to gasoline. The processes are usually exothermic and similar to polymerisation.  Another example is the formation of 2,2-Dimethylbutane from ethylene and isobutane:

Alkylation reactions include the binding of an alkyl group to:

1. Carbon (to make products such as gasoline alkylates, ethylbenzene etc)
2. Oxygen of a hydroxyl group of an alcohol or phenol (ethers, alkaloids)
3. Trivalent nitrogen (amines)
4. A tertiary nitrogen compound (quaternary ammonium compounds)
5. Metals
6. Miscellaneous elements such as sulphur or silicon  the alkyl is in the form of alkyl halide or ester.

Apart from gasoline, other classes of products from alkylation reactions include pharmaceuticals, detergents, disinfectants, dyes and plastics.

Alkylates of active methylenes are easily prepared using a base such as ethoxide, EtO-.

Methyl and primary halides are most suitable for alkylation reactions. In principle both of the hydrogens can be replaced with alkyl groups:

This can be utilized to form a cyclic system by using a dihalide as shown below:

Alkylations with alkyl halides are important reaction steps in industrial scale chemistry, predominantly for the synthesis of pharmaceuticals or agricultural chemicals. Some often used alkyl halides are methyl chloride, methyl iodide, ethyl chloride, isopropyl chloride, tert-butyl chloride, and benzyl chloride.

Chemical reaction

The following equation shows an example of methylation with methyl chloride:

Side reactions: The effect of possible side reactions must be considered individually, but generally the use of lower alkyl halides leads to the formation of a variety of lower molecular compounds, e.g:

Operations

Because alkylation reactions are diverse in nature, there is no universal method of carrying them out. The production of each compound needs to be considered individually, taking into account the chemical, engineering, and economic factors.