Introduction
An alkane is a saturated hydrocarbon, in which there are no double bonds, and is made up entirely of Hydrogen and Carbon atoms. The formula for an alkane is CnH2n+2 although this might be different if a ring is present in the hydrocarbon chain.
The naming of straight chain hydrocarbons is as follows:
which have been discussed in the previous Chapter: Introduction to Organic Chemistry.
Apart from straight chain alkanes, one can also find ring structures, with the most common being:
which would have a formula of CnH2n.
Halogenation – Radical Substitution
Halogenation of an alkane is normally performed as a free radical substitution, in which three steps can be observed, initiation, propagation and termination. Initiation is a reaction which produces free radicals from a neutral molecule, propagation is a transfer of the radical charge while the termination is when two radicals join together to form a neutral molecule removing the radical charge. In the halogenation of alkanes this is seen as follows:
Cracking
There are two different types of cracking, thermal cracking and catalytic cracking.
Thermal cracking
This is performed in a chamber at a temperature of 450 – 750oC and a pressure of up to 70atm. This would break a Carbon to Carbon bond forming free radicals which can then react in different ways.
A simple reaction might be C15H32 → 2C2H4 + C3H6 + C8H18 in which two alkenes and an alkane are formed from a long chained alkane.
Catalytical cracking
This is performed at a temperature of around 500oC but a much-lowered pressure using a catalyst such as a zeolite.