THE HALOGENATION OF ALKANES AND CYCLOALKANES
Alkanes
The reaction between alkanes and fluorine
This reaction is explosive even in the cold and dark, and you tend to get carbon and hydrogen fluoride produced. It is of no particular interest. For example:
The reaction between alkanes and iodine
Iodine doesn't react with the alkanes to any extent - at least, under normal lab conditions.
The reactions between alkanes and chlorine or bromine
There is no reaction in the dark.
In the presence of a flame, the reactions are rather like the fluorine one - producing a mixture of carbon and the hydrogen halide. The violence of the reaction drops considerably as you go from fluorine to chlorine to bromine.
The interesting reactions happen in the presence of ultra-violet light (sunlight will do). These are photochemical reactions, and happen at room temperature.
We'll look at the reactions with chlorine. The reactions with bromine are similar, but rather slower.
Methane and chlorine
Substitution reactions happen in which hydrogen atoms in the methane are replaced one at a time by chlorine atoms. You end up with a mixture of chloromethane, dichloromethane, trichloromethane and tetrachloromethane.
What is cracking?
Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst.
The source of the large hydrocarbon molecules is often the naphtha fraction or the gas oil fraction from the fractional distillation of crude oil (petroleum). These fractions are obtained from the distillation process as liquids, but are re-vaporised before cracking.
There isn't any single unique reaction happening in the cracker. The hydrocarbon molecules are broken up in a fairly random way to produce mixtures of smaller hydrocarbons, some of which have carbon-carbon double bonds. One possible reaction involving the
The reaction between alkanes and fluorine
This reaction is explosive even in the cold and dark, and you tend to get carbon and hydrogen fluoride produced. It is of no particular interest. For example:
The reaction between alkanes and iodine
Iodine doesn't react with the alkanes to any extent - at least, under normal lab conditions.
The reactions between alkanes and chlorine or bromine
There is no reaction in the dark.
In the presence of a flame, the reactions are rather like the fluorine one - producing a mixture of carbon and the hydrogen halide. The violence of the reaction drops considerably as you go from fluorine to chlorine to bromine.
The interesting reactions happen in the presence of ultra-violet light (sunlight will do). These are photochemical reactions, and happen at room temperature.
We'll look at the reactions with chlorine. The reactions with bromine are similar, but rather slower.
Methane and chlorine
Substitution reactions happen in which hydrogen atoms in the methane are replaced one at a time by chlorine atoms. You end up with a mixture of chloromethane, dichloromethane, trichloromethane and tetrachloromethane.
What is cracking?
Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst.
The source of the large hydrocarbon molecules is often the naphtha fraction or the gas oil fraction from the fractional distillation of crude oil (petroleum). These fractions are obtained from the distillation process as liquids, but are re-vaporised before cracking.
There isn't any single unique reaction happening in the cracker. The hydrocarbon molecules are broken up in a fairly random way to produce mixtures of smaller hydrocarbons, some of which have carbon-carbon double bonds. One possible reaction involving the