In the Friedel-Crafts alkylation reaction, an aromatic substitution occurs, in which the aromatic ring attacks a carbo cation electrophile. The electrophile is formed by the reaction of a Lewis acid catalyst, such as aluminum chloride, with an alkyl halide. An excess amount of this catalyst is added to act as a dehydrant to allow the Friedel-Crafts reaction to proceed. Electrophilic aromatic substitution products generally are very large molecules with a high degree of electron dislocation that cause intense coloring.