Dicyclopentadiene and Reactions

Dicyclopentadiene abbreviated as DCPD, is a compound with the chemical formula C10H12.At room temperature it is a white, brittle wax, but less pure samples may be a straw colored liquid.The pure material smelled a bit like bean wax or camphor, and the less pure sample had a stronger acrid smell.It has an energy density of 10,975 Wh/l.Dicyclopentadiene is a large by-product of the steam cracking of naphtha and gas oil to ethylene.Mainly used in resins, especially unsaturated polyester resins.It is also used in inks, adhesives and paints.The world's top seven suppliers had a combined annual capacity of 179 kilotons (395 million pounds) in 2001.

Reactions 

Above 150 °C, dicyclopentadiene undergoes a retro-Diels-Alder reaction at an appreciable rate to cyclopentadiene.The reaction is reversible and cyclopentadiene dimerizes to reform dicyclopentadiene within hours at room temperature.Cyclopentadiene is a useful diene in the Diels-Alder reaction and a precursor of metallocenes in organometallic chemistry.Due to the rapid formation of dicyclopentadiene, it is not commercially available as a monomer; therefore, it must be prepared by "cracking" dicyclopentadiene (heating the dimer and separating the monomer by distillation) shortly before it is needed.Thermodynamic parameters of the process were measured.At gas phase temperatures above about 125 °C, dissociation to cyclopentadiene monomer begins to become thermodynamically favorable (dissociation constant Kd = [cyclopentadiene]2 / [dicyclopentadiene] > 1).For example, the Kd values at 149 °C and 195 °C are 277 and 2200, respectively.By extrapolation, Kd is about 10–4 at 25 °C, which is not favorable for dissociation. Consistent with the negative values of ΔH° and ΔS° for the Diels-Alder reaction, the dissociation of dicyclopentadiene is thermodynamically more favorable at high temperature.Equilibrium constant measurements show ΔH° = –18 kcal/mol and ΔS° = –40 eu for cyclopentadiene dimerization.

Polymerization of dicyclopentadiene.Forms copolymers with ethylene or styrene.The "norbornene double bond" was involved in using ring-opening metathesis polymerization to form the homopolymer polydicyclopentadiene.Hydroformylation of DCP yields a dialdehyde known as TCD dialdehyde (TCD = tricyclodecane).Such dialdehydes can be oxidized to dicarboxylic acids and diols.All these derivatives are of some use in polymer science.Hydrogenation of dicyclopentadiene gives tetrahydrodicyclopentadiene,C10 hours16, which is a component of jet fuel JP-10,and rearranges to adamantane with aluminum chloride or acid at high temperature.