Intensification of Cyclopentadiene Dimerization by Ultrasound Irradiation

Abstract

Cyclopentadiene and isoprene are produced in large quantities by the steam cracking of naphtha and gas oils to produce ethylene. At room temperature, cyclopentadiene slowly dimerizes in a Diels-Alder reaction to give dicyclopentadiene. This work presents a new method for accelerating the Diels-Alder reaction in the presence of ultrasonic irradiation under ambient conditions. The effects of various reaction conditions such as ultrasonic reaction time and reaction temperature on cyclopentadiene dimerization and oligomerization of cyclopentadiene and isoprene were investigated. The results showed that the two reactions could be significantly enhanced by ultrasonic irradiation. The kinetic results revealed that the introduction of ultrasonic irradiation lowered the activation energy of both reactions, but not to the same degree. The increased difference in activation energy between the two reactions is the driving force to produce more dicyclopentadiene in the presence of ultrasonic irradiation.

Spirocyclization enhances the Diels–Alder reactivities of geminally substituted cyclopentadienes and 4H‐pyrazoles

“…[15][16][17] At 50 C, the rate constant suggests that the dimerization of 4-Cp occurs $220-fold faster than the dimerization of Cp. [15,18] The increased rate of dimerization observed in 4-Cp interests us because it suggests that spirocyclization enhances the Diels-Alder reactivity of 5-membered dienes.…”

Supramolecular Catalysis of a Catalysis-Resistant Diels–Alder Reaction: Almost Theoretical Acceleration of Cyclopentadiene Dimerization inside Cucurbit[7]uril

“…35 At the same time, it is the textbook example of a Diels−Alder reaction that is extremely difficult to accelerate through the choice of the reaction conditions; 36 the use of ionic liquids with 60% AlCl 3 37 leads only to a sixfold rate enhancement, while ultrasound does not even reach a factor of 2. 38 This leaves only the universal possibility of increasing temperature or, since Diels−Alder reactions have negative volumes of activation, high pressure to speed up this slow reaction. 24 Moreover, in none of the numerous examples involving supramolecular catalysis of Diels−Alder reactions between heteroatom-containing dienophiles and CPD as diene has an accelerated dimerization of the hydrocarbon been reported as an interfering side reaction (see Table 1).…”

“…The dimerization of cyclopentadiene (CPD) is the prototype of a Diels–Alder reaction of a simple hydrocarbon that follows the endo rule (Chart ). At the same time, it is the textbook example of a Diels–Alder reaction that is extremely difficult to accelerate through the choice of the reaction conditions; the use of ionic liquids with 60% AlCl 3 leads only to a sixfold rate enhancement, while ultrasound does not even reach a factor of 2 . This leaves only the universal possibility of increasing temperature or, since Diels–Alder reactions have negative volumes of activation, high pressure to speed up this slow reaction .…”

Supramolecular Catalysis of a Catalysis-Resistant Diels-Alder Reaction: Rapid Dimerization of Cyclopentadiene inside Cucurbit[7]uril

“…At the same time, it is the textbook example of a Diels-Alder reaction that is extremely difficult to accelerate through the choice of the reaction conditions; 33 the use of ionic liquids with 60% AlCl3 34 leads only to a 6-fold rate enhancement, while ultrasound does not even reach a factor of 2. 35 This leaves only the universal possibility of increasing temperature or, since Diels-Alder reactions have negative volumes of activation, high pressure to speed up this slow reaction. 24 Moreover, in none of the numerous examples involving supramolecular catalysis of Diels-Alder reactions between heteroatomcontaining dienophiles and CPD as diene 9,26,30,[36][37][38] has an accelerated dimerization of the hydrocarbon been reported as an interfering side reaction.…”