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The process, which is catalyzed by platinum supported by aluminium oxide, is exemplified in the conversion methylcyclohexane (a naphthene) into toluene (an aromatic). [2] Dehydrocyclization converts paraffins (acyclic hydrocarbons) into aromatics. [3] A related aromatization process includes dehydroisomerization of methylcyclopentane to benzene:
Cyclopentadiene is a highly reactive diene in the Diels–Alder reaction because minimal distortion of the diene is required to achieve the envelope geometry of the transition state compared to other dienes. [11] Famously, cyclopentadiene dimerizes. The conversion occurs in hours at room temperature, but the monomer can be stored for days at ...
The spontaneous dimerization of neat cyclopentadiene at room temperature to form dicyclopentadiene proceeds to around 50% conversion over 24 hours and yields the endo isomer in better than 99:1 ratio as the kinetically favored product (about 150:1 endo:exo at 80 °C). [6] However, prolonged heating results in isomerization to the exo isomer.
The reaction of cyclopentadiene and butenone for example is 700 times faster in water relative to 2,2,4-trimethylpentane as solvent. [14] Several explanations for this effect have been proposed, such as an increase in effective concentration due to hydrophobic packing [15] or hydrogen-bond stabilization of the transition state. [16]
The 1971 synthesis consisted of treating cyclopentadiene with methyllithium in dimethyl ether and then with dichloromethane and methyllithium in diethyl ether at −45 °C. It can also be formed in low yield (along with fulvene and Dewar benzene) by irradiation of benzene at 237 to 254 nm. [5]
Such a benzene derivative reacts with 1,7-octadiyne in the presence of a suitable catalyst to generate a naphthalene system. [15] This is an example of a hexadehydro Diels–Alder reaction . Trimerisation of three 2-butyne (dimethylacetylene) molecules yields hexamethylbenzene . [ 16 ]
Unilever voluntarily recalled two types of Suave spray deodorant on March 30 after they were found to contain “slightly elevated levels” of a cancer-causing ingredient called benzene ...
The main limitation of such approach, however, is the need to use constrained dienes, such as furan and cyclopentadiene. [14] In 2009 Buszek and co-workers synthesized herbindole A using aryne [4+2]-cycloaddition. [29] 6,7-indolyne undergoes [4+2] cycloaddition with cyclopentadiene to afford complex tetracyclic product.