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In addition to m-cymene, there are two other geometric isomers called o-cymene, in which the alkyl groups are ortho-substituted, and p-cymene, in which they are para-substituted. p-Cymene is the most common and only natural isomer. The three isomers form the group of cymenes. Cymenes can be produced by alkylation of toluene with propylene. [1] [2]
Symmetrical examples include diphenylacetylene and 3-hexyne. They may also be asymmetrical, such as in 2-pentyne. Terminal alkynes have the formula RC≡CH, where at least one end of the alkyne is a hydrogen atom. An example is methylacetylene (propyne using IUPAC nomenclature). They are often prepared by alkylation of monosodium acetylide. [4]
m- and p-Cymene are prepared by alkylation of toluene with propylene: CH 3 C 6 H 5 + 2 CH 3 CH=CH 2 → CH 3 C 6 H 4 CH(CH 3) 2. These alkylations are catalyzed by various Lewis acids, such as aluminium trichloride. m- and p-Cymene are mainly of interest as precursors to the respective cresols, which exploits the Hock rearrangements. [1]
In the cymene–cresol process, toluene is alkylated with propylene to give isomers of cymene, which can be oxidatively dealkylated analogous to the cumene process. Another method, involves carbonylation of a mixture of methallyl chloride and acetylene in the presence of nickel carbonyl .
Friedel-Crafts alkylation: alkylbenzenes can be synthesized from olefins or alkyl halides with aromatic compounds in the presence of a catalyst such as AlCl 3, HF, or H 2 SO 4. [ 4 ] Gattermann-Koch reaction : named after German chemists Ludwig Gattermann and Julius Arnold Koch , the Gattermann-Koch reaction is a catalyzed formylation of ...
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The largest example of this takes place in the alkylation units of petrochemical plants, which convert low-molecular-weight alkenes into high octane gasoline components. Electron-rich species such as phenols are also commonly alkylated to produce a variety of products; examples include linear alkylbenzenes used in the production of surfactants ...