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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]
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]
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]
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 ...
In addition to p-cymene, two less common geometric isomers are o-cymene, in which the alkyl groups are ortho-substituted, and m-cymene, in which they are meta-substituted. p-Cymene is the only natural isomer, as expected from the terpene rule. All three isomers form the group of cymenes. Cymene is also produced by alkylation of toluene with ...
In commercial applications, the alkylating agents are generally alkenes, some of the largest scale reactions practiced in industry.Such alkylations are of major industrial importance, e.g. for the production of ethylbenzene, the precursor to polystyrene, from benzene and ethylene and for the production of cumene from benzene and propene in cumene process:
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Several modifications of alkynylation reactions are known: In the Arens–van Dorp synthesis the compound ethoxyacetylene [7] is converted to a Grignard reagent and reacted with a ketone, the reaction product is a propargyl alcohol.