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Electrophilic Aromatic Synthesis

Electrophilic Aromatic Synthesis ReactionsThere are five key types of electrophilic aromatic synthesis (EAS) that are used in introductory organic chemistry:

  • Halogenation
  • Nitration
  • Sulfonation
  • Friedel-Crafts
  • Alkylation

Halogenation is the process of adding a halogen onto an aromatic ring. In order to attach Bromine or Chlorine efficiently a catalyst is used. A recommended catalyst for this is Iron III Bromide/Chloride (FeBr3/FeCl3; the catalyst matches the halogen being added). Iodine can be added without a catalyst, although Iodine is light sensitive and will detach from the ring if in the presence of intense light or heat.

Nitration adds a nitrite group (NO2) to an aromatic molecule. This is conducted by adding fuming sulfuric acid (H2SO4(f)), fuming nitric acid (HNO3(f)), and nitrite ions (NO2+). Fuming sulfuric acid is a mixture of sulfuric acid and sulfur trioxide. Fuming nitric acid is a combination of nitric acid and a nitrogen-oxygen compound.

Sulfonation is similar to nitration but adds a hydrogen sulfite group (HSO3) onto an aromatic ring. The synthesis is done by applying fuming sulfuric acid and hydrogen sulfite ions (HSO3+).

Friedel-Crafts is a type of reaction that adds a carbon chain to the aromatic compound. The synthesis is conducted by using a halogenated carbon chain of what is desired and a catalyst of AlX3 (X being the halogen used on the carbon chain being added). An important limitation of this reaction is the carbon chain will rearrange to add at the most substituted carbon if possible.Electrophilic Aromatic Synthesis Friedel-Crafts Rearrangement

An example is 1-propyl bromide will create a bond between the secondary carbon and the aromatic, not the primary carbon and aromatic. However, if allyl bromide is used as the halogenated carbon chain in the reaction, it will create the bond to the primary carbon because allyl bromide cannot rearrange.

Alkylation is a type of Friedel-Crafts reaction that adds an acyl group to an aromatic molecule. The process is done by adding the desired acyl group in halogenated form (an acyl halide) and using a catalyst such as AlX3 (X matching the halogen used on the acyl halide).

Electrophilic aromatic synthesis gives a base of additions that can help direct and create more complex molecules with other reactions. How these addition effect further reactions will be covered later on.

Peyton Young

Author Peyton Young

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