During the synthesis of 1,3,6,8-tetrabromopyrene, nitrobenzene was used as solvent, so I feel that it was used as a solvent may be because the reaction requires high temperature to form the products, and since nitrobenzene is a high boiling solvent , so it was used. Also, the solubility criteria may be the other one.
Apart from that what are the roles of nitrobenzene in this reaction ?
Does this work as lewis acid for the formation of bromonium carbocation, so that the bromonium carbocation addition could take place on 1,3,6, or 8 positions of pyrene which are electron rich, and electrophilic aromatic substitution can take place there !
Nitrobenzene is used in this reaction mainly for three reasons. As the solvent, nitrobenzene has a high boiling point and high dielectric constant. Moreover, nitrobenzene has strongly deactivating nitro group, so it does not participate in electrophilic substitution under these conditions.
I have never heard about bromonium carbocation – it is bromonium ion. In these reactions, any bromonium ions do not arise. It is an electrophilic substitution to the aromatic ring. Bromonium ions arise commonly in addition of bromine to alkenes. In this case, only bromo-substituted arenium ion is an intermediate species.
Nitrobenzene is used in this reaction mainly for three reasons. As the solvent, nitrobenzene has a high boiling point and high dielectric constant. Moreover, nitrobenzene has strongly deactivating nitro group, so it does not participate in electrophilic substitution under these conditions.
I have never heard about bromonium carbocation – it is bromonium ion. In these reactions, any bromonium ions do not arise. It is an electrophilic substitution to the aromatic ring. Bromonium ions arise commonly in addition of bromine to alkenes. In this case, only bromo-substituted arenium ion is an intermediate species.
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