So when u take an acyl group the chloride is taken away by the AlCl3 and u get a R-CO+ ion with the charge on the carbon.
Now the oxygen donates its electron pair to stabilize the carbon. Infact this is how it exists. The charge doesnt appear on the carbon at all.
But why does this happen. Its cuz polar pi bonds are more stable. Infact the carbon oxygen pi bond is super stable.
When we draw the mot diagram for the carbon oxygen system u will realize that the oxygen with lower orbital energy contribute more towards the bonding pi orbitals and hence this bond is super strong.
Rearrangement doesnt occur cuz charge is never really present on the carbon.
So when u take an acyl group the chloride is taken away by the AlCl3 and u get a R-CO+ ion with the charge on the carbon.
Now the oxygen donates its electron pair to stabilize the carbon. Infact this is how it exists. The charge doesnt appear on the carbon at all.
But why does this happen. Its cuz polar pi bonds are more stable. Infact the carbon oxygen pi bond is super stable.
When we draw the mot diagram for the carbon oxygen system u will realize that the oxygen with lower orbital energy contribute more towards the bonding pi orbitals and hence this bond is super strong.
Rearrangement doesnt occur cuz charge is never really present on the carbon.
During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.
Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution.
A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl (CLEMMENSON’S REDUCTION)
During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.
Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution.
A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl (CLEMMENSON’S REDUCTION)
It’s not possible in a laboratory setting. The alkyl substituent activates the ring greatly so that after just a miniscule yield the alkylated ring reacts faster than the benzene starting material.
It’s not possible in a laboratory setting. The alkyl substituent activates the ring greatly so that after just a miniscule yield the alkylated ring reacts faster than the benzene starting material.
Friedel-Crafts reaction of phenol is not as simple as that of benzene, because the OH of phenol is much more reactive towards both catalyst AlCl3 and reagent RCOCl. Usually, AlCl3 is first added to the pure liquid reactant, like benzene, or in a solvent (e.g., CS2). Therefore, when you add AlCl3 to phenol, OH readily reacts with it forming Al-phenoxide (Al(OPh)3) and HCl. If you now add RCOCl to this, there is very little chance to get the acylation product.
However, there is a modified procedure acylated phenol, called Fries rearrangement, which involves first to esterify the phenol using acyl chloride or acid anhydride, followed by treating the dry phenyl ester Ph-O-CO-R with AlCl3 and heating the mixture. Moderate heating gives mainly o-acylated product, strong heating gives p-acylated product, because o-isomer rearranges to more stable p-isomer.
Friedel-Crafts reaction of phenol is not as simple as that of benzene, because the OH of phenol is much more reactive towards both catalyst AlCl3 and reagent RCOCl. Usually, AlCl3 is first added to the pure liquid reactant, like benzene, or in a solvent (e.g., CS2). Therefore, when you add AlCl3 to phenol, OH readily reacts with it forming Al-phenoxide (Al(OPh)3) and HCl. If you now add RCOCl to this, there is very little chance to get the acylation product.
However, there is a modified procedure acylated phenol, called Fries rearrangement, which involves first to esterify the phenol using acyl chloride or acid anhydride, followed by treating the dry phenyl ester Ph-O-CO-R with AlCl3 and heating the mixture. Moderate heating gives mainly o-acylated product, strong heating gives p-acylated product, because o-isomer rearranges to more stable p-isomer.
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So when u take an acyl group the chloride is taken away by the AlCl3 and u get a R-CO+ ion with the charge on the carbon.
Now the oxygen donates its electron pair to stabilize the carbon. Infact this is how it exists. The charge doesnt appear on the carbon at all.
But why does this happen. Its cuz polar pi bonds are more stable. Infact the carbon oxygen pi bond is super stable.
When we draw the mot diagram for the carbon oxygen system u will realize that the oxygen with lower orbital energy contribute more towards the bonding pi orbitals and hence this bond is super strong.
Rearrangement doesnt occur cuz charge is never really present on the carbon.
So when u take an acyl group the chloride is taken away by the AlCl3 and u get a R-CO+ ion with the charge on the carbon.
Now the oxygen donates its electron pair to stabilize the carbon. Infact this is how it exists. The charge doesnt appear on the carbon at all.
But why does this happen. Its cuz polar pi bonds are more stable. Infact the carbon oxygen pi bond is super stable.
When we draw the mot diagram for the carbon oxygen system u will realize that the oxygen with lower orbital energy contribute more towards the bonding pi orbitals and hence this bond is super strong.
Rearrangement doesnt occur cuz charge is never really present on the carbon.
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During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.
Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution.
A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl (CLEMMENSON’S REDUCTION)
During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.
Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution.
A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl (CLEMMENSON’S REDUCTION)
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It’s not possible in a laboratory setting. The alkyl substituent activates the ring greatly so that after just a miniscule yield the alkylated ring reacts faster than the benzene starting material.
It’s not possible in a laboratory setting. The alkyl substituent activates the ring greatly so that after just a miniscule yield the alkylated ring reacts faster than the benzene starting material.
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Friedel-Crafts reaction of phenol is not as simple as that of benzene, because the OH of phenol is much more reactive towards both catalyst AlCl3 and reagent RCOCl. Usually, AlCl3 is first added to the pure liquid reactant, like benzene, or in a solvent (e.g., CS2). Therefore, when you add AlCl3 to phenol, OH readily reacts with it forming Al-phenoxide (Al(OPh)3) and HCl. If you now add RCOCl to this, there is very little chance to get the acylation product.
However, there is a modified procedure acylated phenol, called Fries rearrangement, which involves first to esterify the phenol using acyl chloride or acid anhydride, followed by treating the dry phenyl ester Ph-O-CO-R with AlCl3 and heating the mixture. Moderate heating gives mainly o-acylated product, strong heating gives p-acylated product, because o-isomer rearranges to more stable p-isomer.
Ph-OH + CH3COCl → Ph-O-CO-CH3
Friedel-Crafts reaction of phenol is not as simple as that of benzene, because the OH of phenol is much more reactive towards both catalyst AlCl3 and reagent RCOCl. Usually, AlCl3 is first added to the pure liquid reactant, like benzene, or in a solvent (e.g., CS2). Therefore, when you add AlCl3 to phenol, OH readily reacts with it forming Al-phenoxide (Al(OPh)3) and HCl. If you now add RCOCl to this, there is very little chance to get the acylation product.
However, there is a modified procedure acylated phenol, called Fries rearrangement, which involves first to esterify the phenol using acyl chloride or acid anhydride, followed by treating the dry phenyl ester Ph-O-CO-R with AlCl3 and heating the mixture. Moderate heating gives mainly o-acylated product, strong heating gives p-acylated product, because o-isomer rearranges to more stable p-isomer.
Ph-OH + CH3COCl → Ph-O-CO-CH3
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