AMIDE
Amide is a compound that is not reactive, since the
protein consists of amino acids linked by amide bonds. Amide does not react
with the halide ion, carboxylate ion, alcohol, or water because in each case,
the incoming nucleophile is a weak base of the amide group to go. 
Amide can react with water and alcohol if the reaction mixture is heated under acidic conditions.
Molecular orbital theory can explain why the amide is not reactive. Amide has an important resonance contributor in which shares one pair of nitrogen with the carbonyl carbon, which contains a lone pair orbital overlap of the empty orbital of the carbonyl group.
Lower energy state overlap-one partner is not a base or nucleophilic, and raises the energy of the orbital of the carbonyl group, making it less reactive toward nucleophiles. Amide NH 2 groups can be dehydrated to a nitrile. Dehydrating reagents commonly used for this purpose is P2O5, POCl3, and SOCl3.
Hydrolysis of amides with acid catalyst
When the amide is hydrolyzed in acidic conditions, acid proton of the carbonyl oxygen, increase the susceptibility of the carbonyl carbon to nucleophilic attack. Nucleophilic attack by water on the carbonyl carbon causes the tetrahedral intermediate compound I, which is in equilibrium with form rather than protons, tetrahedral intermediate II. Reprotonasi can occur either at the tetrahedral intermediates of oxygen to reform the I or the nitrogen to form a tetrahedral intermediate III. Protonation at nitrogen is preferred because the NH2 group is a stronger base than OH groups. Of the two possible groups to go on a tetrahedral intermediate III group (-OH and NH3), NH3 is a weak base, so it is released, forming carboxylic acids as end products. Because the reaction is carried out in acid solution, NH3 be protonated after expelled from the tetrahedral intermediates. This prevents the reverse reaction.
Mechanism of hydrolysis of amides with acid catalyst:
Why can not hydrolyze amide without a catalyst?
BalasHapusAnd what can we use base catalyst in the reaction ???
In the reaction without a catalyst, not the protonated amide. Therefore, the water, a very poor nucleophile, to attack neutral amides are much more susceptible to nucleophilic attack than the protonated amide. In addition, the group of the tetrahedral intermediate is not protonated in the reaction without a catalyst. Therefore, the-OH group is away from the tetrahedral intermediate-because-OH is a weak base of the amide-NH2 reform. An amide to react with alcohols under acidic conditions for the same reason will react with water under acidic conditions. I think we can use base catalyst in the reaction. Because in amide hydrolisis has two catalyst. They are acid and base catalyst.
I am thankfull to you yuli, after read your blog i got new knowledge. But i wanna ask you "why we hydrolyze amide with acid catalyst? why not we hydrolyze with other catalyst? and what happend if we hydrolyze it without catalyst?" Thankyou....
BalasHapusAnd please(also) post your answer in my blog http://vebriachemistry.blogspot.com
wanna try to answer about why we use acid catalyst in the hydrolysis of an amide,,
BalasHapusThe purpose of the acid catalyst in the hydrolysis of an amide is to enhance the electrophilicity of the amide carbonyl carbon
because the amide is a compound that is not reactive, since the protein consists of amino acids linked by amide bonds. Amide does not react with the halide ion, carboxylate ion, alcohol, or water because in each case, the incoming nucleophile is a weak base of the amide group to go.
BalasHapusAmide can react with water and alcohol if the reaction mixture is heated under acidic conditions.
Molecular orbital theory can explain why the amide is not reactive. Amide has an important resonance contributor in which shares one pair of nitrogen with the carbonyl carbon, which contains a lone pair orbital overlap of the empty orbital of the carbonyl group.
Lower energy state overlap-one partner is not a base or nucleophilic, and raises the energy of the orbital of the carbonyl group, making it less reactive toward nucleophiles. Amide NH 2 groups can be dehydrated to a nitrile. Dehydrating reagents commonly used for this purpose is P2O5, POCl3, and SOCl3.
In our amide hydrolysis using an acid catalyst because when the amide is hydrolyzed in acidic conditions, acid proton of the carbonyl oxygen, increase the susceptibility of the carbonyl carbon to nucleophilic attack. Nucleophilic attack by water on the carbonyl carbon causes the tetrahedral intermediate compound I, which is in equilibrium with form rather than protons, tetrahedral intermediate II. Reprotonasi can occur either at the tetrahedral intermediates of oxygen to reform the I or the nitrogen to form a tetrahedral intermediate III. Protonation at nitrogen is preferred because the NH2 group is a stronger base than OH groups. Of the two possible groups to go on a tetrahedral intermediate III group (-OH and NH3), NH3 is a weak base, so it is released, forming carboxylic acids as end products. Because the reaction is carried out in acid solution, NH3 be protonated after expelled from the tetrahedral intermediates. This prevents the reverse reaction.
In the reaction without a catalyst, not the protonated amide. Therefore, the water, a very poor nucleophile, to attack neutral amides are much more susceptible to nucleophilic attack than the protonated amide. In addition, the group of the tetrahedral intermediate is not protonated in the reaction without a catalyst. Therefore, the-OH group is away from the tetrahedral intermediate-because-OH is a weak base of the amide-NH2 reform. An amide to react with alcohols under acidic conditions for the same reason will react with water under acidic conditions.