Problem about hydrolisis of amides
1. Why the atmosphere of acid hydrolysis of the
amide compounds produce as much as 88-90% carboxylate ion in alkaline
conditions, while only 5%, please explain?
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. Nukleofilik by attack of water on the carbonyl carbon causes the tetrahedral intermediate compound I, which beradadalam equilibrium with form rather than protons, tetrahedral intermediates II.Reprotonasi can occur either at the tetrahedral intermediates of oxygen to reform I ataupada nitrogen to form a tetrahedral intermediate III. Protonation of the NH2 group because nitrogen like is a stronger base than OH groups. Of the two possible groups to go on a tetrahedral intermediate III group (-OH danNH3), NH3 is a weak base, so it is released, forming a carboxylic acid end sebagaiproduk. Because the reaction is carried out in acidic solutions, protonated NH3 will setelahdiusir of tetrahedral intermediates. This prevents the reverse reaction. The catalytic mechanism of amide hydrolysis.
Compared to amines, amides are very weak bases. While the conjugate acid has a pKa of amine darisuatu about 9.5 while the conjugate acid of an amide has pKa around -0.5. Therefore, the amide does not possess a clearly visible as the acid-base in water. Lack of basicity is explained by the nature of the electron-withdrawing groups karbonil where the nitrogen lone pair of electrons delocalized by resonance. On the other hand,
amide is a stronger base of carboxylic acids, esters, aldehydes, and ketones (asamkonjugasi pKa between -6 and -10). Due to the larger electronegativity of oxygen, carbonyl (C = O) is stronger than the NC more dipole. It allows amides to act as H-bond acceptor. In primary and secondary amides, the presence of NH amide dipole H-bond donor allow too. Thus amides can participate in hydrogen bonding protic solvents with water and others; oxygen and nitrogen atom can accept bonds hydrogen from water and NH hydrogen atoms can donate H-bonds. As a result of interaction, amide solubility in water is greater than the corresponding hydrocarbons.
The Nature Of Basa amideamide
Unlike compounds containing the-NH2, an amide is a neutral compound. Group-containing compound NH2seperti ammonia, NH3, or aminaprimer like metilamina, CH3NH2 is a weak base. Padaatom active lone pair of nitrogen in ammonia can be joined by a hydrogen ion (proton) darisenyawa another, in other words, ammonia acts as a base.
2. Why can not hydrolyze amide without a catalyst?
In the reaction without catalyst, amidatidak protonated. 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.
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. Nukleofilik by attack of water on the carbonyl carbon causes the tetrahedral intermediate compound I, which beradadalam equilibrium with form rather than protons, tetrahedral intermediates II.Reprotonasi can occur either at the tetrahedral intermediates of oxygen to reform I ataupada nitrogen to form a tetrahedral intermediate III. Protonation of the NH2 group because nitrogen like is a stronger base than OH groups. Of the two possible groups to go on a tetrahedral intermediate III group (-OH danNH3), NH3 is a weak base, so it is released, forming a carboxylic acid end sebagaiproduk. Because the reaction is carried out in acidic solutions, protonated NH3 will setelahdiusir of tetrahedral intermediates. This prevents the reverse reaction. The catalytic mechanism of amide hydrolysis.
Compared to amines, amides are very weak bases. While the conjugate acid has a pKa of amine darisuatu about 9.5 while the conjugate acid of an amide has pKa around -0.5. Therefore, the amide does not possess a clearly visible as the acid-base in water. Lack of basicity is explained by the nature of the electron-withdrawing groups karbonil where the nitrogen lone pair of electrons delocalized by resonance. On the other hand,
amide is a stronger base of carboxylic acids, esters, aldehydes, and ketones (asamkonjugasi pKa between -6 and -10). Due to the larger electronegativity of oxygen, carbonyl (C = O) is stronger than the NC more dipole. It allows amides to act as H-bond acceptor. In primary and secondary amides, the presence of NH amide dipole H-bond donor allow too. Thus amides can participate in hydrogen bonding protic solvents with water and others; oxygen and nitrogen atom can accept bonds hydrogen from water and NH hydrogen atoms can donate H-bonds. As a result of interaction, amide solubility in water is greater than the corresponding hydrocarbons.
The Nature Of Basa amideamide
Unlike compounds containing the-NH2, an amide is a neutral compound. Group-containing compound NH2seperti ammonia, NH3, or aminaprimer like metilamina, CH3NH2 is a weak base. Padaatom active lone pair of nitrogen in ammonia can be joined by a hydrogen ion (proton) darisenyawa another, in other words, ammonia acts as a base.
2. Why can not hydrolyze amide without a catalyst?
In the reaction without catalyst, amidatidak protonated. 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.
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