hydrolisis of amides

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.

HYDRONIUM ION

THE HYDRONIUM ION

Introduction

The hydronium ion is an important factor when dealing with chemical reactions that occur in aqueous solutions. Its concentration relative to hydroxide is a direct measure of the pH of a solution. It can be formed when an acid is present in water or simply in pure water. It's chemical formula is H₃O⁺. It can also be formed by the combination of a H⁺ ion with an H₂O molecule. The hydronium ion has a trigonal pyramidal geometry and is composed of three hydrogen atoms and one oxygen atom.  There is a lone pair of electrons on the oxygen giving it this shape. The bond angle between the atoms is 113 degrees.

H₂O_(l) ↔ OH^-_(aq)+ H⁺_(aq)

As H⁺ ions are formed, they bond with H₂O molecules in the solution to form H₃O⁺ (the hydronium ion). This is because hydrogen ions do not exist in aqueous solutions, but take the form the hydronium ion, H₃O⁺. A reversible reaction is one in which the reaction goes both ways. In other words, the water molecules dissociate while the OH^- ions combine with the H⁺ ions to form water. Water has the ability to attract H⁺ ions because it is a polar molecule. This means that it has a partial charge, in this case the charge is negative.  The partial charge is caused by the fact that oxygen is more electronegative than hydrogen. This means that in the bond between hydrogen and oxygen, oxygen "pulls" harder on the shared electrons thus causing a partial negative charge on the molecule and causing it to be attracted to the positive charge of H⁺ to form hydronium. Another way to describe why the water molecule is considered polar is through the concept of dipole moment. The electron geometry of water is tetrahedral and the molecular geometry is bent. This bent geometry is asymmetrical, which causes the molecule to be polar and have a dipole moment, resulting in a partial charge.

An overall reaction for the dissociation of water to form hydronium can be seen here:

2H₂O_(l) ↔ OH^-_(aq)+ H₃O⁺_(aq)

ORGANIC CHEMISTRY II

Mechanism of Acid-Catalyzed Amide Hydrolysis

Acid-catalyzed amide hydrolysis proceeds via
the customary two stages:

                1)            formation of tetrahedral intermediate
                2)            dissociation of tetrahedral intermediate

First stage:  formation of tetrahedral intermediate

water adds to the carbonyl group of the amide

this stage is analogous to the acid-catalyzed addition of water to a ketone

Second stage:  cleavage of tetrahedral
intermediate

Mechanism of formation of tetrahedral intermediate

Step 1

carbonyl oxygen is protonated because cation produced is stabilized by electron delocalization (resonance).

Step 2

Step 3

Cleavage of tetrahedral intermediate

Step 4

Step 5

Step 6

Mechanism of Amide Hydrolysis in Base

Involves two stages:

                1)            formation of tetrahedral intermediate
                2)            dissociation of tetrahedral intermediate

First stage:  formation of tetrahedral intermediate

water adds to the carbonyl group of the amide

this stage is analogous to the base-catalyzed addition of water to a ketone

Second stage:  cleavage of tetrahedral intermediate

Mechanism of formation of tetrahedral intermediate

Step 1

 

Step 2

 

Dissociation of tetrahedral intermediate

Step 3

Step 4

Step 5