Why is imine formation slow under acidic conditions?
Too low the pH, gives an efficient protonation of the oxygen, but also of the nitrogen of the amine, so the production of the imine results inefficient. On the other hand, at higher pH values, the oxygen does not get protonated enough to trigger the reaction.
What happens if imine formation is carried out at very low pH?
The reaction of aldehydes and ketones with ammonia or 1º-amines forms imine derivatives, also known as Schiff bases (compounds having a C=N function). At low pH most of the amine reactant will be tied up as its ammonium conjugate acid and will become non-nucleophilic.
Are imines acidic?
8.02. Iminium ions (or salts) are derived from reaction of aldehydes or ketones with secondary amines and from protonation of imines (under acidic conditions). Iminium ions are more reactive toward reduction and nucleophilic attack than imines.
Are imines acidic or basic?
Acid-base reactions Somewhat like the parent amines, imines are mildly basic and reversibly protonate to give iminium salts. Iminium derivatives are particularly susceptible to reduction to the amines using transfer hydrogenation or by the stoichiometric action of sodium cyanoborohydride.
Can imines form under basic conditions?
Recall that nitrogen is less electronegative than oxygen and much more willing to donate its lone pair of electrons. As such, nitrogen use as a nucleophile may occur under acidic/basic, or neutral conditions. Imines are formed from the carbonyl compound and either ammonia or a 1° amine.
What is imine formation?
Imine formation is a reversible process that starts with the nucleophilic addition of a primary amine to the carbonyl group of an aldehyde or ketone. Acid protonation of the carbinolamine oxygen converts it into a better leaving group which is subsequently eliminated as water producing an iminium ion.
Which of the following could be produced by hydrolysis of an imine or an enamine?
A) Hydrolysis of an imine produces an aldehyde, while hydrolysis of an enamine produces a ketone. B) The process occurs in the presence of dilute aqueous acid.
Can an imine be hydrolyzed?
Figure 3 Imines can be hydrolysed (split with water) to give the starting aldehyde (or ketone) and amine. Note that the reaction is acid assisted. Schiff base (imine) formation and hydrolysis are highly important in biological chemistry. Many enzymes employ imines as part of their reaction mechanisms.
Can an imine be hydrolyzed to a ketone?
Description: Treatment of imines with water leads to their hydrolysis back to aldehydes (or ketones) and an amine. Notes: The reaction is assisted through the use of an acid catalyst.
What is hydrolysis of enamine?
Because of this enamines can be used as synthetic equivalents as enolates in many reactions. Formation of the enamine, Reaction with an eletrophile to form an iminium salt, Hydrolysis of the iminium salt to reform the aldehyde or ketone.
What is the reverse of imine hydrolysis?
Imine Hydrolysis. The reverse of imine formation is called imine hydrolysis, yielding the corresponding amine and carbonyl containing compound (aldehyde or ketone). In this process, the imine undergoes an addition of water.
How can iminium ions be isolated from amines?
These imines are best reduced directly and not isolated. Iminium ions (or salts) are derived from reaction of aldehydes or ketones with secondary amines and from protonation of imines (under acidic conditions).
What is the hydrolysis of enamines?
The hydrolysis of enamines also starts with a protonation, however, this time it is the double-bonded carbon that participates in this step: The resulting intermediate is now very electrophilic and the C=O carbon is attacked by water forming an unstable tetrahedral intermediate.
What happens to the imine when it is added to water?
In this process, the imine undergoes an addition of water. Water requires an activation step before it can be added; a base (proton acceptor) pulls a hydrogen ion (proton) off the water molecule.