Which bases can be used to make an enolate anion?
Some bases that have been used for enolate anion formation are: NaH (sodium hydride, pKa > 45), NaNH2 (sodium amide, pKa = 34), and LiN[CH(CH3)2]2 (lithium diisopropylamide, LDA, pKa 36). Ether solvents like tetrahydrofuran (THF) are commonly used for enolate anion formation.
What does an enolate do?
Enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds.
What is the nature of enolate?
The structures of enolates have been examined through magnetic resonance studies (NMR) and with X-ray crystallography. It has been observed that solvated enolates exist as dimers, tetramers or hexamers, depending on the enolate structure, the nature of the cation and the solvent.
How can enolate anion be prepared?
Aza enolate is generated by LDA reacting with pivaldehyde, which then reacts with an alkyl halide to form an Oulema melanopus intermediate. Aza enolates can also be formed with Grignard reagents and react with other soft electrophiles, including Michael receptors.
What is meant by Enolization explain?
Enolization or a keto-enol tautomerism is a process of converting a ketone or an aldehyde to a corresponding enol (in acidic conditions) or an enolate (in basic conditions). When we refer to the enolization, we specifically refer to the process that takes you from a ketone or an aldehyde to an enol or an enolate.
Is the enolate anion an electrophile or a nucleophile?
The two possible valence-bond structures of the enolate anion, 7a and 7b, show that the anion should act as an ambident nucleophile – a nucleophile with nucleophilic properties associated with both carbon and oxygen.
What does an enolate act as?
An enolate ion is the anion that forms when a proton is removed next to a carbonyl. Other oxygen anions are also able to act as strong bases, unless there is some resonance factor that delocalises the anion and makes it less reactive. Methoxide ion and butoxide ion are also common strong bases.
What are enolate give examples?
Deprotonation of enolizable ketones, aldehydes, and esters gives enolates. Typically enolates are generated from using lithium diisopropylamide (LDA). Often, as in conventional Claisen condensations, Mannich reactions, and aldol condensations, enolates are generated in low concentrations with alkoxide bases.
How are two enolates formed in the alkylation reaction?
The alkylation product is formed by the S N 2 reaction. This reaction works best with methyl and primary alkyl halides. Hindered alkyl halides and those with halides bonded to sp² hybridized carbon do not undergo substitution. With unsymmetrical ketones that have α hydrogen on both sides of the carbonyl group, two possible enolates can be formed.
When is equilibrium established between alternative Enolate Anions?
– Equilibrium among enolate anions is established when the ketone is in slight excess, a condition under which it is possible for proton-transfer reactions to occur between an enolate anion and an α-hydrogen of an unreacted ketone. Thus, equilibrium is established between alternative enolate anions.
Which is the strongest base in the alkylation process?
The enolate ion is a fairly strong base. When forming the enolate for an alkylation process, the choice of base is important in order to avoid side effects. With a stronger base, such as LDA, these problems are avoided. With this base, the ketone is irreversibly and quantitatively deprotonated to form enolate ions.
Which is the electrophile in the reaction of enolates?
chloroacetone Chloroacetone is used in tear gas. In this reaction, chlorine is the electrophile that reacts with the nucleophilic enolate. The first step of the reaction is the formation of the enolate by using lithium diisopropylamide (LDA) (also depicted as :B – in some cases below).