Question

Acetone gives addition elimination reaction with:
(This question has multiple correct options)
(a) Hydroxylamine
(b) Sodium bisulphite
(C) Hydrogen sulphide
(D) Ylide

Answer 1

We need to look into the nucleophilic reactions of aldehydes and ketones namely nucleophilic addition reaction and addition elimination reaction. The addition reaction involves the formation of a tetrahedral product which occurs by the attack of a nucleophile on the carbonyl carbon. Addition elimination involves the formation of a product through the formation of the tetrahedral intermediate which loses a small molecule to give the product.

Complete step by step answer:
Aldehydes and ketones can undergo two types of reaction:
(i) Nucleophilic addition reaction: The carbonyl group of ketone or aldehyde is very polar because of large electronegativity of oxygen in comparison to carbon. Due to this, the carbon atom of the carbonyl group carries a small positive charge and behaves as an electrophile. So, a nucleophile readily attacks the electrophilic carbon of the carbonyl group in a direction perpendicular to the plane of the ${ sp }^{ 2 }$ hybridised orbitals of the carbonyl carbon which leads to a complete transfer of the $\pi$ electrons of the carbon-oxygen double bond from carbon to oxygen atom; the hybridisation of the carbon changes from ${ sp }^{ 2 }$ to ${ sp }^{ 3 }$ and a tetrahedral alkoxide intermediate is formed. This alkoxide then picks up a proton to give the neutral addition product. The reaction between acetone and sodium bisulphite is an example of nucleophilic addition reaction:
${ CH }_{ 3 }-C(O)-{ CH }_{ 3 }+{ NaHSO }_{ 3 }\rightarrow { (CH }_{ 3 }{ ) }_{ 2 }-C(OH)-{ SO }_{ 3 }^{ - }{ Na }^{ + }$

(ii) Addition elimination reaction: In these reactions, the nucleophile attacks the carbon atom of the carbonyl group in the same manner as that of the nucleophilic addition reaction leading to the formation of a tetrahedral intermediate. But now, the tetrahedral intermediate collapses due to the loss of a small molecule from the intermediate such as water in order to give a new product.
In the reaction between acetone and hydroxylamine, the hydroxylamine first attacks the carbonyl carbon to form a tetrahedral intermediate which suffers a loss of water molecule leading to the formation of the final product oxime. This reaction is catalysed by acids. The reaction is shown below:
${ CH }_{ 3 }-C(O)-{ CH }_{ 3 }+{ H }_{ 2 }N-OH\xrightarrow [ { H }^{ + } ]{ pH\quad 3.5 } { (CH }_{ 3 }{ ) }_{ 2 }C=N-OH+{ H }_{ 2 }O$
Acetone reacts with hydrogen sulphide in the same manner. The reaction is shown below:
${ CH }_{ 3 }-C(O)-{ CH }_{ 3 }+{ H }_{ 2 }S\rightarrow { (CH }_{ 3 }{ ) }_{ 2 }C=S+{ H }_{ 2 }O$

Similarly acetone reacts with phosphorus ylide to give an alkene and phosphine oxide derivative.
${ CH }_{ 3 }-C(O)-{ CH }_{ 3 }+{ (C }_{ 6 }{ H }_{ 5 }{ ) }_{ 3 }P={ CH }_{ 2 }\rightarrow { (CH }_{ 3 }{ ) }_{ 2 }-C=C({ R) }_{ 2 }+O=P({ C }_{ 6 }{ H }_{ 5 }{ ) }_{ 3 }$
So, the correct answer is “OptionA, C and D”.

Note: Aldehydes and ketones do not undergo just nucleophilic reactions. They themselves can act as nucleophiles as well. This is because the hydrogen atoms attached to the alpha carbon are acidic due to the resonance stabilisation of the enolate ion. Hence they can easily lose their alpha hydrogen atoms to alkalies such as sodium hydroxide in order to enolate ions which act as a nucleophile.