Question

CH3CH2COCH2CH3 reacts with hydrogen cyanide to form a cyanohydrin.

Which feature applies to the product?
A It has one chiral centre.
B It is formed by electrophilic addition.
C It is formed via a C–OH intermediate.
D Its formation requires the use of cyanide ions as a catalyst

Answer 1

i know that A,B,C are incorrect but can anyone explain D

Answer 2

you need to make HCN a nucleophile, and you do so by deprotonating it.

Answer 3

HCN⇌H+ + CN-

Answer 4

thats the ionization reaction

Answer 5

i think what they're getting at is that you add a bit of \(CN^-\) to the mix, this reacts, the product makes an alkoxide ion which deprotonates the next HCN, leading to another \(CN^-\) and the process repeats- hence a catalyst.

Answer 6

Sodium Cyanide is the catalyst of this reaction so it ionises to provide a source of CN-. Cyanide reacts with the Ketone The C=O is polar hence the carbon is electron deficient
CN- contains lone pair. lone pair attacks electrophile so pi bond breakts heterolytically and the intermediate is tetrahedral CH3CH2COCNCH2CH3 the lone pair attacks hydrogen cyanide HCN breaks heterolytically and generate cyanide ions are generated is this correct?

Answer 7

yep, except you're missing the charge in the intermediate (because of the alkoxide).

Answer 8

oh thank you :D

Answer 9

no problem !