(a) Write the products formed when CH3CHO reacts with the following reagents: (i) HCN (ii) H2N−OH (iii) CH3CHO in the presence of dilute NaOH (b) Give simple chemical tests to distinguish between the following pairs of compounds: (i) Propanal and Propanone.

(a)(i) Acetaldehyde (CH3CHO) reacts with hydrogen cyanide HCN to give 2-hydroxypropanenitrile as a product.
H
|
CH3−CHO + HCN → CH3−C−CN
Acetaldehyde + Hydrogen Cyanide → 2-hydroxypropanenitrile
OH
(ii) Acetaldehyde (CH3CHO) reacts with Hydroxylamine (NH2OH) to give acetaldoxime as a product.
CH3CHO + NH2OH → CH3−CH=NOH + H2O
Acetaldehyde + Hydroxylamine → Acetaldoxime
(iii) Reaction of acetaldehyde with acetaldehyde in the presence of dilute NaOH; this is a kind of Aldol reaction by which 3-hydroxybutanal is obtained as a product. Further reaction proceeds when heat is applied, giving the aldol condensation product, But-2-enal.
CH3CHO + CH3CHO → CH3−C−CH2−CHO
dilute NaOH |
Acetaldehyde + Acetaldehyde → 3−Hydroxybutanal (aldol)
OH
Δ → −H2O → CH3−CH=CH−CHO
But−2−enal (Aldol condensation product)
(b) Chemical tests to distinguish the following compounds:
(i) Propanal and propanone: These two are distinguished by the iodoform test. Propanone gives a positive iodoform test when it reacts with I2 in the presence of NaOH, while propanal does not.
CH3COCH3 + 3NaOI → CHI3 + CH3COONa + 2NaOH
Yellow ppt
CH3CH2CHO + NaOI → No ppt of CHI3 formed