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Question

(a) Write the products formed when CH3CHO reacts with the following reagents:
(i) HCN
(ii) H2NOH
(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.

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Solution

(a)
(i) Acetaldehyde (CH3CHO) reacts with hydrogen cyaide HCN to give 2-hydroxypropapanenitrile as product.
H|CH3CHOAcctaldehyde+HCNHydrogenCyanideCH3C|CN2hydroxypropanenitrileOH

(ii) Acetaldehyde (CH3CHO) reacts with Hydroxylamine (NH2OH) to give acetaldoxime as a product.

CH3CHOAcetaldyde+NH2OHHydroxylamineCH3CH=NOH+H2OAcetaldoxime

(iii) Reaction of acetaldehyde with acetaldehyde in the presence of dilute NaOH, this is the kind of Aldol reaction by which obtained 3-hydroxybutanal as product. Further proceed reaction when using heat in the reaction, its gives aldol condensation product which is But-2-enal.
CH3CHOAcetaldehyde+CH3CHOAcetaldehydediluteNaOHCH3C|OHHCH2CHO3Hydroxybutanal(aldol)Δ−−−H2OCH3CH=CHCHOBut2enal(Aldol condensation product)

(b) Chemical tests to distinguish the following compounds:

(i) Propanal and propanone : These two are distinguished by the iodoform test when it reacts with I2 in the presence of NaOH while propanone give iodoform test when reacts with I2 in the presence of NaOH.

CH3COCH3+3NaOICHI3+CH3COONa+2NaOH Yellow ppt

CH3CH2CHO+NaOl No ppt of CHI3 formed

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