(a) Illustrate the following reactions giving a suitable example for each.
(i) Cross aldol condensation
(ii) Decarboxylation
(b) Give simple tests to distinguish between the following pairs of compound
(i) Pentan-2-one and pentan-3-one
(ii) Benzaldehyde and Acetophenone
(ii) Phenol and Benzoic acid

Explanation

(i) Cross aldol condensation : When aldol condensation is carried out between two different aldehyde and ketones, it is called acdol condensation. Ketones can also be used as one compound in cross aldol reactions.
`CH_(3)CHO+CH_(3)CH_(2)CHOoverset(1.NaOH)underset(2.NaOH)rarrunderset("But-2-enal")(CH_(3)-CH)=CHCHO+underset("2-methyl pent-2-enal")(CH_(3)CH_(2)=overset(CH_(3))overset(|)(C)-CHO`
From two moleculesfrom two molecules of ethanol of propanal
`underset("2-methulbut-2-enal")(CH_(3)-CH=underset(CH_(3))underset(|)(C)-CHO)+underset("Pent-2-enal")(CH_(3)CH_(2)-CH)=CHCHO`
from one molecules of ethanal and one molecules of propanal
(ii) Decarboxylation : Carboxylic acid lose carbon dioxide to form hydrocarbons whe their sodium salt are heated with sodium salts are heated with sodaline. The reaction is known as decarboxylation.
`R-COONaunderset("Heat")overset(NaOH & CaO)rarr R-H + Na_(2)CO_(3)`
`2CH_(2)COONa(aq) + 2H_(2)O overset("electrolysis")rarr CH_(3)CH_(3)+2CO+2BNaOH+H_(2)`
(b) (i) `CH_(3)-overset(O)overset(||)(C)-CH_(2)CH_(2)-CH_(3)` gives yellow percipitate of Iodoform with NaOH with `NaOH` and iodine.
`H_(3)C-CH_(2)-overset(O)overset(||)(C)-underset("Pentane-3-one")(CH_(2)-CH)` does not give yellow ppt.
(ii)
Give yellow precipitate of iodoform with `NaOH` and iodine.
(iii) Benzoic acid decomposes `NaHCO_(3)`.
`C_(6)H_(5)COOH + NaHCO_(3) rarr C_(6)H_(5)COONa+CO_(2) +H_(2)O`
`C_(6)H_(5)COH+NaHCO_(3)rarr "No reaction "`.