Write short notes on the following : (i) Kolbe's electrolytic rea…

Question

Write short notes on the following :
(i) Kolbe's electrolytic reaction
(ii) Hell-Volhard-Zelinsky reaction
(iii) Esterification reaction
(iv) Decarboxylation reaction(v) Hunds-Diecker reaction

✓

Answer

(i) Kolbe's electrolytic reaction : In Kolbe's electrolytic reaction aqueous solution of sodium or potassium salts of fatty acids are electrolysed to give alkanes.
$2 RCOONa \longrightarrow 2 ROO ^{-}+2 Na ^{+}$(ionisation)
$2 H _2 O \longrightarrow 2 OH ^{-}+2 H ^{+} \quad$ (ionisation)
At anode,
$2 RCOO ^{-}-2 e^{-} \longrightarrow \underset{\text { (unstable) }}{2 RCOO } \longrightarrow \underset{\text { Alkane }}{2 CO _2+ R - R }$
At cathode, $\quad 2 H ^{+}+2 e^{-} \longrightarrow H _2 \uparrow$
(ii) Hell-Volhard-Zelinsky reaction : In presence of red phosphorus carboxylic acids react with chlorine or bromine to give $\alpha$-chloro or $\alpha$-bromo acid.
$CH _3 COOH \xrightarrow[- HCl ]{ Cl _2, \text { red } P } ClCH _2 COOH$$\frac{ Cl _2, \text { red } P }{- HCl } \rightarrow Cl _2 CHCOOH$$Cl _3 CCOOH \frac{ Cl _2, \text { red } P }{- HCl }$
(iii) Esterification reaction : Alcohols react with carboxylic acids to form ester. The process is known as esterification.

(iv) Dicarboxylation reaction : Sodium salts of carboxylic acid when distilled with soda lime $( NaOH +$ CaO ) undergo dicarboxylation to yield alkanes.

(v) Hunds-Diecker reaction : Silver salts of carboxylic acid react with $Br _2$ in refluxing $CCl _4$ to give corresponding bromides containing 1 carbon less than the parent acid.
For example,
$\underset{\text { Silver acetate }}{ CH _3 COOAg + Br _2} \xrightarrow{ CCl _4, \text { Reflux }} \underset{\text { Methyl bromide }}{ CH _3- Br + CO _2+ AgBr }$

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