Q. 20

(a) Exemplify the

Answer :

a(i)


In Rosenmund reduction reaction Acyl chloride (which is ClC=Oacid chloride) is hydrogenated on the catalytic reaction of palladium (Pd) in presence of barium sulphate.



a(ii)


In Kolbe electrolysis reaction


The Kolbe electrolysis reaction mechanism involves a two-stage radical process.: electrochemical decarboxylation gives a radical intermediate, then two such intermediates combine to form a covalent bond.


(b)


When HCN is attacking while in a reaction it is attacking as the nucleophile CN- .


Hence, as the negative charge on a species increases its reactivity towards HCN decreases.


Amongst the given compounds, +I (electron releasing effect ) increases as



Therefore the correct order of increasing reactivity of the given compounds towards HCN is: Acetaldehyde > Acetone> Di-tert-butyl ketone. This is due to the +I effect also for the increasing steric hindrance (therefore decreasing reactivity ) among the compounds.


OR


a(i)


This is an example of Hell-Volhard-Zelinsky reaction , where the propanoic acid which has α-H atoms gets halogenated on reaction with chlorine and presence of small amount of phosphorus and forms corresponding


α-halocaboxylic acid, 2-chloropropanoic acid


Hence the product will be 2-chloropropanoic acid, .


a(ii)


This is an example of Etard reaction , where Chromyl chloride(CrO2Cl2)at first oxidises the methyl group of the given aromatic compound toluene to a chromium complex then by hydrolysis it gives corresponding benzaldehyde.


.


(b)


The correct increasing order of acid strength of the given acids 4-Methoxybenzoic acid< Benzoic acid<4-Nitrobenzoic acid.


This is due to the nature (electron donating/withdrawing property) of the functional groups attached to the aromatic ring and as electron donating (such as –OCH3) groups decreases the acidity of benzoic acids and ele ctron donatuiob groups ( such as NO2) increases their acidity the order is justified.



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