Explain HVZ reaction with an example.

Carboxylic acid react with chlorine or bromine in the presence of phosphorus to give α - halogenated carboxylic acids. The halogenation continues till all the hydrogen atom in the α - position are replaced by halogen atoms. This reaction is called HVZ (Hell-Volhard-Zelinsky) reaction. CH 3 COOH Acetic acid → - HCl Cl 2 , P 4 ClCH 2 COOH Chloroacetic acid → - HCl Cl 2 , P 4 Cl 2 CHCOOH Dichloroacetic acid → - HCl Cl 2 , P 4 Cl 3 CCOOH Trichloroacetic acid

Complete the following reaction:

Carboxylic acid reacts with thionyl chloride SOCl 2 to form acid chloride. During the reaction - OH group of the carboxylic acid is replaced by - Cl group of thionyl chloride. In the given reaction phthalic acid on reaction with thionyl chloride gives phthaloyl chloride.

Complete the following reaction: C 6 H 5 CHO → H 2 NCONHNH 2 ?

Aldehyde and ketones react with semicarbazide NH 2 NH . CONH 2 to form semicarbazone. It is a nucleophilic addition reaction. C 6 H 5 CHO Benzaldehyde → H 2 NCONHNH 2 C 6 H 5 - CH = N . NH . CONH 2 Benzaldehyde semicarbazone + H 2 O Water This test is used for identification and characterisation of aldehydes and ketones.

What happens when acetone reacts with HCN ?

The addition of HCN to acetone is a nucleophilic addition reaction. This reaction is carried out in the presence of basic catalyst. Acetone (Propanone) on reaction with hydrogen cyanide give acetone cyanohydrin (Propanone cyanohydrin).

What is Fehling’s solution test?

Fehling’s solution test is used to differentiate aldehyde and ketones. Fehling’s solution is an alkaline solution of copper sulphate containing sodium potassium tartarate (Rochelle salt). When Fehling's solution is warmed with an aldehyde, a red precipitate of cuprous oxide is formed. This test is commonly called Fehling’s solution test. Ketone do not give Fehling’s solution test. RCHO + 2 Cu 2 + + 5 OH - from Fehling ' s solution → RCOO - + 3 H 2 O + Cu 2 O Red ppt .

Describe the Etard reaction and give the reaction involved in it.

Etard reaction is used to prepare aromatic aldehydes. The oxidation of toluene with chromyl chloride CrO 2 Cl 2 in CCl 4 or CS 2 to form benzaldehyde is called Etard reaction. The chromyl chloride first forms a brown complex with toluene, which when decomposed with water gives benzaldehyde.

Describe the aldol condensation reactions and give the reaction involved in it.

Aldehyde and ketones having at least one α -hydrogen atom in the presence of dilute alkali dil . NaOH , Na 2 CO 3 , Ba OH 2 , etc . undergoes rearrangement to give β -hydroxyaldehyde or a β -hydroxyketone is called aldol condensation Example: When acetaldehyde is warmed with dil.NaOH, aldol ( β -hydroxybutyraldehyde) is formed, which on heating gives but-2-enal. CH 3 CHO + CH 3 CHO → NaOH CH 3 - CH ( OH ) - CH 2 CHO → - H 2 O heat CH 3 - CH = CH - CHO

What is acylation reaction? Give an example.

Introduction of acyl group CH 3 CO in a reacting molecule is called acylation reaction. Example: Friedel-Craft's acylation reaction- Benzene on reaction with ethanoyl chloride (acetyl chloride) in the presence of anhydrous aluminium chloride give acetophenone. C 6 H 6 + CH 3 COCl → AlCl 3 anhyd . C 6 H 5 COCH 3 + HCl

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Aldehydes, Ketones and Carboxylic Acids>Nagaland Board-2019>Q 7

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12th Nagaland Board

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