Aldehydes, ketones and Carboxylic Acids

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Aldehydes ketones and Carboxylic Acids
Aldehydes ketones and Carboxylic Acids

Aldehydes, ketones and Carboxylic Acids- CBSE NCERT easy notes

Definition of Aldehyde and ketones

Those compounds which have carbonyl group present in them are known as carbonyl group ( Aldehyde and ketones). Aldehyde and ketones  have same molecular formula CnH2nO and are functional isomers of each other.

Preparation of aldehydes and ketones

  1. Controlled oxidation of alcohols in the presence of K2Cr2O7 / dil. H2SO4, KMnO4 / dil. H2SO4 or Cu metal at 573K result in the formation of aldehydes and ketones
  2. Dry distillation of some calcium salts of acids gives simple ketones.
  3. Mixture of calcium salts of formic acid and calcium salts of any other carboxylic acid on dry distillation gives an aldehydes.
  4. Addition of Grignard reagents to alkyl or aryl cyanides followed by hydrolysis with dil. acids gives ketones while with HCN, aldehydes are formed.
  5. Addition of H2O on alkynes in presence of H2SO4 and HgSO4 yields aldehydes (by terminal alkynes) and ketones (by non-terminal)

Uses of Aldehydes and Ketones

  • They are used as solvents, starting materials and reagents for the synthesis of other products in chemical industry.
  • To preserve biological specimens, formalin (40% solution of formaldehyde) solution is used and also in making bakelite, urea-formaldehyde glues and other polymeric products.
  • Acetaldehyde is used primarily as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate and drug.
  • Some of the aldehydes and ketones are used for preparing materials like adhesives, paints, perfume, plastic, etc.
Aldehydes ketones and Carboxylic Acids

What is Silverisation or silver mirror?

When an aldehydes is heated with Tollen’s reagent, then the aldehyde gets oxidised to carboxylic acid which reacts with ammonia to form ammonium salt whereas Tollen’s reagent gets reduced to metallic silver. This metallic silver gets collected on the inner side of test tube to form a silver mirror. This reaction is known as silverisation.

What is Tollen’s reagent?

It is an ammoniacal silver nitrate(AgNO3 + NH4OH) solution. It is a mild oxidising agent.

What is Cannizzaro’s Reaction?

Those aldehydes which does not have \alpha -hydrogen atoms gives salt disproportion reaction with conc. NaOH or KOH to give salt of carboxylic acid or alcohol.

E.g. \underset {Formaldehyde}{2HCHO} \longrightarrow \underset {Sodium formate}{HCOONa} + \underset {Methyl alcohol} {{CH}_{3}OH}

What is Aldol Condensation?

Aldol Condensation is given by aldehydes and ketones that have \alpha —hydrogen atom in the presence of dilute alkali. It involves carbanion as an intermediate.

What is Schiff’s reagent?

This is solution of rosaniline and sulphuric acid in water. It is used for testing of aldehydes. In this reaction aldehydes gives pink colour.

What is Clemmensen reduction?

Clemmensen reduction of aldehydes and ketones (Zn-Hg/conc. HCl) gives alkanes.

What is Wolff-Kishner reduction?

The carbonyl group of aldehydes and ketones is reduced to —CH2 group on treatment with hydrazine followed by heating with KOH in ethylene glycol.

What is Carboxylic Acid?

Those carbon compounds which have carbonyl group as active group are known as carboxylic acid. The general formula of carboxylic acid is CnH2nO2.

What is Fatty acids?

Higher aliphatic acids are also known as fatty acids.

What are the Physical Properties of carboxylic acids?

Carboxylic acid soluble in water due to formation of H-bonding. Therefore boiling point of carboxylic acid higher than carboxyls.

Define Saponification.

Alkaline hydrolysis of esters is called saponification.

Define  Formic acid.

This gets oxidised easily, thus it acts as reductant and reduce Tollen’s reagent, Fehlings solution, acidic KMnO4, mercuric acid, etc.

Define Benzoic acid.

Benzoic acid has lesser acidic strength than formic acid.

Define Acetic acid (CH3COOH)

It is prepared by fast reaction from acetylene or ethanol.

Carboxylate ions

Carboxylate ions have more acidic strength than phenoxide ion due to delocalisation of lone pair of electrons over more electronegative two oxygen atoms.

Define Aromatic carboxylic acids

Aromatic carboxylic acids are prepared by side chain oxidation of alkyl benzenes.

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