Structure, uses and qualitative tests of carbonyl compounds

Carbonyl Compounds

(Aldehydes and Ketones)

Contents

• Qualitative tests

• Structure and uses of important compounds

Learning
Objectives

At the end of this
lecture, student will be able to

• Explain the qualitative tests for carbonyl compounds

• Write the structure and uses of carbonyl compounds

Test for
aldehydes and ketones

2,4-dinitrophenyl
hydrazine test (2,4-DNP test)

• 2,4-dinitrophenyl hydrazine can be used to qualitatively
detect the carbonyl group of an aldehyde or ketone

• A positive result is indicated by the formation of an
yellow or orange-red precipitate of 2,4-dinitrophenyl hydrazone

Differentiating tests
for aldehydes

• Aldehyde is readily oxidised to carboxylic acid whereas
ketones cannot be oxidised easily

• Schiff’s test- Aldehydes give pink or magenta colour with
Schiff’s reagent

• Tollen’s test- Tollen’s reagent is ammoniacal silver
nitrate.

Aldehydes react with Tollen’s reagent to form elemental
silver

Differentiating tests
for Ketones

• Following tests are given by ketones but not by aldehydes:

• m-dinitrobenzene
Test

• Ketones react with m-dinitrobenzene to give a violet
colouration.

• Sodium
nitroprusside Test

• The anion of ketone formed by a alkali reacts with
nitroprusside ion to form a red coloured complex.

Formaldehyde

Structure

• Simplest aldehyde

• Also known as methanol

Uses

• Disinfectant

• Used in vaccine production

• Tissue fixative agent

• Production of industrial resins

• In 2011, US NTP described as human carcinogen

Paraldehyde

Structure

• Trimer of acet. aldehyde molecules

• Slowly oxidizes in air with an odor of acetic

• Quickly reacts with plastic and rubber

Uses

• Hypnotic

• Sedative

• Anti-convulsant

Acetone

Structure

• Named propanone

Uses

• Good solvent in chemistry

• Also as solvent for plastics and synthetic fibres

• Cleaning tools, paints and varnishes, degreasing

Chloral
hydrate

Structure                            

• Geminal diol

Uses

• Limited use- sedative and hypnotic

• To prepare permanent or semi-permanent microscopic slides
of small organisms and histological sections

• Serves as desiccant and building blocks in synthesis

Hexamine

Structure

• Also called as hexamethylenetetramine

• Or methenamine- (CH2)6N4

Uses

• Preparation of resins

• In treatment of urinary tract infection

• Decomposes at acidic pH to formaldehyde and ammonia

• Food additive as preservative

Benzaldehdye

Structure

• Simplest aromatic aldehyde with almond like flavor

• Primary component of bitter almond oil

Uses

• Employed to confer almond flavor to foods

• As precursor to many organic compounds

• As bee repellant

Vanillin

Structure

• Functional groups- aldehyde, hydroxyl and ether

• Primary component of vanilla bean

Use

• Pharmaceutical aid as flavouring agent in food, beverages
and pharmaceuticals

• Used in ice creams, confections, baked goods, perfumes

Cinnamaldedhye

Structure

• Gives cinnamon- its flavor and odor

• Essential oil of cinnamon

Uses

• As flavor in chewing gums, ice cream, candy, beverages,
perfumes

• Fungicide- agrochemical

• Antimicrobial

Summary

• Qualitative tests for carbonyl compounds

• Differentiating tests for aldehdyes

• Differentiating tests for ketones

• Paraldehyde is hynotic

• Chloral hydrate

• Serves as desiccant and building blocks in synthesis

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