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