Introduction

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Introduction

ALDEHYDES AND KETONES Possess Carbonyl group (>C=0) General formula - CnH2nO Aldehydes and ketones are collectively called Carbonyl Compounds. In Aldehydes, carbonyl group is linked to one Alkyl group and to one H-

atom. Aldehydic group is monovalent group,chain terminating group. In ketones,carbonyl group.is joined to two alkyl groups which may be same

or different. It is a divalent group. If R groups are similar - it is called simple ketone, If R groups are different - it is called mixed ketone. STRUCTURE OF CARBONYL GROUP:

In carbonyl group carbon atom is sp2 hybridised. Bond angle is 120∘.

Preparation of aldehydes and ketones

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By oxidation and dehydrogenation of alcohols

1. Oxidation of alcohols : CH3−CH2−OH−→−−−−−−−−−−−−−−−−−ORPCC(or)PDCK2Cr2O7/H+(or)KMnO4/H+CH

3CHO

PCC = Pyridiniumchlorochromate,(C5H5N+HCrO3Cl−) PDC = Pyridiniumdichromate 2. Dehydrogenation of alcohols

(CH3COO)2Ca+(HCOO)2Ca−→−−−−−−−Drydistillation2CH3CHO+2CaCO3

Ethylalcohol

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By dry distillation

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ROSENMUND'S REDUCTION

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HYDROLYSIS OF GEMDIHALIDES

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WACKERS METHOD

CH2=CH2+PdCl2+H2O−→−−−−−CuCl2/H+CH3CHO+Pd+2HCl

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STEPHEN REACTION

RCN+SnCl2+HCl→RCH=NH−→−H2ORCHO

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DRY DISTILLATION

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FROM PROPYNE-OXYMERCURATION-DEMERCURATION

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HYDROLYSIS OF GEMDIHALIDES

CH3−C(Cl2)−CH3−→−−−−−HydrolysisCH3−C(OH)2−CH3

CH3−C(OH)2−CH3−→−−−H2O(CH3)2CO

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Wackers Method

CH3−CH=CH2+PdCl2+H2O−→−−−−−CuCl2/H+(CH3)2CO+Pd+2HCl

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OXIDATION OF ALCOHOLS

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DEHYDROGENATION OF ALCOHOLS

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By side chain chlorination followed by hydrolysis

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GATTERMANN KOCH

Gatterman - Koch benzal chloride reaction: Here, benzene is treated with carbon monoxide and HCl in the presence of

anhydrous AlCl3 and CH2Cl2

Uses of aldehydes and ketones

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USES (ACETALDEHYDE)

1. In the preparation of Acetic acid, Acetic anhydride ethyl acetate, chloral, 1,3-butadiene (used in Rubber) dyes and drugs. 2. Used as antiseptic inhalent in nose troubles. 3. In the preparation of paraldehyde (hypnotic) and Metaldehyde (Solid fuel, for killing slugs & snails) 4. Used in spirit lamp.

5. In the preparation of acetaldehyde ammonia (a rubber accelerator)

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USES (ACETONE)

1) As a solvent for cellulose accetate, cellulose nitrate, celluloid, resins etc. 2) Used in storing of acetylene. 3) In the manufacture of Cordite - a smokeless explosive. 4) Used as nail polish remover. 5) Used in the preparation of plexiglass (unbreakable glass), Synthetic rubber.

6) Used in the prep. of chloroform, iodoform and chloretone.

Chemical properties of aldehydes and ketones

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NUCLEOPHILIC ADDITION MECHANISM - 4

Carbonyl compounds undergo nucleophilic addition reactions. In the polar carbonyl group, carbon with partial positive charge is more reactive than oxygen with partial negative charge. Hence, carbonyl group is first attacked by nucleophile followed by the attacking of electrophile. Relative reactivities towards nucleophilic

addition HCHO>R−CHO>R−CO−R Aldehydes are more reactive towards nucleophilic attack than ketones. This is because alkyl groups are more electron donating compared to hydrogen atom and an aldehyde has a greater positive charge on its carbonyl carbon than a ketone. Steric factors also contribute to the greater reactivity of an aldehyde compared to a ketone. Among ketones, those with smaller alkyl groups are more

reactive than those with bigger alkyl groups .

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NUCLEOPHILIC ADDITION MECHANISM - 1

If the attacking nucleophilic is strong, it will readily attack the carbonyl carbon. The resulting addition product can be readily protonated by the solvent or by the added acid.

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NUCLEOPHILIC ADDITION MECHANISM - 1

A poor nucleophile requires an acid catalyst to make the nucleophilic reaction occur at a reasonable rate. The acid protonates the carbonyl oxygen, thus increasing the susceptibility of the carbonyl carbon to nucleophilic attack.

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NUCLEOPHILIC ADDITION MECHANISM - 3

If the attacking atom of the nucleophile has a pair of non-bonding electrons in the addition product, water will be eliminated from the addition product. Hence the reaction

is called as nucleophilic addition - elimination reaction.

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NUCLEOPHILIC ADDITION REACTION

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NUCLEOPHILIC ADDITION REACTION

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NUCLEOPHILIC ADDITION REACTION

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NUCLEOPHILIC ADDITION REACTION

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Condensation Reactions

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REDUCTIONS

15.−→−−−−−−−−−H2/NiLiAIH4orNaBH4CH3CH2OH(Ethylalcohol) 16. Clemmensons Reduction

CH3CHO−→−−−Zn−Hg4(H)CH3−CH3+H2O 17. Wolf-Kishner reduction CH3CHO−→−−−−−−−−−KOH/(CH2OH)2NH2NH2CH3−CH3 Ethane

18. −→−−−−−−30∘Conc.H2SO4(CH3CHO)3(HYPNOTIC) Paraldehyde

19.−→−−−−−−−−0∘/Conc.H2SO4(CH3CHO)4 Metaldehyde(Solid Fuel)

20. CH3COCH3−→−Pcl5CH3CHCl2+POCl3

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NUCLEOPHILIC ADDITION REACTIONS

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CONDENSATION REACTIONS

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CONDENSATION REACTIONS

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CONDENSATION REACTIONS

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CONDENSATION REACTIONS

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CONDENSATION REACTIONS

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CANNIZZARO’S REACTION

Aldehydes that have no α− hydrogen atom undergo this reaction involving disproportionation (self oxidation and reduction) on treating with strong conc. alkali.

Eg. 1) HCHO+HCHO−→−−−−−−Conc.NaOHCH3OH+HCOONa

Eg. 2) C6H5CHO+C6H5CHO−→−−−−−Conc.KOHC6H5CH2OH+C6H5COOK

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DISTINCTION OF ALDEHYDES AND KETONES

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HALOFORM REACTION (Iodoform Test)

Characteristic test for the detection of presence of -COCH3 (Methyl ketone group) TESTS FOR ACETONE : a) LEGAL TEST :

CH3COCH3+ Sodium Nitroprusside+NaOH → Wine red colour changes to yellow b) INDIGO TEST : Ortho nitro benzaldehyde +2ml. of Acetone + diluted with KOH gives blue colour of indigo tin.

Isomerism

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TYPES OF ISOMERISM IN ALDEHYDES

a) Show -functional isomerism - with ketones, unsaturated alcohols,unsaturated ethers.

CH3CH2CHO CH3COCH3 Propional dehyde Propanone

CH2=CH−CH2OH CH2=CH−O−CH3 Allylalcohol Vinyl methyl ether b) Show-tautomerism: with alcohols

CH3CHO CH2=CHOH

Acetaldehyde vinylalcohol

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Chain isomerism in ketones

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Functional isomerism in ketones

Functional isomerism

CH3CH2CHO CH3COCH3 Propionaldehyde propanone CH2=CH−CH2OH CH2=CHOCH3

Allyl alcohol Vinyl methyl ether

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Tautomerism in ketones

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Metamerism in ketones