ALDEHYDES and ketones

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Preparation : 

Preparation Aldehydes and Ketones

Preparation of aldehydes and ketones : 

Preparation of aldehydes and ketones From alcohols Oxidation of alcohols RCH2OH ? RCHO Dehydrogenation of alcohols RCH2OH ? RCHO From hydrocarbons Ozonolysis of alkenes Hydration of alkynes CrO3 Cu 573K

OZONOLYSIS OF ALKENES : 

OZONOLYSIS OF ALKENES R H C C R R’ O3 Zn,H2O OR CH3SCH3 Ketone +Aldehyde

Hydration of alkynes : 

Hydration of alkynes H3C C C H H3C CH2 CHO Ethylene Acetaldehyde Hg2+,H2SO4

Preparation : 

Preparation Aldehydes

Preparation of aldehydes : 

Preparation of aldehydes

From acyl choride (Acid chloride) : 

From acyl choride (Acid chloride) Rosenmund reduction Acyl chloride is hydrogenated over catalyst, palladium on barium sulphate (Pd-BaSO4) e.g. benzoyl chloride benzaldehyde

From Nitriles and Esters : 

From Nitriles and Esters Stephen reaction Nitriles + stannous chloride ?imine ?aldehyde

Slide 9: 

From Nitriles and Esters

Slide 10: 

From Nitriles and Esters

Aldehydes from Esters and Amides : 

Aldehydes from Esters and Amides

From Hydrocarbons : 

From Hydrocarbons By oxidation of methylbenzene Use of chromyl chloride(CrO2Cl2) Use of chromic acid(CrO3) By side chain chlorination followed by hydrolysis By Gatterman-Koch reaction

Slide 13: 

From Hydrocarbons By oxidation of methylbenzene Use of chromyl chloride(CrO2Cl2) Chromium complex benzaldehyde

Slide 14: 

From Hydrocarbons By oxidation of methylbenzene Use of chromic acid(CrO3)

From Hydrocarbons : 

From Hydrocarbons By oxidation of methylbenzene By side chain chlorination followed by hydrolysis

Slide 16: 

By oxidation of methylbenzene By Gatterman-Koch reaction From Hydrocarbons Benzene+CO+HCl ? Benzaldehyde

Preparation : 

Preparation Ketones

Preparation of ketones : 

Preparation of ketones From acyl chlorides From nitriles From benzene or substituted benzenes

Preparation of ketones : 

From acyl chlorides 2R-Mg-X + CdCl2?R2Cd + 2Mg(X)Cl 2R’-CO-Cl + R2Cd ?2R’-CO-R+ CdCl2 Preparation of ketones

Preparation of ketones : 

From nitriles Preparation of ketones

Preparation of ketones : 

From benzene or substituted benzenes Friedel-Crafts acylation Preparation of ketones

PHYSICAL PROPERTIES : 

PHYSICAL PROPERTIES Aldehydes and Ketones

Physical states : 

Physical states Methanal Gas at room temp. Ethanal Volatile Liquid Other Liquid or solid at room temperature

Boiling point : 

Boiling point Aldehydes and ketones possess higher boiling point than hydrocarbons and ethers Order: Hydrocarbons< ethers< aldehydes< ketones< alcohols

Why the order?? : 

Why the order?? Alcohols: Vander waals forces, intermolecular H-Bonding. Aldehydes and ketones: Dipole –Dipole interaction, weak molecular association Aldehydes are more polar than ethers Strong Dipole –Dipole interaction

Solubility : 

Solubility In water Methanal, ethanal and propanal Miscible with water Because of H- bonding Solubility decreases as the alkyl chain increases. In organic solvents Soluble in benzene,ether,methanol,cloroform

Fragrance : 

Fragrance Lower aldehydes----- Pungent odours Higer aldehydes------ More fragrant Aldehydes and ketones are used in perfumes and flavouring agents

Chemical reactions : 

Chemical reactions Aldehydes and ketones

CHEMICAL REACTIONS : 

CHEMICAL REACTIONS

Addition Reactions Aldehydes and Ketones : 

Addition Reactions Aldehydes and Ketones Addition reactions of C=O is related to the reactions of an alkene in that: Pi bond is broken between two atoms A new bond is made to “add” a group to each of these two atoms. It is different from the alkene addition reactions in that: C=C bond is nonpolar; C=O bond is polar NaBH4 prefers C=O; H2 prefers C=C Pi bond in C=C bond is easy to break; Pi bond in C=O requires heat / pressure / catalyst to break.

Addition of H2O: carbonyl group versus alkene group : 

Addition of H2O: carbonyl group versus alkene group Addition of H2O to C=C According to Markonikov’s rule H attaches to the one with more H to begin with R OH \ | C=O + HOH R - C - OH / | R’ R’ Addition of H2O to C=O According to polarity: ?+ C=O ?- ?+ group attaches to ?- end H attaches to the O in C=O

NUCLEOPHILIC ADDITION REACTIONS : 

NUCLEOPHILIC ADDITION REACTIONS Mechanism Reactivity Examples Addition of HCN Addition of NaHSO3 Addition of Grignard reagent Addition of alcohol Addition of NH3 & its derivatives

Relative Reactivity of Aldehydes and Ketones : 

Relative Reactivity of Aldehydes and Ketones Aldehydes are generally more reactive than ketones in nucleophilic addition reactions The transition state for addition is less crowded and lower in energy for an aldehyde (a) than for a ketone (b) Aldehydes have one large substituent bonded to the C=O: ketones have two

Electrophilicity of Aldehydes and Ketones : 

Electrophilicity of Aldehydes and Ketones Aldehyde C=O is more polarized than ketone C=O As in carbocations, more alkyl groups stabilize + character Ketone has more alkyl groups, stabilizing the C=O carbon inductively

Nucleophilic Addition of HCN: Cyanohydrin Formation : 

Nucleophilic Addition of HCN: Cyanohydrin Formation Aldehydes and unhindered ketones react with HCN to yield cyanohydrins, RCH(OH)C?N

Mechanism of Formation of Cyanohydrins : 

Mechanism of Formation of Cyanohydrins Addition of HCN is reversible and base-catalyzed, generating nucleophilic cyanide ion, CN (HCN+OH-?:CN-+H20) Addition of CN? to C=O yields a tetrahedral intermediate, which is then protonated Equilibrium favors adduct

Uses of Cyanohydrins : 

Uses of Cyanohydrins The nitrile group (?C?N) can be reduced with LiAlH4 to yield a primary amine (RCH2NH2) Can be hydrolyzed by hot acid to yield a carboxylic acid

Addition of NaHSO3 : 

Addition of NaHSO3 The hydrogensulphite addition product is water soluble. Can be converted back to carbonyl compound by treating with acid or alkali. Useful for separation and purification of aldehydes. C O +NaHSO3 C OSO2Na OH

Nucleophilic Addition of Grignard Reagents and Hydride Reagents: Alcohol Formation : 

Nucleophilic Addition of Grignard Reagents and Hydride Reagents: Alcohol Formation Treatment of aldehydes or ketones with Grignard reagents yields an alcohol Nucleophilic addition of the equivalent of a carbon anion, or carbanion. A carbon–magnesium bond is strongly polarized, so a Grignard reagent reacts for all practical purposes as R : ? MgX +.

Mechanism of Addition of Grignard Reagents : 

Mechanism of Addition of Grignard Reagents Complexation of C=O by Mg2+, Nucleophilic addition of R : ?, protonation by dilute acid yields the neutral alcohol Grignard additions are irreversible because a carbanion is not a leaving group

Slide 41: 

#3 synthesis of alcohols. Used to build larger molecules from smaller organic compounds.

Slide 43: 

Planning a Grignard synthesis of an alcohol: The alcohol carbon comes from the carbonyl compound. The new carbon-carbon bond is to the alcohol carbon. New carbon-carbon bond

Slide 44: 

or

Slide 45: 

ROH RX -C=O RMgX R´OH HX Mg ox. H2O larger alcohol

Nucleophilic Addition of Amines: Imine and Enamine Formation : 

Nucleophilic Addition of Amines: Imine and Enamine Formation RNH2 adds to C=O to form imines, R2C=NR (after loss of HOH) R2NH yields enamines, R2N?CR=CR2 (after loss of HOH) (ene + amine = unsaturated amine)

Nucleophilic Addition of Alcohols: Acetal Formation : 

Nucleophilic Addition of Alcohols: Acetal Formation One equivalent of ROH in the presence of an acid catalyst add to C=O to yield hemiacetals, R2C(OR?)(OH) Two equivalents of ROH in the presence of an acid catalyst add to C=O to yield acetals, R2C(OR?)2

Slide 48: 

Addition of alcohols

Addition of Alcohols toaldehydes and ketones : 

Addition of Alcohols toaldehydes and ketones Addition of ROH to C=O ? Hemiacetal / hemiketal formation R OR \ | C=O + ROH R - C – OH / | R’ R’ ?+ ?-

Addition of alcohols toaldehydes and ketones : 

Addition of alcohols toaldehydes and ketones Addition of ROH: Hemiacetal / hemiketal formation R OR \ | C=O + ROH R - C – OH / | R’ R’ ?+ ?-

addition of alcohols toaldehydes and ketones : 

addition of alcohols toaldehydes and ketones Addition of ROH to an aldehyde ?Hemiacetal R OR \ | C=O + ROH R - C – OH / | H H ?+ ?- ?+ ?- hemiacetal: C has - R, - OR, - H, - OH

Addition of alcohols toaldehydes and ketones : 

Addition of alcohols toaldehydes and ketones Addition of ROH to a ketone ? hemiketal R OR \ | C=O + ROH R - C – OH / | R’ R’ ?+ ?- ?+ ?- hemiketal: C has - R, - OR, - R, - OH

addition of alcohols toaldehydes and ketones : 

addition of alcohols toaldehydes and ketones Addition of excess ROH to hemiketal ? ketal OR OR | | R - C – OH + ROH R - C – OR + HOH | | R R H+ ketal: C has - R, - OR, - R, -OR

addition of alcohols toaldehydes and ketones : 

addition of alcohols toaldehydes and ketones Addition of excess ROH to hemiacetal ? acetal OR OR | | R - C – OH + ROH R - C – OR + HOH | | H H H+ acetal: C has - R, - OR, - H, -OR

Can this compound make a stable cyclic Hemiacetal? : 

Can this compound make a stable cyclic Hemiacetal? CH2?CH2? CH2? C ?CH3 ? OH O 4CH2? 3CH2?2CH2? 1C ?CH3 ? 5OH O 5-member ring is stable A cyclic hemiketal exists. O CH3 / 1C - OH 2 4 5 3

What class is this? : 

What class is this? Indicate if this is a hemiacetal, (b) acetal, (c) hemiketal, (d) ketal, or (e) none of these. hemiacetal: C has - H, - OH, - R, -OR acetal: C has - H, - OR, - R, -OR hemiketal: C has - R, - OH, - R, -OR ketal: C has - R, - OR, - R, -OR

What class is this? : 

What class is this? Indicate if this is a hemiacetal, (b) acetal, (c) hemiketal, (d) ketal, or (e) none of these. hemiacetal: C has - H, - OH, - R, -OR acetal: C has - H, - OR, - R, -OR hemiketal: C has - R, - OH, - R, -OR ketal: C has - R, - OR, - R, -OR

What class is this? : 

What class is this? Indicate if this is a hemiacetal, (b) acetal, (c) hemiketal, (d) ketal, or (e) none of these. hemiacetal: C has - H, - OH, - R, -OR acetal: C has - H, - OR, - R, -OR hemiketal: C has - R, - OH, - R, -OR ketal: C has - R, - OR, - R, -OR

Slide 60: 

“The Grignard Song” (sung to the tune of “America the Beautiful”) Harry Wasserman The carbonyl is polarized, the carbon end is plus. A nucleophile will thus attack the carbon nucleus. The Grignard yields an alcohol of types there are but three. It makes a bond that corresponds from “C” to shining “C.”

Slide 61: 

Formaldehyde is the most easily oxidized aldehyde. When mixed with another aldehyde that doesn’t have any alpha-hydrogens and conc. NaOH, all of the formaldehyde is oxidized and all of the other aldehyde is reduced. Crossed Cannizzaro:

Slide 62: 

Grignard synthesis of 4-methyl-2-pentanol from alcohols of four-carbons or less: Step one: determine the carbonyl compound and Grignard reagent that you would use: CH3 CH3CHCH2CHCH3 OH H2O CH3 CH3CHCH2MgBr + CH3CH=O Step two: show the syntheses of the Grignard reagent and the carbonyl compound from alcohols…

Slide 63: 

CH3 HBr CH3 Mg CH3 CH3CHCH2OH CH3CHCH2Br CH3CHCH2MgBr H+ K2Cr2O7 CH3 CH3CH2OH CH3CH=O CH3CHCH2CHCH3 special cond. OH 4-methyl-2-pentanol

Slide 64: 

2-phenyl-2-propanol

Slide 65: 

1-methylcyclohexanol

Slide 66: 

cyclohexylmethanol

Slide 67: 

aldehyde RCOOH ketone ROR alkyne alkene RH RX ROH Alcohols are central to organic syntheses

Slide 68: 

ROH RX -C=O RMgX R´OH HX Mg ox. H2O larger alcohol

Slide 69: 

Addition of derivatives of ammonia G --- Ar,OH,NH2,C6H5NH,NHCONH2

Slide 70: 

1) 2) 3)

EXAMPLES : 

EXAMPLES

REDUCTION : 

REDUCTION ALDEHYDES AND KETONES

Slide 74: 

To alcohols

EXAMPLES : 

EXAMPLES

Slide 76: 

EXAMPLES

Hydride Addition : 

Hydride Addition Convert C=O to CH-OH LiAlH4 and NaBH4 react as donors of hydride ion Protonation after addition yields the alcohol

Slide 78: 

Then + H+ ? alcohol

Slide 79: 

To hydrocarbons

Wolff-Kishner Reduction : 

Wolff-Kishner Reduction

Wolff-Kishner Reduction : 

Mechanism Wolff-Kishner Reduction

Oxidation of Aldehydes and Ketones : 

Oxidation of Aldehydes and Ketones Conversion of Aldehydes to Carboxylic acids Oxidation of Aromatic Aldehydes/Ketones to Benzoic acid derivatives Haloform reaction of methyl carbonyls Periodic acid cleavage of vicinal dials/diketones

Aldehyde / Ketone Oxidations : 

Aldehyde / Ketone Oxidations

Reactions due to ?-Hydrogen : 

Reactions due to ?-Hydrogen Aldol condensation CH3-CHO? CH3CH(OH)CH2CHO?CH3CH-CHCHO Dil.NaoH -H2O

Aldol condensation : 

Aldol condensation Mechanism

Cross Aldol condensation : 

Cross Aldol condensation When aldol condensation is carried out b/w two different aldehydes and ketones it is called Cross Aldol condensation.

Other reactions : 

Other reactions Cannizaro reactions Electrophilic substitution reaction

Slide 89: 

Cannizzaro reaction. (self oxidation/reduction) a reaction of aldehydes without a-hydrogens REDUCTION TO ALCOHOL AND OXIDATION TO CARBOXYLIC ACID

The Cannizzaro Reaction : 

The Cannizzaro Reaction The adduct of an aldehyde and OH? can transfer hydride ion to another aldehyde C=O resulting in a simultaneous oxidation and reduction (disproportionation)

Electrophilic substitution reaction : 

Electrophilic substitution reaction CHO CHO

Uses of aldehydes and ketones : 

Uses of aldehydes and ketones Solvents Starting materials Reagents Formalin- Preservative of biological specimens To prepare bakelite Urea-formaldehyde----glue Other polymeric products

Uses of aldehydes and ketones : 

Acetaldehyde Starting material for acetic acid, polymers,drugs,ethyl acetate,vinyl acetate Benzeldehyde Perfumery and dye industry Acetone and ethylmethyl ketone Industrial solvents Butyraldehyde,vanillin, acetophenone,camphor Odours and flavours Uses of aldehydes and ketones