CHAPTER 13: ALDEHYDES AND KETONES

Before you can learn about aldehydes and ketones, you must first know something about the nomenclature of carboxylic acids since many of the names of aldehydes and ketones are derived from the names of the corresponding carboxylic acids.

Carboxylic acids:

R-COOH, R-CO2H,

Common names:

HCO2H formic acid formica ant

CH3CO2H acetic acid acetum vinegar

CH3CH2CO2H propionic acid “first salt”

CH3CH2CH2CO2H butyric acid butyrum butter

CH3CH2CH2CH2CO2H valeric acid valerans

ALDEHYDES COMMON NAMESSTEM PLUS ALDEHYDE

R-CHO R-CO2H

HCHO

FORMALDEHYDE

HCO2H

FORMIC ACIDFORMICA - ANTS

CH3CHO

ACETUM - SOUR

CH3COOHACETALDEHYDE

ACETIC ACID

CH3CH2CHO CH3CH2CO2H

PROPIONALDEHYDE PROTOS PION - FIRST FAT PROPIONIC ACID

CH3CH2CH2CHO CH3CH2CH2CO2H

BUTRYM - BUTTERBUTYRALDEHYDEBUTYRIC ACID

CH3CH2CH2CH2CH2CHO

CAPROALDEHYDE CAPER - GOAT

CH3CH2CH2CH2CH2CO2H

CAPROIC ACID

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Chapter 18

NAMING ALDEHYDES

IUPAC: Replace -e with -al. The aldehyde carbon is number 1. If -CHO is attached to a ring, use the suffix -carbaldehyde.

CH

O

HCH3

Cl

C

O

H

OH

H3CHC=HC C

O

H

2-Chloropropanal 3-Hydroxypropanal 2-Butenal

C

O

H H CH3

O

H CH3 CH2 C

O

H H3CH2CH2C C

O

H

Common Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde

IUPAC Methanal Ethanal Propanal Butanal

NOMENCLATURE

Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde.

Benzaldehyde p-Nitrobenzaldehyde o-Hydroxybenzaldehyde p-Methoxtbenzaldehyde

O

H

O

H

O2N

O

H

OH O

H

H3CO

KETONES: STRUCTURE AND NOMENCLATURE General formula: RCOR’ (R and R’=alkyl or aryl) Common name: listing the alkyl substitutents attached

to the carbonyl group, followed by the word ketone. IUPAC system: relpace the ending –e by the suffix –one.

The chain is numbred in such a way as give the lowest number to the C=O group.

Common Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone

Acetone Acetophenone Benzophenone

IUPAC Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone

CH3 C CH3

O

CH3 C C6H5

O

CH3 C CH=CH2

O

H5C6 C

O

C6H5

CH3CH2CCH3

O

CH3CH2CCH2CH3

O

ethyl methyl ketone diethyl ketone

CH3CCH2CH2CH3

O

methyl n-propyl ketone

(o)phenones:

Derived from common name of carboxylic acid, drop –ic acid, add –(o)phenone.

CR

O

C

O

H3CC

O

benzophenone acetophenone

C2H5 C

O

O

C2H5

CHO

O

OH

C2H5 C

O

O

C2H5

CHO

O

OH

Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal

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Chapter 18

BOILING POINTS More polar, so higher boiling point than

comparable alkane or ether. Cannot H-bond to each other, so lower boiling

point than comparable alcohol.

=>

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Chapter 18

SOLUBILITY

Good solvent for alcohols. Lone pair of electrons on oxygen of carbonyl

can accept a hydrogen bond from O-H or N-H. Acetone and acetaldehyde are miscible in

water.

=>

Aldehydes synthesis 1) oxidation of primary alcohols:

RCH2-OH + K2Cr2O7 (potassium dichromate) RCH=O+ H2

RCH2-OH + C5H5NHCrO3Cl RCH=O+ H2

(pyridinium chlorochromate, or PCC)

[With other oxidizing agents, primary alcohols RCOOH]

CH3CH2CH2CH2CH2OH

+ K2Cr2O7 CH3CH2CH2CH2CO2H

1-pentanol

pentanoic acid

K2Cr2O7, special conditions!CH3CH2CH2CH2CH=O

pentanalvaleraldehyde

CH2OHC5H5NHCrO3Cl

pyridinium chlorochromate

CH=O

benzaldehydebenzyl alcohol

CH3CH2CH2CH2CH2OH

1-pentanol

Aldehyde synthesis: Primary alcohols

Aldehyde synthesis: 2) reduction of acid chloride

LiAlH(O-t-Bu)3

lithium aluminum hydride tri-tert-butoxide

O

Cl

isovaleryl chloride

O

Hisovaleraldehyde

RC

O

Cl

LiAlH(O-t-Bu)3

RC

O

H

CO

Cl

LiAlH(O-t-Bu)3C

O

H

LiAlH(O-t-Bu)3

benzoyl chloride benzaldehyde

CH3CHCH2CO

Cl

CH3

CH3CHCH2CO

H

CH3

isovaleryl chloride isovaleraldehyde

Ketone synthesis: 1) oxidation of secondary alcohols

NaOCl

cyclohexanol cyclohexanone

isopropyl alcohol acetone

K2Cr2O7

H OH O

H3CC

CH3

O

CH3CHCH3

OH

Ketone synthesis: 2) Friedel-Crafts acylation

RCOCl, AlCl3 + ArH + HClAlCl3

ArCR

O

Aromatic ketones (phenones) only!

CH3CH2CH2CO

Cl+

AlCl3CH3CH2CH2C

O

butyrophenone

+AlCl3

m-nitrobenzophenone

O2N

C Cl

O

CO

O2N

+AlCl3

C Cl

O

NO2

NR

Friedel Crafts acylation does not work on deactivated rings.

ACETALS ANDHEMICETALS Acetal: two –OR groups bonded to the same

carbon Hemiacetal: one –OR group and one –OH

group bonded to the same carbon

ENOLIZATION Keto-Enol Tautomerism

Tautomerism: interconversion between two structures that differ by the placement of an atom or group

Slow in neutral conditions, sped up in acid or base catalyzed systems

Enol content is very small, <<<1% for most aldehydes and ketones