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 L. formica ant

CH3CO2H acetic acid L. acetum vinegar

CH3CH2CO2H propionic acid G. “first salt”

CH3CH2CH2CO2H butyric acid L. butyrum butter

CH3CH2CH2CH2CO2H valeric acid L. valerans

R COH

O

Carboxylic acids, common names:

…

CH3(CH2)4CO2H caproic acid L. caper goat

CH3(CH2)5CO2H ---

CH3(CH2)6CO2H caprylic acid

CH3(CH2)7CO2H ---

CH3(CH2)8CO2H capric acid

CH3(CH2)9CO2H ---

CH3(CH2)10CO2H lauric acid oil of lauryl

5 4 3 2 1C—C—C—C—C=Oδ γ β α used in common names

CH3CH2CH2CHCOOH

BrCH3CHCH2COOH

CH3

bromovaleric acid -methylbutyric acid

isovaleric acid

COOH

COOH COOH COOH

CH3

CH3CH3

benzoic acid

o-toluic acid m-toluic acid p-toluic acid

Special names!

ALDEHYDES AND KETONES

“carbonyl” functional group:

Aldehydes Ketones

HC

H

O

RC

H

O

RC

R'

O

R can be Ar

C

O

Nomenclature:

Aldehydes, common names:

Derived from the common names of carboxylic acids;

drop –ic acid suffix and add –aldehyde.

CH3

CH3CH2CH2CH=O CH3CHCH=O

butyraldehyde isobutyraldehyde (α-methylpropionaldehyde)

CHO

benzaldehyde

CHO

CH3

o-tolualdehyde

HC

H

O

formaldehyde

CH2CH=O

phenylacetaldehyde

Aldehydes, IUPAC nomenclature:

Parent chain = longest continuous carbon chain containing the carbonyl group; alkane, drop –e, add –al. (note: no locant, -CH=O is carbon #1.)

CH3

CH3CH2CH2CH=O CH3CHCH=O

butanal 2-methylpropanal

H2C=O CH3CH=O

methanal ethanal

Ketones, common names:

Special name: acetone

“alkyl alkyl ketone” or “dialkyl ketone”

H3CC

CH3

O

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

Ketones: IUPAC nomenclature:

Parent = longest continuous carbon chain containing the carbonyl group. Alkane, drop –e, add –one. Prefix a locant for the position of the carbonyl using the principle of lower number.

CH3CH2CCH3

O

CH3CH2CCH2CH3

O

2-butanone 3-pentanone

CH3CCH2CH2CH3

O

2-pentanone

Physical properties:

polar, no hydrogen bonding

mp/bp are relatively moderate for covalent substances

water insoluble

(except: four-carbons or less)

C O sp2 120o

C O C O

Spectroscopy:

IR: C=O stretch, strong ~1700 cm-1

RCHO 1725 ArCHO 1700

R2CO 1710 ArCOR 1690

C—H stretch for aldehydes 2720

nmr: -CHO 9-10 ppm

C=Ostretch

acetophenone

valeraldehyde

CHOC—Hstretch2720 cm-1

C=O stretch

valeraldehyde

CH3CH2CH2CH2CH=O

a b c d e

-CHO

Oxidation/Reduction:

oxidation numbers:

oxidation

-4 -2 0 +2 +4 CH4 CH3OH H2C=O HCO2H CO2

alkane alcohol aldehyde carboxylic acid

reduction

Aldehydes, syntheses:

1. Oxidation of 1o alcohols

2. Oxidation of methylaromatics

3. Reduction of acid chlorides

Ketones, syntheses:

1. Oxidation of 2o alcohols

2. Friedel-Crafts acylation

3. Coupling of R2CuLi with acid chloride

Aldehydes synthesis 1) oxidation of primary alcohols:

RCH2-OH + K2Cr2O7, special conditions RCH=O

RCH2-OH + C5H5NHCrO3Cl RCH=O

(pyridinium chlorochromate)

[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: 2) oxidation of methylaromatics:

+ CrO3, (CH3CO)2O

geminal diacetate

H2O, H+

CH3

BrBr

CH OOC C

H3C

OO

H3C

Br

CHO

p-bromobenzaldehyde

Aromatic aldehydes only!

CH3

CH3O CH3

CrO3

(CH3CO)2O

CrO3

(CH3CO)2O

H2O

H2O

CHO

CH3O CH=O

2-methylnaphthalene 2-naphthaldehyde

p-methylanisole p-anisaldehyde

Aldehyde synthesis: 3) 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.

Mechanism for Friedel-Crafts acylation EAS

RC

Cl

O+ AlCl3 RC=O + AlCl4

+ RC=ORDS

H

CR

O

H

CR

O

+ AlCl4 C R

O+ HCl + AlCl3

Ketone synthesis: 3) coupling of RCOCl and R2CuLi

RCOCl + R'2CuLiR

C

O

R'

Cl

O

+ (CH3CH2)2CuLi

O

Isobutyryl chloride 2-Methyl-3-pentanone

lithium diethylcuprate

CuLi

2

+ CHCH2CH2CH3

O

ClCCH2CH2CH3

O

butyrophenone

CH3CH2CH2CO

Cl+ CH3CH

CH3

2

CuLi CH3CH2CH2CCHCH3

O

CH3

2-methyl-3-hexanone

Aldehydes, syntheses:

1. Oxidation of 1o alcohols

2. Oxidation of methylaromatics aromatic only

3. Reduction of acid chlorides

Ketones, syntheses:

1. Oxidation of 2o alcohols

2. Friedel-Crafts acylation aromatic only

3. Coupling of R2CuLi with acid chloride

aldehyde

1o alcohol

Ar-CH3

acid chloride

CrO3 H2O

(AcO)2O

LiAlH(O-t-Bu)3

K2Cr2O7, special cond.

or C5H5NHCrO3Cl

ketone

2o alcohol

acid chloride + ArH

acid chloride + R2CuLi

NaOCl, etc.

AlCl3

1. outline three different syntheses for benzaldehyde

2. outline three different syntheses for benzophenone

3. outline a different synthesis for each of the following compounds:

cyclohexanone, 4-bromobenzaldehyde, 2-pentanone, valeraldehyde, acetophenone, isobutyraldehyde,

CH2OH

K2Cr2O7

special conditions

CH3

CrO3

(CH3CO)2O

CH(OOCCH3)2

H2O

C

O

Cl

LiAlH(O-t-Bu)3

CH=O

benzaldehyde

Synthesize benzaldehyde three different ways.

CH

OH NaOCl

CO

Cl+

AlCl3

CO

Cl+ CuLi

2

C

O

Synthesize benzophenone three different ways.

cyclohexanone, 4-bromobenzaldehyde, 2-pentanone, valeraldehyde, acetophenone, isobutyraldehyde, using a different method for each one.

OBr CHO

CH3CH2CH2CCH3

OCH3CH2CH2CH2CHO

CH3C

O

CH3CHCHO

CH3

oxidation of 2o alcohol oxidation of Ar-CH3

R2CuLi + R'COCl

Friedel-Crafts acylation

oxidation of 1o alcohol

reduction of acid chloride

O

CH3CH2CH2CCH3

O

CH3C

O

OHH

K2Cr2O7

CH3 CCl

O+

AlCl3

(CH3CH2CH2)CuLi + CH3 CCl

O

Br CHO

CH3CH2CH2CH2CHO

CH3CHCHO

CH3

Br CH3

CH3CH2CH2CH2CH2-OHK2Cr2O7

special conditions

CrO3

(CH3CO)2O

H2O

CH3CHC

CH3 O

Cl

LiAlH(O-t-bu)3

The methods could be reversed for the last two syntheses.