lecture# cho and co

8/6/2019 Lecture# CHO and CO

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Aldehydes and Ketones


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Nomenclature:

Aldehydes, common names:

Derived from the common names of carboxylic acids;

drop ic acid suffix and add aldehyde.

CH3CH3CH2CH2CH=O CH3CHCH=O

butyraldehyde isobutyraldehyde(-methylpropionaldehyde)


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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


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Ketones, common names:

Special name: acetone

alkyl alkyl ketone or dialkyl ketone

H3CC

CH3

O

CH3CH2CCH3O

CH3CH2CCH2CH3O

ethyl methyl ketone diethyl ketone

CH3CCH2CH2CH3O

methyl n-propyl ketone


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(o)phenones:

Derived from common name of carboxylic acid, drop ic

acid, add (o)phenone.

CR

O

C

O

H3CC

O

benzophenone acetophenone


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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


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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


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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]


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Aldehyde synthesis: 2) oxidation of methylaromatics:

+ CrO3, (CH3CO)2O

geminaldiacetate

H2O, H+

CH3

Br Br

CH O

OC C

H3C

O

O

H3C

Br

CHO

p-bromobenz ldehyde

Aromatic aldehydes only!


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Aldehyde synthesis: 3) reduction of acid chloride

LiAlH(O-t-Bu)3

lithium aluminum hydride tri-tert-butoxide

O

Cl

isovaleryl chloride

O

H

isovaleraldehyde

RC

O

Cl

LiAlH(O-t-Bu)3

RC

O

H


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Ketone synthesis: 1) oxidation of secondary alcohols

NaOCl

cyclohexanol cyclohexanone

isopropyl alcohol acetone

K2Cr2O7

H OH O

H3C C CH3

O

CH3CHCH3

OH


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Ketone synthesis: 2) Friedel-Crafts acylation

RCOCl, AlCl3 + ArH + HCl

AlCl3

ArCR

O

Aromatic ketones (phenones) only!

CH3CH2CH2CO

Cl+

AlCl3CH3CH2CH2C

O

butyrophenone


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Ketone synthesis: 3) coupling of RCOCl and R2CuLi

RCOCl + R'2CuLi

RC

O

R'

Cl

O

+ ( 3 2)2 uLi

O

Isobutyryl chloride 2-Methyl-3-pentanone

lithium diethylcuprate


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Aldehydes & ketones, reactions:

1) Oxidation

2) Reduction

3) Addition of cyanide

4) Addition of derivatives of ammonia

5) Addition of alcohols

6) Cannizzaro reaction

7) Addition of Grignard reagents

8) (Alpha-halogenation of ketones)

9) (Addition of carbanions)


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nucleophilic addition to carbonyl:

CO

+ Y Z C

Z

OY

H

H


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Mechanism: nucleophilic addition to carbonyl

C

O

+ Z

RDS

C

O

Z

CO

Z

+ Y COY

Z

1)

2)


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Mechanism: nucleophilic addition to carbonyl, acid catalyzed

C

O

+ H C

OH

C

OH+ H

RDS

C

OH

H

C

OH

H

C

OH

+ H

1)

2)

3)


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1) Oxidation

a) Aldehydes (very easily oxidized!)

CH3CH2CH2CH=O + K nO4, etc. CH3CH2CH2COOH

carboxylic acid

CH3CH2CH2CH=O + Ag+ CH3CH2CH2COO

- + Ag

Tollens test for easily oxidized compounds like aldehydes.

(AgNO3, NH4OH(aq))

Silver mirror


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b)Methyl ketones:

RC

CH3

O

+ OI-

RC

O-

O

+ CHI3

iodoform

test for methyl ketonesYellow ppt

CH3CH2CH2CCH3 + (xs) NaOI CH3CH2CH2CO2- + CHI3

O

2-pentanone


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2) Reduction:

a) To alcohols

H2, i

aBH4 or Li lH4

then H+

C

O

C

OH

H


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H2, Pt

1. NaBH4

2. H+

O

cyclopentanone

OH

cyclopentanol

C CH3

O

CHCH3

OH

acetophenone 1-phenylethanol

H


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Reduction

b) To hydrocarbons

NH2NH2, OH-

Zn(Hg), HCl

Clemmensen

Wolff-KishnerC

O

CO

CH2

CH2


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3) Addition of cyanide

C

O 1. CN-

2. H+

C

CN

OH

cyanohydrin

O + NaCN; then H+

OH

CN


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4) Addition of derivatives of ammonia

O+

N+ H2OH2N G

(H+)

G

HN

phenylhydrazine

H2N NH2

hydrazine

H2N OH

hydroxylamine

HN NO2

O2N

2,4-dinitrophenylhydrazine

H2N NH

O

NH2

semicarbazide

H2NH2N


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CH2 CHO

phenylacetaldehyde

+ H2NOH CH2 CH NOH

an oxime

O + H2NHNCNH2

O H+

NHNCNH2

O

a semicarbazonecyclohexanone

CH3CH2CH2CH2CHO + NHNH2

phenylhydrazine

hydroxylamine

semicarbazide

pentanalCH3CH2CH2CH2CH N NH

a phenylhydrazone


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5) Addition of alcohols

C

O+ ROH, H+

C

OR

OR acetal

C

OH

OR hemiacetal


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CH2CHO(xs) EtOH, H+

CH2 CHOEt

OEt

O (xs) CH3OH, dry HClOCH3

OCH3

acetal

ketal


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6) Cannizzaro reaction. (self oxidation/reduction)

a reaction ofaldehydes without -hydrogens

CHO

Br

conc. NaOH

CH2OH COO-

Br Br

+

CH3OH + HCOO-H2C=O

conc. NaOH


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CH3 HBr CH3 g CH3CH3CHCH2OH CH3CHCH2Br CH3CHCH2 gBr

H+

K2Cr2O7 CH3CH3CH2OH CH3CH=O CH3CHCH2CHCH3

special cond. OH

4-methyl-2-pentanol


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Formaldehyde is the most easily oxidized aldehyde. When

mixed with another aldehyde that doesnt have any alpha-

hydrogens and conc. NaOH, all of the formaldehyde is

oxidized and all of the other aldehyde is reduced.

Crossed Cannizzaro:

CH=O

OCH3

OH

vanillin

+ H2C=Oconc. NaOH

CH2OH

OCH3

OH

+ HCOO-


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7) Addition of Grignard reagents.

C

O

+ RMgX C

O

R

MgBr

C

O

R

MgBr

+ H2O C

OH

R

+ Mg(OH)Br

largeralcohol


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Planning a Grignard synthesis of an alcohol:

a) The alcohol carbon comes from the carbonylcompound.

b) The new carbon-carbon bond is to the alcohol carbon.

C

O

+ RMgXH+

C

OH

R

New carbon-carbon bond

lecture# cho and co

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