Matriculation Chemistry ( Carbonyl Compound )

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CARBONYLCOMPOUNDS

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Objective

Describe aldehydes and ketones. Draw the structure and name the

compound according to IUPAC nomenclature and common names.

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INTRODUCTION

Functional group: carbonyl, C=O General formula: CnH2nO Aldehyde & Ketone are isomeric Carbonyl compounds are polar In general, an aldehyde > reactive than ketone

towards nucleophilic addition reaction

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INTRODUCTION ALDEHYDE

R = alkyl, aryl @ H

KETONE

R & R’ = alkyl, aryl

C

O

R H

C

O

R R’

δ+

δ-

δ+

δ-

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Naming of Aldehyde

Aldehyde is named by substituting the letter –e of the corresponding alkane with –al

Basic name depends on the longest chain with

–CHO group The chain must be numbered by starting with

–CHO group as C-1

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Naming of Aldehyde

Structure IUPAC name General name

H-C-H

methanal formaldehyde

CH3-C-H

ethanal acetyldehyde

CH3CH2-C-H

propanal propionaldehyde

O

O

O

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Naming of AldehydeStructure IUPAC name General name

CH3CH2CH2-C-H

butanal n-butyraldehyde

CH3(CH2)3-C-H

pentanal n-valeraldehyde

Ph-C-H

benzaldehyde(phenylmethanal)

benzenecarbaldehyde

O

O

O

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Naming of Aldehyde

O

CH2C-H

Phenylethanal

(phenylacetyldehyde)

CH2=CHCH2C-H

O

3-butenal

CH3CHCHC-H

O

OH

H3C-H2C

2-ethyl-3-hydroxybutanal

4 3 2 1

4 3 2 1

2 1

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Naming of Ketone

Ketone is named by substituting the letter –e of corresponding alkane with –one

The longest chain with carbonyl group is numbered so that C in carbonyl group gets the smallest number

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Naming of KetoneStructure IUPAC name General name

CH3CCH3

propanone acetone

(dimethyl ketone)

CH3CCH2CH3 Butanone methyl ethyl ketone

CH3CCH2CH2CH3 2-pentanone methyl propyl ketone

O

O

O

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Naming of KetoneStructure IUPAC name General am

Ph-C-CH3

phenylethanone

acetophenone(phenyl methyl ketone)

Ph-C-Ph diphenylmethanone

benzophenone

(diphenyl ketone)

CH3CH2CCH2CH33-pentanone diethyl ketone

O

O

O

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O

CH2C-CH3

phenylpropanone

CH2=CHCH2CCH3

O

4-penten-2-one

CH3CCH2CH2CCH3

O

2,5-hexanadione

O

O

OH

CH2CH3

2-ethyl-2-hydroxycyclopentanone

-CH2C-CH2-

O

1,3-diphenylpropanone

5 4 3 2 1

1 2 3 4 5

1 2 3

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a. c.

b. d.

EXCERCISE

1. Write the names of the following compounds according to IUPAC nomenclature

CH3 O

CH3CHCH2CH2CH2CHC H 3CH 2C H 2C H C H

O

CH2

CH3

CH3CH2CH2C

O

CHCH3

CH3

CH3CH

2C CH2CH2CH2CH3

O

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2. Write down all structural formulae of compound with molecular formula C5H10O and name them according to IUPAC nomenclature.

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Objective

Explain the preparation of carbonyl compounds through these reactions:

a)Oxidation of alcoholsb)Ozonolysis of alkenesc) Friedel–Crafts acylation to produce aromatic

ketones

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Preparation of Carbonyl 1. Oxidation of Alcohols

[O] of 1o R-OH to form aldehyde [O] of 2o R-OH to form ketone

CH3CH2CH2CH2-OH + PCC CH3CH2CH2CH=OCH2Cl2

1-butanol butanal

-OH =OKMnO4

H+

cyclopentanol cyclopentanone

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2. Ozonolysis of alkene

(i) H3CC=CHCH3 H3CC=O + O=CCH3

CH3 CH3 H(i) O3

(ii) Zn/H2O

(ii) O=CH(CH2)4CH=O(i) O3

(ii) Zn/H2O

Preparation of Carbonyl

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4. Friedel-Crafts Acylation

-a good method for preparing of aromatic ketones

+ R-C-Cl + AlCl3 -C-R

O O

+ R-C-O-C-R + AlCl3 -C-R

O OO

Preparation of Carbonyl

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Practice Questions

(a) CH3CH(Br)CH(CH3)OH + K2Cr2O7/H2SO4

(b) CH3CH=CCH(CH3)2

CH3

(i) O3

(ii)H2O/Zn

(c) + -C=OAlCl3

Cl

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1. Oxidation

2. Reduction

3. Nucleophilic addition reaction

4. Condensation

5. Haloform reaction

CHEMICAL PROPERTIES

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To explain the chemical properties with reference to these reactions :

a) oxidation with KMnO4, K2Cr2O7,Tollens, Fehling, Benedict and Schiff reagents to differentiate between aldehydes and ketones.

b) reduction to alcohol using LiAlH4,NaBH4 and catalytic hydrogenation.

Objective

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1.0 Oxidation Aldehydes are easily oxidised to carboxylic acid by

strong oxidising reagents e.g. KMnO4/H+, K2Cr2O7/H+

Mild oxidising agents such as Tollens’, Schiff, Fehlings’ & Benedicts’ solutions can also oxidise aldehydes.

Ketones are resistant towards oxidation because they do not have hydrogen attached to the carbonyl carbon atom.

KMnO4

H+

H+

KMnO4

RCHO

RCR’

O

No reaction

RCOOH

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1.1 TOLLENS’ TEST

For identifying aldehydes and ketones. It is a mixture of aqueous silver nitrate and

ammonia. It contains Ag(NH3)2

+

In this reaction aldehyde is oxidised to carboxylate ion and argentum is deposited on the wall of the the test tube as silver mirror.

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CH

Contoh

2[Ag(NH3)2]+

+ OH-

+

RCOO-

+ NH3+Ag2 2 + NH4+

2cermin perak

CH3CH2CHO +OH-

[Ag(NH3)2]+

2+

RCH

O

O

+2[Ag(NH3)2]+

OH-

+

cermin perakNH4

+2+22Ag + NH3+CH3CH2COO

-

cermin perakNH4

+2+22Ag + NH3+

O

C O-

silver mirror

silver mirror

silver mirror

Example:

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1.2 FEHLING and BENEDICT TEST(Cu2+ tartarate complex)

Fehling reagent will oxidise aldehydes but not ketones

Used to identify aldehydes Reaction with aldehydes will produce

carboxylate ion and copper(I) oxide which is red in colour.

In this reaction copper(II) is reduced to copper(I)

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Equation;

Brick red

Brick red

blue

blue

RCHO Cu4 2+ OH-

5+ +

RCOO-

Cu2O2+

+ H2O3

CH3CH

O

3H2O+

+2Cu2O

++ OH-

5Cu4 2+ CH3CO-

Oexample

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1.3 Schiff’s reagent

Aldehyde reacts with Schiff’s reagent to give a pink colouration

Ketone give negative result

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Reduction Aldehydes are reduced to 1o R-OH & ketones to 2o

R-OH

Reagents (a) LiAlH4 @ NaBH4 in ether + H+

(b) Zn, H+, heat

(c) H2(g), Ni @ Pt, heat

2.0 Reduction

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CH3CH2CH CH3CH2CH

O OH

H

LiAlH4

H+

-C-CH3 -CH-CH3 O OH

H2 , Ni

Example:

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To explain the chemical properties with reference to these reactions :

a) nucleophilic addition with HCN, Grignard reagent, alcohol, sodium bisulphite and water.

Objective

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In C=O, the e- density is drawn more towards the O atom making the C atom deficient in e. Thus, the C atom becomes the site for Nu- attack.

When carbonyl C is attacked by Nu-, breaking the carbonyl bond & tetrahedral intermediate is formed

Hybridisation of sp2 C atom changes to sp3

3.0 Nucleophilic addition

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The HCN is prepared ‘in situ’ by the reaction of a mixture of KCN or NaCN with H2SO4

Reagents : NaCN @ KCN (aq) followed by dilute H2SO4

-C=O

HNaCN

H2SO4

-C-OH

H

CN

CH3CHCCH3

CH3

OKCN

H2SO4

CH3-CH-C-CH3

CH3

OH

CN

3.1 Addition of HCN

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yields gem-diols

H H

C=O + H2O

H+ C

H H

OH OH

H3CH2C

H3C

C=O + H2O

H+

C

OH OH

H3CH2C

H3C

3.2 Addition of Water

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Aldehyde yields hemiacetal & ketone yields hemiketal

R H

C=O + R’OH

H+ C

R H

OH OR’

hemiacetal

R R’

C=O + R’’OH

H+ C

R R’

OH OR’’

hemiketal

3.3 Addition of alcohol

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Hemiacetal & hemiketal in acidic solution react further to form acetal & ketal

H+ C

R H

OR’’ OR’

acetal

H+ C

R R’

OR’’’

OR’’

ketal

C + R’’OH

R H

OH OR’

C + R’’’OH

R R’

OH OR’’

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Examples:-

H

C=O + CH3OH

H+ C

H

OH OCH3

CH3

C=O + CH3OH

H+ C

OH OCH3

CH3

CH3 CH3

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HCHO

(i)RMgX (ii)H3O+

RCH2OH

1o Alcohol

R’CHO

(i)RMgX (ii)H3O+

R’-CH-R

2o Alcohol

OH

R’CR’’

(i)RMgX (ii)H3O+

R’-C-R’’

3o Alcohol

OHO

R

Example:

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•NaHSO3 react with aldehyde & ketone to form carbonyl bisulphite which is soluble in water

•This reaction is used for purification of aldehyde @ ketone from other non-soluble organic compounds

•Pure carbonyl compound is obtained when treated with aqueous base

3.5 Addition of sodium bisulphite

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NaHSO3 + -C-CH3 -C-CH3

O OH

OSO2-Na+

Bisulphite salt

Sodium bisulphite

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To explain the chemical properties with reference to these reactions :

a) condensation with NH3 and ammonia

derivatives eg hydrazine, phenylhydrazine, hydroxylamine and 2,4 – dinitrophenylhydrazine as identification test for carbonyl compounds.

b) iodoform test to identify compounds with these structures

Objective

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•NH3 & its derivatives react as nucleophile and react with carbonyl compounds

•Involved addition reaction followed by dehydration (elimination of H2O molecule to form C=N)R

C=O + NH3

4.0 Condensation

R

C

O-H

N-H

Carbinolamine‘Unstable intermediate’

R

R

R

C=NH R

H

+ H2Oaddition elimination

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R’ C=O NNH- -NO2

R

H

H NO2

R’ C=NNH- -NO2 + H2O

R NO2

2,4-dinitrophenylhydrazine

Brady’s reagent

yellow @ orange

precipitate

characteristic reaction of carbonyl compounds

Example:

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NH3 derivatives Name Product Name

R-NH2 @

Ar-NH2

primary amine

C=N-R @

C=N-Ar

imine

NH2NH2 hydrazine C=NNH2Hydrazone

NH2-OH hydroxyl amine

C=N-OH oxime

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NH3 derivatives Name Product Name

NH2NHC6H5

phenyl hydrazine

C=NNHC6H5 phenyl hydrazone

NH2NHCNH2

semi

carbazide C=NNHCNH2

semi

carbazone

O O

•Carbonyl react with hydrazine @ phenylhydrazine also give yellow precipitate

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Reagent : I2 in NaOH(aq), heat forms NaIO(Sodium iodate (i))

Formation of yellow precipitate, CHI3 , indicate that organic compound consist of methyl carbonyl or methyl alcohol:-

-C-CH3 @ -C-CH3

O OH

H

5. Iodoform reaction

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GENERAL REACTION:-

RCCH3 RCCI3 RCO- + CHI3

O O OI2

OH-

OH-

RCHCH3 RCCH3 RCCI3 RCO- + CHI3

OH OI2

OH- OH-

OOH-

OI2

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EXAMPLE:-

CH3CH2CCH3 CH3CH2C-O- + CHI3

O ONaIO

-C-CH3 -C-O- + CHI3

O O

I2 / NaOH

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EXAMPLE:-

H-CCH3 H-C-O- + CHI3

O OI2/NaOH

-C-CH3 -C-O- + CHI3

OH O

I2 / NaOH

H

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Practice Questions

(a) CH3CCH2CH3 + H2NNH NO2

NO2

H+

O

(b) CH3CCH2CH3 + H2NOH O

H+

(c) CH3CCH2CH3 + I2 / NaOH O

(d) CH3C-CH2-Ph + LiAlH4 O

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Practice Questions

The molecular formula of an unknown compound A is C7H14. Ozonolysis of A gave two products B and C, whereby both B and C reacted with 2,4-dinitrophenylhydrazine to give solid derivatives. B gave positive results to Tollens’ and Iodoform tests, while C gave negative result to both of the tests. Suggest the structural formula of A, B and C. Explain your answer.