Chapter 3 ketone
-
Upload
miza-kamaruzzaman -
Category
Technology
-
view
1.787 -
download
5
Transcript of Chapter 3 ketone
SUBTOPICS
Nomenclature – common and IUPAC names for ketones
Physical properties of ketones : Boiling points and solubility
Preparation of ketone
Oxidation of 2 °Alcohol Friedel – Crafts Acylation
Reactions of aldehyde
Reduction To 2 ° Alcohol Nucleophilic Addition Reaction with Grignard Reagent Iodoform Reaction
• Functional group: carbonyl group
C O
C
O
R'R
ketone
R, R' = substituents
Ketone: the carbon atom in the carbonyl group is
bonded to two hydrocarbon groups.
Ketones
• The IUPAC name of a ketone is derived from the name of the alkane corresponding to the longest carbon chain that contains the ketone-carbonyl group.
• The parent name is formed by changing the –e ending of the alkane to -one.
propane propanone one
IUPAC NAME
If the carbon chain is longer than 4 carbons, it’s numbered so that the carbonyl carbon has the smallest number possible, and this number is prefixed to the name of the ketone.
This end of the chain is closest to the C=O.
Begin numbering here.
IUPAC NAME
7
Common Names of Ketones
: :
R C
O
R'
alkyl alkyl ketone
• Most common names for ketones are formed
by naming both alkyl groups on the carbonyl
carbon, arranging them alphabetically, and
adding the word “ketone”.
cyclohexanone 4-methylcyclohexanone
O
O
CH3
1 234
56
phenylethanone diphenylmethanone
C
O
CH3 C
O
Aromatic compound:
- phenyl is used as part of the name.
• The parent name is formed by changing the –e ending of the cycloalkane to -one.
• Carbonyl carbon is designated C1.
NOMENCLATURE OF CYCLIC KETONES AND AROMATIC COMPOUNDS
A ketone group can also be named as a substituent on
a molecule with another functional group as its root.
The ketone carbonyl is designated by the prefix oxo-.
Carboxylic acids frequently contain ketone group
named as substituents.
CH2 C
O
CCH3CH2
O
H CH2 C
O
CCH3
O
OH
3-oxopentanal
12345
3-oxobutanoic acid
1234
NOMENCLATURE OF KETONES CONTAINING TWO DIFFERENT FUNCTIONAL GROUPS
10
Physical Properties : Boiling point
• Oxygen is more electronegative than carbon (3.5
vs 2.5) and, therefore, a C=O group is polar
•Ketones are polar due to this C=O bond and
therefore have stronger intermolecular forces than
hydrocarbons making their boiling points higher.
C O C O –
Polarity of acarbonyl group
-+C O
+
More importantcontributing
structure
::: : :
11 11
Physical Properties : solubility
The small ketones are freely soluble in water but solubility falls
with chain length.
The reason for the solubility is that they can form hydrogen
bond with water molecules.
One of the slightly positive hydrogen atoms in a water
molecule can be sufficiently attracted to one of the lone pairs
on the oxygen atom of a ketone for a hydrogen bond to be
formed.
12 12
Physical Properties : solubility
• Ketones can form hydrogen bonds with water and therefore low
molecular weight ketones have appreciable water solubility
14
• Examples
• Ketones can be made from 2o alcohols by oxidation
* [O] =
2.1 Oxidation of 2 °Alcohol
15
• Aromatic ketones can be made by Friedel-Crafts Acylation
• Examples
2.2 Friedel – Crafts Acylation
16
REACTIONS
REDUCTION TO 2 ° ALCOHOL
NUCLEOPHILIC addition
REACTION with grignard reagent
IODOFORM REACTION
REACTIONS OF KETONES
Reduction
Addition
Condensation
Iodoform reaction
Reaction with Grignard reagent
Ketones can be reduced to alcohols using:
a) lithium aluminium hydride (LiAlH4)
b) sodium borohydride (NaBH4)
c) catalytic hydrogenation
H+ = diluted acid such as H2SO4
R C R'
O-
H
R C R'
OH
H
H+
2o alcohol
R C R'
O
LiAlH4 or NaBH4 or H2, Niketone
CH3 C CH3
O-
H
H+
2-propanol
CH3 C CH3
O
H2/Ni
propanone
CH3 C CH3
OH
H
Example:
3.1 Reduction to Secondary Alcohols
C
O
R R' HCN
C
O
CH3 CH3 HCN
CR R'
OH
CN
CCH3 CH3
OH
CN
ketone
cyanohydrin
example
propanone
2-hydroxy-2-methylpropanenitrile
* Cyanohydrin may be formed using liquid HCN with a
catalytic amount of sodium cyanide or potassium cyanide.
3.2a Nucleophilic addition of hydrogen cyanide
C
O
R R' HCN
C
O
CH3 CH2CH3 HCN
CR CN
OH
R'
CCH3 CN
OH
CH2CH3
ketone
cyanohydrin
example
propan-2-one
H2O/H+
CR COOH
OH
R
a-hydroxyacid
NH4+
H2O/H+
CCH3 COOH
OH
CH2CH3
NH4+
'
Cyanohydrin can be hydrolysed to give α-hydroxyacids.
The nitrile (-CN) group is converted to the –COOH group by
reflux the cyanohydrin with dilute sulphuric acid (H2O/H+) or
concentrated HCl.
3.2a Nucleophilic addition of hydrogen cyanide
When shaken with an aqueous of sodium bisulphite, most
aldehydes and ketones formed carbonyl bisulphite (a
colourless crystal).
The reaction takes place more readily with aldehydes than
with ketones.
The nucleophile is the hydrogensulphite ion, HSO3-
Example:
NaHSO3 C
O
CH3 C
OH
CH3
OSO2- Na+
Bisulphite salts
3.2b Nucleophilic addition of sodium bisulphite
(NaHSO3)
Aldehydes and ketones condense with ammonia derivatives such as
hydroxylamine and substituted hydrazines to give imine derivatives.
i) Reaction with hydrazine:
Hydrazines derivatives reacts with aldehydes or ketones to form
hydrazones.
R C
O
R' H2N-NH2 R C
N
R'
NH2H+
H2Oaldehyde or ketone hydrazine
hydrazone derivative
Example:
C
O
H2N-NH2H+
hydrazineH2O
propanonepropanone hydrazone
H3C CH3 C
NNH2
H3C CH3
3.3 Condensation with hydrazines, hydroxlamine,
phenylhydrazine and 2,4-dinitrophenylhydrazine
ii) Reaction with hydroxylamine:
Hydroxylamine reacts with ketones and aldehydes to form
oximes.
R C
O
R' H2N-OH R C
N
R'
OHH+
H2Oaldehyde or ketone hydroxylamine oxime
Example:
H2N-OH H+
hydroxylamine
H2O
phenyl-2-propanone phenyl-2-propanone oxime
O N
OH
3.3 Condensation with hydrazines, hydroxlamine,
phenylhydrazine and 2,4-dinitrophenylhydrazine
iii) Reaction with phenylhydrazine:
R C
O
R' R C
N
R'
NH-PhH+
H2Oaldehyde or ketone phenylhydrazine
phenylhydrazone
Example:
H+
H2O
penta-2-onepenta-2-one phenylhydrazone
H N NH
H
Ph
phenylhydrazine
H N NH
H
PhO N-NH-Ph
3.3 Condensation with hydrazines, hydroxlamine,
phenylhydrazine and 2,4-dinitrophenylhydrazine
NO2
NO2NH2N
H
NO2
NO2NN
H
C
CH3
H2Oroom
temperature
butan-2-one 2,4-dinitrophenylhydrazonebutan-2-one 2,4-dinitrophenylhydrazine
C O
NO2
NO2NH2N
H
NO2
NO2NN
H
CR'
R
H2Oroom
temperature
2,4-dinitrophenylhydrazine
R
R'
2,4-dinitrophenylhydrazone(yellow-orange precipitate)
aldehyde or ketone
Example:
CH3 C CH2CH3
O
CH3CH2
iv) Reaction with 2,4-dinitrophenylhydrazine:
3.3 Condensation with hydrazines, hydroxlamine,
phenylhydrazine and 2,4-dinitrophenylhydrazine
A Grignard reagent (a strong nucleophile resembling a
carbanion, R:- attacks the electrophilic carbonyl carbon atom to
give an alkoxide intermediate.
Subsequent protonation gives an alcohol.
MgBrCH3CH2C O
H3C
H3CC O- +MgBr
CH3
CH3
CH3CH2
C OH
CH3
CH3
CH3CH2
H3O+
2-methyl-2-butanol
alkoxideacetoneethylmagnesium bromide
3.4 Reaction with Grignard Reagent
IODOFORM TEST
- Reagent: solution of I2 in an alkaline medium such as NaOH or KOH.
- Iodoform test is useful for the methyl ketone group (CH3C=O) in ketones.
- when ketones containing methyl ketone group is warmed with iodoform reagent, a yellow precipitate of triiodomethane (iodoform) is formed.
The overall reaction is
R C
O
CH3 3I2heat
NaOH R C
O
O- Na+ CHI3 3HI
salts iodoform(yellow precipitate)
3.5 Haloform Reaction
TESTS ALDEHYDES KETONES
Tollens’ Test / silver mirror test
Reagent and condition:
- ammoniacal silver nitrate
solution ([Ag(NH3)2]+)
Observation:
Formation of silver mirror
Observation:
Silver mirror did not formed
* Ketones do not react with
Tollens’ reagent
Fehling’s test / Benedict’s test
Reagent and condition:
-Solution of Cu2+ (aq) ions in an
alkaline solution of sodium
potassium tartate.
*Can be used to distinguish
between:
i) Aldehydes and ketones
ii) Aliphatic aldehydes and
benzaldehyde
Observation;
Blue colour of the Fehling’s
solution dissappears and
brick-red precipitate is
obtained
* Except benzaldehyde
Observation:
Blue colour remains.
* Ketones do not react with
Fehling’s/Benedict’s reagent
Schiff’s test
Reagent and condition:
- Schiff’s reagent
Observation:
Formation of magenta-pink
colour (simple aldehydes)
* Except benzaldehyde and
a few aromatic aldehydes)
Observation:
Ketones (except propanone)
do not react with Schiff’s
reagent.
Tests to Distinguish Aldehydes and Ketones, and Aliphatic Aldehydes and
Aromatic Aldehydes
Question a. A compound , J (C4H10O), has three isomers K,L
and M. K is 2-methyl-1-propanol and L is 2-
methyl-2-propanol.
i) Draw the structural formulae of K and L
ii) Describe how you would prepare K using
Grignard reagent
iii) Draw structural formula of M and name it.
b. Compare and provide justification for the acidity
of phenol, ethanol and water.