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Alcohols and Phenols
Dr. Seham ALTERARY
Chapter 7
Chem 145
1434-1435
2013-2014
2nd semester
Chapter Head LinesIntroduction
Types and Classifications.
Nomenclature of Alcohols and Phenols.
Physical Properties.
Acidity of Alcohols and Phenols.
Preparation of Alcohols and Phenols:A. Preparation of Alcohols
2- Hydration of Alkenes
1- Hydration of Alkyl halide
3- Oxidation of Alkenes to vicinal diol.
4- Reduction of Carbonyl group.
5- Nucleophilic Addition of Grignard Reagents to carbonyl group
B. Preparation of PhenolsReactions of Alcohols and Phenols:
I- Reactions involving oxygen-hydrogen bond breakingII- Reactions involving carbon-oxygen bond rupturing
III. Oxidation IV- Reaction of Aromatic Ring of Phenols
Introduction
-Alcohols are characterized by the hydroxyl group -OH
-The general formula for Alcohols is
Alcohols
O
H
H
HH
H H
CC
OHR C
sp3As all alcohols are the compounds containing hydroxyl group (-OH)
attached to the alkyl group, hybridization is sp3
Phenols or, Aryl alcohols
Are hydroxyl derivatives of aromatic hydrocarbons, which are
derived by replacing hydrogen atom attached to sp2 hybridized
carbon atom(s) of benzene ring by hydroxyl group.
OH
Phenols , ArOH
OHsp2
Alcohols and phenols have a common functional group
the hydroxyl group, —OH.
Alcohols and phenols may be viewed as organic derivatives of water.
H-O-H R-O-H or PhCH2OH Ph-O-H
Water Alcohol Phenol
OHOHOH
Types of Alcohols
3. Polyhydroxyls: containing more than two hydroxyl groups on
different carbon atoms.
1. Monohydroxyls: containing one hydroxyl group.
Example; ethanol (C2H5OH)
2. Dihydroxyls (glycols): containing two hydroxyl groups connected
by different carbon atoms.
Example; 1,2-Ethanediol
Ethylene glycol
(CH2OH-CH2OH).
Example; 1,2,3-propanetriol
Glycerol or Glycerin
(CH2OH-CHOH-CH2OH).
Classification of Monohydroxyl Alcohols
The mono hydroxyl alcohols can be classified into three types
according to the type of the carbon atom connected to the hydroxyl
group:
C HR
H
OH
C RR
H
OH
C RR
R
OH
1̊ alcohol 2̊ alcohol 3̊ alcohol
C HH
H
OH
Methyl alcohol
Ethanol 2-Propanol 2-Methyl-2-PropanolExamples
Draw the structures of the above alcohols?
Nomenclature
1) Common Nomenclature (Alkyl + alcohol)
Examples:
- In the common system, you name an alcohol by listing the alkyl
group and adding the word alcohol.
CH3 OH OHCH3CH2
Methyl alcohol Ethyl alcohol
CH3CH2CH2OH
Propyl alcohol
- You can use both the common and IUPAC systems to name alcohols.
CH3CHCH3
OH
Isopropyl alcohol
Vinyl alcohol
CH2 CHCH2 OH
CH3CCH3
CH3
OH
Allyl alcohol
t-butyl alcohol
CH2 OH
Benzyl alcohol
Examples:
CH2 CH OH
2) IUPAC Nomenclature
3) Number the longest continuous carbon chain so as to give
the carbon atom bearing the hydroxyl group the lower number.
1) Select the longest continuous carbon chain to which the
hydroxyl is directly attached.
2) Change the name of the alkane corresponding to this chain
by dropping the final -e and adding the suffix –ol.
Examples
CH3CHCH2CH2CH2OH
CH3
2 1345
4-Methylpentan-1-ol
Not 2-Methylpentan-5-ol
CH3CH2CH2OH
n-Propanol
CH3CHCH2CH3
OH
2-Butanol
4) OH group is preferred over the double or triple bond in numbering.
OH
Hept-5-en-2-ol
HC CCH2CH2 OH
But-3-yn-1-ol
ClCH2CH2CH2OH
3-chloropropan-1-ol
CH3CHCH2CCH3
CH3
CH3OH
12321 3 4 5
4,4-Dimethylpentan-2-ol
5) If a compound contains both OH and a double or triple bond,
choose the chain that include them both even if this is not the
longest chain.
HO
1
2
3
4
Example
3-Ethylbut-3-en-2-ol
OH
Methylcyclohexylalcohol
HO
Cyclopentylalcohol Allylalcohol
HOExample
Common:
IUPAC: Cyclopentanol 1-Methyl-1-cyclohexanol 2-Propen-1-ol
Examples
OH
Cl
HOOH
Pent-4-ene-2-ol Cyclohex-2-enol
12
3
4-Chloro-3-methyl-heptan-1-ol
1
234
5
6
7
C6H5
Br OH
3-Bromo-2-phenyl cyclopentanol
1
2
3
OH
123
1-Cyclobutylpropan-2-ol
OH
1
23
4
2-Methyl-4-phenyl butan-2-ol
Examples
HO
pent-4-yn-1-ol
OH
5-Ethyl-hex-5-en-3-ol
HO
4-methyl-2-cyclohexen-1-ol
HO
2-phenyl ethanol
CH3CH2CHCH2CHCH3
OHCH2
H3C
4-Ethyl-hexan-2-ol
(CH3)2C CHCHCHCH3
OH
5-Methyl-4-hexen-2-ol
• In the IUPAC system, the suffix diol is added to the name of the
parent hydrocarbon when two hydroxyl groups are present, and
the suffix triol is added when there are three OH groups.
• Common names, two OH groups on adjacent carbons are known as
1,2-glycols.
IUPAC:
Common:
1,2-Ethanediol
Ethylene glycol
1,2-Propanediol
propylene glycol
1,2,3-Propanetriol
glycerol or glycerin
Examples:
Nomenclature of Phenols
Compounds that have a hydroxyl group attached directly to a benzene
ring are called phenols.
The ortho, meta, para system is used in common names.
While the numbering system is employed in IUPAC names and in this
case numbering of the ring begins at the hydroxyl-substituted carbon and
proceeds in the direction of the next substituted carbon that possesses the
lower number.
OHOH
NH2
Phenol 4- Aminophenol
Examples:
Examples:
NO2
OH
Br
Cl
Cl
Cl
Cl
Cl
OH
2,3,4,5,6-Pentachlorophenol4-Bromo-2-nitrophenol
Picric acid
NO2
NO2
O2N
OH
Common name:
2,4,6-Trinitrophenol
O
HO
O
HO
HO
2-hydroxybenzaldehyde 2-hydroxybenzoic acid
Salicyaldehyde
o-hydroxybenzaldehyde o-hydroxybenzoic acid
Salicyalicacid
δ+
δ+
δ-
δ+
δ-
δ+
δ-
δ+
δ+
δ-
δ+
δ-
δ-δ+ δ+
•The solubility of lower
alcohols is due to the
existence of hydrogen
bonds between water and
polar -OH group of alcohol
molecules.
•The first three members are completely miscible with water. The
solubility rapidly decreases with increase in molecular mass. The higher
members are almost insoluble in water but are soluble in organic solvents
like benzene, ether etc.
1. Solubility • Alcohols
Hydrogen bonding between alcohols and water molecules
Physical Properties of Alcohols & Phenols
•The solubility increases with branching of chain.
OH
OH
OH
OH
Increase solubility
HOHO
OHOH
OH
HO
OH
HO
OH OH
•The number of hydroxyl groups increases the solubility.
δ+δ-
δ+
δ-
δ+
δ-δ+
δ+
δ+δ-
δ+
δ-
δ+
Phenols differ from alcohols in that the -OH is directly attached to
the aromatic ring.
•The -OH group in phenols contain a hydrogen bonded to an
electronegative oxygen atom. Thus they form hydrogen bonds with
water molecules
• Phenols
δ-
δ+
• Phenols are sparingly soluble in water but readily soluble in organic
solvents .
Boiling point of alcohols are much higher than those of alkanes, halo alkanes
or ethers of comparable molecular masses.
CH3CH2CH3
•This is because in alcohols
intermolecular hydrogen bonding
exists due to which a large amount
of energy is required to break these
bonds.
OHCH3CH2
Ethanol n-propane Dimethylether
Mol wt = 46; bp= 78°C Mol wt = 46; bp= -24°CMol wt = 44; bp= -42°C
3.Boiling points• Alcohols
Boiling points of alcohol increases in regular manner with increase in
molecular weight.
δ-
δ+
δ+
δ-
Representations of
intermolecular hydrogen bonding in alcohols
δ+
δ-
H3C O CH3
• Among isomeric alcohols, the boiling point decreases with increase in
branching in the alkyl group.
• Boiling points of 1o alcohol > 2o alcohol > 3o alcohol
OHCH3CH2CH2CH2
1-Butanol
(mol wt = 74; bp = 118°C)
OHCH3CHCH2
CH3
2-Methyl-1-propanol(mol wt = 74; bp = 108°C)
CH3CH2CHCH3
OH
2-Butanol
(mol wt = 74; bp = 99.5°C)
CH3CCH3
CH3
OH
2-Methyl-2-propanol(mol wt = 74; bp = 83°C)
• boiling points increase with the increase of the number of hydroxyl groups .
Note that!
Exercise:
1- Rank the following molecules in order of decreasing B.P.
PentanolButanol ButanePropylchloride Propanol
I II III IV V
2- Which of the following molecules has the highest B.P?
Br HO
OH
HO O
A) B)
C) D)
Phenols tend to have higher boiling points than alcohols of similar
molecular weight because they have stronger intermolecular hydrogen
bonding.
Representations of intermolecular hydrogen bonding in phenol
• Phenols
O
H δ+
δ-
O
H
δ-
δ+
O
H
δ-
δ+
O
H
δ-
δ+
Acidity of Alcohols & Phenols
The anion dervived by the deprotonation of an alcohol is the alkoxide.
The pKa for most phenols is (10).
Phenols are more acidic than alcohols.
The anion derived by the deprotonation of an phenols is the phenoxide ion.
R O H H+ + RO-
An alcohol An alkoxide ion
O H H+ + O-
A phenol A phenoxide ion
Both alcohol and phenol show acidic property to a certain degree since the
hydrogen in the hydroxy group (-OH) can be removed by a base as a proton.
Alcohols are slightly acidic (pKa 16-18).
- Introduction of electron-withdrawing groups (EWG), such as NO2
or CN, X on the ring increases the acidity of phenol.
- Also, introducing electron-donating groups (EDG), such as NH2,
R, OR decrease the acidity of phenols.
Acidity order
Effect of substituents on the acidity of phenols
OH
NO2
OH
Cl
OH
CH3
OH
OCH3
˃˃˃˃
OH
- The greater the number of electron withdrawing at o- and p-
position, more in the acidic character of phenol.
OH
NO2
OH
NO2
NO2
OH
NO2
NO2NO2
˂ ˂ ˂
OH
pKa
Phenol 4-Nitrophenol 2,4-Dinitrophenol 2,4,6-Dinitrophenol
10.0 7.2 4.0 0.4
Example: In each of the following pairs of compounds,
indicate which is more acidic.
(a) p-chlorophenol or p-nitrophenol
(c) o-Creasol or o-Nitrophenol
(d) o-Methoxyphenol or m-Methoxyphenol
(b) 2,4-dinitroophenol or 3,5-dinitrophenol
1- Hydration of alkenes
H3O+ OH
+
OH
major minor
KMnO4
OH
OH
OH/ H2O
cis glycol2- From alkyl halide
alcohol,KOH
CH3CH2CH2Cl
heat
dil OH-
CH3CH2CH2OH
H3C CH
CH2
A. Preparation of alcohols:Alcohols can be prepared by the following methods:
3-Reduction of Aldehydes, Ketones, Acids and Esters
The carbonyl group of several functional groups may be converted to the
alcohol by reducing agents.
Reducing Agents
LiAlH4 NaBH4
Sodium borohydride
or
Sodium tetrahydridoborate
Lithium aluminium hydride
O OH
3-a. Reduction of Aldehydes and Ketones
Aldehydes and ketones are most readily reduced with hydride reagents,
LiAl H4 or NaBH4 .
The reducing agents LiAlH4 and NaBH4 act as a source of (hydride ion, H-),
the hydride reacts with the carbonyl group, C=O, in aldehydes or ketones to
give alcohols.
LiAlH4
or
NaBH4
General Equation
+ C
O
HHC H
H
H
OH
+ C
O
HR C H
R
H
OH
+ C
O
R'RC R'
R
H
OH
Formaldehyde
Methanol
Aldehyde
Ketone
1° alcohol
2° alcohol
Examples
CH
O(1) LiAlH4 or NaBH4
(2) H3O+
CH2OH
Propanal 1-Propanol
OH
O(1) LiAlH4 or NaBH4
(2) H3O+
OH
Cyclohexanone Cyclohexanol
3-b. Reduction of Acids and Esters
Each reaction requires that 2 hydrides (H-) be added to the carbonyl of
acids or esters.
Carboxylic acids and esters are less reactive to Nu than aldehydes or
ketones.
As a result they can only be reduced by LiAlH4 but NOT by the less
reactive NaBH4.
General Equation
C
O
R OHC R
H
H
OH
+ H2OLiAlH4 +
Acid
Ester
C
O
R OR'LiAlH4 + C R
H
H
OH
+ R'O H
Examples
ROR'
O
(1) LiAlH4
(2) H3O+
ROH
C OH
O(1) LiAlH4
(2) H3O+
OH
Pentanoic acid 1-Pentanol
Aryl ester Aryl alcohol
Grignards react with aldehydes and ketones to give intermediate products
that form alcohols when hydrolyzed.
The special value of Grignard reagents is that they provide excellent ways to
form new C-C bonds.
As a result of the difference in electronegativity between carbon and
magnesium the charge distribution in the Grignard reagent is such that
the organic group (R) is partially negative and the –MgX group is partially
positive [ Rδ- δ+MgX].
4- From Grignard reagent
Grignard reagent + formaldehyde → 1º ROH
Grignard reagent + other aldehydes → 2º ROH
Grignard reagent + ketones → 3º ROH
Grignard reagent + Esters → 3º ROH
4.1-Grignard + formaldehyde yields a primary alcohol with one additional
carbon.
4.2-Grignard + aldehyde yields a secondary alcohol.
1° alcohol
2° alcohol
2) H2O/ HClH3CH2C CH2
OH
H H
O
H3CH2C MgBr +
1) Dry Ether
H3CH2C CH2
O [MgBr]+
H3CH2C MgBr
+H3C H
O
1) Dry EtherH3CH2C CH
O
CH3
[MgBr]+
2) H2O/ HCl H3CH2C CH
OH
CH3
4.3-Grignard + ketone yields a tertiary alcohol.
2) H2O/ HCl
OH
CH2CH3
4.4 -Grignard + ester yields a tertiary alcohol.
3° alcohol
The esters are less reactive than aldehydes and ketones. However they give tertiary
alcohols with excess (2 moles) of Grignard reagent.
O
O+Ph MgBr
1) Dry Ether
2) H2O/ HCl
OH
Ph
Ph
2
3° alcohol
O
+
H3CH2C MgBr 1) Dry Ether
O
CH2CH3
[MgBr]+
Hydrolysis of diazonium salt.
Preparation of phenols
Reactions of alcohols and phenols
I-Reactions of alcohols:
1-Those that involve the breaking of oxygen-hydrogen bond
Alcohols undergo two kinds of reactions;
2- Those that involve the rupture of carbon-oxygen bond C OH
CO H
II-Reactions of phenols:
1-Those that involve the breaking of oxygen-hydrogen bond
phenols undergo two kinds of reactions;
2-Those that involve the benzene ring reactions.
OH
O H
Alcohols and phenols can act as acids whenever they donate a proton to a base.
Alcohols with alkali metals (active metals) like sodium Na or Potassium K to
form the salt (alkoxide).
(1) Salt Formation
General Equation
Example
2R O H + NaOH No Reaction
+ Na 2NaOCH3 + H22 CH3O H
Note That!
A- Reactions involving oxygen-hydrogen bond breaking
CO H
+ Na2 R O H 2NaOR + H2
OH
2 + Na2
O- Na+
+ H2
General Equation
Example
OH
2 + NaOH2
O- Na+
+ H2O
Note That!
Phenols are more acidic than alcohols and may be converted to their
sodium salts by reaction with aqueous NaOH; sodium hydroxide.
+ Na 2NaOAr + H22Ar O H
(2) Reaction of alcohols with carboxylic acids :Ester formation
Alcohols can be converted to esters by means of the Fischer
Esterification Process. In this method, an alcohol is reacted with a
carboxylic acid in the presence of an inorganic acid catalyst such as,
H2SO4 or HCl.
+H+
Heat
R' C
O
OHR OH R' C
O
OR + H2O
General Equation
CH3CH2OH + CH3C
O
OHH+
HeatCH3C
O
OCH2CH3 + H2O
Ethanol
(alcohol)
Acetic acid
(acid)
Ethylacetate
(ester)
Example
B- Reactions involving carbon-oxygen bond rupturing
1- Dehydrations of alcohols:
Since water is ―removed‖ from the alcohol, this reaction is known as a
dehydration reaction (or an elimination reaction):
• Heating alcohols in concentrated sulfuric acid (H2SO4) at 180°C removes
the OH group and a H from an adjacent carbon to produce an alkene,
with water as a by-product.
General Equation
Example
CH3CHCH3
H2SO4
180° C
OH
CH3CH CH2 + H2O
Propanol Propene
C OH
1.1 Formation of alkenes.
+ H2OC C
R
R
R
R
OHH
C CR
RR
RH2SO4
180° C
• If there is more than one possible product of a dehydration reaction, the
major product can be predicted from Zaitsev’s Rule:
• Zaitsev’s Rule— when an alkene is produced in an elimination reaction,
the major product is the one with the more highly substituted double bond.
OH
H2SO4 / 180°C+ + H2O
OH
H2SO4 / 180°C
OH
CH3
H2SO4 / 180°C
Excercise
Example
Major product
90%
Manor product
10%
• Heating alcohols (R—OH) in concentrated sulfuric acid (H2SO4) at
140°C removes a molecule of water from two alcohol molecules, causing
the two ―R‖ groups to become attached to an oxygen atom, forming an
ether functional group:
1-Dehydration of Alcohols :
+ HO R'R OH H2SO4
140° C+ H2OR O R'
General Equation
Examples
2 CH3CH2OHH2SO4
140° CCH3CH2
CH2CH3O + H2O
Ethanol Diethylether
1.2 Ethers Formation
2- Replacement of the OH group by Halide: Alkyl Halides Formation.
The hydroxyl group -OH of alcohols can be replaced by halide to form alkyl
halides.
The net equation is:
Alkyl fluoride; R—F, are not prepared from alcohols.
3-Reaction with phosphorus halides, PX3 or PX5.
2-Reaction with thionyl chloride SOCl2.
1-Reaction with hydrogen halides HX: Lucas test.
Replacement of the OH group by Halide
R OH R X (X= Cl, Br, or I)
Alcohols Alkyl halide
• Alcohols can be oxidized by removing two H atoms from the
molecule; the exact products of the reaction will depend on the type
of alcohol.
Oxidation of Alcohols to Carbonyl Compounds
• An oxidation reaction occurs when a molecule loses electrons. This
is usually manifested as an increase in the number of oxygen atoms
or a decrease in the number of hydrogen atoms.
• Some common oxidizing agents include potassium permanganate
(KMnO4), chromic acid (H2CrO4), sodium dichromate (Na2Cr2O7),
and other Cr6+ salts.
[O] = oxidation
R2CHOH + [O] → R2C=O + H2O
Oxidation of alcohols gives different products depending on; the class of
alcohols that is oxidized & the kind of oxidizing agent that is used.
Primary alcohols yields aldehydes when treated with mild oxidizing agent
such as hot metalic copper; Cu or CrO3 in pyridine .
1° alcohol
When 1° alcohols are allowed to react with stronger oxidizing agents,
such as chromic acid, H2CrO7, or neutral potassium permenganate, KMnO4,
the intermediate aldehydes formed initially are oxidized further to carboxylic
acids, RCOOH.
A- Oxidation of Primary alcohols
R C O
H
H
H
+ H2OR C
H
O R C O
OH[O] [O]Cu
or
CrO3/ pyridine
H2CrO7
Aldehyde Carboxylic acid
General Equation
CH3CH2OHCu or CrO3/ pyridine
C
H
OCH3
Ethanol Ethanal
Acetaldehyde
CH3CH2OH C
OH
OCH3
H2Cr2O7
Ethanol Acetic acid
Example
with mild oxidizing agent
with stronger oxidizing agents
oxidation of primary alcohols to aldehydes requires special reagents
to avoid over-oxidation to the acid.
Secondary alcohols are oxidized to ketones, which cannot be oxidized any
further:
B- Oxidation of 2° Secondary Alcohols
General Equation
Example
2- Propanol Acetone
H3C C CH3
OH
H
[O]CH3CH3C
O
+ [O] R C
R
H2O+OR C O
H
R
H
2° alcohol Ketone
+ [O]R C O
H
R
R
C- Oxidation of 3° Tertiary Alcohols
Do not react with oxidizing agents under normal conditions.
3° Tertiary alcohol
Note That!
Tertiary are stable to oxidation under normal conditions.
under drastic conditions, tertiary alcohols give ketones and acids,
each containing less carbons than alcohols.
Reactions of phenols
OH
6- Reaction of aromatic ring of phenols
1-Halogenation
OH
Br
OH
Br
OH
Br
Br
Br
Br2/ CS2 or CCl4
5°C
25° C
Br2/ H2O
2,4,6-Tribromophenol
o-Bromophenol p-Bromophenol
+
OH
In polar solvents
phenols react with
halogens (chlorine
water or bromine
water) at a very fast
rate substituting all
the available ortho-
and para-positions.
However, halogenation can be stopped at monohalogenation stage
if reaction is carried out in presence of non-polar or less polar
solvents at low temperature.
Electrrophilic Substitution Reaction
Home Work
1)
2)
3)
MgBr
H3O+
+
O H2C
HCH
OH3O+
+
MgCl
KMnO4
OH-/H2O
4) The IUPAC name of
is:
A) 4-Ethyl-5-heptyn-3-ol
B) 4-Ethyl-5-heptan-3-ol
C) 4-Ethyl-5-hepten-3-ol
D) 4-Etyl-2-hepten-5-ol
OH
5) The IUPAC name of
is:
A) 3-Methyl-1-bromocyclohexanol
B) 2-Bromo-3-methylcyclohexanol
C) 4-Bromo-2-methylcyclohexanol
D) 3-Bromo-1-methylcyclohxanol
6) The common name of 2-methyl-2-propanol is:A) Allyl alcohol
B) Isopropyl alcohol
C) tert-Butyl alcohol
D) Benzyl alcohol
7) The following reaction gives
A) 4-Ethylphenol
B) 2-Ethylphenol
C) Ethylphenyl ether
D) Ethylphenyl ketone
NaOHOH
1)
CH3-CH2-Br2)
Thank youFor your attention
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