Transcript Alcohols and phenols - Home - KSU Faculty Member websites

Dr Nahed Elsayed
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Learning Objectives
Chapter six concerns alcohols and phenols and by the end of this chapter the student
will:
 know the difference in structure between alcohols and phenols
Know the different classes of alcohols
 Know how to name alcohols and phenols
 Know the physical properties (solubility, boiling and melting points)
 Know how hydrogen bonds are formed and its effect on boiling points of
alcohols
Know the acidic properties of alcohols and phenols
know the different methods that can be used to prepare alcohols and
phenols.
 Know the chemical reactions of these compounds ( some reactions are
review, others are extensions of the chemistry that will be discussed on
chapters 8, 9 & 10
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King Saud University
Chemistry Department
Structure Of Alcohols and Phenols
 Alcohols and phenols may be viewed as organic derivatives of water.
H-O-H
Water
R-O-H or PhCH2OH
Alcohol
Ph-O-H
Phenol
 Alcohols and phenols have a common functional group, the hydroxyl group,
—OH.
- In alcohols the hydroxyl group is attached to an alkyl group, —R.
- In phenols the hydroxyl function is directly attached to benzene ring
OH
OH
OH
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Phenol
Benzyl alcohol
Cyclohexanol
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Classification and Nomenclature of Alcohols
Alcohols are classified according to the type of the carbon
atom connected to the hydroxyl group (carbinol carbon) into:
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Chemistry Department
NOMENCLATURE OF ALCOHOLS
IUPAC Nomenclature Of Alcohols
Alcohols are named according to the following rules:
1.
Select the longest continuous carbon chain that contains the -OH group. Replace
the ending e of the alkane by the suffix –ol
2. If a molecule contains both an -OH group and a C=C or cΞc bond;
 Choose the chain that include both of them even if this is not the longest chain.
The name should include suffixes indicate presence of both the OH group and the
unsaturated groups.
The OH group takes precedence over the double or triple bonds in getting the
lower number.
Cyclic alcohols are named using the prefix cyclo-, the carbon bearing the hydroxyl group
is assumed to take number 1.
3. The suffix diol or triol is added to the name of the parent hydrocarbon when there are
two OH or three OH groups respectively.
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Chemistry Department
Common Nomenclature Of Alcohols
 List the names of alkyl substituents attached to the hydroxyl group, followed by the
word alcohol.
 If two OH groups present on two adjacent carbons these known as glycols
Primary alcohols
CH3OH
CH3CH2OH
Common
Methyl alcohol
Ethyl alcohol
IUPAC
Methanol
Ethanol
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CH2=CHCH2OH
Allyl alcohol
2-Propen-1-ol
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Secondary and tertiary alcohols
OH
OH
CH3
OH
Common Isopropyl alcohol
IUPAC
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2-Propanol
Cyclopentyl alcohol
Cyclopentanol
Methylcyclohexyl alcohol
1-Methyl-1-cyclohexanol
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Examples
OH
OH
OH
2-Phenylethanol
1-Phenylmethanol
Benzyl alcohol (common name)
4-Methyl-2-cyclohexen-1-ol
1
5
4 3 2
(CH3)2C=CHCH(OH)CH3
Cl
OH
4-Chloro-2-methyl-pent-1-en-3-ol
4- Methyl-3-penten-2-ol
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Chemistry Department
Examples
Cl
OH
OH
OH
But-3-en-2-ol
Pent-4-yn-1-ol
5-Ethyl-hex-5-en-3-ol
OH
4-Chloro-2-methyl-1-penten-3-ol
OH
OH
CH3
HO
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OH
OH
IUPAC
Ethane-1,2-diol
Propane-1,2-diol
or 1,2-Propanediol
Common
Ethylene glycol
Propylene glycol
OH
OH
Propane-1,2,3-triol
or 1,2,3,-Propantriol
Glycerol or Glycerin
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Chemistry Department
Physical Properties of Alcohols
1) Solubility Of Alcohols and Phenols
 Alcohol and water contain hydroxyl group that can form hydrogen bonds.
 The hydroxyl group is hydrophilic “water loving”
 The alkyl group of alcohols is hydrophobic “ water hating”
 As the number of the –OH group in alcohol increases, the solubility in water increases.
 The lower alcohols are completely miscible with water
Diols and triols are more soluble in water than monohydroxyalcohols.
 As the number of carbons in the alcohol increases, the solubility in water decreases.
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Chemistry Department
Physical Properties of Alcohols
2) Boiling Points of Alcohols
The boiling points increase with increase in molecular weights.
OH
>
>
OH
OH
 Alcohols have higher boiling points(b .p.) than alkanes of similar weight this is
due to the presence of hydrogen bonds between molecules of alcohols.
hydrogen bond
OH
>
OH
>
OH
>
Br
>
Melting & boiling points
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Increases in this direction
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Chemistry Department
3) Acidic Properties of Alcohols
 Alcohols are very weak acids
The hydroxyl proton of an alcohol is weakly acidic
A strong base can abstract the hydroxyl proton to give an alkoxide ion
B
R-O-H
R-O
CH3CH2OH
+ B-H
ClCH2CH2OH
CH3OH
15.5
PKa= 15.9
less acidic
15.3
most acidic
Electron-withdrawing group (-I) increase acidity
Electron-releasing group (+I) decrease acidity
Cl
Cl
Cl
OH
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Cl
>
OH
>
OH
>
H3CO
OH
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Chemistry Department
Synthesis (Preparation) of Alcohols
1- From Alkenes (Hydration and oxidation of alkenes)
H3O+
i) Hydration of alkenes
OH
+
major
minor
OH
OH
ii) Oxidation of alkenes
KMnO4
OH-/H2O
OH
cis glycol
2- From alkyl halide by nucleophilic substitution
(N.B. elimination of HX using base gives alkene
alcohol,KOH
heat
H3C C CH2
H
(elimination of HX using base gives alkene)
CH3CH2CH2Cl
dil OH-
CH3CH2CH2OH
(nucleophilic substitution gives alcohol)
or aq. KOH
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3- Reduction of aldehydes, ketones and carboxylic acids
O
H3C C H
H
i) LiAlH4
ii)
H3C C H
OH
H3O+
Aldehyde
Primary alcohol
O
H3C C CH3
i) LiAlH4 or NaBH4
ii) H3O+
H
H3C C CH3
OH
or H2/Pt
Ketone
O
H3C C OH
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Acid
Secondary alcohol
i) LiAlH4
ii) H3O
+
H
H3C C H
OH
Primary alcohol
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4Addition
ketones
of
Methanal (formaldehyde)
Aldehyde
Ketone
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Primary alcohol
Secondary alcohol
MgCl
O
CH3CCH3 +
Grignard compounds to aldehydes &
OH
H3C C CH3
OMgBr
H3C C CH3
H3O+
Tertiary alcohol
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Reaction of Alcohols
1. Dissociation of O-H Bond
A. Formation of Salt
CH3CH2OH
Na
H2
H3C C ONa
Sodium ethoxide
B.
Formation of Esters
H+
H+/ H2O
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2. Dissociation of C-O Bond i.e. cleavage of C‫ــــ‬OH bond
A. Elimination Reactions
CH3CH2OH
conc.H2SO4
H2C CH2
B. Substitution Reaction
CH3CH2OH
HCl/ ZnCl2
H3C CH2Cl
or SOCl2
or PCl3
or PCl5
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C. Oxidation Reactions
CH3CH2OH
O
H3C CH
Cu /
or PCC
Aldehyde
PCC ( Pridinium Chloro chromate) =
, CrO3. HCl
Primary alc.
N
CH3CH2OH
H3C
Primary alc.
OH
CH3CHCH3
Secondary alc.
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O
KMnO4
C-OH
Acid
Cu /
or KMnO4
or PCC
O
H3C C-CH3
Ketone
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Chemistry Department
Nomenclature and acidity of Phenols
Phenols (compounds having hydroxyl group directly attached to a benzene
ring ) are generally named as derivatives of the simplest member of the
family, phenol
Acidity :
 Alcohols and phenols have weak acidic properties.
 Phenols are much stronger acids than alcohols.
 Introduction of electron-withdrawing groups, such as NO2 or CN, on
the ring increases the acidity of phenols.
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OH
OH
OH
OH
OH
NO2 O2N
<
<
<
NO2
CH3
4- Methyl phenol
Cresol
pH > 10
OH
Phenol
pH= 10
NO2
<
NO2
NO2
p-Nitrophenol
pH= 7
2,4-Dinitrophenol
2,4,6-Trinitrophenol (Picric acid)
pH= 0.25
pH=4
OH
OH
CHO
COOH
Cl
2-Hydroxy-benzaldehyde
o-Hydroxybenzaldehyde (common)
Salicylaldehyde (common)
2-Hydroxy-benzoic acid
o-Hydroxybenzoic acid (common)
Salicylic acid (common)
NH2
3-Amino-5-chloro-phenol
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Chemistry Department
Synthesis of Phenols
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Reactions Phenols
Ethers formation
O
CrO3 / H+
O
p-Benzoquinone
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Chemistry Department
2. Electrophilic Substitution Reactions
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Chemistry Department
Home Work
KMnO4
OH-/H2O
MgCl
O
HCH +
O
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H3O+
H2C MgBr
H3O+
+
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Chemistry Department
4) The IUPAC name of
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
5) The IUPAC name of
is:
OH
is:
A) 3-Methyl-1-bromocyclohexanol
B) 2-Bromo-3-methylcyclohexanol
C) 4-Bromo-2-methylcyclohexanol
D) 3-Bromo-1-methylcyclohxanol
6) The most acidic compound is
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7) The common name of 2-methyl-2-propanol is:
A) Allyl alcohol
B) Isopropyl alcohol
C) tert-Butyl alcohol
D) Benzyl alcohol
8) The following reaction gives
A) 4-Ethylphenol
B) 2-Ethylphenol
C) Ethylphenyl ether
D) Ethylphenyl ketone
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9) The major product for the following reaction is
10) The product of the reaction shown below is
11) Which of the following compounds has the highest boiling point?
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Questions?