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When you know chemistry, there’s a new
level of looking at the world around you.
The voltage needed to create an electron is about one million
volts. This is the voltage that creates a bolt of lightning. This
voltage pushes electrons from the sky to the ground, but the
electrons are slowed down by the air. If they weren’t, it would
be possible that two electrons accelerated by a million volts
striking the ground would give off light of enough energy to
create a new electron.
Alcohol Chemistry
Alcohols are derivatives of hydrocarbons in which an –OH
group has replaced a hydrogen atom.
Alcohols have one or more hydroxyl (–OH)
functional groups
A family of compounds with the same general
formula, similar chemical properties and a graduation
in physical properties.
C5H11OH pentanol
C4H9OH butanol
C3H7OH propanol
C2H5OH ethanol
CH3OH methanol
C6H13OH hexanol
5
4
3
2
1
NameNo. of
carbon atoms
Molecular
formula
6
Chemistry
changes
the way
you look at
the world.
I found te
picture of
the eyes
but added
various
autoshape
objects.
They were
rotated
with the
Spin
Emphasis
effect,
which was
set to
repeat
using the
“Effect
Option”
menu.
Structure of alcohol
 Hydroxyl (OH) functional group
 Oxygen is sp3 hybridized
 O – H bond is polar
Classification of alcohol – monohydroxy derivative
 Primary: carbon with –OH is bonded to one other carbon.
 Secondary: carbon with –OH is bonded to two other carbons.
 Tertiary: carbon with –OH is bonded to three other carbons.
 Aromatic (phenol): -OH is bonded to a benzene ring.
OH
RH
H
OH
HH
H
OH
RH
R
OH
RR
R
Methanol 10
alcohol 20
alcohol 30
alcohol
CH3 CH
CH3
CH2OH
CH3 CH
OH
CH2CH3
CH3 C
CH3
CH3
OH
OH
Here I do two effects on
the text at the same time.
For example, I’m using
motion paths with either
a fade in zoom or a fade
out. On the original
slide, I followed this
animation with a movie
clip from the Matrix.
If you choose
to stay in this
class…
IUPAC Nomenclature – general rules
 Identify the parent chain: Longest chain having –OH group – Replace letter ‘e’
of parent alkane by letter ‘ol’ with the appropriate position number
before the name.
 Number the parent chain: Carbon having –OH group should have lowest
number.
 Name the substituents and place them alphabetically in front of the parent
chain.
 Assign stereochemistry (stereocenters present in molecule).
OH
H
H
3-methylbutan-1-ol
OH
H
OH
(S)-4-methylpentan-2-ol 2-methyl-4-phenylbutan-2-ol
1234
5
1
1
2
2
3
3
4
4
IUPAC Nomenclature – Polyhydroxy compounds
When there is more than one OH group, the name must specify the total number
and positions of the functional groups.
An alcohol with two OH groups is a diol, one with three OH groups is a triol, and
so on. Note that the ‘e’ on the end of the alkane root name is retained
12
4
OH
OH
1
23 OH
propane-1,2,3-triol
HO OH
ethane-1,2-diol
HO OH
ethane-1,2-diol
1
2
OH
OH
1
23 OH
HO
butane-1,2,3,4-tetraol
HO
OH
OH
OH
OH
OH
hexane-1,2,3,4,5,6-hexaol
(sorbitol)
IUPAC Nomenclature – cyclic alcohols
The ring is the parent chain, give number to the ring so as the hydroxyl group
carbon of the ring has lowest number.
The name of parent alcohol is cycloalkanol.
Arrange the substituents alphabetically before the name of parent alcohol
with number where they are attached.
OH
OH
OH
OH
OH
OH
cyclopropanol cyclobutanol cyclopentanol cyclohexanol
3-methylcyclohexanol3-methylcyclopentanol
When two OH groups or substituents are present and are attached to different C
atoms in the saturated ring, stereoisomers are possible then specify their
stereochemistry with number before the name of parent alcohol.
OH
HO
HO
OH
HO
OH
OH
HO
trans-cyclohexane-1,4-diolcis-cyclohexane-1,4-diol
Naming Alcohols CH3CHCHCH3
OH
CH3
3-methyl-2-butanol
1. Name the parent compound – 4 carbons = butane
2. Replace the –e with –ol = butanol
3. Number the parent chain to minimize number of carbon with the –OH
group = number from right to left
4. Identify, name, and number all substituents = methyl on C-3
OH
CH3
3-methylcyclohexanolOH must be at C-1
1. Name the parent compound – 6 carbon ring = cyclohexane
2. Replace the –e with –ol = cyclohexanol
3. Number the ring to minimize number of carbon with the –OH group =
number counter-clockwise.
4. Identify, name, and number all substituents = methyl on C-3
• R-O-H has a structure similar to that of water,
• Hydroxyl group is very polar,
• Hydrogen bonds can form readily.
Physical Properties of alcohols
Pure form
Aq. solution
Alcohols have abnormally high boiling
points relative to their molecular
weights due to their ability to hydrogen
bond. CH3
CH2
OH
CH3O CH3
CH3CH2CH3
bp -42 oC
bp -23 oC
bp +78.5 oC
Physical Properties of alcohols
Low molecular weight alcohols (up to 5-6
carbons) are soluble in water –
Because of polar nature of –OH group
CH3CH2OH very soluble
CH3OCH3 barely soluble
CH3CH2CH2CH2OH, 7 g per 100 mL
HOCH2CH2CH2CH2OH is very soluble
Solubility decreases as the size of the alkyl group increases -
Ratio of hydroxyl
groups to carbons in
the chain determines
solubility
Na+ Cl- Oil
droplet
Oil
droplet
S
O4
-
S
O4
-
S
O
4
-
S
O
4
-S
O
4
-
S
O
4
-
Acidic and basic properties of alcohol
Alcohols can act both so donate a proton (acts as a Brønsted acid) and accept a proton (acts
as Brønsted base). Aliphatic alcohols act as weak acids and bases.
pKa of alcohol is 13 - 16
O
H + H+ O
H
H
Protonation of alcohols by mineral acids is analogous to the formation of the oxonium
ion which is important for nucleophilic substitution reaction in which it converts –OH into
the molecule with a good leaving group (i.e. H2O)
R1
OHR2
R3
R1
HR2
R3
H
2Ocat.concH
2SO
4
R1
HH
H
R2 = R3 = H
Hg(OAc)2H2O
R1
HH
H
H HgOAc
R1
HR2
R3
B2H6
R1
HR2
R3
H B
H2O2/HO-
R1
H
R2
R3
X
HO
-
R1
R2
R3
O
R1 -H - aldehyde
H2/Pt, Pd, Ni, Ru
R1
R2
R3
O
ketone
R1
R2
R3
O
R1 -H - aldehyde
R1
R2
R3
O
ketone
R1
R2
R3
O
acid or its derivative
R1 - OH, OR, X, NR2, etc
or LiAlH4
NaBH4
MgBr
R2
R3
R4
R1
O
H
R4 -H - aldehyde
R4
R1
O
ketone
R
R1
O
acid or its derivative
R - OH, OR, X,
NR2, etc; R4 - H
1. 2.H3O+
Reduction
Reduction
Reduction
Hydration
Nucleophilic
Substitution
By using Grignard reagent
Epoxide
Synthesis/Preparations
of alcohols
From alkene – Hydration (acid catalyzed)
Reversible reaction
From alkene – Hydration (by using mercury(II) acetate)
Addition of water to the carbon-carbon double bond of an alkene produces an alcohol
From alkene – Hydration (by using borane in presence of alkaline peroxide)
Hydrolysis of alkyl halides
Reduction of aldehydes and ketones - Hydrogenation
Heterogeneous catalysis
Reduction of aldehydes and ketones – Hydride reducing agent
Synthesis of alcohol - Using Grignard reagent
H
OHR2
R3
MgBrR2
R3
H
H
O
H
Formaldehyde
R4
R1
O
ketone
R
R1
O
acid or its derivative
R - OH, OR, X, NR2, etc; R4 - H
1.
2.H3O+
R1
O
H
Aldehyde
MgBr
R2
R3
1.
2.H3O+
10
- alcohol
R1
OHR2
R3
H 20
- alcohol
MgBr
R2
R3
1.
2.H3O+
R1
OHR2
R3
R4 30
- alcohol
MgBr
R2
R3
1.
2.H3O+
R1
O
R2
R3
30
- alcohol
Synthesis by
using Grignard
Reagent
O
Epoxide R2
R3 OHMgBr
R2
R3
1.
2.H3O+
10
- alcohol
Reactions
of alcohols R
OH
HX
R
O
H
H R
X
Substitution - SN1 / SN2
HCl/ZnCl2
X = Br, I
Lucas Test - Zn2+
lewis acidR
Cl
H2SO4
R
O
H
H
H
R
-H2O
Dehydration
Elimination - E1 / E2
H2SO4 R
O
H
H
H
R OH R
O
H
R
-H2O
Williamson
synthesis
POCl3
py
R
O
H
P
H
O
Cl
Cl
R
Dehydration
2 Na
R
ONa
H
R1X R
O
H
R1
PBr3
SOCl2
R
O
H
P
H
Br
Br
Br-
R
Br
Synthesis of ether
R
O
H
S
H
O
Cl
Cl-
R
Cl
Synthesis of
alkyl halide
oxidation R
O
Reagent - Cu/heat, CrO3, H2CrO4,
Na2Cr2O7, KMnO4, PCC, PDC, COCl2,
HIO4, etc.aldehyde/ketone
R1COOH
R
O
C
H
O
R1
Ester synthesis
Alcohol
Reactions of
Alcohol
Substitution Reactions
Computation between
substitution product, and
elimination product.
But
substitution product is
major, because
elimination product will
undergo addition reaction
with HX.
Carbocation
rearrangement
Synthesis of alkyl halide – using PX3
Synthesis of alkyl halide – using SOCl2
Dehydration – using POCl3
Elimination – ring expansion of cyclic alcohols
To minimize the ring/angle strain
Dehydration
Carbocation
rearrangement
Saitzev’s rule of elimination reaction
Dehydration - Williamson ether synthesis
R OH + 2 Na2 R O-
Na+
+ H2
O H3C I O
CH3
+
Computation between
elimination & substitution
Alcohols are converted into ethers by the formation of corresponding alkoxide ion
followed by the reaction with alkyl halide, a reaction is known as Williamson ether
synthesis.
Alcohol
Aldehyde
NO REACTION
Ketone
Dehydration
If primary
If tertiary
If secondary
+ H+ and heat
Alkene CarbonylReduction
Oxidation
Oxidation of alcohol – important for functional group interconversion
Carboxylic acids
Oxidation of alcohol
Swern oxidation
Ester formation
The reaction between an alcohol and a carboxylic acid or acyl chloride produces an ester.
Reversible
An alternative method of preparing esters is the condensation reaction between an acyl
chloride and an alcohol in which HCl is eliminated. The librated HCl is neutralized by
weak base.
• What product would be formed from the reaction of the following?
a. 2-bromobutane and hydroxide ion
b. (R)-2-bromobutane and hydroxide ion
c. (S)-3-chlorohexane and hydroxide ion
d. 3-iodopentane and hydroxide ion
• Give the product formed from the reaction of each of the following alcohols with
a. an acidic solution of sodium dichromate:
b. by Swern oxidation of:
1. 3-pentanol 3. 2-methyl-2-pentanol 5. cyclohexanol
2. 1-pentanol 4. 2,4-hexanediol 6. 1,4-butanediol
Chemistry of Phenol
Phenols are compounds that have a hydroxyl group bonded directly to a benzene
or benzenoid ring i.e. on sp2 hybridized carbon atom.
The parent compound of this group, C6H5OH, called simply phenol.
OH
sp2
hybridized carbon
Aromatic ring
OH
OH
naphthalen-1-ol naphthalen-2-olphenol
Nomenclature of phenol derivatives
An old name for benzene was phene, and its hydroxyl derivative came to be called
phenol which acceptable name by IUPAC.
The names methyl phenols are also accepted by IUPAC, are known as o-, m-, and
p-cresol.
The common names for the two hydroxy derivatives of naphthalene are 1-
naphthol and 2-naphthol is also acceptable.
phenol
HO HO CH3
m-cresol
HO HO HO
HO
OH
OH
pyrocatechol resorcinol hydroquinone
1
2
3
4
5
6
1
2
3
4
5
6
1
2
3
4
5
6
(1,2-benzenediol) (1,3-benzenediol) (1,4-benzenediol)
OH
OH
naphthalen-1-ol
(1-Naphthol)
(-Naphthol)
naphthalen-2-ol
(1-Naphthol)
(-Naphthol)
For the compounds containing phenolic OH and carboxylic or acyl group, the
during predication of IUPAC nomenclature, Carboxyl and acyl groups are
consider as parent group and the phenolic hydroxyl is the substituent.
Numbering of the ring begins at the hydroxyl-substituted carbon and proceeds
in the direction that gives the lower number to the next substituted carbon.
Substituent's are cited in alphabetical order.
HO
Cl
HO Cl
A B
H3COC HOOC
OH
1
2
3
4
5
6
1
2
3
4
5
6
OH
1-(2-hydroxy-4-methylphenyl)ethanone 4-hydroxybenzoic acid
Resonance stabilization of phenoxide ion
Phenol is planar, with a C-O-H bond angle of 1090, which is almost the same as the
tetrahedral angle and not much different from the bond angle C-O-H (108.50) of
methanol.
The carbon–oxygen bond distance (136 pm) in phenol is slightly less than that in
methanol (142 pm). The shorter C-O bond length is observed due to the partial
double-bond character that results from conjugation of the unshared electron pair
of oxygen with the aromatic ring. This resonance is used to explain many
properties of phenol.
Some of them are listed here. The hydroxyl oxygen is less basic (less electron
density); the hydroxyl proton more acidic, in phenols than in alcohols;
Electrophiles attack the aromatic ring of phenols much faster than they attack
benzene.
O
phenol
H
O
H
O
H
O
H
O
H
Resonance structures of phenol(Stable)
(Stable)
Physical properties and acidic character
Because of acidic property of phenol, it was known as carbolic acid.
Phenols are more acidic than alcohols but less acidic than carboxylic acids.
The ionization constants pKa of carboxylic acids have of approximately 5; whereas
the pKa’s of alcohols are in the range of 16 to 20 and of phenol is 10.
The more acidic character of phenol than ethanol is explained by comparing the
ionization equilibria for phenol and ethanol.
phenol
H+
HO +
Na-
O
H3C
H2
C
O
H H3C
H2
C
O- + Ka = 10-16
(pKa = 16)
H++ Ka = 10-10
(pKa = 10)
ethanol ethoxide ion
phenoxide
1. The negative charge in ethoxide ion is localized on oxygen and is stabilized only
by solvation forces but the negative charge in phenoxide ion is stabilized both by
solvation and by electron delocalization (resonance effect of pi-electron of ring)
into the ring.
2. The OH group of phenol is attached to an sp2 carbon that is more
electronegative than the sp3 carbon to which the OH group of alcohol is attached.
Greater inductive electron withdrawal by the carbon stabilizes the conjugate base by
decreasing the electron density of its negatively charged oxygen.
O O OO-
Resonance structures of phenolate ion
OH
H+
+
phenol
The substituent attached to phenol ring affect the acidic character of it.
- electron donating group decreases the acidity because of less stabilization of
phenoxide ion intermediate
- -electron withdrawing substituent such as nitro group shows substantial change
in acidity.
Question
• Which one of the following has the lowest pKa?
• A) B)
• C) D)
Question
• Which of the following compounds is more acidic?
• A) o-Cresol
• B) o-Chlorophenol
• C) o-Methoxyphenol
• D) o-nitrophenol
• E) m-nitrophenol
PHENOL - REACTIONS OF THE OH GROUP
Water phenol is a weak acid
it dissolves very slightly in water to form a weak acidic solution
it is a stronger acid than aliphatic alcohols
the ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq) C6H5O¯(aq) + H+(aq)
NaOH phenol reacts with sodium hydroxide to form a salt - sodium phenoxide
it is ionic and water soluble
C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l)
Sodium phenol reacts with sodium to form an ionic salt - sodium phenoxide
hydrogen is also produced
this reaction is similar to that with aliphatic alcohols such as ethanol
2C6H5OH(s) + 2Na(s) ——> 2C6H5O¯ Na+(s) + H2(g)
Physical properties and acidic character
The physical properties of phenols are strongly influenced by the hydroxyl group, which
permits phenols to form hydrogen bonds with other phenol molecules and with
polar molecules like water, alcohol and carboxylic acid.
 Phenols have higher melting points and boiling points.
 Phenols are more soluble in water than arenes and aryl halides of comparable
molecular weight.
 The hydroxyl oxygen is less basic (less electron density), and the hydroxyl proton
more acidic, in phenols than in alcohols.
O
H
O
H
O
H
O
H
O
H
Intermolecular H-bonding - phenol
O
Intermolecular H-bonding - aq. phenol
H
O
H
O
H
O
H O
H
OH
H O H
H
O
H
H
O
H
H
Intramolecular H-bonding - o-nitrophenol, salicylic acid
O H
N O
O
O H
O
O
H
Preparation of phenols
Pyrolysis of sodium benzene sulfonate
phenol
H+
HO+
Na-
OHO3S NaO3S
NaOH
3500
NaOH
H2O H2O
In this process, benzene sulfonic acid is reacted with aqueous sodium hydroxide.
The resulting salt is mixed with solid sodium hydroxide and fused at a high
temperature. The reaction proceeds by the addition-elimination mechanism of
nucleophilic aromatic substitution.
Preparation of phenols
Dow process
Cl
phenol
HO
3000
/3000 psi
dilute NaOH
1-chlorobenzene
In the Dow process, chlorobenzene is reacted with dilute sodium hydroxide at
300°C and 3000 psi pressure. It is Nucleophilic substitution reaction.
Preparation of phenols
Air oxidation of cumene
HO
phenol
H
H3C CH3
cumene
O2
100-1300
O
H3C CH3
O H
H3O+ O
H3C CH3
+
Cumene
hydroperoxide
The mechanism for the formation and degradation of cumene hydroperoxide is
given below. The cumene hydroperoxide was formed by a free radical chain
reaction. A radical initiator abstracts a hydrogen from cumene lead to formation of
a tertiary free radical. The creation of the tertiary free radical is the initial step in the
reaction.
H
H3C CH3
cumene
O2
100-1300
O
H3C
CH3
O H
+
Cumene
hydroperoxide
+ R
-RH
H3C CH3
O
H3C CH3
O
H
H3C CH3
cumene
+
H3C CH3
Initiation
Preparation of phenols
Air oxidation of cumene
The cumene hydroperoxide undergoes degradation in presence of acid catalyst. In
the first step, a pair of electrons on the oxygen of the hydroperoxide’s “hydroxyl
group” is attracted to a proton of the H3O+ molecule, forming an oxonium ion
which undergoes dehydration forming new oxonium ion. A phenide ion shift to
the oxygen atom (which creates a tertiary carbocation) stabilizes the positively
charged oxygen. The carbocation is stabilized by an acid-base reaction with a water
molecule, leading to the formation of an intermediate which undergoes degradation
in presence of acid catalyst forming phenol and acetone.
HO
phenol
O
H3C CH3
O H
O
H3C CH3
+
Cumene
hydroperoxide
H+ O
H3C CH3
O
H
H
O+
H3C CH3
O
HH+
H3C
CH3
O
O
HH
CH3
CH3O
O
HH
CH3
CH3O
O H -H+
CH3
CH3O
O H H+
H
oxonium ion
Preparation of phenols
Synthesis from aniline
HO NO2
3-nitrophenol
H2N NO2
1. NaNO2, H2SO4, H2O
2. H2O, heat
3-nitrobenzenamine
The most important synthesis of phenols in the laboratory is from amines by
hydrolysis of their corresponding diazonium salts, as shown below.
Reactions of phenols
Isomerisation
HO
phenol
(enol form - stable)
O
H H
(keto form)
[Tautomerism of phenol]
Phenol is unusual in that its enol tautomer is more stable than its keto tautomer
because the enol tautomer is aromatic, but the keto tautomer is not.
Reactions of phenols
Although a hydroxyl group strongly activates an aromatic ring toward electrophilic
attack, an oxyanion substituent is an even more powerful activator. Electron
delocalization in phenoxide anion leads to increased electron density at the
positions ortho and para to oxygen.
-
O
phenoxide
HO
phenol
+H+
O O O
Resonance stabilization of
negative charge
Reactions of phenols
Electrophilic substitution reactions
HO
phenol
+ Y+
OH
OH
OH
H
Y
Y
H
Y H
ortho
meta
para
OH
H
Y
OH
H
Y
OH
H
Y
OH
OH
Y
H
Y H
OH
OH
Y
H
Y H
OH
Y H
Relatively
stable
Relatively
stable
The electrophile attacks either on hydroxyl oxygen or the aromatic ring, therefore
the reactions of phenols classified in two types – electrophilic aromatic substitution
and O – substitution reactions.
The –OH group is activating so the electrophilic substitution occurs at o- and or p-
position rather than meta-position which can be explain by the stabilization of
intermediate cation as below.
Reactions of phenols
HO
phenol
Br2
Br2
ClCH2
CH2
Cl
00
H2O, 250
HO
HO
Br
Br
Br Br
4-bromophenol
2,4,6-tribromophenol
Bromination
Nitration
HO
NO2
HO
HNO3
acetic acid
50O2N
4-nitrophenol
+
2-nitrophenol
Sulfonation
HO
SO3H
H2SO4 1000
+ HO
SO3H
Friedel-Crafts alkylation
HO
C(CH3)3
(CH 3
) 3
COH
H 3
PO 4
, 60
0
Friedel-Crafts acylation
Cl
O
HO
O
OH O
+
AlCl3
(74%) (16%)
Reactions of phenols
Nitrosation:
On acidification of aqueous solutions of sodium nitrite, the nitrosonium ion (:N≡O+)
is formed, which is a weak electrophile and attacks the strongly activated ring of a
phenol. The product is a nitroso phenol
OH
HNO2, H2SO4, H2O
00
C
OH
N
O
naphthalen-2-ol
1-nitrosonaphthalen-2-ol
(99%)
Reactions of phenols
Reaction with arenediazonium salts:
Adding a phenol to a solution of a diazonium salt formed from a primary aromatic
amine leads to formation of an azo compound. The reaction is carried out at a pH
such that a significant portion of the phenol is present as its phenoxide ion. The
diazonium ion acts as an electrophile toward the strongly activated ring of the
phenoxide ion.
OH
00
C
OH
N
N
naphthalen-2-ol
C6H5N2Cl
C6H5
(E)-1-(phenyldiazenyl)
naphthalen-2-ol
OH
N
N
C6H5
+
(Z)-1-(phenyldiazenyl)
naphthalen-2-ol
Reactions of phenols
Kolbe–Schmitt carboxylation reaction (synthesis of aspirin):
The best known aryl ester is O-acetylsalicylic acid, better known as aspirin. The first
step in the industrial synthesis of aspirin is known as the Kolbe–Schmitt
carboxylation reaction.
The phenolate ion reacts with carbon dioxide under pressure followed by the
treatment of acid to form o-hydroxybenzoic acid, also known as salicylic acid.
Acetylation of salicylic acid with acetic acid anhydride forms acetylsalicylic acid
(aspirin)
O O
O-
Salicylic acid
O
O
O
HO
phenol
base
-
O
phenoxide
+ O C O
pressure
H+
OH O
OH
Acetyl salicylic acid
aspirin
O O
OH
O
OH O
O-
H
Reactions of phenols
The Kolbe–Schmitt reaction is an equilibrium process governed by thermodynamic
control.
Salicylate anion
HO
phenol
HO
O
O-
base
-
O
phenoxide
+ O C O
OH O
O-
rather
than
O O-
O
H
strong base: ka
of conjugate acid,
10-10
weakest base: ka
of conjugate acid,
1.06 x 10-3
a base: ka of conjugate
acid, 3.3 x 10-5
p-hydroxybenzoate
anion
intra-molecular Hydrogen
bonding in salicylate anion
Reactions of phenols
Synthesis of aryl ethers:
Aryl ethers are best prepared by the Williamson method. Alkylation of the
hydroxyl oxygen of a phenol takes place readily by treating a phenoxide anion with
an alkyl halide. The synthesis is normally performed only by heating a solution of
the phenol and alkyl halide in the presence of a suitable base such as potassium
carbonate.
Allyl aryl ethers undergo an interesting reaction, called the Claisen
rearrangement, on being heated. The allyl group migrates from oxygen to the ring
carbon ortho to it.
HO
phenol
+
base
-
O
phenoxide
SN2 O
allyl phenyl ether
Br
K2CO3
acetone
allyl
bromide
HO
phenol
+
O
allyl phenyl ether
Br
K2CO3
acetone
allyl
bromide
HO
o-allyl phenol
(73%)
*
*
O
*
O
*
H
rearrangement
aromatization
*
Reactions of phenols
Acylation of phenol
Acylation agents, such as acyl chlorides and carboxylic acid anhydrides, can react with
phenols either at the aromatic ring (C-acylation) or at the hydroxyl oxygen (O-acylation):
O
R
O
OH O
R
HO
R Cl
O
+
phenol
O
R O R
O
+
Aryl ester
(O-acylation)
HO
O
R
Aryl ketones
(C-acylation)
Friedel Craft reaction
In the absence of aluminum chloride (lewis acid), however, O-acylation occurs instead.
HO
C7H15 Cl
O
+
NaOH/H2O O
O
C7H15
+ HCl
phenol phenyl octanoate
OH O
O
O
+
O
O
+ sodium acetate
H2SO4
F F
4-fluorophenol 4-fluorophenyl acetate
(84%)
HO OH O
O
O
+
NaOH/H2O
2
O O
O
O
+ sodium acetate
resorcinol 1,3-diacetoxybenzene
Acid anhydride to a more powerful acylating agent by protonation of one of its carbonyl
oxygens. Addition of a few drops of sulfuric acid is usually sufficient.
Synthesis of aryl ethers:
the Fries rearrangement
The C-acyl isomers are more stable, which will be formed more effectively by
using aluminum chloride as catalyst. It is more effective catalyst for the conversion
of aryl esters to aryl ketones. This isomerization is called the Fries rearrangement.
O
C6H5
O
OH O
C6H5
HO
O
C6H5
AlCl3
+
phenyl benzoate o-hydroxybenzophenone p-hydroxybenzophenone
(9%) (64%)
Give each of the following compounds a systematic name, and indicate whether
each is a primary, secondary, or tertiary alcohol:
OH
HO
OH
Cl
OH OH Cl
OH
(a) (b) (c)
(d)
(e) (f)
• Write structural formulas for each of the following compounds:
(a) Pyrogallol (1,2,3-benzenetriol) (c) 3-Nitro-1-naphthol
(b) o-Benzylphenol (d) 4-Chlororesorcinol
OH
HO
OH
Cl
OH OH
Cl
OH
(a) (b) (c)
(d) (e) (f)
pentan-1-ol 4-methylcyclohexanol 5-chloro-2-methylpentan-2-ol
5-methylhexan-3-ol 2,6-dimethyloctan-4-ol 4-chloro-3-ethylcyclohexanol
OH
OH
OH
OH
NO2
OH
HO OH
Cl
benzene-1,2,3-triol 3-nitronaphthalen-1-ol 2-benzylphenol 4-chlorobenzene-1,3-diol
•Give the major product obtained from the acid-catalyzed hydration of each of the
following alkenes:
(a) (b)
(c) (d)
(a) (b)
(c) (d)
OH OH
OH
OH
+
OH
Problems
Give the major product obtained of the following reactions -
(a)
(b)
(c)
(d)
OH
OCH3
+ Br K2CO3
acetone
ONa
+
OH
Cl OH
CHO
HO
OCH3
HNO3, acetic acid, heat
H
N
O
O
heat
(a)
(b)
(c)
(d)
OH
OCH3
+ Br K2CO3
acetone
ONa
+
OH
Cl OH
CHO
HO
OCH3
HNO3, acetic acid, heat
H
N
O
O
heat
O
OCH3
O
OH
OH
CHO
HO
OCH3
O2N
H
N
O
OH
Reactions of phenols
• Write a balanced chemical equation for each of the following reactions:
(a) Phenol - sodium hydroxide
(b) Product of part (a) + ethyl bromide
(c) Product of part (a) + butyl p-toluenesulfonate
(d) Product of part (a) + acetic anhydride
(e) o-Cresol + benzoyl chloride
(f) m-Cresol + ethylene oxide
(g) 2,6-Dichlorophenol + bromine
(h) p-Cresol + excess aqueous bromine
(a) (b) (c) (d)
(e) (f)
ONa O
(g) (h)
O
S
O
O
O
O
O
O
O
OH OH
Cl
Cl
Br
OH
Br
Br
Give the product formed from the reaction of each of the following alcohols with
a. an acidic solution of sodium dichromate:
b. the reagents required for a Swern oxidation:
1. 3-pentanol
2. 2-methyl-2-pentanol
3. Cyclohexanol
4. 1-pentanol
5. 2,4-hexanediol
6. 1,4-butanediol
Write chemical equations, showing all necessary reagents, for the preparation of 1-
butanol by each of the following methods:
(a) Hydroboration–oxidation of an alkene
(b) Use of a Grignard reagent
(c) Use of a Grignard reagent in a way different from part (b)
(d) Reduction of a carboxylic acid
(e) Reduction of a methyl ester
(f) Reduction of a butyl ester
(g) Hydrogenation of an aldehyde
(h) Reduction with sodium borohydride
Write structural formulas for each of the following compounds:
(a) Pyrogallol (1,2,3-benzenetriol) (c) 3-Nitro-1-naphthol
(b) o-Benzylphenol (d) 4-Chlororesorcinol
Which is the stronger acid in each of the following pairs? Explain your reasoning.
(a) Phenol or p-hydroxybenzaldehyde
(b) m-Cyanophenol or p-cyanophenol
(c) o-Fluorophenol or p-fluorophenol
Write a balanced chemical equation for each of the following reactions:
(a) Phenol _ sodium hydroxide
(b) Product of part (a) + ethyl bromide
(c) Product of part (a) + butyl p-toluenesulfonate
(d) Product of part (a) + acetic anhydride
(e) o-Cresol + benzoyl chloride
(f) m-Cresol + ethylene oxide
(g) 2,6-Dichlorophenol + bromine
(h) p-Cresol + excess aqueous bromine

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Alcohol chemistry

  • 1.
  • 2. When you know chemistry, there’s a new level of looking at the world around you.
  • 3. The voltage needed to create an electron is about one million volts. This is the voltage that creates a bolt of lightning. This voltage pushes electrons from the sky to the ground, but the electrons are slowed down by the air. If they weren’t, it would be possible that two electrons accelerated by a million volts striking the ground would give off light of enough energy to create a new electron.
  • 4. Alcohol Chemistry Alcohols are derivatives of hydrocarbons in which an –OH group has replaced a hydrogen atom. Alcohols have one or more hydroxyl (–OH) functional groups A family of compounds with the same general formula, similar chemical properties and a graduation in physical properties. C5H11OH pentanol C4H9OH butanol C3H7OH propanol C2H5OH ethanol CH3OH methanol C6H13OH hexanol 5 4 3 2 1 NameNo. of carbon atoms Molecular formula 6
  • 5. Chemistry changes the way you look at the world. I found te picture of the eyes but added various autoshape objects. They were rotated with the Spin Emphasis effect, which was set to repeat using the “Effect Option” menu.
  • 6. Structure of alcohol  Hydroxyl (OH) functional group  Oxygen is sp3 hybridized  O – H bond is polar Classification of alcohol – monohydroxy derivative  Primary: carbon with –OH is bonded to one other carbon.  Secondary: carbon with –OH is bonded to two other carbons.  Tertiary: carbon with –OH is bonded to three other carbons.  Aromatic (phenol): -OH is bonded to a benzene ring. OH RH H OH HH H OH RH R OH RR R Methanol 10 alcohol 20 alcohol 30 alcohol CH3 CH CH3 CH2OH CH3 CH OH CH2CH3 CH3 C CH3 CH3 OH OH
  • 7. Here I do two effects on the text at the same time. For example, I’m using motion paths with either a fade in zoom or a fade out. On the original slide, I followed this animation with a movie clip from the Matrix. If you choose to stay in this class…
  • 8. IUPAC Nomenclature – general rules  Identify the parent chain: Longest chain having –OH group – Replace letter ‘e’ of parent alkane by letter ‘ol’ with the appropriate position number before the name.  Number the parent chain: Carbon having –OH group should have lowest number.  Name the substituents and place them alphabetically in front of the parent chain.  Assign stereochemistry (stereocenters present in molecule). OH H H 3-methylbutan-1-ol OH H OH (S)-4-methylpentan-2-ol 2-methyl-4-phenylbutan-2-ol 1234 5 1 1 2 2 3 3 4 4
  • 9. IUPAC Nomenclature – Polyhydroxy compounds When there is more than one OH group, the name must specify the total number and positions of the functional groups. An alcohol with two OH groups is a diol, one with three OH groups is a triol, and so on. Note that the ‘e’ on the end of the alkane root name is retained 12 4 OH OH 1 23 OH propane-1,2,3-triol HO OH ethane-1,2-diol HO OH ethane-1,2-diol 1 2 OH OH 1 23 OH HO butane-1,2,3,4-tetraol HO OH OH OH OH OH hexane-1,2,3,4,5,6-hexaol (sorbitol)
  • 10. IUPAC Nomenclature – cyclic alcohols The ring is the parent chain, give number to the ring so as the hydroxyl group carbon of the ring has lowest number. The name of parent alcohol is cycloalkanol. Arrange the substituents alphabetically before the name of parent alcohol with number where they are attached. OH OH OH OH OH OH cyclopropanol cyclobutanol cyclopentanol cyclohexanol 3-methylcyclohexanol3-methylcyclopentanol When two OH groups or substituents are present and are attached to different C atoms in the saturated ring, stereoisomers are possible then specify their stereochemistry with number before the name of parent alcohol. OH HO HO OH HO OH OH HO trans-cyclohexane-1,4-diolcis-cyclohexane-1,4-diol
  • 11. Naming Alcohols CH3CHCHCH3 OH CH3 3-methyl-2-butanol 1. Name the parent compound – 4 carbons = butane 2. Replace the –e with –ol = butanol 3. Number the parent chain to minimize number of carbon with the –OH group = number from right to left 4. Identify, name, and number all substituents = methyl on C-3 OH CH3 3-methylcyclohexanolOH must be at C-1 1. Name the parent compound – 6 carbon ring = cyclohexane 2. Replace the –e with –ol = cyclohexanol 3. Number the ring to minimize number of carbon with the –OH group = number counter-clockwise. 4. Identify, name, and number all substituents = methyl on C-3
  • 12.
  • 13. • R-O-H has a structure similar to that of water, • Hydroxyl group is very polar, • Hydrogen bonds can form readily. Physical Properties of alcohols Pure form Aq. solution
  • 14. Alcohols have abnormally high boiling points relative to their molecular weights due to their ability to hydrogen bond. CH3 CH2 OH CH3O CH3 CH3CH2CH3 bp -42 oC bp -23 oC bp +78.5 oC Physical Properties of alcohols Low molecular weight alcohols (up to 5-6 carbons) are soluble in water – Because of polar nature of –OH group CH3CH2OH very soluble CH3OCH3 barely soluble CH3CH2CH2CH2OH, 7 g per 100 mL HOCH2CH2CH2CH2OH is very soluble Solubility decreases as the size of the alkyl group increases - Ratio of hydroxyl groups to carbons in the chain determines solubility
  • 16. Acidic and basic properties of alcohol Alcohols can act both so donate a proton (acts as a Brønsted acid) and accept a proton (acts as Brønsted base). Aliphatic alcohols act as weak acids and bases. pKa of alcohol is 13 - 16 O H + H+ O H H Protonation of alcohols by mineral acids is analogous to the formation of the oxonium ion which is important for nucleophilic substitution reaction in which it converts –OH into the molecule with a good leaving group (i.e. H2O)
  • 17. R1 OHR2 R3 R1 HR2 R3 H 2Ocat.concH 2SO 4 R1 HH H R2 = R3 = H Hg(OAc)2H2O R1 HH H H HgOAc R1 HR2 R3 B2H6 R1 HR2 R3 H B H2O2/HO- R1 H R2 R3 X HO - R1 R2 R3 O R1 -H - aldehyde H2/Pt, Pd, Ni, Ru R1 R2 R3 O ketone R1 R2 R3 O R1 -H - aldehyde R1 R2 R3 O ketone R1 R2 R3 O acid or its derivative R1 - OH, OR, X, NR2, etc or LiAlH4 NaBH4 MgBr R2 R3 R4 R1 O H R4 -H - aldehyde R4 R1 O ketone R R1 O acid or its derivative R - OH, OR, X, NR2, etc; R4 - H 1. 2.H3O+ Reduction Reduction Reduction Hydration Nucleophilic Substitution By using Grignard reagent Epoxide Synthesis/Preparations of alcohols
  • 18. From alkene – Hydration (acid catalyzed) Reversible reaction From alkene – Hydration (by using mercury(II) acetate) Addition of water to the carbon-carbon double bond of an alkene produces an alcohol
  • 19. From alkene – Hydration (by using borane in presence of alkaline peroxide)
  • 21. Reduction of aldehydes and ketones - Hydrogenation Heterogeneous catalysis
  • 22. Reduction of aldehydes and ketones – Hydride reducing agent
  • 23. Synthesis of alcohol - Using Grignard reagent H OHR2 R3 MgBrR2 R3 H H O H Formaldehyde R4 R1 O ketone R R1 O acid or its derivative R - OH, OR, X, NR2, etc; R4 - H 1. 2.H3O+ R1 O H Aldehyde MgBr R2 R3 1. 2.H3O+ 10 - alcohol R1 OHR2 R3 H 20 - alcohol MgBr R2 R3 1. 2.H3O+ R1 OHR2 R3 R4 30 - alcohol MgBr R2 R3 1. 2.H3O+ R1 O R2 R3 30 - alcohol Synthesis by using Grignard Reagent O Epoxide R2 R3 OHMgBr R2 R3 1. 2.H3O+ 10 - alcohol
  • 24. Reactions of alcohols R OH HX R O H H R X Substitution - SN1 / SN2 HCl/ZnCl2 X = Br, I Lucas Test - Zn2+ lewis acidR Cl H2SO4 R O H H H R -H2O Dehydration Elimination - E1 / E2 H2SO4 R O H H H R OH R O H R -H2O Williamson synthesis POCl3 py R O H P H O Cl Cl R Dehydration 2 Na R ONa H R1X R O H R1 PBr3 SOCl2 R O H P H Br Br Br- R Br Synthesis of ether R O H S H O Cl Cl- R Cl Synthesis of alkyl halide oxidation R O Reagent - Cu/heat, CrO3, H2CrO4, Na2Cr2O7, KMnO4, PCC, PDC, COCl2, HIO4, etc.aldehyde/ketone R1COOH R O C H O R1 Ester synthesis Alcohol Reactions of Alcohol
  • 25. Substitution Reactions Computation between substitution product, and elimination product. But substitution product is major, because elimination product will undergo addition reaction with HX. Carbocation rearrangement
  • 26. Synthesis of alkyl halide – using PX3 Synthesis of alkyl halide – using SOCl2
  • 27. Dehydration – using POCl3 Elimination – ring expansion of cyclic alcohols To minimize the ring/angle strain
  • 29. Dehydration - Williamson ether synthesis R OH + 2 Na2 R O- Na+ + H2 O H3C I O CH3 + Computation between elimination & substitution Alcohols are converted into ethers by the formation of corresponding alkoxide ion followed by the reaction with alkyl halide, a reaction is known as Williamson ether synthesis.
  • 30. Alcohol Aldehyde NO REACTION Ketone Dehydration If primary If tertiary If secondary + H+ and heat Alkene CarbonylReduction Oxidation Oxidation of alcohol – important for functional group interconversion Carboxylic acids
  • 32. Ester formation The reaction between an alcohol and a carboxylic acid or acyl chloride produces an ester. Reversible An alternative method of preparing esters is the condensation reaction between an acyl chloride and an alcohol in which HCl is eliminated. The librated HCl is neutralized by weak base.
  • 33. • What product would be formed from the reaction of the following? a. 2-bromobutane and hydroxide ion b. (R)-2-bromobutane and hydroxide ion c. (S)-3-chlorohexane and hydroxide ion d. 3-iodopentane and hydroxide ion • Give the product formed from the reaction of each of the following alcohols with a. an acidic solution of sodium dichromate: b. by Swern oxidation of: 1. 3-pentanol 3. 2-methyl-2-pentanol 5. cyclohexanol 2. 1-pentanol 4. 2,4-hexanediol 6. 1,4-butanediol
  • 34. Chemistry of Phenol Phenols are compounds that have a hydroxyl group bonded directly to a benzene or benzenoid ring i.e. on sp2 hybridized carbon atom. The parent compound of this group, C6H5OH, called simply phenol. OH sp2 hybridized carbon Aromatic ring OH OH naphthalen-1-ol naphthalen-2-olphenol
  • 35. Nomenclature of phenol derivatives An old name for benzene was phene, and its hydroxyl derivative came to be called phenol which acceptable name by IUPAC. The names methyl phenols are also accepted by IUPAC, are known as o-, m-, and p-cresol. The common names for the two hydroxy derivatives of naphthalene are 1- naphthol and 2-naphthol is also acceptable. phenol HO HO CH3 m-cresol HO HO HO HO OH OH pyrocatechol resorcinol hydroquinone 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 (1,2-benzenediol) (1,3-benzenediol) (1,4-benzenediol) OH OH naphthalen-1-ol (1-Naphthol) (-Naphthol) naphthalen-2-ol (1-Naphthol) (-Naphthol)
  • 36. For the compounds containing phenolic OH and carboxylic or acyl group, the during predication of IUPAC nomenclature, Carboxyl and acyl groups are consider as parent group and the phenolic hydroxyl is the substituent. Numbering of the ring begins at the hydroxyl-substituted carbon and proceeds in the direction that gives the lower number to the next substituted carbon. Substituent's are cited in alphabetical order. HO Cl HO Cl A B H3COC HOOC OH 1 2 3 4 5 6 1 2 3 4 5 6 OH 1-(2-hydroxy-4-methylphenyl)ethanone 4-hydroxybenzoic acid
  • 37. Resonance stabilization of phenoxide ion Phenol is planar, with a C-O-H bond angle of 1090, which is almost the same as the tetrahedral angle and not much different from the bond angle C-O-H (108.50) of methanol. The carbon–oxygen bond distance (136 pm) in phenol is slightly less than that in methanol (142 pm). The shorter C-O bond length is observed due to the partial double-bond character that results from conjugation of the unshared electron pair of oxygen with the aromatic ring. This resonance is used to explain many properties of phenol. Some of them are listed here. The hydroxyl oxygen is less basic (less electron density); the hydroxyl proton more acidic, in phenols than in alcohols; Electrophiles attack the aromatic ring of phenols much faster than they attack benzene. O phenol H O H O H O H O H Resonance structures of phenol(Stable) (Stable)
  • 38. Physical properties and acidic character Because of acidic property of phenol, it was known as carbolic acid. Phenols are more acidic than alcohols but less acidic than carboxylic acids. The ionization constants pKa of carboxylic acids have of approximately 5; whereas the pKa’s of alcohols are in the range of 16 to 20 and of phenol is 10. The more acidic character of phenol than ethanol is explained by comparing the ionization equilibria for phenol and ethanol. phenol H+ HO + Na- O H3C H2 C O H H3C H2 C O- + Ka = 10-16 (pKa = 16) H++ Ka = 10-10 (pKa = 10) ethanol ethoxide ion phenoxide
  • 39. 1. The negative charge in ethoxide ion is localized on oxygen and is stabilized only by solvation forces but the negative charge in phenoxide ion is stabilized both by solvation and by electron delocalization (resonance effect of pi-electron of ring) into the ring. 2. The OH group of phenol is attached to an sp2 carbon that is more electronegative than the sp3 carbon to which the OH group of alcohol is attached. Greater inductive electron withdrawal by the carbon stabilizes the conjugate base by decreasing the electron density of its negatively charged oxygen. O O OO- Resonance structures of phenolate ion OH H+ + phenol The substituent attached to phenol ring affect the acidic character of it. - electron donating group decreases the acidity because of less stabilization of phenoxide ion intermediate - -electron withdrawing substituent such as nitro group shows substantial change in acidity.
  • 40. Question • Which one of the following has the lowest pKa? • A) B) • C) D)
  • 41. Question • Which of the following compounds is more acidic? • A) o-Cresol • B) o-Chlorophenol • C) o-Methoxyphenol • D) o-nitrophenol • E) m-nitrophenol
  • 42. PHENOL - REACTIONS OF THE OH GROUP Water phenol is a weak acid it dissolves very slightly in water to form a weak acidic solution it is a stronger acid than aliphatic alcohols the ring helps weaken the O-H bond and stabilises the resulting anion C6H5OH(aq) C6H5O¯(aq) + H+(aq) NaOH phenol reacts with sodium hydroxide to form a salt - sodium phenoxide it is ionic and water soluble C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l) Sodium phenol reacts with sodium to form an ionic salt - sodium phenoxide hydrogen is also produced this reaction is similar to that with aliphatic alcohols such as ethanol 2C6H5OH(s) + 2Na(s) ——> 2C6H5O¯ Na+(s) + H2(g)
  • 43. Physical properties and acidic character The physical properties of phenols are strongly influenced by the hydroxyl group, which permits phenols to form hydrogen bonds with other phenol molecules and with polar molecules like water, alcohol and carboxylic acid.  Phenols have higher melting points and boiling points.  Phenols are more soluble in water than arenes and aryl halides of comparable molecular weight.  The hydroxyl oxygen is less basic (less electron density), and the hydroxyl proton more acidic, in phenols than in alcohols. O H O H O H O H O H Intermolecular H-bonding - phenol O Intermolecular H-bonding - aq. phenol H O H O H O H O H OH H O H H O H H O H H Intramolecular H-bonding - o-nitrophenol, salicylic acid O H N O O O H O O H
  • 44. Preparation of phenols Pyrolysis of sodium benzene sulfonate phenol H+ HO+ Na- OHO3S NaO3S NaOH 3500 NaOH H2O H2O In this process, benzene sulfonic acid is reacted with aqueous sodium hydroxide. The resulting salt is mixed with solid sodium hydroxide and fused at a high temperature. The reaction proceeds by the addition-elimination mechanism of nucleophilic aromatic substitution.
  • 45. Preparation of phenols Dow process Cl phenol HO 3000 /3000 psi dilute NaOH 1-chlorobenzene In the Dow process, chlorobenzene is reacted with dilute sodium hydroxide at 300°C and 3000 psi pressure. It is Nucleophilic substitution reaction.
  • 46. Preparation of phenols Air oxidation of cumene HO phenol H H3C CH3 cumene O2 100-1300 O H3C CH3 O H H3O+ O H3C CH3 + Cumene hydroperoxide The mechanism for the formation and degradation of cumene hydroperoxide is given below. The cumene hydroperoxide was formed by a free radical chain reaction. A radical initiator abstracts a hydrogen from cumene lead to formation of a tertiary free radical. The creation of the tertiary free radical is the initial step in the reaction. H H3C CH3 cumene O2 100-1300 O H3C CH3 O H + Cumene hydroperoxide + R -RH H3C CH3 O H3C CH3 O H H3C CH3 cumene + H3C CH3 Initiation
  • 47. Preparation of phenols Air oxidation of cumene The cumene hydroperoxide undergoes degradation in presence of acid catalyst. In the first step, a pair of electrons on the oxygen of the hydroperoxide’s “hydroxyl group” is attracted to a proton of the H3O+ molecule, forming an oxonium ion which undergoes dehydration forming new oxonium ion. A phenide ion shift to the oxygen atom (which creates a tertiary carbocation) stabilizes the positively charged oxygen. The carbocation is stabilized by an acid-base reaction with a water molecule, leading to the formation of an intermediate which undergoes degradation in presence of acid catalyst forming phenol and acetone. HO phenol O H3C CH3 O H O H3C CH3 + Cumene hydroperoxide H+ O H3C CH3 O H H O+ H3C CH3 O HH+ H3C CH3 O O HH CH3 CH3O O HH CH3 CH3O O H -H+ CH3 CH3O O H H+ H oxonium ion
  • 48. Preparation of phenols Synthesis from aniline HO NO2 3-nitrophenol H2N NO2 1. NaNO2, H2SO4, H2O 2. H2O, heat 3-nitrobenzenamine The most important synthesis of phenols in the laboratory is from amines by hydrolysis of their corresponding diazonium salts, as shown below.
  • 49. Reactions of phenols Isomerisation HO phenol (enol form - stable) O H H (keto form) [Tautomerism of phenol] Phenol is unusual in that its enol tautomer is more stable than its keto tautomer because the enol tautomer is aromatic, but the keto tautomer is not.
  • 50. Reactions of phenols Although a hydroxyl group strongly activates an aromatic ring toward electrophilic attack, an oxyanion substituent is an even more powerful activator. Electron delocalization in phenoxide anion leads to increased electron density at the positions ortho and para to oxygen. - O phenoxide HO phenol +H+ O O O Resonance stabilization of negative charge
  • 51. Reactions of phenols Electrophilic substitution reactions HO phenol + Y+ OH OH OH H Y Y H Y H ortho meta para OH H Y OH H Y OH H Y OH OH Y H Y H OH OH Y H Y H OH Y H Relatively stable Relatively stable The electrophile attacks either on hydroxyl oxygen or the aromatic ring, therefore the reactions of phenols classified in two types – electrophilic aromatic substitution and O – substitution reactions. The –OH group is activating so the electrophilic substitution occurs at o- and or p- position rather than meta-position which can be explain by the stabilization of intermediate cation as below.
  • 52. Reactions of phenols HO phenol Br2 Br2 ClCH2 CH2 Cl 00 H2O, 250 HO HO Br Br Br Br 4-bromophenol 2,4,6-tribromophenol Bromination Nitration HO NO2 HO HNO3 acetic acid 50O2N 4-nitrophenol + 2-nitrophenol Sulfonation HO SO3H H2SO4 1000 + HO SO3H Friedel-Crafts alkylation HO C(CH3)3 (CH 3 ) 3 COH H 3 PO 4 , 60 0 Friedel-Crafts acylation Cl O HO O OH O + AlCl3 (74%) (16%)
  • 53. Reactions of phenols Nitrosation: On acidification of aqueous solutions of sodium nitrite, the nitrosonium ion (:N≡O+) is formed, which is a weak electrophile and attacks the strongly activated ring of a phenol. The product is a nitroso phenol OH HNO2, H2SO4, H2O 00 C OH N O naphthalen-2-ol 1-nitrosonaphthalen-2-ol (99%)
  • 54. Reactions of phenols Reaction with arenediazonium salts: Adding a phenol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound. The reaction is carried out at a pH such that a significant portion of the phenol is present as its phenoxide ion. The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion. OH 00 C OH N N naphthalen-2-ol C6H5N2Cl C6H5 (E)-1-(phenyldiazenyl) naphthalen-2-ol OH N N C6H5 + (Z)-1-(phenyldiazenyl) naphthalen-2-ol
  • 55. Reactions of phenols Kolbe–Schmitt carboxylation reaction (synthesis of aspirin): The best known aryl ester is O-acetylsalicylic acid, better known as aspirin. The first step in the industrial synthesis of aspirin is known as the Kolbe–Schmitt carboxylation reaction. The phenolate ion reacts with carbon dioxide under pressure followed by the treatment of acid to form o-hydroxybenzoic acid, also known as salicylic acid. Acetylation of salicylic acid with acetic acid anhydride forms acetylsalicylic acid (aspirin) O O O- Salicylic acid O O O HO phenol base - O phenoxide + O C O pressure H+ OH O OH Acetyl salicylic acid aspirin O O OH O OH O O- H
  • 56. Reactions of phenols The Kolbe–Schmitt reaction is an equilibrium process governed by thermodynamic control. Salicylate anion HO phenol HO O O- base - O phenoxide + O C O OH O O- rather than O O- O H strong base: ka of conjugate acid, 10-10 weakest base: ka of conjugate acid, 1.06 x 10-3 a base: ka of conjugate acid, 3.3 x 10-5 p-hydroxybenzoate anion intra-molecular Hydrogen bonding in salicylate anion
  • 57. Reactions of phenols Synthesis of aryl ethers: Aryl ethers are best prepared by the Williamson method. Alkylation of the hydroxyl oxygen of a phenol takes place readily by treating a phenoxide anion with an alkyl halide. The synthesis is normally performed only by heating a solution of the phenol and alkyl halide in the presence of a suitable base such as potassium carbonate. Allyl aryl ethers undergo an interesting reaction, called the Claisen rearrangement, on being heated. The allyl group migrates from oxygen to the ring carbon ortho to it. HO phenol + base - O phenoxide SN2 O allyl phenyl ether Br K2CO3 acetone allyl bromide HO phenol + O allyl phenyl ether Br K2CO3 acetone allyl bromide HO o-allyl phenol (73%) * * O * O * H rearrangement aromatization *
  • 58. Reactions of phenols Acylation of phenol Acylation agents, such as acyl chlorides and carboxylic acid anhydrides, can react with phenols either at the aromatic ring (C-acylation) or at the hydroxyl oxygen (O-acylation): O R O OH O R HO R Cl O + phenol O R O R O + Aryl ester (O-acylation) HO O R Aryl ketones (C-acylation) Friedel Craft reaction In the absence of aluminum chloride (lewis acid), however, O-acylation occurs instead. HO C7H15 Cl O + NaOH/H2O O O C7H15 + HCl phenol phenyl octanoate OH O O O + O O + sodium acetate H2SO4 F F 4-fluorophenol 4-fluorophenyl acetate (84%) HO OH O O O + NaOH/H2O 2 O O O O + sodium acetate resorcinol 1,3-diacetoxybenzene Acid anhydride to a more powerful acylating agent by protonation of one of its carbonyl oxygens. Addition of a few drops of sulfuric acid is usually sufficient.
  • 59. Synthesis of aryl ethers: the Fries rearrangement The C-acyl isomers are more stable, which will be formed more effectively by using aluminum chloride as catalyst. It is more effective catalyst for the conversion of aryl esters to aryl ketones. This isomerization is called the Fries rearrangement. O C6H5 O OH O C6H5 HO O C6H5 AlCl3 + phenyl benzoate o-hydroxybenzophenone p-hydroxybenzophenone (9%) (64%)
  • 60. Give each of the following compounds a systematic name, and indicate whether each is a primary, secondary, or tertiary alcohol: OH HO OH Cl OH OH Cl OH (a) (b) (c) (d) (e) (f)
  • 61. • Write structural formulas for each of the following compounds: (a) Pyrogallol (1,2,3-benzenetriol) (c) 3-Nitro-1-naphthol (b) o-Benzylphenol (d) 4-Chlororesorcinol
  • 62. OH HO OH Cl OH OH Cl OH (a) (b) (c) (d) (e) (f) pentan-1-ol 4-methylcyclohexanol 5-chloro-2-methylpentan-2-ol 5-methylhexan-3-ol 2,6-dimethyloctan-4-ol 4-chloro-3-ethylcyclohexanol OH OH OH OH NO2 OH HO OH Cl benzene-1,2,3-triol 3-nitronaphthalen-1-ol 2-benzylphenol 4-chlorobenzene-1,3-diol
  • 63. •Give the major product obtained from the acid-catalyzed hydration of each of the following alkenes: (a) (b) (c) (d)
  • 64. (a) (b) (c) (d) OH OH OH OH + OH
  • 65. Problems Give the major product obtained of the following reactions - (a) (b) (c) (d) OH OCH3 + Br K2CO3 acetone ONa + OH Cl OH CHO HO OCH3 HNO3, acetic acid, heat H N O O heat
  • 66. (a) (b) (c) (d) OH OCH3 + Br K2CO3 acetone ONa + OH Cl OH CHO HO OCH3 HNO3, acetic acid, heat H N O O heat O OCH3 O OH OH CHO HO OCH3 O2N H N O OH
  • 67. Reactions of phenols • Write a balanced chemical equation for each of the following reactions: (a) Phenol - sodium hydroxide (b) Product of part (a) + ethyl bromide (c) Product of part (a) + butyl p-toluenesulfonate (d) Product of part (a) + acetic anhydride (e) o-Cresol + benzoyl chloride (f) m-Cresol + ethylene oxide (g) 2,6-Dichlorophenol + bromine (h) p-Cresol + excess aqueous bromine
  • 68. (a) (b) (c) (d) (e) (f) ONa O (g) (h) O S O O O O O O O OH OH Cl Cl Br OH Br Br
  • 69. Give the product formed from the reaction of each of the following alcohols with a. an acidic solution of sodium dichromate: b. the reagents required for a Swern oxidation: 1. 3-pentanol 2. 2-methyl-2-pentanol 3. Cyclohexanol 4. 1-pentanol 5. 2,4-hexanediol 6. 1,4-butanediol
  • 70. Write chemical equations, showing all necessary reagents, for the preparation of 1- butanol by each of the following methods: (a) Hydroboration–oxidation of an alkene (b) Use of a Grignard reagent (c) Use of a Grignard reagent in a way different from part (b) (d) Reduction of a carboxylic acid (e) Reduction of a methyl ester (f) Reduction of a butyl ester (g) Hydrogenation of an aldehyde (h) Reduction with sodium borohydride
  • 71. Write structural formulas for each of the following compounds: (a) Pyrogallol (1,2,3-benzenetriol) (c) 3-Nitro-1-naphthol (b) o-Benzylphenol (d) 4-Chlororesorcinol
  • 72. Which is the stronger acid in each of the following pairs? Explain your reasoning. (a) Phenol or p-hydroxybenzaldehyde (b) m-Cyanophenol or p-cyanophenol (c) o-Fluorophenol or p-fluorophenol
  • 73. Write a balanced chemical equation for each of the following reactions: (a) Phenol _ sodium hydroxide (b) Product of part (a) + ethyl bromide (c) Product of part (a) + butyl p-toluenesulfonate (d) Product of part (a) + acetic anhydride (e) o-Cresol + benzoyl chloride (f) m-Cresol + ethylene oxide (g) 2,6-Dichlorophenol + bromine (h) p-Cresol + excess aqueous bromine