Dr Nahed Elsayed
Chapter six concerns alcohols and phenols and by the end of this chapter the student
know the difference in structure of alcohols and phenols
Know the types of alcohols
Know the different classes of monohydroxy alcohols
Know how to name alcohols and phenols
Know the physical properties (solubility, boiling and melting points) of alcohols and
phenols and factors affecting them.
Know how hydrogen bonds are formed and its effect on solubility and boiling points of
Know how to differentiate between alcohols and phenols using NaOH
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
Structure Of Alcohols and Phenols
Alcohols are the family of compounds that contain one or more hydroxyl (-OH)
groups. The OH group is bound to a carbon atom.
They can be considered both derivatives of hydrocarbons (by replacing a hydrogen
atom with a hydroxyl group -OH) and water (H2O) derivatives (the result of the
substitution of a hydrogen atom by an organic radical).
Thus the chemical formula of alcohols is ROH or ArCH2OH
On the other hand Phenol’s chemical formula is C6H5OH, it has the OH group
directly attached to the benzene ring.
Phenol Benzyl alcohol Cyclohexanol
Types Of Alcohols
Monohydroxyls: containing one hydroxyl group (for example ethanol C2H5OH)
Dihydroxyls (glycols): containing two hydroxyl groups connected by different
carbon atoms for example: Ethylene glycol CH2OH-CH2OH.
Polyhydroxyls: containing more than two hydroxyl groups on different carbon atoms
(for example: 1,2,3-propanetriol 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:
- primary alcohols
- secondary alcohols
- tertiary alcohols
Primary 1° Secondary 2° Tertiary 3°
H3C OH R CH2 OH R CH OH R C OH
Carbinol Primary alcohol Secondary alcohol
Methanol CH3OH, ethanol CH3-CH2-OH, allyl alcohol CH2=CHCH2OH are primary
2-Propanol CH3-CH(OH)-CH3 is a secondary alcohol
2-Methyl-2-propanol CH3-C(CH3)OH-CH3 is a tertiary alcohol.
NOMENCLATURE OF ALCOHOLS
Common Nomenclature Of Alcohols
Alcohols are named as alkyl alcohols i.e. name the alkyl group and follow it by the
CH3OH CH3CH2OH CH2=CHCH2OH
Common names Methyl alcohol Ethyl alcohol Allyl alcohol
H3C C CH3
Common names Isopropyl alcohol Cyclopentyl alcohol Methylcyclohexyl
The alcohols containing 2 hydroxyl groups (diols) connected to two different carbons
are called glycols for example: CH2OH-CH2OH is called ethylene gylcol
CH3-CH(OH)-CH2(OH) is called propylene gylcol 6
IUPAC Nomenclature Of Alcohols
Find the longest chain of C atoms containing the O-H group; to obtain the root name
of the parent alkane
Replace the e ending by ol suffix in the basic name
Number the chain starting from the end nearer to the O-H group and add a locator
number for OH group just before the ol suffix or before the full name
e.g. CH3CH(OH)CH2CH3 is named 2 -butanol or butan-2-ol
Identify the substituents, allocate them numbers, then list them in alphabetical order.
CH3 - CH(CH3) - CH2 - CH2 - CH(OH) - CH3 is named 5-methylhexan-2-ol
6 5 4 3 2 1 or 5-methyl-2-hexanol
If a molecule contains both an OH group and a c=c or c=c bond, the name should
include suffixes indicate presence of both OH group and the unsaturated groups. The
OH group takes precedence over the double or triple bonds in getting the lower
5 4 3 2 1
If the parent hydrocarbon contain two hydroxyl groups, the suffix diol is added to
the name; the suffix triol is added when there are three OH groups. In each case
the relative positions of OH groups must be identified.
HO OH OH OH
IUPAC Propane-1,2-diol Propane-1,2,3-triol
or 1,2-Propanediol or 1,2,3,-Propantriol
Common Ethylene glycol Propylene glycol Glycerol or Glycerin
Nomenclature Of Phenols
Phenols are generally named as derivatives of the simplest member of the family,
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.
Some phenols have common names as shown in the following examples
OH OH OH OH OH
NO2 O2N NO2 Cl Cl
Br No2 NH2 Cl
Phenol 4-Bromo-2-nitrophenol 2,4,6-Trinitrophenol 2,3,4,5,6-Pentachlorophenol
OH OH OH
IUPAC: 2-Methyl-phenol 3-Methyl-phenol 4-Methyl-phenol
Common: o-Cresol m-Cresol p-Cresol
OH OH OH OH
IUPAC: 2-Hydroxyphenol 3-Hydroxyphenol 4-Hydroxyphenol 2,3-Dihydroxyphenol
Common: Catechol Resorcinol Hydroquinone Pyrogallol
Physical Properties of Alcohols
1) Boiling Points of Alcohols and Phenols
Phenols have higher boiling and melting points than corresponding aliphatic alcohols
(due to they form stronger H-bonds with themselves).
A hydrogen bond is the attractive interaction of a hydrogen atom with an
electronegative atom, like nitrogen, oxygen or fluorine. The hydrogen must be
covalently bonded to another electronegative atom to create the bond. These bonds
can occur between molecules (intermolecularly), or within different parts of a
single molecule (intramolecularly).
Intermolecular hydrogen bonding is responsible for the high boiling point of water
Alcohols have higher boiling points than alkanes of similar mass this is due to the
presence of inter-molecular hydrogen bonding that connect molecules together
thus more energy is required to separate them.
Mr. Wt bp / °C
Propane C3H8 44 42
Ethanol C2H5OH 46 78
The boiling points increases with increase in molecular weights
Boiling point is higher for straight chain isomers i.e. branching decreases the
Butan-1-ol Butan-2-ol 2-Methylpropan-2-ol
Bp/°C 118 100 83
Boiling point increased as number of OH groups in a molecule increase
Thus triols > diol> monohydroxy alcohols
2) Solubility Of Alcohols and Phenols
Low molecular mass alcohols (4 or less C’s) are miscible with water due to
hydrogen bonding between the two molecules
While heavier alcohols are less miscible i.e. as the number of carbon atoms
increase the miscibility decrease.
Phenol itself is crystalline solid moderately soluble in water (H-bonds), other
phenols are not very soluble.
As the number of OH groups present in a molecule increase the miscibility increase.
Thus the order of solubility is as follows triols > diols > monohydroxyl alcohols.
Also benzene diols (catechol, resorcinol and hydroquinone) are more soluble than
phenol which in turn more soluble than benzene.
3) Acidity and Acidic Properties of Alcohols and Phenols
Acidity refers to the ease with which a compound donates a hydrogen ion.
In alcohols and phenols, the most acidic hydrogen is the one attached to the oxygen
and its acidity depends on the presence of "electron withdrawing" groups ( such as
COOH, CHO, CN, NO2) or electronegative elements (X) elsewhere in the molecule
Alcohols are very weak acids (due to difference in electro negativity) thus they can
lose H+ with very reactive metals but not with bases
R O H RO + H+
ROH + Na RO Na+ + 1/2 H2
phenol is slightly acidic, thus phenol molecule has weak tendency to lose the H+ ion
from the hydroxyl group, resulting in the highly water-soluble phenolate anion C6H5O−,
called phenoxide anion.
Compared to aliphatic alcohols, phenols shows much higher acidity (about 1
million times more acidic) thus they can react with bases.
N.B. Phenols are less acidic than carboxylic acids.
Thus NaOH (base) can be used to differentiate between alcohols and phenols
+ NaOH No reaction
OH O- Na+
+ NaOH + H2O
One explanation for the increased acidity over alcohols is resonance stabilization of
the phenoxide anion by the aromatic ring. In this way, the negative charge on oxygen is
shared by the ortho and para carbon atoms.
OH O O O
Resonance structures of phenoxide anion
Introduction of electron withdrawing groups such as NO2, CHO, COOH, SO3H, or
CN i.e. all m-directors and halogens on the benzene ring increases the acidity of
phenols, While introduction of electron releasing groups (e.g. OR, R, NH2) i.e. all o,p-
directors except for halogens decrease the acidity of phenols compared to
unsubstituted phenol as shown in the following examples.
OH OH OH OH OH
< < < <
OH OH OH OH OH
NO2 O2N NO2
< < < <
CH3 NO2 NO2 NO2
Preparation of Alcohols
1- From Alkenes
1) B2H6 H3C OH
CH2 2) H2O2 / NaOH Anti-Markovnikov's product
H2O / H2SO4 OH
KMnO4 / OH
1) RCO3H OH
2) H2O2 / NaOH
2- From alkyl halide by nucleophilic substitution
3- By reduction of aldehydes, ketones and carboxylic
acids using metal hydrides
1) LiAlH4 or NaBH4
Aldehyde R C R CH2-OH Primary alc.
1) LiAlH4 or NaBH4
R R' R C-OH Secondary alc.
Acid R 1) LiAlH4 or NaBH4
C R CH2-OH Primary alc.
4- By nucleophilic addition of Grignard reagent to
aldehydes, ketones and esters
Addition of RMgX to formaldehyde gives 1◦ alc.
Addition of RMgX to any other aldehyde gives 2◦ alc.
Addition of RMgX to ketones and esters give 3◦ alc.
Preparation of Phenols
1- Via hydrolysis of Diazonium salts
N2+ Cl- OH
H2SO4 / H2O
2- Via fusion of sodium hydroxide with benzene-sulfonates
SO3H O- Na+ OH
NaOH / 350 °
3- From alkyl halide:
Cl O- Na+ OH
NaOH / 350°
Reaction of Alcohols and Phenols
1) Salt Formation By Reaction With Active Metals
2R OH + 2 Na 2R ONa + H2
Alcohol Sodium alkoxide
H3C OH + 2 Na 2 CH3 ONa + H2
Methanol Sodium methoxide
+ 2 Na or NaOH
2) Elimination Of Water (Dehydration)
Reagent/catalyst conc. sulphuric acid (H2SO4)
Conditions reflux at 180°C
CH3 H2SO4 or H3PO4
180 °C- H2O
OH 1- Butene 2-Butene
While dehydration of alcohols at lower temperature will give ethers
3) Ester Formation
Carboxylic acids react with alcohols in presence of strong acid catalyst (e.g.
conc. H2SO4) to produce esters
R + R'OH R + H2O
+ CH3OH + H2O
4) Alkyl Halides Formation
R OH + HX R X + H2O
R OH + SOX2 R X + SO2 + HCl
R OH + PX3 R X + HOPX2
R OH + PX 5 R X + HOPX4
5) Oxidation Of Alcohols
Alcohols can be oxidised depending on their class
Oxidation is used to differentiate between primary, secondary and tertiary alcohols
The usual reagent is acidified potassium dichromate (VI) K2Cr2O7
Primary Easily oxidised to aldehydes and then to carboxylic acids.
e.g. CH3CH2OH(l) + [O] ——> CH3CHO(l) + H2O(l)
it is essential to distil off the aldehyde before it gets oxidised to the acid
CH3CHO(l) + [O] ——> CH3COOH(l)
ethanal ethanoic acid
Secondary Easily oxidised to ketones
Tertiary Not oxidised under normal conditions.
They do break down with very vigorous oxidation
PRIMARY 1° SECONDARY 2° TERTIARY 3°
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent
C and O atoms.
1° R C O + [O] R C O + H2O
2° R C O + [O] R C O + H 2O
This is possible in 1° and 2° alcohols but not in 3° alcohols.
3° R C O + [O]
H2 Cr2O7 or Na2CrO7 / H
or KMnO4 / heat
Secondary alcohol Ketone
OH O OH
H2Cr2O7 or Na2CrO7 / H KMnO4 / heat
or KMnO4 / heat
O OH 29
Phenol [1,4]Benzoquinone Hydroquinone
Reactions Of Aromatic Ring In Phenols
Br2 / H2O
Br2 / CCl4 +
conc. H2SO4 SO3H