ALCOHOLS
PHENOLS AND ETHERS
Alcohols R-OH
Phenols: C6 H 5
-OH Ethers R-O-R
(1)
Reimer
Tiemann. Reaction –
(2)
Transesterification
(3)
Williamson
synthesis
(4)
Kolbe
reaction
(5)
Friedel
craft
Trans esterification : When
an ester treated with excess of another alcohol [other than the one from
which ester has been derived ] in presence of corresponding sod. or pot.
alkoxide or an acid H2SO4 / HCl as catalyst i.e. also
cleavage by an alcohol , calcolysis
O
|
O
|
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H+
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R –C –OR + R –O
–H ↔
|
R –C –OR + R –OH
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Williamson synthesis:- Reaction
of alkyl halide with sodium alkoxide or sod. Phenoxide to give ether is
called Williamson synthesis.
R –X + R1
–O –Na
R –O - R’+ NaX
CH3I +
CH3CH2ONa
CH3O.CH2
–CH3 + NaI
CH3CH2
–I + PhONa
PhOH + NaI
Both simple and
mixed ether can be produced.
CH3
(3) CH3C O CH3
+ H I
(CH3)3
- C –I +CH3 - OH
CH3
(iii) CH3 –CH –Br + CH3 –CH2
–O- - Na+
CH3
|
|||
CH3
–CH = CH2
|
CH3
–CH –OCH2 –CH3
|
||
79%
|
21%
|
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Kolbe
reaction
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DISTINCTION
BETWEEN PAIR OF COMPOUNDS
When
10,20, and 30 alcohol treated with lucas
reagent [con, HCl + an hydrous ZnCl2] at room temp
(i)
If turbidity appears immediately alcohol
is 30.
(ii)
If turbidity appears in five minutes
alcohol is20.
(iii)
10 alcohol does not react with
L.R. at room temp.
(II) All those compound like alcohol, aldehyde Ketones
which on oxidation giving CH3 - CO- Group undergoes
iodoform test.
e.g.
(i) CH3CH2 OH
(II)
CH3 CHO
(III)
(CH3) –CH –OH
(V)
C6H5 –CO CH3
OH
(VII)
CH3 –C –CH2- CH2 –CH3
(2) Preparation of
phenol from Cumene
(3)Preparation of
aspirin
Explain phenol is
acidic?
Phenoxide ion is
resonance stabilized
If
electron withdrawing group are attached into the benzene ring it enchance
acidic character and vice versa.
2,4,6
trinitrophenol > 2,4, dinitrophenol > 4-nitrophenol > phenol
Phenol > m-
cresol > P cresol > O cresol
m-methoxyphenol > phenol > O methoxy phenol >
P methoxy phenol.
O chloro phenol > O bromophenol > O iodo phenol
> O fluoro phenol
FORMATION
OF PICRIC ACID
(I)
withBr2 2,4,6 tribromo phenol (white ppt)
(I)Phenol
gives violet colour with FeCl3 solution .
CONCEPTUAL
QUESTIONS
Q1) Preparation of ethers by acid dehydration of
secondry or 30 alcohols is not a suitable method?
Ans:-
The formation of ethers by dehydration of alcohol is a bimolecular reaction (SN2)
group is hindered. as a result elimination dominates substitution as 30
carbocation is more stable. Hence ,in place of others , alkenes are formed.
Ans:- The lone pair on oxygen of O-H in phenol is
being shared with benzene ring through resonance.Thus,lone pair is not fully
present on oxygen and hence phenols do not undergo protonatian reactions.
Q3) Ortho-
nitrophenol is more acidic than ortho –methoxy phenol ? why?
Ans:- NO2 group is electron with drawing
which increases acidic charcter due to easily ease
REASONING
QUESTIONS
Q1. Explain why propanol has higher boiling point than
that of the hydrocarbon, butane?
ANS.The
molecules of Butane
are held together by vander Waals
Forces of attraction while those of propanol are held
together by stronger intermolecular hydrogen bonding.
Q2. Alcohols are
comparatively more soluble in water than hydrocarbons of comparable molecular
masses. Explain this fact.
ANS. Alcohols can form hydrogen bonds with water and
break the hydrogen bonds already existing between water molecules Therefore
they are soluble in water. Whereas hydrocarbons cannot form hydrogen bonds with
water and hence are insoluble in water.
Q3. While separating a
mixture of ortho and para nitrophenols by steam distillation, name the isomer
which will be steam volatile. Give reason.
ANS. O-nitrophenol is steam volatile due to
intramolecular hydrogen bonding and hence can be separated by steam
distillation from p-nitrophenol which is not steam volatile because of
inter-molecular hydrogen bonding.
Q4. Explain why is
ortho nitrophenol more acidic than ortho methoxyphenol?
Ans.
The nitro-group is an electron-withdrawing group. The presence of this group in
the ortho position decreases the electro a result, it is easier to lose a
proton. Also, the o-nitrophenoxide ion formed after
the loss of protons is stabilized by resonance. Hence,
ortho nitrophenol is a stronger acid. On the other hand, methoxy group is an
electron-releasing group. Thus, it increases the electron proton cannot be
given out easily.Therefore ortho-nitrophenol is more acidic than
ortho-methoxyphenol.
Q5. Preparation of ethers by acid dehydration of
secondary or tertiary alcohols is not a suitable method. Give reason.
ANS.
The formation of ethers by dehydration of alcohol is a bimolecular reaction
(SN2) involving the attack of an alcohol molecule on a protonated alcohol
molecule. In the method, the alkyl group should be unhindered. In case of
secondary or tertiary alcohols, the alkyl group is hindered. As a result, elimination
dominates substitution.
Q7. Give the
equations of reactions for the preparation of phenol from cumene.
Q8. Write chemical reaction for the preparation of
phenol from chlorobenzene. ANS. Chlorobenzene is fused with NaOH at 623K and
320 atmospheric pressure. Phenol is obtained by acidification of sodium
phenoxide so produced.
Q9.
How is aspirin (Acetylsalicylic acid) prepared from salicylic acid? ANS.
Acetylation of salicylic acid produces aspirin.
Q10. Which out of propan-1-ol and propan-2-ol is
stronger acid? ANS Propan-1-ol is stronger acid than propan-2-ol. The acidic
strength of alcohols is in the order 10>20>30.
Q11. What is
denaturation of an alcohol?
ANS. The commercial alcohol is made unfit for drinking
by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul
smelling liquid). It is known as denaturation of alcohol.
Q12.
Give IUPAC name of CH3OCH2OCH3
ANS. Dimethoxymethane
Q13. Diethyl ether does
not react with sodium. Explain.
ANS. Diethyl ether does
not contain any active hydrogen.
2 MARKS QUESTIONS
Q1. Give two reactions that show the acidic nature of
phenol. Compare acidity of phenol with that of ethanol.
ANS. The acidic nature of phenol can be represented by
the following two reactions: (i) Phenol reacts with sodium to give sodium
phenoxide, liberating H2.
(i)
Phenol
reacts with sodium hydroxide to give sodium phenoxide and water as by-products
Why the acidity of phenol is more than that of
ethanol. ?
Q2. How does
phenol react with dilute and conc. HNO3 ?
and para nitrophenols. (ii) With concentrated nitric
acid, phenol is converted to 2,4,6-trinitrophenol. The product is commonly
known as picric acid.
Q3. How does
phenol react with Br2 in CS2 and Bromine water?
ANS. (i) When the reaction is carried out in solvents
of low polarity such as CHCl3 or CS2 and at low temperature, monobromophenols
are formed.
(ii)
When
phenol is treated with bromine water, 2,4,6-tribromophenol is formed as white
precipitate.
Q4. How do you account for the fact that unlike
phenol, 2, 4-dinitrophenol and 2, 4, 6-trinitrophenol are soluble in aqueous
solution of sodium carbonate?
ANS 2, 4-Dinitrophenol and 2, 4, 6-trinitrophenol are
stronger acids then carbonic acid (H2CO3) due to the presence of electron
withdrawing –NO2 groups. Hence, they react with Na2CO3 to form their
corresponding salts and dissolve in aq. Na2CO3 solution.
Q5. (i) Why is the Dipole moment of methanol higher
than that of phenol? (ii) . Explain why phenols do not undergo substitution of
the –OH group like alcohols.
ANS.
(i) Due to electron withdrawing effect of phenyl group, the C—O bond in phenol
is less polar, whereas in case of methanol the methyl group has electron
releasing effect and hence C—O bond in it is more polar. (ii) C—O bond in
phenols has partial double bond character due to resonance and hence is
difficult to cleave.
Q6.
Account for the following:
a.
Boiling point of the C2H5OH is more than
that of C2H5Cl
b.
The solubility of alcohols in water
decreases with increase in molecular mass.
ANS. a. Because of hydrogen bonding. b. With increase
in molecular mass the non-polar alkyl group becomes more predominant.
Q7. Answer the
following
b.
How will you account for the solubility of
lower alcohols in water?
Ans: a.
10>20>30.
b. Here—OH group is predominant and the alcohol
molecules can form hydrogen bonds with water molecules.
Q8.
Give reasons: i)Nitration of phenol gives ortho- and para- products only.
ii)Why do alcohols have higher boiling points than the haloalkanes of the same
molecular mass?
ANS (1) -OH group
increases the electron density more at ortho and para positions through its
electron releasing resonance effect. (2) Alcohols are capable of forming intermolecular
H-bonds.
Q9. Account for the
following: i) Phenols has a smaller dipole moment than methanol ii) Phenols do
not give protonation reactions readily.
ANS a. In phenol the
electron withdrawing inductive effect of –OH group is opposed by electron releasing
the resonance effect of –OH. b. The lone pair on oxygen of –OH in phenol is
being shared with benzene ring through resonance. Thus, lone pair is not fully
present on oxygen and hence phenols do not undergo protonation reactions.
Q10. Explain the fact that in aryl alkyl ethers (i)
The alkoxy group activates the benzene ring towards electrophilic substitution
and (ii) It directs the incoming substituents to ortho and para positions in
benzene ring.
ANS. (i)
In aryl alkyl ethers, due to the +R effect of the
alkoxy group, the electron density in the benzene ring increases as shown in
the following resonance structure.
Thus, benzene is activated towards electrophilic
substitution by the alkoxy group. (ii) It can also be observed from the resonance
structures that the electron density increases more at the ortho and para
positions than at the meta position. As a result, the incoming substituents are
directed to the ortho and para positions in the benzene ring.
3 MARKS QUESTIONS
Q1. How are primary, secondary and tertiary alcohols
prepared from Grignard Reagents?
Q2. Give the equations of
oxidation of primary, secondary and tertiary alcohols by Cu at 573 K.
Q3. Give equations of the following reactions: (i)
Oxidation of propan-1-ol with alkaline KMnO4 solution. (ii) Bromine in CS2 with
phenol. (iii) Dilute HNO3 with phenol.
6ANS. (i)
(ii)
Q4. Show how will
you synthesize:
(i)
1-phenylethanol from a suitable alkene.
(ii)
(ii) cyclohexylmethanol using an alkyl
halide by an SN2 reaction.
(iii)
(iii) pentan-1-ol using a suitable alkyl
halide?
(iv)
ANS. (i) By acid-catalyzed hydration of
ethyl benzene (styrene), 1-phenylethanol can be synthesized.
(ii) When chloromethylcyclohexane is treated with
sodium hydroxide, cyclohexylmethanol is obtained.
(iii)
When
1-chloropentane is treated with NaOH, pentan-1-ol is produced.
Q5.
How are the following conversions carried out?
(i)
Propene
→Propan-2-ol
(ii)
(ii)
Benzyl chloride →
Benzyl alcohol
(iii)
(iii)
Ethyl magnesium.chloride →
Propan-1-ol
ANS. (i) If propene is allowed to react with water in
the presence of an acid as a catalyst, then propan-2-ol is obtained.
(ii) benzyl
chloride is treated with NaOH (followed by acidification) then benzyl alcohol
is produce
(i)
Oxidation of a primary alcohol to
carboxylic acid.
(ii)
(ii) Oxidation of a primary alcohol to
aldehyde.
(iii)
Bromination of phenol to
2,4,6-tribromophenol.
ANS.
(i) Acidified potassium permanganate
(ii)
Pyridinium chlorochromate (PCC)
(iii)
Bromine water
Q7. How is
1-propoxypropane synthesised from propan-1-ol? Write mechanism of this
reaction.
ANS. 1-propoxypropane can be synthesized from
propan-1-ol by dehydration. Propan-1-ol undergoes dehydration in the presence
of protic acids (such as H2SO4, H3PO4) to give 1-propoxypropane.
The mechanism of
this reaction involves the following three steps:
Step
1: Protonation
Step 2:
Nucleophilic attack
Step 3: Deprotonation
Q8.
Write the equation of the reaction of hydrogen iodide with:
(i) 1-propoxypropane (ii) Methoxybenzene and (iii)
Benzyl ethyl ether ANS. (i)
ii
(iii)
5 MARKS QUESTIONS
Q1.
Write equations of the following reactions:
(i)
Friedel-Crafts reaction−alkylation of
anisole
(ii)
Nitration of anisole.
(iii)
Bromination of anisole in ethanoic acid
medium.
(iv)
Friedel-Craft‘s acetylation
of anisole.
VALUE
BASED QUESTIONS
Q1. Water
is a universal solvent. But alcohol also dissolves most of the
substances soluble
in water. And also many more. Boiling point of water is 1000 c and
that of alcohol is 800C. The specific heat of water is much higher
than the specific heat of alcohol.
a. List out three possible differences if
instead of water as the liquid in our body we had alcohol. (3)
b. What
value can you derive from this special property of water and its
innumerable uses
in sustaining life on earth? (1)
Ans:
a. I.
Even a small raise in temperature in the surroundings will raise the
temperature of the
body because the specific heat of alcohol is much less
than the specific
heat of water. In order to cool the body more sweating
will take place.
II. As
there is less H bonding in alcohol it will get evaporated faster. The
alcohol will be
evaporated at such a fast rate that the liquid has to be
ingested always.
III. Ice
which floats on water helps aquatic life to exist even in winter as
water insulates
the heat from liquid below it to go back to the
surroundings.
Solid alcohol does not have such special properties.
b.
Praise is to the almighty that has so thoughtfully given such special
properties to
water and made it a liquid that could sustain life.
Q2. Laboratory
alcohol should not be used for sterilization of wounds.
a. Why?
(2)
b. What
values do you derive from this? (1)
Ans:
a. Laboratory alcohol is denatured with methanol.
Methanol is extremely poisonous. Hence it should not be used.
b. Laboratory
reagents/equipments should not be used for any purpose
other than in
using for laboratory works
Q3. In a
locality a large number of people fell ill after drinking liquor sold by a
local vender. Many people started
vomiting, some shouted that they are not able to see properly and some others
went unconscious. Ram’s father also
suffered from severe stomach ache after consuming liquor. Everyone in Ram’s family peaked. Neighbours
family was also weeping loudly. Ram calmed down his mother and helped her to
call ambulance for his father and also for other people. They also informed the
police about the incident.
(i) Mention the values shown by Ram.
(ii) Write the probable cause of poisoning by
liquor.
(iii) Write
the reaction showing the conversion of ,mollases to Ethyl alcohol using yeast.
i) Decision-making,
critical analysis of situation & presence of mind.
Ii) Consumption of methanol.
C12H22O11
→ C6H12O6
+ C6H12O6 (glucose+fructose)
C6H12O6→
2C2H5OH + 2CO2 (Rx.s occur in presence of enzymes
invertase & zymase)
Q4. Some students
enter the chemistry lab for doing practical. Some students are not serious
about learning and want to create trouble. They remove the lables from two
bottles containing methanol and dimethyl ether. Mohan approaches the teacher
and informs about the incident.
(i) Mention the values shown try Mohan.
(ii) If the teacher asks the some students to perform
chemical test to identify methanol and demethyl ether, write the reaction
involved for the test.
A
i) Social responsibility,
courage to state the fact.
Methanol is an alcohol, it will give +ve
victor-meyer test /Lucas test.
Q5. An owner of a paint company who was using
ethanol as solvent noted that
his
stock of ethanol was misused by his employee.
To
prevent this misuse, he decided to add small amount of a blue colour
compound
(A) and another nitrogen containing heterocyclic base (B) which
gives
a foul smell to alcohol.
(a) Do you think that he took right decision?
(b) Write the names of compound A& B ?
Name process of adding compound A
&
B to ethanol ?
(c)Mention
the values associated with above decision.
A a) yes
bCopper sulphate & pyridine. It is called
denaturation of alcohol.
a) Social welfare, Social reposibility,
Scientific attitude, Concern & care for employee.
1. Ethanol
is treated with phosphorus tribromide.
Ans. 3CH3CH2OH+PBr3
à 3CH3CH2Br + H3PO3
2. Phenol
is heated with Zn dust.
Benzene
is formed.
Ans. C6H5OH + Zn → C6H6
3. Phenol
is warmed with CCl4 in presence of aqueous NaOH .
Ans. Salicyclic acid is form.
C6H5OH + CCl4
+ NaOH → C6H5 (OH)COOH
4. Alkene
is hydrolysed in the presence of Concentrated H2SO4.
Ans. Ethanol is formed
CH2=CH2 + H2O --H2SO4→ C2H5OH
5. Methanal is treated with Grignard reagent followed by
hydrolysis.
Ans. Gives primary alcohol
HCHO
+ RMgX → HCH(R)OMgX --- H2O--→ CH3CH2OH
6. Secondary
alcohol are passed over heated copper at 573K.
Ans. Gives
ketones
R-CH(OH)- R’ →
RCOR’
HOTS(HIGHER
ORDER THINKING SKILL)
1. Which
is more acidic :H2O or ROH?
Give reason to support your answer.
Ans H2O is more acidic as there
is an alkyl group present in ROH which
has +I Effect making liberation of H+ ion mor difficult from O—H
bond.
2. Which
enzyme is responsible for conversion of glucose to ethanol?
Ans zymase
3. How
will you synthesize aspirin from phenol?
Ans first phenol is converted into salicylic
acid, followed by acetylation
4. Why
high molecular mass alcohols are insoluble inwater?
Ans Due to hydrophobic nature of higher alkyl
group
5. Fermentation
is carried out in dilute solution why?
Ans The bacteria which are helpful in
fermentation can survive and grow in dilute medium only
6. While
separating a mixture of ortho and para
nitrophenols by steam distillation, name the isomer which will be steam
volatile . Give reason.
Ans O nitro phenol is steam volatile due to
intramolecular H bonding and hence can be separated by steam distillation from
p – nitro phenol which is not steam volatile because of inter molecular H bonding.
7
Phenol do not give protonation reaction readily. Why ?
Ans The lone pair on oxygen of O-H in phenol
is being shared with benzene ring through resonance. Thus lone pair is not
fully present on oxygen and hence phenol do not undergo protonation reactions.
8
Prepare
phenol from Diazonium salts?
9
How will
you distinguish between primary, secondary and tertiary alcohols?
When
primary, secondary, tertiary alcohols are treated with Lucas reagent at room
temperature, then
(i)
If turbidity appears immediately, alcohols
is tertiary
(ii)
If
turbidity appears in 5 minutes, alcohols is secondary
(iii)
If
no reaction, alcohols are primary.
(Lucas reagent is conc.HCl
+anhydrous zinc chloride)
(MLL)
1 Alcohols are comparatively more
soluble in water than the hydrocarbons of comparable molecular masses?Explain?
Alcohols
can form hydrogen bonds with water and therefore these are soluble whereas
hydrocarbon cannot form H-bonding and therefore are insoluble in water.
2
Explain
why is orthonitrophenol more acidic than orthomethoxy phenol?
The
nitro- is an electron withdrawing group .the presence of this group in the
ortho position decreases the electron density .As a result, it is easier to
lose a proton.
Also
the orthonitrophenoxide ion formed is
stabilized by the resonance. Hence, orthonitrophenol is a stronger acid
On the other hand, methoxy group is an electron-releasing group. Thus,
it increases the electron density. Therefore proton cannot be given out easily.
So,
orthonitrophenol more acidic than
orthomethoxy phenol.
3
Why
lower alcohols soluble in water but higher alcohol not?
Due
to the formation H-Bonds lower alcohol are soluble in water. Higher alcohol are
less soluble due to the presence of higher alcohols.
4
How
will you distinguish between primary, secondary and tertiary alcohols?
When
primary, secondary, tertiary alcohols are treated with Lucas reagent at room
temperature, then
(iv)
If turbidity appears immediately, alcohols
is tertiary
(v)
If turbidity appears in 5 minutes,
alcohols is secondary
(vi)
If
no reaction, alcohols are primary.
(Lucas reagent is
conc.HCl +anhydrous zinc chloride)
5
Phenol is acidic in nature.
Phenol is acidic in nature because:
a) phenol
, due to resonance, the positive charge rests on oxygen making of electrons more towards oxygen and
hydrogen as H+
b) The carbon attached to OH is sp2
hybridize and is more electronegative,
the electron density on oxygen, increasing the polarity of O-H bond and
ionization of phenol.
c) The phenoxide ion formed by loss of H+
is more resonance stabilized than
phenol itself.
6
Diethyl ether does not react with sodium. Explain.
Diethyl ether does not contain any
active hydrogen.
7
Write
the reaction showing formation of aspirin?
8.
How will you chemically distinguish
between a) phenol and ethanol
Ans.
Neutral FeCl3 test-
phenols respond, alcohols do not respond.
9.Write short notes on:
a)
Reimer Tiemann Reaction
b)
Kolbe’s Reaction
c)
Williamson’s Synthesis
Ans (a) When phenol reacts with chloroform in
presence of sodium hydroxide Salicyldehyde is formed .
Phenol
salicyldehyde
Ans (b)
When phenol reacts with CO2 and NaOH in presence of elevated temp
Salicylic
acid is formed as a product.
Kol
|
Phenol
Salicylic acid
Ans (c)
When sodium alkoxide reacts with alkyl halide ethers are formed as a
product .
CH3-Br + CH3-ONa
CH3-O- CH3 + NaBr
Methyl Bromide sodium methoxide Methoxy methan
(VAQ)
1. A
teacher ordered ethanol for laboratory. She preferred denatured alcohol over
absolute alcohol.
a) Give reason for the decision taken by
the teacher.
b) What value
was kept in mind while taking the decision?
Teacher should make sure that laboratory chemicals
specifically used for laboratory works only. So she preferred denaturated
alcohol over absolute alcohols.
Value Points:-
Maintaining discipline
Concern for environment
Responsible behaviour
Social obligation.
2
Duty free ethyl alcohol is supplied to
laboratory. This alcohol is mixed with some chemical to make it unfit for
drinking. This alcohol is poisonous and should not be used for drinking.
a) Name
the compound which are mixed with ethyl alcohol to make it unfit for drinking.
b) What
purpose are served by those chemicals
c) what
is denatured spirit
d) write
the value associated with the example
ans: poisonous chemicals are(i) methanol
(ii)
pyridine
(iii)
copper sulphate
Pyridine
is a foul smelling substance. Copper sulphate makes alcohol blue appearance.
Denatured
spirit is another nameof denatured alcohol.
One
should not be dishonest and should not do anything which is harmful for the
self and society
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