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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5852_Библиотеки_им_академика_М_И_Перельмана.pdf
C H A P T E R 12 u Alcohols
c. 3º alcohols are generally resistant to oxidation in neutral or alkaline medium. This is the due to lack
of a hydrogen. Thus in order to oxidize a tertiary alcohol; C–C bond must be broken. On vigorous
oxidation with acidic oxidizing agent, 3º alcohols are degraded to give a mixture of ketones and
carboxylic acids. Thus it does not change the orange colour of the acidied Na2Cr2O7 as under
ordinary conditions as it does not oxidize it. It requires drastic conditions.
451
—
—
Isobutylene
—
—
—
—
—
—
alcohol
It may be noted that both ketone and carboxylic acid contain lesser number of carbon atoms in their molecules than the original tertiary alcohols.
4. Action with hot reduced copper (catalytic dehydrogenation): When vapours of alcohols are passed
over the freshly prepared hot reduced copper at 573 K, different types of alcohols give different products.
a. A primary alcohol is dehydrogenated to an aldehyde:
—
—
Ethyl alcohol
(Ethanol)
Acetaldehyde
(Ethanal)
b. A secondary alcohol is dehydrogenated to a ketone:
—
—
—
—
Isopropyl alcohol
(2-Propanol)
c. A tertiary alcohol is not dehydrogenated but gets dehydrated to form an alkene:
—
—
—
—
-Butyl alcohol
tert
(2-methyl-2-propanol)
d. Action of halogens: Chlorine and bromine, being moderate oxidizing agents, oxidize primary and
secondary alcohols to aldehyde and ketones, respectively, when they undergo halogenation.
(−2HCl)
Acetaldehyde Chloral
—
—
Isobutylene
452
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
12.8 DISTINCTION BETWEEN 1º, 2º AND 3º ALCOHOLS
1. Lucas test: Lucas test is based upon the difference in reactivity of primary, secondary and tertiary
alcohols with HCl. The alcohol under examination is treated with Lucas reagent (a mixture of equimolar quantities of concentrated hydrochloric acid and anhydrous ZnCl
) at room temperature when
2
turbidity appears due to the formation of insoluble alkyl chloride. Since the order of reactivity of
alcohol with halogen acids is 3
º > 2º > 1º.
Therefore, the alcohols are differentiated from each other on the basis of time required for the appearance
of cloudiness.
a. If turbidity (due to the formation of water-insoluble R—X) appears immediately, the alcohol is
tertiary.
b. If turbidity appears within ve minutes, the alcohol is secondary.
c. If turbidity does not appear at room temperature the alcohol is primary.
1º Alcohol 2º Alcohol 3º Alcohol
—CH2—OH R
R
+ HCl + ZnCl
2
CH—OH R3C—OH
2
+ HCl + ZnCl
2
+ HCl + ZnCl
2
i i i
RCH
Cl + H2O
2
No turbidity at room tempera-
ture, but appears on heating
R
CH—Cl + H2O R3C—Cl +H2O
2
Turbidity appears within ve
minutes
Turbidity appears immediately
2. Victor Meyer’s method
This test consists of the following steps:
a. The alcohol under examination is converted into corresponding iodide by treatment with phospho-
rus and iodine.
b. Alkyl iodide is then treated with silver nitrite to form corresponding nitroalkane.
c. Nitroalkane is next treated with nitrous acid. (NaNO2 + dil. HCl) and the resulting solution is made
alkaline with an aqueous solution of sodium hydroxide.
1º Alcohol 2º Alcohol 3º Alcohol
R—CH2—OH R2CH—OH R3C—OH
P/I
2
P/I
2
P/I
2
RCH2—I R2CH—I R3C—I
Iodo derivative Iodo derivative Iodo derivative
-AgI
AgNO
2
-AgI
AgNO
2
-AgI
AgNO
2
C H A P T E R 12 u Alcohols
453
RCH2—NO2 R2CH—NO
2
R3C—NO
2
Nitroalkane Nitroalkane Nitroalkane
HNO
—
O O
—H
2
RC—NO
N—OH —H2O HO—N
—
2
R
|
N—OH
Nitrolic acid
NaOH
Pseudonitrole
NaOH
Blood red colour Blue colour
C—NO
2
—
N
—
—
O
—
2
No action
O
Colourless
2
aq. NaOH
A primary alcohol gives blood red colour, secondary alcohol gives blue colour and tertiary alcohols give
no colour.
3. Oxidation or acidied potassium dichromate test: The three types of alcohols behave differently
on oxidation and thus it is possible to know the nature of the alcohol under examination. 1º and 2º
alcohols change the orange colour of acidied Na
to green while 3º does not.
2Cr2O7
4. Action with hot reduced copper: When vapours of alcohols are passed over hot reduced copper at
573 K, 1º and 2º alcohols are dehydrogenated to aldehydes and ketones, respectively, while 3º alcohols are dehydrated to alkenes.
5. Iodoform test: All alcohols containing CH3CHOH group give iodoform test. Methyl alcohol (CH3OH)
does not give this test as it does not contain CH
Analytical tests for alcohols
CHOH group.
3
The presence of a hydroxyl group in an unknown organic compound may be detected with the help of fol-
lowing tests. If the compound is a solid it is dissolved in an inert solvent, e.g. dry ether or benzene.
1. Alcohols are neutral substances towards litmus: The colour of blue or red litmus does not change
when alcohol is added to it.
2. Sodium metal test: A small piece of sodium metal is added to the compound or its solution. Evolu-
tion of hydrogen gas indicates the presence of –OH group in the organic compound.
3. Acylation test: When acetyl chloride is added to the given compound or its solution, if hydrogen
chloride is evolved, it shows that the organic compound is an alcohol.
4. Ceric ammonium nitrate test: The freshly prepared solution of ceric ammonium nitrate has yellow
colour. When few drops of this reagent are added to the given compound or its solution and if colour
changes from yellow to red, the compound contains a hydroxyl group.
454
Na
C H ONa + 1/2 H
2 5 2
CH COOH/Conc. H SO
3 2 4
CH COOC H + H O
3 2 5 2
CH COCl/Pyridine
3
CH COOC H + HCl
3 2 5
(CH CO) O
3 2
CH COOC H + CH COOH
3 2 5 3
RMgX
C H OMgX + RH
2 5
Conc. HCl/Anhy. ZnCl
2
C H Cl + H O
2 5 5
CH CHO, HCl
3
CH CHOH
3
CH – CH – OC H
3 2 5
—
OC H
2 5
—
OC H
2 5
HCl
C H OH
2 5
Hemiacetal Acetal
PCl
5
C H Cl + POCl + HCl
2 5 3
KBr/Conc. H SO
2 4
C H Br + H O
2 5 2
(Fischer-Speier
Esterification)
(Zerewitnoff method)
KI/Conc. H PO
3 4
C H I + H O
2 5 2
PX
3
C H X + H PO (X may be Cl, Br, I)
2 5 3 3
SOCl /Pyridine
2
C H Cl + SO + HCl
2 5 2
(Darzen’s procedure)
Cu/573
CH CHO + H
3 2
[O]; K Cr O /H SO
2 2 7 2 4
CH COOH
3
Conc. H SO
2 4
383 K
410 K
433 K
Under reduced pressure
C H HSO + H O
2 5 4 2
(C H ) O + H O
2 5 2 2
C H + H O
2 4 2
(C H ) SO + H O
2 5 2 4 2
∆
O ;Acetobacter
2
CH COOH + H O
3 2
HI
C H I + H O
2 5 2
HI; Red P
C H + H O + I
2 6 2 2
NH ; Al O , 633 K
3 2 3
C H NH + H O
2 5 2 2
Chloral
C H OH
2 5
Ethyl alcohol
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
MEMORY FOCUS
1. Some important reactions of alcohols with special reference of C2H5OH have been summed up as
follows:
C H OH
2 5
Ethyl alcohol
Na
CH COOH/Conc. H SO
3 2 4
CH COCl/Pyridine
3
(CH CO) O
Conc. HCl/Anhyd
3 2
RMgX
. ZnCl
CH CHO, HCl
3
[O], K Cr O /H SO
PCl
5
KBr/Conc. H SO
KI/Conc. H PO
SOCl /Pyridine
2 2 7 2 4
513–523 K, Al O
Cl ; oxidation
2
2 4
3 4
PX
3
2
Cu/573
2 3
–2HCl
C H ONa + 1/2 H
2 5 2
CH COOC H + H O
CH COOC H + HCl
CH COOC H + CH COOH
C H OMgX + RH
2 5
2
C H Cl + H O
2 5 5
CH CHOH
3 2 5 2
3 2 5
3 2 5 3
OC H
2 5
—
C H OH
2 5
3
HCl
(Fischer–Speier
Hemiacetal Acetal
C H Cl + POCl + HCl
2 5 3
C H Br + H O
2 5 2
C H I + H O
2 5 2
C H X + H PO (X may be Cl, Br, I)
2 5 3 3
C H Cl + SO + HCl
2 5 2
CH CHO + H
3 2
CH COOH
3
C H –O–C H + H O
2 5 2 5 2
CH CHO
3
3CI
2
CCI CHO + 3HCl
3
esterification)
(Zerewitinof
—
CH CH C H
3 5
OC H
—
2 5
—
f method)
O
2
(Darzen’s procedure)
C H A P T E R 12 u Alcohols
Na
C H ONa + 1/2 H
2 5 2
CH COOH/Conc. H SO
3 2 4
CH COOC H + H O
3 2 5 2
CH COCl/Pyridine
3
CH COOC H + HCl
3 2 5
(CH CO) O
3 2
CH COOC H + CH COOH
3 2 5 3
RMgX
C H OMgX + RH
2 5
Conc. HCl/Anhy. ZnCl
2
C H Cl + H O
2 5 5
CH CHO, HCl
3
CH CHOH
3
CH – CH – OC H
3 2 5
—
OC H
2 5
—
OC H
2 5
HCl
C H OH
2 5
Hemiacetal Acetal
PCl
5
C H Cl + POCl + HCl
2 5 3
KBr/Conc. H SO
2 4
C H Br + H O
2 5 2
(Fischer-Speier
Esterification)
(Zerewitnoff method)
KI/Conc. H PO
3 4
C H I + H O
2 5 2
PX
3
C H X + H PO (X may be Cl, Br, I)
2 5 3 3
SOCl /Pyridine
2
C H Cl + SO + HCl
2 5 2
(Darzen’s procedure)
Cu/573
CH CHO + H
3 2
[O]; K Cr O /H SO
2 2 7 2 4
CH COOH
3
Conc. H SO
2 4
383 K
410 K
433 K
Under reduced pressure
C H HSO + H O
2 5 4 2
(C H ) O + H O
2 5 2 2
C H + H O
2 4 2
(C H ) SO + H O
2 5 2 4 2
∆
O ;Acetobacter
2
CH COOH + H O
3 2
HI
C H I + H O
2 5 2
HI; Red P
C H + H O + I
2 6 2 2
513–523 K, Al O
2 3
NH ; Al O , 633 K
3 2 3
C H NH + H O
2 5 2 2
C H –O–C H + H O
2 5 2 5 2
Cl ; oxidation
2
CH CHO
3
CCI CHO + 3HCl
3
–2HCl
3CI
2
Chloral
5
C H OH
2 5
Ethyl alcohol
2
2
455
1. Wood spirit. Methyl alcohol (CH3OH) is called wood spirit. It is obtained by destructive distillation of
2. Grain alcohol. Ethyl alcohol (C2H5OH) is called grain alcohol. It is used in preparation of various bever-
3. Methylated spirit or denatured spirit. Ethyl alcohol containing 5–10% methyl alcohol is called methyl-
4. Absolute alcohol. 100% Ethanol is called absolute alcohol. It is generally prepared by azeotropic distil-
5. Power alcohol. A mixture of 80% petrol, 20% absolute ethyl alcohol with cosolvent benzene is called
6. Rectified spirit. Ethyl alcohol (95.87%) + water (4.13%) mixture is known as rectified spirit.
7. Pyroligneous acid contains acetic acid (10%), methyl alcohol (2.5%) and acetone (0.5%).
8. Tincture of iodine is 2–3% alcoholic solution of iodine.
9. Primary alcohols can be oxidized to aldehydes stage by Collins reagent (CrO3·2C5H5N) or pyridinium
10. In the oxidation of alcohol by acidified K2Cr2O7, its colour changes from orange to green due to the
11. 3º Alcohols are resistant to oxidation due to the lack of a-hydrogen.
12. 1º Alcohols on dehydrogenation with red hot copper form aldehydes, 2º alcohols form ketones and 3º
13. Fischer–Speier esterification
I + NaOH/Warm
2
CI + NaOH/2∆
Anhyd. CaCI
wood. Drinking of methanol causes blindness.
ages, by using different percentages.
ated spirit. It is unfit for drinking purposes. It is also called denatured spirit. Denaturing can also be
done by adding 0.5% pyridine, petroleum naphtha, rubber distillate (caoutchoucine) or CuSO
lation.
power alcohol. It is used to run automobiles.
chloro chromate (PCC, CrO
formation of Cr
(SO4)3.
2
alcohols form alkenes by dehydration.
CaOCl /
∆
2
2
CHCI
CHI
CHCI
CaCI 4C H OH
3
3
3
.
NHCI) in anhydrous medium.
3·C5H5
CH COOH + HOC H
Acetic acid
3 2 5
Ethyl alcohol Ethyl acetate
Dry HCI
CH COOC H + H O
3 2 5 2
.
4
456
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
14. The rates of esterification of three types of alcohols (R´O – H) are quite different and can be employed
in their distinction. The percentages of esters obtained by 1º, 2º and 3º alcohols with acetic acid are
45.7, 5.4 and 1.4%, respectively (because reactivity order is 1º > 2º > 3º).
15. Alcohols cannot be dehydrated using anhydrous CaCl
pound, CaCl
·4CH3OH or MgCl26CH3OH.
2
or MgCl2 because it forms an addition com-
2
16. Pinacol–Pinacolone rearrangement. The reaction involves dehydration of diols through the formation
of carbocation intermediate, which rearranges to more stable compound.
OH
—
—
—
C C CH
CH
3 3
—
CH
3CH3
OH
—
— —— —
—
+
H
–H O
2
CH3C C CH
H
C
—
3
—
CH
O
3
3
Pinacol Pinacolone
17. Order of acidity
H
O > ROH (1º) > ROH (2º) > ROH (3º) > RC CH > RCH = CH2 > RCH3
2
12.9 ETHYLENE GLYCOL
Ethylene glycol (also called 1,2-ethanediol or simply glycol) is a prominent member of the class of dihydroxy alcohols known as glycols, dihydric alcohols or diols. Glycols with two hydroxyl groups attached
to the adjacent carbon atoms are called 1,2-glycols or
a
-glycol or vicinal glycols. In the common system,
vicinal glycols are named after the olens from which they are derived. When the two hydroxyl groups
are situated at alternate or 1,3-positions, the glycols are called
extreme ends of a chain of carbon atoms, glycols are referred to as
b
-glycol and when two OH groups are the
b
-glycols and named as polymethylene
glycols. These are named according to the number of methylene groups present in the molecule. In the
IUPAC system, both the types of glycols are named as diols of parent alkanes and the positions of hydroxyl
groups are shown by suitable number. Some examples are given below:
—
CH CH
—
—
2 2
OH OH
Ethylene glycol
(an -glycol)
α
1,2-Ethanediol
—
—
CHCH H
3
—
C
—
OH OH
Propylene glycol
1,2-Propanediol
— —
—
H
2
O CH CH CH CH OH
2 2 2
Tetramethylene glycol (a ω-glycol)
Butane-1,4-diol
2
—
CH CH CH
—
—
—
2
2
OH OH
Trimethylene glycol
A, -glycol
β
1,3-Propanediol
2
12.9.1 Preparation of Ethylene Glycol
Glycol is prepared by the following methods:
1. From ethylene. By hydroxylation of ethylene. When the ethylene is treated with Baeyer’s reagent (cold
dilute alkaline solution of potassium permanganate), hydroxylation takes place at both the carbon atoms.
C H A P T E R 12 u Alcohols
—
—
—
Ethylene glycol
457
Alk. KMNO
—
4
2. From ethylene oxide (commercial method): By hydrolysis of ethylene oxide. Ethylene oxide (also
called ethylene epoxide) obtained after catalytic oxidation of ethylene is hydrolyzed in the presence
of a dilute acid or base at high temperature to ethylene glycol.
—
—
—
Ethylene
Ethylene glycol
3. From oxalic esters: Oxalic esters on reduction with sodium and alcohol give ethylene glycol.
—
—
4. From ethylenediamine: Ethylenediamine on treatment with nitrous acid (NaNO2 + HCl) gives ethyl-
ene glycol.
—
—
5. By catalytic reduction of glyoxal: On reduction with hydrogen in the presence of metal catalyst like
Ni, glyoxal gives ethylene glycol.
—
—
Glyoxal
—
—
6. From ethylene chlorohydrin
a. With NaHCO3: On a commercial scale, ethylene glycol is prepared by passing ethylene into hypo-
chlorous acid and subjecting the product formed (ethylene chlorohydrin) to hydrolysis by boiling
with aqueous sodium bicarbonate.
Ethylene
Ethylene chlorohydrin
—
Aq.
—
Ethylene glycol
458
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
b. With Ca(OH)2: Ethylene chlorohydrin on treatment with calcium hydroxide gives ethylene oxide
which on subsequent treatment with hot dilute acid solution.
O
—
—
2H CCICH OH + Ca (OH )
—
2 2
2
O
—
—
— —
CH CH + H O
2 2 2
—
CH CH + CaCl + 2 H O
2 2 2 2
Ethylene oxide
+
H , 473 K
CH OH
2
CH OH
2
12.9.2 Physical Properties
1. Glycol is a colourless, sweet and viscous liquid.
2. As it has two hydroxyl groups per molecule, it takes part in hydrogen bonding more effectively than
a monohydroxy alcohol of comparable mass. This is evident from its high boiling point (470 K), low
freezing point and high solubility in water.
12.9.3 Chemical Properties
Glycol undergoes most reactions of primary alcohols like formation of ethers, esters, halides, etc., and in
such reactions one or both hydroxyl groups react to form the corresponding compounds. Sometimes one
OH group reacts easily but the second OH group needs more vigorous conditions for the reaction to occur.
1. Reaction with sodium: At 323 K, sodium gives monosodium salt while at 433 K, it gives disodium
glycolate as there are two active hydrogens in it.
—
Glycol
—
glycolate
—
D
glycolate
2. Reaction with hydrogen chloride: At 433 K, ethylene glycol forms ethylene chlorohydrin with
hydrogen chloride, while at 473 K, it form ethylene dichloride. HBr reacts with glycol in the similar
way.
—
glycol
—
chlorohydrin
—
dichloride
C H A P T E R 12 u Alcohols
3. With HI only ethylene is obtained
CH OH
2
—
CH OH
2
+ 2HI
—
CH I
2
–2H O
—
2
—
CH I
2
Ethylene diiodide
(unstable)
CH
CH
2
+ I
2
2
4. Action with phosphorus pentahalides: Ethylene glycol reacts with PCl5 in two steps, as follows:
459
CH OH
—
2
CH OH
2
+ PCl
CH Cl
2
—
5
CH OH
2
+ HC + POCl l
3
Ethylene
chlorohydrin
CH Cl
—
2
CH OH
2
Ethylene
chlorohydrin
+ PCl
5
CH Cl
—
2
CH Cl
2
Ethylene
dichloride
l l
+ HC + POC
3
5. With thionyl chloride: Ethylene glycol reacts to form ethylene dichloride.
—
glycol
—
Ethylene
dichloride
6. Action with phosphorus trihalides: Ethylene glycol reacts with PCl3 or PBr3 in the same manner as
with PCl
. For example,
5
Ethylene
CH OH
—
2
CH OH
2
glycol
CH Br
P
Br
3
—
2
CH OH
2
P
Ethylene
bromohydrin
Br
3
CH Br
2
—
CH Br
2
Ethylene
dibromide
However, with phosphorus tri-iodide, ethylene glycol forms ethylene. Ethylene di-iodide formed initially,
being unstable, readily eliminates iodine.
—
—
—
—
I
—
—
—
I
460
—
—
—
—
—
———
—
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
7. Reaction with nitric acid: Glycol gives ethylene dinitrate with a mixture of conc. HNO3 and conc.
H
.
2SO4
—
Ethylene
glycol
—
Ethylene
dinitrate
8. Reaction with monocarboxylic acids: Glycol reacts with monocarboxylic acid like acetic acid in the
presence of conc. H
—
Ethylene
glycol
to form monoacetate and nally diacetate.
2SO4
—
Glycol
monoacetate
—
Glycol
diacetate
9. Reaction with acetyl chloride/acetic anhydride: Ethylene glycol reacts with two moles of acetyl
chloride or acetic anhydride to form glycol diacetate.
———
—
—
—
—
—
—
———
+2CH3COOH
—
—
Glycol
+2CH3 C O C CH
—
—
3
—
—
10. Action with dicarboxylic acids: When ethylene glycol is heated with bicarboxylic acids or their es-
ters in the presence of an acid or a base, condensation polymerization takes place to form polyesters.
Thus, the polyester, terene, is obtained when glycol is heated with terephthalic acid.
Similarly simplest glyptal, i.e. poly(ethylene phthalate) is formed by the condensation of ethylene glycol
and phthalic acid and is used in the manufacture of paints and lacquers.