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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5574_Библиотеки_им_академика_М_И_Перельмана.pdf
C H A P T E R 12 u Alcohols
8. Reaction with potassium hydrogen sulphate (Dehydration): When heated with dehydrating agents
like potassium hydrogen sulphate (or phosphorus pentoxide or concentrated sulphuric acid), glyceral
eliminates two molecules of water to form acrolein, an
a, b-unsaturated aldehyde having very offen-
sive odour. It has two π- and seven σ-bonds. It gives all the tests of aldehydes (Fehling, Tollen and
Schiff reagent tests):
H
—
—
—
C
H
—
—
—
C
HO H
—
—
—
C
H
—
H
OH
OH
KHSO , ∆
4
–2H O
2
CH
2
CH
CHOH
CH
2
CH
—
CHO
Acrolein
Glycerol
Acrolein test: Heat a small quantity of glycerol with conc. H2SO4 or KHSO4; very offensive odour is
produced due to formation of acrolein.
9. a. Oxidation: Upon oxidation, glycerol yields a number of products depending on the nature of oxi-
dizing agent.
471
CH OH
—
2
CH OH
—
CH OH
2
CH OH
(O)
—
2
C O
—
CH OH
2
Dihydroxy acetone
CHO
—
(O)
CHOH
—
CH OH
2
Glycerol aldehyde Glyceric acid
(O)
(O) (O)
COOH
—
C O
—
COOH
Mesoxalic acid
COOH
—
CHOH
—
CH OH
2
COOH
—
CHOH
—
COOH
Tartronic acid
i. Dilute nitric acid gives glyceric acid and tartronic acids.
ii. Bismuth nitrate and sodium nitrate gives mesoxalic acid.
iii. Fenton’s reagent (H2O2 + FeSO4) or sodium hypobromite or bromine water yield mixture of
glyceraldehyde and dihydroxyacetone at 283–293 K, the mixture is commonly known as glycerose.
b. Oxidation with HIO4:
—
—
Similarly, (CH3COO)4Pb oxidizes glycerol to formaldehyde and formic acid.
472
Glyceric acid
Tartonic acid
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
MEMORY FOCUS
—
CH OH
2
—
CH
—
O
—
—
CH H
O
2
Glycerol
Na
Room temp.
KHSO
or Conc. H SO or P O
4
2 4 2 5
CH ONa
2
—
CHOH
— —
OH
CH
2
CH CH CHO
2
Na
High temp.
—
CH ONa
2
—
CHOH
—
CH ONa
2
Acrolein
CH ONO
2 2
Conc. H SO
2 4 3
, HNO
,
298 K
CHONO
—
CH ONO
2 2
2
(Glyceryl trinitrate)
CH I
2
H
(Limited)
KMnO
4
3HI
—
CHI
—
CH I
2
COOH
—
CH
2
–I
2
CH
—
CH I
2
+ CO + H O
2 2
HI (excess)
CH
CHI
—
CH
3
3
COOH
FeSO /H O
4 2 2
(Fenton’s reagent)
dil. HNO
3
CH OH
2
—
CHOH
—
CHO
Glyceraldehyde
Glycerose
COOH
—
CHOH
—
CH OH
2
CH OH
2
—
+
C O
—
CH OH
2
Dihydroxyacetone
COOH
—
+
CHOH
—
COOH
Na
CHOH
CH OH
2
Na
High temp.
CHOH
CH ONa
2
KHSO
or conc. H SO or P O
4
2 4 2 5
CH = CH – CHO
2
Acrolein
Conc. H SO ; HNO 298 K
2 4 3
CH ONO
2 2
CHONO
2
CH ONO
2 2
(Glyceryl trinitrate)
3HI
(Limited)
CH I
2
CHI
CH I
2
–I
2
CH
2
CHI
CH I
2
HI (excess)
CH
3
CHI
CH
3
KMnO
4
COOH
COOH
+ CO + H O
2 2
FeSO /H O
(Fenton’s reagent)
4 2 2
CH OH
2
CHOH
CHO
+
CH OH
2
C=O
CH OH
2
Glyceraldehyde
Dihydroxyacetone
Glycerose
HNO , dil.
3
COOH
CHOH
CH OH
2
+
COOH
CHOH
COOH
Glyceric acid
Tartonic acid
—
2
—
2
Room temp.
C H A P T E R 12 u Alcohols
473
Bismuth nitrate
∆
2HIO ,
4
(COOH) , 385 K
2
–CO
2
(COOH) , 510 K
2
–2H O, –2CO
2 2
HOOC C COOH (Mesoxalic acid)
2HCHO + HCOOH + 2HIO + H O
CH OH
—
CHOH
—
CH OH
Glycerol
CH
CH
CH OH
(Allyl alcohol)
O
—
2
+ HO C H
2
2
2
—
— —
3 2
O
Uses of Glyerol
1. As a sweetening agent in confectionary, beverages and medicines.
2. As an antifreeze in automobile radiators because it lowers the freezing point of water.
3. As a lubricant in watches.
4. In the formation of glycerol trinitrate used in making dynamite.
5. As a plasticizer for cellophane.
6. In the preparation of nondrying inks, stamp pads and printing inks.
7. In the preparation of good quality of soaps and cosmetics.
8. In the manufacture of acid-proof cement.
9. As a moisture conditioner for tobacco products.
10. In the preparation of various organic compounds like formic acid, allyl alcohol, acrolein, etc.
11. Because of its hygroscopic nature it is used as a preservative for fruits and eatables, which are required to be kept moist.
Metabolism: Although the alcohol functional group is relatively stable in vitro, it is readily metabolized
in the body by a variety of enzymes, most notably cytochrome P450 enzymes and alcohol dehydrogenase.
Both primary and secondary alcohols are prone to oxidation by oxidative enzymes, resulting in the formation of carboxylic acids and ketones. The tertiary alcohol is relatively stable to oxidize enzymes. Another
common metabolic fate of the alcohol is conjugation with glucouronic acid to give a glucuronide or with
sulphuric acid to give sulphate conjugate. Both of these conjugates show a considerable increase in water solubility. The glucuronide has several additional alcohol functional groups that exhibit dipole–dipole
bonding to water.
474
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
NOTEWORTHY POINTS
1. Glyceryl trinitrate is an inorganic ester.
2. Glyceryl trinitrate is a colourless, oily liquid insoluble in water and is called Nobel's oil.
3. On detonating, it explodes violently giving CO
4C
4. It is a safer explosive when adsorbed on kieselguhr and is known as dynamite.
5. Its mixture with cellulose nitrate is known as blasting galetin or gelignite.
6. Its mixture with cellulose nitrate (gun cotton) and vaseline is called cordite. It is a smokeless powder.
7. Nobel's oil is also used in the treatment of angina pectoris and asthma.
8. Dunstan's test for glycerol. A drop of phenolphthalein is added to approx. 5 mL of borax solution. The
pink colour appears. On adding 2–3 drops of glycerol, the pink colour disappears. The pink colour
reappears on heating and disappears on cooling again.
9. Hydroxylation of alkene can be carried out either by cold alkaline KMnO
(HCO
OH). Hydroxylation by either reagent is stereoselective and stereospecific. Cold alkaline KMnO4
2
gives syn addition and peroxy acid gives anti addition.
3H5
(ONO2)
12CO2 + 10H2O + 6N2 + O
3
2, N2, O2
as gaseous products.
2
on peroxyformic acid
4
SUMMARY
1. Acidity of alcohols decreases as the +I-effect increases (1° > 2° > 3°). Alcohols are even weaker
acids than water. Therefore, H
O decomposes alkoxides to form alcohols.
2
2. Alcohols give three types of reactions: (i) those involving cleavage of O—H bond, (ii) those involving cleavage of C—OH bond and (iii) those involving alcohol molecule as a whole.
3. The general order of reactivity of alcohols involving cleavage of O—H bond is 1° alcohol > 2°
alcohol > 3° alcohol. Some important reactions of this category are as follows:
a. Due to acidic nature, alcohols react with active metals like Na, K, Mg, Zn, Al, etc., forming their
corresponding alkoxides/phenoxides with the evolution of H2 gas.
b. Esterication:
i. With carboxylic acids: Alcohols react with carboxylic acids in presence of a few drops of
cone. H
or dry HCl gas to form esters.
2SO4
Reactivity of alcohols: CH3OH > CH3CH2OH > (CH3)2CHOH > (CH3)3COH
Reactivity of acids: HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH
C H A P T E R 12 u Alcohols
ii. With acid chlorides and anhydrides: Esterication of alcohols can also be carried out with
acid chlorides or anhydrides to form the corresponding esters. With acetyl chloride or anhydride, this reaction is called acetylation while with benzoyl chloride, it is called benzoylation.
The reaction of alcohols with benzoyl chloride in the presence of NaOH is called Schotten–
Baumann reaction.
iii. Alcohols react with RMgX to form alkanes (RH) corresponding to alkyl group of the Grignard
reagent.
4. The general order of reactivity of alcohols involving the cleavage of C—OH bond is 3° alcohol > 2°
alcohol > 1° alcohol. Some important reactions of this category are listed below:
a. Reaction with halogen halides: Alcohols react with halogen acids to form alkyl halides and
water. The order of reactivity of different halogen acids is HI > HBr > HI.
i. 1° and 2° alcohols react with HCl in presence of ZnCl2 as catalyst (Groves’ process) while no
such catalyst is needed in case of 3° alcohols.
ii. Alkyl bromides and iodides can be prepared by reuxing alcohols with constant boiling HBr
(48%) and HI (57%) respectively. HBr and HI required for the purpose can also be prepared
in situ by the reaction of NaBr and NaI with H
3PO4
.
b. Reaction with phosphorus halides:
i. Alcohols react with PCl5 to give alkyl chlorides, POCl3 and HCl, while with PCl3 alkyl chloride
and H
if SOCl
SO
2
are formed. In either case alcohol has to be freed from POCl3 or H3PO3. However,
3PO3
is used in place of PCl5 or PCl3, alkyl chlorides are obtained in almost pure state since
2
and HCl which are formed during the reaction (gases) escape into the atmosphere.
ii. Alcohols react with PBr3 (P + Br2) or PI3 (P + 2I2) to form the corresponding alkyl bromides
and iodides, respectively.
475
5. Some important reactions involving alcohol molecule as a whole are (a) dehydration (b) oxidation
of alcohols.
a. Dehydration of alcohols to form alkenes is carried out by heating an alcohol with conc. H2SO4
at 433–443 K. This reaction occurs through carbocation intermediates. If the-initially formed
carbocation is 1° or 2° and if the structure permits, it rearranges either by 1, 2-hydride shift or
1, 2-alkyl shift to form the more stable 2° or 3° carbocations before losing a proton to form the
alkene. Thus, dehydration of many alcohols gives rearranged products. For example, the major
product of dehydration of 2-methyl-2-butanol is not the expected alkene, i.e. 2-methyl-1-butene
but is the rearranged product, i.e. 2-methyl-2-butene.
b. Alcohols react with conc. H2SO4 at different temperatures to form different products:
i. At 383, alkyl hydrogen sulphates are formed, which when heated under reduced pressure
form dialkyl sulphates.
ii. At 413 K, alkyl hydrogen sulphates react with excess of alcohol to form ethers.
iii. At 443 K, in presence of excess of conc. H2SO4, alkyl hydrogen sulphates eliminate a mol-
ecule of H
to form alkenes.
2SO4
476
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
c. Oxidation of alcohols: Reagents used for oxidation or alcohols are neutral, acidic or alkaline
KMnO
, acidied K2Cr2O7 and dilute HNO3.
4
i. 1º Alcohols give rst aldehydes and then carboxylic acids, both having the same number of
C-atoms as the original alcohol.
ii. 2º Alcohols give rst ketones with the same number of carbon atoms and then acids with lesser
number of carbon atoms than the original alcohol.
iii. 3º Alcohols are resistant to oxidation by neutral or alkaline KMnO4 solution but are readily oxi-
dized by acidic oxidizing agents (K
2Cr2O7/H2SO4
or KMnO4/H2SO4) to give a mixture of a
ketone and an acid, both containing lesser number of carbon atoms than the original alcohols.
The oxidation of 3° alcohols presumably occurs via alkenes formed through dehydration of alcohols
under acidic conditions.
ALCOHOLS
6. Distinction of 1º, 2º and 3º alcohols.
a. Lucas test (conc. HCl + anhyd. ZnCl2)
3° Alcohols: Cloudiness appears immediately.
2° Alcohols: Cloudiness appears in about ve minutes.
1° Alcohols: Cloudiness does not appear at room temperature.
b. Victor–Meyer's test: The various steps are treatment of alcohols with: (i) red P + I2, (ii) AgNO
(iii) HNO2 and (iv) aqueous NaOH or KOH.
1° Alcohols give blood red colouration, 2º alcohols give blue colouration, 3º alcohols give no
colouration.
c. Action of hot copper: When vapours of alcohols are passed overheated copper at 573 K, 1º
Alcohols give aldehydes, 2º alcohols give ketones while 3º alcohols give alkenes.
2
7. Glycerol is commercially prepared either by saponication of oils and fats or from propylene.
8. Due to extensive intermolecular H-bonding, glycerol is a highly viscous liquid. It forms H-bonds
with water and hence is highly soluble in water. Since it decomposes at its boiling point, it is puried
by distillation under reduced pressure.
9. With PCl5 or PCl3, glycerol forms 1,2,3-trichloropropane, and with PBr3 it forms 1,2,3-tribromopropane.
10. With a small amount of HI or PI3, glycerol gives allyl iodide while with excess of HI or PI3, it gives
isopropyl iodide.
11. Nitration of glycerol with a mixture of conc. HNO3 + conc. H2SO4 gives nitroglycerine (Nobel's
oil). It explodes violently on heating or detonation. However, Alfred Nobel, the scientist in whose
name Nobel Prizes have been instituted, found that nitroglycerine can be stabilized by absorbing
over kieselguhr, a kind of porous earth.
12. A mixture of glyceryl trinitrate and glyceryl dinitrate absorbed on kieselguhr is called dynamite.
13. When heated with KHSO4 or anhyd. ZnCl2 or conc. H2SO4, glycerol undergoes dehydration to form
acrolein.
C H A P T E R 12 u Alcohols
14. Glycerol on oxidation with different oxidizing agents give different products: (a) With dilute HNO3,
it gives a mixture of glyceric acid and tartronic acid. (b) With conc. HNO
acid. (c) With Bi(NO
Fenton's reagent (H
(e) With HIO
, it gives one molecule of formic acid and two molecules of formaldehyde.
4
, only mesoxalic acid is formed. (d) With sodium hypobromite (NaOBr) or
3)3
+ FeSO4), a mixture of glyceraldehyde and dihydroxyacetone is obtained.
2O2
, it mainly gives glyceric
3
15. With oxalic acid at 383 K, glycerol gives formic acid, while at 503 K, it gives allyl alcohol.
REVISION QUESTIONS
1. What are polyhydric alcohols? How is glycerol obtained from oils and fats? How glycerol reacts
with (i) excess HI, (ii) KHSO4, (iii) conc. HNO3 and (iv) conc. H2SO4.
2. What are primary, secondary and tertiary alcohols? How can you obtain each one of these by using
Grignard reagent? What happens when these classes of alcohols are (i) oxidized with K2Cr2O7 and
H
and (ii) passed overheated copper.
2SO4
3. (a) How is phenol obtained commercially from (i) benzene and propene and (ii) chlorobenzene?
(b) How phenol reacts with
477
i. Br2 water, (ii) Br2 in CS2, (iii) CHCl3 + NaOH at 340 K and (iv) CO2 at 400 K under pressure
of 4–7 atm.
4. Draw the structure of eight isomeric pentyl alcohols, C5H11OH and name each alcohol according to
IUPAC system and indicate each as primary, secondary or tertiary.
5. How is phenol obtained from (i) benzene sulphonic acid and (ii) benzenediazonium chloride? Convert it into (i) benzene, (ii) salicylaldehyde, (iii) phenolphthalein, (iv) picric acid and (v) phenyl
benzene.
6. Write synthesis of glycerol starting from its elements.
7. Write IUPAC names of following compounds.
l l
— —
—
— —
—
—
— —
— —
8. How will you convert glycerol into (i) allyl alcohol, (ii) acrolein and (iii) isopropyl iodide?
9. Write resonance structures of phenol (which are similar to that of chlorobenzene) and explain why
phenol is more acidic than ethanol? Explain whether p-nitrophenol should be more or less acidic
than phenol.
478
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
10. How will you obtain the following starting from ethyl alcohol?
(i) Ethyl acetate, (ii) Ethyl bromide, (iii) Sodium ethoxide, (iv) Acetaldehyde,
(v) Ethylene, (vi) Iodoform and (vii) Diethyl ether.
11. Give one method each for industrial preparation of (i) methyl alcohol, (ii) ethyl alcohol and
(iii) phenol.
12. Discuss the following (with the help of reactions):
(a) Relative reactivity of alcohols towards Lucas reagents.
(b) Glycerol is treated with excess of HI.
(c) Phenols are acidic while alcohols are not though both have –OH group.
(d) How is phenol converted into (i) well-known acid base indicator and (ii) p-bromophenol.
13. Give the synthesis of each of the following alcohols from an alkene with the same number of carbon:
—
—
i
.
— —
—
ii
.
—
iii
.
—
14. How will you distinguish primary, secondary and tertiary alcohols. Explain with reactions.
MULTIPLE CHOICE QUESTIONS
1. The number of structural isomers of alcohols with molecular formula C3H7OH is
(a) 5 (b) 4
(c) 3 (d) 2
2. The high boiling points of alcohols, as compared to the corresponding alkanes, are due to
(a) Hydrogen bonding (b) Heavy oxygen atom
(c) Water solubility (d) None of these
3. Methanol is known as:
(a) Rubbing alcohol (b) Grain alcohol
(c) Wood alcohol (d) Denatured alcohol
C H A P T E R 12 u Alcohols
4. Rectied spirit is
(a) 100% Ethanol (b) 90% Ethanol
(c) 100% Methanol (d) 95% Ethanol
5. Grain alcohol is another name for
(a) Methyl alcohol (b) Isopropyl alcohol
(c) Ethyl alcohol (d) n-Propyl alcohol
6. Lucas reagents is
(a) HCl/NaNO2 (b) H2/Pd
(c) HCl/ZnCl
(d) H2/Pd/BaSO4
2
7. Which of the following compounds reacts slowest with Lucas reagent at room temperature?
(a) 1-Butanol (b) 2-Propanol
(c) 2-Butanol (d) 2-Methyl-2-propanol
8. Which of the following compounds will react fastest with Lucas reagent?
(a) 1-Propanol (b) 2-Methyl-1-propanol
(c) 2-Propanol (d) 2-Methyl-2-propanol
479
9. When ethanol is treated with sodium metal:
(a) Sodium ethoxide is formed
(b) Sodium is oxidized
(c) Acidic hydrogen is reduced
(d) All these occur
10. Ethyl alcohol can react with concentration H2SO4 to give
(a) Ethylene (b) Diethyl ether
(c) Ethyl hydrogen sulphate (d) All of these
11. Hydroboration–oxidation of propene gives
(a) Isopropyl alcohol (b) n-Propyl alcohol
(c) Isobutyl alcohol (d) tert-Butyl alcohol
12. Which of the following compounds will not be easily oxidized?
(a) Primary alcohol (b) Secondary alcohol
(c) Tertiary alcohol (d) Aldehyde
13. Oxidation of a secondary alcohol with K2Cr2O7/H+ produces
(a) A carboxylic acid (b) A ketone
(c) An aldehyde (d) An ester
480
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
14. The mechanism of dehydration of an alcohol to give an ether involves formation of:
(a) Carbonium ions (b) Carbanions
(c) Free radicals (d) Carbenes
15. The acid-catalysed dehydration mechanism for alcohols is best described as a(n):
(a) E1 (b) E
(c) SN1 (d) SN
2
2
16. When ethanol is heated with concentration H2SO4, a gas is produced. Which of the following compounds is formed when this gas is treated with bromine in CCl
4
(a) Bromomethane (b) 1,2-Dibromoethane
(c) Bromoethane (d) 1,1,2,2-Tetrabromoethane
17. Ethylene glycol reacts with excess of PCl5 to give
(a) Chloroethane (b) 1,2-Dichloroethane
(c) Hexachloroethane (d) 1,3-Dichloroethane
18. 1,2-Ethanediol reacts with anhydrous zinc chloride to form
(a) Ethylene (b) Acetaldehyde
(c) Hexachloroethane (d) Ethyl chloride
19. When ethylene glycol is heated with concentrated HNO3, it forms
(a) Oxalic acid (b) Ethylene oxide
(c) Dioxane (d) Ethyl chloride
20. Which of the following is used as an antifreeze?
(a) Ethylene glycol (b) Glycerol
(c) Diethyl ether (d) Picric acid
21. When glycerol is heated with oxalic acid at 260ºC, it gives
(a) 1,2-Propanediol (b) Vinyl alcohol
(c) 1,3-Propanediol (d) Allyl alcohol
22. Glycerol on warming with a small amount of hydriodic acid gets converted to
(a) Propene (b) Acetic acid
(c) 1,3-Diiodopropane (d) Propionic acid
23. When glycerol is heated with potassium hydrogen sulphate (KHSO4), it forms
(a) Acrolein (b) Acetic acid
(c) Allyl alcohol (d) Propionic acid
24. When glycerol is treated with a mixture of concentrated HNO3 + H2SO4, it forms