Class 12 Chemistry Alcohol Notes

Class 12 Chemistry Alcohol Notes
Chapter 10 – Alcohols | Nepal eNotes
CHEMISTRY • CHAPTER 10

Alcohols

Exact typing reconstruction from the supplied handwritten notes.

Original Scanned PDF – View Notes

Open PDF Full Screen
Open PDF in Google Drive
PDF Page 1

ALCHOLS

Alcohol are the hydroxy (−OH) derivative of alkane (ano) in which at least one hydrogen atom is replaced by hydroxy group.

R−H −H / +OH→ R−OH

Alkane → Alcohol

Eg =

CH3−OH

Methanol

(Methyl alcohol)

CH3−CH2−OH

Ethanol

(Ethyl alcohol)

CH3−CH2−CH2−OH

propan−1−ol

(propyl alcohol)

CH3−CH(OH)−CH3

propan−2−ol

(Iso propyl alcohol)

C4H10O
CH3−CH2−CH2−CH2−OH

butan−1−ol

(n−butyl alcohol)

CH3−CH(OH)−CH2−CH3

butan−2−ol

(secondary butyl alcohol)

CH3−CH(CH3)−CH2−OH

2−methylpropan−1−ol

(isobutyl alcohol)

(CH3)3C−OH

2−methylpropan−2−ol

tert−butyl alcohol

PDF Page 2
CH3−CH2−CH2−CH2−CH2−OH

pentan−1−ol

(n−pentyl alcohol)

(CH3)3C−CH2−OH

2,2−dimethylpropan−1−ol

(neo−pentyl alcohol)

HO−CH2−CH2−OH

ethan−1,2−diol

(Glycol)

HO−CH2−CH(OH)−CH2−OH

propan−1,2,3−triol

(Glycerine)

Types of alcohol

A) On the basis of number of hydroxy groups

i) Monohydric alcohol

The alcohol having only one hydroxy group is called monohydric alcohol.

Eg = CH3−CH2−OH    Ethanol.

ii) Dihydric alcohol

The alcohol having two hydroxy group is called dihydric alcohol.

Eg = HO−CH2−CH2−OH    (ethane−1,2 diol)
PDF Page 3

iii) Trihydric alcohol

The alcohol having three hydroxy group is called trihydric alcohol.

Eg = HO−CH2−CH(OH)−CH2−OH

propan−1,2,3−triol
(Glycerene)

B) On the basis of hydroxy group attached carbon atom

i) Primary (1°) alcohol

The alcohol in which hydroxy group is attached with primary (1°) carbon atom is called primary alcohol.

Eg = CH3−CH2−OH    Ethanol

ii) Secondary (2°) alcohol

The alcohol in which hydroxy group is attached with secondary (2°) carbon atom is known as secondary alcohol.

Eg = CH3−CH(OH)−CH3    Propan−2−ol
PDF Page 4

iii) Tertiary (3°) alcohol

The alcohol in which hydroxy group is attached with tertiary (3°) carbon atom is called tertiary alcohol.

Eg = (CH3)3C−OH

2−methylpropan−2−ol
(Tert. butyl alcohol)

Isomerism in alcohol

Alcohol can exist three types of structural isomers.

1) Chain isomers

The isomers in which only longest carbon chain is different is called chain isomers.

CH3−CH2−CH2−CH2−OH

Butan−1−ol

CH3−CH(CH3)−CH2−OH

2−methylpropan−1−ol

2) Position isomers

The isomers in which only position of functional group is different is called position isomer.

CH3−CH2−CH2−OH    and    CH3−CH(OH)−CH3

propan−1−ol     propan−2−ol

PDF Page 5

iii) Functional isomers

The isomers in which only functional group is different is called functional isomers.

Alcohol and ether are functional isomers of each other.

CH3−CH2OH    and    CH3−O−CH3

ethanol     methoxymethane

CH3−CH2−CH2−OH    and    CH3−CH2−O−CH3

propan−1−ol     methoxyethane

NOTE:
Alcohol → Ether
Aldehyde → Ketone
Cyanide → Isocyanide
Nitride → Nitro
Carboxylic acid → Ester
Functional isomer of each other.

Victor Meyer’s test

In the distinction of primary, secondary and tertiary alcohol by victor meyer test first alcohol is treated with red P and I2 gives iodoalkane then treated with AgNO2 gives nitro alkane. At last HNO2 is added and solution is made alkaline by adding strong alkali like NaOH/KOH. Finally colour of the soln is observed.

PDF Page 6
Blood red colour indicates 1° alcohol.
Blue colour indicates 2° alcohol.
colourless indicates 3° alcohol.

for 1° alcohol:

R−CH2−OH Red P and I2→ R−CH2−I AgNO2→ R−CH2−NO2

1° alcohol → Iodoalkane → Nitroalkane

R−CH2−NO2 + HNO2 → R−C(NO2)=NOH + H2O

Nitrolic acid

Nitrolic acid NaOH→ Sod. salt of Nitrolic acid

Red colour

for 2° alcohol:

R2−CH−OH Red P and I2→ R2−CH−I AgNO2→ R2−CH−NO2

2° alcohol → Iodoalkane → Nitroalkane

R2−CH−NO2 + HNO2 → R2C(NO2)−N=O

(Pseudonitrol)

Pseudonitrol NaOH→ Blue colour
PDF Page 7

for 3° alcohol

R3−C−OH Red P and I2→ R3−C−I AgNO2→ R3−C−NO2
R3−C−NO2 + HNO2 → No rxn NaOH→ colourless

Lucas test

The mixture of conc HCl and anhydrous ZnCl2 is called Lucas reagent.

1°, 2°, 3° alcohol can be distinguished by Lucas test.

3° alcohol

3° alcohol react with Lucas reagent produce cloudiness immediately.

(CH3)3C−OH + HCl anhydrous ZnCl2, conc→ (CH3)3C−Cl + H2O

Cloudiness

R3−C−OH + HCl anhyd. ZnCl2, conc→ R3−C−Cl + H2O

Cloudiness

2° alcohol

2° alcohol react with lucas reagent produce cloudiness within a five minutes.

R2−CH−OH + HCl anhyd. ZnCl2→ R2−CH−Cl + H2O

Cloudiness

PDF Page 8

1° alcohol

1° alcohol gives cloudiness only heating.

R−CH2−OH + HCl Δ→ R−CH2−Cl + H2O

Cloudiness

General preparation of monohydric alcohol

1) From haloalkane

a) By hydrolysis with aq KOH

Haloalkane react with aq KOH gives alcohol.

CH3−CH2−Br + KOH aq→ CH3−CH2−OH + KBr
CH3−CH(Br)−CH3 + KOH aq→ CH3−CH(OH)−CH3 + KBr

propan−2−ol (isopropyl alcohol)

b) By rxn with moist Ag2O

Haloalkane react with moist Ag2O gives alcohol.

Ag2O + H2O → 2AgOH
CH3−CH2−Br + AgOH → CH3−CH2−OH + AgBr

2) From primary amine

Primary amine react with nitrous acid gives alcohol.

PDF Page 9
CH3−CH2−NH2 + HNO2 NaNO2 + HCl, 0−10°C→ CH3−CH2−OH + N2↑ + H2O
CH3−CH(NH2)−CH3 + HNO2 NaNO2 + HCl, cold→ CH3−CH(OH)−CH3 + N2↑ + H2O

3) From Ester

a) Acid hydrolysis of ester

Ester on acid hydrolysis gives alcohol and carboxylic acid.

CH3COOC2H5 + H2O H+⇌ C2H5OH + CH3COOH

Ethyl ethanoate → ethyl alcohol + ethanoic acid (acetic acid)

b) Alkaline hydrolysis of ester

Ester when hydrolysis with alkali gives alcohol.

CH3COOC2H5 + NaOH → C2H5OH +
PDF Page 10
+ CH3COONa    Na ethanoate / Na−acetate

c) Reduction of ester

Ester on reduction gives alcohol.

CH3COOCH2−CH3 + 2[H] LiAlH4→ 2CH3−CH2OH

4) From grignard reagent

Synthesis of alkane

Grignard reagent when react with H2O / NH3 or alkyl halide gives alkane.

CH3−CH2−MgBr    Ethylmagnesium bromide
CH3−CH2−MgBr + H−OH → CH3−CH3 + Mg(OH)Br

Ethane

CH3−CH2−MgBr + H−NH2 → CH3−CH3 + Mg(NH2)Br

Ethane

CH3−CH2−MgBr + CH3−Br → CH3−CH2−CH3 + MgBr2

Propane

ii) Synthesis of carbon

[No further explanatory content is written under this heading on the supplied page.]

PDF Page 11

5. From Alkyl halide

Haloalkane react with aqueous alkali (NaOH/KOH) gives alcohol.

CH3−CH2−Br + KOH aq→ CH3−CH2−OH + KBr

ethanol

CH3−CH(Br)−CH3 + KOH → CH3−CH(OH)−CH3 + KBr

2−Bromopropane → propan−2−ol

6) By the reduction of aldehyde, carboxylic acid and ketone

On the reduction of aldehyde, carboxylic acid or ketone gives alcohol.

Aldehyde and carboxylic acid gives primary alcohol.

CH3−COOH + [H] LiAlH4→ CH3−CHO + [H] → CH3−CH2−OH

ethanoic acid → ethanal → ethanol

CH3−COOH + [H] LiAlH4→ CH3−CH2−OH + H2O
PDF Page 12
CH3−CH2−CHO + [H] LiAlH4→ CH3−CH2−CH2−OH

Ketone gives secondary alcohol

CH3−CO−CH3 + [H] LiAlH4→ CH3−CH(OH)−CH3

propanone → propane−2−ol

CH3−CH2−CO−CH2−CH3 LiAlH4→ CH3−CH2−CH(OH)−CH2−CH3

pentan−3−one → pentan−3−ol

Industrial preparation of alcohol

Fermentation of carbohydrates

The fermentation of carbohydrate into alcohol is one of the best method for the industrial preparation of alcohol. The process of decomposition of complex organic compound into simpler compound by the effect of biological catalyst (enzyme) is called fermentation.

a) Ethanol from Sugar or molasses

Molasses is dark coloured thick syrupy mother liquor left after the crystallization of sugarcane solution.

C12H22O11 + H2O Invertase enzyme→ C6H12O6 + C6H12O6

Glucose + Fructose

C6H12O6 zymase, rum yeast→ 2C2H5OH + 2CO2
PDF Page 13

The fermented liquid which contain 8−10% ethanol is called Wort WASH.

b. Ethanol From starch

C6H10O5 + H2O diastase enzyme→ C12H22O11

(maltose sugar)

C12H22O11 + H2O maltase→ C6H12O6

Glucose / Fructose

C6H12O6 zymase→ 2C2H5OH + 2CO2

Ethanol

Imp: Oxo process

Alkene react with water gas (CO + H2) in presence of dicobalt octacarbonate gives aldehyde which on reduction produce alcohol.

CH3−CH=CH2 + CO + H2 [Co(CO)4]2, high temp/pressure→ CH3−CH2−CHO H2/Ni→ CH3−CH2−CH2−OH

propene → butan−1−ol

CH2=CH2 + CO + H2 [Co(CO)4]2→ CH3−CH2−CHO H2/Ni→ CH3−CH2−CH2−OH

propan−1−ol

PDF Page 14
This page repeats the same material that appears on PDF Page 12. It is preserved because it appears physically in the supplied source.
CH3−CH2−CHO + [H] LiAlH4→ CH3−CH2−CH2−OH

Ketone gives secondary alcohol

CH3−CO−CH3 + [H] LiAlH4→ CH3−CH(OH)−CH3

propanone → propane−2−ol

CH3−CH2−CO−CH2−CH3 LiAlH4→ CH3−CH2−CH(OH)−CH2−CH3

pentan−3−one → pentan−3−ol

Industrial preparation of alcohol

Fermentation of carbohydrates

The fermentation of carbohydrate into alcohol is one of the best method for the industrial preparation of alcohol. The process of decomposition of complex organic compound into simpler compound by the effect of biological catalyst (enzyme) is called fermentation.

a) Ethanol from Sugar or molasses

Molasses is dark coloured thick syrupy mother liquor left after the crystallization of sugarcane solution.

C12H22O11 + H2O Invertase enzyme→ C6H12O6 + C6H12O6
C6H12O6 zymase, rum yeast→ 2C2H5OH + 2CO2
PDF Page 15
This page repeats the same material that appears on PDF Page 13. It is preserved because it appears physically in the supplied source.

The fermented liquid which contain 8−10% ethanol is called Wort WASH.

b. Ethanol From starch

C6H10O5 + H2O diastase enzyme→ C12H22O11
C12H22O11 + H2O maltase→ C6H12O6
C6H12O6 zymase→ 2C2H5OH + 2CO2

Imp: Oxo process

Alkene react with water gas (CO + H2) in presence of dicobalt octacarbonate gives aldehyde which on reduction produce alcohol.

CH3−CH=CH2 + CO + H2 [Co(CO)4]2, high temp/pressure→ CH3−CH2−CHO H2/Ni→ CH3−CH2−CH2−OH
PDF Page 16

Hydroboration of alkene

Alkene react with diborane and the followed by alkaline hydrolysis gives alcohol.

CH2=CH2 + B2H6 H2O2 / OH−→ CH3−CH2−OH + B(OH)3

ethyl alcohol    Boric acid

Properties of alcohol

  • lower member of alcohol are highly soluble in water but solubility decreases on increasing molecular mass.
  • alcohol soluble in water because it produce intermolecular Hydrogen bond with water.
Fig: Intermolecular H-bond R−O−H O H H R−O−H O H H
  • Alcohol are generally high boiling point because alcohol produce intermolecular hydrogen point.
Fig: Intermolecular H-bond betn alcohol R−O−H O−H−R O−H−R
PDF Page 17

But its functional isomers (ether) as low boiling point because ether doesn’t produce intermolecular H−bond.

Boiling point of alcohol increases with increases in molecular mass. In the case of isomeric alcohol on increasing branching decreases the surface area which decreases boiling point.

CH3−CH2−CH2−CH2−OH

Butan−1−ol

B.P = 118°C

CH3−CH(CH3)−CH2−OH

2−methylpropan−1−ol

B.P = 99°C

(CH3)3C−OH

2−methylpropan−2−ol

B.P = 83°C

Chemical properties

1) Acidic character

Alcohol contain electron donating ethyl group which donate electron toward oxygen atom due to which electron rich character of oxygen atom decreases and release of H+ ion becomes difficult but due to phenomenon alcohol bond in water hence alcohol are weaker then water.

PDF Page 18
H2O > CH3−OH > CH3−CH2−OH > CH3−CH2−CH2−OH

a) Reaction with metal

Alcohol react with highly reactive metal gives hydrogen gas.

2CH3−CH2−OH + 2Na → 2CH3−CH2−ONa + H2↑

ethyl alcohol → sod. ethoxide

2) Esterification rxn [COOR]

Alcohol when react with carboxylic acid in presence of conc H2SO4 gives ester.

CH3COOH + HO−C2H5 conc. H2SO4→ CH3COOC2H5 + H2O

ethyl ethanoate / ethyl acetate

3. Dehydration of alcohol

a) By conc H2SO4

Primary alcohol when heated with conc H2SO4 at 100°C gives alkyl hydrogensulphate.

CH3−CH2−OH + H−HSO4 conc. H2SO4, 100°C→ CH3−CH2−HSO4 + H2O

ethyl alcohol → ethyl hydrogen sulphate

alcohol when heated with conc H2SO4 at 140°C gives symmetrical ether.

PDF Page 19
CH3−CH2−OH + HO−CH2−CH3 conc H2SO4, 140°C→ CH3−CH2−O−CH2−CH3 + H2O

ethoxyethane / diethyl ether

Alcohol when heated with conc H2SO4 at 170°C gives alkene.

CH3−CH2−OH conc H2SO4, 170°C→ CH2=CH2 + H2O

ethyl alcohol → ethene

B) By heated alumina [Al2O3]

Alcohol when heated with alumina at 250°C gives symmetrical ether.

CH3−CH2−OH + HO−CH2−CH3 Al2O3, 250°C→ CH3−CH2−O−CH2−CH3 + H2O

ethoxyethane / diethyl ether

Alcohol when heated with alumina at 350°C gives alkene.

CH3−CH2−OH Al2O3, 350°C→ CH3−CH2 + H2O

ethyl alcohol → ethene

PDF Page 20

4) Oxidation of alcohol

Primary alcohol on oxidation gives aldehyde which further oxidized into carboxylic acid.

CH3−CH2−OH + [O] KMnO4/H+→ CH3−CHO [O]→ CH3−COOH

ethanol → ethanal → ethanoic acid

The rxn b/w ethanol and acidified potassium dichromate is used in breath analyser to test for ethanol in drunk people. It contain orange crystal of potassium dichromate which are reduced in green.

3CH3−CH2−OH + 2K2Cr2O7 + 8H2SO4 → 3CH3−COOH + 2K2SO4 + 2Cr2(SO4)3 + 11H2O

green

Secondary alcohol on oxidation gives ketone which further oxidation in drastic condition gives carboxylic acid with one less no. of carbon.

CH3−CH(OH)−CH3 + [O] KMnO4/H+→ CH3−CO−CH3 [O], drastic condition→ CH3−COOH + CO2 + H2O
PDF Page 21

At ordinary condition tertiary alcohol doesn’t undergoes oxidation but at drastic condition gives ketone with one less no of carbon.

2−methyl propan−2−ol (Tert butyl alcohol) + [O] oxidation→ CH3−CO−CH3 + CO2 + H2O

propanone (acetone)

At ordinary condition ordinary alcohol doesn’t undergo oxidation because due to the absence of α hydrogen.

Catalytic dehydrogenation

When vapour of alcohol passed over heated copper then dehydrogenation takes place.

Primary alcohol undergo dehydrogenation gives aldehyde.

CH3−CH2−OH Cu, 300°C→ CH3−CHO + H2

ethanol or ethyl alcohol → ethanal or acetaldehyde

Secondary alcohol undergoes dehydrogenation gives ketone.

CH3−CH(OH)−CH3 Cu, 300°C→ CH3−CO−CH3 + H2

propane−2−ol (isopropyl alcohol) → acetone (propanone)

PDF Page 22

Tertiary alcohol doesn’t undergo dehydrogenation due to the absence of α hydrogen but undergoes dehydration gives alkene.

(CH3)3C−OH Cu, 300°C→ CH3−C(CH3)=CH2 + H2O

2methyl propene

Iodoform test

There are only 2 alcohol which gives iodoform test:

  1. CH3−CH2−OH   ethyl alcohol (primary alcohol)
  2. CH3−CH(OH)−CH3   propan−2−ol / Isopropyl alcohol (secondary alcohol)
CH3−CH2−OH + 4I2 + 6NaOH → CHI3↓ + HCOONa + 5NaI + 5H2O

yellow ppt iodoform

CH3−CH(OH)−CH3 + I2 + NaOH → CHI3↓ + CH3COONa + 5NaI + 5H2O

yellow ppt iodoform    sod. acetate

PDF Page 23

Alcohol industry

1) Rectified spirit

95% pure ethyl alcohol is called Rectified spirit.

2) Absolute alcohol

95.5 to 100% pure ethyl alcohol is called absolute alcohol.

3) Denaturated alcohol

If the poisonous substance like methyl alcohol, acetone or pyridine mixed with ethyl alcohol then its become poisonous and unfit for drinking purpose. Such type of alcohol is called denaturated alcohol or methylated alcohol.

4. Power alcohol

The mixture of ethyl alcohol and gasoline (petrol/diesel) in 20:80 ratio is called power alcohol. Power alcohol is used to control the crisis of fuel.

5. Alcoholic beverage

The beverage which are used for drinking purpose are called alcoholic beverage.

a) Undistilled

Eg: wine, beer, redbull, appeldar

b) Distilled

Eg: Whisky, Vodka, brandy

KEEP LEARNING View All Posts

Discussion

Share a helpful question, idea, or explanation with other students.

Leave a Comment

Write a clear question, answer, or helpful explanation.
Your email will not be published.

Download Our Offline App

Study class-wise notes even when internet is not available. Get the app from Play Store.

Nepal eNotes offline app preview
Get it on Google Play