Alcohols

 10. Alcohols

Introduction, Classification, Nomenclature & Isomerism

Alcohols are derivatives of hydrocarbon where one or more of the hydrogen is replaced by –OH groups.

Compounds having 1, 2, 3 and many –OH groups are called monohydric, dihydric, trihydric and polyhydric alcohols respectively.

Carbohydrates can be taken as examples of polyhydric alcohols.

Monohydric alcohols

Monohydric alcohols can further be classified into primary, secondary and tertiary alcohols depending upon the carbon atom to which the –OH group is bonded.

Structure	IUPAC name	Common name	Degree
CH3-OH	Methanol	Methyl alcohol	10
CH3-CH2-OH	Ethanol	Ethyl alcohol	10
CH3CH2CH2OH	Propan-1-ol	n-propyl alcohol	10
	Propan-2-ol	isopropyl alcohol	20
CH3CH2CH2CH2OH	Butan-1-ol	n-butyl alcohol	10
	Butan-2-ol	sec-butyl alcohol	20
	2-methylpropan-1-ol	iso-butyl alcohol	10
	2-methylpropan-2-ol	tert-butyl alcohol	30

1.       Give the IUPAC name of the following compound: CH₂=CHCH₂OH

2.       Write down the structural formula and IUPAC name of tert-butyl alcohol.     1

3.       Write the structure of secondary and tertiary alcohols of C₄H₁₀O and give their IUPAC and common names.                                                                                                     2

4.        Write down the isomers of monohydric alcohols from C₃H₈O and give their IUPAC name.    3

5.       Write the structural formula for 3^o alcohol of C₄H₁₀O.                      1

Structural isomerism

a.       Chain isomers:

Alcohols with 4 or more carbons exhibit this type of isomerism. e.g. Butan-2-ol and 2-methylpropan-2-ol.

b.      Position isomers:

Alcohols with more than 2 carbons can show this kind of isomerism. e.g. Propan-1-ol and Propan-2-ol.

c.       Functional isomers

Alcohols exhibit functional isomerism with ethers. E.g Ethanol and Methoxy methane; CH₃-CH₂-OH (C₂H₆O), CH₃-O-CH₃ (C₂H₆O) , Propan-1-ol and Methoxyethane etc.

6.       Write the Isomeric alcohols of C₃H₈O.                                            1

7.       Write the structural formula of the secondary alcohol of C₃H₈O.            1

8.        Write down the isomers of monohydric alcohols from C₃H₈O and give their IUPAC name. How would you convert one isomer into another and vice versa?                                       3

1.       What is the IUPAC name of tert-butyl alcohol?

a.       Propan-2-ol                                 c. Butan-2-ol

b.       2-methylpropan-2-ol                 d. 2-methylpropan-1-ol

2.       Pentan-3-ol is an example of

a.       Aromatic alcohol                        c. Primary alcohol

b.       Secondary alcohol                      d. Tertiary alcohol

3.       Ethanol is an isomer of

a.       Methoxymethane                                c. Propanone

b.       Methoxymethanoate                          d. Methylmethanoate

4.       Alcohols are isomeric with

a.       Carboxylic acids                                   c. Aldehydes

b.       Ketones                                                 d. Ethers

5.       The functional isomer of Methoxyethane is

a.     Propane              b. Propanal            c. Propanol            d. Propanone

6.       How many primary alcohols are possible for the molecular formula C₄H₁₀O?

a.     1                           b. 2                         c. 3                          d. 4

Victor-Meyer Method for distinction of 1^o, 2^o and 3^o alcohols

For the distinction of 1^o, 2^o and 3^o alcohols,

First, the given alcohols are treated with PI₃ (a mixture of red phosphorus and iodine, P₄+ I₂) to get corresponding Iodoalkane.

The Iodoalkane is then treated with alc. AgNO₂ to get corresponding Nitroalkane.

The Nitroalkane is treated with nitrous acid (formed in situ by reaction of NaNO₂ and HCl) and then finally with aqueous alkali.

If blood red colouration is obtained, the alcohol is primary (1⁰),

If blue colouration is obtained, the alcohol is secondary (2⁰),

If no colouration is obtained, the alcohol is tertiary (3⁰).

 

9.       Write short notes on distinction of 1^o, 2^o and 3^o alcohols by Victor-Meyer method.          5

10.   Describe Victor-Meyer's method to distinguish primary, secondary and tertiary alcohols.          5

11.   How would you distinguish Ethanol and Propn-2-ol by the Victor-Meyer method?          3

12.   Describe the Victor-Meyer method to distinguish Propan-2-ol and 2-methylpropan-2-ol.  5

13.   Write down the isomeric alcohols of C₃H₈O with their IUPAC names. Also, give Victor-Meyer method to distinguish them.                                                                            5

14.   How would you distinguish Ethanol, Propan-2-ol and 2-methylpropan-2-ol by Victor Meyer method? 

General Methods of Preparation

1.       From Haloalkane (studied in substitution reactions of haloalkanes)

2.       From Esters (By hydrolysis in acidic/alkaline medium and reduction)

a.       Acidic hydrolysis

b.      Hydrolysis in basic medium

c.       Reduction by Na/C₂H₅OH or LiAlH₄

3.       From Primary amines (by reaction with nitrous acid)

Primary amines react with nitrous acid (prepared in situ by reacting sodium nitrite with hydrochloric acid) in ice-cold conditions resulting in alcohols.

e.g.

Industrial preparation

1.      Oxo process

Alkenes react with carbon monoxide and hydrogen in the presence of octocarbonyldicobalt or cobalt tetracarbonyl at high temperature and pressure to produce aldehydes, aldehydes can be changed into alcohols by hydrogenation.

15.   Write the chemical reaction for the preparation of primary alcohol by oxo process.     1

16.   Write a correct example of the Oxo process.                                         1

17.   Write an example of carbonylation reaction.                                    1

2.      Fermentation of sugar

(Study from book and homework copy)

 

18.   Write short note on fermentation.                                                4

19.   Give the reactions for the conversion of cane sugar into ethyl alcohol 2

20.   Write short note on fermentation of ethyl alcohol.                            2

21.   What is fermentation?                                                                    2

22.   How would you obtain Ethanol from cane sugar? Write reaction only.2

23.   Starting form cane sugar, how would you obtain ethyl alcohol?        2

24.   Ethyl alcohol is common alcohol and is used to manufacture alcoholic beverage. It can be prepared from sugar containing materials like molassess by fermentation process.

i) Define fermentation.

ii) What is meant by molassess?

iii) Mention the function of yeast in the formation of cane sugar into ethyl alcohol.

3.       Hydroboration of Ethene(Alkene)

Alkenes can be treated with Diborane (BH₃ or (BH₃)₂ or B₂H₆) followed by treatment with alkaline hydrogen peroxide to yield 1⁰ alcohols.

25.   Write an example of hydroboration oxidation reaction.                     1

 

7.       When Propan-1-ol is treated with P₄/I₂, AgNO₂ and HNO₂ successively, it gives

a.       Nitrolic acid          c. Pseudonitrol     d. Nitroalkane       d. 2⁰ Nitroalkane

8.       In Victor Meyer's test Pseudonitrol is given by

a.       Primary alcohol                                    c. Secondary Alcohol

b.       Tertiary alcohol                                    d. Quaternary alcohol

9.       In Victor Meyer's test, nitrolic acid is given by

a.     Primary alcohol                    c. Secondary alcohol

b.     Tertiary alcohol                    d. Quarternary alcohol

10.    In Victor Meyer's test, blood red colouration is given by

a.       Primary alcohol                    c. Secondary Alcohol

b.       Tertiary alcohol                    d. Quaternary alcohol

11.    Primary, Secondary and Tertiary alcohols can be distinguished by

a.       Tollen's test                          c. Iodoform test

b.       Hoffmann's test                   d. Victor Meyer's test

12.    Formation of alcohols and carboxylic acids from ester is an example of

a.       Esterification         b. Etherification    c. Hydrolysis          d. Oxidation

13.    Amines can be changed into alcohols by

a.       Acidified KMnO₄    b. HNO₂                           c. HNO₃                           d. aq. KOH

14.    Action of nitrous acid on methylamine gives

a.       CH₄                                      b. CH₃OH               c. NH₃                     d. CH₃NO₂

15.    The enzyme that converts sucrose to glucose and fructose is

a.     Diastase                  b. Invertase           c. Maltase              d. Zymase

16.    The enzyme that converts glucose into alcohol is

a.     Zymase                   b. Invertase           c. Maltase              d. Diastase

17.    The enzyme used during the production of alcohol from carbohydrates by fermentation is

a.     insertase                b. starch                 c. molasses            d. zymase

Absolute alcohol, methylated spirit, rectified spirit: alcoholic beverages

·         Pure (100%) and anhydrous Ethyl alcohol is called absolute alcohol.

·         Rectified spirit is the 95% pure alcohol containing 5% water.

·         Undrinkable Ethyl alcohol containing poisonous substances especially Methyl alcohol is called denatured alcohol or methylated spirit.

·        Alcoholic beverages are liquors for drinking purposes. They contain Ethanol, water, coloring materials and flavoring materials. They may be distilled e.g. vodka, gin, whisky, brandy etc. or undistilled e.g. beer, wine etc.

26.   Give the differences between absolute alcohol and denatured alcohol. 1

Physical Properties

1.    State:

The lower members are usually colorless liquids with the characteristic hospital odour, whereas higher members are usually colorless and odorless solids.

 

2.    Solubility:

i.      The solubility of alcohols is higher than that of the solubility of corresponding aliphatic hydrocarbons (alkanes), haloalkanes and ethers of comparable molecular masses. This is due to formation of hydrogen bond by the alcohol molecules with water due to polar O-H bond.

ii.    There is gradual decrease in the solubility in homologous series with increase in molecular weight due to increasing size of alkyl group which is insoluble in water.

 

3.    Boiling and melting points:

i.          The boiling and melting points of alcohols are higher than the corresponding ethers, haloalkanes of comparable molecular masses. This is due to the higher polarity and formation of intermolecular hydrogen bonding between alcohol molecules.

ii.        The melting and boiling points increase with increasing molecular masses in a homologous series this is due to the increased Van der Waal’s force of attraction between the molecules with increasing molecular masses.

iii.      For isomeric alcohols the melting and boiling points decrease with increase in branching which is due to decrease in surface area with branching. Hence the order of melting and boiling points 3⁰ < 2⁰ < 1⁰.

27.   Alcohols of low molecular weight are moderately soluble in water, whereas ethers of about same molecular weight are not. Explain.                                                                             2

28.   Why is the boiling point of Ethanol higher than its isomer Methoxymethane? 2

29.   Why is boiling point of Ethanol greater than that of Ethoxyethane?   2

30.   Isopropyl alcohol has lower boiling point than n-propyl alcohol though they have same molecular mass' explain.                                                                                                     2

 

18.    Ethanol and Methanol are soluble in water due to

a.       Van der Waal's forces                         c. Hydrogen bond

b.       Covalent bond                                      d. Electrovalent forces

19.    Which of the following is highly soluble in water?

a.     Ethane                    b. Ethyl iodide      c. Diethyl ether    d. Ethanol

20.    Alcohols boil at higher temperature than corresponding alkanes due to

a.       Intermolecular hydrogen bonding   c. Intramolecular hydrogen bonding

b.       Van der Waal's force of attraction    d. Dipole Dipole interaction

21.    Which of the following has highest boiling point?

a.     Propan-1-ol           b. Butane               c. Chloropropane d. Methoxyethane

22.    The compound with highest boiling point is

a.     CH₃CH₃                     b. CH₃Cl                  c. CH₃Br                 d. CH₃OH

23.    What is the correct order for boiling points of isomeric alcohols?

a.     1⁰ > 2⁰ > 3⁰             c. 3⁰ > 2⁰ > 1⁰             b. 2⁰ > 3⁰ > 1⁰        d. 3⁰ > 1⁰ > 2⁰

Chemical properties

[A] Reaction involving the cleavage of O-H bond

1. Action with active metals like Li, Na, K (acidic nature of alcohol)

When alcohols are treated with active metals like Na, K, Mg etc. these liberate hydrogen with the formation of metal alkoxides. This shows acidic nature of alcohol. E.g.,

     However, alcohols are weak acids, weaker than water. They neither turn litmus red nor neutralize even strong alkali or aq. alkali solutions.

31.   Give a reaction to show that the H-atom of the –OH in alcohol is weakly acidic.        1

 

2. Reaction with carboxylic acid - Esterification (test of alcohol)

When a mixture of alcohol and carboxylic acid is heated in presence of calculated amount of conc. H₂SO₄ an ester is formed. The ester has characteristic fruity smell. Hence this reaction is used as a test of both alcohol and carboxylic acid functional groups.

 

Concentrated sulphuric acid acts as dehydrating agent and intermolecular dehydration occurs between the alcohol and carboxylic acid functional groups. Equilibrium can be shifted in right side by removing water as soon as it is formed.

32.   Give an example of Esterification.                                                2

33.   Give a suitable reaction to convert Ethanoic acid into Methyl ethanoate.

34.    What happens when ethyl alcohol is treated with acetic acid?          1

 

[B] Reaction involving cleavage of C-O bond (Nucleophilic Substitution rxⁿ)

1. Reaction with HX, PX₃, PCl₅, SOCl₂ (studied in preparations of haloalkanes)

35.   Write the action of Propan-2-ol with PCl₅.                                       1

[C] Other Reaction

1. Dehydration of alcohols

Alcohols can be dehydrated under different condition with concentrated sulphuric acid producing Ether or Alkene.

a.  When excess amount of ethyl alcohol is heated with conc. H₂SO₄ as a dehydrating agent at about 140⁰C, ethyl alcohol undergoes intermolecular dehydration to give diethyl ether.

This reaction is supposed to occur in following two steps.

b.   When calculated amount of ethyl alcohol is heated with excess of conc. H₂SO₄ at about 170⁰C, intramolecular dehydration results Ethene.

36.   What happens when Ethyl alcohol is treated with conc. H₂SO₄?

37.   What action takes place when excess of Ethanol is heated with conc. Sulphuric acid at about 140^oC?  2

38.    What action takes place when Ethanol is heated with conc. H₂SO₄ at about 160-170^oC?         2

39.   Write down the reaction for the preparation of Ethoxyethane from Ethanol.

2. Oxidation of primary, secondary and tertiary alcohols

1⁰ alcohol: Primary alcohols can be oxidized into aldehydes, the reaction does not stop there, and the aldehydes are further oxidized into carboxylic acid without change in the number of carbon atom in the main skeleton. Different oxidizing agents like alkaline or acidified potassium permanganate, sodium dichromate, potassium dichromate etc. can be used.

 

2⁰ alcohol: Secondary alcohols are oxidized into ketones with same number of carbon on oxidation.

The ketones are not further oxidized easily.

 

3^o alcohol: Tertiary alcohols are quite resistant for oxidation. But when oxidation is carried under drastic acidic with strong oxidizing agent like KMnO₄ and conc. H₂SO₄, tertiary alcohol first undergoes dehydration into alkenes. The alkene formed is then oxidized to ketone, which is finally oxidized to carboxylic acid with lesser number of carbon atoms. e.g.

40.       Write down the oxidation products of primary, secondary & tertiary alcohols.

41.    Write down the oxidation of primary and secondary alcohols.          3

42.   Oxidation of various classes of alcohols given various products.

I)         Name mild and strong oxidizing agent used in the oxidation of alcohols.

II)       Write down the oxidation of 1⁰, 2⁰ and tertiary alcohols.         1+4

a)      Catalytic dehydrogenation of alcohols

Primary and secondary alcohols decompose to give aldehyde and ketones respectively in presence of Cu at 300^oC.

  

This process is also called dehydrogenation.

43.   ­How is Propanone prepared from Isopropyl alcohol?                        1

44.    How is Propanone prepared from Propan-2-ol?                               1

Laboratory test of Ethanol

1.       Esterification test- (as studied in chemical properties-esterification reaction)

2.       Iodoform test (test for  group)

Alcohols having CH₃CH(OH)- group respond to this test. When alcohols having above mentioned group are treated with I₂ and aq. Alkali (NaOH) iodoform is formed which is a yellow crystalline precipitate with characteristic hospital smell.

CH₃CH(OH)R  + 6 NaOH + 4 I₂   → CHI₃  +  5 NaI  +  RCOONa + 5 H₂O

                                                                     Iodoform             Sodium alkanoate      

45.   What is the laboratory test of Ethanol                                              2

46.   Give a suitable test of Ethanol that distinguishes it from Propanol. (must be Propan-1-ol)  2

47.   Name any suitable secondary alcohol that gives iodoform test and write the test reaction.       2

48.   Give an example of Iodoform test.                                                  1

49.   What happens when Ethanol is heated with iodine in presence of aqueous NaOH?     2

50.   Name the isomer of C₃H₈O which undergoes iodoform test.             2

51.   What is the isomeric alcohol of C₃H₈O that gives iodoform test? Write the test reaction.         2

52.   Write down the isomers of monohydric alcohols from C₃H₈O and give their IUPAC name.  What chemical test would you apply to distinguish them? Write chemical reaction for it. 3

 

Conversions

53.   How is Ethanol prepared from Ethyne?                                           1

54.   How would you obtain Methoxyethane from Ethanol?                     1

55.   Write down the isomers of monohydric alcohols from C₃H₈O and give their IUPAC names. How would you convert one isomer into another and vice versa?                                          3

56.   Convert Propan-1-ol to Propan-2-ol.                                               2

57.   An organic compound M gives H₂ gas with sodium metal. On treatment with alkaline iodine gives yellow ppt and on oxidation with CeO₂ forms an aldehyde (C₂H₄O). Name the compound M and write the reactions involved. What happens when M is heated with P₂O₅?                                   5

58.   A 1⁰ alcohol with molecular weight 46 is boiled with sodium hydroxide and iodine. When the same alcohol is heated with Ethanoic acid in presence of conc. H₂SO₄ one of the derivatives of carboxylic acids is obtained. Write the reaction involved in both conditions. What would be the product obtained when the same alcohol is heated with conc. H₂SO₄? How would you distinguish above alcohols from Methanol?

24.    Ethanol shows acidic character in the reaction with

a.     HCl                          b. CH₃COOH          c. Na                       d. K₂Cr₂O₇/H⁺

25.    2 R-OH + 2 Na → 2 RONa + H₂; is an example of

a.       Acidic nature of alcohol                     c. Electrophilic substitution reaction

b.       Basic nature of alcohol                       d. Nucleophilic  substitution reaction

26.    1 mole of sodium reacts with excess of alcohol to give

a.     1 mole of O₂               b. 1/2 mole of H₂  c. 1 mole of H₂         d. 2 mole of H₂

27.    Alcohol vapours can be dehydrogenated by passing over

a.     Conc. H₂SO₄                b. Heated Al₂O₃     c. Heated Cu         d. Anhydrous CaCl₂

28.    The reaction of alcohol with carboxylic acid is

a.     Hydrogenation      b. Hydrolysis         c. Esterification     d. Etherification

29.    Conversion of Ethanol into Ethanal using acidified KMnO₄ is an example of

a.     Reduction              b. Oxidation          c. Hydrolysis          d. Rearrangement

30.    When vapours of Ethyl alcohol is passed over red hot copper, the product formed is

a.     Ethanoic acid        b. Ethylene            c. Ethyne                d. Ethanal

31.    When Ethanol is heated with concentrated H₂SO₄ at temperature 160⁰C to 170⁰C, it gives

a.       Ethoxyethane                                       c. Ethene

b.       Ethyl hydrogensulphate                     d. Ethyne

32.    Which of the following is an example of elimination reactions?

a.       Chlorination of CH₄             c. dehydration of C₂H₅OH

b.       Nitration of benzene          d. hydroxylation of C₂H₄

33.    Tertiary alcohol in 1^st  oxidation gives

a.     Alkene    b. Carboxylic acids               c. Ketone               d. Aldehyde

34.    Which of the following is an example of elimination reactions?

a.       Chlorination of CH₄                                            c. Dehydration of C₂H₅OH

b.       Nitration of benzene                          d. Hydroxylation of C₂H₄

35.    In the laboratory, Ethanol can be distinguished from Methanol by

a.       Reaction with HCl                                c. Reaction with NH₃

b.       Solubility in water                                d. Iodoform test

36.    Which of the following compound gives iodoform test?

a.       CH₃OH                    c. CH₃CH₂OH         c. CH₃CH₂CH₂OH  d. CH₃CH₂CH₂CH₂OH

37.    Which one of the following is laboratory test of alcohol?

a.     Iodoform test                                        c. Victor Meyer test            

b.     Esterification test                                 d. Oxidation test

 

***This is not a complete note. It is just to guide you. It is recommended to study prescribed textbooks along with this material.***