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Chapter 33. Hydroxy Compounds. 33.1 Introduction 33.2 Nomenclature of Hydroxy Compounds 33.3 Physical Properties of Hydroxy Compounds 33.4 Acidic Properties of Hydroxy Compounds 33.5 Preparation of Hydroxy Compounds 33.6 Reactions of Alcohols 33.7 Reactions of Phenol 33.8 Uses of Alcohols.

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Hydroxy compounds

Chapter 33

Hydroxy Compounds

33.1Introduction

33.2Nomenclature of Hydroxy Compounds

33.3Physical Properties of Hydroxy Compounds

33.4Acidic Properties of Hydroxy Compounds

33.5Preparation of Hydroxy Compounds

33.6Reactions of Alcohols

33.7Reactions of Phenol

33.8Uses of Alcohols


Hydroxy compounds

33.1 Introduction (SB p.206)

Hydroxy compounds:Organic compounds with the hydroxy group(s) (–OH) attached to an alkyl group or aromatic ring

  • 1.Alcohols

  • Compounds containing one or more –OH attached to an alkyl group

  • General formula for alcohols with –OH group: CnH2n+1OHe.g.


Hydroxy compounds

33.1 Introduction (SB p.206)

Primary alcohol

Secondary alcohol

Tertiary alcohol

  • Depending on the number of alkyl groups attached to the carbon which is bonded to the hydroxy group

  • Alcohols can be classified as:


Hydroxy compounds

33.1 Introduction (SB p.207)

  • Phenols

  • Compounds that have a – OH group directly attached to a benzene ring

  • General formula for phenols: Ar – OHe.g.


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.207)

Alcohols

1.Select the longest possible straight chain to which the hydroxyl group is directly attached. Change the name of the alkane correspending to this chain by dropping the final ‘-e’ and adding the suffix ‘-ol’.


Hydroxy compounds

2.Number the longest possible straight chain in such a way so as to give the carbon atom bearing the hydroxyl group the lower number.

3.Designate the position of the hydroxyl group by using this number, and also the positions of other substituents by using the numbers corresponding to their positions along the carbon chain.


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.207)

Examples:


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.208)

Phenols

  • Phenol will be the parent name when a benzene ring containing a –OH group

  • When substituents are present, the –OH group is assumed to be in position 1, and numbers are assigned to the substituents according to their positions in the benzene ring

  • e.g.


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.208)

Solution:

(a)(i)

(ii)A secondary alcohol

(b)(i)

(ii)A primary alcohol

(c)(i)

(ii)A secondary alcohol

Example 33-1

For each of the following hydroxy compounds:

(i)Draw the complete structural formula.

(ii)Classify them as primary, secondary or tertiary alcohols.

(a)Hexan-3-ol

(b)3-Methylbutan-1-ol

(c)2-Methylcyclopentanol

Answer


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.209)

(a)

Check Point 33-1

(a)Draw the structural formulae of all isomers of alcohols having the molecular formula C4H10O. Give their IUPAC names.

Answer


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.209)

(b)

4-Bromophenol

Check Point 33-1

(b)Draw the structural formulae of three isomeric bromophenols with the molecular formula C6H4BrOH. Give their IUPAC names.

Answer


Hydroxy compounds

33.3 Physical Properties of Hydroxy Compounds (SB p.209)


Hydroxy compounds

33.3 Physical Properties of Hydroxy Compounds (SB p.210)

Boiling Point and Melting Point

Intermolecular hydrogen bonds between alcohol molecules is stronger than van der Waals’ forces between alkane molecules

 alcohols have higher b.p. and m.p.


Hydroxy compounds

33.3 Physical Properties of Hydroxy Compounds (SB p.210)

Branching of the carbon chain reduces the surface area in contact with other molecules

Reduction in the extent of intermolecular hydrogen bonds that can be formed between neighbouring molecules


Hydroxy compounds

33.3 Physical Properties of Hydroxy Compounds (SB p.211)

Density

  • Simple alcohols are less dense than water at 20°C

  • Phenols are slightly denser than water at 20°C

  • The densities of alcohols increase with increasing relative molecular masses


Hydroxy compounds

33.3 Physical Properties of Hydroxy Compounds (SB p.211)

Solubility

  • Alcohols with a relatively short carbon chain (e.g. methanol, ethanol, propan-1-ol and propan-2-ol) are completely miscible with water

  • The solubility decreases as the hydrocarbon chain increasese.g. the solubility of butan-2-ol is 8 g per 100 g of water


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.209)

(a)

Check Point 33-2

(a)Arrange the following compounds in order of increasing boiling points:

Answer


Hydroxy compounds

33.2 Nomenclature of Hydroxy Compounds (SB p.209)

(b)(i)CH3CH2OH

(ii)

(iii)

Check Point 33-2

(b)Which member in each of the following pairs is more soluble in water?

(i)CH3CH2OH or CH3CH2CH2CH2OH

(ii)

(iii)

Answer


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.212)

  • Alcohols are neutral

  • Alcohols show acidic properties when reacting with strong bases (e.g. sodium metal)

  • The acidic property depends on the stability of the alkoxide ion formed which is partly influenced by the structure of the carbon chain


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.213)


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.213)

  • 3° alkoxide ions are the least stable

  • ∵3 electron-releasing alkyl groups release electrons to the negatively charged oxygen atom

  • 3° alcohol is the least acidic

Phenols have smaller pKa stronger acids than alcohols


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.214)

  • Phenols are more acidic than alcohols

  • ∵phenoxide ion is more stable than alkoxide ion due to resonance stability (4 resonance structures can be drawn)


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.214)

The negative charge disperses over the entire benzene ring and oxygen atom by extended delocalized  electron cloud phenoxide ion is stabilized


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.214)

Simple tests to distinguish alcohols, phenols, carboxylic acids

Sodium hydroxide

Sodium hydrogencarbonate

Alcohols

Phenols

Carboxylic acids

No reaction

React to give salts and water

React to give salts and water

No reaction

No reaction

CO2 evolved

Phenol is acidic enough to react with NaOH but not Na2CO3

The order of acidity of some organic compounds and water:


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.215)

Solution:

The acidity of the compounds increases in the order:

Example 33-2

Arrange the following compounds in order of increasing acidity.

Answer


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.215)

(a)CF3CH2OH is more acidic, because –CF3 is a strong electron-withdrawing group. It exerts a negative inductive effect on the conjugate base of CF3CH2OH (i.e. CF3CH2O–) and thus stabilizes the CF3CH2O– ion.

Check Point 33-3

Which of the following compounds is more acidic? Explain briefly.

(a)CF3CH2COH and CH3CH2OH

Answer


Hydroxy compounds

33.4 Acidic Properties of Hydroxy Compounds (SB p.215)

(b)is more acidic. The reason is that the conjugate

base is stabilized by the negative inductive and resonance effects of the –NO2 group.

Check Point 33-3

Which of the following compounds is more acidic? Explain briefly.

(b)

Answer


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.216)

amylase

60°C

2(C6H10O5)n + nH2O  nC12H22O11

C12H22O11 + H2O  2C6H12O6

C6H12O6 2CH3CH2OH + 2CO2

The concentration of ethanol can be increased by fractional distillation

maltase

15°C

zymase

15°C

Preparation of Alcohols

Fermentation of Carbohydrates


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.216)

Alkaline Hydrolysis of Haloalkanes

  • Nucleophilic substitution reaction of haloalkanes whereby 1°, 2° and 3° alcohols can be prepared

  • The equilibrium lies towards the right∵OH– is a better nucleophile than halide ion


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.216)

Reduction of Aldehydes and ketones

  • Reduction of aldehydes and ketones respectively by powerful reducing agents (e.g. LiAlH4 in dry ether) produces 1° and 2° alcohols


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.217)

Preparation of Phenol

Industrial Process

  • Alkaline hydrolysis of chlorobenzene under severe conditions of high temperature and pressure produces phenol


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.217)

Laboratory Process

  • By refluxing benzene and conc. sulphuric(VI) acid for 1 day to form benzenesulphonic acid and then subject to alkaline hydrolysis


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.217)

  • By hydrolysis of benzenediazonium salt


Hydroxy compounds

33.5 Preparation of Hydroxy Compounds (SB p.216)

Example 33-3

Comment on the feasibility of the following preparation of hydroxy compounds in the school laboratory.

(a)KOH

CH3CH2CH2Cl  CH3CH2CH2OH

(b)

Solution:

(a)The preparation of the alcohol is feasible in this way. It is a nucleophilic substitution reaction of haloalkanes, and the nucleophile is the hydroxide ion, OH–.

(b)The preparation of phenol is not feasible in this way. It is because halobenzenes do not undergo nucleophilic substitution reactions unless under severe reaction conditions.

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.218)

Reactions of alcohols can be classified into two main types:1.Reactions involving the cleavage of the C – O bond:

2.Reactions involving the cleavage of the O – H bond:


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.218)

Reaction Involving Cleavage of the C – O bond

Formation of Haloalkanes

Reaction with Hydrogen Halides

  • Alcohols react with hydrogen halides by nucleophilic substitutions

  • The order of reactivity of hydrogen halides:

  • HI > HBr > HCl

  • The order of reactivity of alcohols: 3° > 2° > 1° < methyl


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.219)

Reactions of Alcohols with Hydrogen Chloride

  • Secondary and tertiary alcohols

  • 2° and 3° alcohols react by SN1 mechanism

  • e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.219)

Step 1:The alcohol is protonated

Step 2:The protonated alcohol dissociates to give a carbocation and water


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.219)

Step 3:The carbocation reacts with a nucleophile to give the product


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.219)

2.Primary alcohols and methanol

  • 1° alcohol and methanol react by SN2 mechanism

  • Step 1:The alcohol is protonated


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.220)

Step 2:The halide ion displaces a molecule of water from the carbon to give the product


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.220)

Lucas Test

  • Lucas reagent: Solution of ZnCl2 in conc. HCl

  • Used to to differentiate between simple primary, secondary and tertiary alcohols

  • When an alcohol is treated with Lucas reagent, the corresponding chloroalkane is formed.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.220)

  • 1°, 2°, 3° alcohols react with Lucas reagent at different rates


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.221)

  • The order of the reactivity of alcohols towards Lucas reagent:3° alcohol > 2° alcohol > 1° alcohol

  • The reactions are believed to take place via the SN1 mechanism which involves the formation of carbocation in the rate-determining step


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.221)

The relative stability of carbocations:

tertiary carbocations are formed rapidly from tertiary alcoholsprimary carbocations are difficult to form, so primary alcohols react very slowly


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.221)

Reactions of Alcohols with Hydrogen Bromide

  • Alcohols react with hydrogen bromide to give bromoalkanes

  • Hydrogen bromide is generated in situ by adding excess conc. H2SO4 to NaBr

  • Iodoalkanes cannot be prepared by reacting HI with alcohols as iodide will be oxidized by conc. H2SO4


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.222)

Laboratory set-up for the reaction of an alcohol with PBr3

Reaction with Phosphorus Halides


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.222)

  • PI3 is used in iodination of alcohols

  • 3R – OH + PI3 3R – I + H3PO3

  • Chloroalkanes are formed readily from the reaction of alcohols with PCl5R – OH + PCl5 R – Cl + POCl3 + HCl

  • SOCl2 converts 1° and 2° alcohols to chloroalkanesR – OH + SOCl2 R – Cl + SO2 + HCl(1° or 2°)


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.222)

Dehydration of Alcohols

Formation of Alkenes

  • Alkenes are formed when alcohols are heated with strong acids

  • Elimination reactions are favoured at high temperatures


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.223)

Laboratory set-up for dehydration of an alcohol

Dehydration occurs when passing alcohol vapour over aluminium oxide at 350°C


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.223)

  • The experimental conditions required to bring the dehydration are related to the structure of alcohols

  • 1° alcohols are the most difficult to dehydratee.g.

  • 2° alcohols usually dehydrate under milder conditionse.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.223)

  • 3° alcohols dehydrate at very mild conditionse.g.

The order of the relative ease of alcohols to undergo dehydration:


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.223)

When 2° or 3° alcohols having more than 3 carbon atoms is dehydrated, two or more alkenes are formed.

But-2-ene is major product ∵ more highly substituted alkene (Saytzeff’s rule)


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.224)

Formation of Ether

  • Dehydration of an alcohol to an ether takes place at lower temperature than that to an alkene


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.225)

The major product is 3-methylpent-2-ene. Its structural formula is: CH3CH = C(CH3)CH2CH3

Check Point 33-4

Give the structural formula and IUPAC name of the major product formed by reacting 3-methylpentan-2-ol with heated aluminium oxide.

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.225)

Reaction Involving Cleavage of the O – H bond

Formation of Alkoxides

  • These reactions are less vigorous than the reaction of the metal with water∵alcohols are weaker acids than water


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.225)

Example:

  • This reaction provides a safe way of disposing sodium residues

  • Addition of water regenerates the alcohol as the propoxide ion is a very strong baseCH3CH2CH2O–Na+ + H2O  CH3CH2CH2OH + NaOH

  • The evolution of hydrogen with sodium metal is a useful test for the presence of –OH group


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.226)

Esterification

Esterification:Alcohols react with carboxylic acids to form esters through a condensation reaction

e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.226)

  • Esterification reactions are acid-catalyzed

  • Conc. H2SO4 is used as catalyst

  • The reactions proceed very slowly in the absence of catalyst but reach an equilibrium within few hours when a carboxylic acid and an alcohol are refluxed with a small amount of conc. H2SO4

  • The equilibrium can be shifted to the product side with the use of an excess of either the carboxylic acid or the alcohol

  • The yield of the reaction can be increased by removing water from the reaction mixture as it is formed


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.226)

Esters can be synthesized by the reaction of alcohols with acyl chlorides in the absence of an acid catalyst

e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.227)

Acid anhydrides react with alcohols to form esters in the absence of an acid catalyst

e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.227)

Oxidation of Alcohols

Oxidation of Primary Alcohols

  • 1° alcohols are first oxidized to aldehydes and then to carboxylic acids by oxidizing agents such as acidified KMnO4 and acidified K2Cr2O7


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.228)

1.Oxidation of primary alcohols to aldehydes

  • The oxidation is difficult to stop at the aldehyde stage because aldehydes are a reducing agent

  • To obtain aldehydes, distill off the aldehydes from the reaction mixture as they are formed

  • Oxidizing agent: acidified K2Cr2O7

  • e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.228)

A laboratory set-up for the conversion of ethanol to ethanal


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.228)

2.Oxidation of primary alcohols to carboxylic acids

  • 1° alcohols can be oxidized to carboxylic acids by powerful oxidizing agents (e.g. acidified KMnO4)

  • The oxidation of 1° alcohols by acidified KMnO4will not stop at the aldehydes

  • e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.229)

(a)

(b)

(a)A reflux apparatus for the oxidation of ethanol to ethanoic acid

(b)A distillation apparatus for the separation of ethanoic acid from the reaction mixture after reflux


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.229)

Breathalyser is used by police to rapidly estimate the ethanol content of the breath of suspected drunken drivers

  • The breathalyser is based on the oxidation of ethanol by acidified K2Cr2O7

  • As the driver blows into the bag, ethanol molecules reduce orange Cr2O72- to green Cr3+


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.229)

Oxidation of Secondary Alcohols

  • 2° alcohols are oxidized to ketones by either acidified KMnO4 or acidified K2Cr2O7

  • 2° alcohols cannot be oxidized to carboxylic acids because it would involve the breaking of strong carbon-carbon bond


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.230)

Example:


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.230)

Oxidation of Tertiary Alcohols

  • 3° alcohols are generally resistant to oxidation∵oxidation involves the breaking of carbon-carbon bonds

  • 3° alcohols can be oxidized by acidified KMnO4 to give a mixture of ketones and carboxylic acids, both with fewer carbon atoms than the alcohol

e.g.


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.230)

  • 1° alcohols are oxidized to aldehydes which can be detected by the reaction with 2,4-dinitrophenylhydrazine or Tollen’s reagent

  • 2° alcohols are oxidized to ketones which can be detected by the reaction with 2,4-dinitrophenylhydrazine but not Tollen’s reagent

  • The carboxylic acid formed from the oxidation of 3° alcohols can be detected by the reaction with sodium hydrogencarbonate or ester formation


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.230)

(a)CH3CH2Cl

(b)CH3CH2Br

(c)CH3CH2CH2Cl

(d)CH3CH2COOH

(e)

Check Point 33-5

Draw the structural formulae for the major organic products in the following reactions.

(a)PCl5

CH3CH2OH 

(b)P, Br2

CH3CH2OH 

reflux

(c)SOCl2

CH3CH2CH2OH 

(d)K2Cr2O7/H+

Propan-1-ol 

reflux

(e)K2Cr2O7/H+

Propan-2-ol 

reflux

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.231)

Alcohols containing the group react with

iodine in sodium hydroxide (known as iodoform reagent) to give iodoform(CHI3)

Triiodomethane Formation (Iodoform Reaction)


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.231)

  • The iodoform test:

  • The iodoform reaction serves as a test for alcohols containing the group

  • The iodoform formed is a yellow crystal with characteristic odour


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.231)

Solution:

(a)

(b)

Example 33-3

Write equations to show how each of the following transformations can be accomplished. Some conversions may require more than one step.

(a)

(b)

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.231)

Solution:

(c)

(d)

Example 33-3

Write equations to show how each of the following transformations can be accomplished. Some conversions may require more than one step.

(c)

(d)

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.231)

Solution:

(e)

(f)

Example 33-3

Write equations to show how each of the following transformations can be accomplished. Some conversions may require more than one step.

(e)

(f)

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.232)

Example 33-4

Give a simple chemical test that can distinguish between the compounds in each of the following pairs:

(a)Ethanol and methoxymethane

(b)Propan-1-ol and propene

(c)Propan-1-ol and propan-2-ol

(d)Pentan-3-ol and pentan-2-ol

Solution:

(a)Sodium reacts with ethanol to give hydrogen gas while methoxymethane does not.

(b)Propene decolourizes bromine in 1,1,1-trichloroethane while propan-1-ol does not.

(c)On the addition of Lucas reagent, propan-2-ol will give a cloudy appearance in a shorter time than propan-1-ol.

(d)On the addition of iodine in sodium hydroxide, pentan-2-ol will give a yellow precipitate (due to the formation of iodoform) while pentan-3-ol will not.

Answer


Hydroxy compounds

33.6 Reactions of Alcohols (SB p.233)

Check Point 33-6

Draw the structural formulae for the missing products A, B and C in the reactions below.

Answer


Hydroxy compounds

33.7 Reactions of Phenols (SB p.233)

  • The lone pair electrons on oxygen interact with the delocalized  electron cloud of benzene ring

  • The resonance structures withdraw the electron from oxygen, making it slightly electron-deficient

  • This strengthens the C – O bond but weakens the O – H bondreaction of phenols involve the cleavage of O – H bond


Hydroxy compounds

33.7 Reactions of Phenols (SB p.234)

Reaction with Sodium

Phenols react with sodium to form sodium phenoxide and hydrogen gas


Hydroxy compounds

33.7 Reactions of Phenols (SB p.234)

Reaction with Sodium Hydroxide

  • Phenol is a weaker acid than carboxylic acids or mineral acids do not react with sodium hydrogencarbonate

  • Phenol is a stronger acid than alcohols react with sodium hydroxide while alcohols do not


Hydroxy compounds

33.7 Reactions of Phenols (SB p.234)

Esterification

  • Phenol does not react with carboxylic acids to give esters∵the lone pair electrons on oxygen atom delocalized into the benzene ring, making it less nucleophilic and less likely to undergo reaction


Hydroxy compounds

33.7 Reactions of Phenols (SB p.234)

  • Esterification can be carried out by converting phenol to sodium phenoxide firstly and then treating with acyl chlorides or acid anhydrides


Hydroxy compounds

33.7 Reactions of Phenols (SB p.235)

Examples:


Hydroxy compounds

33.8 Uses of Alcohols (SB p.235)

As Solvents

  • Methanol and ethanol are good solvents in the laboratory and industry

  • e.g.methylated spirit (which contains 95% ethanol/water mixture and 5% methanol) is commonly used as an industrial solvent


Hydroxy compounds

33.8 Uses of Alcohols (SB p.235)

Ethanol is used as a fuel

As Fuels

  • Alcohols usually burn with a clean, blue, hot and non-luminous flame with a very small amount of soot is formed

  • As alcohols are too expensive, they are not widely use as domestic fuel


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

As Alcoholic Drinks

  • Ethanol is the major component in alcoholic beverages

  • The ethanol is produced by the fermentation of sugar or starch


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

As a Motor Fuel Blending Agent

  • Ethanol (80%) is mixed with gasoline (20%) to produce a motor fuel, known as gasohol

  • Gasohol is an alternative to gasoline and it produces less pollutants when burnt

  • It is widely used in Brazil where sugar cane is abundant and fermented to ethanol


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

As an Antifreeze

  • Ethane-1,2-diol is formed in the laboratory by bubbling ethene into a cold and dilute alkaline solution of KMnO4

  • Ethane-1,2-diol is miscible with water in all proportions and has a high boiling point

  • Use as an anti-freeze in car radiators in cold countries


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

As a Raw Material for Making Terylene

  • Terylene (or Dacron) is a polyester which is formed by condensation polymerization of ethane-1,2-diol and benzene-1,4-dicarboxylic acid


Hydroxy compounds

33.8 Uses of Alcohols (SB p.237)

  • Properties: strong, light and does not ‘wet’

  • Uses: making clothing and sails


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

As a Raw Material for Making Plastics

Phenol-methanal:by polymerization of phenol and methanal in acidic medium

Bakelite:using excess methanal, further reactions with phenol-methanal to form cross links


Hydroxy compounds

33.8 Uses of Alcohols (SB p.236)

  • Bakelite is a rigid, three-dimensional, cross-linked polymer

  • Phenol-methanal and bakelite are thermosetting plastics and are good insulators of heat and electricity

  • Uses:making kitchenware (e.g. handles of saucepans) and electrical appliances (e.g. electric plugs)


Hydroxy compounds

The END


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