chapter 1 alcohol

CHAPTER 1:

ALCOHOLS

NORFAZRIN MOHD HANIF FACULTY OF APPLIED SCIENCE

UITM NEGERI SEMBILAN

Nomenclature – common and IUPAC names for alcohols & phenols

Classification of alcohol as 1°, 2°, and 3°.

Physical properties of alcohol. Preparation of alcohol

–Grignard synthesis –Hydrolysis of alkyl halides –Industrial and laboratory preparations of ethyl alcohol

Reactions of alcohol –Oxidation –Esterification –Dehydration –Halogenation –Formation of alkoxides

SUBTOPICS

Alcohols are compounds whose molecules have a hydroxyl group

(-OH) attached to:

saturated C atom of a simple alkyl group

unsaturated C atom of an alkenyl or alkynyl group

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

are called phenol

CH3 OH CH2 OHCH3 CH2 CH3CH3

OH

Methanol Ethanol 2-Propanol

CH CH2 OHCH2

2-Propenol

CH CH2 OHCH

2-Propynol

OHPhenol

INTRODUCTION

• According to the type of carbinol carbon atom (C bonded to the –OH group).

C OHClasses:

i) Primary alcohol

- -OH group attached to a primary carbon atom

- one or no alkyl group attached to the carbon bonded to the –OH group

ii) Secondary alcohol

- -OH group attached to a secondary carbon atom

- two alkyl group attached to the carbon bonded to the –OH group

iii) Tertiary alcohol

- -OH group attached to a tertiary carbon atom

- three alkyl group attached to the carbon bonded to the –OH group

CLASSIFICATION

Primary (1°) Alcohol Secondary (2°) Alcohol

H C C

H

H OH

H

C H

H

H

Tertiary (3°) Alcohol

H C C

H

H OH

C

C H

H

H

HH

H

H C C

H

H H

H

C OH

H

H

CLASSIFICATION

• Alcohols that contain more than one OH group attached to different carbons are called polyhydroxy alcohols.

• Monohydroxy: one OH group per molecule.

• Dihydroxy: two OH groups per molecule.

• Trihydroxy: three OH groups per molecule.

Polyhydroxy Alcohols

CLASSIFICATION

Select the longest

continuous chain of carbon

atoms containing –-OH .

Change the name of the

alkane corresponding to this

chain by dropping the final-e

and adding the suffix –ol.

Number the parent chain to

give the -OH group the lowest

possible number.

1 2

3 a. IUPAC names

b. Common names

Name the alkyl group followed by the word alcohol

NOMENCLATURE

1-Propanol(Propyl alcohol)

2-Propanol(Isopropyl alcohol)

1-Butanol(Butyl alcohol)

OH

OH

OH

2-Butanol(sec-Butyl alcohol)

2-Methyl-1-propanol(Isobutyl alcohol)

2-Methyl-2-propanol(tert -Butyl alcohol)

OH

OHOH

Examples

IUPAC :

COMMON:

IUPAC :

COMMON:

NOMENCLATURE

Compounds containing more than one -OH group are named diols, triols, etc.

C H 3 C H C H 2

H O O H

C H 2 C H 2

O H O H

C H 2 C H C H 2

H O H O O H

1,2-Ethanediol (Ethylene glycol)

1,2-Propanediol (Propylene glycol)

1,2,3-Propanetriol (Glycerol, Glycerine)

NOMENCLATURE

Unsaturated alcohols

Name compounds containing a double bond and an alcohol group as alkenol.

Give the alcohol carbon the lower number.

Examples:

3-Buten-2-ol

C CH CH CH3

OH

CH3

CH3

4-Methyl-3-penten-2-ol

CH2 CH CH CH3

OH

NOMENCLATURE

Unsaturated alcohols

Name compounds containing a triple bond and an alcohol group as alkynol. Give the alcohol carbon the lower number. Examples:

CH C CH2CH2 OH

3-Butyn-1-ol

C CHCH2C

OH

CH3

CH3

2-Methyl-4-Pentyn-2-ol

NOMENCLATURE

Phenols is the parent name & the substituent is simply indicated by prefix.

COMMON:

IUPAC: phenol 3-Bromophenol 2-Methylphenol

NOMENCLATURE - Phenol

COMMON:

IUPAC: 1,2-Benzenediol 1,3-Benzenediol 1,4-Benzenediol

NOMENCLATURE - Phenol

• PHYSICAL STATES OF ALCOHOLS

- simple aliphatic alcohols and lower aromatic alcohols (such as phenylmethanol, C6H5CH2OH) → liquids at room temperature.

- highly branched alcohols and alcohols with twelve or more carbon atoms → solids.

PHYSICAL PROPERTIES

Alcohols are polar compounds

they interact with themselves and with other polar

compounds by dipole-dipole interactions

Dipole-dipole interaction: the attraction between the positive end of one dipole and the negative end of another

O

HH

H

CH

+

-

+

O

HH

H

CH

+

-

+

…………….........

hydrogen

bonding

PHYSICAL PROPERTIES

Hydrogen bonding: when the positive end of one dipole is a H bonded to F, O, or N (atoms of high electronegativity) and the other end is F, O, or N

▫ the strength of hydrogen bonding in water is approximately 21 kJ (5 kcal)/mol

▫ hydrogen bonds are considerably weaker than covalent bonds

▫ nonetheless, they can have a significant effect on physical properties

PHYSICAL PROPERTIES

In relation to alkanes of comparable size and molecular weight, alcohols

– have higher boiling points

– are more soluble in water

The presence of additional -OH groups in a molecule

further increases solubility in water and boiling point

Boiling point & solubility

i) Alcohols with short carbon chains (such as methanol, ethanol, and propanol) dissolve in water.

- when alcohols dissolve in water, hydrogen bonds are formed between the –OH group of the alcohol molecule and the –OH group of the water molecule.

ii) The solubility of alcohols in water decreases sharply with the increasing length of the carbon chain. Higher alcohols are insoluble in water.

- alcohol contains a polar end (-OH group) called ‘hydrophilic’ and a non-polar end (the alkyl group) called ‘hydrophobic’.

- the water solubility decreases as the alkyl group becomes larger.

A. Solubility

iii) alcohols with more than one hydroxyl group (polyhydroxy alcohols) are more soluble than monohydroxy alcohols with the same number of carbon atoms. This is because they can form more hydrogen bonds with water molecule.

iv) branched hydrocarbon increases the solubility of alcohol in water.

- reason: branched hydrocarbon cause the hydrophobic region becomes compact.

* Phenol is unusually soluble (9.3%) because of its compact shape and the particularly strong hydrogen bonds formed between phenolic –OH groups and water molecules.

A. Solubility

Use basic solubility rule: “like dissolves like”

Each alcohol consists of a nonpolar carbon chain

(hydrophobic part) and a polar OH group (hydrophilic part).

As water is polar, it attracts OH group while carbon chain

on the other hand as nonpolar is repelled. Solubility of

alcohols is determined by the stronger of the two forces.

Another factor in understanding solubility is the capability

to form hydrogen bonding to water.

H O

H δ+

O

HH

H

CH

+

-

+

…………..

hydrogen

bonding

A. Solubility

Structural Formula Name bp(°C)

Solubilityin Water

Methanol 32 65 Infinite

Ethane 30 -89 Insoluble

Ethanol 46 78 Infinite

Propane 44 -42 Insoluble

1-Propanol 60 97 Infinite

Butane 58 0 Insoluble

1-Pentanol 88 138 2.3 g/100 g

1,4-Butanediol 90 230 Infinite

Hexane 86 69 Insoluble

8 g/100 g117741-Butanol

Pentane 72 36 Insoluble

CH3 CH2 CH2 OH

CH3 CH2 CH2 CH3

CH3 OH

CH3 CH3

CH3 CH2 OH

CH3 CH2 CH3

CH3 ( CH2 ) 3 CH2 OH

HOCH2 ( CH2 ) 2 CH2 OH

CH3 ( CH2 ) 4 CH3

CH3 ( CH2 ) 2 CH2 OH

CH3 ( CH2 ) 3 CH3

MW

A. Solubility

i) The boiling points of alcohols are higher than those of alkanes and chloroalkanes of similar relative molecular mass.

- For example:

C2H5OH CH3CH2CH3 CH3Cl

Relative molecular mass: 46 44 50.5

Boiling point: 78°C -42°C -24°C

- Reason:

* intermolecular hydrogen bonds exist between the –OH

groups in the alcohol molecules.

RO

HO

H R

ArO

HO

H Ar

hydrogen bonding hydrogen bonding

δ+

δ-

δ+ δ-

δ-

δ-

ii) Branched chain alcohols boils at a lower temperature (more volatile) than the straight chain alcohols with the same number of carbon atoms.

B. Boiling point

• Their boiling points are dramatically different

– ethanol forms intermolecular hydrogen bonds which increase attractive forces between its molecules resulting in a higher boiling point

– there is no comparable attractive force between molecules of dimethyl ether & ethane.

bp -24°C Ethanol bp 78° C

Dimethyl ether

C H 3 C H 2 O H C H 3 O C H 3 C H 3 C H 3 Ethane

bp -89°C

B. Boiling point

OCTOBER 2008

APRIL 2009

• Alcohol is weakly acidic.

• In aqueous solution, alcohol will donated its proton to water

molecule to give an alkoxide ion (R-O-).

R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18

alkoxide ion

Example

CH3CH2-OH + H2O CH3CH2-O- + H3O

+

The acid-dissociation constant, Ka, of an alcohol is defined by the

equilibrium

R-OH + H2O R-O- + H3O+ K

a Ka = [H3O

+] [RO-]

[ROH]

pKa = - log (Ka)

* More smaller the pKa

value, the alcohol is

more acidic

C. Acidity

Alcohol is weakly acidic.

In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O-).

CH3 O H : HO

H

[ CH3OH]

[ CH3O-] [H3O

+]

CH3 O:–

O

H

HH+

+

= 10- 15 .5

pKa = 1 5.5

Ka =

+

pKa decrease, acidity increase

alkoxide ion

C. Acidity

(CH3 ) 3COH

(CH3 ) 2CHOH

CH3CH2OH

H2 O

CH3OH

CH3COOH

HCl

15.5

15.7

15.9

17

18

4.8

Hydrogen chloride

Acetic acid

Methanol

Water

Ethanol

2-Propanol

2-Methyl-2-propanol

Structural Formula

Stronger acid

Weaker acid

*Also given for comparison are pKa values for water, acetic acid, and hydrogen chloride.

Compound pKa

-7

C. Acidity

Acidity depends primarily on the degree of stabilization and solvation of the alkoxide ion

▫ the negatively charged oxygens of methanol and ethanol are about as accessible as hydroxide ion for solvation; these alcohol are about as acidic as water

▫ as the bulk of the alkyl group increases, the ability of water to solvate the alkoxide decreases, the acidity of the alcohol decreases, and the basicity of the alkoxide ion increases

CH3OH

Methanol

H2O

Water

pKa = 15.5 pKa = 15.7

CH3CH2OH

Ethanol

pKa = 15.9

CH3CH2(OH)CH3

2-Propanol

pKa = 17.0

C. Acidity

• Phenol is a stronger acid than alcohols and water.

OH H2O O- H3O

+

phenol phenoxide ion

R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18

alcohol alkoxide ion

Ka = 1.2 x 10-10

H2O + H2O HO- + H3O+ Ka = 1.8 x 10-16

hydroxide ion

C. Acidity of phenols

Phenol is more acidic than alcohols by considering the resonance effect.

ii) The phenoxide ion - one of the lone pairs of electrons on the oxygen atom is delocalised

into the benzene ring. - the phenoxide ion is more stable than the alkoxide ion because the

negative charge is not confined to the oxygen atom but delocalised into the benzene ring.

- the phenoxide ion is resonance stabilised by the benzene ring and

this decreases the tendency for the phenoxide ion to react with H3O+.

O O O O

C. Acidity of phenols

i) The alkoxide ion (RO-) - the negative charge is confined to the oxygen and is not

spread over the alkyl group. - this makes the RO- ion less stable and more susceptible to

attack by positive ions such as H+ ions.

C. Acidity

Grignard Synthesis Hydrolysis of alkyl halides Acid-catalyzed Hydration of

alkenes

PREPARATION

• The grignard reagent (RMgX) is prepared by the reaction of

metallic magnesium with the appropriate organic halide. This

reaction is always carried out in an ether solvent, which is

needed to solvate and stabilize the Grignard reagent as it forms.

R-X + Mg R-Mg-X

(X = Cl, Br or I) organomagnesium halide

(Grignard reagent)

CH3CH2OCH2CH3

Grignard reagents may be made from primary, secondary, and

tertiary alkyl halides, as well as from vinyl and aryl halides.

Alkyl iodides are the most reactive halides, followed by bromides

and chlorides. Alkyl fluorides generally do not react.

1.Grignard Synthesis

CH3I Mg

CH3CH2Br Mg

Br Mg

CH3MgI

MgBr

CH3CH2MgBr

EXAMPLES

ether

ether

ether

1.Grignard Synthesis

Grignard Reagents react with Formaldehyde to give a 1° alcohol

General formula:

R MgX + C O

CH3

CH3

Ether

H3O+

R C OH

CH3

CH3

Grignard reagent

alcohol

Carbonyl compound

CH3CH2 MgBr + C O

H

H

Ether

H3O+

CH3CH2 C OH

H

H

alkyl halide

alcohol

1.Grignard Synthesis

• Grignard reagents

act as nucleophiles

toward the carbonyl

group

R MgX + C O

R'

R''

Ketone

R C O

R'

R''

MgXNH

4Cl

R C OH

R'

R''

3o alcohol

H2O

Grignard Reagents react with ketone to give a 3° alcohol

Ether

Grignard Reagents react with all other aldehyde to give a 2° alcohol

R MgX + C O

R'

H

aldehyde

R C O

R'

H

MgXH

3O+

R C OH

R'

H

2o alcohol

Ether

1.Grignard Synthesis

General formula:

Alkyl Halide Alcohol

Examples:

R X + OH- R OH + HXΔ

CH3 Cl + OH- CH3 OH + HClΔ

CH3CH2CH2 Cl + OH- ?Δ

(CH3)2CH Br + OH- ?Δ

2. Hydrolysis of alkyl halide

• Alkyl halides can be

converted to

alcohols using

water or hydroxide

as the nucleophile.

• Mechanism is a

simple nucleophilic

substitution

General formula:

C C

CH3

CH3

CH3

CH3

Alkene

+ H2O

H+

C C

H

CH3

CH3

CH3

OH

CH3

Examples:

H2C CH2

Ethene

+ H2O

H+

C C

H

H

H

H

OH

H

Ethanol

Industrial &

laboratory

preparation of

ethanol

3. Acid catalyzed hydration of alkene

• Note that this is not

a reaction

mechanism, but an

equation for the

overall reaction.

• Hydronium ion is a

required catalyst.

Examples:

C CHCH3

CH3

CH3

2-Methyl-2-butene

+ H2O

H+

C C

CH3

OH

CH3

H

H

CH3

2-Methyl-2-butanol

+ C C

CH3

H

CH3

OH

H

CH3

3-Methyl-2-butanol

* Markovnikov’s rule : in the addition of H-OH to an alkene, the H atom adds to

the C atom of the double bond that already has the greater number of H atom.

(Major product) (Little formed)

3. Acid catalyzed hydration of alkene

Oxidation Dehydration Halogenation Esterification Formation of alkoxides

REACTION

1. Oxidation

Oxidation of 1°Alcohol to Aldehyde : RCH2-OH RCHO

CH3CH2OH + PCCCH

2CI

2CH3 C H

O

Ethanol Ethanal25oC

PCC: Pyridinium chlorochromate

Oxidation of 1°Alcohol to Carboxylic Acid : RCH2-OH RCOOH

CH3CH2OH CH3 C OH

O

Ethanol Ethanoic Acid

H2CrO

4

acetone35oC

CH3CH2OH CH3 C OH

O

Ethanol Ethanoic Acid

KMnO4/ H+

[O]

[O]

1. Oxidation

Oxidation of 2°Alcohol to Ketone : RCHR'

OH[O]

R C R'

O

CH3CHCH2

OH

CH3

H2CrO

4

2-Butanol

acetone35oC

CH3CCH2

O

CH3

2-Butanone

KMnO4/H+

cyclohexanol cyclohexanone

OH O

1. Oxidation

A Chemical Test for 1o, 2o and 3o Alcohol

CH3CH2OH CH3 C OH

O

Ethanol Ethanoic Acid

H2CrO

4

acetone35oC

+ Cr3+

orange

green 1oAlcohol

2oAlcohol

3oAlcohol H

2CrO

4

2-Methyl-2-propanol

acetone35oC

CH3 C CH3

OH

CH3

No reaction!

H2CrO

4

2-Butanol 2-Butanoneacetone

35oC

CH3CHCH2CH3

OH

CH3C CH2CH3

O

orange

green

+ Cr3+

1. Oxidation

• When heated with strong acids catalysts (most commonly H2SO4,

H3PO4), alcohols typically undergo a reactions to generate an alkene and

water. Also known as dehydration since it involves the removal of a

molecule of water.

• Dehydration of alcohols will formed alkenes and the products will followed

Zaitsev’s rule .

conc. H2SO4

R-CH2-CH2-OH R-CH=CH2 + H2O

CH3CH2-CH-CH3

OH

H+

H+

CH3CH=CH-CH3 + H2O

CH3CH2-CH=CH2 + H2O

2-butanol2-butenemajor product

1-butene

2. Dehydration

* Zaitsev’s rule : The major product of the reaction favor the more stable alkene.

Dehydration of Alcohol to form Alkene:

+ H2O

H+

C C

CH3

CH3 CH3

CH3

C C

CH3

CH3

CH3OH

CH3

CH3180oC

+ H2O

H+

C C

CH3

CH3

CH3OH

CH3

CH3C C

CH3

CH3

CH3 OH

CH3

O C C

CH3

CH3

CH3

CH3

CH3

140oC

Dehydration of Alcohol to form Ether:

2. Dehydration

Examples:

CH3CH2OH

CH2 CH2

CH3CH2OCH2CH3

Ethene

Diethyl ether

H+

H+

180oC

140oC

2. Dehydration

Halogenation of Alcohol to form Alkyl halide from

1. Hydrogen Halide (H-X)

2. Phosphorus trihalide (PX3)

3. Thionyl Chloride (SOCl2)

R OH + H X R X + H2O

alkyl halidehydrogen halide

X = Cl, Br, I

CH3CH2OH + H Br CH3CH2 Br + H2O

Examples:

1. Hydrogen Halide (H-X)

3. Halogenation

LUCAS’S TEST:

(CH3)3COH + H Cl (CH3)3C Cl + H2O

ZnCl2

25oC3o

(CH3)2CHOH + H Cl (CH3)2CH Cl + H2O

ZnCl2

25oC2o

CH3CH2CH2CH2OH + H Cl No reactionZnCl

2

25oC1o

•LUCAS TEST : used to differentiate 3o, 2o and 1o alcohol.

• Alcohol’s reactivity : 3o>2o>1o

Immediate white

cloudiness of solution

formed

White cloudiness of

solution formed after 5

min

Clear homogenous solution

Clear homogenous solution

Clear homogenous solution

3. Halogenation

2. Phosphorus trihalide (PX3)

CH3 OH + P Br3 CH3 Br

3. Thionyl Chloride (SOCl2)

CH3 OH + SOCl2 CH3 Cl + SO2 + HCl

3R OH + P X33R X + H

3PO

3

X = Cl, Br, I

R OH + SOCl2 R Cl + SO2 + HCl

3. Halogenation

The reaction between an alcohol and a carboxylic acid to form

an ester and H2O.

R C

O

O H O R'H

H+

CH3CH2-O-H CH3 C

O

O H

CH3-O-H C

O

OHH

+

H+

R C

O

O R'

C

O

OCH3

CH3 C

O

OCH2CH3

H2O

H2O

H2O

carboxylic acid alcohol ester

EXAMPLES

ethanol ethanoic acid ethyl ethanoate

methanol benzoic acid methyl benzoate

H+ = catalyst

4. Esterification

General formula:

R C Cl

O

R' OH + R C OR'

O

+ HCl

Acid Chloride Ester

Esterification also occurs when alcohols react with

derivatives of carboxylic acids such as acid chlorides

C6H5C Cl

O

CH3OH + C6H5C OCH3

O

+ HCl

Examples:

4. Esterification

2R OH + 2RO Na + H22Na

- +

2R OH + 2RO K + H22K

- +

General formula:

R OH + NaOH no reaction

alkoxide salt

alkoxide salt

* Reactivity towards active metal: 1o>2o>3o alcohol

5. Formation of alkoxides

End of Chapter 1…

Thank you