Alcohols and Phenols

Dr. Seham ALTERARY

Chapter 7

Chem 145

1434-1435

2013-2014

2nd semester

Chapter Head LinesIntroduction

Types and Classifications.

Nomenclature of Alcohols and Phenols.

Physical Properties.

Acidity of Alcohols and Phenols.

Preparation of Alcohols and Phenols:A. Preparation of Alcohols

2- Hydration of Alkenes

1- Hydration of Alkyl halide

3- Oxidation of Alkenes to vicinal diol.

4- Reduction of Carbonyl group.

5- Nucleophilic Addition of Grignard Reagents to carbonyl group

B. Preparation of PhenolsReactions of Alcohols and Phenols:

I- Reactions involving oxygen-hydrogen bond breakingII- Reactions involving carbon-oxygen bond rupturing

III. Oxidation IV- Reaction of Aromatic Ring of Phenols

Introduction

-Alcohols are characterized by the hydroxyl group -OH

-The general formula for Alcohols is

Alcohols

O

H

H

HH

H H

CC

OHR C

sp3As all alcohols are the compounds containing hydroxyl group (-OH)

attached to the alkyl group, hybridization is sp3

Phenols or, Aryl alcohols

Are hydroxyl derivatives of aromatic hydrocarbons, which are

derived by replacing hydrogen atom attached to sp2 hybridized

carbon atom(s) of benzene ring by hydroxyl group.

OH

Phenols , ArOH

OHsp2

Alcohols and phenols have a common functional group

the hydroxyl group, —OH.

Alcohols and phenols may be viewed as organic derivatives of water.

H-O-H R-O-H or PhCH2OH Ph-O-H

Water Alcohol Phenol

OHOHOH

Types of Alcohols

3. Polyhydroxyls: containing more than two hydroxyl groups on

different carbon atoms.

1. Monohydroxyls: containing one hydroxyl group.

Example; ethanol (C2H5OH)

2. Dihydroxyls (glycols): containing two hydroxyl groups connected

by different carbon atoms.

Example; 1,2-Ethanediol

Ethylene glycol

(CH2OH-CH2OH).

Example; 1,2,3-propanetriol

Glycerol or Glycerin

(CH2OH-CHOH-CH2OH).

Classification of Monohydroxyl Alcohols

The mono hydroxyl alcohols can be classified into three types

according to the type of the carbon atom connected to the hydroxyl

group:

C HR

H

OH

C RR

H

OH

C RR

R

OH

1̊ alcohol 2̊ alcohol 3̊ alcohol

C HH

H

OH

Methyl alcohol

Ethanol 2-Propanol 2-Methyl-2-PropanolExamples

Draw the structures of the above alcohols?

Nomenclature

1) Common Nomenclature (Alkyl + alcohol)

Examples:

- In the common system, you name an alcohol by listing the alkyl

group and adding the word alcohol.

CH3 OH OHCH3CH2

Methyl alcohol Ethyl alcohol

CH3CH2CH2OH

Propyl alcohol

- You can use both the common and IUPAC systems to name alcohols.

CH3CHCH3

OH

Isopropyl alcohol

Vinyl alcohol

CH2 CHCH2 OH

CH3CCH3

CH3

OH

Allyl alcohol

t-butyl alcohol

CH2 OH

Benzyl alcohol

Examples:

CH2 CH OH

2) IUPAC Nomenclature

3) Number the longest continuous carbon chain so as to give

the carbon atom bearing the hydroxyl group the lower number.

1) Select the longest continuous carbon chain to which the

hydroxyl is directly attached.

2) Change the name of the alkane corresponding to this chain

by dropping the final -e and adding the suffix –ol.

Examples

CH3CHCH2CH2CH2OH

CH3

2 1345

4-Methylpentan-1-ol

Not 2-Methylpentan-5-ol

CH3CH2CH2OH

n-Propanol

CH3CHCH2CH3

OH

2-Butanol

4) OH group is preferred over the double or triple bond in numbering.

OH

Hept-5-en-2-ol

HC CCH2CH2 OH

But-3-yn-1-ol

ClCH2CH2CH2OH

3-chloropropan-1-ol

CH3CHCH2CCH3

CH3

CH3OH

12321 3 4 5

4,4-Dimethylpentan-2-ol

5) If a compound contains both OH and a double or triple bond,

choose the chain that include them both even if this is not the

longest chain.

HO

1

2

3

4

Example

3-Ethylbut-3-en-2-ol

OH

Methylcyclohexylalcohol

HO

Cyclopentylalcohol Allylalcohol

HOExample

Common:

IUPAC: Cyclopentanol 1-Methyl-1-cyclohexanol 2-Propen-1-ol

Examples

OH

Cl

HOOH

Pent-4-ene-2-ol Cyclohex-2-enol

12

3

4-Chloro-3-methyl-heptan-1-ol

1

234

5

6

7

C6H5

Br OH

3-Bromo-2-phenyl cyclopentanol

1

2

3

OH

123

1-Cyclobutylpropan-2-ol

OH

1

23

4

2-Methyl-4-phenyl butan-2-ol

Examples

HO

pent-4-yn-1-ol

OH

5-Ethyl-hex-5-en-3-ol

HO

4-methyl-2-cyclohexen-1-ol

HO

2-phenyl ethanol

CH3CH2CHCH2CHCH3

OHCH2

H3C

4-Ethyl-hexan-2-ol

(CH3)2C CHCHCHCH3

OH

5-Methyl-4-hexen-2-ol

• In the IUPAC system, the suffix diol is added to the name of the

parent hydrocarbon when two hydroxyl groups are present, and

the suffix triol is added when there are three OH groups.

• Common names, two OH groups on adjacent carbons are known as

1,2-glycols.

IUPAC:

Common:

1,2-Ethanediol

Ethylene glycol

1,2-Propanediol

propylene glycol

1,2,3-Propanetriol

glycerol or glycerin

Examples:

Nomenclature of Phenols

Compounds that have a hydroxyl group attached directly to a benzene

ring are called phenols.

The ortho, meta, para system is used in common names.

While the numbering system is employed in IUPAC names and in this

case numbering of the ring begins at the hydroxyl-substituted carbon and

proceeds in the direction of the next substituted carbon that possesses the

lower number.

OHOH

NH2

Phenol 4- Aminophenol

Examples:

Examples:

NO2

OH

Br

Cl

Cl

Cl

Cl

Cl

OH

2,3,4,5,6-Pentachlorophenol4-Bromo-2-nitrophenol

Picric acid

NO2

NO2

O2N

OH

Common name:

2,4,6-Trinitrophenol

O

HO

O

HO

HO

2-hydroxybenzaldehyde 2-hydroxybenzoic acid

Salicyaldehyde

o-hydroxybenzaldehyde o-hydroxybenzoic acid

Salicyalicacid

δ+

δ+

δ-

δ+

δ-

δ+

δ-

δ+

δ+

δ-

δ+

δ-

δ-δ+ δ+

•The solubility of lower

alcohols is due to the

existence of hydrogen

bonds between water and

polar -OH group of alcohol

molecules.

•The first three members are completely miscible with water. The

solubility rapidly decreases with increase in molecular mass. The higher

members are almost insoluble in water but are soluble in organic solvents

like benzene, ether etc.

1. Solubility • Alcohols

Hydrogen bonding between alcohols and water molecules

Physical Properties of Alcohols & Phenols

•The solubility increases with branching of chain.

OH

OH

OH

OH

Increase solubility

HOHO

OHOH

OH

HO

OH

HO

OH OH

•The number of hydroxyl groups increases the solubility.

δ+δ-

δ+

δ-

δ+

δ-δ+

δ+

δ+δ-

δ+

δ-

δ+

Phenols differ from alcohols in that the -OH is directly attached to

the aromatic ring.

•The -OH group in phenols contain a hydrogen bonded to an

electronegative oxygen atom. Thus they form hydrogen bonds with

water molecules

• Phenols

δ-

δ+

• Phenols are sparingly soluble in water but readily soluble in organic

solvents .

Boiling point of alcohols are much higher than those of alkanes, halo alkanes

or ethers of comparable molecular masses.

CH3CH2CH3

•This is because in alcohols

intermolecular hydrogen bonding

exists due to which a large amount

of energy is required to break these

bonds.

OHCH3CH2

Ethanol n-propane Dimethylether

Mol wt = 46; bp= 78°C Mol wt = 46; bp= -24°CMol wt = 44; bp= -42°C

3.Boiling points• Alcohols

Boiling points of alcohol increases in regular manner with increase in

molecular weight.

δ-

δ+

δ+

δ-

Representations of

intermolecular hydrogen bonding in alcohols

δ+

δ-

H3C O CH3

• Among isomeric alcohols, the boiling point decreases with increase in

branching in the alkyl group.

• Boiling points of 1o alcohol > 2o alcohol > 3o alcohol

OHCH3CH2CH2CH2

1-Butanol

(mol wt = 74; bp = 118°C)

OHCH3CHCH2

CH3

2-Methyl-1-propanol(mol wt = 74; bp = 108°C)

CH3CH2CHCH3

OH

2-Butanol

(mol wt = 74; bp = 99.5°C)

CH3CCH3

CH3

OH

2-Methyl-2-propanol(mol wt = 74; bp = 83°C)

• boiling points increase with the increase of the number of hydroxyl groups .

Note that!

Exercise:

1- Rank the following molecules in order of decreasing B.P.

PentanolButanol ButanePropylchloride Propanol

I II III IV V

2- Which of the following molecules has the highest B.P?

Br HO

OH

HO O

A) B)

C) D)

Phenols tend to have higher boiling points than alcohols of similar

molecular weight because they have stronger intermolecular hydrogen

bonding.

Representations of intermolecular hydrogen bonding in phenol

• Phenols

O

H δ+

δ-

O

H

δ-

δ+

O

H

δ-

δ+

O

H

δ-

δ+

Acidity of Alcohols & Phenols

The anion dervived by the deprotonation of an alcohol is the alkoxide.

The pKa for most phenols is (10).

Phenols are more acidic than alcohols.

The anion derived by the deprotonation of an phenols is the phenoxide ion.

R O H H+ + RO-

An alcohol An alkoxide ion

O H H+ + O-

A phenol A phenoxide ion

Both alcohol and phenol show acidic property to a certain degree since the

hydrogen in the hydroxy group (-OH) can be removed by a base as a proton.

Alcohols are slightly acidic (pKa 16-18).

- Introduction of electron-withdrawing groups (EWG), such as NO2

or CN, X on the ring increases the acidity of phenol.

- Also, introducing electron-donating groups (EDG), such as NH2,

R, OR decrease the acidity of phenols.

Acidity order

Effect of substituents on the acidity of phenols

OH

NO2

OH

Cl

OH

CH3

OH

OCH3

˃˃˃˃

OH

- The greater the number of electron withdrawing at o- and p-

position, more in the acidic character of phenol.

OH

NO2

OH

NO2

NO2

OH

NO2

NO2NO2

˂ ˂ ˂

OH

pKa

Phenol 4-Nitrophenol 2,4-Dinitrophenol 2,4,6-Dinitrophenol

10.0 7.2 4.0 0.4

pKa values for substituted phenols.

Example: In each of the following pairs of compounds,

indicate which is more acidic.

(a) p-chlorophenol or p-nitrophenol

(c) o-Creasol or o-Nitrophenol

(d) o-Methoxyphenol or m-Methoxyphenol

(b) 2,4-dinitroophenol or 3,5-dinitrophenol

1- Hydration of alkenes

H3O+ OH

+

OH

major minor

KMnO4

OH

OH

OH/ H2O

cis glycol2- From alkyl halide

alcohol,KOH

CH3CH2CH2Cl

heat

dil OH-

CH3CH2CH2OH

H3C CH

CH2

A. Preparation of alcohols:Alcohols can be prepared by the following methods:

3-Reduction of Aldehydes, Ketones, Acids and Esters

The carbonyl group of several functional groups may be converted to the

alcohol by reducing agents.

Reducing Agents

LiAlH4 NaBH4

Sodium borohydride

or

Sodium tetrahydridoborate

Lithium aluminium hydride

O OH

3-a. Reduction of Aldehydes and Ketones

Aldehydes and ketones are most readily reduced with hydride reagents,

LiAl H4 or NaBH4 .

The reducing agents LiAlH4 and NaBH4 act as a source of (hydride ion, H-),

the hydride reacts with the carbonyl group, C=O, in aldehydes or ketones to

give alcohols.

LiAlH4

or

NaBH4

General Equation

+ C

O

HHC H

H

H

OH

+ C

O

HR C H

R

H

OH

+ C

O

R'RC R'

R

H

OH

Formaldehyde

Methanol

Aldehyde

Ketone

1° alcohol

2° alcohol

Examples

CH

O(1) LiAlH4 or NaBH4

(2) H3O+

CH2OH

Propanal 1-Propanol

OH

O(1) LiAlH4 or NaBH4

(2) H3O+

OH

Cyclohexanone Cyclohexanol

3-b. Reduction of Acids and Esters

Each reaction requires that 2 hydrides (H-) be added to the carbonyl of

acids or esters.

Carboxylic acids and esters are less reactive to Nu than aldehydes or

ketones.

As a result they can only be reduced by LiAlH4 but NOT by the less

reactive NaBH4.

General Equation

C

O

R OHC R

H

H

OH

+ H2OLiAlH4 +

Acid

Ester

C

O

R OR'LiAlH4 + C R

H

H

OH

+ R'O H

Examples

ROR'

O

(1) LiAlH4

(2) H3O+

ROH

C OH

O(1) LiAlH4

(2) H3O+

OH

Pentanoic acid 1-Pentanol

Aryl ester Aryl alcohol

Grignards react with aldehydes and ketones to give intermediate products

that form alcohols when hydrolyzed.

The special value of Grignard reagents is that they provide excellent ways to

form new C-C bonds.

As a result of the difference in electronegativity between carbon and

magnesium the charge distribution in the Grignard reagent is such that

the organic group (R) is partially negative and the –MgX group is partially

positive [ Rδ- δ+MgX].

4- From Grignard reagent

Grignard reagent + formaldehyde → 1º ROH

Grignard reagent + other aldehydes → 2º ROH

Grignard reagent + ketones → 3º ROH

Grignard reagent + Esters → 3º ROH

4.1-Grignard + formaldehyde yields a primary alcohol with one additional

carbon.

4.2-Grignard + aldehyde yields a secondary alcohol.

1° alcohol

2° alcohol

2) H2O/ HClH3CH2C CH2

OH

H H

O

H3CH2C MgBr +

1) Dry Ether

H3CH2C CH2

O [MgBr]+

H3CH2C MgBr

+H3C H

O

1) Dry EtherH3CH2C CH

O

CH3

[MgBr]+

2) H2O/ HCl H3CH2C CH

OH

CH3

4.3-Grignard + ketone yields a tertiary alcohol.

2) H2O/ HCl

OH

CH2CH3

4.4 -Grignard + ester yields a tertiary alcohol.

3° alcohol

The esters are less reactive than aldehydes and ketones. However they give tertiary

alcohols with excess (2 moles) of Grignard reagent.

O

O+Ph MgBr

1) Dry Ether

2) H2O/ HCl

OH

Ph

Ph

2

3° alcohol

O

+

H3CH2C MgBr 1) Dry Ether

O

CH2CH3

[MgBr]+

Hydrolysis of diazonium salt.

Preparation of phenols

Reactions of alcohols and phenols

I-Reactions of alcohols:

1-Those that involve the breaking of oxygen-hydrogen bond

Alcohols undergo two kinds of reactions;

2- Those that involve the rupture of carbon-oxygen bond C OH

CO H

II-Reactions of phenols:

1-Those that involve the breaking of oxygen-hydrogen bond

phenols undergo two kinds of reactions;

2-Those that involve the benzene ring reactions.

OH

O H

Alcohols and phenols can act as acids whenever they donate a proton to a base.

Alcohols with alkali metals (active metals) like sodium Na or Potassium K to

form the salt (alkoxide).

(1) Salt Formation

General Equation

Example

2R O H + NaOH No Reaction

+ Na 2NaOCH3 + H22 CH3O H

Note That!

A- Reactions involving oxygen-hydrogen bond breaking

CO H

+ Na2 R O H 2NaOR + H2

OH

2 + Na2

O- Na+

+ H2

General Equation

Example

OH

2 + NaOH2

O- Na+

+ H2O

Note That!

Phenols are more acidic than alcohols and may be converted to their

sodium salts by reaction with aqueous NaOH; sodium hydroxide.

+ Na 2NaOAr + H22Ar O H

(2) Reaction of alcohols with carboxylic acids :Ester formation

Alcohols can be converted to esters by means of the Fischer

Esterification Process. In this method, an alcohol is reacted with a

carboxylic acid in the presence of an inorganic acid catalyst such as,

H2SO4 or HCl.

+H+

Heat

R' C

O

OHR OH R' C

O

OR + H2O

General Equation

CH3CH2OH + CH3C

O

OHH+

HeatCH3C

O

OCH2CH3 + H2O

Ethanol

(alcohol)

Acetic acid

(acid)

Ethylacetate

(ester)

Example

B- Reactions involving carbon-oxygen bond rupturing

1- Dehydrations of alcohols:

Since water is ―removed‖ from the alcohol, this reaction is known as a

dehydration reaction (or an elimination reaction):

• Heating alcohols in concentrated sulfuric acid (H2SO4) at 180°C removes

the OH group and a H from an adjacent carbon to produce an alkene,

with water as a by-product.

General Equation

Example

CH3CHCH3

H2SO4

180° C

OH

CH3CH CH2 + H2O

Propanol Propene

C OH

1.1 Formation of alkenes.

+ H2OC C

R

R

R

R

OHH

C CR

RR

RH2SO4

180° C

• If there is more than one possible product of a dehydration reaction, the

major product can be predicted from Zaitsev’s Rule:

• Zaitsev’s Rule— when an alkene is produced in an elimination reaction,

the major product is the one with the more highly substituted double bond.

OH

H2SO4 / 180°C+ + H2O

OH

H2SO4 / 180°C

OH

CH3

H2SO4 / 180°C

Excercise

Example

Major product

90%

Manor product

10%

• Heating alcohols (R—OH) in concentrated sulfuric acid (H2SO4) at

140°C removes a molecule of water from two alcohol molecules, causing

the two ―R‖ groups to become attached to an oxygen atom, forming an

ether functional group:

1-Dehydration of Alcohols :

+ HO R'R OH H2SO4

140° C+ H2OR O R'

General Equation

Examples

2 CH3CH2OHH2SO4

140° CCH3CH2

CH2CH3O + H2O

Ethanol Diethylether

1.2 Ethers Formation

2- Replacement of the OH group by Halide: Alkyl Halides Formation.

The hydroxyl group -OH of alcohols can be replaced by halide to form alkyl

halides.

The net equation is:

Alkyl fluoride; R—F, are not prepared from alcohols.

3-Reaction with phosphorus halides, PX3 or PX5.

2-Reaction with thionyl chloride SOCl2.

1-Reaction with hydrogen halides HX: Lucas test.

Replacement of the OH group by Halide

R OH R X (X= Cl, Br, or I)

Alcohols Alkyl halide

• Alcohols can be oxidized by removing two H atoms from the

molecule; the exact products of the reaction will depend on the type

of alcohol.

Oxidation of Alcohols to Carbonyl Compounds

• An oxidation reaction occurs when a molecule loses electrons. This

is usually manifested as an increase in the number of oxygen atoms

or a decrease in the number of hydrogen atoms.

• Some common oxidizing agents include potassium permanganate

(KMnO4), chromic acid (H2CrO4), sodium dichromate (Na2Cr2O7),

and other Cr6+ salts.

[O] = oxidation

R2CHOH + [O] → R2C=O + H2O

Oxidation of alcohols gives different products depending on; the class of

alcohols that is oxidized & the kind of oxidizing agent that is used.

Primary alcohols yields aldehydes when treated with mild oxidizing agent

such as hot metalic copper; Cu or CrO3 in pyridine .

1° alcohol

When 1° alcohols are allowed to react with stronger oxidizing agents,

such as chromic acid, H2CrO7, or neutral potassium permenganate, KMnO4,

the intermediate aldehydes formed initially are oxidized further to carboxylic

acids, RCOOH.

A- Oxidation of Primary alcohols

R C O

H

H

H

+ H2OR C

H

O R C O

OH[O] [O]Cu

or

CrO3/ pyridine

H2CrO7

Aldehyde Carboxylic acid

General Equation

CH3CH2OHCu or CrO3/ pyridine

C

H

OCH3

Ethanol Ethanal

Acetaldehyde

CH3CH2OH C

OH

OCH3

H2Cr2O7

Ethanol Acetic acid

Example

with mild oxidizing agent

with stronger oxidizing agents

oxidation of primary alcohols to aldehydes requires special reagents

to avoid over-oxidation to the acid.

Secondary alcohols are oxidized to ketones, which cannot be oxidized any

further:

B- Oxidation of 2° Secondary Alcohols

General Equation

Example

2- Propanol Acetone

H3C C CH3

OH

H

[O]CH3CH3C

O

+ [O] R C

R

H2O+OR C O

H

R

H

2° alcohol Ketone

+ [O]R C O

H

R

R

C- Oxidation of 3° Tertiary Alcohols

Do not react with oxidizing agents under normal conditions.

3° Tertiary alcohol

Note That!

Tertiary are stable to oxidation under normal conditions.

under drastic conditions, tertiary alcohols give ketones and acids,

each containing less carbons than alcohols.

Reactions of phenols

OH

6- Reaction of aromatic ring of phenols

1-Halogenation

OH

Br

OH

Br

OH

Br

Br

Br

Br2/ CS2 or CCl4

5°C

25° C

Br2/ H2O

2,4,6-Tribromophenol

o-Bromophenol p-Bromophenol

+

OH

In polar solvents

phenols react with

halogens (chlorine

water or bromine

water) at a very fast

rate substituting all

the available ortho-

and para-positions.

However, halogenation can be stopped at monohalogenation stage

if reaction is carried out in presence of non-polar or less polar

solvents at low temperature.

Electrrophilic Substitution Reaction

Home Work

1)

2)

3)

MgBr

H3O+

+

O H2C

HCH

OH3O+

+

MgCl

KMnO4

OH-/H2O

4) The IUPAC name of

is:

A) 4-Ethyl-5-heptyn-3-ol

B) 4-Ethyl-5-heptan-3-ol

C) 4-Ethyl-5-hepten-3-ol

D) 4-Etyl-2-hepten-5-ol

OH

5) The IUPAC name of

is:

A) 3-Methyl-1-bromocyclohexanol

B) 2-Bromo-3-methylcyclohexanol

C) 4-Bromo-2-methylcyclohexanol

D) 3-Bromo-1-methylcyclohxanol

6) The common name of 2-methyl-2-propanol is:A) Allyl alcohol

B) Isopropyl alcohol

C) tert-Butyl alcohol

D) Benzyl alcohol

7) The following reaction gives

A) 4-Ethylphenol

B) 2-Ethylphenol

C) Ethylphenyl ether

D) Ethylphenyl ketone

NaOHOH

1)

CH3-CH2-Br2)

Thank youFor your attention