Wk 12 C18 Alcohol ,Amines

8/9/2019 Wk 12 C18 Alcohol ,Amines

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1818 Alcohols,Alcohols,amines andamines andrelatedrelated

compoundscompoundsPrepared by

Emma Bartle

University of Western Australia


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18.1 Alcohols18.1 Alcohols

Alcohols contain the functional group

OH, a hydroxyl group

This hydroxyl group is bonded to an sp3

hybridised carbon atom

The oxygen atom is also sp3 hybridised

Two sp3 hybrid orbitals form bonds to

carbon and hydrogen The remaining two sp3 hybrid orbitals each

contain an unshared pair of electrons


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Alcohols are named the same way as

alkanes, with the following differences

The parent alkane is the longest chain ofcarbon atoms containing the OH group

Change the suffix of the parent alkane

from e to ol, and use a number to

show the location of the OH group

Name and number substituents and list

them in alphabetical order


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To derive common names for alcohols,

we name the alkyl group bonded to the

OH group and add the word alcohol

Ethanol(Ethyl alcoh ol)

1-Propanol(Propy l alcoho l)

2-Propanol(Is opropy l alcoho l)

1-Butanol(Butyl alcoho l)

OH

OH

OH

OH

2-Butanol

(s ec-Bu tyl alcoho l)2-Methyl-1-propanol

(Is obutyl alcoh ol)

2-Methyl-2-propanol(t ert-Butyl alcohol )

OH

Cyclohexanol(Cyclohexyl alcoho l)

OH

OH

OH


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We classify alcohols as primary (1), secondary (2) or

tertiary (3), depending on whether the OH group is on a

primary, secondary or tertiary carbon atom.Classify each of the following alcohols as primary, secondary or tertiary.

secondary (2) tertiary (3) primary (1)


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Compounds containing 2 OH groups

are named as diols

Compounds containing 3 OH groups

are named as triols

CH3

CHCH2

HO OH

CH2 CH2

OHOH

CH2 CHCH2

OHHOHO

1,2-Ethanedio lEthylene glycol

1,2-PropanediolPropylene glycol

1,2,3-Propanetrio lGlycerol, Glycerin)


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Physical properties

Both the C-O and O-H bonds of an

alcohol are polar covalent

Alcohols are polar molecules

This is demonstrated for methanol below

H-

H+

H+O

H

HH

C

H


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Alcohols have higher boiling points and

water solubility than hydrocarbons

CH3CH2 CH2OH

CH3CH2 CH2CH3

CH3OH

CH3CH3

CH3CH2 OH

CH3CH2 CH3

CH3CH2 CH2CH2CH2OH

HOCH2CH2CH2CH2 OH

CH3CH2 CH2CH2CH2CH3

Structural Formula Name

Molecular

Wei ht(g/mol)

Boiling

Point(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


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Alcohols associate in the liquid state by

hydrogen bonding



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Preparation of alcohols

Alcohols can be prepared from many

functional groups

Discussed here are:

Preparation from alkenes

Preparation from haloalkanes

Reduction of carbonyl compounds Addition of Grignard reagents to carbonyl

compounds


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Preparation from alkenes Acid catalysed hydration of alkenes

Preparation from haloalkanes Nucleophilic substitution with a hydroxide ion



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Reduction of carbonyl compounds

Aldehydes are reduced to primary alcohols

Ketones are reduced to secondary alcohols

Carboxylic acids and esters can be reduced to form

primary alcohols



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18.2 Reactions of alcohols18.2 Reactions of alcohols

Reactions discussed here are:

Acidity of alcohols

Basicity of alcohols Reaction with active metals

Dehydration of alcohols to alkenes

Conversion of alcohols to haloalkanes

Oxidation of alcohols to aldehydes,

ketones and carboxylic acids


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Acidity of alcohols

Alcohols have similar acid ionisation

constants (pKa

) to water (15.7)

Aqueous solutions of alcohols have a pH

close to that of pure water

CH3 O H O H

H

[CH3 O-

][ H3 O+]

[ CH3 OH]

CH3 O H O

H

H+

Ka

=

+ +

= .

Ka= .


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The table below gives the pKa for several

low-molar-mass alcohols

( H3 )3 OH

( H3 )2 HOH

H3 H2OH

H2O

CH3 OH

CH3 COOH

HCl

Co o Ka

-7

15 5

15 7

15 9

17

18

4 8

y roge c lori e

aceticaci

me t a o l

water

et a o l

2- ro a ol

2-met yl-2- ro a ol

Str ct ral

FormulaStro ger

aci

Weaker aci

*A lso give forcom ariso are Ka

values for water,

aceticaci , a y roge c lori e


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Basicity of alcohols

In the presence of a strong acid, theoxygen atom of an alcohol is a weak base

It reacts with the acid by proton transfer toform an oxonium ion

Alcohols can function as both weak acidsand weak bases

CH3 CH2 -O-H H O

H

H O

H

H

H2 SO4CH3 CH2 -O H

H

CH3 CH2 -O H

H HH

O H

Ethylo xon ium ion(pK

a-2.4)

Hydron ium i on(pK

a-1.7)

Ethanol

+

+

++

+

+

+


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Reaction with active metals

Alcohols react with Li, Na, K and other

active metals to form metal alkoxides

Na is oxidised to Na+ and H+ is reduced to H2

Alkoxide ions are stronger bases than thehydroxide ion

Alkoxide ions can be used as nucleophiles in

substitution reactions

2CH3CH2OH 2Na 2CH3CH2O-Na

+ H2+ +

So iu m et oxi e


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140o

yclo exa ol C clo exe e

OH+ H 2 O

H2 SO4

180oCCH3 CH2 OH

H2 SO4CH2 =CH 2 + H 2 O

+ H2 OCH3COH

CH3

CH3

50oC

H2 SO4CH3C=CH2

CH3

2- et yl ro e e

(Isobutyle e)


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Oxidation of 1 and 2 alcohols

Oxidation of a 1 alcohol gives an aldehyde or

carboxylic acid, depending on the experimental

conditions

2 alcohols are oxidised to ketones

3 alcohols are not easily oxidised


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The most common reagent used for the

oxidation of a 1 alcohol to carboxylic acid

and 2 alcohol to a ketone is chromic acid

CrO3 H2 OH2SO4 H2 CrO4+

Chro ic acidChro i (VI)o ide

CH3 (CH2 )6 CH2 OHCrO3

H2SO4 ,H2 OCH3 (CH2 )6 CH

O

CH3 (CH2 )6 COH

O

Octa al( ot isolated)

Octa oic acid1-Octa ol


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The mild oxidising agent PCC is used to

oxidise 1 alcohols to aldehydes

CrO3 HClN N

H

CrO3 Cl

-

Py idinium chlo och omate(PCC)

Py idine

+ ++

OHPCC

CH2 Cl2H

O

Ge aniol Ge anial


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Ester formation

Condensation of alcohols with carboxylic acids,

acid chlorides or anhydrides produces esters

Alcohols can also form esters with inorganic acids,

like nitric acid



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18.4 Ethers18.4 Ethers

Ethers contain an atom of oxygen bonded

to 2 carbon atoms

Oxygen is sp3

hybridised with bondangles of approximately 109.5

H

H O

H

C H

H

H

C


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The OR group bonded to the parent

alkane is named as an alkoxy

Common names are derived by listingthe alkyl groups bonded to oxygen in

alphabetical order and adding ether

CH3

CH3

CH3 CCH3

Et 2

H

Et

E h h n

Di h h

h m h p p nm h t ert-bu h , TBE

t rans-2-E h h n


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Cyclic ethers contain the ether oxygen

as one of the atoms in the ring

Cyclic ethers are generally known bytheir common names

E l

i

T r r

f r , THF

T r r

r

, Di

O O

O

OO


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Physical properties

Ethers are moderately polar compounds

However, only weak forces of attraction existbetween ether molecules



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Ethers have lower boiling points than

alcohols of similar molar mass

CH3 CH2 OH

CH3 OCH3

CH3 CH2 CH2 CH2 CH2 OH

HOCH2 CH2 CH2 CH2 OH

CH3 CH2 CH2 CH2 OCH3

CH3 CH2 CH2 CH2 OH

CH3 CH2 OCH2 CH3

CH3 OCH2 CH2 OCH3 ethylene g lycoldimethyl ethe

90 84 in ini te

8 g/100 g3574diethyl ethe

1-butanol 74 117 7.4 g/100 g

slight7188butyl methyl e the

in ini te230901,4-butanediol

2.3 g/100 g138881-pentanol

7.8 g/100 g-2446dimethyl ethe

in ini te7846ethanol

olubilityin Wate

Boiling

Point(C)

MoleculaWeightNamet uctu al o mu la


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Ethers form hydrogen bonds with water

They are more soluble in water than

hydrocarbons of similar molar mass



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The effect of hydrogen bonding is

illustrated by comparing the boiling

points of ethanol and dimethyl ether

The difference is due to the polar O-Hgroup in the alcohol

This increases the attractive force

between molecules of ethanol

CH3 CH2 OH CH3 OCH3

bp-24C

Ethanol

bp C

Dim thyl ther


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Reactions of ethers

Ethers resemble hydrocarbons in their

resistance to chemical reactions

They do not react readily with oxidising

agents or reducing agents

They are not affected by most acids or bases

at moderate temperature

Because of their good solvent properties

and general inertness to chemical

reaction, ethers are excellent solvents in

which to carry out organic reactions


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SummarySummary

Alcohols

Contain the functional group OH, the

hydroxyl group, bonded to an sp3

hybridised carbon atom

Classified as 1, 2 or 3

IUPAC names are formed by changing

the suffix of the parent alkane to ol Common names are derived by naming

the alkyl group followed by alcohol


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SummarySummary

Reactions of alcohols

Alcohols are polar compounds

Their boiling points are higher than those

of hydrocarbons of similar molar mass

Boiling points of alcohols increase with

increasing molar mass

Alcohols are more soluble in water thanhydrocarbons of similar molar mass


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SummarySummary

Ethers

Contain an oxygen atom bonded to

2 carbons not bonded to a heteroatom

They are moderately polar compounds

Their boiling points are close to those of

hydrocarbons of similar molar mass

They are more soluble in water than arehydrocarbons of similar molar mass


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Wk 12 C18 Alcohol ,Amines

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