ch14alcohols, ethers and thiols
TRANSCRIPT
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
1/60
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
2/60
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
3/60
ALCOHOLSAlcohol:Has an -OH (hydroxyl) group
bonded to a tetrahedral carbon
methanol, CH3OH, is the simplest alcohol
3
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
4/60
CLASSIFICATION OF ALCOHOLS
Aliphatic general formula CnH2n+1OH - provided there are no rings
the OH replaces an H in a basic hydrocarbon skeleton
Aromatic in aromatic alcohols (or phenols)
the OH is attached directly to the ring
an OH on a side chain of a ring behavesas a typical aliphatic alcohol
The first two compounds are
classified as aromatic alcohols
(phenols) because the OH group
is attached directly to the ring.
Structural differences alcohols are classified according to the environment of the OH group
chemical behaviour, eg oxidation, often depends on the structural type
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
5/60
CLASSIFICATION OF ALCOHOLS
Depends on the C which has theOHgroup attached
CH2CH3 OHethanol CH3CHCH3
OH
2-propanol
2-methyl-2-propanol
CH3CCH3
OH
CH31oAlcoholattached to
one C
2oAlcohol
attached to
two Cs
3oAlcohol--attached to
three Cs
5
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
6/60
ALCOHOL NOMENCLATURE
1. Find longest carbon chain that contains the -OH group (parent chain)
2. Number chain from end that gives the -OH
the lower number
3. Change the ending -e to -ol
4. Use a number to show the location of the -OH
group
5. For cyclic alcohols, the carbon with the -OH
group is C-1
6. Name and number substituents and list them
in alphabetical order 6
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
7/60
NOMENCLATURE
Ethanol(Ethyl alcohol)
1-Propanol(Propyl alcohol)
2-Propanol(Isopropyl alcohol)
1-Butanol(Butyl alcohol)
OH
OH
OH
OH
2-Butanol(sec-Butyl alcohol)
2-Methyl-1-propanol(Isobutyl alcohol)
2-Methyl-2-propanol
(t er t -Butyl alcohol)
OH
Cyclohexanol
(Cyclohexyl alcohol)
OH
OH
OH
7
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
8/60
NOMENCLATURE
Write the IUPAC name for each alcohol
(a) (b)OH OH
(c) (d) OH
OH
8
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
9/60
NOMENCLATURE
(a) (b)OH OH
(c) (d) OH
OH
1
22
2 2
4
t rans-2-Methylcyclohexanol4-Methyl-2-pentanol
2-Heptanol
7
5
3
2,2-Dimethyl-1-propanol
1
9
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
10/60
NOMENCLATURE
Alcohols containing more than one hydroxyl
groups are named as a diol, a triol, and so on
IUPAC names for diols, triols, and so on retain
the final "-e" in the name of the parent alkane
Compounds containing two hydroxyl groups
on adjacent carbons are commonly called
glycols
CH3
CHCH2
HO OH
CH2 CH2
OH OH
CH2 CHCH2
OH OHOH
1,2-Ethanediol(Ethylene glycol)
1,2-Propanediol(Propylene glycol)
1,2,3-Propanetriol(Glycerol, Glycerin)
10
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
11/60
NAME THE FOLLOWING
CH2CH2CH2
OHOHHO
OH
11
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
12/60
12
NAME THESE:
CH3 CH
CH3
CH2OH
CH3 C
CH3
CH3
OH
CH3 CH
OH
CH2CH3
2-methyl-1-propanol
2-methyl-2-propanol
2-butanol
OH
Br CH3
3-bromo-3-methylcyclohexanol
=>
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
13/60
PHYSICAL PROPERTIES
Alcohols are polar molecules
the C - O and O - bonds are both polarcovalent
13
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
14/60
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
15/60
Alcohols can also formhydrogen bonds with water
15
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
16/60
PHYSICAL PROPERTIES OF ALCOHOLS
Boiling point increasesas MW increases
Solubility in water decreasesas MW increases
CH3 CH2 CH2 OH
CH3 CH2 CH2 CH3
CH3 OH
CH3
CH3
CH3 CH2 OH
CH3
CH2
CH3
CH3 CH2 CH2 CH2 OH
CH3 CH2 CH2 CH2 CH3
Structural Formula NameMolecular
Weight
bp(C)
Solubilityin Water
methanol 32 65 infinite
ethane 30 -89 insolub le
ethanol 46 78 infinite
propane 44 -42 insolub le
1-propanol 60 97 infinite
butane 58 0 insolub le
8 g/100 g117741-butanol
pentane 72 36 insolub le16
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
17/60
CHEMICAL PROPERTIES OF ALCOHOLS
Acid-Base Chemistry
Dehydration
Oxidation
Combustion Reactions (they burn in O2)
17
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
18/60
ACIDITY OF ALCOHOLS
Alcohols have about the same pKavaluesas water
Aqueous solutions of alcohols have the samepH as that of pure water
Phenols have lower pKavalues than normal
alcohols do (are more acidic)
18
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
19/60
ACIDITY OF ALCOHOLS
Alcohols and phenols both contain an OH group
Phenolsare weak acids and react with strong basessuch as NaOH to form water-soluble salts
pKa= 9.89 for phenol 15 for alcohol
Alcohols are much weaker acids and do notreact inthis manner
OH NaOH H2 O
O-
Na+
H2 O+
Phenol Sodium phenoxide(a water-soluble salt)
+
19
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
20/60
CH3 OH
20
TABLE OF KaVALUES
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
21/60
Aromatic ring and O have delocalization ofelectrons Less pull on H, so it is more acidic.
O H
WHY ARE PHENOLS MORE ACIDIC THAN ALCOHOLS?
21
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
22/60
DEHYDRATION
Dehydration :Removal of waterfromadjacent carbonsto form an alkene
most often occurs by heating an alcohol witheither 85% H3PO4or concentrated H2SO4
CH3 CH2 OHH2 SO4 CH2 = CH2 H2 O+
Ethanol Ethylene180C
22
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
23/60
Dehydration essentially the reverse of
hydration (addition of water to doublebond)
Conditions required depend on kind of
alcohol
23
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
24/60
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
25/60
ACID-CATALYZED DEHYDRATION
CH3
CH2
OHH2 SO4
CH2
= CH2
H2
O+
Ethanol Ethylene180C
OHH2 SO4 H2 O
140CCyclohexanol Cyclohexene
+
CH3
CCH3
OH
CH3
H2 SO4 CH3 C=CH2
CH3
H2 O50C
2-Methyl-2-propanol
(t er t-Butyl alcohol)
2-Methylpropene (Isobutylene)
+
1oca 180oC needed
Hard
2o lower
temperatures
Moderate
3o slightlyabove room
temperature
Easy
25
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
26/60
DEHYDRATION Zaitsevs Rule: When two alkene products are
possible, the alkene having the greater numberof alkyl groups (i.e., C atoms) on the double
bond generally predominates (forms major
product)
Major product favored.
CH3CH
2CHCH
3
OHH3PO4
CH3CH=CHCH
3 CH
3CH
2CH=CH
2
1-Butene
(20%)
2-Butene
(80%)
2-Butanol
+-H2O
CH3 CHCHCH3
OH
CH3 H2 SO4CH3 C= CHCH3
CH3
CH3 CHCH= CH2
CH3
3-Methyl-1-butene2-Methyl-2-butene (major product)
3-Methyl-2-butanol
+- H2 O
(minor product)26
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
27/60
CH3 CHCHCH3
OH
CH3 H2 SO4CH3 C=CHCH3
CH3
CH3 CHCH= CH2
CH3
3-Methyl-1-butene2-Methyl-2-butene
(major prod uct)
3-Methyl-2-butanol
+- H2 O
CH3CH
2CHCH
3
OH
H3PO4 CH3CH=CHCH
3 CH
3CH
2CH=CH
2
1-Butene (20%)
2-Butene (80%)
2-Butanol
+-H2O
27
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
28/60
DEHYDRATION-HYDRATION RELATED
Acid-catalyzed hydration of alkenes andacid-catalyzed dehydration of alcohols arecompeting reactions
Equilibrium between alkene and alcohol
exists
Large amounts of water favor alcohol
formation, while removal of water from the
equilibrium mixture favors alkene formation (LeChatelier's principle)
An alkene An alcohol
C C
H OH
+ H2 O dehydration
hydrationC C
28
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
29/60
DEHYDRATION VS OXIDATION
Dehydration: RemoveOH andH
OH from one C : H from adjacent C
Oxidation : Remove twoH atomsOne H from OH group :
Other H from C that has theOH attached
29
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
30/60
OXIDATION OF ALCOHOLS
Oxidation of a 1 alcohol gives an aldehydeor a carboxylic acid, depending on theexperimental conditions
Oxidation of a 1 alcohol to a carboxylic acidis carried out using an oxidizing agent such aspotassium dichromate, K2Cr2O7, in aqueoussulfuric acid
CH3 ( CH2 )6CH2OHK2Cr2O7
CH3 ( CH2 ) 6CH
O K2Cr2O7
H2SO4 H2SO4CH3 (CH2 )6COH
O
Octanal Octanoic acid1-Octanol 30
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
31/60
OXIDATION OF ALCOHOLS
Can sometimes stop the oxidation at thealdehyde stage by distilling the mixture(Aldehydes usually have lower boilingpoints than either the 1 alcohol or thecarboxylic acid)
CH3( CH
2)6CH
2OH
K2Cr2O7CH
3( CH
2)6CH
O K2Cr2O7
H2SO4 H2SO4CH
3(CH
2)6COH
O
Octanal Octanoic acid1-Octanol
Carboxylic acidAldehydeAlcohol
31
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
32/60
OXIDATION OF ALCOHOL
Oxidation of a 2 alcohol gives a ketone
Tertiary alcohols are resistant to oxidation
CH3
OH
K2Cr2O7
H2SO4
1-Methyl-cyclopentanol
(no oxidation)
OH
K2Cr2O7
H2SO4 O
2-Isopropyl-5-methyl-cyclohexanone
(Menthone)
2-Isopropyl-5-methyl-cyclohexanol
(Menthol)
32
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
33/60
OTHER REACTIONS OF ALCOHOLS
OXYGEN Alcohols make useful fuels
C2H5OH(l) + 3O2(g) > 2CO2(g) + 3H2O(l)
Advantages have high enthalpies of combustion
do not contain sulphur so there is less pollutioncan be obtained from renewable resources
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
34/60
OTHER REACTIONS OF ALCOHOLS
OXYGEN Alcohols make useful fuels
C2H5OH(l) + 3O2(g) > 2CO2(g) + 3H2O(l)
Advantages have high enthalpies of combustion
do not contain sulphur so there is less pollutioncan be obtained from renewable resources
SODIUM
Conditions room temperature
Product sodium alkoxide and hydrogen
Equation 2CH3CH2OH(l) + 2Na(s) > 2CH3CH2O Na+ + H2(g)
sodium ethoxide
Notes alcohols are organic chemistrys equivalent of waterwater reacts with sodium to produce hydrogen and so do alcohols
the reaction is slower with alcohols than with water.
Alkoxides are white, ionic crystalline solids e.g. CH3CH2O Na+
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
35/60
BROMINATION OF ALCOHOLS
Reagent(s) conc. hydrobromic acid HBr(aq) or
sodium (or potassium) bromide and concentrated sulphuric acid
Conditions reflux
Product haloalkane
Equation C2H5OH(l) + conc. HBr(aq) > C2H5Br(l) + H2O(l)
Mechanism The mechanism starts off similar to that involving dehydration(protonation of the alcohol and loss of water) but the carbocation
(carbonium ion) is attacked by a nucleophilic bromide ion in step 3
Step 1 protonation of the alcohol using a lone pair on oxygen
Step 2 loss of a water molecule to generate a carbocation (carbonium ion)
Step 3 a bromide ion behaves as a nucleophile and attacks the carbocation
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
36/60
ESTERIFICATION OF ALCOHOLS
Reagent(s) carboxylic acid + strong acid catalyst (e.g conc. H2SO4)
Conditions reflux
Product esterEquation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l)
ethanol ethanoic acid ethyl ethanoate
Notes ConcentratedH2SO4is a dehydrating agent- it removes water
causing the equilibrium to move to the right and increases the yield
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
37/60
ESTERIFICATION OF ALCOHOLS
Reagent(s) carboxylic acid + strong acid catalyst (e.g conc. H2SO4)
Conditions refluxProduct ester
Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l)ethanol ethanoic acid ethyl ethanoate
Notes Concentrated H2SO4is a dehydrating agent - it removes water
causing the equilibrium to move to the right and increases the yield
Uses of esters Esters are fairly unreactive but that doesnt make them uselessUsed as flavourings
Naming esters Named from the alcohol and carboxylic acidwhich made them...
CH3OH + CH3COOH CH3COOCH3 + H2O
fromethanoic acid CH3COOCH3 frommethanolMETHYLETHANOATE
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
38/60
38
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
39/60
COMMON ALCOHOLS
EthanolEthyl alcohol, grain alcohol
Produced by fermentation
Natural fermentation of sugars andstarches in grains, corn, molasses, fruits,vegetables
Found in beer, wine, and other spirits
C6H12O6 2 CH3CH2OH + 2 CO2
glucose ethanol carbon dioxide39
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
40/60
COMMON ALCOHOLS
Methanol
Methyl alcohol or wood alcohol
Distilled from wood pulp originally
Very toxic, even in small amounts
Reacts to make formaldehyde (a fixative)
CH3OH CH2=O
methanol formaldehyde
40
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
41/60
COMMON ALCOHOLS
Isopropyl alcohol
2-propanol rubbing alcohol
Evaporates quicklyused to reduce fever
Solvent in many cosmetics, perfumes, etc.
CH3CHCH3
OH
2-propanol
41
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
42/60
COMMON ALCOHOLS
1,2-ethanediol
Ethylene glycol
Very soluble in water
Used as antifreeze
Glycerol
1,2,3-propanetriolVery soluble in water
Sweet taste
Part of fats and oils 42
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
43/60
PREPARATION OF IMPORTANT ALCOHOLS
Many alcohols (or their derivatives) canbe formed by reacting smaller molecules.
CO
CO2H
2 CH3 OHO2
CH2 O
CH3 COOHCoal
ormethane Carbon
monoxideMethanol
Acetic acid
Formaldehydeoxidation
catalyst
43
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
44/60
PREPARATION OF IMPORTANT ALCOHOLS
H2 O, H2 SO4
CH3 CH=CH2
CH3 CHCH3
OH
HOCH2 CHCH2 OH
OHPropene
2-Propanol
Gly cerin, gly cerol
several steps
CH2 =CH2
O2
H2 O, H2 SO4
O
H2 C CH2
CH3 CH2 OH
H2 O, H2 SO4
H2 SO4
HOCH2 CH2 OH
CH3 CH2 OCH2 CH3
Ethylene
Ethanol
Ethylene glycol
180CDieth yl ether
catalystEthylene
oxide
44
ETHERS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
45/60
ETHERS
The functional group of an etheris anoxygen atom bonded to two carbonatoms
Simplest ether is dimethyl etherMost common ether is diethyl ether
Often called just ether
CH3 -O-CH3 CH3 CH2 -O-CH2 CH3
Dimethyl ether Diethyl ether45
ETHER NOMENCLATURE
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
46/60
ETHER NOMENCLATURE
Generally use common names for small(low-molecular-weight) ethers
common names are derived by listing the alkyl
groups bonded to oxygen in alphabetical
order and adding the word "ether
alternatively, name one of the groups on
oxygen as an alkoxy group
OCH3CH3 CH2 OCH2 CH3
Cyclohexyl methyl ether
(Methoxycyclohexane)
Diethyl ether46
ETHER NOMENCLATURE
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
47/60
ETHER NOMENCLATURE
Cyclic ether: an ether in which one of the
atoms in a ring is oxygen
Cyclic ethers also known by their common
names
ethylene oxide is an important building blockfor the organic chemical industry; it is also used
as a fumigant in foodstuffs and textiles, and in
hospitals to sterilize surgical instruments
tetrahydrofuran is a useful laboratory and
industrial solvent
Eth ylene oxide Tetrahydrofuran(THF)
OO
47
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
48/60
48
PHYSICAL PROPERTIES OF ETHERS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
49/60
PHYSICAL PROPERTIES OF ETHERS
Ethers are polar compounds
O has a partial negative charge
Each C bonded to it has a partial positive
charge
Only weak forces of attraction exist between ethermolecules in the pure liquid
Boiling points of ethers are close to those ofhydrocarbons of similar molecular weight
Have lower boiling points than alcohols of thesame molecular formula
CH3 CH2 OH CH3 OCH3
bp -24C
Ethanol
bp 78C
Dimethyl ether49
REACTIONS OF ETHERS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
50/60
REACTIONS OF ETHERS
Ethers not very reactive (like hydrocarbons)
Do not react with oxidizing agents such as
potassium dichromate
Do not react with reducing agents such as H2
in the presence of a transition metal catalystNot affected by most acids or bases at
moderate temperatures
Good solvents for carrying out organicreactions, because of their general inertnessand good solvent properties
Diethyl ether and THF (tetrahydrofuran)50
THIOLS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
51/60
THIOLS
Thiol:a compound containing an -SH(sulfhydryl) group
Also called mercaptans
Low-molecular-weight thiols STINKResponsible for smells such as those from
rotten eggs and sewage
the scent of skunks is due primarily to these
two thiols
CH3CH=CHCH2 SH
CH3
CH3 CHCH2 CH2 SH
3-Methyl-1-butanethiol2-Butene-1-thiol51
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
52/60
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
53/60
53
THIOL PHYSICAL PROPERTIES
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
54/60
THIOL PHYSICAL PROPERTIES
S-H bonds are nonpolar covalent
Small difference in electronegativity betweensulfur and hydrogen (2.5 - 2.1 = 0.4)
No hydrogen bonding
Lower boiling points than comparable alcoholsLess soluble in water and other polar solvents
than comparable alcohols
117
78
65
1-butanol
ethanol
methanol
98
35
6
1-butanethiol
ethanethiol
methanethiol
bp (C)Alcoholbp (C)Thiol
54
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
55/60
REACTIONS OF THIOLS
Thiols are weak acids (pKa~10), and arecomparable in strength to phenols
thiols react with strong bases such as NaOH
to form water-soluble thiolate salts
CH3
CH2
SH NaOHH
2O
CH3
CH2
S-Na
+H
2
O+
Ethanethiol(pKa 10)
+
Sodiumethanethiolate
55
REACTIONS OF THIOLS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
56/60
REACTIONS OF THIOLS
The most important thiol reaction inbiological systems is their oxidation todisulfides
Functional group is a disulfide (-S-S-) bond
Disulfide bonds important in protein structure
Thiols are readily oxidized to disulfides by O2
-SH group very susceptible to oxidation and
must be protected from contact with airduring storage
disulfides, in turn, are easily reduced to thiols
by several reducing agents.56
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
57/60
REACTIONS OF THIOLS
Oxidation ofSH groups to form S-S bondsReduction of S-S bonds to formSH groups
2 HOCH2 CH2 SH HOCH2 CH2 S-SCH2 CH2 OH
A disulfide
oxidation
reductionA thiol
57
REACTIONS OF THIOLS
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
58/60
REACTIONS OF THIOLS
Oxidation ofSH groups to form S-S bondsReduction of S-S bonds to formSH groups
58
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
59/60
UNSATURATED ALCOHOLS
Hydroxyl group takes precedence. Assignthat carbon the lowest number.
Use alkene or alkyne name.
4-penten-2-ol (old)
pent-4-ene-2-ol(1997 revision of IUPAC rules)
=>
CH2 CHCH2CHCH3
OH
59
-
8/10/2019 Ch14Alcohols, Ethers and Thiols
60/60