Transcript Chem 150 Unit 8 - Organic Molecules III Alcohols, Thiols

Chem 150
Unit 8 - Organic Molecules III
Alcohols, Thiols, Ethers, Aldehydes
and Ketones
In this unit we continue surveying some of the families of
organic molecules that play important roles in biochemistry;
looking both at their physical and chemical properties. The
Group VIA elements, oxygen and sulfur, typically form two
covalent bonds to attain a filled valence shell. The families that
include oxygen and sulfur with two single bonds include
alcohols C-O-H, ethers C-O-C, thiols C-S-H, sulfides C-S-C
and disulfides C-S-S-C. We will also look at two more
important carbonyl containing functional groups, aldehydes
and ketones.
Introduction
The organic groups covered in this Unit all have important biological
roles
• Alcohols
• Triglycerides
• Amino acids and proteins
• Ethers
• Biologically active molecules
• Thiols
• Amino acids and proteins
• Odorants
• Sulfides
• Amino acids and proteins
• Ketones
• Carbohydrates and metabolic intermediates
• Aldehydes
• Carbohydrates and metabolic intermediates
2
Introduction
Alcohols were first encountered back in Unit 2
• Alcohols comprise a hydroxyl group (-OH) attached to an
alkane-type carbon atom.
C
3
O
H
Introduction
Ethers
• Ethers have an oxygen attached to two alkane-type carbon
atoms.
C
4
O
C
Introduction
Sulfur containing functional groups
• Sulfur, like oxygen, is a Group VIA element
• Sulfur forms functional groups which are analogous to
some of the groups formed by oxygen.
5
Introduction
Thiol
• Thiols look similar to alcohols and comprise a sulfhydryl
(also called mercaptan) group (-SH) bonded to an alkanetype carbon.
C
6
S
H
Introduction
Sulfides
• Sulfides look similar to ethers and contain a sulfur atom
that is bonded to two alkane-type carbon atoms.
C
7
S
C
Introduction
Disulfides
• Disulfides look similar to a sulfide, but contain two sulfur
atoms that are bonded to each other and to two alkanetype carbon atoms.
C
8
S
S
C
Introduction
Ketones
• Ketones are a carbonyl containing functional group in
which the carbonyl carbon is bonded to two other carbon
atoms.
O
C
9
C
C
Introduction
Ketones in the news; Diacetyl
• http://www.usatoday.com/news/health/2007-10-27diacetyl_N.htm
10
Introduction
Aldehydes
• Aldehydes are a carbonyl containing functional group in
which the carbonyl carbon is bonded to at least one
hydrogen atom.
O
C
11
C
H
Question
Circle and label the functional groups found in the following
compounds.
alkene
alcohol
alcohol
alkene
ether
ether
ketone
ether
12
amine
Question
Circle and label the functional groups found in the following
compounds.
thiol
ammonium
ion
alkene
carboxylate
ion
thiol
sulfide
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sulfide
disulfide
Question
Circle and label the functional groups found in the following
compounds.
alcohol
ketone
aldehyde
aldehyde
ether
phenol
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ketone
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
The IUPAC rules for naming alcohols
• Find the longest carbon chain containing the carbon to
which the hydroxyl group is attached.
• Remove the “-e” ending and replace with “-ol”
• Number the carbon chain from the end closest to the
hydroxyl group.
• Identify, name and locate any substituent groups
If the hydroxyl group is being treated as a substituent group,
refer to it as a “hydroxyl” group.
15
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
Examples of alcohol names
16
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
The IUPAC rules for naming thiols
• Find the longest carbon chain containing the carbon to
which the sulfhydryl group is attached.
• Add the ending “-thiol”, without removing the “-e”
• Number the carbon chain from the end closest to the
sulfhydryl group.
• Identify, name and locate any substituent groups
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Alcohols, Ethers, Thiols, Sulfides and
Disulfides
Examples of thiol names
(Common names are shown in parentheses)
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Alcohols, Ethers, Thiols, Sulfides and
Disulfides
We will not use the IUPAC rules for naming the ethers,
sulfides and disulfides.
• Instead of using an ending, the substituents attached to the
oxygen or sulfur will be listed in front fo the family name.
19
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
Examples of ether, sulfide and disulfide names
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Question
Name the following structures.
CH3
A)
CH3 CH
B)
OH
CH
CH3
CH3
CH3
S
CH
CH3
CH3
C)
CH3 CH SH
S
SH5 S
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CH2
CH3
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
Alcohols are also labeled according to the number of carbons
that are attached to the carbon that the hydroxyl group is
attached to.
• This will be important for predicting the products of
oxidation reactions involving alcohols.
OH
CH3 C H
H
primary (1°)
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OH
CH3 C
OH
CH3
H
secondary (2°)
CH3 C
CH3
CH3
tertiary (3°)
Alcohols, Ethers, Thiols, Sulfides and
Disulfides
The hydroxyl groups of alcohols are good hydrogen bonding
donors and acceptors
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Alcohols, Ethers, Thiols, Sulfides and
Disulfides
The other functional groups are not as good at forming
hydrogen bonds.
• Ethers can only accept hydrogen bonds.
• Sulfur has about the same electronegativity as carbon, and
therefore, is non-polar.
This is reflected in the boiling points and solubilities of these
molecules.
24
25
Preparations of Alcohols, Ethers, Thiols and
Sulfides
26
•
In this unit we will be learn many new reactions.
•
Pages 346 and 347 in Raymond contains a nice summary
of all of the reactions that will will cover in this unit.
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Alcohols, Ethers, Thiols and Sulfides can be prepared from
alkyl halides using nucleophilic substitution reactions.
27
•
A nucleophile is an electron rich atom or group or atoms.
•
The halogen atom make a good leaving group.
•
The nucleophile “attacks” that atom to which the halogen is
attached and the halogen leaves.
•
This results in the the nucleophile substituting for the
leaving group.
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Using nucleophilic substitution to prepare alcohols from alkyl
halides:
The OH- attacks
The Cl- leaves
The OH- attacks
The Br- leaves
The OH- attacks
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The I- leaves
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Using nucleophilic substitution to prepare ethers, thiols and
sulfides from alkyl halides:
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Preparations of Alcohols, Ethers, Thiols and
Sulfides
Another way to produce alcohols is the hydration of alkenes
• We saw this reaction back in Unit 2
C
C
alkene
30
+
H 2O
H+
OH
H
C
C
alcohol
Reactions Involving Water (Unit 4)
Hydration
• In the hydration reaction water is also split, but instead of
being used to split another molecule, it is added to another
molecule to produce a single product.
•
•
The water it is added to either an alkene or alkyne:
H OH
The hydration of an alkene produces an alcohol.
H
C
C
H
H
ethene
(an alkene)
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H
+
H
OH
acid
catalyst
H
C
C
H
H
ethanol
(an alcohol)
H
Reactions Involving Water (Unit 4)
Hydration
• This can also be written in shorthand as:
•
•
The H+ below the reaction arrow is used to indicate that this is an acid-catalyzed
reaction.
The shorthand is used to emphasize what happens
H to
OHthe key reactant.
H
C
C
H
H
ethene
(an alkene)
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H
H2O
+
H
H
C
C
H
H
ethanol
(an alcohol)
H
Reactions Involving Water (Unit 4)
Hydration example
• On an earlier slide a reaction from the Citric Acid Cycle
was shown, which involved the dehydrogenation of
succinic acid to produce fumaric acid.
•
The sequent reaction in the Citric Acid Cycle is an example
of a hydration reaction:
O
HO
C
C
C
H
H
fumaric acid
(an alkene)
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H2O
O
C
OH
HO
O
H
OH O
C
C
C
H
H
malic acid
(an alcohol)
C
OH
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Another way to produce
alcohols is the
hydration of alkenes
• When we looked at
hydration reactions
back in Unit 2 we
conveniently picked
reactants that would
only produce one
product.
• It is possible to have
multiple products in
hydration reactions.
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Preparations of Alcohols, Ethers, Thiols and
Sulfides
Multiple products occur whenever there are a different
number of hydrogen atoms attached to the two carbons
double-bonded carbons in the alkene.
• Markovnikov’s Rule can be used to predict which of the
two products is predicted to be the major product.
-The hydrogen from the water in a hydration reaction is added to the
double-bonded carbon atom that originally carried the most hydrogen
atoms.
•
If you consider hydrogens as a source of wealth, this can
be more simply stated as
-“The rich get richer!”
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Preparations of
Alcohols ...
More examples of
hydration reactions:
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Reactions of Alcohols and Thiols
Back in Unit 4 we developed several definitions for OxidationReduction Reactions.
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Oxidation and Reduction (Unit 4)
Ways of recognizing oxidation/reduction reactions:
• Oxidation and reductions always occur together
Oxidation
Reduction
An atom loses
electrons
An atom gains
electrons
An atom gains a
bond to oxygen
An atom loses a
bond to oxygen
An atom loses a An atom gains a
bond to hydrogen bond to hydrogen
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Reactions of Alcohols and Thiols
Back in Unit 7 we saw how the definition “loses hydrogens”
could be applied to the oxidation of hydroquinones to produce
quinones
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Carboxylic Acids & Phenols, Other Reactions
(Unit 7)
The oxidation of
hydroquinones is also
an important biological
reaction.
• A chemical oxidation
of hydroquinones
can be carried out
the oxidizing agent
K2Cr2O7 (potassium
dichromate)
• The K2Cr2O7 is not
40
acting as a base to
remove 2 H+ ions,
instead it is removing
2 H• atoms.
Reactions of Alcohols and Thiols
This same definition can also be applied to the oxidation of
alcohols by potassium dichromate (K2Cr2O7).
The oxidation
requires that
there are
hydrogens to be
removed on the
carbon to which
the hydroxyl is
bound
41
Reactions of Alcohols and Thiols
Application: Breathalyzer(http://science.howstuffworks.com/breathalyzer3.htm
1. The sulfuric acid
removes the alcohol
from the air into a
liquid solution.
2. The alcohol reacts
with potassium
dichromate to
produce:
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1.
2.
3.
* chromium sulfate
* potassium sulfate
* acetic acid
4.
* water
The silver nitrate is a
catalyst
,
Reactions of Alcohols and Thiols
43
•
The oxidation of primary (1°) alcohols is a way for
preparing aldehydes and carboxylic acids.
•
The oxidation of secondary (2°) alcohols is a way for
preparing ketones.
•
The oxidation of tertiary (3°) alcohols does not occur
because there are not hydrogens attached to the carbon to
to which the hydroxyl is attached
Reactions of Alcohols and Thiols
44
Reactions of Alcohols and Thiols
In biological reactions the
coenzyme NAD+ is often used as
the oxidizing agent.
• The NAD+ takes the electrons
away from alcohols to produce
aldehydes, carboxylic acids and
ketones.
45
Reactions of Alcohols and Thiols
Example
• The oxidation of malate to oxaloacetate that occurs in the
citric acid cycle:
O
O
C
HO
O
NAD+
C
H
NADH +
O
C
H+
O
C
CH2
CH2
C
C
O
L-malate
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O
O
O
oxaloacetate
Reactions of Alcohols and Thiols
Thiols can be oxidized to form disulfides using I2 as oxidizing
agent
• We will see this oxidation reaction when we discuss
proteins in Unit 10
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Preparations of Alcohols, Ethers, Thiols and
Sulfides
Another reaction that we saw back in Unit 2 was the
dehydration of alcohols to produce alkenes.
• We saw this reaction back in Unit 2
OH
C
H
C
alcohol
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H+
heat
C
C
alkene
+
H2O
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Like the complement hydration reaction, dehydration can also
produce multiple products.
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Preparations of Alcohols, Ethers, Thiols and
Sulfides
Multiple products occur whenever there are a different
number of hydrogen atoms attached to the two carbons that
are on either side of the carbon to which the hydroxyl is
attached.
• There is a rule that can be used to predict which of the two
products is predicted to be the major product.
-In a dehydration of an alcohol, the hydrogen will be removed from the
neighboring carbon atom that carries the fewest hydrogen atoms.
•
If you consider hydrogens as a source of wealth, and since
we are removing wealth, this can be more simply stated as
-“The poor get poor!”
50
Preparations of Alcohols, Ethers, Thiols and
Sulfides
Examples of dehydration
of alcohols
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Aldehydes and Ketones
Aldehydes and ketones are carbonyl containing functional
group.
O
C
C
aldehyde
•
•
•
52
O
H
C
C
C
ketone
They have an array of important roles to play in biological
chemistry.
We just saw how they can be prepared from the oxidation
of primary and secondary alcohols.
Back in Unit 7, we also saw how they can be prepared
from the decarboxylation of α-keto acids and β-keto acids.
Carboxylic Acids & Phenols, Other Reactions
(Unit 7)
The decarboxylation of β-keto acids produces ketones
The decarboxylation of α-keto acids produces aldehydes
(Raymond’s answers to problems 10.27b and 10.31 are wrong)
53
Aldehydes and Ketones
The IUPAC rules for naming aldehydes
• Find the longest carbon chain containing the carbon to
which the hydroxyl group is attached.
• Remove the “-e” ending and replace with “-al”
• Number the carbon chain from the carbonyl carbon.
• Identify, name and locate any substituent groups
Some of the smaller aldehydes have common names which
are more often used than the IUPAC names.
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Aldehydes and Ketones
The IUPAC rules for naming ketones
• Find the longest carbon chain containing the carbon to
which the hydroxyl group is attached.
• Remove the “-e” ending and replace with “-one”
• Number the carbon chain from end of the chain closest tothe
carbonyl carbon.
• Identify, name and locate any substituent groups
Common names are also used ketones
• The names of the two substituent groups connected to the
carbonyl carbon are listed and followed by the family name
ketone.
55
Aldehydes and Ketones
Examples of names for aldehydes and ketones
56
Aldehydes and Ketones
Aldehydes and ketones can serve has hydrogen bond
acceptors, but not donors.
57
•
This means that they cannot hydrogen bond to themselves,
and so have much lower boiling points than alcohols
•
However, they can hydrogen bond to water, so small
aldehydes and ketones are soluble in water.
Question
Draw structures for the following molecules:
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A)
3-Methylheptanal
B)
3-Methy-2-pentanone
C)
Methyl s-butyl ketone
Oxidation of Aldehydes
We have already seen how aldehydes and alcohols can be
oxidized to carboxylic acids with K2Cr2O7
60
Oxidation of Aldehydes
Aldehydes can also be oxidized with the copper(II) ion (Cu2+)
• This reaction oxidizes aldehydes, but not alcohols.
• The Cu2+ ion forms a clear blue solution
• The Cu+ that is produced in the reaction forms an orange/red
precipitate.
61
Oxidation of Aldehydes
Aldehydes can also be
oxidized with the copper(II)
ion (Cu2+)
• The reaction is called the
Benedict’s reaction, and
has been used for years
in a clinical setting to test
O
H
for the presence
of
C
glucoseH inC the
urine.
OH
HO
C
H
H
C
OH
H
C
OH
CH2
OH
glucose
Cu2+
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Cu2+ + Cu+
Cu+
Reduction of Aldehydes and Ketones
In Unit 4 we saw how H2 could be used to reduce alkenes to
alkanes in the hydrogenation reaction.
• Because this reaction involves adding hydrogens to a
molelcule, it is a reduction reaction.
63
Oxidation and Reduction (Unit 4)
Hydrogenation
• Another type of oxidation/reduction reaction is the
hydrogenation reaction:
•
In this example, an alkene is reduced to an alkane.
‣
•
64
H
H
H
H
This isCconsidered
reduction,
because the hydrogenHis bringing
in
+
H
C
C
C additional
H
2
platinum
electrons to the molecule.
H
H
catalyst
H
H
The alkane that is produced in this reaction is considered “saturated” because it
can no
longer absorb any more hydrogen atoms.
unsaturated
saturated
Oxidation and Reduction (Unit 4)
Often chemist use a shorthand method of writing equations
like these:
• The equation shown on the previous slide can be written
as follows:
H
H
C
H
•
C
H
H2
Pt
H
H
H
C
C
H
H
H
One of the reactants, H2, is placed above the reaction arrow
‣
Technically, this equation is no longer balanced
• The shorthand method of writing a chemical equation is used to emphasize what
happens to a key component of the reaction
‣
65
In this case it is the alkene.
Reduction of Aldehydes and Ketones
The same reaction can also be used to reduce aldehydes
and ketones to alcohols:
66
Reduction of Aldehydes and Ketones
In biochemistry, NADH + H+ is used instead of H2
• The reduction of a ketone containing steroid by the enzyme
Hydroxsteroid dehydrogenase.
67
Reactions of Alcohols with Aldehydes and
Ketones
Aldehydes and ketones
can react with alcohols to
form hemiacetals,
hemiketals, acetals and
ketals.
• Theses reactions will
become in important in
the next unit when we
talk about
carbohydrates.
• This is because
carbohydrates are rich
in aldehydes, ketones
and alcohols
68
O
H
C
CH2 OH
H
C
OH
C
O
HO
C
H
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
CH2 OH
glucose
CH2 OH
fructose
Reactions of Alcohols with Aldehydes and
Ketones
The first reaction, which is similar to the reduction of
aldehydes and ketones, involves adding an alcohol across
the carbonyl to form a hemiacetal (from aldehydes) or a
hemiketal (from ketones).
O
H3C
CH2 C
H
+
O
CH2 CH3
Propanal
(Aldehyde)
Ethanol
(Alcohol)
O
H
+
O
CH2 CH3
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CH2 C
O
CH2 CH3
(Hemiacetal)
O
H
CH3 C
O
CH3
CH3
Propanone
(Ketone)
H
H
H
CH3 C
H3C
O
Ethanol
(Alcohol)
(Hemiketal)
CH2 CH3
Reactions of Alcohols with Aldehydes and
Ketones
Hemiacetal and hemiketal formation is catalyzed by acids.
70
Reactions of Alcohols with Aldehydes and
Ketones
As we will see with the carbohydrates, the carbonyl group
and the alchohol that react can come from the same
molecule.
• This will produce a ring molecule.
71
Reactions of Alcohols with Aldehydes and
Ketones
A hemiacetal or hemiketal can react with a second alcohol to
form an acetal or ketal.
• This is a substitution reaction and produces an water
molecule:
O
H3C
CH2 C
H +
O
H
H +
O
H
O
CH2 CH3
CH2 CH3
72
CH2 CH3
CH2 C
O
Ethanol
(Alcohol)
CH2 CH3 +
H
O
H
H
O
H
H
(Acetal)
O
CH3 C
CH2 CH3
O
CH3
CH3
(Hemiketal)
O
H3C
Ethanol
(Alcohol)
(Hemiacetal)
CH3 C
CH2 CH3
CH2 CH3
H
O
O
(Ketal)
CH2 CH3 +
Reactions of Alcohols with Aldehydes and
Ketones
Sometimes the two
reactions are
combined into a single
reaction equation:
73
Question
Complete the following reaction:
O
CH3 CH2
74
C
H
+
2 CH3 CH2 OH
Question
Draw the structure of the hemiacetal that can form from this
molecule:
OH
CH3 CH
75
O
CH2
CH2
CH2
C
H
The End