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Transcript
Chem 1152: Ch. 13
Alcohols, Phenols and Ethers
Introduction
• Alcohol: Any cmpd with a hydroxy (-OH)
functional group attached on aliphatic carbon.
R
OH
• Phenol: Hydroxy functional group attached to
benzene ring, where the parent is a
combination of the benzene ring and the (OH) group.
OH
• Ether: Oxygen with carbon attached on either
side.
O
R
Water structure analogs to alcohol and ether
alcohol
H
ether
OH
O
H
R
H
OH
O
R
R
R
Classification of Alcohols
H
Primary (1°)
Hydroxy bearing C is attached
to either 0 or 1 other C
R
Hydroxy bearing C is attached
to 2 other C
R
Tertiary (3°)
Hydroxy bearing C is attached
to 3 other C
O
H
R
Secondary (2°)
H
O
H
R
R
H
R
O
H
H OH
H H
Examples of Alcohols
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Examples of Alcohols
• Antifreezes
1,2-ethanediol (ethylene glycol)
• 1,2-propanediol (propylene glycol)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Rules for naming alcohols
For single hydroxy (-OH) group
• Step 1: Identify longest chain that includes (-OH) group. Drop –e from
hydrocarbon name, and replace with ending –ol.
• Step 2: Number this parent chain to give lowest number to carbon with
attached (-OH) group.
• Step 3: Locate position of (-OH) group.
• Step 4: Locate and name all branches attached to parent chain.
• Step 5: Include names of all branches (still in alphabetical order) in prefix
of compound name. Include location of (-OH) group.
• Note: Multiple (-OH) groups are named by addiing diol, triol, etc, to end
of alkane without removing -e.
1
5
H3C
2
4
3
OH
H3C
2 3
CH3
2-ethyl-1-pentanol
HO
1
4
OH
2-methyl-1,4-butanediol
Naming Alcohols
HO
CH3
H3C
OH
CH3
Br
HO
H3C
H3C
OH
CH3
OH
CH3
OH
H3C
H3C
OH
OH
H3C
CH3
HO
CH3
H3C
H3C
OH
CH3
H3C
CH3
OH
OH
OH
CH3
Naming Alcohols
HO
CH3
H3C
OH
CH3
Br
HO
H3C
H3C
OH
CH3
2,2,4-trimethyl-3-hexanol
OH
CH3
5-bromo-3-ethyl-1-pentanol
OH
H3C
H3C
OH
OH
1,2,4-hexanetriol
H3C
CH3
HO
CH3
3-butyl-2,4-hexanediol
H3C
2,2-dimethylcyclopentanol
H3C
OH
CH3
H3C
3-methyl-3-pentanol
CH3
OH
OH
OH
CH3
1,2-cyclohexanediol
2-isopropyl-1-methylcyclopropanol
3-phenyl-1-propanol
Physical Properties of alcohols- Solubility
• Low MW alcohols
(methanol, ethanol,
propanol) are miscible with
water.
• As alkane chain gets longer,
alcohol behaves more like
an alkane:
– More soluble in nonpolar
organic solvents (benzene,
CCl4, ether)
Alcohols that look like water, behave
like water.
Alcohols that look more like alkanes
behave like alkanes.
Due to hydrogen bonding.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
OH
H3C
H3C
OH
OH
OH
H
H3C
H3C
CH3
Hydrogen bonding
• Hydrogen bond: Attractive
interaction of a hydrogen atom
with an electronegative atom
(e.g. N, O, F) from another
molecule or chemical group.
• The H must be covalently
bonded to another
electronegative atom.
– This is why H on hydrocarbon
chain does not participate in Hbonding.
• H-bond relatively weak.
•
•
Bond energy for C-H 413 kJ/mol
H-bond energy 2 kJ/mol
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Effects of hydrogen bonding
• H-bonding between alcohol molecules increases BP for alcohol compared
to similar MW alkane
OH
H3C
OH
H3C
H3C
CH3
O
H3C
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
CH3
Alcohol Reactions
1. Alcohol Dehydration (Elimination Rxn):
R
R
R
R
OH
H
H2SO4
R
180 C
R
R
+ H-OH
R
• Alcohol Hydration (Addition Rxn)
R
R
R
+ H-OH
R
R
R
H2SO4
R
R
OH
H
Alcohol Dehydration to produce alkene
• Alcohol Dehydration (Elimination Rxn):
H
H
H
C
C
H H
H
C
C
H
H
H
H
C
C
H HO H
H
C
C
H
H2SO4
H
H
+ H-OH
H
2-butene
180 oC
H H
H
C
C
H
H
C
H
C H
+ H-OH
H
1-butene
 This rxn (at 180 °C) generates 2 products: 2-butene and 1-butene.
 The major product is 2-butene (90%) because both C=C bond carbons are
attached to at least one other carbon.
 The minor product is 1-butene (10%) because only one of the C=C bond
carbons is attached to at least one other carbon.
 The major product in these rxns will always be the one resulting in the
highest number of carbon groups bonded to the C=C carbons.
Alcohol dehydration in biochemistry
H
-
O OC
C
H
OH
C
CH2
-
COO
Enzyme
-
O OC
citrate
CH2 COO
C
-
COO
-
H
C
+
-
COO
cis-aconitrate
 This rxn is catalyzed by an enzyme rather than an acid in the human body.
 Alcohol dehydration rxns in general are involved in the formation of:
 Carbohydrates
 Fats
 Proteins
H-OH
Examples: Alcohol Dehydration to Produce Alkene
CH3
H2SO4
H3C
CH3
180 oC
OH
CH3
CH3
H2SO4
H3C
CH3
180 oC
OH
H2SO4
CH3
CH3
H3C
180 oC
OH
CH3
H2SO4
CH3
H3C
180 oC
OH
H3C
CH3
CH3
H3C
CH3
CH3
OH
H2SO4
180 oC
Alcohol Dehydration to produce ether
• Alcohol Dehydration (Elimination Rxn):
OH
H
+
H2SO4
O
o
R
R
alcohol
R
O
R
140 C
alcohol
HO
+
H
ether
 This rxn (at 140 °C) generates an ether and water.
 This rxn works mainly with primary alcohols.
H
Primary (1°)
R
Hydroxy bearing C is attached
to either 0 or 1 other C
H3C
OH
+
H
CH3
O
H
O
H
H2SO4
140 oC
H3C
OH
H OH
H H
H3C
O
CH3
H2SO4
140 oC
H3C
O
CH3
+
+
HO
H
HO
H
Alcohol Oxidation
 Oxidation: Loss of hydrogen or gain of oxygen.
 Oxidizing Agent: Compound that oxidizes another compound.
 KMnO4 (potassium permanganate)
 K2Cr2O7 (potassium dichromate)
 This rxn works different depending on whether alcohol is 1°, 2° or 3°.
 H-OH lost in oxidation rxns comes from the same carbon, rather than
adjacent carbons as seen in dehydration rxns to form alkenes.
H
Primary (1°)
Hydroxy bearing C is attached
to either 0 or 1 other C
R
Hydroxy bearing C is attached
to 2 other C
R
Tertiary (3°)
Hydroxy bearing C is attached
to 3 other C
O
H
R
Secondary (2°)
H
O
H
R
R
H
R
O
H
H OH
H H
Alcohol Oxidation for Primary Alcohol
H
H
O
C
R
O
+
H
Primary alcohol
(O)
R
C
H
+
H-OH
aldehyde
O
(O)
R
C
OH
Carboxylic acid
 Immediate product of oxidation of primary alcohol is aldehyde, which is
then readily further oxidized to a carboxylic acid.
 The aldehyde product may be isolated before further oxidation by
maintaining high temp. and boiling aldehyde out of rxn mixture.
 This is possible because aldehydes do not H-bond like alcohols and
carboxylic acids.
Alcohol Oxidation for Secondary and Tertiary Alcohols
H
R
O
C
R
O
+
(O)
H
Secondary alcohol
R
C
R
+
H-OH
ketone
 Product of oxidation of secondary alcohol is a ketone, which resists further
oxidation.
R
R
C
R
O
H
Tertiary alcohol
+
(O)
NO RXN
Examples: Identify Rxn and draw product
CH3
H2SO4
H3C
CH3
180 oC
OH
CH3
H2SO4
H3C
140 oC
OH
CH3
H3C
CH3
+
(O)
+
(O)
OH
CH3
H3C
OH
Examples: Identify Rxn and Draw Product
CH3
CH3
H2SO4
H3C
H3C
CH3
CH3
o
180 C
OH
H
CH3
CH3
H2SO4
H3C
O
H3C
140 oC
OH
H3C
CH3
CH3
CH3
H3C
CH3
+
(O)
H3C
CH3
OH
O
CH3
CH3
H
+
H3C
(O)
H3C
O
OH
(O)
CH3
OH
H3C
O
Summary of Alcohol Reactions
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Phenols
• Phenol: Hydroxy functional group attached to benzene ring, where the
parent is a combination of the benzene ring and the (-OH) group.
• Low MP solid that liquefies at room temp. with small amount of water.
• Weakly acidic in water (due to conjugated pi bonds on benzene ring).
– Can damage proteins in skin.
• In dilute solutions, can be used as antiseptics and disinfectants.
– Phenol first used by Joseph Lister in hospitals in 1800’s.
– Phenol derivatives used today in Lysol, mouthwashes and throat lozenges.
• Other phenol derivatives used as antioxidants.
O
OH
+
H2O
-
+
H3O
+
Naming Phenols
• Substituted phenols are usually named as derivatives
of the parent compound phenol.
• Examples:
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Ethers
• Ether: Oxygen with carbon attached on either side.
• Naming ethers
• Common Names
1.
2.
Name the two groups attached to the oxygen then add the word ether
If both groups the same, can be named with prefix di-.
• IUPAC Names
– O-R group is alkoxy.
– The –yl ending of smaller R group is replaced by –oxy.
O
CH3
H3C
butyl methyl ether
1-methoxybutane
H3C
H3C
O
p-methoxytoluene
CH3
CH3
Cl
CH3
H3C
O
dipropyl ether
1-propoxypropane
CH3
isopropyl propyl ether
1-isopropoxypropane
ethyl propyl ether
1-ethoxypropane
H3C
CH3
O
CH3
CH3
O
H3C
CH3
O
CH3
2-ethoxy-3,4dimethylhexane
H3C
O
CH3
CH3
2-chloro-1-isopropoxypropane
Properties of Ethers
• Oxygen atom of ether can H-bond with water
– Ethers more soluble in water than hydrocarbons, less soluble than alcohols of
comparable MW.
• Ethers cannot H-bond with other ethers in pure state
– Results in low BP close to those of hydrocarbons of comparable MW.
• Ethers mostly inert and unreactive
– Why diethyl ether is useful solvent
– Diethyl ether is also highly-flammable and was historically an important anesthetic
– History Note: First physician to use diethyl ether as anesthesia was Crawford Long in
1842
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Thiols
•
•
•
•
Thiols: Sulfur analogs of alcohols (-SH instead of –OH)
Chemically- similar (i.e., form similar compounds)
More volatile (lower BP) than alcohols but less water-soluble
Thiols stink!
–
–
–
–
This is how skunks defend themselves
Chopped onions emit propanethiol
Thiols found in garlic
Ethanethiol added to natural gas (methane) so you can smell a leak
• IUPAC Names for simple thiols
– The –SH group is a sulfhydryl group.
– Follow the same steps for naming as you do for alcohols, but do not modify alkane
ending; instead add –thiol to end of parent.
SH
H3C
H3C
butanethiol
SH
SH
CH3
2-butanethiol
H3C
CH3
CH3
2-methyl-3-hexanethiol
Thiol/Sulfide Rxns
Oxidation (Formation of disulfide bond)
R
H
S
+
H
R
S
+
O
O
S
R
R
S
+
H2O
Reduction (breaking disulfide bond)
S
R
R
S
+
H
H
R
H
S
+
H
R
S
Polyfunctional Compounds
 Substances that can contain more than 1 functional group.
 Ribose forms backbone of RNA (genetic transcription).
 Phosphorylated ribose becomes subunits of ATP, NADH, and several other
compounds that are critical to metabolism.
http://www.daviddarling.info/encyclopedia/R/ribose.html
http://en.wikipedia.org/wiki/RNA
Multistep Rxns
 The synthesis of most alcohols may require multiple steps (i.e., to get
product X from reactant A, a product (B, C …X) must be created).
 To solve these problems, work backwards from the final product.
O
 Oxidize 2° alcohol to form ketone.
OH
+
O
(O)
+
H-OH
 Use acid-catalyzed hydration (addition) to form alcohol.
+
H-OH
H2SO4
OH
 The completed series of rxns.
+
H-OH
H2SO4
OH
+
(O)
O
+
H-OH