1. Chapter 14 Structure and Synthesis of Alcohols

2. Classification Primary: carbon with –OH is bonded to one other carbon.
Secondary: carbon with –OH is bonded to two other carbons.
Tertiary: carbon with –OH is bonded to three other carbons.
Aromatic (phenol): -OH is bonded to a benzene ring.
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3. Classify these:
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4. IUPAC Nomenclature
Find the longest carbon chain containing the carbon with the -OH group.
Drop the -e from the alkane name, add -ol.
Number the chain, starting from the end closest to the -OH group.
Number and name all substituents
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5. Name these: 2-methyl-1-propanol 2-butanol 2-methyl-2-propanol
3-bromo-3-methylcyclohexanol =>
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6. (1997 revision of IUPAC rules) =>
Unsaturated Alcohols
Hydroxyl group takes precedence. Assign that carbon the lowest number.
Use alkene or alkyne name.
4-penten-2-ol (old)
pent-4-ene-2-ol
(1997 revision of IUPAC rules) =>
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7. Naming Diols Two numbers are needed to locate the two -OH groups.
Use -diol as suffix instead of -ol.
1,6-hexanediol =>
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8. Physical Properties
Unusually high boiling points due to hydrogen bonding between molecules.
Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.
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9. Boiling Points FUNCTIONAL GROUP RANKING BY BOILING POINTS Name B.P
 Brief Explanation
Amide
222o  1
 ethanamide
hydrogen bonds on both the oxygen and the nitrogen
 Acid
118o  2
 ethanoic acid or acetic acid
hydrogen bonding from the of 2 oxygen atoms.
 Alcohol
117o  3
  propanol
hydrogen bonding from the presence one oxygen
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10. Solubility in Water
Solubility decreases as the size of the alkyl group increases =>
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11. USES FOR ALCOHOLS
Fuels
Solvents
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12. Methanol “Wood alcohol” Common industrial solvent
Fuel at Indianapolis 500
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13. Ethanol Fermentation of sugar and starches in grains
12-15% alcohol, then yeast cells die.
MUST BE ANEROBIC or vinegar results
Distillation produces “hard” liquors for drinking
alcohol used as solvent
Gasahol: 10% ethanol in gasoline
Toxic dose: 200 mL ethanol, 30 mL methanol
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14. Chapter 14

15. 2-Propanol “Rubbing alcohol” Catalytic hydration of propene
Much more efficient makes 100% alcohol
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16. Biofuels Pros: Some argue it’s Carbon neutral, but not quite, why?
Protects non-renewable fuels needed for drugs and plastics
Cons
Food is scarce, should we burn it when people are hungry?
Uses a lot of land, water, energy to make
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17.
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18. Reactions of Alcohols 1) Combustion: R-OH  CO2
2) Dehydration: R-OH  C=C (Zaitsev)
Major and Minor Product
3) Oxidation:
a) R-OH (Primary)  R-C-HO  R-COOH
b) R-OH (secondary)  R1R2-C=O
c) Tertiary alcohols do not oxidize as the alpha carbon (containing OH) has no H’s
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19. Combustion Complete C3H7OH(g) + 4.5O2  3CO2 + 4H2O
_________________________________
Incomplete Combustion
C3H7OH(g) + 3O2  3 CO + 4 H2O

20. ALCOHOL OXIDATION 10
gentle heating, a primary alcohol can be oxidised to produce an aldehyde.
BUT
With strong heating and excess [O] (acidified) a carboxylic acid is formed.
To heat strongly we need a Reflux apparatus is generally used to produce carboxylic acids.
Note: Aldehydes must be distilled as they are formed to prevent further oxidation to carboxylic acids..

21. OXIDIZING REAGENTS OXIDIZING AGENTS Tollen's Reagent OXIDAIZING AGENT
OBSERVATIONS
REACTION
ACIDIFIED DICROMATE
ORANGE TO GREEN
Cr2O72-(aq)  to Cr3+(aq)
ORANGE GREEN
Tollen's Reagent
COLOURLESS TO
SILVER MIRROR
Ag+(aq) + e-  Ag(s)
COLOURLESS SILVER
MIRROR
OXIDIZING AGENTS
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22. Ag+  Ag (s) Tollen's Reagent
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23. Not hard, nothing special
This reaction goes easily and quickly,
Nothing special is needed, other than the oxidizing agent is required, a hot water bath will do. The problem is when the aldehyde is made it boils off immediately. To form the –COOH we need to trap the aldehyde and force it back with reflux, or a condenser.
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24. OXIDATION OF PRIMARY ALCOHOLS
Controlling the products
e.g. CH3CH2OH(l) [O] ——> CH3CHO(l) H2O(l)
then CH3CHO(l) [O] ——> CH3COOH(l)
OXIDATION TO ALDEHYDES
DISTILLATION
OXIDATION TO CARBOXYLIC ACIDS
REFLUX
Aldehyde has a lower boiling point so distils off before being oxidised further
Forces Aldehyde to condenses back into the mixture and gets oxidised to the acid

25. OXIDATION OF PRIMARY ALCOHOLS
Primary alcohols are easily oxidised to aldehydes
e.g. CH3CH2OH(l) [O] ——> CH3CHO(l) H2O(l)
ethanol ethanal
it is essential to distil off the aldehyde before it gets oxidised to the acid
CH3CHO(l) [O] ——> CH3COOH(l)
ethanal ethanoic acid
Practical details
the alcohol is dripped into a warm solution of acidified K2Cr2O7
aldehydes have low boiling points - no hydrogen bonding - they distil off immediately
if it didn’t distil off it would be oxidised to the equivalent carboxylic acid
to oxidise an alcohol straight to the acid, reflux the mixture
compound formula intermolecular bonding boiling point
ETHANOL C2H5OH HYDROGEN BONDING °C
ETHANAL CH3CHO DIPOLE-DIPOLE °C (volatile)
ETHANOIC ACID CH3COOH HYDROGEN BONDING °C

26. Stop OR Go We can stop at OH to HO (aldehydes),
But the oxidizing agent is powerful and will continue unless we stop it.
1) Use excess Alcohol reagent, so all the KMNO4 / K2Cr2O7 is used up
2) Remove the Aldehyde as it forms via distillation (bp)
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27. OH all the way to COOH Alcohol 10 Aldehyde Alcohol 10 C.A.
A more simplified ONE step Version
1o Alcohol
Carboxylic Acid

28. Secondary Alcohols
Secondary alcohols are oxidised to produce ketones, then stop. Gentle heating as with aldehydes

29. 2o OH to Ketones e.g. CH3CHOHCH3(l) + [O] ——> CH3COCH3(l) + H2O(l)
propan-2-ol propanone
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30. ALCOHOL TO KETONE e.g CH3CHOHCH3(l) + [O] ——> CH3COCH3(l) + H2O(l)
propan-2-ol propanone
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31. Tertiary Alcohols
These are resistant to oxidation, there will be no colour change.
This is because the carbon (of the alcohol group) is not bonded to any other hydrogen atoms.
Thus, NO COLOUR CHANGE WITH [O]

32. 3o lack a hydrogen Remember , hydrogen removal is the Definition of
Oxidation, as is the addition of oxygen
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33. Test Results
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34. Dehydration of Alcohols
Alcohol  Alkene + water
when heated with an acid catalyst:such as a concentrated acid (a dehydrating agent) or pumice, or Al2O3
with the loss of H and OH to form water
alkene
alcohol 34

35. Zaitsev’s Rule
the dehydration of a secondary alcohol favors the product in which hydrogen is removed from the carbon atom in the chain with the smaller number of H atoms, the poor get poorer, or most substituted carbon 35

36. Zaitsev’s Rule…
A shorter way of thinking of it is that the more substituted product is the one that is preferred, since it is more stable… so which is preferred here? 36

37. Disubstituted vs. monosubstituted…
The pink structure (or 2-pentene) is preferred over 1-pentene since it is disubstituted (vs. monosubstituted) 37

38. Try to draw the product of the reaction shown in your composition book (there is a hint on the next slide)

39. Hint…

40. Answer… Remember that the more substituted product is preferred!
(1-butene also forms, but it is the minor product).

41. This one, then one more… 41

42. The more substituted product is preferred…42

43. Pick out the product, last one

44. Recall that Zaitsev’s rule indicates that the more substituted double bond will form…
Under the OH, CH has 3 H’s, the green arrow
the carbon in the hex chain has only 2 arrows
Minor product
No reaction
Missing the double bond