Chapter 13: Alcohols, Phenols, and Ethers 1

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Chapter 13:

Alcohols, Phenols, and Ethers

1

ALCOHOLS, PHENOLS, AND ETHERS

• Hydroxy group – the –OH functional group

• An alcohol has an –OH group attached to an aliphatic carbon. General formula: R-OH

• A phenol has an –OH group on a benzene ring.

• An ether has the functional group:

General formula: R-OR’

2

NAMING ALCOHOLS

Step 1: Name the longest chain to which the –OH group is attached. Use the hydrocarbon name of the chain, drop the final –e, and replace it with –ol.

Step 2: Number the longest chain to give the lowest number to the carbon with the attached –OH.

Step 3: Locate the –OH position.

Example:

OH

6

CH

3

—CH

2

5

—CH

2

|

—CH—CH

2

—CH

4 3 2 1

3

3-hexanol

3

Step 4: Locate and name any other groups attached to the longest chain.

Step 5: Combine the name and location of other groups, the location of the –OH, and the longest chain into the final name.

Example: CH

3

OH CH

3

6

CH

3

—CH

2

5

| | |

—CH—CH—CH—CH

3

4 3 2 1

2,4-dimethyl-3-hexanol

Note: Alcohols containing two –OH groups are diols, three

–OH groups are triols. The IUPAC names for these compounds have endings of – diol and – triol rather than – ol.

4

NAMING PHENOLS

• Substituted phenols are usually named as derivatives of the parent compound phenol.

Examples:

5

CLASSIFICATION OF ALCOHOLS

6

PHYSICAL PROPERTIES OF ALCOHOLS

• The –OH group is polar and capable of hydrogen bonding.

• This makes low molecular weight alcohols highly soluble in water.

• Hydrogen bonding in a water-methanol solution:

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PHYSICAL PROPERTIES OF ALCOHOLS, cont.

• Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water.

• Water interacts only with the –OH group of

1-heptanol:

8

PHYSICAL PROPERTIES OF ALCOHOLS, cont.

9

PHYSICAL PROPERTIES OF ALCOHOLS, cont.

• The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points.

• Hydrogen bonding in pure ethanol:

10

PHYSICAL PROPERTIES OF ALCOHOLS, cont.

11

ALCOHOL REACTIONS

The removal of water (dehydration) from an alcohol at

180

°

C is an elimination reaction that produces an alkene.

12

ALCOHOL REACTIONS, cont.

• Under slightly different conditions (140 °C)

, a dehydration reaction can occur between two alcohol molecules to produce an ether.

13

ALCOHOL REACTIONS, cont.

• Oxidation – the removal of hydrogen atoms.

• Alcohol oxidations with an oxidizing (O) agent, such as

K

2

Cr

2

O

7 and KMnO

4

:

• Primary alcohols  aldehyde

 carboxylic acid

• Secondary alcohols  ketone

• Tertiary alcohols  no reaction

14

ALCOHOL REACTIONS, cont.

• Primary alcohol oxidation

• Secondary alcohol oxidation

15

IMPORTANT ALCOHOLS

• Methanol (wood alcohol): CH

3

OH

• Production:

•Useful as a solvent and industrial starting material

• Highly toxic, if taken internally causes blindness and/or death

16

IMPORTANT ALCOHOLS, cont.

• Ethanol (ethyl alcohol, grain alcohol): CH

3

CH

2

OH

• Produced commercially from ethylene and through biological (yeast) fermentation of carbohydrates

• Useful as a solvent, industrial starting material, fuel

(gasohol), and found in alcoholic beverages.

• Moderately toxic

17

IMPORTANT ALCOHOLS, cont.

• 2-propanol (isopropyl alcohol) is the main component of rubbing alcohol

• 1,2,3-propanetriol (glycerol) is used as a food moistening agent (nontoxic) and for its soothing qualities (soaps)

18

IMPORTANT ALCOHOLS, cont.

• Antifreezes

1,2-ethanediol (ethylene glycol)

1,2-propanediol (propylene glycol)

19

PHENOLS

• Phenol behaves as a weak acid in water and can react with bases to form salt.

20

USES OF PHENOLS:

• In a dilute solution, phenol is used as a disinfectant.

• Phenol derivatives used as disinfectants:

21

USES OF PHENOLS:

• Phenol derivatives used as antioxidants in food:

22

PROPERTIES OF ETHERS

• Much less polar than alcohols

• More soluble in water than alkanes, but less soluble than alcohols

• Low boiling and melting points because of the inability to hydrogen bond between molecules

• inert and do not react with most reagents (like alkanes)

• highly flammable (like alkanes)

23

• Hydrogen bonding of dimethyl ether: (a) with water and (b) no hydrogen bonding in the pure state:

24

THIOLS: THE –SH (SULFHYDRYL) GROUP

• Most distinguishing characteristic is their strong and offensive odor

• ethanethiol – added to natural gas

• 1-propanethiol – odor in garlic and onions

• trans -2-butene-1-thiol – odor associated with skunks

25

THIOL REACTIONS

• Oxidation forms disulfide (-S-S-) linkages, which are important structural features of some proteins:

26

THIOL REACTIONS, cont.

• Oxidation reactions can be reversed with a reducing agent

(H):

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POLYFUNCTIONAL COMPOUNDS

• Compounds with two or more functional groups

• Functional groups determine chemical properties of compounds.

Example:

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