Chapter 23 Introduction to General, Organic, and Biochemistry, 10e John Wiley & Sons, Inc Morris...

Chapter 23

Introduction to General, Organic, and Biochemistry, 10eJohn Wiley & Sons, Inc

Morris Hein, Scott Pattison, and Susan Arena

Aldehydes and Ketones

Ketones arecommon solventsfor quick-dryingpaints.

23.1 Structures of Aldehydes and Ketones

23.2 Naming Aldehydes and Ketones

23.3 Bonding and Physical Properties

23.4 Chemical Properties of Aldehydes and Ketones

23.5 Common Aldehydes and Ketones

23.6 Condensation Polymers

Chapter 23 Summary

Course Outline

2

3

Aldehydes (i.e. RCHO) and ketones (i.e. R2CO) are compounds with a chemical structure that contains the carbonyl (C=O) functional group as shown in these structures (R– is an alkyl group and Ar– is an aromatic group).

Structures of Aldehydes and Ketones

4

The aldehyde group is often written as CHO. For example,

CH3C

O

HCH3CHO is equivalent to

The ketone group is often written as CO. For example,

CH3CCH3

O

CH3COCH3 is equivalent to

Structures of Aldehydes and Ketones

5

IUPAC Rules for Naming Aldehydes

1. Name the longest continuous carbon chain containing the CHO group.

2. The CHO carbon is the #1 carbon atom. Notice that the aldehyde group is not given a number in the name.

This is the CHO carbon and is numbered as carbon one

Naming Aldehydes and Ketones

6

3. Drop an –e from the corresponding alkane parent name and add the suffix –al.

4. Number and name groups attached to the longest carbon chain.


7

CH3 C H

O

H C CH2CH2CHCH2CH3

O

CH3

Ethane is the longest chain contains two carbon atoms soethan + al = ethanal.

2 3 4 5 61

The longest chain contains six carbon atoms so this would behexan + al = hexanal. The methyl group is attached to C4 so the name is 4-methyhexanal.


8

The IUPAC names and commonly used names of some aldehydes are on Table 23.1.


9

H

O

benzaldehyde

The simplest aromatic aldehyde is called benzaldehyde.


10butanedial


Dialdehydes are compounds that contain two aldehyde groups. They are named by adding the suffix –dial to the corresponding hydrocarbon name.

For example a molecule with four carbons and two aldehyde groups is called butanedial.

11

IUPAC Rules for Naming Ketones

1. Name the longest continuous carbon chain containing the C=O group.

2. Drop the –e from the corresponding alkane parent name and add the suffix –one.


12

3. Carbon chains with four or more carbon atoms are numbered so the carbonyl (C=O) carbon is given the lowest possible number.

4. Attached groups are named and numbered as is done when naming aldehydes.


13


An alternative non-IUPAC method that is often used to name simple ketones lists the names of the alkyl or aromatic groups attached to the carbonyl carbon together with the word ketone. Thus, butanone is also called methyl ethyl ketone.

14


Aromatic ketones are named in a fashion similar to that of aliphatic ketones and often have special names as well.

15

Your Turn!

Write the structure of butyl ethyl ketone.

16

Your Turn!

CH3CH2CH2CH2 C

O

CH2CH3

Write the structure of butyl ethyl ketone.

17

Your Turn!

Give names for the following compounds.

CH3CHCH2CCH2CHCH2CH3

O

CH3

Br

CH3CHCH2CHC

Cl

Cl

O

H

18

Your Turn!

Give names for the following compounds.

CH3CHCH2CCH2CHCH2CH3

O

CH3

Br

CH3CHCH2CHC

Cl

Cl

O

H

2-methyl-6-bromo-4-octanone 2,4-dichloropentanal

19

Your Turn!

Write the structure of cyclohexanone.

20

Your Turn!

O

Write the structure of cyclohexanone.

21

Bonding and Physical Properties

All aldehydes and ketones have carbonyl groups. The carbonyl carbon in a carbonyl group is sp2-hybridized with one pi (π) bond and three sigma (σ) bonds.

The pi (π) bond of the carbonyl group is reactive and undergoes addition reactions.

The carbonyl group is polarized which causes aldehydes and ketones to be reactive.

22


Unlike alcohols, aldehydes and ketones cannot hydrogen-bond to themselves, because no hydrogen atom is attached to the oxygen atom of the carbonyl group.

23


Therefore aldehydes and ketones have lower boiling points than alcohols of comparable molar mass as seen on Table 23.2 on the next slide . . .

24


25


Low-molar-mass aldehydes and ketones are soluble in water.

The lower-molar-mass aldehydes have a penetrating, disagreeable odor. As the molar mass increases, the odor of both aldehydes and ketones—especially the aromatic ones—becomes more fragrant.

Some aldehydes and ketons are used in flavorings and perfumes . . .

26


27


Other naturally-occurring aldehydes and ketones are shown below.

28

Your Turn!

Rank these molecules based on boiling point from lowest to highest.

1. 3-hexanol (molar mass = 102 g/mol)2. 3-hexanone (molar mass = 100 g/mol)3. heptane (molar mass = 100 g/mol)

29

Your Turn!

Rank these molecules based on boiling point from lowest to highest.

1. 3-hexanol (molar mass = 102 g/mol)2. 3-hexanone (molar mass = 100 g/mol)3. heptane (molar mass = 100 g/mol)

heptane 3-hexanone 3-hexanol

Lowest boilingpoint

Highest boilingpoint

30

The carbonyl functional group is the reactive site for aldehydes and ketones. These compounds undergo three broad classes of reactions.

Chemical Properties of Aldehydes and Ketones

Oxidation

Reduction

Addition

Aldehydes Only

Both

Both

Reaction Type Aldehydes or Ketones

31


Oxidation

Aldehydes (RCHO) are oxidized with dichromate to carboxylic acids (RCOOH). Here acetaldehyde oxidizes to acetic acid.

32

Three well-known identification tests for aldehydes are based on the fact that aldehydes are much easier to oxidize than ketones. These tests are Tollens, Fehling, and Benedict tests . . .


33

The Tollens test gives the characteristicsilver-mirror f rom the deposition of silveron a glass surface.


Aldehydes can be identified using the Tollens test (i.e. the silver-mirror test).

34

The aldehyde group (RCHO) is oxidized to a carboxylic acid by Cu2+ ions in both the Fehling and Benedict tests.

The tests are very similar except the Fehling test uses tartaric acid to complex Cu2+ while the Benedict test uses citric acid.


35

The positive test results for these tests are shown here.

Tollens

Fehling

Benedict

Silver mirror

Blue → Brick-red

Blue → Brick-red

Test Positive Test Result for Aldehydes


36

All three tests are used to distinguish aldehydes from ketones.

These tests give a positive test result for aldehydes and a negative test result for ketones.

Tollens test

Fehling/Benedicttests


37

Write the structures of the products, or indicate no reaction, for the following.

Your Turn!

1. Propanone in the Tollens test

2. Pentanal in the Fehling test

38

Write the structures of the products, or indicate no reaction, for the following.

Your Turn!

1. Propanone in the Tollens test

2. Pentanal in the Fehling test

CH3CCH3

O

+ 2Ag+NH3

H2ONo reaction

CH3CH2CH2CH2C

O

H + 2Cu2+NaOH

H2O CH3CH2CH2CH2C

O

O- Na+ + Cu2O(s)

39

Reduction

Aldehydes and ketones are easily reduced to alcohols using LiAlH4, NaBH4 , or H2/Ni . Aldehydes yield primary alcohols and ketones yield secondary alcohols.


40


Oxidation and reduction of aldehydes and ketones is important in biochemistry.

Pyruvic acid is reduced to lactic acid in muscle cells and then lactic acid is oxidized back to pyruvic acid in the liver.

41

This reaction sequence is important because the body uses this sequence as an additional pathway to regenerate glucose.


42

RCHO + ROH

R2CO + ROH

RCHO + 2ROH

R2CO + 2ROH

RCHO or R2CO + HCN

2RCHO

2R2CO

Hemiacetal

Hemiketal

Acetal

Ketal

Cyanohydrin

Aldol

- hydroxy ketone

Reactants Product

Addition

Addition reactions of aldehydes (RCHO) and ketones (R2CO).


43

Hemiacetals, Hemiketals, Acetals and Ketals

Compounds derived from aldehydes and ketones that contain an alkoxy (ether) and a hydroxy group on the same carbon atom are known as hemiacetals and hemiketals.


44

Compounds that have two alkoxy (ether) groups on the same carbon atom are known as acetals and ketals.


45

Addition of Alcohols

Aldehydes react with alcohols and a trace of acid to yield hemiacetals.


46

In the presence of excess alcohol and a strong acid such as dry HCl, aldehydes or hemiacetals react with a second molecule of the alcohol to yield an acetal.


47

Cyclic hemiacetals or hemiketals can form when the alcohol and the carbonyl group exist within the same molecule.


48

Write the structures and IUPAC names for the hemiacetal and acetal formed from the reaction of butanal and ethanol.

Your Turn!

49


Formation of the hemiacetal

Your Turn!

CH3CH2CH2C

O

H CH3CH2 OH+H+

CH3CH2CH2C

OH

H

OCH2CH3

1-ethoxy-1-butanol

50


Formation of the acetal

Your Turn!

CH3CH2CH2C

OH

H

OCH2CH3

1-ethoxy-1-butanol

dry HClCH3CH2 OH+ CH3CH2CH2C

OCH2CH3

H

OCH2CH3

1,1-diethoxybutane

51

Addition of HCN

Addition of HCN to aldehydes and ketones under basic conditions yields cyanohydrins resulting in an increase in the carbon chain by one carbon atom.

A cyanohydrin is a compound that has a cyano group (–CN) and a hydroxyl group (–OH) on the same carbon . . .


52

This is the reaction of acetaldehyde and acetone with HCN.


53

Hydrolysis of cyanohydrins yields an -hydroxy carboxylic acid. Cyanohydrins are important synthetic intermediates for -hydroxy acids as well as amino acids.


54

Aldol Condensations (Self-Addition)

In a carbonyl compound, the carbon atoms are labeled using the Greek alphabet: alpha (), beta (), gamma (), delta (), and so on, according to their positions with respect to the carbonyl group.


55

In an aldol condensation an aldehyde or ketone that contains -hydrogens may add to itself or to another -hydrogen-containing aldehyde or ketone. The product of this reaction contains both a carbonyl group and an alcohol group within the same molecule.


56

The transfer of the -hydrogen occurs in the first step and the addition of the anion to the cation occurs in the second step.


57

Ketones with -hydrogen atoms also undergo aldol reactions.


58

Write the equation for the aldol condensation of pentanal.

Your Turn!

59


First step

Your Turn!

CH3CH2CH2CH2C

O

H

CH3CH2CHCH2C

O

H

H

dilute

NaOH CH3CH2CH2CH2C

OH

H

+ CHCH2C

CH2CH3

O

H-+

60


Second step

Your Turn!

CH3CH2CH2CH2C

OH

H

+

CHCH2C

CH2CH3

O

H-

CH3CH2CH2CH2CHCHCH2C

OH

CH2CH3

O

H

61

The conversion of 2-pentanone to 2-pentanol is a(n):

• Hydration• Dehydration• Hydrolysis• Oxidation• Reduction

Your Turn!

62

Your Turn!

The conversion of 2-pentanone to 2-pentanol is a(n):

• Hydration• Dehydration• Hydrolysis• Oxidation• Reduction

2-Pentanone is a ketone and 2-pentanol is an alcohol. The conversion of a ketone to an alcohol is a reduction.

63


Aldol condensations are common in biochemistry. For example, the strength of collagen depends on aldol condensation reactions. The cross-linking bonds form a strong network.

64

Common Aldehydes and Ketones

Formaldehyde (methanal) is made from methanol by reaction with oxygen in the presence of a silver or copper catalyst.

Formaldehyde is marketed as a 37% aqueous solution called formalin. The largest use of formaldehyde is in the manufacture of polymers. About 1.33 x 109 kg of formaldehyde are manufactured annually in the United States.

65


Acetaldehyde (ethanal) has a general narcotic action and, in large doses, may cause respiratory paralysis.

Its principal use is as an intermediate in the manufacture of other chemicals, such as acetic acid and 1-butanol. Acetic acid is made by air oxidation of acetaldehyde.

66


Acetone (propanone) is widely used as an organic solvent in the manufacture of drugs, chemicals, and explosives; for the removal of paints, varnishes, and fingernail polish; and as a solvent in the plastics industry. It is manufactured by the oxidation of 2-propanol.

67


Methyl ethyl ketone (MEK) is also widely used as a solvent, especially for lacquers. MEK is made by oxidation of 2-butanol.

68

Condensation Polymers

Condensation polymers are substances that are produced when a small molecule such as water is eliminated during polymerization.

Polyesters, polyamides, polyurethanes, and phenolics represent four important classes of condensation polymers.

69


A phenol–formaldehyde condensation polymer (Bakelite) was first marketed a century ago. Polymers of this type are still widely used, especially in electrical equipment, because of their insulating and fire-resistant properties.

Polymers made from phenol are known as phenolics.

70


Each phenol molecule can react with formaldehyde to lose an H atom from the para position and from each ortho position.

Each formaldehyde molecule reacts with two phenol molecules and eliminates water.

71


Similar reactions can occur at the other two reactive sites on each phenol molecule, leading to the formation of the polymer. This polymer is thermosetting because it has an extensively cross-linked network structure.

72

Chapter 23 Summary

• Both aldehydes and ketones contain the carbonyl group. Aldehydes have at least one hydrogen atom bonded to the carbonyl carbon. Ketones have only alkyl or aryl groups bonded to the carbonyl carbon.

• The IUPAC naming of aldehydes and ketones follows a similar process to that used for other organic molecules.

• The carbonyl group in aldehydes and ketones is very polar, with the oxygen pulling electrons from the carbon.

73

Chapter 23 Summary

• Aldehydes and ketones do not hydrogen-bond to themselves. They have lower boiling points than alcohols of comparable molar mass.

• Aldehydes are easily oxidized to carboxylic acids. Ketones are unreactive under similar conditions.

• Both aldehydes and ketones can be reduced. Aldehydes yield primary alcohols, while ketones yield secondary alcohols when reduced.

74

Chapter 23 Summary

• A hemiacetal is formed when an alcohol adds across an aldehyde carbonyl double bond. If an alcohol adds to a ketone, a hemiketal is produced.

• With an excess of alcohol, two alcohols can react with a carbonyl to form an acetal (from an aldehyde) and a ketal (from a ketone).

• Cyanohydrins are formed by the addition of HCN to a carbonyl group.

75

Chapter 23 Summary

• In an aldol condensation, two carbonyl-containing molecules (either aldehydes or ketones) connect together.

• Common aldehydes are formaldehyde and acetaldehyde. Formaldehyde (methanal) is used primarily in the manufacture of polymers. Acetaldehyde (ethanal) is used to produce acetic acid and 1-butanol.

• Common ketones are acetone and methyl ethyl ketone (MEK).

76

Chapter 23 Summary

• Condensation polymers form when monomers combine and eliminate a small-molecule product such as water.

• Common examples of condensation polymers are the phenol–formaldehyde polymers, also known as phenolics.

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Chapter 23 Introduction to General, Organic, and Biochemistry, 10e John Wiley & Sons, Inc Morris...

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