14_Aldehydes and Ketones.pdf

Chapter 14

Bonding Characteristics of Oxygen

 Oxygen is a Group VIA Element

 Has 6 valance electrons

 Two lone pairs

 Two bonding pairs, i.e., it can form two covalent bonds

 Two single or one double bond

O

O

Alcohols Ethers (Chapter 13)

Carboxylic Acids Aldehydes

Ketones Esters

Hydrogen bonding

O

C

R

R





-O

C

R

R

O

C

R

R

O

C

Aldehydes : ends with

-al

 _{Aldehydes have the CHO group when written in}

condensed form. This is a carbonyl C=O bonded to H on one side and C on the other.

O

1-propanal

Ketones: ends with

-one

 Ketones have the carbonyl group C=O bonded to two carbons. This is written (CO) in condensed form.

Since the position of the carbonyl can change it must have a number if not on a ring.

O

2-propanone

O Cl

When a compound has more than

one functional group

 The ending of the name comes from the one that is highest on this list:

 _Aldehyde

 Ketone (oxo-)

 Alcohol (hydroxy)

 Alkene

 Alkyne

 Alkoxy/Alkyl/Halogen

O

 When present in the same molecule, ketone

group is named as a substituent; the oxo- group

Both Aldehyde and Ketone

Functional Group

O O

 Constitutional isomers exist for aldehydes and ketones

 _{Isomers between aldehydes and ketones are called}

functional group isomers

 _{Two types of isomers:}

Isomerism for

Aldehydes and Ketones

O

Butanal

O

2-Methylpropanal

O

2-Pentanone

O

3-Pentanone

Methanal = Formaldehyde

 Like most small aldehydes it has a sharp, unpleasant odor. (BIO LAB)

 _{It is a gas. It is typically bubbled through water}

(soluble) to produce a solution called formalin used as a germicide and a preservative for biological

specimens.

 _{Formaldehyde is used to produce polymers like}

2-Propanone = Acetone

 Excellent solvent for water (soluble) and organics. Used to dry glassware, because it evaporates easily (low boiling point).

 Used in gas treatments to solubilize water so it can pass through the engine and some nail polish

removers.

 _{Acetone is a metabolic product. It is produced in}

Physical Properties



Aldehydes and ketones are polar, but do not

have hydrogen bonding.

Above 11 C’s are solid for both

Boiling Points

Water solubility

 Alcohol> aldehyde, ketone, ether> alkane, alkene for the same molar mass.

Odors

 Low molar mass aldehydes have pungent, unpleasant odors.

 _{Above 8 C aldehydes and ketones are pleasantly}

Preparation of Aldehydes and Ketones

 Aldehydes are prepared by the oxidation of primary alcohols

 Aldehydes can be reduced to produce a primary alcohol (catalyst required; Ni, Pt or Cu)

 Ketones are prepared by the oxidation of secondary alcohols

 Ketones can be reduced to produce a secondary alcohol (catalyst required; Ni, Pt or Cu)

C

OH

R₂

H

R₁ C

O

R₂

R₁ + H₂

Oxidation C OH H H R _C O H

R + H₂

Oxidation Reduction

Chemical Tests to Distinguish

Aldehydes and Ketones

 Use mild oxidizing agents: Ag+1 _{or Cu}+2_.

Only aldehydes oxidize with them!

 Tollen’s Test (Silver Mirror)

Ketones give no reaction

 Benedict’s Test

Ketones give no reaction

R C

O

H + Ag+ NH3, H2O, Heat _R C O

OH + Ag

Silver Mirror Carboxylic Acid

R C

O

H + Cu2+ _R C

O

OH + Cu2O

R C O

H + Ag+ NH3, H2O, Heat _R C O

OH + Ag

Silver Mirror Carboxylic Acid R C O

H + Cu2+ _R C

O

OH + Cu2O

Chemical Reactions: Hemiacetal

 Aldehyde + Alcohol = Hemiacetal

 Hemiacetal: an organic compound in which a carbon atom is

bonded to both a hydroxyl group (—OH) and an alkoxy group (—OR)

Chemical Reactions: Hemiketal

 _{Ketone + Alcohol} 1 _{Hemiacetal (hemiketal)}

Hemi

acetal to Acetal

 Adding an additional alcohol to a hemiacetal or

hemiketal in the presence of an acid catalyst produces an acetal or ketal

 Cyclic Hemiacetals form when the –OH and –OR

functional groups are on the same molecule

 _{Common in carbohydrate chemistry (Chapter 18)!}

 Undergo hydrolysis in acidic solution to form the aldehyde or ketone and alcohols that originally reacted to form the acetal

 Could also produce Aldehyde

Acetal Hydrolysis

C

O

O

CH₃

H3C C

O

CH3

H3C +

CH₂ CH₃

CH3 + H OH CH3 OH + H3C CH2 OH

Acetal + Water ↔ Ketone + 2 Alcohol

 Replacement of carbonyl oxygen with sulfur produces thioaldehydes (thials) and thioketones (thiones)

 These are unstable and readily decompose.

 Replacement of the carbonyl carbon atom with sulfur produces sulfoxides.

 Sulfoxides are much more stable than thiocarbonyls

 Most important example: DMSO (dimethyl sulfoxide)

 DMSO is an odorless liquid with excellent solvent properties

Sulfur-Containing Carbonyl Groups