Aldehyde & Ketone

Reactions

Formation of an AldehydeOxidation of Primary Alcohols

• General equation:– Primary alcohol aldehyde

RCH2CH=O

EXAMPLE:1-propanol

Formation of a KetoneOxidation of Secondary Alcohols

• General equation:– Secondary alcohol ketone

O R-C-R

EXAMPLE:2-propanol

CO

RH

R

H[O ]

Review from Chapter 13!!Oxidation of Tertiary Alcohols

• General equation:– Tertiary alcohol NO REACTION!!!

YOU TRY THESE!

• Write an equation showing the oxidation of the following alcohols. Be sure to name the product formed.

(a) 1-pentanol

(b) 2-butanol

Oxidation of Aldehydes

• Aldehydes are easily oxidized further to form carboxylic acids.

• Oxidation process:Primary alcohol Aldehyde Carboxylic acid1-butanol

2-methyl-1-propanol

[O ] [O ]

[O ] [O ]

Reduction Reactions

• Both aldehydes and ketones are easily reduced back to the corresponding alcohol. This process is called hydrogenation.

O

R1 R2

+H

HH

R2R1

OHCatalyst

Reduction ReactionsPractice Problems

• Reduce 3-pentanone (ketone 2o alcohol)

• Reduce hexanal (aldehyde 1o alcohol)

HOMEWORK

Oxidation and Reduction Reactions

p 419 #41, 42, 45, 57, 60 & 68 (a, c, & d)

p 410 # 13 – 16 (a, c, & d)

Lab Tests for Aldehydes and Ketones

Tollen’s Test•Tests for ALDEHYDES (not ketones)•Silver ion is reduced to silver metal•The aldehyde is oxidized to a carboxylic acid anion•AKA the Silver Mirror Test

Tollen’s Test

O OR-CH + Ag(NH3)2

+ R-C-O- + Ag0

Aldehyde silver ammonia carboxylic silver complex acid anion metal

“Tollen’s Reagent” mirror

Write equations for the following reactions

1. ethanal + Tollen’s reagent

2. 2- pentanone + Tollen’s reagent

3. propanal + Tollen’s reagent

Benedict’s Test Indicates the presence of an aldehyde

A buffered aqueous solution of copper (II) hydroxide and sodium citrate

Reacts to oxidize aldehydes

Forms a red solid – Cu2O

Benedict’s TestAll sugars are aldehydes or ketones

Benedict’s solution can be used to test urine for glucose (an aldehyde), which is common in uncontrolled diabetes

The amount of red precipitate formed is directly proportional to the amount of glucose in the urine.

Benedict’s Test

O OH OH H H HC – C - C - C - C - CH2OH + 2Cu+2

H H OH OH (from Benedict’s Solution)

O OH OH H H-O - C - C - C - C - C -CH2OH + Cu2O H H OH OH red precipitate

HOMEWORK

p 419 #14.46, 47, & 48

Addition ReactionsI. Addition of an Alcohol to an Aldehyde – Acetal formation O H H+ OH HR1-C-H + O-R2 R1-C-OR2 + O-R2

HAldehyde alcohol Hemiacetal (quite reactive)

OR2

H+ R1-C-OR2 + H2O

HAcetal

Addition Reactions

• -OR group is an alkoxyl group

• Hemiacetals are very reactive, so in the presence of acid and excess alcohol, will continue to react to form an acetal

Addition Reactions

2. Addition of an alcohol to a ketone – KETAL formationO H OH H

R1-C-R2 + O-R3 H+ R1-C-OR3 + OR3

R2

Ketone alcohol Hemiketal

OR3

H+ R1-C-OR3 + H2O

R2

Ketal

Practice Problems

• Propanal + Methanol

• 3-hexanone + ethanol

HOMEWORK

p 419#49-56

Keto-Enol Tautomers

• Many aldehydes & ketones exist in a mixture of two constitutional isomers, informally referred to as tautomers.R

1

R2

R3

O R1

R2

R3

OH

Keto form Enol form

Keto-Enol Tautomers

• constitutional = structural

• They differ in the placement of a hydrogen atom & a double bond

• The “keto” form is more stable

Practice• Draw the enol form of the aldehydes and

ketones listed below.– Ethanal

– 2-pentanone

– Butanal

Aldol Condensation• Reaction in which aldehydes & ketones react to

form larger molecules. A new carbon-carbon bond is formed in the process.

• Actually occurs between an aldehyde in the keto form and one in the enol form.

• Used in our cells to make glucose “gluconeogenesis”

R1

OR

2O

+O H - o r

e n z ym eR

1

OH O

R2

Aldehyde Aldehyde Aldol

Aldol Condensation

• The new carbon-carbon bond forms between the carbonyl carbon of one molecule and the α-carbon (the carbon next to the carbonyl carbon) of the other

O O• CH3CH + CH3CH

Example• Write an equation for the aldol condensation of

two molecules of butanal.

O OH+OH O

Butanal Butanal (enol form)3

-hydroxy

-2

-ethylhexanal

More PracticeTry these:

• The aldol condensation of 2 molecules of :propanone

butanone

HOMEWORK

p 419-420#62, 63, & 64