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

OH

Catalyst

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 Test

All 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

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

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

R2

Ketal

Practice Problems

• Propanal + Methanol

• 3-hexanone + ethanol

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

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.

R1

O

R2

O

+O H - o r

e n z ym eR

1

OH O

R2

Aldehyde Aldehyde Aldol

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