A. L. Abdulkareem Hamad Ayfan

Overview Name Reaction

Rules for writing reaction mechanism

Introduction of Stanislao Cannizzaro

What is Cannizzaro Reaction?

Mechanism of Cannizzaro Reaction

Limitation

The Biological Analogue of the Cannizzaro Reaction

Application

Microscale Techniques

Name Reaction Visit Google and search under the specific Name Reaction.

http://www.organic-chemistry.org/namedreactions

http://www.monomerchem.com/display4.html

http://orgchem.chem.uconn.edu/namereact/named.html

http://www.ecompound.com/Reaction%20reference/reaction_index.html

http://www.liv.ac.uk/Chemistry/Links/reactions.html

Name Reactions: A Collection of Detailed Reaction Mechanisms by Jie Jack Li (Hardcover - August 29, 2006)

Rules for writing reaction mechanism

“ ” was used in Resonance Structure

*Resonance structures cannot be distinguished chemically

For example

“ ” was used in Resonance Structure

“ ” was used in Equilibrium

(a) Different sigma bonding pattern, (b) Geometrical change (e.g., isomerization)

For example

“ ” was used in Equilibrium

Questions: R1

R2

R3

I I

R1

R2

R3

(1)

(2)

CHO

OHH

HOH

OHH

OHH

CH2OH

OH

OH

H

OH

H

OHH

OH

CH2OH

H(3)

A:

B:

“ ” for two-electron movement

The arrowtail is drawn from (a) a lone pair of electrons

(b) from two electrons making up a bond

“ ” for a single electron movement

The arrow tail is drawn from (a) a bond made up two electrons

(b) from a center having a single valence electron.

Example of radical reaction

Stanislao Cannizzaro An Italian Chemist

July 13, 1826-May 10, 1910

Major Contribution

Cyanamide

Cannizzaro Reaction

The first to clarify the distinction between molecular and atomic weights

What is Cannizzaro Reaction? Definition: Aldehydes containing NO α-hydrogen undergo a

self-oxidation-reduction reaction when treated with concentrated aqueous base, and The oxidation product is a carboxylic acid and the reduction product is an alcohol.

involves the base-induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position

Example:

O2N CHO O2N CH2OH O2N COOH2

30% KOH

Mechanism of Cannizzaro Reaction

Step 1. Nucleophilic addition

R

O

HOH R

O

OH

H

Mechanism of Cannizzaro Reaction

R

O

OH

H R

O

H R

O

OH

R

O

H

H

Step 2. Hydride (H-) transfer

Mechanism of Cannizzaro Reaction

R

O

O

R

O

H

H R

O

O

R H

O

HH

H

Step 3. Rapid acid-base reaction

Example of Cannizzaro Reaction

For example:

Application of Cannizzaro Reaction

Crossed Cannizzaro Reaction

Intramolecular Cannizzaro Reaction α-Keto aldehydes give the product of an intramolecular

disproportionation in excellent yields.

R

O O

H

HO

O

OH

OH

R

H

(1)

(2) H+

Application of Cannizzaro Reaction

Traditional Industrial Method:

glycolic acid

New Method:

H

O O

H

HO

O

OH

OH

H

H

(1)

(2) H+

NaOH

HCl

O

OH

OH

H

H

O

OH

Cl

H

H

Mechanism of Intramolecular Cannizzaro Reaction

R

O O

H

OH

O

OH

H

O

RStept (1)

O

H

OH

O

R

O

OH

O

R

H

Step (2)

O

OH

O

R

H

O

O

OH

R

H

Stept (3)

Limitation Cannizzaro reaction is limited to aldehydes such as

formaldehyde and benzaldehyde, which has no hydrogen on the carbon next to the –CHO group.

H

O

O

O

HO

Strong Base

2

*Only aldehydes that cannot form an enolate ion undergo the Cannizaro reaction.

Aldol condensation

H

O

H HO

H

O

CH2

O

CH2

H2O

H

O

CH2

H

O

H

O

CH2

O

H

OH H

H

O

CH2

OH

H

HO

Aldehyde and ketone containing hydrogen attached to their α-Carbons undergoes an aldol (aldehyde + alcohol) condensation.

The Biological Analogue of the Cannizzaro Reaction

Enzymes catalyze the reduction of aldehydes and ketones using NADH as the source of the equivalent of H-

The transfer resembles that in the Cannizzaro reaction but the carbonyl of the acceptor is polarized by an acid from the enzyme, lowering the barrier

Microscale Techniques materials in the 0.005-0.5 gram range

Use different glassware

Microscale Glassware Macroscale >> chemicals on the order of 2-100 g Macroscale >> glassware containing between 25 and 500 mL of liquids

Microscale techniques

Pros and Cons

Decrease the economic and environmental costs

less cost of chemicals, storage, and disposal.

Increase safety, minimize accident

More difficult to use, especially in distillation, extraction

Macroscale procedures are required in multiple steps of chemical reaction.

200mL x 8 10% NaOH

20mL x 8 10% NaOH

Distillation Carrying out reaction

Solvent heavier than water

Solvent lighter than water

Thank You!

Video