Cannizzaro Reaction and Microscale Techniques, Exams of Organic Chemistry

Download Cannizzaro Reaction and Microscale Techniques and more Exams Organic Chemistry in PDF only on Docsity!

A. L. Abdulkareem Hamad Ayfan

Overview

  Name ReactionRules for writing reaction mechanism

  Introduction of StanislaoWhat is Cannizzaro Reaction? Cannizzaro

  Mechanism of Cannizzaro ReactionLimitation

  The Biological Analogue of the Cannizzaro ReactionApplication

 Microscale Techniques

Rules for writing reaction mechanism

“ ” was used in Resonance Structure

*Resonance structures cannot be distinguished chemically

“ ” was used in Equilibrium

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

 For example

“ ” was used in Equilibrium

“ ” 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.

Stanislao Cannizzaro

  An Italian ChemistJuly 13, 1826-May 10, 1910

Major Contribution  Cyanamide

  Cannizzaro ReactionThe 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 withconcentrated 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:

2 O 2 N^ CHO^ 30% KOH O 2 N^ CH 2 OH^ O 2 N^ COOH

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

H H

H

Step 3. Rapid acid-base reaction

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 R OH^ O OH

H

(1)(2) H+

Application of Cannizzaro Reaction

Traditional Industrial Method:

glycolic acid

New Method:

H

O O H

HO H OH^ O OH

H

(1)(2) H+

NaOHHCl H OH^ O OH H

O OH

Cl H H