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 “ ” was used in Resonance Structure For example “ ” was used in Equilibrium
(a) Different sigma bonding pattern, (b) Geometrical change (e.g., isomerization) “ ” was used in Equilibrium For example Questions: A: R1 R 1 B: (1) I I R2 R2 R3 R3
(2)
CHO
CH2OH H OH H O H H OH H (3) OH H OH OH H OH H OH H OH
CH2OH “ ” 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:
30% KOH 2 O2N CHO O2N CH2OH O2N COOH
Mechanism of Cannizzaro Reaction
Step 1. Nucleophilic addition
O O OH R H R H OH Mechanism of Cannizzaro Reaction
Step 2. Hydride (H-) transfer
O O O O
R H R H R R H OH OH H
Mechanism of Cannizzaro Reaction
Step 3. Rapid acid-base reaction
H O O O O R H R H
R O H H R O H 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.
O O OH O (1) HO R OH (2) H+ R H H Application of Cannizzaro Reaction
Traditional Industrial Method:
Cl O OH O NaOH H OH H OH HCl H H glycolic acid
New Method: O O OH O (1) HO H OH (2) H+ H H H
Mechanism of Intramolecular Cannizzaro Reaction
O O O O Stept (1) OH R H
R H OH
O O O O
Step (2) R OH R OH
H H
O O OH O
Stept (3) R OH R O
H H Limitation Cannizzaro reaction is limited to aldehydes such as formaldehyde and benzaldehyde, which has no hydrogen on the carbon next to the –CHO group.
O O Strong Base 2 HO H O
*Only aldehydes that cannot form an enolate ion undergo the Cannizaro reaction. Aldol condensation
Aldehyde and ketone containing hydrogen attached to their α-Carbons undergoes an aldol (aldehyde + alcohol) condensation.
O O O
H2O H HO CH H H CH2 2
O
H O H O O O H O OH HO
H CH2 H C H H C H H2 H2 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 20mL x 8 10% NaOH 10% NaOH
Carrying out reaction Distillation
Solvent heavier than water
Solvent lighter than water
Thank You!
Video