a. l. abdulkareem hamad ayfan
TRANSCRIPT
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!
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