Lab report describing the synthesis of the product of an aldol condensation.Full description
Chemistry 35.1, University of the Philippines ManilaFull description
Chemistry 35.1, University of the Philippines ManilaFull description
Kondensasi aldol yang paling sederhana adalah gabungan dua molekul asetaldehid, yang terjadi jika larutan aldehid diberi larutan basa. Hasilnya adalah reaksi dengan 4 karbon dinamakan aldol(…Full description
Full description
kimia organik
kimia organik
Reaksi aldol adalah salah satu reaksi pembentukan ikatan karbon-karbon yang penting dalam kimia organik. Dalam bentuk yang umum, ia melibatkan adisi nukleofilik enolat keton ke sebuah aldehi…Full description
Condensation Induced Water Hammer: Principles and Consequences
this is all about how to write precisely..,Full description
A condensation product CP was successfully synthesized from reaction of dimethyl amino benzaldehyde and aniline giving yields of 80 . The compound was characterized by Fourier Transform Infrared FTIR Spectroscopy. The corrosion inhibiting property of
sintesis
CHEM 3220
Aldol Condensation
Harris/ Dandekar
Aldol Condensation Condensation Chapter 37 37.1: Synthesis of dibenzalacetone O O O
+
benzaldehyde
NaOH 95% EtOH (solvent)
acetone
dibenzalacetone ( E,E isomer)
Theory: •
Reactivity: Acidity of alpha hydrogen atoms: o pK a of hydrogen atoms α to >C=O groups: ~20
•
SO: o
In presence of base, proton abstraction affords “enolate” ions: Resonance stabilized Excellent Nucleophiles Nucleophilic Nucleophilic addition addition to the the carbonyl group gives gives the addition addition product: product: aldol adduct adduct Spontaneous dehydration of the adduct: aldol condensation product Why is dehydration so facile? • Conjugated “enal” or “enone” o E isomers tend to predominate •
•
Different types of aldol condensations: o Normal Same aldehyde (or ketone) as substrate and nucleophile
o
Crossed Two different aldehydes (or ketones) Up to 4 products obtained under these conditions • Synthetically useful when one reactant lacks α- hydrogens •
o
Claisen-Schmidt (mixed aldol) Condensation reaction between an aldehyde and a ketone The aldehyde carbonyl is moe reactive than that of the • ketone, and therefore, reacts rapidly with the anion of the ketone to give a beta-hydroxyketone, which easily undergoes base-catalyzed dehydration Good to use NaOH so that the ketones don’t significantly • self-condense
1
CHEM 3220
Aldol Condensation
Harris/ Dandekar
Forms conjugation between carbonyl group, alkene, and benzene ring
•
Reaction Mechanism: :
O
:
O :
:O : :O :
OH−
H α
−
:O :
:
−
α :
H2O
−
:O :
O
OH
enolate ion
aldol adduct [- H2O] O O
O
OH −
α
repeat all steps at the other α- position
dibenzalacetone ( E,E isomer) •
•
aldol condensation product ( E isomer)
Note Stoichiometry: Need 2 moles of benzaldehyde : 1 mole acetone o By-product: Self-condensation product(s): o It is possible for the enolate ion (from acetone) to add to the carbonyl group of a second acetone molecule, ultimately leading to the corresponding condensation product(s).
:
O:
:
:
− +
O:
:
O:
OH
[- H2O]
2
:O:
:
O:
CHEM 3220
Aldol Condensation
o
Harris/ Dandekar
It is often possible to minimize the formation of this type of by-product by careful experimental design By adding acetone (diluted with solvent) dropwise to a mixture of benzaldehyde and base, the statistical possibility of selfcondensation is minimized.
Experiment: Aldol Condensation: Exp 37.1: Synthesis of Dibenzalacetone • Follow the procedure given on pp. 485-486. • Stoichiometry is critical: • Insufficient quantity of benzaldehyde (i.e., less than 2 mol equivalents) o will decrease yield • Note the role of the solvent(s): Protic solvent: o water (from aq NaOH) and/or ethanol is involved in the mechanism Quantity of ethanol is critical: o Enough to allow the reactants as well as the principal intermediate ( benzalacetone ) to be soluble, but not enough to dissolve the product SO: The product precipitates out • Drives the reaction to completion o During work-up: • The base residue is removed by thorough washing with water o Why not simply neutralize with acid ? Can the product react with aqueous acid? •
•
•
You don’t need to: o weigh your product and determine the percent yield. o Do record the melting point of the product .
Pre-Lab Assignment •
LabBook: Q 3- 4 pp. 488
Reading Assignment • •
LabBook: Chapter Ch 37 Also Read: Aldol condensation and related reactions from an organic textbook (e.g., Jones/Fleming or Solomons/Fryhle)
Post-Lab Assignment •
Draw the structures of the ( E,Z ) and ( Z,Z ) isomers of dibenzal.
3
CHEM 3220
•
Aldol Condensation
Harris/ Dandekar
Do you expect dibenzal to have a characteristic UV absorption? Explain.