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Experiment 2: aldol condensation reaction

Objective

The purpose of this laboratory exercise is to introduce the concept of the Carbon-Carbon bond forming reaction and the basic mechanism of the aldol condensation reaction.

Background information

A useful carbon-carbon bond-forming reaction is known as the Aldol Reaction or Aldol Condensation. It is an example of electrophilic substitution at the alpha carbon in enols or enolate anions. Traditionally, it is the acid- or base-catalyzed condensation of one carbonyl compounds with the enolate/enol of another, which may or may not be the same, to generate aβ-hydroxy carbonyl compound—an aldol. It is reversible in nature. The reaction may occur between two molecules of aldehyde, two molecules of ketones or one molecule of aldehyde and a molecule of ketone. When two different carbonyl compounds react, it is known as mixed aldol/ Crossed aldol condensation.

Reactions in which a larger molecule is formed from smaller components with the elimination of a very small by-product such as water are termed Condensations. Hence the following examples are properly referred to as aldol condensations. The dehydration step of an aldol condensation is also reversible in the presence of acid and base catalysts. Consequently, on heating with aqueous solutions of strong acids or bases, manyα,β-unsaturated carbonyl compounds fragment into smaller aldehyde or ketones, a process known as the retro-aldol reaction. Below, a few examples of aldol condensation reaction are:

The product has both a carbonyl and an alcohol group; since the chemistry was initially developed with aldehydes the name "Ald-ol" (aldehyde-alcohol) was coined and has been applied to the reaction that forms it. For aldol condensation, the presence ofα-H (acidic hydrogen atom) atom is necessary. In the absence ofα-H atom, it can undergo the Cannizaro reaction. Aldol condensation involves the following steps in the mechanism:

1. Addition phase:

(a) Formation of an enol or enolate anion.

(b) Nucleophilic addition

(c) Proton transfer

2. Dehydration phase (If strong base/acid or some heat is applied)

Using acetone as an example:

Step 1: An acid-base reaction occurs first. Ethoxide functions as a base and removes the acidic-hydrogen giving the reactive enolate.

Step 2: The nucleophilic enolate attacks another molecule of acetone at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.

Step 3: An acid-base reaction. The alkoxide deprotonates a solvent molecule (here ethanol) creating hydroxide and the β size 12{β} {} hydroxyaldehydes or aldol product is formed.

There is little difference mechanistically between an acid or base catalyzed mechanism but examples of both have been given for completeness.

In next figure, the actual carbon-carbon bond formation has shown in different color for simplicity.

Acid catalyzed reaction mechanism:

Base catalyzed reaction mechanism:

From the mechanism it is clear that presence of electron withdrawing group in acceptor molecule facilitates the reaction and vice versa.

Questions & Answers

are nano particles real
Missy Reply
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Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
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Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
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Bhagvanji
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Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
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da
Application of nanotechnology in medicine
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Kamaluddeen
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narayan
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Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
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Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
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Alexandre
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Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
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Mahi
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Rafiq
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Anam
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Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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Source:  OpenStax, Chem217labsfall07. OpenStax CNX. Oct 16, 2007 Download for free at http://cnx.org/content/col10463/1.4
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