<< Chapter < Page Chapter >> Page >

Lab 3: grignard reaction

Objective

The purpose of this laboratory exercise is to perform a classic method for the synthesis of secondary alcohols: the addition of a Grignard reagent to an aldehyde (other than formaldehyde).

Background information

After the most remarkable discovery by Victor Grignard in 1900, organometallic (An organic compound containing a metal atom directly attached to a carbon) compounds are very useful in organic synthesis. This discovery changed the course of organic chemistry and earned him the Nobel Prize in 1912. We now refer to such compounds as Grignard Reagents.

The Grignard reaction is one of the characteristic reactions of carbonyl compounds. It is especially useful as a means of forming new carbon-carbon bonds, something that we haven't seen much of until now. In this type of reaction a C-M bond is present (C=carbon and M=metal) which is covalent in nature. The metal is usually magnesium but lithiummore reactive and is also used. The more polar the C-M bond is, the more will be its reactivity. The reactivity order is known from electrochemical series:

M= Li>K>Ca>Na>Mg>Al>Zn>Fe>Sn etc

Traditionally alkyl magnesium halides are known as Grignard reagent (R-Mg-X).

All kinds of alkyl halides react (Iodides are more reactive than bromides which in turn are more reactive than chlorides) and amazingly, even bromobenzene and other aryl bromides and iodides react easily with magnesium. This is particularly surprising since the aromatic halogen is so unreactive. For example, it is inert to refluxing with aqueous sodium hydroxide at temperatures in excess of 200˚C. The unshared pair of electrons on ether oxygen complexing with the Mg is believed to contribute to the stability of the reagent. Note: Aryl halides (ArX) and vinyl halides that are inert to nucleophilic substitution are reactive with this Grignard reaction.

Preparation and mechanism of grignard reagent:

The mechanism of Grignard reagent (GR) is not clear till today, but it is believed that the reaction is taking place on the metal surface. Since GR does not react with aprotic solvents (e.g. ether, THF etc), these solvents are widely used. The mechanism of formation of GR as follows: it goes via one electron transfer, followed by rapid combination of organic group with the metal center. From the mechanistic point of view, carbon-bromine bond should be broken prior to the reaction with magnesium.

Solutions of some Grignard reagents such as methylmagnesium bromide, ethylmagnesium bromide, and phenylmagnesiumbromides are commercially available. Here is an example of Grignard reaction which explains the effect of solvent.

The Grignard reagent is made from the direct reaction of magnesium with an alkyl halide.

The key to the function of the Grignard reagent is the reversal of the normal polarity of bonds to carbon (This type of reversal of polarity in carbon center is known as Umpolung). Because magnesium is more electropositive than carbon the carbon acquires a δ size 12{δ - {}} {} charge whereas carbon, when it has a charge at all, usually has δ + size 12{δ+{}} {} charge from bonding to halogens, oxygen, and nitrogen.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
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
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
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
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
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
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
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
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Chem217labsfall07. OpenStax CNX. Oct 16, 2007 Download for free at http://cnx.org/content/col10463/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chem217labsfall07' conversation and receive update notifications?

Ask