In this article we will discuss about Grignard Reagents - Reactions, Mechanism, and Handling Procedures.
Grignard reaction is an organometallic chemical reaction. It was discovered by Victor Grignard and he was awarded the Nobel Prize (1912) in Chemistry for this work.
Introduction
Hi, Friends in this article we will learn about Grignard reaction. It is well-known named reaction in organic chemistry. It is organometallic - nucleophilic addition reaction. Here we will discuss use of Grignard reagent, mechanism and handling of the reagent.
- It is a Nucleophilic addition reaction on to carbonyl groups.
- In general 3-4 equivalents of reagents are required for the reaction.
- Grignard reagent can be prepared in lab or it is commercially available as well.
Reaction
In general Grignard reagent reacts with the carbonyl
compound to form alcohol product.
 |
| Figure 1: Grignard Reaction |
Mechanism
- Two molecules of Grignard reagent add upon the carbonyl group to form transition state.
- This further forms organometallic intermediate.
- Finally protonation of organometallic intermediate gives neutral product.
 |
| Figure 2: Mechanism of Grignard reaction |
How to measure concentration of Grignard reagent?
- Concentration of the reagent can be measured by titration of the reagent against diphenylacetic acid.
- Dissolve the weighed quantity diphenyl acetic acid in THF and titrate it against the freshly prepared or old reagent.
- The appearance of yellow colour indicates the end point.
 |
| Figure 3: Titration of Grignard reagent |
What are the functional groups transformations can be done by Grignard reagents?
Not only carbonyl group but other electrophilic groups such as nitriles, amides or epoxides can react with Grignard reagent to give amine, ketone or alcohol functional groups respectively.
 |
| Figure 4: Functional group transformation by Grignard reagent |
What are Potential hazards associated with the reagent?
- The reagent is highly flammable liquid and it can catch fire.
- If contact with water it releases flammable gases and causes severe skin burns and eye damage.
- This reagent is extremely destructive to the tissue of mucous membranes and upper respiratory tract.
- The reagent bottles must be kept away from heat, sparks, open flames, direct sunlight and/or hot surfaces.
- Do not allow contact with air; because it may form magnesium organoperoxide; which could be explosive.
Personal protective equipment before you start!
- Safety
glasses with side shields or chemical splash goggles must be worn at
all times when handling chemicals in the lab.
- Gloves are
required when handling this reagent.
- Flame
resistant lab coats are required when handling hazardous chemicals
in the lab.
- And cotton-based, non-synthetic clothing should be worn.
- Also wear Safety shoes.
Special Handling and Storage Requirements
- Grignard reagents should be used under inert gas in a clean fume hood.
- All the glassware's should be very clean and dry.
- Before use, you must ensure that the needle is clog-free.
- Amount of volume needed should not exceed 75% of what the syringe can hold.
- If more than 20 mL of the reagent solution is required, then a syringe and needle should not be used instead of that, an appropriate graduated cylinder with a septum and cannula should be used.
- Never
tip a bottle upside down to retrieve the solution; the needle used
should be long enough to access the liquid without tilting the bottle.
Spill and Accident Procedures
- Do not use water for cleaning the spillage.
- Do not
use combustible materials (paper towels) to clean up the spill, as
these may increase the risk of igniting the reactive compound.
- Soda
ash (powdered
lime) or dry sand should be used for cleaning.
- Used syringes / cannula can be dipped in dry ice for quenching traces of reagent.
Decontamination Procedures
- Laboratory work surfaces should be cleaned at the end of each work day.
- All materials - disposable gloves, wipers, bench paper, etc. that are contaminated with Reagents should be disposed of as hazardous waste.
- Proper and complete hazardous waste labelling of containers is important
Waste Disposal Procedures
- Any unused or unwanted Reagent must be destroyed by transferring the materials to an appropriate reaction flask for hydrolysis /or neutralization with adequate cooling.
- The empty container should be rinsed three times with an inert dry COMPATIBLE solvent.
- This rinse solvent must also be neutralized or hydrolyzed.
To summarize this article, we have learned Grignard reaction
and mechanism. We also have seen various functional groups transformations due to
this organometallic reagent. In addition to this we have discussed storage,
safe handling and disposal of the reagent.
That's all for this topic. Thank you..!
References
No comments:
Post a Comment