Mechanism for reaction of Grignard reagent

In summary, the conversation discusses the need to write out the full mechanism for the reaction of malachite green and crystal violet dyes in an organic chemistry lab course. The reaction involves preparing a Grignard reagent from 4-bromo-N,N-dimethylaniline with magnesium/thf, which then reacts with either ethyl carbonate/HCL or methyl benzoate/hcl. The Grignard reagent is synthetically equivalent to R-, which attacks the carbonyl or carbonate carbons to synthesize the dyes. Multiple molar equivalents of the dimethylaniline magnesium Grignard are needed, followed by a wash with HCl to protonate and eliminate the resulting water.
  • #1
dac091
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I am in an organic chemistry lab course and my lecture and lab do not align nicely. I need to write out the full mechanism for the reaction of malachite green and crystal violet dyes. The reaction starts by preparing a Grignard reagent from 4-bromo-N,N-dimethylaniline with magnesium/thf. The Grignard reagent then reacts with 1. ethyl carbonate/HCL or 2. methyl benzoate/hcl.

Could anyone write out the mechanisms for me for these two chemical pathways? I have no idea what I'm doing!

Thank you!
 
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  • #2
The Grignard reagent RMgX is synthetically equivalent to the synthon R-. The negatively charged synthon will attack the partial positive charge on the carbonyl (or carbonate) carbons. To synthesize these two dyes, you need multiple molar equivalents of the dimethylaniline magnesium Grignard (2 or 3, depending on which dye you're making). Eventually, you'll saturate the carbonyls, giving a tertiary alcohol with 3 phenyl groups around it. The final step is a wash with HCl, which protonates the alcohol and eliminates the resulting water.
 

What is a Grignard reagent?

A Grignard reagent is an organometallic compound made up of an alkyl or aryl group bonded to a magnesium atom. It is highly reactive and commonly used in organic synthesis reactions.

How is a Grignard reagent formed?

A Grignard reagent is formed by reacting an alkyl or aryl halide with magnesium metal in anhydrous ether or THF (tetrahydrofuran) solvent. The halide replaces one of the magnesium atoms to form a carbon-magnesium bond.

What is the mechanism for the reaction of a Grignard reagent?

The mechanism for the reaction of a Grignard reagent involves nucleophilic addition of the carbon-magnesium bond to a carbonyl group, followed by protonation to form an alcohol. The magnesium atom then gets regenerated and the reaction can continue.

What are the common uses of Grignard reagents?

Grignard reagents are commonly used in organic synthesis reactions to form carbon-carbon bonds, particularly in the formation of alcohols, ketones, and carboxylic acids. They can also be used in the synthesis of pharmaceuticals, agrochemicals, and other fine chemicals.

What precautions should be taken when working with Grignard reagents?

Grignard reagents are highly reactive and can react violently with water and air. Therefore, it is important to work with them in a dry and oxygen-free environment. They should also be handled with caution as they can cause severe skin and eye irritation. It is recommended to wear appropriate protective gear and to work under a fume hood when using Grignard reagents.

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