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Synthesis of a Tertiary Alcohol Using a Pre-Made Grignard Reagent

Page history last edited by jbfriesen 9 years, 2 months ago

Student Handout 2011

We compared three ether solvents: ethyl ether, methyl t-butyl ether, and tetrahydrofuran

Student Handout 2009

2009 - instead of benzophenone we used 2, 3, and 4-methyl-1-cyclohexanone as ketones.

Summary of Procedure:

The Grignard reagent is added to a round bottom flask.

A mixture of benzophenone and ether is added to the Grignard over a period of 30 minutes.

The reaction is not heated.

The reaction is stopped by addition of aqueous sulfuric acid.

The triphenylmethanol is extracted with ether.

The product is recrystallized from hexane.

The product can be characterized by melting points, UV, IR, GC, etc...

 

Positive:

+We are learning this reaction in the lecture section. The acid work-up is especially instructive since this concept comes up a lot in reactions.

+Using a commercially available pre-made Grignard is a great idea.

+The reaction turns pink! Very nice.

+experience with an air & water sensitive reaction is important.

 

Neutral:

±Is a there a possibility of using an alternative to ethyl ether for the extracions?

±Triphenylmethanol has poor solubility in practically every solvent.

±Triphenylmethanol is difficult to remove from the round bottom.

±Determining if the two-phase aqueous work-up is a little tricky.

±TLC system should be optimized.

 

Negative:

-Grignard solution is unstable. Buy a fresh bottle for each lab period.

- I have not discovered an easy way to dispense the Grignard reagent from the Sigma-Aldrich bottles without making a big mess.

 

Inquiry & Extension Ideas:

●Versatile reaction: Many different carbonyl substrates can be envisaged. The JCE article suggests acetophenone and 4-chlorobenzophenone in addition to benzophenone.

●Further modification of the alcohol could be performed.

●Qualitative test to confirm the presence of a tertiary alcohol could be done for us low-tech types.

 

Chromatography & Spectra:

2011 GC-FID

2011 IR

UV of triphenylmethanol in methanol 2008 (pdf)

GC-FID Chromatograms 2009

Photos 2009

 

Student Comments 2008: Synthesis of a Triphenylmethanol Using a Pre-Made Grignard Reagent

Student Comments 2009

 

Photo Gallery:

 

 

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