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Topic: Grignard Reactions  (Read 6556 times)

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Offline marvelteen

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Grignard Reactions
« on: August 10, 2009, 08:09:22 PM »
Hi i just have a quick question regarding Grignard reactions and theoretical yields. If someone could help me solve this problem that would be great.

In a reaction of cyclohexylmagnesium chloride with 2-butanone, the Grignard reagent was prepared from 22g of cyclohexyl chloride and was then treated with a solution of 11g of butanone in 55mL of ether which contained 1.1% by weight of water. Calculate the amount of cyclohexane (in g) that would be produced and the maximum theoretical yield of tertiary alcohol corrected fro loss due to cyclohexane formation.


Offline Rabn

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Re: Grignard Reactions
« Reply #1 on: August 10, 2009, 08:58:19 PM »
start with a balanced equation, convert to moles, use densities if necessary etc...most of the time you needn't worry about equilibrium constants in organic reactions. This kind of calculation should be commonplace for you by the time you get to this point in your studies. Show your work if need more help.

Offline marvelteen

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Re: Grignard Reactions
« Reply #2 on: August 10, 2009, 09:17:41 PM »
i'm confused with setting up the equation due to the fact that some of the products are side reactions not meant to happen. Is water included into the formula?

I know cyclohexyl chloride and butanone are reactants, the ether shouldn't be included in the equation since it's just a solvent. Is water included?

do i need to make 2 equations? one for the reaction and one for the side reaction? i haven't done any problem-solving like this in my organic chemistry class.

Offline kd.gns

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Re: Grignard Reactions
« Reply #3 on: August 11, 2009, 03:45:02 PM »
You are looking for Theoretical yield, in other words, the maximum possible yield you could possibly obtain, a side reaction, by definition, is not included. So, determine the product that you want to obtain, and write the balanced equation that generates it, and solve for that. Side reactions will decrease your actual yield, not theoretical.

Offline azmanam

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Re: Grignard Reactions
« Reply #4 on: August 11, 2009, 04:09:50 PM »
I disagree.  specifically because of this clause in the question:

Quote
Calculate the amount of cyclohexane (in g) that would be produced and the maximum theoretical yield of tertiary alcohol corrected fro loss due to cyclohexane formation.

You need to figure out how much cyclohexyl Grignard will react with the water impurity.  That will give you a new amount of cyclohexyl Grignard.  This will be the starting amount from which you can calculate the maximum theoretical yield.
Knowing why you got a question wrong is better than knowing that you got a question right.

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