[yourdeath01]

Hi all, bare with me this is likely my final question on this lab. If you don't know basically did an experiment titled: Wittig Reaction of trans-cinnamaldehyde The objective for this experiment was to prepare the diene (1,4-diphenyl-1,3-butadiene). To do this we had to react trans-cinnamaldehyde with a ylide in order to produce the diene, 1,4-diphenyl-1,3-butadiene. The lab was broken into two parts, first part we produced Phosphonium salt and then used NaOH to turn the salt into a ylide and then reacted ylide with trans-Cinnamaldehyde.

Heres the overall chemical equation for the lab:

https://imgur.com/noF6hFH

I am being asked to calculate the 3 things:

1: % yield of the ylide

2: % yield of the 1,4-diphenyl-1,3-butadiene (diene)

3: % recovery of 1,4-diphenyl-1,3-butadiene

Here is my data:

https://imgur.com/2agDVNc

Here is how I answered the 3 things above:

For the % yield of the ylide, I used the equation from part a of the chemical equation above. Converted benzyl chloride and triphenylphosphine to mols > found out that benzyl chloride was the limiting reagent > since reaction is 1:1 therefore 0.01738 of benzyl chloride = 0.01738 of ylide

Since m.w of benzyltriphenylphosphonium chloride is 388.9 g/mol therefore

0.01738 mols * 388.86 g/mol = 6.759 g theoretical yield of ylide

And since I ended up with 4.561 g of the ylide, therefore 4.561/6.759 = 67.48% yield of the ylide, this is correct?!

Do I have to account for the NaOH to get the % yield of the yilde or does the above calculation look sound to you guys? NaOH deprotanted the benzyltriphenylphosphonium chloride and turned it into a yield so I'm not sure if I should account for that...

Now moving on is the easy part, I am already given that the theoretical yield of the 1,4-diphenyl-1,3-butadiene is 2.063 g

So, I just divide my final purified amount 0.815/2.06 * 100 = 39.56% yield of the 1,4-diphenyl-1,3-butadiene is this correct?

Now, final calculation is % recovery of the 1,4-diphenyl-1,3-butadiene, I am not sure if I did this right but since I had the crude amount of 0.91 g and ended with purified amount of 0.815 g therefore 0.815/0.91*100 =

89.56% recovery of 1,4-diphenyl-1,3-butadiene is this correct?

[chenbeier]

You forgot the 3.9 g Phosphonium salt to produced the Ylid. The others Circulation looking ok for me.

[yourdeath01]

So the phosphonium salt (benzyltriphenylphosphonium chloride) I ended up with 4.561 g of it

But only 3.9 g of it was used so instead of doing

The % yield of the ylide, I used the equation from part a of the chemical equation above. Converted benzyl chloride and triphenylphosphine to mols > found out that benzyl chloride was the limiting reagent > since reaction is 1:1 therefore 0.01738 of benzyl chloride = 0.01738 of ylide

Since m.w of benzyltriphenylphosphonium chloride is 388.9 g/mol therefore

0.01738 mols * 388.86 g/mol = 6.759 g theoretical yield of ylide

And since I ended up with 4.561 g of the ylide, therefore 4.561/6.759 = 67.48% yield of the ylide

I should just do 3.9 g / 4.561g * 100 = 85.50% yield for the yield, is that correct instead?

[chenbeier]

I would say 3,9 g/6,759 g = 57,5% But unclear is what happend with the difference to 4,561 g. Was it remaining in the sample glas or does the reaction only obtain 3,9 g.

[sjb]

Compare https://www.reddit.com/r/chemhelp/comments/dmdbuh/are_we_ever_to_use_theoretical_yield_in_recovery/ also.

[yourdeath01]

I would say 3,9 g/6,759 g = 57,5% But unclear is what happend with the difference to 4,561 g. Was it remaining in the sample glas or does the reaction only obtain 3,9 g.

Oh no, basically I ended up with 4.561 g of yilde BUT the lab specifically said to only use 3.9 g of it to react with the trans-cinnamaldehyde to produce the diene. I think actually 4.561 g/6.739 g is probably the correct % yield here for the yilde cos 4.561 g was my original amount anyways.