[jmgx12]

Hi. So we did the Cannizzaro rxn with 4-chlorobenzaldehyde to make 4-chlorobenzoic acid and 4-chlorobenzyl alcohol. We carried it out with 11M KOH. I understand the mechanism and I am assuming that because this is a strong basic solution, it forms that doubly charged anion as an intermediate. I just have a few questions about the extraction process. Why were the two initial products formed the carboxylate ion and the alcohol. Why was the alcohol protonated?? To separate the layers, we added water first and then CH2Cl2.
When we extracted the organic layer, why did we wash it with bicarbonate? Is this just to get rid of any trace of acid carried over during the extraction? And then we washed it with water again. Why did we do this to this layer?

Lastly, to do the percent yield...should I do the theoretical yield divided by 2 because 2 moles of aldehyde make 1 mole of acid and 1 mole of alcohol?

Thanks!

[jmgx12]

Can someone please help me with this?

[discodermolide]

Hi. So we did the Cannizzaro rxn with 4-chlorobenzaldehyde to make 4-chlorobenzoic acid and 4-chlorobenzyl alcohol. We carried it out with 11M KOH. I understand the mechanism and I am assuming that because this is a strong basic solution, it forms that doubly charged anion as an intermediate. I just have a few questions about the extraction process. Why were the two initial products formed the carboxylate ion and the alcohol. Why was the alcohol protonated?? To separate the layers, we added water first and then CH2Cl2.
When we extracted the organic layer, why did we wash it with bicarbonate? Is this just to get rid of any trace of acid carried over during the extraction? And then we washed it with water again. Why did we do this to this layer?

Lastly, to do the percent yield...should I do the theoretical yield divided by 2 because 2 moles of aldehyde make 1 mole of acid and 1 mole of alcohol?

Thanks!

The alcohol is protonated by the solvent, water.
Presumably the bicarbonate wash is to remove any residual chlorobenzoic acid, although there should be none there. The last water wash just removes the last of the salts.
As to the yield just work it out normally, no need to divide by 2.

[jmgx12]

Ah okay, thank you. And are you sure about the yield? Let's say I started with 1 moles of 4-chlorobenzaldehyde...shouldn't I only be able to make .05 mole of the acid and .05 mole of the alcohol? Because if I do it that way, I got about a 90% yield for each product.

[discodermolide]

Ah okay, thank you. And are you sure about the yield? Let's say I started with 1 moles of 4-chlorobenzaldehyde...shouldn't I only be able to make .05 mole of the acid and .05 mole of the alcohol? Because if I do it that way, I got about a 90% yield for each product.

2 moles gives 1 mol and 1 mol
1 mole gives 0.5mol and 0.5 mol

So what's the difference? None.

[jmgx12]

I know that. I'm saying I should divide the amount of moles of 4-chlorobenzaldehyde (reactant) used by 2 to get the theoretical yield of the products, right?

[discodermolide]

I know that. I'm saying I should divide the amount of moles of 4-chlorobenzaldehyde (reactant) used by 2 to get the theoretical yield of the products, right?

No, if you do that the reaction equation is no  longer balanced.

[orgopete]

If you had 10 bar magnets with N and S painted on the ends of each pole and cut them in half, how many bar magnets would you get with N painted on the end? Hint, there are now twenty magnets and half have an N and half have an S.