Yield for Limonene

FrozenBeak

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(edited 13 years ago)

Reply 1

charco

Study Forum Helper

FrozenBeak

Could you please help me determine why I lost quite a lot of yield, and how I could have increased the yield for next time?

I am really stuck.

Thanks!

Reasons for low yield:

1. Not all the reactants are used up
2. Some reactants react to make unwanted by-products
3. The work-up procedure loses product

Reply 2

FrozenBeak

What do you mean by that 3rd one? and also how could it have been prevented?

Reply 3

Kyri

For reasons 1 in the post above, try leaving the reaction on for longer. Monitor with TLC to see when it is complete, or not going any further. TLC will also tell you if side reactions are occuring (reason 2). If the reaction stops, heating it harder can drive the reaction forward.

For reason 2, you can sometimes get unwanted reactions when heating it too hard. I know I said heat it more to drive the reaction but if it goes to completion easily then try using a different temperature.

The work-up (3rd point) is how you stop the reaction and isolate the product as a pure powder, oil or whatever. How do you purify? If you're recrystallising that can often destory your yield if not done properly or an inappropriate solvent is used. Maybe try different solvents, or try chromatographic purification.

Reply 4

FrozenBeak

I used Anhydrous sodium sulphate but I forgot why I added it lol.

Also, I used salt in the seperating process (water from limonene) but I also can't remember why I did that too lol.

Can you reiterate that to me? Thanks

Reply 5

Kyri

Anhydrous sodium sulfate removes trace amounts of water from organic solvents.

Addition of salt helps prevent some of your product from being lost in the aqueous layer if it is highly polar. Limonene is very non-polar so this won't be the case here. The reason I think you might have used it was to prevent emulsion formation. This is when the organic and aqueous layers don't separate and you get oraganic / water droplets. If you used ethyl acetate as your organic, this has a very similar density as water and is very slightly soluble in water. Ethyl acetate really doesn't like salt though so if the aqueous layer has salt in it then the layers separate much more easily. I presume you added sodium sulfate after this step.

How did you make limonene by the way? Was it a Diels Alder reaction?

Steam Distillation

Steam distillation is a purification technique rather than the reaction. Related to the topic though, this is likely where your yeild went. Unless you distill for a very long time, it's quite likely a lot of it stayed in the intial mixture you're heating. If you're always adding water it's hard to tell when to stop distilling as you'll always see steam going over. Maybe distill for longer next.

Also seeing as I know you steam distilled now, the salt was to separate liquid limonene from the water in the receiving flask. Limonene is non-polar so already dislikes (so is immiscible with) water but a small amount will still mix with it and be lost on separation. Limonene dislikes salt even more however, (as it's even more polar than water), so separates even better from salty water.

Yield for Limonene

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