[uwastudent]

I'm doing a pre-lab for a vanillin extraction experiment and I can't find the answer to the question:
Explaining your answer, predict which phase of a separation each of the following species would prefer:
a) Vanillin
b) Vanillin as its sodium salt
There are two phases: Aqueous layer (Water), and Organic layer (Dichloromethane  DCM), which are used to separate the vanillin component from the other components in a sample. The vanillin is reacted with sodium hydroxide to form its sodium salt. I'm fairly sure that the vanillin would prefer the organic layer, and the sodium salt would prefer the aqueous layer, but I don't know how to explain why. Is it because of their relative solubilities in each layer? I can't seem to find the solubility of vanillin in DCM anywhere.

[discodermolide]

I think you are on the right track here. The sodium salt is soluble in water because it is an …….. substance.
Why don't you measure the solubility of pure vanillin in DCM yourself?

[FreeTheBee]

For solubility data you can check the references on the wikipedia page for vanillin.

[lavoisier]

Calculated 'log P' is often used as a prediction of partition coefficients. There's a lot of free software that calculates that from molecular structures.

Experimentally measured 'log P' is the decimal logarithm of the partition coefficient of a substance A between 1-octanol and water.

log P = log₁₀ ([A]_oct / [A]_w)

So the higher log P, the higher the lipophilicity of your substance, the higher the % of it going into the organic layer.

Another useful parameter is 'log D', which is basically log P at a given pH. For ionizable substances, log D is a function of log P, pH and the pKA of the substance. The formula is a bit complicated to write, but you can easily Google it, and it basically tells you that an acid will become much more hydrophilic when the pH raises above its pKA.

Vanillin is an acid, and making its sodium salt is equivalent to raising the pH a few units above the pKA...

[discodermolide]

Calculated 'log P' is often used as a prediction of partition coefficients. There's a lot of free software that calculates that from molecular structures.

Experimentally measured 'log P' is the decimal logarithm of the partition coefficient of a substance A between 1-octanol and water.

log P = log₁₀ ([A]_oct / [A]_w)

So the higher log P, the higher the lipophilicity of your substance, the higher the % of it going into the organic layer.

Another useful parameter is 'log D', which is basically log P at a given pH. For ionizable substances, log D is a function of log P, pH and the pKA of the substance. The formula is a bit complicated to write, but you can easily Google it, and it basically tells you that an acid will become much more hydrophilic when the pH raises above its pKA.

Vanillin is an acid, and making its sodium salt is equivalent to raising the pH a few units above the pKA...

I'm sure uwastudent will understand that lot!!!