[ajkjmspe]

Hello fellow Chemical Forums members:

I kindly request some assistance with the question of why knowing which nitrogen in caffeine is the most basic nitrogen matters for extracting it using methylene chloride.

(Note that I have already identified the Lewis structure of caffeine and the most basic nitrogen.)

I am really tearing my hair out trying to decipher why knowing which nitrogen is the most basic is important.

A little bit of background: the procedure we performed in the laboratory involved performing an extraction using methylene chloride, boiling off the solvent, redissolving the caffeine crystals in ethanol, and finally recrystallizing the crystals.

I considered the following:

• Due to the lone pair on the most basic nitrogen, caffeine qualifies as a Lewis base (it can donate this electron pair to a Lewis acid)
• Methylene chloride is a Lewis acid
• Ethanol can be both a Lewis acid and a Lewis base

Caffeine is a polar organic molecule, while methylene chloride is a polar organic solvent.  Due to the "like dissolves like" principle, caffeine is more soluble in less polar solvents and thus dissolves more easily in methylene chloride than in water.  Hence, methylene chloride was used to perform the extraction.

However, I cannot see how the most basic nitrogen is relevant to the extraction of caffeine using methylene chloride as there is no chemical reaction that is being performed during the procedure.

Perhaps the most basic nitrogen plays a role in redissolving the caffeine crystals into ethanol?

But in order to make use of the most basic nitrogen, would not a chemical reaction (likely an acid-base reaction) need to occur?

Any assistance would be appreciated with this question!

[Borek]

why knowing which nitrogen is the most basic is important

Who says it is?

In general you are right - for the extraction all that matters is whether the molecule is polar or not, details are secondary.

For other processes understanding the differences between properties of the nitrogens is often crucial, but not here.