Hi,
I think what you're being asked to do is:
1) look at the 2D structure of caffeine
2) look up or make an educated guess as to caffeine's solubility in water versus an organic solvent such as dichloromethane (DCM). Caffeine must have a preference (ie. higher solubility) in one or the other solvents in order for the extraction to work.
[hint: charged (protonated or deprotonated) forms of caffeine are not soluble in DCM, so a base (eg. NaCO
3) would have been added to make the unprotonated form available before you did the extraction)
check out this link:
http://www.pharmainfo.net/exclusive/technical/extraction_of_caffeine_from_tea_leaves/
It may have some clues.. Anyway, to write an equation you should probably show some sort or equlibirum between caffeine in water (in a charged form, then deprotonation upon adding the base?) and caffeine in your solvent
favoured toward the solvent it is more soluble in.