[a confused chiral girl]

Hello everybody,

I'm trying to understand the reason on the chemistry of what is being done in the fungicide "Benomy" extraction. A fruit or veggie sample is blended with ethyl acetate, but I don't see why this does to the chemistry...the ultimate compound that we wnat to analyze is Carbendazim (which is the breakdown of Benomyl). 

I have attached the procedure of what I'm doing with this post...any explainations are welcomed!!

THANK YOU 

[MOTOBALL]

If you put a fruit or vegetable into a blender, you get a mixture of water (mostly) and solids.  To extract ANY organic compounds from the mixture you need an extracting solvent that will (a) solubilize your compound(s) of interest, (b) not itself dissolve in the water, i.e. is immiscible with water, and (c) does not react with the compound to be extracted.

(a) Ethyl acetate (being an ester) is reasonably polar, and I suspect that it is chosen in this case to extract a reasonably polar compound (carbazim) from the mixture [like dissolves like is a good rule of thumb for extractions].

(b) note that EtOAc has slight miscibility with water.

(c) "I don't see why this does to the chemistry..." EtOAc should not do anything to the chemistry.

Good Luck !!
Motoball

[a confused chiral girl]

thank you Motoball for the clarifications! It really made sense and I understand now that the ethyl acetate is used to solubilize the carbendazim from the mixture after blending!! 

however, after the blending and filtering with ethyl acetate, why do we want to evaporate (under a stream of nitrogen gas) the ethyl acetate until ~1mL remains (nearly all dried up) and then reconstitute the compound with 10mL ethyl acetate again?

we already added the ethyl acetate to be blended with the fruit/veggie, so the carbendazim is dissolved in the ethyl acetate, why we do we evaporate it off and then add a bit of ethyl acetate to the test tube when it's dried again?

[JGK]

After blending the vegetable Matter with ETOAc you will liberate water and other liquids from the sample so your "liquid" will not just be ETOAc.  Removing (Evaporating) most of the liquid will ensure your final extract is in predominantly ETOAc.

If you are evaporatiing to 1 mL and adding 10 mL then your final solution is at least 90% ETOAc.

[a confused chiral girl]

OHHH!!!! JGK! that is very true.....indeed the liquid resulted from the blending mixture is not only the ethyl acetate I added, but with a lot of other liquids from the sample!!

but what I don't get is after I evaporate it and add in the HCl, I use hexane to wash away the coextracted compounds and impurities. Then I discard the hexane, and use ethyl acetate to wash (shake in a sep. funnel) and then discard the ethyl acetate as well!

Only after the hexane, EtOAc washes...I add in a Base (NaOH) and then wash 3 more times with EtOAc and then collect them in a flask through filtering anhydrous NaSO4 (to dry them). Why do I discard the first wash with EtOAc? and why do I collect the EtOAc only after I added in the base?

Thank you for helping me understand what I'm doing!!