Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Jotach on December 16, 2020, 04:00:06 AM
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Hello, I’ve got a question concerning a lab report.
We have to explain the use and chemical background of every step and I’ve been searching a lot, but I can’t find the exact explanation of some steps.
This is a part of the experiment we did: (extraction of methylxanthines from tea, here we discuss how to purify the extraction from other element)
3.3 Removal of cellulose
• With the help of the rotavapor, ethanol is evaporated under reduced pressure to the completely almost dry.
• 5g MgO is added to this slurry, followed by 75 ml boiling water.
• The suspension is boiled for about 5 minutes with the aid of a heating mantle.
• In the meantime, prepare a 300 ml conical flask equipped with a funnel with pleated filter.
• The aqueous suspension is filtered warm.
3.4 Removal of tannins and chlorophyll
• 15 ml of dilute sulfuric acid is added to the solution in the conical flask.
• The whole is cooled in an ice bath. Then transfer the solution into a separatory funnel, which is closed with a glass Stop. Extract (shake vigorously for 1 minute and vent every 10 seconds) with
60 ml dichloromethane. Remove the stopper, let the two layers separate and collect the organic layer (Will this be the top or bottom layer? How can you determine this?) In a 300 ml conical flask. Extract twice more and combine all organic extracts in the Erlenmeyer flask.
• The aqueous phase is collected and a sample is stored and released to be examined chromatographically. The rest will be removed.
• The organic extracts are returned to the separatory funnel and washed with 15 ml saturated NaHCO3 solution until the wash water is basic (How can you check this?).
• Then wash the organic phase with 15 ml of saturated NaCl solution until it is neutral.
I’m still searching for
- the exact mechanism that will precipitate cellulose after adding MgO
- The use of adding sulfuric acid and the other acid-base related actions in 3.4
- A clear explanation why tannines an chlorophyll can be eliminated with this procedure
Thank u so much for your time!