CHM 1711 Lecture Notes - Lecture 3: Thin-Layer Chromatography, Silica Gel, Dichloromethane

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22 Sep 2017

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There were no mechanisms involved for this experiment. The purpose of this lab was to review some necessary techniques used often in organic chemistry. These techniques are used to purify or separate products from one another or to simply (cid:498)work-up(cid:499) a chemical reaction. Different techniques used in this lab are extractions, thin layer chromatography (tlc), and re-crystallization. Extraction, tlc, and recrystallization will all be used to isolate caffeine from tea leaves while only tlc and extraction will be used to separate different pigments from spinach leaves. mixture of products. Extraction takes advantage of these compounds chemical and physical properties and uses differences in solubility"s of two immiscible solvents. Extraction is an important technique used for isolating compounds from a. Re-crystallization is a technique based on differences in compounds. The technique uses two solvents, which will always contain an organic and aqueous phase. In the aqueous phase will be salts, charged compounds, and acids/bases.

Related Questions

Organic Chemistry lab QUESTIONS Extraction of Caffiene Lab

â¢Procedure

1) Use hot water to extract the caffeine from the tea leaves.

- tannins and chlorophyll will extract along with caffeine

2) Use dichloromethane to extract caffeine from water using extraction

techniques from last weeks lab.

- dichloromethane is more dense than water and will be the

bottom layer in the separatory funnel.

- perform 3 x 20 mL extractions with dichloromethane

3) Wash the 2 x 20 mL 6M NaOH solution with base to remove acidic

tannins. Tannins will deprotonate and preferentially partition into

the aqueous phase.

4) Dry organic phase with drying agent (CaCl2) to remove residual water.

5) Transfer dichloromethane to flask and evaporate in hood.

6) Recrystallize caffeine from 2mL hexanes and 0.5 mL acetone. Filter, mass product and determine % by weight of caffeine from tea.

7) Analyze for purity via TLC and compare to that that extracted from coke and pure caffeine..

If you were to run the experiment without using any celite 545, what would happen to the purity of your sample and why? Be specific.

Why is Celite 545 labeled as 545? What makes it special?

If you were to use THF, or tetrahydrofuran instead of dicholormethane for this experiment, could you still successfully extract your caffeine? Why or why not? (Consider what is necessary for an extraction to work) Why is dichloromethane different from THF

Only answer what is above. The experiment is written below.

Introduction Caffeine is one of three legal, mind-altering drugs available in the U.S without a prescription. Two common sources of this drug are tea and coffee, both of which are prepared via extraction of the solid foodstuff with liquid water. In this lab you will extract caffeine from food samples with liquid solvents and quantify the amount obtained. Laborator Hypothesis: We can rank various tea and coffee samples by caffeine content by performing a solid-liquid extraction from the foodstuff, followed by analysis via thin-layer chromatography. Experiment: In a 50 mL Erlenmeyer flask were placed 2.0 g of black tea. Dichloromethane (15 mL) and 0.2 M NaOH (5 mL) were added successively, and the stoppered flask was swirled gently by hand for 10 minutes (note: avoid vigorous shaking, as it will cause an emulsion to form). The dicloromethane layer was separated from the leaves and the aqueous layer by vacuum filtration through 7 g Celite 545, and the leaves were washed with a further 15 mL dichloromethane. The combined dichloromethane solution was placed in a 50 mL round bottom flask and concentrated to a minimal volume (ca. 1 mL) via simple distillation. The remaining dichloromethane solutions was transferred to a watch glass via pipet, and the solvent was evaporated in a fume hood. The sample was evaluated by TLC (a mixture of methanol and ethyl acetate as the mobile phase, co-spotted with authentic caffeine). Data: What was your crude yield of caffeine? What was the mass percentage of caffeine in your food source'? Given that the materials we are interested in are UV active, compared to the TLC standard how would you characterize the purity of your caffeine extracts? Conclusions: Can you comment on the purity of your caffeine sample? For all samples your class worked with where does your foodstuff rank in terms of caffeine content? How much caffeine is reported for the typical serving of coffee or tea? How did your extraction and isolation compare with the typical serving?

CHM 1711 Lecture Notes - Lecture 3: Thin-Layer Chromatography, Silica Gel, Dichloromethane

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