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NameLab Section

GTAStation #

5.Extraction

Pre-lab questions

Complete the following questions and submit before beginning the experiment.

1. Which layer will be the aqueous layer when using dichloromethane (methylene chloride) as the solvent (i.e., top or bottom)? Which layer will be the aqueous layer when using ether as the solvent?

2. When everything has been separated in Part D, which compounds will be in test tubes 1, 2, and 3?

3.The partition coefficient of benzoic acid is 3 in dicholormethane (methylene chloride) with respect to water. If 6 grams of benzoic acid is dissolved into 600 mL of water, how much benzoic acid will be extracted with four by 150 mL portions of dichloromethane (methylene chloride)?

4.In part D, you are to test the aqueous layer with litmus paper after removing the sodium bicarbonate layer. If the paper shows that the extracted layer is neutral, what assumption can you make about the contents of tube 1?

5. Using Schemes 1 and 2 in your handout as references, fill in the flowchart on the following page for the separation of an organic acid (R-COOH), a base (R-NH2), and a neutral organic compound.

Pre-lab Notebook preparation

Prepare the following in your lab notebook before beginning the experiment.

1.Start a new page by entering the title of this experiment. 2.Start a section with the subtitle “Part 1 - Procedure” and provide an outline of the experimental procedure to be carried out. Do the same for Part 2.  

5.Extraction

Zubrick:Chapters 15 and 16
127-130 (general introduction)
133-136 (how to extract, sample extraction, washing)
138-139 (extraction hints)
141-143 (microscale extraction information)

Vocabulary:MiscibleTwo or more compounds, which dissolve in one another to form a homogenous solution.

Aqueous contains water.

Organic non-aqueous (does not contain water), usually
hydrophobic

Emulsion No separation of the organic and aqueous layers (usually cloudy).

Partition coefficientThe same as the distribution coefficient. It is the relationship between the solubility ratios of two different layers for a compound, which is soluble in both solvents.

This procedure has been adapted from the microscale procedure described in Macroscale and Microscale Organic Chemistry Experiments by Kenneth L. Williamson.

Background

What is extraction? There are several listings for extraction in the American Heritage Dictionary (p. 466) but in its simplest form, extraction is the separation of something from another. There are numerous examples in our everyday lives. Vanilla extract is used in cooking. The essence of perfume is extracted from flowers, plants, etc. For the organic chemist, extraction is part of the normal work up of a reaction. Sometimes, it is referred to as aqueous workup in the text or manuscript. We wash the organic reaction mixture with water (acidic, neutral and/or basic) to remove any byproducts or inorganic material.

There are three basic types of extraction: liquid/liquid, acid/base and solid/liquid. We will be performing the first two types of extraction in this experiment. First, we have to understand how to choose a solvent for extraction. A couple of things we have to consider are polarity and density of the solvent. The polarity of the solvent is important because “like dissolves like.” So if the extraction is from an aqueous solution, we do not want a solvent that is miscible with water. Thus during the extraction two layers are formed, aqueous and organic. It is important to know the density of the solvent so that we can predict which one is the organic layer. Most chlorinated solvents have densities greater than water (>1 g/mL). Aromatic (toluene, benzene - any compound which contains a benzene ring), aliphatic compounds (hexanes), and...
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