Pre-lab preparation

The pre-lab preparations should be routine by now. Prepare your notebook by constructing a table of physical properties (MW, mp, bp, d) for the compounds that you will handle in this experiment (acetic acid, isopentyl alcohol, conc. sulfuric acid, saturated aqueous sodium bicarbonate [NOTE 1], magnesium sulfate, diethyl ether, and isopentyl acetate), list any unusual hazards that a lab worker should be aware of [NOTE 2], list disposal information for all compounds, and calculate the amounts of reagents that you expect to use (left notebook page and/or under a column called "amount desired" in your table - make sure you list the units).

Online videos. Please review the following videos on lab procedures before lab (these are all from The Interactive Lab Primer). You can wait until week #2 to review the distillation videos. Note: the Lab Primer videos focus on techniques, but don't explain much. The Extraction, Washing, Drying video from MIT does a much better job of explaining the language, rationale, and practice of these techniques. Please watch the MIT video at least once.

	Solvent Extraction (full video) and Extraction, Washing, Drying
	Drying Liquids (full video)
	Simple Distillation (full video) and Fractional Distillation (focus on connection between temperature & liquid collection)

Equipment

The procedure for this experiment provides less information about equipment than previous experiments. We assume that you will be able to figure out your equipment needs partly from prior experience and partly by consulting reference materials.

Rule-of-thumb for container size: When estimating the size of a container (beaker, flask, etc.), estimate how much material will be placed in the container and then double that amount to get the container size. In other words, never fill a container more than half full.

Naturally, this rule has many exceptions. If your material is volatile, might boil or generate a foam, or produce gases, use a larger container. On the other hand, if you are simply storing a nonvolatile material in the container, you can get by with a smaller container.

Wear gloves and goggles and carry out all operations in a fume hood.

Reaction

Combine isopentyl alcohol (0.15 mol), acetic acid (2-3 molar equivalents [NOTE 3]), and concentrated sulfuric acid (1 mL) in a clean, dry, 100 mL round bottom flask. Put a magnetic stir bar in your flask and attach a reflux condenser. Reflux your mixture for 30-40 minutes while stirring [NOTE 4], then stop heating the mixture and allow it to cool to room temperature.

Work up

Special reading: the next "work up" steps, extraction/washing and drying, are routinely used to separate ionic and neutral organic compounds. In this experiment, extraction/washing separates sulfuric acid and acetic acid (water/base layers) from isopentyl alcohol and isopentyl acetate (ether layer). The ether layer is also "wet" because it has been in contact with water, so it must be dried to remove residual water. These procedures are described in Padias p. 116-125 and p. 125-128. Study Figures 3-5, 3-7, and 3-8 particularly carefully so that you understand what is going on. A mistake at this point might accidentally send your product down the drain.

Clamp an iron ring in your fume hood. Rest a 250 mL separatory funnel on the ring, and place an Erlenmeyer flask under the separatory funnel [NOTE 5]. Transfer the cooled reaction mixture to the separatory funnel. Add 50 mL water to the mixture.

Extract the aqueous solution once with 40 mL of "wash grade" diethyl ether . Next, carefully wash the ether solution with one, two, or three 40 mL portions of saturated aqueous NaHCO₃ until the bicarbonate layers are neutral or basic [NOTES 6 AND 7].

Drain the diethyl ether layer into an Erlenmeyer flask and dry it with a small amount of anhydrous MgSO₄. Gravity filter the solution to remove MgSO₄ and rinse the spent drying agent with a small amount of anhydrous diethyl ether (from this point onward, use only anhydrous diethyl ether whenever diethyl ether is called for).

Distillation - Week 2? [NOTE 8]

Special reading: the next step, distillation, is routinely used to separate volatile neutral organic compounds. Distillation can be carried out in several ways: macroscale or microscale, with or without a fractionating column, at atmospheric pressure or reduced pressure (vacuum), and with or without added water/steam. This experiment calls for a simple macroscale distillation at atmospheric pressure of a mixture of diethyl ether, isopentyl alcohol, and isopentyl acetate. Study Padias p. 129-134 and p. 136 carefully so that you understand what is going on.

Distill your dry diethyl ether solution through a clean, dry simple distillation apparatus (boiling chips) [NOTE 9]. Collect fractions by temperature. You can collect all low-boiling material in a single flask if you like, but have additional flasks on hand. In particular, prepare one clean, pre-weighed (tared) collection flask for the distillate corresponding to isopentyl acetate.

Characterization

Weigh your product and analyze it for impurities using gas chromatography [NOTE 10]. Record its FT-IR spectrum. Then prepare an FT-NMR sample [NOTE 11] of your product and leave it with your instructor. FT-NMR measurements will be made for you during the week, and you will return to lab the following week to print your NMR spectrum.

Although we will assist you in printing your NMR data for this experiment, you will be expected to do this on your own in future experiments. Detailed instructions for preparing NMR samples and working with NMR data are provided in the Instrumentation appendix.