10 Initial Considerations

Below are some questions and considerations for which you need to account in your team planning documents.

1. Whenever you do a reaction for the first time, always do it on a small scale (100-200 mg) using small-scale glassware.
2. Start with clean, dry glassware for your reaction. If your glassware is dirty, clean it with soap and water and air dry. Most of the stains can be cleaned with soap water. If your glassware is still dirty, use acetone rinse. If your glassware will have water on it, it may (detrimentally) affect the course of the reaction.
3. If any of your reaction components are water- or air-sensitive, you will need TA approval and instruction on carrying out reactions under an inert atmosphere.

A few minutes of forethought can save you many problems later. Your TA and the resources in this manual can help you design the appropriate procedure. Before you begin, think how you will address the following questions:

• How will you get your reactants into the reaction mixture?

  Will you mix them in the reaction vessel and then let the reaction occur, or will you need to add one component to the other as the reaction progresses? If a simple initial mixture is all that is required, a very simple reaction setup might be only an appropriately sized reaction vessel.

  If you will need to add a reagent during the reaction, you may need to set up a reaction with a dropping funnel or a syringe to add the second component.

  Weigh out one of the reactants in the clean, dry reaction vessel. The other reagent(s) can be weighed onto a piece of weighing paper or into a glass vial in the case of a liquid.

  Another option for obtaining the correct mass of liquid is to find the density of the liquid and measure out the appropriate volume (recall the formula for calculating density, below).

  [latex]\text{density} = \frac{\text{mass}}{\text{volume}}[/latex]

• Does the reaction need a solvent?

  Most organic reactions are done in the presence of a solvent so that all the reactants are in the same phase. Because this course introduces principles of green chemistry, always consult the Greener Solvent List to ensure that the most appropriate benign solvent is used. The greenest choice is solvent-free reaction, also referred to as “neat reaction”. Neat reactions are often used when the reactants are liquids or solids that can effectively mix and react without the need for a solvent.

• Will you need to stir the reaction mixture?

  If so, make sure you set the reaction up on a stirrer, and place a stir bar in the reaction vessel before you start adding reactants.

• Will you need to heat the reaction mixture?
  

  In many cases, you will not know whether you need to heat the reaction until you have monitored it for some time. If in doubt, set up the reaction mixture in a heating bath on a hot/stir plate. This will allow you to heat the reaction mixture more uniformly and in a more controlled fashion than direct contact onto the hot/stir plate.

• How will you monitor the reaction?

  Typically, you will use Thin-Layer Chromatography (TLC), Infrared (IR) Spectroscopy and NMR spectroscopy to follow the progress of the reaction. You need to prepare your chosen monitoring system before you begin the reaction.

• How will you work up the reaction?

  Make sure you understand how to isolate and purify the product before you begin. Consider Extraction, Distillation, Rotary Evaporation, Recrystallization, Precipitation, Drying, and/or Filtration techniques.