When performing a Grignard reaction it is important that air is excluded from th

Question

When performing a Grignard reaction it is important that air is excluded from the reaction vessel.

a. Draw the competing overall reactions that will occur with your Grignard reagent from lab 3 if it is allowed to react with air. (6 pts)

b. Why was anhydrous calcium chloride used in your experiment?

Figure 3-1. Calibrated syringe with blunt needle K1 1. Preparation of Glassware You will need a drying tube, Claisen head adapter, and a 25 mL, round-bottom flask (Figure 3-2).You will also need a stir bar and a rubber septum. Pack the drying tube with cotton and anhydrous calcium chloride pellets following this a small piece of cotton and add drying agent (pack loosely) followed with another piece of cotton to plug the tube. This tube helps prevent moisture from getting inte the system, while providing a vent for vapors. NOTEI Please ensure that you close the lid on the anhydrous calcium chloride vials to prevent it from getting moist and hardening in the vials.

Explanation / Answer

1. Grignard reagent reacts with oxygen present in the air to form peroxides which are transformed into alcohols after aqueous workup.

RMgX + O2 -----------> R-O-O-MgX-------------> R-O-MgX + H2O-------------> ROH + MgX(OH)

they also react with the moisture present in the air to give hydrocarbons

RMgX + H2O ---------------> R-H + MgX(OH)

2. Anhydrous calcium chloride is used to absorb moisture. It is highly hygroscopic in nature thus provides a moisture-free atmosphere.

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