Tetrahydrofuran Lab Report

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Introduction Organometallic compounds are substances that contain carbon-metal bonds. Metals found in these compounds are typically lithium (Li), magnesium (Mg), copper (Cu), mercury (Hg), or other transition metals. Organometallic compounds are also known as Grignard reagents (1). General mechanism of organometallic compounds:
R^1 CH_2-M + X-CH_2 R^2 → R^1 CH_2-CH_2 R^2 + MX

Grignard reagents are among the most important in organic chemistry. The polarization of the bond between the carbon atom and the metal makes the carbon atom a Lewis base. A characteristic property is that the carbon atom is a nucleophile. However, when bonded to more electronegative atoms the carbon acts as an electrophile (1). Grignard reagents are …show more content…

This causes the stabilization of the compound. Diethyl ether or Tetrahydrofuran (THF) are the two commonly used ethereal solvents. Diethyl ether is used over tetrahydrofuran due to cost and the ability to be easily removed from the solution (1). Use caution when opening diethyl ether and tetrahydrofuran containers because they have the ability to create hydroperoxides, which are dangerous because they are explosives.
Hydroperoxides can be tested for using starch/iodine test paper. If the starch/iodine test paper turns a dark shade of purple then hydroperoxides are present in the ethereal solvent (1).
The magnesium used is commonly in the form of magnesium turnings to increase the surface area of the reaction. Forming the Grignard reagent is an exothermic reaction process. The temperature should be regulated as well as the rate of the reaction. The rate of the reaction should be monitored because side reactions can occur if the reaction progresses too quickly. The halide should be added in a dropwise manor over a designated time period. Adding the halide dropwise keeps the reaction rate under control because the concentration of the halide is kept at a low value …show more content…

The glassware used in this experiment (Claisen adapter, separatory funnel, condenser, stir bar, drying tube, and a 50mL round bottom flask) should be baked in an oven to ensure that they are clean and that there is no water left in them.
The reaction color went from cloudy to brown after the reaction with the magnesium turnings began. Once the methyl benzoate was added the color changed from brown to an orangey-pink. After the workup steps the acidity of the aqueous layer was tested and was found to have a pH of approximately 2 due to the pH paper turning a magenta color. The recrystallization of the product was done using cyclohexane.
The melting point of the product was found to be between 158ºC and 160ºC. The percent yield of the product was calculated to be 23.62%. The low yield was caused by accidently spilling some of the reaction during the washes/extractions in the separatory funnel and by the possibility of having had a side reaction occur during the preparation of the Grignard

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