CHE327lecture3

CHE327lecture3 - Assemble in the elevator lobby before lab...

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Assemble in the elevator lobby before lab the lab begins. You will need your gloves this week. Being late for lab is foolish because you will miss announcements and you will not get extra time at the end. If you are more than 40 minutes late you are considered absent and cannot start the lab. TLC Thin Layer Chromatography Thin-Layer Chromatography This Week: TLC as a Method to Monitor Reactions CO 2 CH 3 CO 2 CH 3 Br 2 /h ν CO 2 CH 3 H 3 CO 2 C Dimethyl maleate Dimethyl fumarate Next Week: Chromatographic Separation of Next Week: Chromatographic Separation of Beta-Carotene The Reaction: Isomerization of Dimethylmaleate CO 2 CH 3 CO 2 CH 3 Br 2 /h ν CO 2 CH 3 H 3 CO 2 C Dimethyl maleate Dimethyl fumarate The reaction is catalyzed by bromine in the presence of light. Safety note: Both bromine and CH 2 Cl 2 are hazardous materials that should be used with caution. Mechanism of Reaction Br 2 h ν 2 Br• Br• + CO 2 CH 3 -Br• H 3 2 C The reaction is reversible. CO 2 CH 3 CO 2 CH 3 Br 2 /h ν CO 2 CH 3 H 3 CO 2 C Dimethyl maleate Dimethyl fumarate You are going to watch the progress of the reaction over a 20 minute period using TLC to monitor the disappearance of the dimethyl maleate (starting material) and the appearance of the appearance of the dimethyl fumarate product.
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At the end of the period you will isolate and filter the dimethyl fumarate solid. Use a small part for your final TLC, but then put the rest of it in a labeled vial and store it in your drawer. Next week you can recrystallize it and determine its melting point determine its melting point. Safety note: Both bromine and CH 2 Cl 2 are hazardous materials that should be used with caution. Wear heavy gloves when handling bromine. No CH 2 Cl 2 down the drain!! Use designated waste containers. Multipoint penalty for CH 2 Cl 2 down the drain. Thin-Layer Chromatography To monitor the reaction, we need a method to determine what is in the flask. The method you will use is Thin-Layer Chromatography (TLC) Chromatography (TLC). TLC is one of many different techniques used to separate and identif compo nds in a mi t re all separate and identify compounds in a mixture, all based on the principle of chromatography . What is chromatography? Chromatography (“color writing”) Chromatography is a method for separating mixtures. All types of chromatography involve a stationary phase All types of chromatography involve a and a mobile phase .
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CHE327lecture3 - Assemble in the elevator lobby before lab...

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