CHE_LAB8(Aky)

CHE_LAB8(Aky) - Alkyne Synthesis from Alkene by Bromination...

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Alkyne Synthesis from Alkene by Bromination and Dehydrohalogenation Experiment # 8
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triethylene glycol 160 – 170 ºC Purpose E-Stilbene, an alkene will be halogenated with bromine to form the haloalkane meso - Stilbene dibromide. Meso- Stilbene dibromide will then be used to synthesize the alkyne product diphenylacetylene by a dehydrohalogenation. The success of the synthesis will be determined by TLC and melting point analysis. Results and Discussion Creation of meso-Stilbene Dibromide E-Stilbene (0.1 g) was placed in solution with 2 mL of acetic acid and reacted with 0.2 g of pyridium tribromide. A colorless precipitate formed while cooling indicating a reaction. After filtration, the product ( meso -Stilbene dibromide) was weighed as 0.134 g. Since the limiting reagent is E-stilbene, the theoretical yield was calculated at 0.189 g giving a 71% yield. A small sample of the product meso- Stilbene dibromide was put into solution with Dichloromethane and put under TLC analysis with a hexanes eluent. The Rf value of meso -Stilbene dibromide was 0.026 while the E-Stilbene showed an Rf value of 0.132. The bromination of E-Stilbene created greater polarity to the compound. Thus, a O H 2 Br - 2 2 2 OH K Br Br O C H 3 CH 3 N + H Br Br Br Br - Br Br
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more polar compound will bind to the polar stationary phase, while the non-polar E- Stilbene will travel well with the non-polar mobile phase. This is consistent with original predictions and supported the creation of the haloalkane. Melting point analysis was used. The experimental melting point of meso -Stilbene dibromide was recorded was 191-221 ºC. The obtained value is much lower than the literature value of 236-237. 1
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This note was uploaded on 05/25/2008 for the course CHE 276 taught by Professor Totah during the Fall '07 term at Syracuse.

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CHE_LAB8(Aky) - Alkyne Synthesis from Alkene by Bromination...

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