Addition-Stilbene-Heather+makeup

By Heather Browning

This photo is awesome and kind of hilarious, if I you don't mind me saying so! I want a poster-sized one!

Addition Reaction to (E)-stilbene Introduction
The following experiment is a green experiment involving the bromination of an alkene. In this lab the alkene is stilbene. For this experiment, bromination involves the addition of the halogen atom, bromine, to the π bond of stilbene. This results in the formation of an alkane. Elemental bromine is a hazardous, volatile substance and will thus be synthesized via oxidizing hydorbromic acid with hydrogen peroxide 30%, in situ. Ethanol acts as the reagent Ethanol is just the solvent. and is likewise used due to its less volatile nature allowing for a greener experiment. The reaction synthesis results in the formation of 1,2-dibromo-1.2-diphenylethane (dibromostilbene). This green experiment has demonstrated improved atom economy over traditional methods using pyridinium tribromide. This process can be used to determine degrees of unsaturation.









Procedure
1. Prepare a hot water bath in a crystallization dish on a stirrer/hot plate.

 2. Place a magnetic stir bar, 0.5g of (E)-stilbene, and 10mL of ethanol in a 100mL round-bottom flask. Fit the flask with a water-cooled reflux condenser.

 3. Clamp the flask so that it may be heated and stirred in the hot water bath. Allow the magnetic stir bar to stir while heating the mixture to reflux. Continue heating and stirring until the majority of the solid has dissolved.

 4. Slowly add 1.2mL of concentrated aqueous hydrobromic acid. This will probably cause some of the stilbene to precipitate, but continued heating and stirring should cause the majority of the solid to re-dissolve. (If some stilbene remains undissolved, can still continue with the next step.)

 5. Measure out 0.8mL of 30% hydrogen peroxide and add it drop wise to the reaction mixture. The initially colorless mixture will change in color to a dark golden-yellow.

 6. Continue to stir and heat the reaction mixture at reflux until the dark golden-yellow color fades and the mixture becomes a cloudy white. This typically takes roughly 20 minutes at reflux.

 7. Remove the flask from the hot water bath and allow it to cool to room temperature. Checking with pH paper, carefully adjust the pH of the solution to pH 5 to pH 7 through the addition of concentrated aqueous NaHCO3. In some cases, very little NaHCO3 ﻿is required.

 8. Cool the reaction mixture in an ice bath to bring more product out of the solution. Collect the solid that forms by vacuum filtration, rinsing with cold water. A wash with very cold ethanol can help to remove traces of impurities, but care must be used to avoid dissolving inordinate amounts of the product. Continue to draw air through your product until dry.

 9. Determine the mass of your product and measure its melting point.

Source: Doxsee, K.M.; Hutchison, J.E. //Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments//, Print 2004; pp 125-128.

Data [[image:stilbene_powder.jpg align="left" caption="Stilbene"]]




please cite the source of your pictures. Stilbene substance appeared as a white, glassy, salt like powder. The end product, dibromostilbene, appeared like a fine, dusty white powder. With the addition of hydrogen peroxide a deep, golden yellow hue was noted (c).


 * **Additions to (E)-stilbene 0.501 grams ** || **Changes to color / characteristics ** ||
 * 10.0 mL Ethanol || No color change to stilbene. Glassy characteristic to stilbene still noted but dissolved almost complete over heat bath with stirring. Mild milky color noted when stilbene more dissolved ||
 * 1.2 mL concentrated aqueous hydrobromic acid || Upon addition, a white solid precipitate was generated. Mildly clumpy white milk like fluid. ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.8 mL of 30% hydrogen peroxide || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">With each drop added a deep golden yellow hue manifested. With continued heat and stirring the color changed back to a milky hue within 10 minutes. ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">5.0 mL NaHCO3 || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">No color change was noted. ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">5.0 mL NaHCO3 || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">No color change was noted. ||

<span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;"> 0.501 grams stilbene used initially in step 1 of procedure. 0.804 grams dibromostilbene generated in experiment.

calculation OK, sig figs OK <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**Melting point** of end product, 1,2-dibromo-1.2-diphenylethane. <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;"> Product appeared to sweat at 221.1°C. Product appeared completely melted with a pale yellow/orange hue at 238.1°C. The literature melting point is 241°C. (cited source after procedure.) did it melt or did it decompose? If it turned brown, that's a decomposition and should be noted as such.
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Percent yield calculations **
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.501 g (E)-stilbene / 180.25 g/mol (E)-stilbene = || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.00278 mol (E)-stilbene ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.00278 mol (E)-stilbene X 1 mol dibromostilbene / 1 mole (E)-stilbene = || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.00278 mol dibromostilbene ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.00278 mol dibromostilbene X 340.058 g/mol dibromostilbene = || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">0.945 g dibromostilbene ||
 * <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Theoretical yield 0.804 grams / 0.945 grams =.851 grams = || <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">85.1% percent yeild ||

<span style="font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> The intentions of this experiment were to demonstrate a green chemistry bromination. The bromination process was successfully carried out within the reaction through the oxidation of hydrobromic acid with hydrogen peroxide eliminating the need for caustic solvents. The predicted product yield was approximately 90%. This experimental yield was 85.1%. A comparison of the percentages reflects a successful experiment in terms of predicted A small point of error that may have contributed to a yield below 90% occurred during step 8, vacuum filtration. During the filtration a small amount of precipitant leaked around the edge of the filter paper and fell into the collection flask. Though the amount appeared rather insignificant it may have contributed to a slightly reduced product yield. <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> The melting point of the final product, 221.1 - 238.1°C, was close to the literature of 241°C. The final product may have had a slightly lower melting point than the literature value due to impurities. At approximately 231.5°C a color change was noted. The product appeared to change to a dirty orange which slowly became lighter, as the solid began to sweat more, until it melted into a slightly paler dirty orange hue. <span style="color: #800000; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">What's the significance of the range between "sweat point" and total melting? Any comments about that?



<span style="font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Note <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Green chemistry's philosophy and experiments encourage the design of products and processes that minimize the use and generation of hazardous substances. This is both neccessary and admirable. I am proud to have be taking a class that "speaks with a green voice." <span style="color: #800000; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;"> Thank you!! What a lovely thing to say. I do green chemistry because it benefits all of us, both from an environmental and health standpoint and because it is innovative, and the right thing to do. It's great to have your appreciation.