Experiment 12: Dehydrobromination Discussion In this experiment, a double elimination reaction was performed on meso-stilbene dibromide, to form diphenylacetylene by eliminating two hydrogen and two bromine atoms in he presence of potassium hydroxide. The product was filtered and identified by comparing melting point data, and percent yield was calculated. Since an E2 reaction was performed in this experiment, the ideal conformation for the hydrogen and bromine would have been anticoplanar. However, since the phenyl groups were bulky and the atom was not symmetric, the hydrogen and bromine could at best be antiperiplanar. For an E2 reaction to occur, the two groups being removed had t be anti to each other. This was easily accomplished in …show more content…
In order to overcome this issue, the reaction could have been performed in a regular solvent heated to 190C under extremely high pressure to prevent boiling. However, the lab was not equipped to safely deal with high pressure situations, so instead a solvent with an extremely high boiling point had to be used. In this case, triethylene glycol, which has a boiling point of 260℃, was used. This boiling point is significantly higher than the 190℃ that this reaction was performed at, and the solvent would hence not boil away, even under standard pressure …show more content…
Melting point data was used to confirm the identity of the product as diphenylacetylene. The expected melting point of diphenylacetylene is 59-61℃, according to its MSDS sheet. While there was a discrepancy in this temperature range and the melting point range observed, the melting point was significantly lower than that of meso-stilbene dibromide, which is 241℃. The data hence confirms the formation of diphenylacetylene. The error could have been caused due to impurities in the diphenylacetylene crystals, such as leftover ethanol, or triethylene glycol, which would destabilize the lattice structure of the crystal, making it melt at a lower temperature than expected. The percent yield for this experiment, calculated as described in the discussion, was 61.7%. This was an excellent percent yield, especially considering the fact that this has been a historically difficult experiment to get good yield in. This high yield most likely occurred due to successfully building a good aluminum tent, which conducted the heat towards the reaction, allowing the relatively inefficient hot plates to heat the reaction to the high temperature necessary. The reaction was also stopped exactly at 5 minutes, which likely resulted in very little product burning
The hypothesis was supported by the employed methods. Introduction: This experiment was performed to show how bromination of alkenes reacts, and to be able to successfully synthesize meso-stilbene dibromide. The reaction of bromine with alkenes is an addition reaction where the nucleophilic double bond attacks the electrophilic bromine
As the name implies, the bromination mechanism in an electrophilic aromatic substitution reaction that replaces an atom on the ring with a bromine atom. The addition of the bromine is driven by the presence of a Lewis acid catalyst and a bromine atom. In most bromination mechanisms, liquid bromine is the preferred reagent to complete the reaction. However, due to potential safety concerns, the aromatic ring was brominated by using a compound of hydrobromic acid and potassium bromate in an acetic acid solution (see Figure 2 for the bromine formation).1 Liquid bromine is known for generating hazardous fumes, so this solution is significantly safer for bromine production. This formation of bromine is crucial for the bromination reaction to
The boiling point measured was 86ºC in comparison to the literature boiling point for the desired product, cyclohexene, at 83ºC. The starting materials, cyclohexanol, boiling point was listed as 161ºC. This value is too high for the measured boiling point for the product obtained. As a disclaimer, the thermometers used in lab are alcohol based that result in the skewed boiling point measurements in comparison to the actual literature values. In short, the obtained products boiling point measured was similar enough to the desired product to conclude that the product obtained is indeed the
The goal of the experiment is to synthesize a bromohexane compound from 1-hexene and HBr(aq) under reflux conditions and use the silver nitrate and sodium iodide tests to determine if the product is a primary or secondary hydrocarbon. The heterogeneous reaction mixture contains 1-hexene, 48% HBr(aq), and tetrabutylammonium bromide and was heated to under reflux conditions. Heating under reflux means that the reaction mixture is heated at its boiling point so that the reaction can proceed at a faster rate. The attached reflux condenser allows volatile substances to return to the reaction flask so that no material is lost. Since alkenes are immiscible with concentrated HBr, tetrabutylammonium bromide is used as a phase-transfer catalyst.
The percent recovery for the acid was 42%, but there was actually 40% of o-toluic acid in the mixture. The extra 2% could be the impurity, 1- 4-dibromobenzene, which would be isolated in the next experiment. The procedure for removing the acid was performed successfully, though. Data Tables 1 also shows the final results in the isolation of the acid.
Because the heating block readily increased in temperature, the temperature had to be adjusted accordingly to prevent the overheating the reaction. Initially, the color of the reaction turned into a dark green color and over time became a lighter shade with a minimal solid left. The reaction process lasted for 2 hours. As the reaction heated for 2 hours, a 50 mL beaker was weighed, approximately 12 mL of 20% ethyl acetate in hexane solution was added to a 25 mL Erlenmeyer flask, and 2.0 mL of saturated NaCl solution was added to a labeled test
The solution continued to boil for 25 more minutes until a
Discussion This experiment done in lab was the Bromination of (E)-Stilbene to produce dibromide stilbene. Though there are three products, the meso-stilbene product is the major product. In order to get theunderstand how to get the correct major product, the full mechanism must be done.
Chem 51 LB Experiment 3 Report Scaffold: Bromination of Trans-Cinnamic Acid 1. The goal of this experiment was to perform a halogenation reaction through the addition of two bromides from pyridinium tribromide. This was accomplished by reacting trans-cinnamic acid with pyridinium tribromide. After the reaction took place, melting point analysis was conducted to find out the stereochemistry of the product, which could either be syn-addition, anti-addition, or syn + anti-addition. 2.
The purpose of this experiment is to perform a two step reductive amination using o-vanillin with p-toluidine to synthesize an imine derivative. In this experiment, 0.386 g of o-vanillin and 0.276 g of p-toluidine were mixed into an Erlenmeyer flask. The o-vanillin turned from a green powder to orange layer as it mixed with p-toludine, which was originally a white solid. Ethanol was added as a solvent for this reaction. Sodium borohydride was added in slow portion as the reducing agent, dissolving the precipitate into a yellowish lime solution.
Nevertheless, the latter is not used in this experiment since it is very reactive and extremely flammable. On the contrary, NaBH4 is relatively mild and it can be used with protic solvents. In this manner, 1.507 grs of the ketone 9-fluorenone were mixed with 30.0 ml of 95% ethanol in a 125 ml Erlenmeyer flask. The bright yellow mixture was stirred during 7 minutes until all the components were dissolved.
(150.22g/mol)(3.5 x 10^-3 mol of nucleophile) = 0.525 g Actual yield = 0.441 g, Percent Yield = (0.441g/0.525g) x 100% = 84% 10. Percent recovery from recrystallization = (0.172g/0.441g) x 100% = 38% 11.
Additionally, there were tiny white properties in the mixture. For this lab the experimental yield for the final product is 3.65g, and the melting point of the product came to be 71C. The experimental yield of the product was very close to the theoretical yield, 4.45g, and using the actual and theoretical yield the percent yield was calculated to be 82%. The literature melting point of the final product is 78C, which is very close to the experimental melting point. The experimental melting point was a less than the literature melting point because there were less impurities, the experimental final product was probably purer as a result of the vacuum filtration conducted using methanol and distilled
The percent yield was 22.33%. In most cases, that means that a lot of possible product was lost. However, in this case, that was not true. When Benzaldehyde reacted with the Wittig reagent, it produced two products: E-Stilbene and Z-Stilbene. The Z product was a liquid, while the E product was a solid.
In the synthesized Friedel-Craft acylation reaction mechanism, anisole (methoxybenzene) is the nucleophile. The double bond on the nucleophile attacks the electrophile acetyl. The acetyl compound is then bound to the anisole in the para position, which created the product p-methoxyacetophenone. Since anisole is an activator (electron donor), the acetyl could have bound in either the ortho or para position (or in the meta position, but it is not as likely). However, the reason that acetyl was not bound in the ortho position was because the para position demonstrated the least amount of steric hindrance.