Greener Brominations
Abstract
In this experiment, trans-stilbene was brominated and debrominated with the use of three methods: bromination with pyridinium tribromide, bromination with hydrogen peroxide and hydrobromic acid, and debromination with zinc. The yields of parts A, B, and C are as follows: 68.6 %, 54.6 %, and 55.9 %.
Introduction
In the chemical process of bromination, an alkene is halogenated with bromine. Solvents that are typically used include methylene chloride and carbon tetrachloride along with iodine, the traditional reagent. However, because of the carcinogenic properties of the solvents and the corrosiveness of iodine, other alternatives are utilized : bromination with pyridinium tribromide, bromination
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Finally, the product yield and melting point were recorded.
1Student Notes: Greener Brominations of Stilbene,
Data
molecular weight of (E)-stilbene 180.23 g/mol melting point (lit.) 122-124 °C
molecular weight of stilbene dibromide 338.02 g/mol melting point (lit.) 236-240 °C
A. Bromination of trans-stilbene with pyridinium tribromide
(E)-stilbene 2.0 g filter paper 0.4483 g watch glass 24.4018 g final 27.4208 g product (stilbene dibromide) 2.5707 g melting point 238 °C
Theoretical Yield
= molar quantity of limiting reagent * molar mass of product
= (2.0 g (E)-stilbene / (180.23 g/mol)) * ( (338.02 g/mol) stilbene dibromide)
= 3.75 g
Fractional Yield
= (Actual Yield / Theoretical Yield) * 100 % = (2.5707 g / 3.75 g) * 100 %
= 68.6%
B. Bromination of trans-stilbene with hydrobromic acid and hydrogen peroxide
(E)-stilbene 0.51 g filter paper 0.5184 g final 1.0407 g product (stilbene dibromide) 0.5223 g melting point 220-222 °C
Theoretical Yield
= molar quantity of limiting reagent * molar mass of product
= (0.51 g (E)-stilbene / (180.23 g/mol)) * ((338.02 g/mol) stilbene dibromide)
= 0.957 g
Fractional Yield
= (Actual Yield / Theoretical Yield) * 100 % = (0.5223 g / 0.957 g) * 100 %
= 54.6%
C. Debromination of stilbene dibromide with zinc
stilbene dibromide 0.52 g filter paper 0.6070 g final 0.7618 g product 0.1548 g
melting
* If the price was set at $90,000 the new fixed cost percent would be 23% as that is the closest to $90,000 at $89,997
Discussion: In the synthesis of 1-bromobutane alcohol is a poor leaving group; this problem is fixed by converting the OH group into H2O, which is a better leaving group. Depending on the structure of the alcohol it may undergo SN1 or SN2. Primary alky halides undergo SN2 reactions. 1- bromobutane is a primary alkyl halide, and may be synthesized by the acid-mediated reaction of a 1-butonaol with a bromide ion as a nucleophile. The proposed mechanism involves the initial formation of HBr in situ, the protonation of the alcohol by HBr, and the nucleophilic displacement by Br- to give the 1-bromobutane. In the reaction once the salts are dissolved and the mixture is gently heated with a reflux a noticeable reaction occurs with the development of two layers. When the distillation was clear the head temperature was around 115oC because the increased boiling point is caused by co-distillation of sulfuric acid and hydrobromic acid with water. When transferring allof the crude 1-bromobutane without the drying agent,
6. Summarize in a few sentences the halogenation and controlled oxidation reactions of 1°, 2°, and 3° alcohols.
8. Calculate the return on investment in dollars and as a percentage for an investment that you purchase for $500 and sell for $600. (2.0 points) 20 % ($100 profit)
nominal 6% bond specified in the contract. The formula to find conversion factor is as follows:
The objective of this laboratory experiment is to study both SN1 and SN2 reactions. The first part of the lab focuses on synthesizing 1-bromobutane from 1-butanol by using an SN2 mechanism. The obtained product will then be analyzed using infrared spectroscopy and refractive index. The second part of the lab concentrates on how different factors influence the rate of SN1 reactions. The factors that will be examined are the leaving group, Br versus Cl-; the structure of the alkyl group, 3◦ versus 2◦; and the polarity of the solvent, 40 percent 2-propanol versus 60 percent 2-propanol.
P = F(1 + i)-N where i is 15% as mentioned in the case suggestions and N is 8 as we found above, and F is $1.2375B
6. Purpose: to clarify the mechanism for the cycloaddition reaction between benzonitrile oxide and an alkene, and to test the regiochemistry of the reaction between benzonitrile oxide and styrene; to purify the crude product of either trans-stilbene, cis-stilbene, or styrene reaction.
Once the distillate had been collected into two separate vials, both distillates were washed with aqueous sodium bicarbonate (1.5-ml, 5%). The aqueous layer (lower) was extracted from both vials using a pipette and put into a chemical waste bin. The organic (alkene) layer was then dried with anhydrous calcium chloride pellets (3 pellets per vial). Both distillates were analyzed using gas chromatography, and each peak shown was identified to be one of the alkenes. Analysis of the graph was used to determine the major and minor products of the reaction.
Reaction 1 involved a primary alcohol (OH), weak leaving group in the starting material and a reaction with a strong nucleophile (sodium bromide) and a polar protic solvent (sulfuric acid). The reaction was carried out through reflux and the product had a relatively high yield (75%) (Scheme 1).
The purpose of this experiment is to examine the reactivities of various alkyl halides under both SN2 and SN1 reaction conditions. The alkyl halides will be examined based on the substrate types and solvent the reaction takes place in.
RE = [$1.30 × (1 + 0.060)] / $36.80 + 0.060 = 0.097446 = 9.74 percent (3)
The goal of this experiment was to synthesize an alkene (4-methylcyclohexene) from an alcohol (4-methylcyclohexanol) by dehydration. The reaction, consist of 4-methylcyclohexanol, phosphoric acid, and sulfuric acid, was refluxed at a given time frame. The product was isolated by distillation and purified by adding sodium chloride to help the extraction. The final product had a 125% yield and was characterized by the IR spectroscopy and chemical reaction. The alkene resulted in a colorless liquid after adding molecular bromine dissolved in dichloromethane.
The purpose of this lab is to understand the process of eliminating an alkyl halide to form an alkene. The experiment is carried out by first converting the alcohol, 2-methy-2-butanol, into the alkyl halide of 2-chloro-2-methylbutane that will then be put through dehydrohalogenation that favors elimination reaction (E2) to create a mixture of 2-methyl-2-butene and 2-methyl-1-butene. A fractional distillation will be taken to purify the mixture and an additional gas chromatography will be done to further analyze the mixture composition. A bromide test will be done to determine the product of an alkene in the experiment.
ex. Test tube 1, 0 mol/L solute concentration: 1.6 – 1.3 ÷ 1.3 × 100 = 23.08%