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Formal lab report chem 269...

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Investigating Regioselectivity: Synthesis of a Halohydrin Brianna Jett Chem 269 / Section: 014/ TA: Justin Burroughs April 2, 2021

Abstract The purpose of this experiment is to study and understand an electrophilic addition reaction to an alkene in order to study the different regioselectivity during the synthesis of a halohydrin. After isolating the compound, an IR test can be performed to determine if an alcohol group is present in the final compound; then, a Lucas test is performed in order to determine if the hydroxy group was added to the more or less substituted side of the alkene. After the experiment was completed, the results show a positive Lucas test for 2-phenyl-2-propanol which means it is a tertiary alcohol. The IR spectrum revealed a broad peak at 3446.15 cm-1 indicating that there indeed is an alcohol group present. These results indicate that the hydroxyl group was added to the more substituted side of the alkene, so the final product of our isolated compound is 1-bromo-2-phenyl-2-propanol. Introduction Electrophilic addition is one of the most common reactions of alkenes. Since alkenes are considered nucleophilic, they react with electrophiles. During this reaction, the alkene is first attacked by electrophile and some charged intermediate forms. The next step of an electrophilic addition reaction is that a nucleophile finishes the reaction, and a stable substituted alkane is formed. The regioselectivity of addition of electrophiles is thought to be controlled by the relative thermodynamic stability of the possible products, and the more stable product is always formed in electrophilic additions1. In the case of this experiment, the product we wish to synthesize is a halohydrin. A halohydrin is a term for a type of organic compound consisting of a hydroxyl function group and a halogen on neighboring carbon atoms2. The halogen being observed that is being added to the carbon is bromine which will come from the reagent of Nbromosuccinimide (NBS). Halides, such as bromine, are very reactive, so N-bromosuccinimide

is used as the source of molecular bromine due to the fact that it is safer to handle than molecular bromine and it also is relatively stable3. The halohydrin we will be generating is known as a bromohydrin since it contains bromine. Some of the techniques performed that are vital to this experiment are gravity filtration, evaporation, Lucas testing, and infrared spectroscopy. Gravity filtration is vital for filtering out the excess sodium sulfate form the solution. A rotary evaporator is needed for evaporating the excess solvent from the solution in order to isolate the product. Lucas testing is important in order to determine what type of alcohol our final product is, either a tertiary or a primary alcohol. The IR spectroscopy is imperative because it allows us to look at the final isolated compound to determine if a hydroxyl group is present and if a bromohydrin was actually made in the experiment. The purpose of this experiment is to observe the reactivity and regioselectivity of combining together the three reagents, alpha-methyl styrene, N-bromosuccinimide, and acetone, in order to generate a halohydrin4. This experiment is investigating to see which side of alphamethyl styrene the hydroxy group added to. The hypothesis of this experiment is that the alcohol group will add Markovnikov to the alkene and the major product will be a tertiary alcohol, and this means that the major product formed will be 1-bromo-2-phenyl-2-propanol. For this experiment, alpha-methyl styrene, N-bromosuccinimide, and acetone are combined and stirred in a round bottom flask, and then the acetone is removed. Petroleum ether is then added to the solution, and then the solution is dried with sodium sulfate which is then removed by gravity filtration. The ether is removed off of the compound by evaporation in the rotary evaporator to isolate the final compound. The makeup of the final product is confirmed by the taking an infrared spectroscopy and performing a Lucas test.

Figure 1: Reaction scheme of alpha-methyl styrene and N-bromosuccinimide to form the possible major products

Results and Discussion The final product isolated from the experiment was 1-bromo-2-phenyl-2-propanol. The structure of the final isolated compound is shown in figure 2. The reagents that were used in this experiment are all included in table 1. After evaporating the petroleum ether from the solution, the only solution left in the round bottom flask was a small amount of a yellowish oil. This was the isolated product from the experiment performed. The recorded mass of the amount of the isolated product was 0.653 grams.

Table 1: List of Reagents utilized and molecular weight, amount used, and melting/boiling points. Reagent Molecular Melting/Boiling Density Amount Used Point (°C) Weight (g/mL) (g/mol) Alpha-methyl styrene 118.18 g/mol 175 °C 0.91 g/mL 1 mL

Mol

0.0077 mol

N-bromosuccinimide (NBS)

177.98 g/mol

221 °C 175 °C

2.1 g/mL

1.373 g

0.01164 mol

Acetone

58.08 g/mol

221 °C -95 °C

0.792 g/mL

24 mL

0.3273 mol

86.18 g/mol

56 °C...