Lab 6 bromination full report PDF

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Organic Chemistry 654.02 3/24/20 Bromination of Vanillin Laboratory Report Introduction The goal of this lab is to determine the structure of bromovanillin. In this lab the vanillin is brominated in order to get on or a mix of three products: 2-bromovanillin, 5- bromovanillin, or 6- bromovanillin (see Figure 1).1 In this lab we are using a bromination of vanillin to get to the final bromovanillin product. Vanillin is a substance that can “undergo a variety of electrophilic aromatic substitution reactions” which is why there are three different possible products.1 The data taken from the product left after the bromination reaction will help determine what version of bromovanillin is present.

Figure 1: Vanillin structure and Bromovanillin Isomers An electrophilic aromatic substitution reaction is one where an atom that is attached to an aromatic system is replaced by an electrophile. The atom usually replaced is a hydrogen atom. In an E.A.S. reaction there are ortho, para, and meta directors that will dictate where the electrophile attaches on the aromatic ring. In a normal bromination reaction bromine with a lewis acid catalyst is used to brominate the aromatic ring. The original reaction would use a liquid bromine, but the substance used to brominate vanillin in this lab was different. Instead of using

1 Joiner, S. L. The Bromination of Vanillin Procedure University of New Hampshire, Durham, NH, 2020

liquid to brominate the aromatic ring a mixture of potassium bromate and hydrobromic acid was used in a solution of acetic acid. This mixture is much safer compared to liquid bromine as liquid bromine produces toxic red fume that are dangerous to inhale.1 The hypothesis formed before the experiment took place was that the bromovanillin collected at the end of lab was most likely to be 5-bromovanillin. This hypothesis was formed based on the knowledge that the OH bond on vanillin is a very strong ortho para director. This meant that since the para position was already taken up that the electrophile would add onto the ortho position. This hypothesis was supported by the final product and the data collected from it.

Results and Discussion There were multiple steps required to obtain the final product in this lab. The first step was to dissolve vanillin into acetic acid and then add potassium bromate and hydrobromic acid to the solution and allow to stir for 45 minutes. This was a very critical step because this is where the electrophilic substitution is occurring. Without this step the vanillin would not react to form bromovanillin. Ice cold water was then added to the solution as the inorganic material would dissolve into that leaving the organic material, bromovanillin, in the organic layer which was then separated use vacuumed filtration. No thiosulfate was added as the mixture was already yellow. A recrystallization was done to purify the bromovanillin sample so data could be obtained from it to use for analysis of what isomer it was. Based off previous knowledge the purified product should have been white but even after the recrystallization it was yellow. Without looking at the melting point data it would just seem that the product still contained impurities, but the melting point had a very small range which indicates purity even though the actual melting point was much lower than the known melting

point of bromovanillin. The reason for this discrepancy was that the original substance provided which was thought to be pure vanillin was in fact pure o-vanillin. This is a very similar product to that of vanillin it just has a different placement of the OH group. The reaction run was also similar to the vanillin electrophilic aromatic substitution and even resulted in the isomer of 5-obromovanillin being formed. The data provided by Dr. Joiner after lab indicated that had vanillin been supplied instead of o-bromovanillin the melting point collected would have been around 166 degrees Celsius, which is that of 5-bromovanillin. Using this information as well as the provided IR and NMR spectra of bromovanillin the product was analyzed as though it was bromovanillin. The product formed in this reaction was 5-bromovanillin. This was decided by using the 1

H NMR spectra to determine placement of substituents. The IR data was not helpful in

identifying which isomer of bromovanillin as all isomers of bromovanillin have the same connections just different placements. The 1H NMR data indicates that the bromine was not placed on the meta positions as there were two points (7.65, 7.37) on the NMR that showed that there was a carbon with hydrogen bonds present there. The presence of C-H bonds there indicates that the bromine could not be there. The product formed is consistent to that of the one predicted in the hypothesis.

Experimental: Pure vanillin (0.761g) was dissolved in acetic acid (10 mL, 0.0017 m) in a 50 mL Erlenmeyer flask. Potassium bromate (0.375g 0.0017 m) and 48% hydrobromic acid (1.0mL, 0.0033m) were added into the mixture. The mixture was stirred at room temperature for 45 minutes. After stirring the mixture was poured into an 125 mL Erlenmeyer flask containing 75

mL of ice cold water and stirring was continued for 20 minutes. No 30% sodium thiosulfate solution was added. After the 20 minutes of stirring the mixture was separated using vacuum filtration. The crude product obtained from the vacuum filtration was then recrystallized. After recrystallization a yellow powder was formed and the following data was obtained: [0.820 g, 52.8% yield, MP: 128.2-129.1 degrees C, IR: 3265.91, 3008.53, 2941.99, 1672.01, 1579.94, 1043.82,675.79 cm-1, 1H NMR (440 MHz, CDCl¬3) δ 9.80 (s, 1H), 7.65 (s, 1H), 7.37 (s, 1 H), 6.46 (s, 1H), 3.99 (s, 3H)]

References 1. Joiner, S. L. The Bromination of Vanillin Procedure University of New Hampshire, Durham, NH, 2020...