Final lab report - Grade: A PDF

Preview

Summary

final lab report ...

Description

April 10, 2018 Sulfanilamide Synthesis Report The general goal of this experiment was to synthesize sulfanilamide over a time period of two weeks. Sulfanilamide is an important synthetic antibiotic that has saved countless lives over the course of decades. The synthesis concluded with an unsuccessful attempt to create the target molecule with 100% certainty, as displayed by the NMR and IR. Stereoselectivity is an important concept in organic chemistry; when a mechanism undergoes SN2 the stereochemistry is flipped. If the mechanism undergoes SN1 a racemic mixture is produced. LeChatelier’s Principle can be used to maximize yields by pulling or pushing the reaction to the products. For example, in the case of transforming aniline to anilinium ion, this reaction is reversible, so an excess amount of HCl will push the reaction forward. Some reactions are moisture sensitive because they may react with water and produce unwanted side products; such as the reaction with chlorosulfonic acid and water. Protecting groups are an important component of these mechanisms because they prevent unwanted reactions that lead to different products. The acetanilide created during the first part of the synthesis was required to dry because it would react with chlorosulfonic acid during the second week. If the acetanilide was still moist, the water would react with the strong acid and destroy any useful results. During the first step of the EAS reaction, the mixture had to be under cool conditions to facilitate the addition to the para position. If there was added energy in the mixture, the ortho substitution could’ve resulted from an increased energy state. Ammonia is the best nucleophile present in aqueous ammonium hydroxide due to the fact that it has a lone pair of electrons. Ammonia is favored in this mixture because it has a higher pka. In the hydrolysis of the amide, HCl reacts to form hydronium ion

and water, necessary for the hydrolysis reaction. This reaction must be heated to provide the necessary activation energy for the reaction to progress. Ultimately, amides are not very reactive to nucleophilic acyl substitution. Amide protecting groups were used in this reaction to prevent unwanted side reactions. Acetanilide was used over aniline for the EAS reaction because aniline would have done acid-base chemistry, which is faster. Nitrobenzene couldn’t have been used first because it could have also performed acid-base chemistry before EAS chemistry. For the first week of the synthesis, nitrobenzene was reduced to anilinium ion using zinc, ammonium chloride, and water. The anilinium ion then underwent a proton transfer with the addition of sodium hydroxide to aniline. Next, the aniline was reacted with acetic anhydride to be protected, transforming into acetanilide. During the second week of the synthesis, acetanilide was reacted with chlorosulfonic acid under cool conditions to create a para substituted product, then reacted under heat to form replace the alcohol group to a chloride group. This intermediate was then reacted with ammonium hydroxide to replace the chloride group with an amide group. Lastly, this intermediate was reacted with 10% HCl to undergo hydrolysis and reacted with sodium carbonate to create the sulfanilamide. For a discussion of the results, the IR and NMR provide conflicting results, indicating that there could’ve been a grave mistake made along the way of the synthesis. The IR spectrum displays several notable peaks that correlate to the expected spectrum. For example, the important peaks of the amine groups are displayed at 3475 cm-1 for the terminal amine group on the aromatic ring. The IR spectrum also displays a peak at 3381 cm-1, which correlates to the amine group connected to the SO 2NH2 group. The aromatic ring functional group was maintained through the synthesis, with peaks appearing at 1595 and 1503 cm-1. The presence of the amine groups distinguish the product from the starting materials, indicated by the downfield

peaks at 3381 and 3475 cm-1. One important missing peak in the IR is the absence of the sp2 hybridized carbon-hydrogen bond typical of the aromatic ring around 3000 cm-1. Ultimately, from the IR, one could draw the conclusion that the product was formed due to the fact of the distinguishing peaks related to the amine groups from 3300 to 3500 cm-1. The HNMR provides strikingly different results, and it’s difficult to be able to draw the same conclusion. The ideal HNMR of sulfanilamide should show four unique protons. Protons C should appear as a doublet with an integration value of 2H and should be placed around 7.5 ppm. Protons B should also appear as doublets with an integration value of 2H and should be placed around 6.5 ppm. Protons A of the terminal amine on the aromatic ring should appear as a singlet with an integration value of 2H and should be placed around 5.75 ppm. Protons D of the sulphonamide should also appear as a singlet with an integration value of 2H and should be placed around 7 ppm. The experimental NMR does not show any of these peaks. Although the NMR displays four peaks (albeit some are very near), none of them occur around the expected range. This could be due to the fact that the NMR was not prepared properly, because there was an error with inserting the material into the NMR tube. The spatula used was most likely contaminated, or the product was not pure, which is more likely. Ultimately, from the NMR, it is impossible to conclude from the spectrum if the correct product was synthesized, due to the fact that there was an obvious error with preparation of the sample. The NMR spectrum could also suggest that there were impurities in the tube, such as water at 3.296 ppm and a solvent residual peak around 2.50 ppm. Sulfanilamide has a literature melting point at 165 C, and experimentally tested at a range of 140-145 C. It is strange because that the NMR did not display the correct peaks. This was most likely due to the fact that the NMR tube was improperly prepared. The IR spectrum showed many of

the distinguishing peaks of the IR, and the melting point range was relatively narrow with a difference of 5 degrees C. The end product looked similar to what the expected product should look like. Percent yield:...