Aniline Synthesis

Abstract – This multi-step synthesis uses aniline as the starting reagent to synthesize five compounds employing several reactions such as acetylation, diazo coupling, nitration, bromination, and hydrolysis. The isolated products were analyzed with TLC and spectral data that determined most products were pure while some had a few impurities indicated by GC, LC, and a wide melting point range was shown for products 2 and 3. The presence of water in product 2 and 7 was indicated by the IR. Acetanilide and diazoaminobenzene had good yields compared to the other products with low-moderate yields.
Introduction:
The purpose of this lab is to develop problem solving skills needed to scale synthetic procedures for five products derived from aniline.
Results: Product 1 was white having a 67.5% yield, both product 2 and 3 were yellow with a 28.5% yield and 4.2% yield respectively, product 7 was white with a 42.5% yield, and product 8 was golden with a 78.7% yield (Table 1). Refer to Figure 1 for TLC plates and Table 1 for the isolated products’ associated melting point ranges, IR, MS, and 1H-NMR data. The mechanisms for each synthetic step is presented in Scheme 1 to Scheme 5. Refer to Scheme 6 for the general scheme with possible side products.

Discussion: The observed color for all the products matched the literature, product 1 being white, product 2 and 3 as yellow, product 7 stated to be white, and product 8 being golden.5 Experimental melting point ranges were narrow (~1-2oC) and within the literature values for product 1 measured as 116-117.4oC close to acetanilide (114oC), product 7 melted at 165.8-168.1oC matching p-bromoacetanilide (165-169oC), and product 8 had a range of 95.8-96.9oC corresponding to diazoaminobenzene (98oC).5 These small ranges indicate high purity as the crystal structure of each is well-preserved,
The range for acetanilide is slightly higher than expected likely due to loading slightly too much sample or insufficient packing. The other two products had a wide and depressed melting point range, product 3 melted from 136.6-148.1oC was lower than expected of the p-nitroaniline (148.5oC) and product 2 had a range of 90-103.3oC was significantly depressed from the expected p-nitroacetanilide (212-215oC).5 For product 3, this large range suggests impurities such as reagent remaining from product 2. For product 2, it is likely that the alternative ortho product was made to a larger portion, note o-nitroacetanilide melts at 90-94oC.5 Scenarios where the o-nitroacetanilide is synthesized with high yields is when acetyl nitrate attacks by a proposed reagent-substituent coordination between the amide and nitrate.3 Acetyl nitrate is typically generated from HNO3 and acetic anhydride, however it is suspected acetic acid with HNO3 caused its formation.3 Large excess of acetic acid was used to dissolve the acetanilide as it was challenging to dissolve in glacial and 10% acetic acid. In future experiments, I recommend refluxing to better dissolve the reagent in a