Experiment 6 Iodination of Salicylamide

CHEM 21 March 2022 EXPERIMENT 6: IODINATION OF SALICYLAMIDE DATA Mass Salicylamide (g) Final Product Mass (g) Product Melting Point (°C) Percent Yield (%) 1.011 0.627 244 - 245 32.33 Table 1. Pertinent data points collected for the iodination of salicylamide. Figure 1. IR spectrum of the final product, along with its enlarged fingerprint region. Wavenumber (cm-1) Associated Properties 815.09 1,2,4-trisubstituted aromatic ring 778.74 Weak 1,2,3-trisubstituted ring indicator 1221.50 Secondary alcohol indicator 3203.12 Aromatic C—H stretch 1674.12 Secondary carbonyl connected to an amide Table 2. IR spectrum analysis and property assignments of pertinent peaks and wavenumbers. SUMMARY In this experiment, an electrophilic aromatic substitution (iodination) reaction was performed on the aromatic compound salicylamide, and its final product was characterized through means of IR spectroscopy analysis, and acquisition of the product yield and melting point. DISCUSSION As aforementioned, this experiment features an electrophilic aromatic substitution, which is a versatile reaction with many uses. The reaction mechanism features the replacement of a proton around the ring with an electrophile, resonance delocalization of the cationic intermediate, and deprotonation of a hydrogen on the same site as the electrophile (by a base of some sort) in order to regenerate aromaticity of the ring. Reactions that operate on this general mechanism include halogenation, sulfonation, nitration, and (Friedel-Crafts) alkylation and acylation. Where the electrophile decides to attack in the first step depends heavily on the substituents around a benzene ring. Substituents can operate as ortho-, -para- or meta activators, or deactivators. Activators render an aromatic compound more reactive to electrophiles (usually electron donating groups), while deactivators quite predictably do the opposite (usually electron withdrawing groups). Ortho-directors will direct an electrophile to attack in the position ortho to—one placement away from— the substituent of interest. Para- directors will cause the electrophile to react para to said substituent (three placements away), and meta- directors cause the electrophile to react in the meta- position relative to the pertinent substituent (two placements away). Figure 2. Examples of how ortho-, para- and meta- positions would appear in an electrophilic substitution reaction. (Note: the arrows do not indicate a flow of electrons. They simply indicate electrophile placement.) The structure of salicylamide features an alcohol group and an amide. Alcohol groups are incredibly strong ortho- para- activators, while amides tend to be strong meta- deactivators due to the carbonyl group. In an electrophilic aromatic substitution, the substituent with the highest level of activation will dictate the placement of the electrophile. Hence, because the alcohol is the most strongly reactive substituent, the electrophile will place in positions ortho and para to the alcohol group as follows: Figure 3. Portrayal of possible positions of electrophilic attack by the electrophile on salicylamide. The general mechanism of the reaction of interest for this experiment proceeds as follows: Figure 4. Mechanism for the iodination of salicylamide. Ortho and para products can be formed; para product formation is depicted. A common first step to electrophilic aromatic substitutions is the generation of an electrophile. In the experiment, sodium hypochlorite and sodium iodide reacted in a redox reaction to form the electrophile I+. Salicylamide was then added to the mix and iodinated. Excess hypochlorite ions in the reaction were removed with the use of sodium thiosulfate, and hydrochloric acid was used to restore neutrality to the basic reaction mixture caused by hydroxide ions present in reaction. Neutrality in the reaction mixture was vital to reach in order to collect the precipitate product later on. The solid product was finally collected via vacuum filtration. From the IR spectrum obtained, the product of the iodination reaction (iodosalicylamide) can be identified as a 1,2,4-trisubstituted benzene ring. Such an observation confirms that the major product resulted from the iodine cation attacking the position para to the hydroxyl group on salicylamide. It is of interest to note that the spectrum also exhibited weak peaking indicative of a 1,2,3-trisubstituted ring, which would mean that some product possibly featured the iodine in a position ortho to the hydroxyl group. The IR spectrum also confirms that the other two substituents of salicylamide remained preserved in the reaction (i.e. no reaction occurred to alter the hydroxyl and amide groups). The final melting point obtained confirms the purity of the final product, as it is almost identical to that of the literature value recorded for iodosalicylamide (244 - 246 °C). Decimal values to the tenth’s place of the melting point were unable to be obtained however, due to technical difficulties concerning the temperature readers used in the experiment. Thus, further accuracy was unable to be observed. The yield of the reaction can be considered poor, with less than half of the product recovered (refer to table 1). Therein lies the possibility that some amount of final product was lost at some point during the vacuum filtration process, be it through evaporation or through previous fractions collected and not identified as the product. The iodination of salicylamide’s reaction occurs in a 1:1 mole ratio. Hence, the percent yield was converting the initial mass of salicylamide into a molar value, and performing the appropriate molar conversion in order to determine the theoretical yield of iodosalicylamide. This mass was then divided with the actual yield and multiplied by one hundred to obtain the percent yield (1.011/137.136 = 0.007372 * 263.03 = 1.939 g; [0.627/1.939]*100 = 32.33%). CONCLUSION Overall, completion of objectives was accomplished successfully. Iodination of salicylamide and collection of its pure product was successfully achieved with minimal obstacles. The product collected was also accurately analyzed for its structure with the acquisition of the IR spectrum, and the melting point found for the final product also corroborated the identity of the product as the one intended. The IR spectrum (and its fingerprint region in particular) was vital in understanding the composition of the final product, and the fact that such wealth of information was gauged from the collected spectrum further cements the viability of the final product collected. Finally, while the yield was not as high as one could hope for, the acquisition of some of the theoretical final yield still confirms a slightly successful performance of pure product isolation and collection.