Lab report Electrophilic Aromatic Substitution PDF

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Summary

Lab Report 5 of CHEM 238...

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Electrophilic Aromatic Substitution: Iodination of Salicylamide

Mechanism: Iodination of Salicylamide (meta attack):

Iodination of Salicylamide (para attack):

Procedures: Procedures in lab manual should be sufficient. Data Table: Reactants Salicylamide Sodium Iodide

MW 137.14 g 149.9 g

Products Crude Recrystallized Crude

Amount Used 1.029 g 1.20 g

MW 263.03 g/mol 263.03 g/mol

Mol .00750 mol .00801 mol

Amount Obtained 2.405 g .009 g

Mol Equivalent 1 1 % Yield 122% .4% (%recovery)

Results and Discussions:

Iodination is an example of electrophilic aromatic substitution. The purpose of this experiment was to demonstrate the regiochemistry of electrophilic aromatic substitutions for the iodination of salicylamide. In other words, observe substitution patterns when reacting salicylamide with ethanol, sodium iodide, and sodium hypochlorite. Although salicylamide is used to make analgesic, antipyretic, antirheumatic drugs and other pharmaceutical products, we used it as a reactant to produce iodosalicylamide. Salicylamide has two functional groups substituted on two adjacent carbons of a 6 carbon benzene ring; a hydroxyl and an amide group. To accurately design an experiment involving an electrophilic substitution reaction performed on salicylamide, several factors must be considered. One factor is the relative rate of the reaction. The substituent group

that decreases the reaction rate relative to the reaction rate of salicylamide is called the deactivator. Deactivators withdraw electrons and decrease the electron density of the aromatic ring. The amide group attached to salicylamide is a meta directing electronwithdrawing group that can withdraw electrons from the ring either by resonance or by induction. This can occur because the amide group is highly electronegative. Pi bonds that overlap a p orbital on the substituent with the pi system of the aromatic ring cause resonance electron-withdrawing effects. Most resonance withdrawing groups have a positive or partially positive atom directly connected to the ring. A substituent group that increases the relative rate of a reaction is called an activator. Activators can donate electrons to the aromatic ring in either of two ways, thus increasing the electron density of the aromatic ring. Most activators donate electrons by resonance. Resonance donators have a lone pair of electrons on the atom directly connected to the ring. These electrons overlap with the pi cloud of the aromatic system. The OH is the activating/ resonance donator in this experiment. It is also ortho and para directing. Sodium hypochlorite is an oxidizing agent of the iodine atom. We started off our experiment with 20ml of absolute ethanol to dissolve 1.029g salicylamide. The salicylamide dissolves in ethanol because ethanol forms enough hydrogen bonds with both hydroxyl and amide group of the salicylamide to make it soluble in ethanol. We then added 1.20g of sodium iodide and allow it to cool in an ice bath for 5 min. Iodine is the least reactive of the halogens. By itself, it is unreactive towards aromatic rings; it requires oxidizing agent such as ethanol or sodium hypochlorite solution to speed up the reaction. After the flask has cooled off we then quickly added 9.5mL of 6% sodium hypochlorite solution. Sodium hypochlorite is used to oxidize sodium iodide, which contributes its iodine atom to the aromatic ring product. The iodine ion formed in this reaction is a strong electrophile that reacts quickly in an electrophilic aromatic substitution reaction. We observed a mixture with a yellow bottom layer and a top layer that looked like a mixture of orange and red. After mixing it went from a light orange to yellow and then finally a pale yellow. Precipitate was then observed. This occurred after the iodide is attached to the salicylamide. The sodium hypochlorite solution deprotonates the hydroxyl group on the salicylamide and the hydrochloric acid adds the H back on, forming a solid. Sodium thiosulfate was then used to remove any residual iodine from the solution. It acted as reducing agent and reduced iodine to sodium iodide and stops the reactivity towards electrophilic substitution, which can be easily removable in water wash. Th i so c c u r st h r o u ghar e d o xr e a c t i o ni nwh i c h t h i o s u l f a t ei so xi d i z e dt ot e t r a t h i o n a t ea n dI o di n ei sr e d u c e dt oi o di d e . After we added hydrochloric acid to the solution it formed a white precipitate. The electrophilic aromatic substitution proved to be an effective way of observing substitution aptterns in the iodination of salicylamide, but we only had the IR to show for it. Our crude product percent yield was 122%, while our percent recovery was .4%. Our high yield was due to water weight. We allowed it to dry for 30 minutes and it did not seem to make a difference. We recrystallized our crude with hot ethanol. Although our crude looked similar to other groups in out bay, we had barely any recrystallize crude to compare with other groups. It lead us to believe we made an error during the

recrystallization phase of this experiment. The low yield also be associated with the leftover amount of impurties left in the product. Upon inspecting the IR spectra from small sample of our final produce, we determined the iodine would be substituted at two positions, ortho and para to the hydroxyl group of the salicylamide. The major being the para position and the minor being the ortho position. By comparing the IR spectras of salicylamide and iodosalycilamide, the iodosalicylamide IR showed a peak at 847.13 cm -1 and 778.70 cm-1, which indicates that our product had molecules that exhibited 1,2,4 carbon substitution and others that showed 1,2,3 carbon substitution. The first point corresponds to the para substitution while the other suggests product with ortho substitution. The peak observed at 847.13 cm-1 was deeper than that at 778.70 cm-1; indicating that the para posistion had a better yield than the ortho substitution in our sample. Para subsitution may be favored as there is less steric hindrance when the salycilamide attacks NaI allowing better addition of Iodine. Conclusion: Overall the iodination of salicylamide using electrophilic aromatic substitution was a success. The percent yield obtained from the crude was 122% with a % recovery of .4%. As predicted in our prelab questions the substitution pattern obtained was simillar to the one with the absoption of 800-850cm-1. The analysis of our IR spectra showed the iodine substituion favored the position ortho and para to the hydroxyl group. The para position being the major....