please answer the following pre-lab questions for Electrophilic Aromatic Substit
ID: 479690 • Letter: P
Question
please answer the following pre-lab questions for Electrophilic Aromatic Substitution: Iodination of Salicylamide Lab:
Pre-lab Questions
1. What types of directors are present on salicylamide?
2. Predict the most likely site of iodination of the salicylamide ring and explain your prediction. Determine how each product will differ in its IR spectrum.
3. What is the limiting reagent in this procedure for the iodination of salicylamide?
Iodination of Salicylamide
(GEMs: http://greenchem.uoregon.edu)
Under electrophilic aromatic substitution reactions, H on a benzene ring is replaced by the electrophile. Substituents present on the ring determine where the incoming electrophile substitution occurs. Electron-donating groups direct incoming groups ortho and para whereas electron-withdrawing groups direct incoming groups meta.
In this experiment, we will study the directing effects of a pair of substituents on a single aromatic ring. Salicylamide (see structure below) is a component of some analgesics.
The electrophile that will be used is formed from the reaction of sodium hypochlorite (NaOCl, bleach) with iodide ion. The I+ ion formed in this reaction is a strong electrophile that reacts quickly in an electrophilic aromatic substitution reaction.
H2O + NaOCl + I- I+ + Na+ + HO- + Cl-
Determining Substitution Patterns using IR
The fingerprint region of the IR is instrumental in determining the substitution pattern of benzene rings.
The following table can be used to determine these patterns:
Ring Substitution Pattern
Expected peaks (cm-1)
Monosubstituted
770-715 (strong)
1,2-Disubstituted
770-730 (strong)
1,3-Disubstituted
820-760 (strong)
1,4-Disubstituted
870-800 (strong)
1,2,3-Trisubstituted
790-750 (strong)
1,2,4-Trisubstituted
850-800 (strong)
1,3,5-Trisubstituted
910-830 (strong)
Experimental Procedure
1.Add approximately 1 g of salicylamide (record the actual mass) to a 100-ml round-bottom flask. Dissolve the salicylamide in 20 ml of absolute ethanol, warming the flask with your hand to speed up the dissolution.
2.Once the salicylamide is completely dissolved, add 1.2 g of sodium iodide (NaI) to the reaction mixture, stirring with a spatula until the solution is homogeneous.
3.Place the 100-ml round-bottom flask into an ice bath (ice + water). When the reaction has (about 5 minutes), remove the reaction vessel from the ice bath and quickly add 9.2 ml of 6% (w/v) sodium hypochlorite solution (ultra strength household bleach). Swirl the flask vigorously to completely mix the contents. The solution will change colors from the initial clear reaction mixture to a dark-red brown to increasingly lighter shades of yellow. When the solution reaches a faint, pale yellow color, the reaction is complete. (Typically, this takes less than 5 minutes.) Allow the reaction vessel to sit on the benchtop undisturbed for 10 minutes.
4.Add 10 ml of 10% (w/v) sodium thiosulfate to the reaction solution and swirl the flask until the contents are thoroughly mixed.
5.Acidify the reaction by slowly adding 10% hydrochloric acid. Monitor the acidity of the solution using litmus paper. You will notice a white solid beginning to form in the reaction vessel. At this point, the pH of the solution is near the desired acidity. Continue adding 10% HCl, but carefully monitor the acidity.
6.Once the mixture is acidic, filter precipitated product using vacuum filtration. Collect the precipitate and recrystallize from a minimum amount of 95% ethanol. (After the recrystallization mixture has cooled to room temperature, place it in an ice bath for 15 minutes to complete recrystallization.)
7.Filter recrystallized product; continue to vacuum filter until crystals are dry. Determine the mass and % yield of dried product.
8.Determine the substitution pattern by running an IR using the ATR attachment. See instructor for instructions on using the ATR.
Ring Substitution Pattern
Expected peaks (cm-1)
Monosubstituted
770-715 (strong)
1,2-Disubstituted
770-730 (strong)
1,3-Disubstituted
820-760 (strong)
1,4-Disubstituted
870-800 (strong)
1,2,3-Trisubstituted
790-750 (strong)
1,2,4-Trisubstituted
850-800 (strong)
1,3,5-Trisubstituted
910-830 (strong)
Explanation / Answer
Electrophilic aromatic substitution of salicylamide with iodine
1. Salicylamide has -OH group as the directing group which is an ortho and para directing group.
2. The most likely products of this reaction would be, 6-iodo-salicylamide and 4-iodo salicylamide. In the IR, 6-iodo salicylamide would show strong peaks in region 750-790 cm-1. Whereas, 4-iodo salicylamide would show peaks in the region 800-850 cm-1 region.
3. The limiting reactant here would be salycylamide. Iodide is in excess.
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