Electrophilic Aromatic Subtitution 1. (3 points) What would happen if a student

Question

Electrophilic Aromatic Subtitution

1. (3 points) What would happen if a student added 0.5 mL of the Br2 solution instead of 0.75 mL? How could you find out what were the consequences? Explain.

2. (1 point) When you learned in lecture about EAS, you learned that one needs a catalyst in order to run this type of reaction. However, in our procedure we did not use a catalyst. Why do you think we could perform the reaction without a catalyst?

3. (2 points) The brominated product from the anisole reaction does not readily precipitate. Why is it essential to push this reaction “to completion” to obtain solid product?

Procedure

CHEM 242 EXPERIMENT #9-Electrophilic Aromatic Substitution Summary: In textbook discussions of electrophilic aromatic substitution (EAS) on mono- ted as activating ortholpara-directors. In this experiment the relative activating abilities of these substituents will be determined by reacting aniline, anisole and acetanilide with a bromine reagent, under uniform time and temperature conditions. The degree of bromination, and therefore activating ability, is determined from the products obtained. The products.canbeidentitied by tbe possible products. Products are of sufficient purity that they need not be After 20 minutes add 5 mL of water and 1 mL of a saturated sodium bisulfite solution to each test tube while still in the water bath and thoroughly stir contents to quench the reactions. Continue to stir until the orange solution color has disappeared (it may be necessary to use a glass stirring rod at this point, but do not cross contaminate these reactions). Replace the water bath with an ice bath and continue stirring for 10 minutes If the brominated product of the anisole reaction does not crystallize (impure samples often "oil out") ask your TA for assistance. Collect the solid products by vacuum filtration. Wash each with small portions of cold water while filtering. Dispose of all aqueous filtrates in the sink within your fume hood with dilution scaution! residual SO2 fumes). Actively dry these three solid products under vacuum for 15 minutes and obtain melting points and yields this lab period. Return the small stir bars to your TA. Any missing stir bars will be charged to your student account! substituted benzenes, the amino, alkoxy and acetamido groups are all acetamido groups are al recrystallized in order to draw accurate conclusions. Safety Notes: All starting materials and products are toxic and irritants. Aniline is a cancer suspect agent; bromine is an oxidizer; acetic acid and hydrobromic acid are corrosive. The use of gloves is recommended Identify each product by comparing your observed melting point to the literature values given below. Arrange the 3 ortho/para-directing groups in order of increasing ability to activate the benzene ring to electrophilic aromatic substitution, based upon the degree of bromination (mono, di, tri) determined in this experiment Reaction Scheme Anisole Aniline Substituents 2-Bromo 4-Bromo 2,4-Dibromo 2,6-Dibromo 2,4,6-Tribromo Br Acetanilide Br XNH,, -OCH,, -NHCOCH HBr 32 x=1, 2, or 3 145 209 232 it. mp/bp Density (g/mL) Simriutre: .ii. Uuurbp ]De:ntaity (yJinl.) %Yield o Reagent aniline anisole 122 02 C6H5NH2 bp 184°C 0.995 1.22 WASTE DISPOSAL-CHEM 242 Experiment #9 l. Aqueous filtrates [from all three reactions] rinse down fume hood sink 2. Filter paper [after removing samples] ->regular trash 3. Melting point capillaries after mp determinations] glass disposal box Typical yields of brominated products acquired through this procedure EXPERIMENTAL PROCEDURE - Students will work in pai 3. Melting point capillaries [after mp determinations]-> glass disposal box 4. Three solid samples after TA evaluation discard in solid waste Transfer 67 mg acetanilide, 54 mg (54 L) anisole, and 46 mg (45 L) aniline separately into three large, labeled test tubes. Add to each a small stir bar and 0.75 mL of glacial acetic acid. Place all three in a 100-mL beaker containing water maintained at 35±1°C (monitor with thermometer probe). Allow the solutions to equilibrate at this temperature for 10 minutes with stirring. Take the beaker and its contents over to the reagent hood and directly dispense into each test tube 0.75 mL of 2.0 M bromine in 48% hydrobromic acid. Return these to your hood and vigorously stir the reactions. Maintain the 35°C bath temperature and record observations

Explanation / Answer

The concentration of the species present at equilibrium can be determined by spectrophotometric methods. Equilibrium calculations, Equilibrium constants, reaction quotients, and the state of equilibrium and disturbing equilibrium- Le Chatelier’s principle In this experiment we will study the equilibrium properties of the reaction between iron (III) ion and thiocyanate ion: Fe3+ + SCN- [Fe(SCN)]2+ Equation 1 Metal ion + ligand metal-ligand complex ion When solutions containing Fe3+ ion and thiocyanate ion (SCN- ) are mixed, Reaction 1 occurs to some extent, forming the FeSCN2+ complex ion, which has a deep red color. As a result of the reaction, the equilibrium amounts of Fe3+ and SCN- will be less than they would have been if no reaction occurred; for every mole of FeSCN2+ that is formed, one mole of Fe3+ and one mole of SCN- will react. According to the Law of Chemical Equilibrium, the equilibrium constant expression Kc. for Reaction 1 is formulated as follows: [FeSCN2+] = Kc [Fe3+][ SCN- ] Equation 2 Overview of this experiment. In this experiment you will use 0.050 M HNO3, 0.0020 M KSCN and 0.200 M Fe(N03)3 solutions to prepare a series of solutions that contain known concentrations of [Fe(SCN)]2+ ions. From equilibrium concentrations of the absorbing [Fe(SCN)]2+ ions, the stoichiometry of the reaction (Eq. 2), and the initial concentrations of Fe(N03)3 and KSCN, the equilibrium concentrations of all species can be calculated

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