Bromination of Acetanilide Objectives:a) To Perform an Electrophilic Aromatic Su

Question

Bromination of Acetanilide Objectives:a) To Perform an Electrophilic Aromatic Substitution b) To collect & analyze the product. p-bromoacetanilide. Introduction Electrophilic aromatic substitution reaction involves the reaction between an aromatic ring, which serves as a source of electrons, and a positive or partially positive electrophile. The general reaction and mechanism is very similar to the nitration lab, except there is a different nucleophile. Be sure your lab write-up shows the formation of the electrophile. When the electrophile adds to the electron rich ring, a benzene carbocation is formed. The Nucleophile extractes the hydrogen which promotes the formation of the product. Acetanilide is an ortho-para director. Para is the major product because the acetamide group sterically hinderes the ortho attack. Formation of the ortho product would be a side reaction. Formation of 2,4-dibromoacetanilide is also a side reaction. Include both of these side reactions in your lab report. rRany 166-7 -169.1 The general reaction for this lab is as follows; + H-Br Procedure Initiate the reaction. This procedure is to be carried out in the hood. Place 1.25 grams of acetanilide in 7.5 mL of glacial acetic acid in a 50 mL Erlenmeyer flask. To this solution, slowly add with constant swirlingand shaking mL ofa 33%bromine solution. Cool the reaction in an ice bath if the mixture is warmer than room temperature. When the addition is complete, let the mixture stand in the hood for ten minutes with occasional shaking. Pour the reaction mixture into 35 ml of cold water in a 100 mL. beaker. Discharge an orange or yellow-brown color by the dropwiseaddition of20%sodiumbisume with stirring. Collect the crystals on a Hirsch funnel using suction (this may be done outside the hood); wash then with 5-10 drops of cold water, and allow the crystals to dry. Chemistry 223 Organic Laboratory, "Bromination of Acetanilide" Electrophilic Aromatic Substitution

Explanation / Answer

In the given eelectrophilic aromatic bromination reaction

1. Ortho isomer is the other minor product. meta-isomer is the least formed product

2. -NH2 is electron donating group and activated benzene ring, thus we get trisubstituted product. -NHCOCO3 is a weaker electron donating group (lone pair of N is delocalized in C=O group) and thus we get only monosubstituted product.

3. -NHCOCH3 is a weak electon donating group which activates the ortho/para position of the ring and thus we get ortho/para product.

4. Br2 by itself does not react with acetanilide as other alkenes does in addition reaction. Insetad presence of FeBr3 lewis acid catalysts is a must for Br2 to react in a substiution fasion with acetanilide. This proves substitution and not addition has occured.

5. excess bromine is removed by bisulfite NaHSO3

reaction,

NaHSO3 + Br2 + 3NaOH --> Na2SO4 + 2NaBr + 2H2O

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