B. Experimental Procedure 1. Tribromination of Phenol Reaction: Measure 50. mg o
ID: 706433 • Letter: B
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B. Experimental Procedure 1. Tribromination of Phenol Reaction: Measure 50. mg of phenol into a a small test tube supported in a 100-mL. beaker. Add 5 mL of water to dissolve the phenol. Next add 20% bromine in actic acid solution dropwise mixing thoroughly throughout the addition. Bromine addition should be ceased once a permanent red/brown color persists. At this point, bromination is complete. Add 5-10 drops of aqueous NaHsOs with thorough miking to destroy the excess bromine. Collect the solid product via Hirsch filtration, washing the solid with 2-3 mL of cold water. Recrystallzation': After briefly air drying the solid, transfer it to a Craig tube and dissolve it in a minimum amount of hot ethanol. This is achieved by placing the Craig tube in a 100-mL beaker half-flled with water, heated to boiling. Ethanol can then be added a few drops at a time until the solid all dissolves. Remove the Craig tube from the hot water bath and allow the solution to cool slowly to room temperature at which time crystals should begin to form. Finally, place the mixture in an ice bath to complete crystallization. Collect the solid product by centrifugation. While waiting for crystallization, you can begin experiment 2 Data Collection: Determine the yield, measure the melting point, and record an IR the final product. spectrum of 2. Competitive Nitration In this experiment, you will investigate the relative reactivities of acetanilide and methy benzoate toward electrophilic nitration. Based on the experimental results, you will be able to provide experimental evidence to support your theoretical hypothesis as to which one of the two aromatic compounds is more reactive in electrophilic aromatic substitution. NH NO2 0.9 equiv. CH3CO2H or NO2 1 equiv 1 equiv NO2 The actual product will come from the more reactive aromatic starting material (methyl benzoate or acetanilide) When performing this experiment, it is imperative that a deficiency of nitric acid be used. Otherwise, once the more reactive aromatic compound has reacted away, the less reactive one will begin to react, skewing your results. The reagent table below is based on 50. mg of nitric acid, however, once you weigh out the nitric acid for the experiment, you will need to adjust the requires masses of acetanilide and methyl benzoate based on the actual amount of nitric acidExplanation / Answer
Pre-lab
1. -NH2 is an electron donating group bu resonance and therefore is a ring activator. Presence of this group makes the benzene ring electron rich and electrophilic reactions such as bromination proceeds with much ease. On the other hand, -NH3+ group with a positive charge does not have any lone pair available for resonance and is not an activator like -NH2 group. The reactivity of the Ph-NH3+ would therefore be much lower than Ph-NH2 substrate.
2. Drawn below are the resonance structures for Ph-NH2, the ortho and para position as can be seen in the picture have additional -ve charge, that is electron rich centers in the molecule and therefore, electrophilic substitution on aniline occurs at ortho/para positions.
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