One of the supplements often prescribed to patients with lowered thyroid activit

Question

One of the supplements often prescribed to patients with lowered thyroid activity is a combination of iodine and tyrosine. Tyrosine is a natural amino acid, and its iodination product is a precursor to the essential thyroid hormones (thyroxines) T3 and T4: in fact, the difference in structure between T3 and T4 is the number of iodine atoms attached to the aromatic rings. In this experiment, you will synthesize a thyroid hormone precursor analog via an electrophilic aromatic substitution reaction. Unfortunately, elemental iodine is a controlled substance (see Breaking Bad for why), so we will use an alternate method of halogenation, whereby we will brominate a substituted phenol with copper (II) bromide. You will synthesize bromo-4-tert-butylphenol, analyze the regioselectivity of your reaction by 'H NMR spectroscopy and compare the NMR spectrum with that of natural lodotyrosine. The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read these and answer the following questions: Which chemical is the most dangerous in this lab? Explain why you chose your answer for ), and the safety precautions you will take when handling this material. Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactive materials. Based on your answers to Q2, which is the limiting reagent in this reaction? Calculate the Theoretical Yield of your product, i.e. the mass you would expect to recover, assuming 100% conversion to product.

Explanation / Answer

1 a) Acetonitrile CH3CN

b) The safety ratings as per MSDS for CH3CN: Health 2, Flammability:3 while for 4-tert butyl phenol: health : 2, flammability : 1 and for CuBr2: Health : 2 and flammability : 0.

Precautions: Since the material is highly flammable, it should be kept away from heat and sources of ignition. The fumes should not be ingested. Contact with skin and eyes should be avoided.

2)

3) Limiting reagent is 4 tertbutylphenol since this is the reactant which will run out first.

4) Theoretical yield: Mass of product = 1.66 * 10^-3 moles * 229 g/mole= 0.380 g

Name Formula mol-eq mol wt mmol amount 4-tertbutylphenol C10H14O 1.00 150. 1.66*10^-6 0.250g copper(II)bromide CuBr2 3.00 223 4.93*10^-6 1.10g Acetonitrile - - - - 3 ml Product C10H13BrO 229

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