Calculate the atom economy of this process. How does this compare to an alternat

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Calculate the atom economy of this process. How does this compare to an alternative procedure using [HBr + H2O2 --> Br2 2H2O] as the reagent? Really stuck on both parts of this question. PROCEDURE CAUTION: Use caution when handling the materials used in this experiment. Wear gloves and appropriate eye protection at all times during this procedure. Pyridinium tribromide is corrosive and a lachrymator. Clean up any spills immediately, especially on the balance, the metal parts of which will quickly be corroded. Br Br2 Br Place o 200 g of E-stilbene and 2 mL solvent-grade (95%) ethanol in a 10-mL roundbottom flask with a stir bar. Add 0.400 g of pyridinium tribromide to the solution, using an additional 2 mL of ethanol as necessary to rinse down the sides. Attach an air condenser and clamp the setup in place over a stirrer hot plate using a ring stand. Reflux with stirring for five minutes. The color of the solution should turn from red to yellow during this time period. Once the reaction is complete, remove from the heat Gust turn the clamp away from the hot plate) and allow to cool to room temperature. The product should begin to crystallize as the solution cools. Once the solution is at room temperature, transfer the roundbottom flask to an ice bath and continue cooling for ten minutes. Collect the product by vacuum filtration. Wash the isolated solid with a small amount of ice- cold ethanol to remove any adsorbed pyridinium salts. Once your product is dry (next laboratory period) weigh it, obtain a melting point, and collect an IR spectrum. (Ask your TA for help if necessary) OIJFSTIONS

Explanation / Answer

The atom economy for a chemical reaction is defined as

Atom economy = (mass of atoms in desired product)/(mass of atoms in reactants)*100

Consider the given reaction:

E-stilbene + Br2 -----> Desired product

Molar mass of E-stilbene = (14*12 + 12*1.008) = 180.096g/mol.

Molar mass of Br2 = (2*79.904) = 159.808 g/mol.

Sum total of molar mass of reactants = (180.096 + 159.808) g/mol = 339.904 g/mol.

Molar mass of desired product = (14*12 + 2*79.904 + 12*1.008) g/mol = 339.904 g/mol.

Atom economy of the process = (339.904 g/mol)/(339.904 g/mol)*100 = 100 (ans).

Theoretically, addition reactions give 100% atom economy since there are no by-products.

Consider the next reaction:

2 HBr + H2O2 ------> Br2 + 2 H2O

Desired mass of product (here Br2 is the desired product) = (2*79.904 g/mol) = 159.808 g/mol.

Molar mass of HBr = (1.008 + 79.904) g/mol = 80.912 g/mol.

Molar mass of H2O2 = (2*1.008 + 2*16) g/mol = 34.016 g/mol.

Sum total of mass of reactants = (2*80.912 + 34.016) g/mol = 195.84 g/mol.

Atom economy = (159.908 g/mol)/(195.84 g/mol)*100 = 81.65% (ans).

The atom economy is lower because we have water as the by-product.

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