- 1). Write the chemical equation for the reaction that takes place and balance it. Imagine, for example, that you add a Grignard reagent, methyl magnesium chloride, to acetone followed by acid-water workup. The reaction equation would be as follows:
CH3MgCl + (CH3)2CO + H2O ----> (CH3)3COH + Mg(OH)Cl
Notice first that you are not particularly concerned about the inorganic products -- as is usual in organic chemistry. What you want is the organic product you have synthesized, the tert-butyl alcohol (more properly, 2-methyl-2-propanol). - 2). Note the ratios between reactants and products in your chemical equation.
Example: The chemical equation is CH3MgCl + (CH3)2CO + H2O ----> (CH3)3COH + Mg(OH)Cl. The ratio between the Grignard reagent and acetone is 1:1, and the ratio between either of these and the product is 1:1. Therefore, for every 1 mole of methyl magnesium chloride you mix with 1 mole of acetone, you should get 1 mole of product. - 3). Determine how much of each reagent you used in your synthesis. Typically, when you perform an experiment, you will weigh or measure the quantity of reagents you use before you do so.
Example: Suppose you were able to calculate how much Grignard reagent you had from the amount of magnesium you added to the methyl chloride when preparing your Grignard, and suppose that you found you had approximately four grams of magnesium methyl chloride. Suppose that you also had 10 grams of acetone. - 4). Find the molar mass of each reactant and product by multiplying the number of times each element appears in the formula by its weight listed on the periodic table.
Example: Acetone contains three carbons, six hydrogens and an oxygen, so to find its molar mass, multiply the mass of carbon on the periodic table by 3, the mass of hydrogen by 6 and the mass of oxygen by 1, then add all these numbers together.
(12)x3 + 6x1 + 16x1 = 58 grams per mole.
The molar mass of tert-butyl alcohol is 74 grams per mole, and the molar mass of methyl magnesium chloride is 39 grams per mole. - 5). Convert the masses of reagents that you added to moles by dividing the mass of each by its molar mass.
Example: You added four grams of the methylmagnesium chloride in diethyl ether solution and 10 grams of acetone. The molar mass of methylmagnesium chloride is 39 grams, and that of acetone is 58 grams. Therefore:
4 / 39 = 0.103 moles methylmagnesium chloride
10 / 58 = 0.172 moles acetone - 6). Determine how many moles of product could be produced based on the moles of reactants present. This is your maximum theoretical yield.
Example: The ratio between the reactants in the equation is 1:1, and the ratio between each reactant and the product is 1:1. Consequently, you can only produce as many moles of tert-butyl alcohol as there are moles of reactants, and whichever reactant is present in lesser quantity will determine how much product you can theoretically produce. You have more moles of acetone than you do methylmagnesium chloride, so methylmagnesium chloride limits how many moles of product you can make. Since the ratio between methylmagnesium chloride and tert-butyl alcohol in the equation is 1:1, you can only produce 0.103 moles of tert-butyl alcohol at most. This is your theoretical yield in moles. - 7). Convert moles of maximum theoretical yield to grams (if desired) by multiplying the moles of product by the molar mass of the product.
Example: The molar mass of tert-butyl alcohol is roughly 74 grams per mole, so 0.103 moles x 74 grams per mole = 7.622 grams.
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