Question

6. Write the theoretical yield calculations for this reaction

In the laboratory The essential reactants guaifenesin synthesis are provided in Table 1. Table 1. Compound 2-methoxyphenol bp (°C) Reactants used amount used mmol 550 L calculate MW 124.14 d (g/mL) 1.13 NaOH (25% soln.) 40 1 mL ethanol 46.07 18 water Sodium sulfate (+)-3-chloro-1,2- propanediol 142.04 110.54 500 uL calculate 1.32

Answer 1

The reaction is

    [ 2-methoxy phenol] + [3-chloro 1,2 propanediol] $\rightarrow$        [guaifenesin] + [HCl]

   m.wt in mg / mmol            124.14                    110.54                                       198.23    36.5

Initial amount taken             550 $\mu$ L                     500 $\mu$ L    

   =   621.5 mg       = 660 mg

   = 5 mmol = 5.97 mmol    0 0

final quantity 0 0.97 mmol 5 mmol    5 mmol

The amount of 2 methoxy phenol taken = 550 $\mu$ L

since the density = 1.13 g / mL = 1.13 mg $\mu$ L    since 1 g / mL = 1000 mg / 1000 $\mu$ L = 1 mg / $\mu$ L

molecular wt of 2 methoxy phenol = 124.14 g / mol = 124.14 mg / mmol                                                             [since 1 g / mol = 1000 mg / 1000 mmol = 1 mg / mmol ]

therefore the amount of 2 methoxy phenol taken = 550 $\mu$ L x 1.13 mg / $\mu$ L / 124.14 mg / mmol

= 5 mmol

Similarly the amount of 3 chloro 1,2 propandiol taken = 500 $\mu$ L x 1.32 mg / $\mu$ L / 110.54 mg / mmol

    = 5.97 mmol

As per the equation, the stoichiometric ratio of the reactants = 1. Thus the reagent which is less no of moles will be completely consumed in the reaction and hence that is the limiting reagent. Here the limiting reagent is 2methoxy phenol.

[ limiting reagent is that reactant which gets completely consumed in the reaction. The quantity of product formed based on the quantity of this limiting reactant]

Thus the amount of product formed = 5 mmoles

The molecular mass of guaifenesin = 198.23 g /mol = mg / mmol

and hence the quantity of guaifenesin formed = 5 mmol x 198.23 mg / mmol = 991.15 mg

Thus the theoretical yield of formation of guaifenesin = 991.15 mg

ON ОСН3 2 methoxy phenol OH OH I NAOH - Etory 3-chloro 1,2, propanediol (M. Wt 11054) 500 ML 660 mg 5.97 mmol (Mont 124.14) 550ML 621-5 mg 5 mona) (limiting reagent) Guaifenesin 5 mmol m.wt = 198.23 991-15ing