1. The two starting materials 1 and 2 are essentially equimolar. (Confirm this a
ID: 993332 • Letter: 1
Question
1. The two starting materials 1 and 2 are essentially equimolar. (Confirm this and show your work). How many molar equivalents of each of the following reagents is being used? (a) sodium borohydride; (b) acetic acid; (c) acetic anhydride; and (d) water (quench reaction). While you’re at it, determine the theoretical yield of the product (5). Be sure to also copy these into your reagent table. As for all calculations, please show your work!
ortho-vanillin (400mg)
4-toluidine (281mg)
ethanol (8ml)
sodium borohydride (52mg)
glacial acetic acid (1ml) Density: 1.05g/cm^3
acetic anhydride (1.5ml) Density: 1.08g/cm^3
de-ionized h2o (36ml)
2. Discuss the molar equivalents of sodium borohydride. Does this make sodium borohydride the limiting reagent? Why or why not. (a couple sentences are sufficient).
H2N OH Ar 2) precipitate using H2O OH N 4-toluidine (2) EtoH5 solventless mine 2) AcOH quench the excess NaBH4 4 ortho-vanillin (1) formation! H3CO 5Explanation / Answer
1. moles of ortho-vanillin = 0.4 g/152.15 g/mol = 2.63 mmol
moles of 4-toluidine = 0.281 g/107.15306 g/mol = 2.62 mmol
So the two starting materials A and B are almost in equimolar ratio.
moles of (a) sodium borohydride = 52 mg/37.83 g/mol = 1.37 mmol
molar equivalent to A = 1.37/2.63 = 0.52 eq
moles of (b) acetic acid = 1 ml x 1.05 g/ml/60.05 g/mol = 17.48 mmol
molar equivalent to A = 17.48/2.63 = 6.64 eq
moles of (c) acetic anhydride = 1.5 ml x 1.08 g/ml/102.09 g/mol = 15.87 mmol
molar equivalent to A = 15.87/2.63 = 6.03 eq
moles of (d) water = 36 ml/18 g/mol = 2000 mmol
molar equivalent to A = 2000/2.63 = 760 eq
theoretical yield of (5) = 2.62 mmol x 285 g/mol = 746.7 mg
2. 1 mole of Sodium borohydride has 4 hydride in it, so the molar equivalent of it with respect to starting material is lower than 1 eq. This is still not the liming reagent as 1 mole of sodium borohydride can essentially reduce 4 moles of imine product. So it is still in excess.
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