[lbr9349]

Fischer Esterfication of Benzocaine from p-aminobenzoic acid

1. Is p-aminobenzoic acid the limiting reagent?
2. If so, is it a 1:1 ratio for benzocaine? How do I determine the ratio?
3. If it is 1:1 ratio, would my theoretical yield be 0.54g of benzocaine?
(If I started with 3.31x10^-3 moles of PABA then I should get 3.31x10^-3 moles of benzocaine, which is 0.54g)

Info about reagents used:

p-aminobenzoic acid
Amt used: 0.50g
Molecular weight: 137 g/mol
Moles: 3.31x10^-3

Benzocaine
Amt retrieved: 0.72g
Molecular weight: 165 g/mol
Moles: 4.36x10^-3

Other Reagents
Etoh (6.5mL)
H2SO4 (0.5ml)
Sodium Carbonate 2M (approx 7mL)

[zengjia1029]

Hi, I am very puzzled about the result! Why can you obtained more the ester than the theoretical amount, and if so, the yield will exceed 100%.

[sHaY]

Start by writing a balanced equation.
Yes PABA is your limiting reagent because your using excess of ethanol.
yes it is 1:1 ratio (Balanced equation...)
I would recheck your theoretical yield calculation.

Did you weight the product when it was dry?  

[lbr9349]

Well there was a problem in the experiment, no one in the lab was successful with the experiment and the instructor is still trying to figure out what went wrong.

[lbr9349]

How is my calculation incorrect?

If the limiting reagent is A and the amount is #moles....Isn't the product B the same number of moles if it is a 1:1 ratio?

[sHaY]

(0.5g)/(137g/mol) = 3.65x10^-3