(1 point) Draw the structure of the precipitate that forms upon addition of the
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(1 point) Draw the structure of the precipitate that forms upon addition of the sulfuric acid to the p-aminobenzoic acid and ethanol. 5. 6, (2 points) Why is it necessary to use 95% ethanol and water to recrystallize the product, rather than just 95% ethanol? 7. (2 points) List two important differences you would expect between the IR spectra of p-aminobenzoic acid and benzocaine. (2 points) List hwo important diferences you would expect between the 1H NMR spectra of p-aminobenzoic acid and benzocaine. 8. (2 points) How many signals would you expect in the 13C NMR spectra of p- aminobenzoic acid and benzocaine? 9. p-aminobenzoic acid benzocaineExplanation / Answer
5. P-amino benzoic acid reacts with H2SO4 in presence of ethanol and forms white precipitated salt( HO2C-C6H4-NH3+ HSO4 -). NH2 groups becomes NH3+ HSO4-.
6.Recrystallization means recrystallized the solid product and purify it from any other impurities. So it necessary to mix solvents for recrystallization. If we use only 95% ethanol then all the product along with impurities dissolved and we can't purify it. Instead, by using 95% ethanol and water we can separate pure product from impurities and recrystallized the pure product.
7. i. P-amino benzoic acid has carboxylic acid group, so it gives broad peak in the range from 2500-3300 cm-1 because of -OH group of carboxylic acid. But benzocaine has ester group, not acid group, so there is no such peak.
ii. C-O stretching absorption band appears near1250 cm-1 for p-amino benzoic acid. But in case of benzocaine, two C-O stretching absorption peak appears near1250 cm-1 and 1050 cm-1..
8. i. In case of p-amino benzoic acid, there are a peak near 12 ppm for carboxylic acid hydrogen. But this peak is absent for benzocaine.
ii. There are a peak near 3.8 ppm for two hydrogens due to two hydrogens which is attached with a carbon that is directly attached with oxygen atom of ester group. And also three hydrogens near 2 ppm for sp3 hydrogens( CH3 of -O-CH2CH3 group) in case of benzocaine. But there is no such peak in case of p-amino benzoic acid.
9. There are total 5 signals for p-amino benzoic acid( four for symmetrical aromatic carbons, one for carboxylic acid carbon).
There are total 7 signals for benzocaine( four for symmetrical aromatic carbons, one for carboxylic acid carbon, two for ethyl part of ester group).
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