Question

1. The following synthesis of aspirin was monitored by TLC before attempting to separate the reaction mixture by column chromatography.In the TLC plates below, salicylic acid was spotted in lane A and the reaction mixture was spotted in lane B. Answer the following questions. (Note: acetic anhydride was never visualized.) H$_3$PO$_4$ OH + O OH salicylic acid acetic anhydride A. Assuming that there is no intermediate product in this reaction, at what time should the reaction be stopped? Explain why. B. Which compound is more polar, salicylic acid or aspirin? Explain your answer based on structure. C. What is one possible explanation for the second spot seen in lane B at 2 hours? OH aspirin A B A B A B A B ? 00 time = 0 hour 0.5 hour 1 hour 2 hour 2. Suppose the following compounds have the same high R$_f$ on a silica gel TLC plate, and eluting with a polar solvent. Without changing the plate or solvent, what modification could you do in order to discern the compounds by TLC? OH NH$_2$ OH

          1. The following synthesis of aspirin was monitored by TLC before attempting to separate the
reaction mixture by column chromatography.In the TLC plates below, salicylic acid was spotted in
lane A and the reaction mixture was spotted in lane B. Answer the following questions. (Note:
acetic anhydride was never visualized.)
H$_3$PO$_4$
OH
+ O
OH
salicylic acid acetic anhydride
A. Assuming that there is no intermediate product
in this reaction, at what time should the reaction
be stopped? Explain why.
B. Which compound is more polar, salicylic acid or
aspirin? Explain your answer based on structure.
C. What is one possible explanation for the second
spot seen in lane B at 2 hours?
OH
aspirin
A B A B A B A B
?
00
time = 0 hour 0.5 hour 1 hour 2 hour
2. Suppose the following compounds have the same high R$_f$ on a silica gel TLC plate, and eluting with
a polar solvent. Without changing the plate or solvent, what modification could you do in order
to discern the compounds by TLC?
OH
NH$_2$
OH

1. The following synthesis of aspirin was monitored by TLC before attempting to separate the
reaction mixture by column chromatography.In the TLC plates below, salicylic acid was spotted in
lane A and the reaction mixture was spotted in lane B. Answer the following questions. (Note:
acetic anhydride was never visualized.)
H3PO4
OH
+ O
OH
salicylic acid acetic anhydride
A. Assuming that there is no intermediate product
in this reaction, at what time should the reaction
be stopped? Explain why.
B. Which compound is more polar, salicylic acid or
aspirin? Explain your answer based on structure.
C. What is one possible explanation for the second
spot seen in lane B at 2 hours?
OH
aspirin
A B A B A B A B
?
00
time = 0 hour 0.5 hour 1 hour 2 hour
2. Suppose the following compounds have the same high Rf on a silica gel TLC plate, and eluting with
a polar solvent. Without changing the plate or solvent, what modification could you do in order
to discern the compounds by TLC?
OH
NH2
OH

Added by Roberto R.

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