4. Why does naproxen need to be protonated before using on the TLC plates? 5. A

Question

4. Why does naproxen need to be protonated before using on the TLC plates? 5. A student spots an unknown sample on a TLC plate. After developing in hexanesiethyl acetate 50:50. heishe saw a single spot with an Rf of 0.55. Does this indicate that the unknown material is a pure compound? What can be done to verify the purity of the sample? 6. Suppose you carry out a TLC analysis of acetaminophen, aspirin and ibuprofen on silica gel using a hexane:ether 1:3 eluting solvent system. Predict what their relative Rf values would be (i.e. order them low to high or high to low, your choice, but be clear). Explain.

Explanation / Answer

ANSWER:

1) Naproxen is a salt and sats do nt rise up on silical in tlc because of strong ionic interaction between the salt and silic. Hence Naproxen should be protonated first to convert it to acid.

2)A single spot on tlc is indication of pure sample. To check the purity we can elute the sample in other solvent system which is less polar. We can also check melting point. A sharp melting point is indication of pure substnce.

3) Acetaminophen < Asprin <Ibuprofen. Becuse Acetaminophen is most pola of the three and Ibuprofen is least polar.

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