You\'re the TA compounds in an organic lab and the students are running a column

Question

You're the TA compounds in an organic lab and the students are running a column to separate the following OH trans-cinnamic acid methyl cinnamate HW 1. Student A calls you over and explains that after running his column and showing you the TLC of fractions 1-5 which only have one spot by UV. He combined these fractions, 38°C and not 133°C. How would you advise him? HW 2. Student B calls you over and explains that after running her column on a mixture of two compounds and collecting 25 fractions, the first compound has come off the column completely (eluted advise her to do to expedite the collection of the second spot? Explain your reasoning ). She's got to run to class and needs to collect the second compound. What would you

Explanation / Answer

HW1:

Since, trans-cinnamic acid contains a polar carboxyl group, the compound will adsorb strongly to the surface of silica gel. So, the trans-cinnamic acid will elude bit later than methyl cinnamate.

Methyl cinnamate is an ester compound which is nonpolar, therefore it elutes first. Therefore, the initial fraction 1-5 contains methyl cinnamate. Methyl cinnamate melting point is 34-38 oC. Hence, there is nothing wrong in the student's observation.

HW2:

There are only two compounds present in the mixture, and methyl cinnamate is eluted completely. Therefore, there is only one compound remaining on the column (trans-Cinnamic acid), so it is recommended to increase the polarity of the solvent to get the second compound. Since we have only one compound on the column, you can even wash with a pure polar solvent (ethylacetate or dichloromethane) to get the second compound faster.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.