Question

Reduction of Ketone

During this experiment we had to reduce 9-fluorenone to 9-fluorenol. We took pure fluorenone and fluorenol and mixed with acetone then spotted them on lanes one and two on our TLC plate. We then took 9-fluorenone and and mixed with methanol, and began mixing. We then spotted the methanol fluorenone mixture on our TLC plates in different time intervals, lane three 0 seconds, lane four 30 seconds, lane five 60 seconds, lane six 120 seconds, lane seven 240 seconds, and lane eight 600 seconds. We then took the resulting mixutre and dumped some water in it and two seperate layers appeard in the beaker. I just need some help on what I saw in the experiment and what the TLC reustls mean.

1. what is the purpose of adding the water to the methanol fluorenone mixture after mixing?

2. what is causing the difference in colors in the beaker after the water has been added?

3. Did the reaction go to completion, how do I know?

4. At which point did we know producct began to appear?

5. How did the final compound differ from the reaction solution before adding water?

6.What spots during the procedure did we potentially lose material?

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Answer 1

Ans:

The reduction 9-fluorenone in methanolic sodium borohydride takes place as per the below reaction in two steps.

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Q-1:     What is the purpose of adding the water to the methanol fluorenone mixture after mixing?

Ans-1: As seen in the above reaction, the water react with the intermediate and forms the final product, 9-fluorenol.

Hence, addition of water brings the reaction to full completion and also the solid final 9-fluorenol separates

out as a solid from the reaction mass, which can be filtered easily from the reaction mass.

Q-2:     What is causing the difference in colors in the beaker after the water has been added?

Ans-2: The starting material and the intermediates are yellowish in color, and when reacts with the water, forms the final product alcohol, which is colorless.

Q-3:     Did the reaction go to completion, how do I know?

Ans-3: No, it did not go to the completion, as we have seen that the starting material 9-fluorenone was still present in the reaction mass even after 600 seconds.

Q-4:     At which point did we know product began to appear?

Ans-4: At 30 seconds (lane-4) we can see the product spot appearing in the TLC run.

Q-5:     How did the final compound differ from the reaction solution before adding water?

Ans-5: The final compound is insoluble in methanol-water mixture. The reaction solution has the negatively charged intermediate as shown the above reaction.

Q-6:     What spots during the procedure did we potentially lose material?   

Ans-6: Between lane 5 and lane 6 (60 seconds – 120 seconds), the starting material spot (9-fluornone) is relatively bigger than the product, could be the spot,

where we might have lost some material.