These question petain to a microscale distillation in which sulfuric acid was ad

Question

These question petain to a microscale distillation in which sulfuric acid was added to pinacolyl alcohol (acid catalyzed dehydration), then the mixture was heated to 100 degrees celcius. Fractions were take from the mixture in a Hickmans still and that sample was dried over anhydronous potassium carbonate and then the drying agent was removed via filter pipet into clean collection vial and then ran through the GC machine.

1. Jeremy was the first student done with his synthesis and the first in line to use the GC. He was patting himself on the back when the chromatogram evidenced 3 peaks with relative areas that conformed to his predictions. But just before he stopped the run, a nice broad peak...peak number 4!... appeared on his chromatogram. What could it be? (It wasn’t air or water!) Explain how it might have gotten there and why it came after the other 3 peaks.

2. In the set-up for microscale distillation, the water condenser is positioned above the Hickmann distillation column where the product is being collected. In a simple or fractional microscale distillation, the water condenser is between the distillation column and collecting flask. Hmmm...why does this different microscale arrangement work? Visualize what’s happening at the molecular level and explain how your products wind up in the Hickman’s collection well. (pictures may help get your point across) What would happen if you placed the Hickman above the water condenser?

Explanation / Answer

1. In the distillation of products of pinacolyl alcohol dehydration reaction we would get 3 types of alkene product. The products were separated on the column. Some of the unreacted alcohol would be the last one to come out of the column and is seen as a broad peak in the GC spectrum.

2. When the liquid is heated in Hickmann distillation setup, the liquid boils and the vapors in equilibrium with the liquid condenses back in the collection flask of the apparatus. this process continues until all the vapor of the component is coolected at a particular temperature.

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