Predict the order of elution of a mixture of triphenylmethanol, biphenyl. benzoi

Question

Predict the order of elution of a mixture of triphenylmethanol, biphenyl. benzoic acid, and methyl benzoate from an alumina column. (Williamson, Q. 1) What would be the effect of collecting larger fractions when carrying out the experiments in this chapter? (Williamson, Q. 2) What would have been the result if a large quantity of petroleum ether alone were used as the eluent in this experiment? (Williamson, Q. 3) Once the chromatographic column has been prepared, why is rt m port ant to allow the level of the liquid in the column to drop to the level of the alumina before applying the solution of the compound to be separated? (Williamson, Q. 4) Which column packing method did you use for this experiment? What is an alternate way of packing a column?

Explanation / Answer

1. Separation of the given compounds elution order would be,

First eluted

biphenyl

methylbenozate

triphenylmethanol

benzoic acid

Last to elute

2. Collecting larger fractions may result in compounds getting eluted be contaminated with each other insetad of pure compound in the fractions.

3. Petroleum ether is non-polar solvent, so larger portion of its use would give give only the non-polar compound elute out of the column. The other compounds would not come out of the system.

4. If the level of solvent is not dropped to level of alumina, the compound mixture would get diluted in the solvent and it would form a larger band on the column which would take longer time to separate.

5. Column packing method is suspend alumina in petroleum ether and pour into the column. One may pour solid alumina first and then pour solvent and let it pass with a mild inert gas pressure from the top.

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