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Phosphoric acid catalyst

Discussion: Dehydration of cyclohexenol to cyclohexene is unfavorable reaction. Cyclohexanol is the organic compound that is related to cyclohexene ring by replacement of one hydrogen atom by a hydroxyl group. Hydroxyl group is a very poor living group, so hydroxyl group need to be converted to a better living group in order to undergo the reaction. Phosphoric acid is a strong acid that protonated hydrogen atom to the hydroxyl group to make better living group, H2O. Cyclohexene is more volatile than cyclohexanol, so the mixture is heated in order to change the equilibrium to collected cyclohexene by a fractional distillation.

The distillate is not pure cyclohexene (B. p 83 ? C) from first distillation because it has lower and broader boiling point (71? C? C -78 ? C). Water, cyclohexanol, some remaining phosphoric acid and some impurities in the crude removed by washing the crude with water and adding the drying agent, CaCl2. If excess water or phosphoric acid is present in the crude, equilibrium will change to a favorable direction since dehydration is a reversible reaction. Higher and narrower boiling point range (80? C – 82?

C) of cyclohexene from second simple distillation implies that more purified cyclohexene collected compared to the crude. The ratio of the area of the cyclohexene is higher than cyclohexanol on the GC analysis which supports that dehydration of cyclohexanol is driven. Also, the calculated percent of purity of cyclohexene (96%) proves that dehydration of cyclohexanol is driven to a relatively pure cyclohexene. Low percentage of recovery (24. 4%) happens due to loss mainly by spilling the crude when it is submitted to the GC analysis.

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