I. Pre-Lab Report
A. Introduction
The purpose of this experiment is to analyze the products of the dehydration of 2-methylcyclohexanol using gas chromatography. Dehydration of the 2-methylcyclohexanol will take place via distillation with sulfuric acid on a microscale level to yield 1-methylcyclohexene and 3-methylcyclohexene. The proportions of these two products will then be determined by analyzing the graphs produced by a gas chromatograph.
B. Main Reaction
2-methylcyclohexanol + H2SO4 = 1-methylcyclohexene + 3-methylcyclohexene + H3O+
C. Mechanism
The reaction took place via an E1 mechanism. Refer to the attached sheet.
D. Side Reactions
There were no side reactions.
E. Table of Reactants and Product(s)
| Compound | Molecular Weight (g/mol) | Grams Used (g) | Moles Used (mol) | Melting Point (ºC) | Boiling Point (ºC) | Hazards |
| 2-methylcyclohexanol | 114.2 | 2.28 | 2.00 x 10-2 | -9.5 | 165-166 | Flammable, irritant |
| Sulfuric Acid | 98.078 | 0.44 | 4.49 x 10-3 | 10 | 290 | Corrosive |
| Aqueous Sodium Hydroxide | 40.0 | 0.24 | 6.00 x 10-3 | 318 | 1390 | Irritant |
| Anhydrous Calcium Chloride | 110.99 | 772 | 1600+ | Irritant | ||
| 1-methylcyclohexanol | 114.2 | 25 | 155 | Flammable | ||
| 3-methylcyclohexanol | 114.2 | -5.5 | 174 | Flammable |
II. Post-Lab Report
A. Experimental Procedure
The experimental procedure was followed pretty much as written. The fractionating column was not wrapped with aluminum foil and it was not needed to add additional water to the round bottom flask during heating. The dehydrated 2-methylcyclohexanol solution was not centrifuged after being washed and then dried with calcium chloride. It was allowed to stand for a few minutes instead.
B. Observed Yield and Observed Melting Point or Boiling Point of Product(s)
Area of Peak A = 25
Area of Peak B = 112.5
Percentage of Product A: 18.2%
Percentage of Product B: 81.8%
C. Calucations
Percentage of Product A = (Area of Peak A) / (Area of Peak A + Area of Peak B)
Percentage of Product B = (Area of Peak B) / (Area of Peak A + Area of Peak B)
D. Conclusions
In analysis of the graph produced by the graph chromatograph, the ratio of the two products produced was about 4 to 1. The product with the higher yield should theoretically be 1-methylcyclohexanol. This is because the double bond in 1-methylcyclohexanol is trisubstituted, which is favored over disubstituted and monosubstitued double bonds according to Zaitsev’s rule. The product with the lower yield should be 3-methylcyclohexanol. The double bond in 3-methylcyclohexanol is only disubstituted, which is less favored. There were a few very small peaks on the graph which may be negligible. However, I think one of them could possibly be representative of methylenecyclohexane, which is the third product formed from the dehydration of 2-methylcyclohexanol. This proportion of this product would be minute and it is usually not observed, so this would be highly unlikely.
