Dehydration and Gas Chromatography of Methylcyclohexanols

The experimental confirmation of the “Evelyn Effect” was performed in this report. This effect, first described by David Todd of Pomona College in 1994, describes the formation of 1-methylcyclohexene and 3-Methylcyclohexene (structures shown below) derived from the dehydration and distillation of a mixture of cis-2-methylcyclohexanol and trans-2-methylcyclohexanol (structures shown below) when reacted with phosphoric acid.Figure 1. Stereochemical Structures of Methylcyclohexanols.This reaction was carried out according to the following mechanisms.Figure 2. Reaction Mechanism of Dehydration of cis/trans-2-methcylohexanol Mixture.Procedure150 mmol (� 18.419 g) of 2-methylcyclohexanol (cis – trans mixture) was placed into a 50 mL round bottom flask. Mixed in this flask was 5 mL of 85% phosphoric acid, 3 drops of sulfuric acid (to quicken reaction), and a few acid resistant boiling chips. A simple apparatus for distillation was assembled and two 10 mL graduated cylinders were used to collect the distillate.The contents of the 50 mL round bottom flask were gently brought to a boil and the temperature of the vapor was approximately 115 �C. The rate of heating/boiling was controlled so that the rate of collection in the first 10 mL graduated cylinder was approximately 1 drop per second. When the contents of the distillate in the 10 mL graduated cylinder reached approximately 8 mL in volume the first 10 mL graduated cylinder was removed and a second clean 10 mL graduated cylinder was put in its place to collect an addition 6 mL of distillate.The first distillate product was the transferred to a clean seperatory funnel and washed with 5 mL of saturated aqueous sodium bicarbonate. The aqueous layer was drained off and the organic distillate product was washed with 5 mL of saturated aqueous sodium bicarbonate for a second time. The aqueous layer was then drained off and the organic distillate layer was collected and saved for gas chromatographic analysis. This procedure was repeated for the second distillate sample.A small portion of magnesium sulfate was then added to each organic distillate sample in order to remove any remaining water in the sample. The mixtures of organic distillate and magnesium sulfate were then filtered through gravity filtration to remove the magnesium sulfate from the organic distillate.Gas chromatographic analysis was then performed individually on each organic distillate sample in order to obtain a distinct gas chromatogram for each sample.DataTable 1. Experimental Calculations and Data.Sample Weight DataMolecular Mass of 2-methyl-cyclohexanolReagent Volume Use CalculationFigure 3. Organic Distillate Gas Chromatograms*.Organic Distillate Sample 1Organic Distillate Sample 2*Arrow indicates 1-methylcyclohexene calculated from standard gas chromatograph of pure 1-methylcyclohexene with retention time of 2.6 minutes.Table 2. Organic Distillate Gas Chromatograph Calculations.Organic Distillate Sample 1 Area and Retention Time CalculationsOrganic Distillate Sample 1 Total Area% Composition of Constituents in Organic Distillate Sample 1Organic Distillate Sample 2 Area and Retention Time CalculationsOrganic Distillate Sample 2 Total Area% Composition of Constituents in Organic Distillate Sample 2Table 3. Automatic Gas Chromatograph Data.Gas Chromatograph Model Number350ColumnCarbowax 8′ x .25’Cover GasHelium (He)Set Temperature50 �CColumn Temperature50 �CDetector TypeTCDDetector Temperature100 �CFlowrate� 40 mL/minInjection Volume4 �LTable 4. Physical and Chemical Properties of Reagents.M.W.B.P.d12-methylcyclohexanola114.2 amu166 �C0.9301-methylcyclohexene96.2 amu110 �C0.8133-methylcyclohexene96.2 amu104 �C0.801Phosphoric acid (85%)98.0 amu1.70ResultsThe results and experimental calculations seem to correlate directly to the confirmation of the existence of the “Evelyn Effect.” This is evident as the formation of 1-methycyclohexene decreased from sample one to sample two at a rate of 19.7225% while the formation of the products increased from sample one to sample two at a rate of 19.7225%.DiscussionThe “Evelyn Effect,” as predicted by David Todd in 1994, appears to be supported by the evidence accumulated in this experiment (see results section). The dehydration of the mixture of cis/trans-2-methylcyclohexanol isomers forms two direct products along with water as a byproduct of the removal of the hydroxyl group from the 2-carbon position of cis/trans-2-methylcyclohexanol. As the reaction proceeds cis-2-methylcyclohexanol reacts first with phosphoric acid to form 1-methylcyclohexene in greater quantity than the byproducts of the reaction of the trans isomer of 2-methylcyclohexanol. This conclusion is confirmed by the indication in the gas chromatogram of a higher percent composition of the 1-methylcyclohexene than 3-methylcyclohexene (55%;35%). In the gas chromatogram of sample two 3-methcyclohexene is in higher concentration (44%;64%). This seems to infer that trans-2-methylcyclohexanol reacts slower than the cis isomer of the same molecule. All of this information directly points to the existence of the “Evelyn Effect.”Error was a substantial issue during the calculations of the areas of the different compound spikes as shown on the gas chromatogram. The unlabeled compound spike in the chromatogram of organic distillate two has a peak but very little downward slope is shown. This lack of slope caused significant error in calculating the exact area underneath of the spike in which to obtain measurements for use in the calculation of spike area.Even accounting for this error, however, it seems unlikely that this jeopardized the validity of the experimental results. While the product yields were significantly lower than those predicted by Todd the results were significant enough in order to see the appearance of the “Evelyn Effect.”Furthermore examining the physical/chemical properties of both 1-methylcyclohexene and 3-methylcyclohexene it is apparent that 1-methylcyclohexene is slightly more stable than 3-methylcyclohexene. This property can be deduced by examining the boiling points of the two isomers. The boiling point of 1-methylcyclohexene is 110 �C while the boiling point of 3-methylcyclohexene is slightly lower at 104 �C. The slightly larger amount of heat energy required to boil 1-methcycyclohexene (6 �C) than 3-methylcyclohexene shows that the latter is slightly more stable. In this context it becomes apparent that 3-methylcyclohexene is more apt to convert to 1-methylcyclohexene; the more stable of the two isomers.

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