DEHYDRATION OF METHYLCYCLOHEXANOLS
Nicholas Van Horssen
CHMY 321
TA: Michael Giroux
10/31/17
Introduction: The purpose of this lab was to carry out a dehydration reaction of 2-methylcyclohexanol by heating it in the presence of phosphoric acid and determining which alkene product would be the major product. Methylcyclohexanols were dehydrated in an 85% phosphoric acid mixture to yield the minor and major alkene product by elimination reaction, specifically E1. The alkenes were distilled to separate the major and minor products and gas chromatography was used to analyze the results and accuracy of the experiment. The hypothesis was the major product of the reaction would be the most substituted product. This conclusion was made because of
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Distillation of the first product began at 83 °C. A Pasteur pipette was used to remove 1-ml of the distillate into a vial. A second vial was filled with distillate until it reached 1-ml. As the second vial is being filled, observe the temperature and remove the apparatus from the heat source if there is an observed drop in temperature. Once the distillate had been collected into two separate vials, both distillates were washed with aqueous sodium bicarbonate (1.5-ml, 5%). The aqueous layer (lower) was extracted from both vials using a pipette and put into a chemical waste bin. The organic (alkene) layer was then dried with anhydrous calcium chloride pellets (3 pellets per vial). Both distillates were analyzed using gas chromatography, and each peak shown was identified to be one of the alkenes. Analysis of the graph was used to determine the major and minor products of the reaction.
Results: M.W. (g/mol) Boiling point (°C) Density (g/mL)
2-methylcyclohexanol 114.2 166 0.930
Phosphoric Acid (85%) 98.0 - 1.70
1-methylcyclohexene 96.2 110 0.813
3-methylcyclohexene 96.2 104 0.801
Table 1: Properties of the reagents and possible products for the reaction. The boiling point of Phosphoric acid is not important because it is a reagent.
Figure 2: Gas Chromatography analysis from the first sample. From top to bottom the peaks are ordered as followed: 3-methylcyclohexanol (A), 1-methylcyclohexanol (B), and 2-methylcyclohexanol
The objective of this lab was to create a ketone through an oxidation reaction using a using a secondary alcohol and oxidizing agent in order to use that ketone in a reduction reaction with a specific reducing agent to determine the affect of that reducing agent on the diastereoselectivity of the product. In the first part of this experiment, 4-tert-butylcyclohexanol was reacted with NaOCl, an oxidizing agent, and acetic acid to form 4-tert-butylcyclohexanone. In the second part of this experiment, 4-tert-butylcyclohexanone was reacted with a reducing agent, either NaBH4 in EtOH or Al(OiPr)3 in iPrOH, to form the product 4-tert-butylcyclohexanol. 1H NMR spectroscopy was used to determine the cis:trans ratio of the OH relative to the tert-butyl group in the product formed from the reduction reaction with each reducing agent. Thin-layer chromatography was used in both the oxidation and reduction steps to ensure that each reaction ran to completion.
The purpose of this experiment is to examine the stoichiometric relationship between reagents and the identity of the products by using three acid/base neutralization reactions of a triprotic acid, phosphoric acid, and varying molar equivalents of sodium hydroxide. The data will be used to determine the formula weight of the products and identify the remaining salt for all three reactions.
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