Dehydration of an Alcohol lab report

Topics: Distillation, Sulfuric acid, Stoichiometry Pages: 7 (1201 words) Published: February 20, 2014
Experiment 9-Dehydration of 2-methylcyclohexanol
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Abstract

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Introduction

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Reaction Scheme and Curly arrow mechanism

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Table

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Experimental Procedure

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Calculation (percentage yield and composition of isolated materials) 1
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Results and Discussion (include GC)
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Lab 9 Report Template: Acid Catalyzed Dehydration of 2-Methylcyclohexanol Abstract
In Experiment 9, distillation was used to carry out the dehydration of 2-methylcyclohexanol using 4:1 mixture of phosphoric and sulfuric acid. Gas Chromatography was then used to measure the products. Two products were formed. The theoretical yield of the alkene mixture was 3.914 g. The actual yield of the mixture was 0.73 g. The percent yield for the reaction was 18.65%. Peak A had an area of 0.3 mm2 and a percentage of 4.6 %. Peak B had an area of 6.21 mm2 and a percentage of 95.39%. Introduction

The acid used speeds up the dehydration of the alcohols. This is an elimination reaction. Water is eliminated from the reaction and the products formed are alkenes. The reaction follows Zaitsev’s rule because it is an elimination reaction. Zaitsev’s rule says that the double bond that is more highly substituted or more stable will be dominant in the products.

In the experiment the dehydration of 2-methylcyclohexanol takes place. 2 methyl-cyclohexanol has a very poor leaving group which is the hydroxyl group (OH-). When a strong acid such as H+ protonates the oxygen in the hydroxyl group, it becomes a good leaving group in the form of water. The leaving group leaves as water, and a carbocation intermediate is formed because of experiment conditions. Since there is no other nucleophile present besides water, the intermediate must undergo elimination to reach stability. Each alpha carbon loses a proton and produces the alkenes 3-methylcyclohexene, and 1-methylcyclohexene. According to Zaitsev’s rule, 1-methylcyclohexane is more substituted and will therefore be the major product.

In the first half of the experiment, the alkenes produced were distilled to prevent the reverse reaction from taking place, and to obtain the greatest possible yield. In part two, Gas Chromatography was used to show the amount of major products formed. Gas Chromatography was also used to determine how much of each alkene was present in the final product, and to determine if those results correlated with the results predicted by Zaitsev’s rule. Reaction Scheme

2-methyl-cyclohexanol 3-Methylcyclohexene 1-Methylcyclohexene C7H14OC7H12C7H12
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Curly Arrow Mechanism

Table of Physical Constants*.

Experimental Procedure
Part 1
A simple distillation apparatus was set up using a 25 mL round bottom flask. 5 mL of 2-methylcyclohexanol and 1mL of 4:1 phosphoric acid: sulfuric acid solution was added to the round bottom flask. The flask was briefly swirled to mix reagents. The flask was heated and a temperature was maintained below 100 oC. The distillation continued until approximately 3 mL of distillate was collected. Sodium sulfate was then added to a beaker and weighed. The distillate was then added to the beaker. The beaker was covered and left for a week. Part 2

A vial was obtained and weighed. The distillate was taken out of the beaker with the sodium...
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