Alcohol dehydration to produce alkenes is a fundamental reaction in organic chem

Question

Alcohol dehydration to produce alkenes is a fundamental reaction in organic chemistry. The reaction is essential for metabolic processes (e.g., fatty acid biosynthesis, citric acid cycle) and for laboratory and industrial alkene synthesis. In this experiment, a mixture of isomeric alkenes will be produced by the acid catalyzed dehydration of 2-methyl-2-butanol. This reaction is endothermic and the equilibrium favors reactants over products. However, the great difference in boiling points of the reactants and products makes it possible to remove the product by distillation and, thereby, continually shift the equilibrium towards alkene formation. After completing distillation, separation and cleanup of the crude product, you will calculate the overall yield. IR spectra of representative alkene mixtures will be posted on Canvas. Since the reaction is thermodynamically controlled, you should be able to predict which of the isomers should predomination in the mixture based on its structure. However, the NMR spectrum of a representative student sample will be provided for determination of the actual ratio of alkene isomers. Techniques used in this experiment: distillation, extraction, drying agents, IR. Background reading and preparation: Acid catalyzed dehydration: Review Bruice Section 11.4. Review IR and NMR using Bruice or Zubrick as necessary, especially with regard to alkene hydrogen chemical shifts and stretching frequencies. Include a reaction scheme, theoretical yield calculation, and a table of important reagents. Be sure to include pertinent physical and safety data in the reagent table. Provide an experimental outline.

Explanation / Answer

Pre-lab

Shown above is the acid-catalyzed dehydration of alcohol to alkene

The reaction scheme is already shown in the text above. (on top)

Theoretical yield of product = moles of starting material x molar mass of product

1 mole of alcohol gives mole of alkene

So,

say we start with 1 g of 2-methyl-2-butanol

theoretical yield = (1 g/88.15 g/mol) x 70.14 g/mol

                          = 0.796 g

Table of reagents

reagent                          Formula        FW      density(g/ml)       mass(g)        mmol       ml            Hazards

2-methyl-2-butanol        C5H12O      88.15        0.805                  1.0            11.34     1.24         

H2SO4                           H2SO4       98.08          1.84                  0.25             2.5        0.20        

Potential risks of chemicals used,

2-methyl-2-butanol : Highly flammable, irritant, chronic to respiratory system

H2SO4 : Highly corrsoive, irritant, carcinogenic

Experiment : To a clean dry round bottom flask connected to a distillation setup was taken 2-methyl-2-butanol and added to it was concentrated H2SO4. Heat the flask gently. Distillation of the products formed favors the completion of the reaction.

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