Dehydration of 2-Methylcyclohexanol
Hornback; 2nd ed.; pp. 378-380
& Mohrig, Technique 20.1-20.2,
& 20.5, pp. 341-349, 353-358 or 3rd edition Techniques 23.1-23.2, &23.5, pp. 406-413, 417-422.
Technique 18.1-18.4, pp. 228-236 & 18.6-18.9, pp. 243-267or 3rd edition Techniques 201.-20.4 pp. 277-285.
Appendix and Mohrig,
2nd edition, See Figure 11.15 in Technique 11.4,
p. 144 or 3rd edition, see Figure 13.17 in Technique 13.4, p. 160.
(Please turn in the answers to these questions when you arrive to lab.)
1. What are the reaction(s) that you will be doing in lab?
2. Why is it important that the temperature on your thermometer never go over 95 degrees Celsius?
3. How will you know when approximately 5 mL of distillate has been collected?
4. What is the theoretical yield for today's reaction? (Since you will not be separating your two alkene products, please determine one theoretical yield, in grams, for both of them together, theoretically.) Please show ALL work.
5. What differences should we see between the FTIR of 2-methylcyclohexanol and the FTIR of your products if the reaction is successful? (Please list frequencies and bond types.)
6. Does this reaction have all 4 components of a nucleophilic substitution? If not, what is missing?
7. What's Zaitsev's Rule?
the TPC below (including a theoretical yield) and insert it in your notebook.
Table of Physical Constants (TPC)*
g OR mL
(50/50 of cis-(d,l)
|| Theoretical Yield
eth, bz, peth,
* CRC Handbook
of Chemistry and Physics, 52nd ed.
* CRC Online (87th edition)
Dehydration (elimination of water)
of 2-methylcyclohexanol can give either
or both of two major products: 1-methylcyclohexene and/or 3-methylcyclohexene.
The course of the reaction can be determined by analysis of the product
using gas chromatography
(GC), mass spectrometry and infrared
- To determine which
alkene (1-methylcyclohexene or 3-methylcyclohexene) is most likely to
form in the dehydration of 2-methylcyclohexanol by doing the following:
of 2-Methylcyclohexanol. See Experimental Procedure below.
Chromatography and Mass Spectrometry. Identify the peaks and determine
the % composition of the alkene products.
Infrared spectrum of starting material and product. Compare your
spectra to note any changes in functional groups. Use the
table to obtain literature values.
The dehydration products formed in this reaction are flammable and volatile. Work in the hood and keep your product covered to avoid loss through evaporation.
Handle phosphoric acid with care--it is corrosive if spilled on your skin. In case of a spill, wash with water for several minutes.
In a 50 mL standard taper flask obtained from your instructor, place
5.0 mL of 2-methylcyclohexanol [50/50 of cis-(d,l) and trans-(d,l)],
of 15M phosphoric acid, and a boiling chip. Attach the flask to a fractional
distillation apparatus (See
Figure 11.15 in Technique 11.4,
p. 144). Set Control at 60-65% of 120V.
The flask should be heated at such a rate that the temperature of the
distillate is not allowed to
rise above 95oC. Higher temperatures result in the distillation
of too much unreacted alcohol. Continue heating until about 5 mL of product
has been collected in a standard taper flask set in an ice bath. What compounds should be present in your distilled 5 mL of product?
Transfer the distillate to a 60 ml separatory funnel. Wash the product
with 3 mL of saturated sodium hydrogen carbonate solution, allow the
layers to separate, and remove the aqueous layer. Wash the organic layer
water, remove the aqueous layer, and dry the organic layer with phase
paper and anhydrous magnesium sulfate, filtering the solution into a
the vial and contents, and calculate the % yield of product. What's the purpose of each extraction and the phase paper and magnesium sulfate?
Prepare a dilute (approximately 10%) solution of your sample in methylene chloride for GC/MS. Using a disposable glass pipet, measure 3-4 drops of your sample into a small test tube. Use another disposable glass pipet to add approximately 2-3 mL methylene chloride to the test tube. Transfer this solution to a GC/MS vial, and give your sample to the student lab assistant or your instructor for them to run your sample overnight.
Obtain and FTIR
spectrum of your neat product. Obtain an FTIR spectrum of the
starting material (2-methylcyclohexanol) from your instructor. Analyze both IR spectra accompanying
each one with an appropriate data table listing functional group and specific bond causing the absorbtion.
Store your left-over product in a clean 20 mL screw top vial in your tote.
Waste Disposal and Clean-up
- Dispose of the phosphoric acid aqueous waste from your reaction in the phosphoric acid waste bottle.
- Dispose of the aqueous and bicarbonate washes in the sodium hydrogen carbonate waste bottle.
- Dispose of your excess GC-MS solution in the flammables waste container.
- Rinse your glassware with acetone and dispose of the acetone rinse in the flammables waste bottle.
- Wash your glassware in hot soapy water and return to the appropriate storage area.
(Please turn in the answers to these questions when you arrive at your NEXT lab.)
Obtain your GC/MS information from this Dehydration
Lab. You should obtain the entire gas chromatograph and the mass
of 3 PRODUCTS from this lab. (Note
that you might also have some left-over reactant!)
Copy and paste the spectra into your e-lab. Draw
out the mechanism by which the reaction occurs using either ChemDraw or a handwritten mechanism that you have taken a picture of with your laptop/smartphone.
- Do your results
show that this reaction occurred?
- Tell me as much as possible about the structures of the
three major product peaks in the GC of your product (2 expected and 1 unexpected).
- Calculate the
overall % yield for your reaction, assuming all that is isolated is
alkene. Show ALL your calculations please.
- Find the percentage
of each expected compound in your product using your GC data. Please ignore all other peaks in your GC except your two expected products. Remember; please use only the ‘Area’ column in the Percent Report to determine the % composition of just your two major products. From this data, please state which proton was easiest to abstract from 2-methylcyclohexanol.
- Write the mechanism for the reaction that produced your major product. Please show how phosphoric acid was used as a catalyst.
- Are your results
consistent with Zaitsev's Rule?
- Why did we want to obtain the FTIRs of 2-methylcyclohexanol and your organic product? Did they help in your analysis of your products? Why?
- Discuss any unexpected results
in your experiment. What you would do differently if you were
to do this lab again?