Expt #3. Preparation of 2-Naphthyl Butyl Ether

References - (1) Experiment adapted from Esteb, J. J.; Magers, J. R.; McNulty, L.; Morgan, P.; Wilson, A. M J. Chem. Educ.2009, 86, 850. (2) Also see Wenkert, E.;  Youssefyeh, R. D.; Lewis, R. G. J. Am. Chem. Soc. 1960, 82, 4675. (3) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512-7515.

Overview – The S_N2 reaction is a versatile and stereospecific reaction that can be used for the preparation of a multitude of functional group families. These facts contribute to its great importance as a method for organic synthesis. The reaction generally involves a nucleophile attacking the electrophilic carbon of an unhindered alkyl halide (or alkyl sulfonate) displacing the halide (or sulfonate) leaving group.

In the reaction that you will be carrying out, the nucleophile is the naphthoxide ion formed from the reaction of  2-naphthol with sodium hydroxide.  The alkyl halide is 1-iodobutane and the expected product is butyl naphthyl ether (eq 1).

                  (1)

Procedures

Running the reaction.

1. To a 25-mL round bottom flask (rbf), add 0.28 g of NaOH and 0.50 g of 2-naphthol.
   
2. Add 10 mL ethanol and a few boiling chips to the flask. Make sure to use boiling chips that are stable to strongly basic solutions.
   
3. Reflux the solution for 15 min or until all of the solids have dissolved. 
4. Add 0.50 mL 1-iodobutane by Pasteur pipet through the top of the condenser and then reflux for 1 h.

Work-up procedures.

1. Cool the reaction mixture on a cold water bath for 5 min. Slowly pour the solution over 15 g ice in a 100-mL beaker.
   
2. Rinse the rbf with 15 mL ice-cold water and add this to the beaker.
   
3. Swirl or stir the contents of the beaker until all of the ice has melted.
   
4. Make sure the mixture is thoroughly chilled on an ice bath and then collect the solid product from the ice cold solution by vacuum filtration.
   
5. Wash the product with a few mL of ice-cold water and then dry it somewhat by allowing air to flow through the solid for 5-10 min.
6. Determine the yield and percent yield of your product.
   

Characterization of Product

Obtain the melting point. (A literature value can be found in the references). Please note that your product is not expected to extremely pure because it was not subjected to a final recrystallization step.

Obtain the ¹H NMR spectrum using CDCl₃ as the solvent. One team will also be asked to obtain C-13 and DEPT-135 spectra that will be available to the entire class on the class storage folder.

Report

Please try to integrate the answers to the assigned questions into your results and conclusions section for this report (rather than answering each sequentially).

For printing NMR spectra, it is highly desirable that the printout is labeled with spectrum parameters such as MHz, file name and date. To do so in Delta after you go to File/Print select the "Delta" tab and check the "Print parameters" box before printing.

NMR - For both the C-13 and the proton NMR label the spectrum prominently with the compound structure with C's or H's labeled as necessary to be able to label the peaks in the spectrum. Literature spectra for this compound are available at the SDBS website. However, these spectra were obtained at a higher field strength (400 MHz) than yours, so they are more ideal with less peak overlap in the proton NMR

¹H NMR - Be careful to identify and label solvent peaks including CHCl₃ and water (see reference 3) Integrate all peaks and normalize so that the integrations directly show the number of hydrogens for each resonance. Several protons' resonances overlap to form messy multiplets. These multiplets can still be identified as to which protons are included and should be reported in the results table as multiplicity = "m" and with the range of ppm values that they span given as the chemical shift. Make a results table that lists the chemical shifts, literature shifts, peak assignments, multiplicities, and integrations,

¹³C NMR/DEPT-135 - Simply label all peaks on the spectrum to show the specific carbon(s) causing them.  Make a results table that gives the chemical shifts, literature shifts, peak assignments, and DEPT-135 result (CH₃/CH, CH₂, or C).

Questions:

1. Why is it important to react the naphthol with sodium hydroxide first before adding the electrophile? What unwanted side reaction would occur to a greater extent if all three reactants were added together at the start and the mixture refluxed?
2. Why is it important to fully cool the product in an ice bath prior to vacuum filtration?  Why is the product washed with ice water instead of room-temp water?
3. Why is the reaction of 2-naphthol with hydroxide expected to have a favorable equilibrium constants. Use both Ka values and the ARIO principle to explain.