Synthesis and Analysis of Butyl Naphthyl Ether via SN2 Reaction

utylnaphthyl ether was synthesized by an SN2 reaction mechanism using 2-napththol, iodobutane, and sodium hydroxide. The success of the procedure was then determined by finding the melting point range, IR spectrum, and percent yield of the final product.

Reaction Mechanism:

O- O---H

+ Na++ + Na+

Results:

Table 1. Masses of reactants and final product and melting point range of final product

The theoretical yield can be calculated as follows using values fom Table 1:

1.01 g 2-napthol x x x = 1.40 g butylnaphthyl ether

Using this value and the final mass, the percent yield can be calculated.

Percent yield = x 100% = x 100% = 41.4%

Round, yellowish-white pellets of NaOH were added to flat, pale-pink chips of 2-naphthol. Ethanol, a clear liquid, was then added.

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After refluxing, the mixture began to turn a yellowish-brown color. Iodobutane, another clear liquid, was then added. The solution cooled in ice, after which it turned much thicker and appeared to be a light orange color. After suction filtration, shiny, pale-orange crystals were left behind as the final product.

Discussion:

The measured melting point range of the final product was 28.4 ˚C – 31.2 ˚C. This is a 2.8 ˚C range, which is rather narrow, indicating that few impurities remained after the reaction was completed. The actual melting point range of butylnaphthyl ether is 31.5 ˚C – 32.0 ˚C. Because the measured range is lower but still quite close to the actual range, it can be assumed that, though a few impurities remained, the product was mostly pure (“2-butoxynaphthalene”).

The pale-orange color of the crystals also indicates impurities in the product. Butylnaphthyl ether should be a white crystalline solid (“2-butoxynaphthalene”). The pale-orange color was similar to that of the pale-pink 2-naphthol, which could mean that some of the 2-naphthol did not fully react.

As shown in the IR spectrum below in Figure 1, the strong absorption around 2975 cm-1 is consistent with sp3 C-H stretching (Ruttledge). There are also strong peaks around 850 cm-1 and 1500 cm-1, which are consistent with aromatic C-H bending and aromatic C=C bending respectively (“Table of IR…”). There is also a peak around 1250 cm-1, which is consistent with C-O stretching in ethers (Glagovich, 2005). There is no characteristic O-H stretching past 3000 cm-1, nor is there a strong peak between 1600 cm-1 and 1900 cm-1 indicating C=O stretching (Ruttledge). Thus, the C-O stretching is likely due to the presence of an ether.

The IR spectrum of the final product looks very similar to the sample IR spectrum (Spectral Database for Organic Compounds SDBS) shown in Figure 2. Thus, the final product obtained appears to have been butylnaphthyl ether.

The percent yield was only 41.4%, meaning the mass of the final product was much lower than expected. This may have been because, while pouring the solution over ice, some of it remained in round-bottom flask. Additionally, while pouring the pouring the solution into the vacuum filtration apparatus, some of it spilled out.

Ethanol, which is polar and protic, was used as the solvent in this reaction. However, SN2 reactions proceed most effectively in polar aprotic solvents. With ethanol, unwanted side reactions could occur. For example, the solvent can form hydrogen bonds with the nucleophile, making it less effective. If a polar aprotic solvent, such as THF, was used, unwanted side reaction could have been avoided, which could have subsequently produced more final product. Additionally, it is important to mix the 2-naphthol with sodium hydroxide before adding the electrophile, iodobutane. This is because the 2-naphthol must be allowed to deprotonate first so that it can then undergo nucleophilic substitution. This is demonstrated in the reaction mechanism shown above.

To isolate the product, the reaction mixture was poured onto ice. However, the product could have also been separated using distillation methods, as the boiling points of the starting material and product would be different. Thus, they would boil at different points of time, allowing them to be distinguished.

This reaction is unlikely to proceed using an SN1 mechanism, as, because it is not a concerted mechanism, it will form a primary carbocation on the iodobutane. This type of carbocation is highly unstable, and will thus likely undergo rearrangement. This would change the final product.

References:

1. “2-Butoxynaphtalene .” Syntechem , Syntechem Co., Ltd, 2014.
2. Glagovich , Neil. “Infrared Spectroscopy .” Central Connecticut State University , Neil
3. Glagovich, 2005.
4. Ruttledge, Tom. CHEM 2510: Introduction to Experimental Organic Chemistry, 28 Feb. 2019.
5. Cornell University. Lecture.
6. Spectral Database for Organic Compounds SDBS, 2019, National Institute of Advanced
7. Industrial Science and Technology (AIST).
8. “Table of IR Absorptions .” WebSpectra, Craig A. Merlic, Barry C. Fam and The Regents of
9. University of California, 2000.