ABSTRACT: Through the reaction of 2-naphthol with sodium hydroxide, naphthoxide ions are formed which will act as a nucleophile that will displace the halide to form butyl naphthyl ether and sodium halide. Under the same condition, the reactions of butyl chloride and butyl iodide will be compared through a TLC plate. With the TLC plate, it is observed that the butyl iodide had a faster reaction rate than butyl chloride. Butyl naphthyl ether was isolated through a liquid-liquid extraction and purified with column chromatography and crystallization. The mass of the product obtained was 0.1364 g which was calculated to be a yield of 19.711%.
The overall goal of the experiment is to perform a SN2 reaction with butyl chloride and butyl iodide and compare the reaction rate between the two halides. The SN2 reaction is also known as bimolecular nucleophilic substitution reaction because the reaction involves the alkyl halide and the nucleophile to collide with each other. In this experiment, the halides are butyl iodide and butyl chloride and the nucleophile are the naphthoxide ions.
SN2 reactions are very important in organic chemistry and biological synthesis because many bond formations are formed through the use of this versatile reaction pathway, so many functional groups can be formed through SN2 reaction. In addition, SN2 reaction is also connected with the rate law because the rate of reaction is dependent on the concentration of the alkyl halide and the nucleophile. This means that if the concentration of alkyl halide is doubled, the reaction rate will double, and by doubling the concentration of the nucleophile, the reaction rate will also double, creating a second-order process for SN2 reactions.
In the experiment, the sodium hydroxide deprotonated the 2-naphthol, creating the naphthoxide ion, and the naphthoxide ion would then displace the halide which is iodide. In the end, the products butyl naphthyl ether, sodium halide, and water are produced.
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Figure 1. SN2 reaction of butyl iodide and 2-naphthol.
The two electrophiles and leaving groups involved in the experiment, butyl iodide and butyl chloride, have different reactivities which would explain the difference in their reaction rate. The stability of the carbocations plays a role in the reaction rate of SN2 reaction because the less the stable the carbocation is, the faster the rate of reaction. Primary carbocations are less stable than secondary carbocation, and secondary carbocations are less stable than tertiary carbocations, so because primary carbocation was involved in the experiment, the reaction rate of the SN2 reaction would be faster than if a secondary or tertiary carbocation were to be involved in the experiment. The leaving group involved in the SN2 reaction experiment also plays a role in the rate of reaction in the experiment. The more stable the conjugate base of the leaving group is, the better leaving group is. Therefore, butyl iodide would have a faster rate of reaction than butyl chloride because the conjugate base of iodide is more stable than the conjugate base of chloride.
RESULTS AND DISCUSSION
The reaction was set up by placing a v-vial filled with 2-naphthol, sodium hydroxide, and ethanol in an aluminum block that was on top of the heating plate. The mixture was removed from the heating plate after 10 minutes and butyl iodide was added. In order butyl iodide to be safely added to the v-vial, the mixture was allowed to cool, and butyl iodide was added with a syringe to prevent the chance of the v-vial exploding due to the buildup of pressure.
Figure 2. Reaction apparatus setup.
2-naphthol react with sodium hydroxide because of the -OH ion produced by the sodium hydroxide. This is due to the fact that Na+ is a spectator ion because sodium hydroxide would disassociate completely, so the -OH ions would react and deprotonate the 2-napthol to produce the naphthoxide ions. Ethanol will not react with 2-napthol to the same extent as sodium hydroxide because ethanol is not as strong as a base as sodium hydroxide. Furthermore, ethanol does not dissociate completely as sodium hydroxide does, so it is even harder for ethanol to deprotonate 2-naphthol.
Throughout the experiment, the reaction progress was monitored with TLC. Both butyl chloride and butyl iodide were spotted onto the TLC plate and placed in Hexane/Ethyl Acetate 20:1, and after the eluent has traveled up the TLC plate to a certain extent, the TLC plate was removed. Under the ultra-violet light, it was observed that butyl iodide had traveled up the TLC plate more than butyl chloride because the butyl iodide had a large spot towards the top of the TLC plate while butyl chloride had a larger spot towards the bottom of the TLC plate. This shows that butyl iodide has a faster rate of reaction than butyl chloride because there was more product produced by butyl iodide than butyl chloride since the product is nonpolar, so it would travel up the TLC plate faster than polar compounds. Therefore, butyl iodide is a better electrophile than butyl chloride because iodide is a better leaving group than chloride. It is because the more stable the conjugate base the leaving group is, the better the leaving group, so because iodide is a more stable conjugate base than chloride, it is a better leaving group.
Figure 3. TLC results.
It was necessary to perform the extraction step before column chromatography, so the mixture can be separated into ethereal layer and the aqueous layer. Furthermore, the compound of interest was contained in the ethereal layer, not in the aqueous layer, so by separating mixture into ethereal and aqueous layer, it would be easier to purify the compound of interest with column chromatography.
In the column chromatography step, nine different fractions were collected. The purpose of column chromatography is to purify the collected ethereal layer. Column chromatography works because the silica gel is polar, so the nonpolar compound would travel down the column faster than the polar compound since the polar compound would have a stronger interaction with polar silica gel. Due to this, the ethereal layer can be purified and separated into nonpolar and polar compounds. The fractions that were combined were fractions 4-8 because these fractions only contained the nonpolar compound which is the compound of interest of the experiment, so the column chromatography was a success.
Figure 4. Column chromatography fractions 1-6.
Figure 5. Column chromatography fractions 4-9.
If there were time remaining to analyze IR spectra of 2-naphthol and the reaction product, butyl naphthyl ether, their IR spectra would look very similar to the IR spectra provided below (See Figure 6 and 7). 2-naphthol would have an IR spectrum very similar to Figure 6 because of the band from 3600-3400 nm which is a characteristic of a -OH function group which only 2-naphthol have and butyl naphthyl ether does not. Due to this, the IR spectrum of butyl naphthyl ether would a very similar to Figure 7.
Figure 6. IR spectrum of 2-naphthol.
Figure 7. IR spectrum of reaction product.
During the crystallization process, fractions 4-8 were combined because these fractions contained only the nonpolar compound. Before the crystallization process, the product was transparent like water, but after the product was crystallized, the product turned into a white solid that formed at the top of the ice water. Through vacuum filtration, the mass of the product obtained was 0.1364 g. which is a 19.77% yield. The percent yield was based off the reagent 2-naphthol because it was the limiting reagent in the experiment. Percent yield can be calculated with the following equation:
“Percent yield = ” “Actual Yield” /”Theoretical Yield ” *100%
“Percent yield=” “0.1364 g” /”0.692 g” ” * 100% = 19.711%”
An experimental error that occurred in the experiment is the loss of product during the transferring process. This experimental error could not be prevented because even if the all product were transferred from the filter paper to the glazed paper, there would still be a small amount of products that are trapped in the pores of the filter paper. Another experimental error is the heating of the mixture because with the pressure building up in the v-vial, a small amount of the mixture could shoot out of the v-vial, which may be prevented if the mixture was heated up at a slower rate.
In conclusion, the rate of reaction between butyl iodide and butyl chloride was determined with TLC. Butyl iodide has a faster reaction rate than butyl chloride because butyl iodide has a better leaving group than butyl chloride. By combining the fractions 4-8 obtained from the column chromatography, the mass of the product obtained in the experiment was 0.1364 g which is a 19.711% yield.
Figure 8. TLC plate setup.
Figure 9. Column chromatography setup.
Figure 10. Gravity filtration setup.
Figure 11. Vacuum filtration setup.
Rotavap was used to evaporate the solvent to obtain butyl naphthyl ether.
Heating butyl iodide: 0.285 g of NaOH and 0.4998 g of 2-naphthol were added to a 5 mL v-vial. Next, 5 mL of ethanol and a spin vane were also added to the v-vial. The v-vial containing the mixture was placed on a heating plate and heated for 10 minutes. After 10 minutes, 0.75 mL of butyl iodide was added to the mixture with a syringe. Finally, the v-vial was once again placed back on the heating plate and heated for an addition 30 minutes.
Heating butyl chloride: 0.263 g of NaOH and 0.4972 g of 2-naphthol were added to a 5 mL v-vial. Next, 5 mL of ethanol and a spin vane were also added to the v-vial. The v-vial containing the mixture was placed on a heating plate and heated for 10 minutes. After 10 minutes, 1 mL of butyl chloride was added to the mixture with a syringe. Finally, the v-vial was once again placed back on the heating plate and heated for an addition 30 minutes.
TLC plate: After 30 minutes of heating the mixtures, the mixtures were allowed to cool to room temperature. Next, 2 drops of butyl iodide and butyl chloride were added to separate small test tubes containing 5 drops of ethyl acetate. The mixtures then place back on the heating plate after combine the mixtures with ethyl acetate. The butyl iodide, butyl chloride, and 2-naphthol were then spotted onto a TLC plate. The TLC plate was placed in Hexane/Ethyl Acetate 20:1, and after the eluent has traveled up the TLC plate to a certain distance, the TLC plate was removed from the eluent. The TLC plate was then allowed to dry and then was placed under ultra-violet light to analyze the TLC. The results on the TLC plate was observed and recorded.
Separation of mixture: The butyl iodide mixture was removed from the heating plate and cooled to room temperature. Next, the butyl iodide mixture was transferred into a separatory funnel containing 15 mL of distilled water and 10 mL diethyl ether. The mixture separated into ethereal and aqueous layer, and the aqueous layer was extracted. Next, ethereal layer was poured out of the separatory funnel and the aqueous layer was returned back into the separatory funnel. This process was repeated again with 10 mL of diethyl ether and 7 mL of brine. The organic layer was dried with magnesium sulfate, filtered with gravity filtration (See Figure 10), and the solvent evaporated with a rotovap.
Column Chromatography: The crude product was purified with Hexane/Ethyl Acetate 20:1 in the column chromatography (See Figure 9). Nine different fractions were extracted with column and each fraction were spotted onto TLC plates. The TLC plates were placed in Hexane/Ethyl Acetate 20:1 and then allowed to dry. The TLC plates were then analyzed under the ultra-violet light and was determined to combine and concentrate fractions 4-8 with a rotovap.
Crystallization: The product was dissolved in 1 mL of ethanol and poured into a small beaker containing crushed ice and water. The content in the beaker was swirled until all of the ice were melted. The product was then carefully filtered through vacuum filtration (See Figure 11) and air-dried. Finally, the mass of the product was weighed and used to calculate the percent yield.