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Usage of Substitution Reacations on Different Alcohol Containing Compound to Ceate Alkyl Halides Yooran Im*, Alax Gregory Department of Chemistry and Chemical Biology, IUPUI, 402 N. Blackford St., Indianapolis, IN 46202 [email protected]

The purpose of the experiment was to prove the reaction mechanism and to determine the structure of the products for given reactions. Before the experiment was conducted, the reaction mechanisms of the reactions were predicted based on the given information such as the solvent used and the degree of substituent. From the observation made, it was determined that reaction one will go through Sn2 mechanism while reaction two will go through Sn1 mechanism. To prove the observation made experimentally, different lab techniques introduced previously in the course were used. Both reaction one and two went through reflux, which is a technique used to condense the reactant without losing any yield, then they were separated into organic and inorganic layers. Later, infrared spectroscopy (IR), gas chromatography (GC), proton nuclear magnetic resonance (HNMR), and Thin layer chromatography (TLC) were performed to analyze the product. The final product made for the reaction 1 was 0.52g and the experimental yield of 11.92%; for reaction 2, 1.54g was created with the experimental yield of 42%. As the result of the experiment, it was proven that the reaction one followed Sn2 mechanism while reaction two followed Sn1 mechanism. Organic chemistry was first introduced in nineteenth century. Since then, many organic reactions have been discovered. Every reaction discovered can be categorized into different groups based on varying topics. For example, they can be classified by mechanistic class or type of organic reagent. However, the most common and basic way of categorizing the organic reactions are by mechanisms. There are five different reaction classes reactions can fall into: substitution, elimination, addition, radical, and oxidationreduction .2 The reactions presented above show alcohol attached organic molecule as reactant and alkyl halides as products. To

create alkyl halides, substitution reaction and elimination reaction can be used. However, since the reactions do not have presence of strong bases, they will be going through substitution reaction. The nucleophilic substitution reactions were closely studied by two British chemists, Christopher Ingold and Edward Hughes in 1930s .3 One of their notable accomplishment is discovery of unimolecular nucleophilic substitution (Sn1) and bimolecular nucleophilic substitution (Sn2) pathways. Sn1 gained the name from the rate of the reaction. The rate of this reaction is determined by electrophile, which is unimolecular. Sn1 reaction must have carbon that is secondary, or tertiary substituted and if the solvent is used, the solvent must be protic meaning the solvent must have hydrogen that can be donated. Having protic solvent allows the rearrangement to happen, creating more than one product. These products are mixture of enantiomer, also known as racemic mixture. From the products produced, product will higher degree will be major product, which is also more stable, and the product with lower degree will be minor product. In Sn1 pathway, the starting material will lose the leaving group then form a carbocation. Then nucleophilic attack will take place where nucleophile(halogen) is attached to the carbocation. Like Sn1, Sn2 also got the name from the rate of the reaction. This reaction determines the rate based on the organic substrate and the nucleophile, which is bimolecular. Therefore, unlike in Sn1 reaction, there will be a step in the mechanism where the organic substrate and nucleophile interact. Solvent used in Sn2 pathway is aprotic, meaning that Sn2 will not allow rearrangement to happen. In Sn2 pathway, nucleophile will attack that carbon with leaving group which will remove the leaving group from the carbon. From the given reaction schemes and the known information of Sn1 and Sn2, it was possible to hypothesize that the reaction 1 will go under Sn2 pathway while reaction 2 undergoes Sn1 pathway. Only product of reaction 2 discussed will be the major product. Scheme 1. Substitution of 3-phenyl-1-propanol to form (3bromopropyl) benzene

This scheme will experience Sn2 reaction. OH is a strong base, meaning it is not a good leaving group. Therefore, OH had to be protonated with the proton from H2SO4. It will become a water molecule, which is a better leaving group. Water is a good leaving group because it is conjugate base of H3O+, a strong acid. As the leaving group leaves the molecule, Br- ion will attack the carbocation after H2O leaves the starting material, forming the final product of 1-bromo-3phenylpropane. The reaction happened under the acidic environment, and the benefit of have such environment was that E2 reaction was prevented because this specific elimination reaction needs strong base for the reaction to happen. Since the reactant had low boiling point, the reflux

was done under lower heat to prevent the burnt product which would result lower yield. TLC, IR, and HNMR tests were done to the product. IR graph indicated that the product was prepared incorrectly because OH peak was present at 3384cm^-1 when OH group should have been substituted by Br- ion. In addition, peaks were found near 1100cm^-1, indicating there in presence of CO bonds. Some of the large peaks were presented at 560cm^1 to 744.56cm^-1 . These peaks are for halogens and with only one halogen, Br, presented in the reaction, the peaks were concluded as Br peaks. Looking at the TLC, Rf value of the reactant was 0.29 and the Rf value of the product was 0.548. This indicates that the product traveled farther down the silica jell. This shows that the product was less polar, which is true .5 Br- ion is less polar than OH group. Therefore, the product has traveled farther on the silica jell. The HNMR graph is not a huge help in understanding with this product. If the IR indicates no presence of OH group, HNMR group will play better role, because OH and Br- would have different shielding, resulting different HNMR graph. However, in this case, since OH group still exists in the product, the HNMR will not show if the experimental product was produced successfully. The reaction was demonstrated four times. During a trial, distillation was used, hoping to increase the purity of the product. However, most of the product was lost after the distillation, so the technique wasn’t done for further trials. During the first trial, direct heat was used to heat the reactant but with the low boiling point of the reactant, product burnt. After this trial, reflux was done under indirect heat method such as hot water bath. To overcome the OH peak presented in the IR graph, different concentration of the sodium bicarbonate could be used for the wash but it was not acted on. During one of the trial, the product was washed with water, however, using the water pushed back the reaction to the reactant side due to the Le Chatelier’s principle and resulted zero product. Few of the possible sources of the OH peak presented in the IR graph is contaminated reactant or the complete reaction didn’t take place. The reaction wouldn’t have completed reaction if the temperature of the reflux was too low. If the experiment could be done again, higher temperature for reflux will be used and extra step on determining the contamination of the tools would be done. The reaction one involving 3-phenyl-1-propanol, NaBr, and H2SO4 did produce alkyl halide as the product showed presence of Br- or a halogen in the product on IR graph and TLC, even though, the exact product described in the scheme was not created as the product showed trace of OH group.

Scheme 2. Substitution of 2,4-dimethylcyclohexanol to form 2chloro-2,4-dimethylpentane.

With aprotic solvent and tertiary substituted carbocation, it was determined that this scheme will go under a stepwise Sn1 pathway with the production of racemic mixture. As in the reaction 1, OH will receive a proton, H, from HCl and become a better leaving group. Then as it leaves electrophile, the nucleophile will attack the electrophile producing the products. The products formed by this reaction are 2-Chloro2,4-dimethylpentane and 3-Chloro-2,4-dimethylpentane. Since 2-Chloro-2,4-dimethylpentane has chlorine paced on more substituted carbon, it is the major product of the reaction which is also more stable. IR peaks considered important for this reaction were 2966.11cm^-1 and 440.50cm^-1. 2966.11cm^-1 indicates sp^3 hybridized CH bond which is presented and 440.40cm^-1 peak indicates presence of chlorine in the product. One peak IR graph shouldn’t have was OH peak which is a large curve located above 3000cm^-1peak and it was not found in the IR graph. GC graph had 2peaks with 37.3 to 62.7 ratio. The longer peak indicates more polarity and the shorter peak indicates less polarity. Reactant should have higher peak due to OH presented, which is more polar than Cl-. Combining this knowledge to the calculated area shows that the 37.3% is the product while 62.7% didn’t react. Lastly when HNMR was analyzed, 2 multiplets and one sextet were displayed. The HNMR graph obtained was compared to the theoretical HNMR, extra sextet was needed and one less multiplet was not needed. However, since muliplet indicates anything higher than doublet, the extra multiplet was understood as sextet. The reaction was demonstrated 4 different times and every trial had small changes made. Reflux was the first step for every tria. lAnother important technique used was separation of layers. It separates the solution by the density, creating aqueous and organic layer. It is important to know which layer is going to be product. If product layer is unknown, it is possible for one to use aqueous layer for IR, HNMR, GC graphs, which will indicate wrong result. First time the experiment was done, the reflux was done with water bath. It took longer than expected for the mixture to reach the boiling point, which led to change made for the rest of the trials. For the rest of the trials, the reflux was done under the direct heat. Changing to the direct heat from water bath reduced the time it needed to reach the boiling point by 20-30 minutes. There are few changes that can be made if the experiment will be done again in the future. First, the beakers and flasks will be washed more thoroughly. Even though beakers and flasks were washed multiple times, there was white particle left behind that couldn’t be washed. Getting rid of the particles would increase the purity of the product. Another change is that starting materials should be measured in mass instead of the volume. For convenience, the materials were measured using volume instead of mass. This could result in less accurate amount of chemicals used. The reaction three where 2,4-dimethylpentane reacted with Lucas reagent was proved successfully through the experiment. The IR graph did not have any trace of OH groups, the theoretical HNMR aligned with the actual HNMR, furthermore, Cl peak was shown on the IR graph and GC

showed that the product is less polar, which indicates alkyl halide with less electronegativity was formed.

4.

“2-Chloro-2,4-Dimethylpentane.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, https://pubchem.ncbi.nlm.nih.gov/compound/2-Chloro2_4-dimethylpentane

5.

Chromatography Today. “What Is Retention Time?” Chromatography Today, https://www.chromatographytoday.com/news/gcmdgc/32/breaking-news/what-is-retention-time/31159.

6.

Libretexts. “Alkenes from Dehydration of Alcohols.” Chemistry LibreTexts, Libretexts, 5 June 2019, https://chem.libretexts.org/Bookshelves/Organic_Chemistr y/Supplemental_Modules_(Organic_Chemistry)/Alkenes/S ynthesis_of_Alkenes/Alkenes_from_Dehydration_of_Alco hols.

7.

Wolters, Lando P, et al. “Understanding E2 versus SN2 Competition under Acidic and Basic Conditions.” ChemistryOpen, WILEY-VCH Verlag, Feb. 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943610/.

8.

Kimia, Ilmu, et al. “Deciding SN1/SN2/E1/E2 (2) - The Nucleophile/Base.” Master Organic Chemistry, 24 Aug. 2019, https://www.masterorganicchemistry.com/2012/11/30/decid ing-sn1sn2e1e2-2-the-nucleophilebase/.

9.

Wolters, Lando P, et al. “Understanding E2 versus SN2 Competition under Acidic and Basic Conditions.” ChemistryOpen, WILEY-VCH Verlag, Feb. 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943610/.

Experimental Section All reactions were carried out under standard atmospheric conditions. Chemicals were used directly from the manufacturer’s bottle unless otherwise mentioned. H NMR spectra were gathered using a Bruker 500 MHz spectrometer. IR spectra were gathered using a Thermo-Nicolet 380 FT-IR. Gas chromatographs were obtained using a GOW-MAC 69400-TCD GC. 1-bromo-3-phenylpropane (1). Prepare the reactant by combining 3mL 3 phenyl- 1-propanol, 2.4g of solid NaBr, and 3mL H2SO4 (9M) in a round bottom flask. Reflux the mixture under simmering for 4 minutes. Let the mixture cool to the room temperature then transfer the contents to a separatory funnel. The organic layer will be located at the bottom due the higher density. Therefore, use pipet to remove the aqueous top layer from the funnel. Wash the organic layer with 10mL 7% sodium bicarbonate. Lastly, remove the organic layer from the funnel and transfer to flask to be used for TLC, IR, and HNMR analysis.1 (3.68 g, 0.017 mol, 75%). H NMR (CDCl3, 500 MHz) 7.4 (tm 5H), 3.4 (t, 2H), 2.8 (m, 2H), 2.1 (t, 2H), 2.12. IR (cm -1) 3384.51, 3084.81, 2939.10 2858.97, 560.93. TLC rf value (0.290, 0.548) 2-chloro-2,4-dimethylpentane (2). Preparation of reaction 2 started with combining 3.6mL of alcohol attached starting material, 2,4- dimethyl- 3- pentanol(3g, 0.0211mol) and 4mL of Lucas Reagent, which is made with 1:1 ratio of HCl and ZnCl2( 0.048mol) in a round bottom flask. The mixture were heated under the standard reflux condition for 30 minutes then cooled down to the room temperature. The content was transferred to separatory funnel where it was washed with 2 separate portions of 10mL of 5% sodium bicarbonate (3g/60mL). The organic layer, the product, will be located above the aqueous layer. Then the organic layer was extracted and dried with sodium sulfate to ensure that there was zero trace of inorganic material in the final product. Lastly, the product was moved to a vial to be used for IR, GC, and HNMR analysis. H NMR (CDCl 3, 500 MHz) 2.4 (sextet, 2H), 1.6(sextet, 3H), 0.8(multuplet, H). IR(cm1) 2966.11, 1651.53 1466.33, 574.00, 440.50. GC 37.3:62.7 Acknowledgement. This work was made possible by the Department of Chemistry and Chemical Biology at IUPUI. References. 1.

Denton, R.E.; Audu, C. “Investigating Substitution Reactions of Various Alcoholic Compounds.” Fake Journal of Organic Chemistry 2010, 77, 3452-3453.

2.

“Types of Organic Reactions: Explanation, Examples, Reactions, Videos.” Toppr, 3 Dec. 2019, https://www.toppr.com/guides/chemistry/organicchemistry/types-of-organic-reactions/. Ingold, Christopher K. “Edward David Hughes. 1906-1963.” Biographical Memoirs of Fellows of the Royal Society, vol. 10, 1964, pp. 147–182. JSTOR, www.jstor.org/stable/769317.

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