Competetive Nucleophiles

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Competitive Nucleophiles
Introduction:
The purpose of this experiment was to compare the relative nucleophilicities of chloride ions and bromide ions in two different reactions. One reaction involved n-butyl alcohol and the other involved t-pentyl alcohol. We performed the reactions and compared the percentages of alkyl chloride and alkyl bromide in the product. To perform this experiment, we used methods including heating reaction mixture under reflux, extraction using a separatory funnel, drying with anhydrous sodium sulfate, and refractometry.

Experiment Scheme:
First, we prepared the solvent-nucleophile medium. We combined 44mL 7.7M sulfuric acid with 4.75g ammonium chloride and 8.75g ammonium bromide, and we heated the mixture with stirring to dissolve the salts. We put 17mL into a separatory funnel for use in the second reaction, and placed the rest into a reflux apparatus for our first reaction. We performed the first reaction of the competitive nucleophiles with 1-Butanol. We added 2.5mL of 1-butanol to the solvent-nucleophile medium in the reflux apparatus with a boiling stone and heated the mixture under reflux for 75 minutes. After reflux was completed, we allowed it to cool in an ice bath, and transferred the solution to a clean separatory funnel. The different phases separated, and we drained the lower aqueous layer. We added 5mL water to organic layer, mixed and collected the lower organic layer. We extracted the organic layer with 5mL sodium bicarbonate, drained organic layer and dried with anhydrous sodium sulfate. We decanted the alkyl halide solution and set it aside to be analyzed by refractometry.

We performed the second reaction of competitive nucleophiles with 2-methyl-2-butanol. We measured 2.5mL of 2-methyl-2-butanol into the separatory funnel containing 17mL of the solvent-nucleophile medium. We swirled the mixture, venting occasionally until pressure equalized, then shook it vigorously with occasional venting for 2 minutes. We then allowed phases to separate. We drained the lower aqueous layer and poured the top organic layer into a small beaker containing 0.5g sodium bicarbonate. When bubbling stopped and clear liquid was obtained, we decanted the alkyl halide and began analysis by refractometry of the products from both reactions. By refractometry, we measured the refractive index of the products and used Equation 1 and 2 to calculate the percentages of each product (Pavia, Lampman, Kriz, and Engel, Organic Chemistry Laboratory Manual p. 47-50). Reaction 1 (Pavia, Lampman, Kriz, and Engel, Organic Chemistry Laboratory Manual p. 47-50)

Reaction 2

Equation 1
%Cl=(RI(Br)-RI(product))/(RI(Br)-RI(Cl))*100%
Equation 2
%Br=100%-%Cl

Figure 1. Reflux apparatus
Data:
Table 1. (Sigma Aldrich)
Chemical Reagents/Products and Useful Physical Properties
Chemical nameMolecular FormulaMolecular Weight (g/mol)Amount#MolesState of MatterDensity (g/mL) (g/cm3)MP/BP (°C)Hazards

Sulfuric acidH2SO498.144.0mL0.339Liquid1.84BP 290.0Skin/eye burns Ammonium chlorideNH4Cl53.54.75g0.0890Solid1.53MP 340.0Harmful if inhaled Ammonium bromideNH4Br97.98.75g0.0890Solid2.43MP 452.0Harmful if inhaled 1-butanolC4H10O74.12.50mL0.0270Liquid0.810BP 116-118Respiratory tract irritation Sodium bicarbonateNaHCO384.00.50.00600Solid2.16MP 300Eye/skin irritant Anhydrous sodium sulfateNa2SO4142--Solid2.68MP 884Harmful if swallowed 2-methyl-2-butanolC5H12O88.22.5mL0.023Liquid0.805BP 102Eye/skin irritant

Table 2. Refractive Index Standard Values – AT 13°C
CompoundRefractive Index AT 13°C
1-chlorobutane1.4045
2-chloro-2-methylbutane1.4075
1-bromobutane1.4425
2-bromo-2-methylbutane1.4440

Table 3. Results and Observations
CompoundAppearanceMeasured Refractive...
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