Lab Report Nucleophilic substitution PDF

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Nucleophilic Substitution Reactions of Alkyl Halides

Performed by. James Forst, Sibora Peca Performed on 10/31/19 Submitted on 11/21/19

Abstract In this experiment several samples were prepared to demonstrate how nucleophilic reactions and substitutions can occur in the laboratory. In this experiment several observations were concluded based on the reactions that occurred mainly as a result of electron transfers. In our experiment we prepared two sets of test tubes that contained nine different compounds to be tested for SN1 reactions and SN2 reactions. Each set of test tubes was prepared with a stopper and the appropriate solvents. SN1 reactions were observed in Ethanoic AgNO3 where as SN2 reactions were prepared with NAI. Overall the same procedure was performed with each part of the experiment. In our data observations and compound are noted. Each compound in the presence of alkyl halides had a unique observation. Objective To demonstrate in the laboratory setting Nucleophilic substitution reactions of alkyl halides. In this experiment a nucleophilic substitution reaction will be represented by the addition of a solvent to mixtures of alkyl halides. Any change will be noted and represents a reaction. Introduction Nucleophilic substitution is one of the most valuable and well-studied class of organic reactions. These reactions can occur by a variety of mechanisms. SN2 and SN1 are the reactions in question. In this experiment SN2 reaction occurs in a single step but the overall procedure did not differ. The process goes as follows, the nucleophile enters as the leaving group which usually is a halide ion and it departs. The reaction in the experiment has a rate that is proportional to the concentration of the solvents used and the nucleophile in question. In the SN1 reaction loss of the “leaving group” occurs first to generate a carbocation intermediate. The carbocation then takes a nucleophile, often the solvent In this case the reaction is called a solvolysis. Since the first step is rate-determining in a SN1 reaction it displays first-order kinetics and its rate depends only on the concentration of the halide used. Which mechanism occurs under a certain set of conditions and how fast it occurs depend on a variety of factors. These factors include structure, the available leaving group, the nucleophile being tested, and the solvent use all play a role in the reaction that takes place. The objective of this laboratory experiment is to learn how variations in halide structure affects the rates of SN1 and SN2 reactions. Within this experiment a main part of the procedure is measuring reaction rates. This involves monitoring the rate of change of the products during the experiment. In this experiment it is important to determine reaction rates by measuring the time required for a visible change to occur. The most common physical change is the formation of a precipitate. To create an SN2 reaction mechanism in the laboratory a solution of NaI in acetone will be used. Iodide is a good nucleophile, and if it displaces bromide or chloride, NaBr or NaCl it is known to precipitate (Organic Experiments 2010). To emulate an SN1 reaction mechanism AgNO3 in ethanol will be used. Ethanol use as it is a polar protic solvent and can promote

ionization of certain halides used in the experiment. If halide ion is released a precipitate of AgCl or Gab will form in the experiment. Overall our procedure included using test tubes. For the SN1 reaction 1ml of alkyl halides will be used with an addition of 1ml of ethanoic AGNO3. For SN2 the procedure is similar except 0.1ml of alkyl halides is used, and 1ml of NaI is used. The procedure then remains the same as 9 compounds will be added and observed for reaction while wax stoppers are used to prevent spilling. If we did not note a reaction 50-degree C water was available to expose the test tubes to heat to see if a reaction would occur. Heat was only used if evidence of a reaction was not noted within 5 minutes.

Materials Material Test Tubes Hot Plate Micro Pipettes Stop-Watch 100ml Beakers Graduated Cylinder

Purpose Used to observe and contain solutions. Used for heating/Warming. Used for transferring solutions. Used to time reaction start and end times. Used to hold solution. Used for heat bath Used for measurement of liquids.

Thermometer Temporary Labels

Used to monitor temperature of heat bath Used to label test tubes in order to avoid confusion.

Table of Physical Constants Compound

Name

Melting Point (c ) 230238.0 168.0

1bromobutene 1chlorohexane 2-chlorobutane 135.0

Molecula r Weight (g) 194.11

Density

1.23g/ml

151.16

1.3g/cm3

180.16

1.4g/cm3

77.0

88.11

704kg/m3

109 1 -bromopropan e propalbromide n-butyl 96.8 chloride z-bromobutane 782 sac-butyl bromide

83.98

2.1g/cm3

84.93

13mg/ml

110.98

0.745g/m l

2-metyl propane

t-butyl bromide

-114

36.46

82.3g/100g

Apparatus

Test Tubes

Hot Plate

Procedure and Observations Procedure 1. Obtain 18 test tubes and holders. 9 for SN1 and 9 for SN2. 2. For SN1 add 1ml of Alkyl Halide and 1ml of 10% Ethanoic AgNO3 to each test tube. 3. For SN2 0.1 ml Alkyl Halide and 1ml of 18% NaI to each test tube. 4. Add each compound one at a time by pippette and place a stopper. 5. Record the time and observations for each compound. Use a stopwatch. 6. If a reaction does not occur within 5 minutes for a given test expose the test tube to heat. 7. After observations are noted we discarded labels for each test tube. 8. To clean rinse each tube with pure ethanol. Dispose solid precipitate with solid waste and liquid waste in liquid containers. 9. Determine the rate of reaction based on if it uni-molecular or bimolecular.

Observation We had to clean our tubes before use. We used smaller tubes. We added 20 drops to equal 1ml for accuracy

We added 1 drop to equal 0.1 ml for accuracy We labeled each tube to avoid confusion and used different micropipettes for each solution We used multiple timers on our phones to track each reaction. We needed to expose two reactions to heat during the SN2 test. We created a code for each to simplify logging in our lab note book. The majority of our tests resulted in a precipitate.

We determined rate of reaction based on the rate of reaction for each sample separately

Flow Chart

Prepare test tubes

Add each compound one at a time

Create a data table for SN1 and SN2

Add 1 ml of Alkyl Halides for SN1, 1ml of AgNO3

Add 0.1 ml of Alkyl Halide 1ml of NaI

Place a wax paper stoper on each test tube

Record time for each reaction

Determine and calculate the rate of reaction

Waste Disposal and Safety Precautions In terms of waste disposal and safety precautions in this experiment we used the proper lab wear. This lab wear includes closed toe shoes, a closed lab coat, eye wear, and rubber gloves. All of these lab wear items work together in order to protect the experimenter from the chemicals and apparatus they are working with. In terms of protection eye wear is the most important as many chemicals can irritate or damage the eyes. Gloves protect the experimenter from hot surfaces and direct skin reactions from chemicals. The lab coat and closed toe shoes protect experimenters from spills and damaging their clothes. Waste disposal is almost as important as the experiment itself. Not only is proper waste disposal safer as it prevents reactions and environmental damage it helps to prevent lab accidents. In our experiment all items went into their appropriate bins solids with solids, liquids with liquids and non-reactive chemicals went down the drain or into a marked trash bin.

Results and Discussion Compound 1-Bromobutane

Sn1

Sn2 x

Time (min) 1:10

1-Chlorohexane

x

:40

2-Chlorobutnae T-butyl Chloride 2metyl propane 1-bromo propalromide n-butyl chloride

x x

0 5:00

x

2:30

x

5:00

x

3:30

x

Instant

x

Instant

Sn2

Time (min) 1:25

z-bromobutane sacbutyl bromide 1bromohexopentane t-butyl bromide

Observation Cloudy, yellowish crystal-like formation Instant color change, dark yellow, layer formation No precipitate or color change No initial reaction, Yellow color after addition of heat Color change after 2:30 to lightyellow Visible layer formation around 5:00 Instant color change, gas formed after 3:30 Instant separation into layers. One was cloudy the other clear Instant color change to light yellow

Figure 1. SN2 Observations Compound 1-bromo propane

Sn1 x

t-butyl bromide

x

:00

n-butyl chloride 2-bromo butane

x x

11:45 :19

1-bromo hexadecane 1-bromobutane

x

10:13

x

2:04

1chlorohexandecane t-butyl chloride x 2-chlorobutane Figure 2. SN1 Observations

X

Observation Cloudy, white crystal-like formation Appeared cloudy and yellow precipitate formation Color change occurred, cloudy No initial reaction, became cloudy Visible separation into small layers (white/clear) Light cloudy deposits, small crystal-like No reaction

:20 X

Large white precipitate formed No reaction

Based on our observations and knowledge of chemical reactions and electron transfer in nucleophilic reactions there is evidence of substation mechanisms present in our experiment. Based on our knowledge that iodide is a good nucleophile, and if it displaces bromide or chloride, Nab or NaCl it is known to precipitate. This as apparent in figure 1 as the reactions occurred with ally halides that contained these molecules. SN2 reactions produced similar results

despite the substitution order differing. Overall time of reaction was very comparable between our preparations of SN2 and SN1 reactions. Between our total of 18 tests, two SN1 tests, 1chlorohexandecane and 2-chlorobutane did not show physical evidence of reaction despite following the same procedure as other test tubes in this experiment. These two that did not show reaction were both observed for several minutes and exposed to heat. Based on the lack of reaction we can claim possible error in our experiment or that no nucleophilic substitution occurred in our timed experiment conditions. Conclusion Overall the purpose of this experiment is to demonstrate in the laboratory setting Nucleophilic substitution reactions of alkyl halides. In this we aimed to observe nucleophilic substitution reactions, SN1 and SN2 will by the addition of a solvent to mixtures of alkyl halides. In order to make this experiment effective we used a standard procedure and noted observations while each reaction occurred. Overall our procedure included using test tubes. For the SN1 reaction 1ml of alkyl halides will be used with an addition of 1ml of ethanoic AGNO3. For SN2 the procedure is similar except 0.1ml of alkyl halides is used, and 1ml of NaI is used. The procedure then remains the same as 9 compounds will be added and observed for reaction while wax stoppers are used to prevent spilling. If we did not note a reaction 50-degree C water was available to expose the test tubes to heat to see if a reaction would occur. Heat was only used if evidence of a reaction was not noted within 5 minutes. For SN1 Reactions a unimolecuar formula for rate was used where as in due to nature different rate law was used for SN2 as it is a bi-molecular substitution.

References I.

Williamson, Kenneth L. Organic Experiments. Vol. 9, Cengage Learning, 2011.

II.

Morrison, Robert Thornton., et al. Organic Chemistry. Pearson, 2011....