CHEM 51LB Lecture Notes - Purified Water, Scientific Reports, Fume Hood

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1 Mar 2014

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This is the first part of a two-part experiment in which you will learn several techniques used regularly in the organic chemistry laboratory. You will react an unknown base with one of three possible electrophiles in the presence of sodium hydroxide to synthesize a benzyl ether product. In the next lab period you will purify and identify your product. Technique 7: assembling a reaction apparatus in techniques in organic. Technique 14: melting point in techniques in organic chemistry 3rd ed. pgs 175- Supplementary information in janice gorzynski smith (3rd ed), chapter 7 & 8. Follow the instructions in the 51lb report & presentation guidelines document located on the course website to prepare your pre-lab. Complete the required forms and agreements assignment on sapling. Wear gloves, work in the fume hood, and wash immediately if it comes into contact with bare skin. Benzyl bromide is a lachrymator and is irritating to skin and mucous membranes.

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Organic chemistry

Part1

Question1:

Page 1 of 3 In this session you will carry out two experiments to demonstrate chemistry of the carbonyl group. The two step synthesis of an amide from a ketone in Part 1 involves a nucleophilic addition reaction. In Part 2 you will convert an unknown amine to an amide using Part 1 Two Step Synthesis of an Amide from a Ketone This laboratory activity involves the synthesis of an amide from a ketone in two steps. In the first step, benzophenone is converted to diphenylmethanone oxime (Scheme. This reaction is a straightforward nucleophilic addition of an amine to a carbonyl that occurs with elimination of a water molecule. In the presence of phosphorus pentachloride, the oxime e (Scheme 2). The mechanism for the second step is less straightforward and your demonstrator will discuss it with you during the laboratory class. The intermediate oxime and the amide final product have the same molar mass and molecular formula, you will see how they may be differentiated using spectral data. 0 N-OH 1. HONH2H, NaOH + H20 Scheme 1 Scheme 2 Conversion of the ketone to an oxime (nucleophilic addition) Place the following in a 50 mL round bottom flask: Benzophenone (2.5 g), hydroxylamine hydrochloride (1.5 g), ethanol (5 mL) and water (1 mL). Add sodium hydroxide pellets (2.8 g) in portions with swirling and if vigorous reaction occurs, cool the flask under running tap water, When all the sodium hydroxide has been added, attach a reflux condenser and boil the mixture for 5 minutes. Allow the mixture to cool while you prepare an acidic solution by adding concentrated hydrochloric acid (7.5 mL) to water (50 mL) in a 100 mL beaker. Pour the cooled reaction mixture into the acidic solution and isolate the precipitate using vacuum filtration. Wash the solid with cold water and dry in an oven at 40Â°C or in a vacuum desiccator. Record the melting point and the yield of the oxime. Using the balance in the fume hood, rapidly weigh out phosphorus pentachloride (2.5 g) into a plastic vial. In a 100 mL conical flask dissolve the oxime prepared earlier (2.0 g) in dry diethyl ether (30 mL). Cool the flask in an ice bath and add about half of the phosphorus pentachloride. When the heat generated in the reaction subsides, add another small portion of phosphorus pentachloride and continue this process until all the material has

Can someone please help me figure this out? We have to figure out an experiment to get at least 90% yield of compound B.

These are the topics covered that we can use to plan this experiment:

1) Basic Operations: Using a weighing balance; Separation, Density.
2)Separating the Components of Panacetin - Acid-Base Reactions, Stoichiometry Techniques: Separation, extractions
3) Identifying the Constituents of Panacetin: Key techniques: Recrystallization and Melting point
4)Synthesis of Salicylic acid . Key techniques: Reflux, Recrystallization, Melting point
5) Separation of Unknown by Chromatography-Concepts: Polarity, capillary action, Technique: Column and Thin layer chromatography
6)Dehydration of cyclohexanol to an cycloalkene. Key Concepts: Preparation, and Reactions Hydration, Halogenation & Hydro halogenation of Alkenes;
7)Polarimetric Analysis of Unknown Sugars. Key concepts: Stereochemistry Techniques: Optical rotation
8)Properties of organic compounds -Concepts: Solubility, Hydrogen bonding; Technique: Distillation
9)Preparation of 2-chloro-2-methylbutaneâAn Sn1 reaction - Key concepts: Nucleophilic Substitution reactions

Nucleophilic Substitution â Synthesis of an Alkyl Halide

Introduction

Alkyl halides can be prepared from alcohols by reactions with hydrogen halides (HCl, HBr, or HI) via nucleophilic substitution. In this type of reaction, the nucleophile displaces a leaving group from a carbon atom of an organic substrate (here the alcohol once protonated). Both electrons of the new bond to the carbon are provided by the nucleophile while the leaving group departs with both electrons of its bond to the substrate. There are two limiting mechanisms that are most common in describing nucleophilic substitution reactions at sp3 carbon centres : (1) a direct displacement (SN2) process and (2) a process that generates an intermediate carbocation (SN1). Which mechanism is a better description depends on the structure of the molecule containing the leaving group, the nature of the leaving group, the size of the nucleophile, and the polarity of the solvent. This experiment is a near-perfect example of an SN1 substitution. H3C OH CH3 H3C + HCl H3C Cl CH3 H3C + H2O (Equation 1) In this reaction, you will prepare 2-chloro-2-methylpropane (t-butyl chloride) from 2- methyl-2-propanol (t-butyl alcohol) using HCl as the strong acid and chloride source. Note that HCl first activates the alcohol in an acid/base reaction before the SN1 reaction proceeds. The final product is characterized by its yield, boiling point, and density. The presence of a halide atom is confirmed with a silver nitrate test.

1) State which of the electrophiles given below will react preferentially by i) SN1, ii) by SN2, or iii) capable of reacting by either of the two mechanisms depending on the given conditions. How can you affect those conditions to favour SN1 or SN2? Reason your predictions based on the structures of the compounds. Br-CH3, Br-CH2CH3, Br-CH(CH3)2, Br-C(CH3)3, Br-CH2-C5H6; C5H6 = phenyl

2) Rank the nucleophiles given below based on high, mediocre, and low nucleophilicity and reason why based on their structures. HO-CH3, H2N-CH3, KO-CH3, KO-C(CH3)3

3) Name two solvents that are commonly used for SN2 reactions. because they considerably slow down SN1 reactions.

4) Can you ever have only SN2 or only SN1?

5) Iodine is a better leaving group than bromine. But iodine is a better nucleophile than bromine. Why is that?

6) Using orbitals, draw the transition state of the SN2 reaction between sodium cyanide and bromomethane. Which orbitals are interacting with which? Why is the bond breaking? Why is the orientation important? Is there another angle besides backside attack that could theoretically work based on orbital geometry? Why doesnât this happen?

7) Name four reagents you can use to dry solvent. Why do we use magnesium sulfate in this lab instead of them?

8) Draw a mechanism with all the proper arrows for the reaction from this experiment.

9) What are we removing with the water wash? Why donât we just add the sodium bicarbonate directly to the reaction mixture instead of doing a water wash?

CHEM 51LB Lecture Notes - Purified Water, Scientific Reports, Fume Hood

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