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ChemDraw and Chem3D Exercises

The ability to represent chemical structures and to produce reaction mechanisms is an important part of modern chemistry, especially organic chemistry.  In this exercise you will use ChemDraw and Chem3D to show chemical structures and some reaction mechanisms.  You will also use these computer programs during the semester so that you can include chemical structures in your written reports.

Exp I: Electrophilic Aromatic Substitution: Friedel-Crafts Alkylation

We used an electrophilic aromatic substitution (EAS) reaction to nitrate methyl benzoate. In this experiment we will use a different electrophile (the t-butyl cation) to alkylate 1,4-dimethoxybenzene. The primary difference between Friedel-Crafts EAS reactions and other EAS reactions is that in a Friedel-Crafts reaction, the electrophilic atom is a carbon atom (e.g., in this experiment it is a t-butyl carbocation). In many cases, the Friedel-Crafts electrophile is generated using a chlorine-containing (e.g., an acid or alkyl chloride) electrophile and a Lewis acid (e.g., AlCl₃) catalyst. Alternatively, we can use any stable carbocation (2° or 3° carbocation) as the electrophile.  As long as the cation is stable, and cannot rearrange, this is a good way to generate the electrophile for a Friedel-Crafts alkylation. The t-butyl cation which is used as the electrophile in this reaction is a 3° cation which cannot rearrage, so it works well. However, this reaction illustrates one problem with Friedel-Crafts alkylations: it is often difficult to avoid producing significant amounts of dialkylation products because the alkyl group being attached to the aromatic ring is electron-donating, and therefore activates the ring to further alkylation.

Exp II: Grignard Synthesis: Synthesis of Benzoic Acid and of Triphenylmethanol

In this experiment, you must first prepare the Grignard reagent, phenylmagnesium bromide.  Phenylmagnesium bromide is then used to produce either benzoic acid following reaction with CO₂ or triphenylmethanol when reacted with benzophenone (or you could use ethyl benzoate). The organic portion of the Grignard reagent functions as the carbanion nucleophile.  The two reactions you will perform, in addition to the synthesis of the Grignard reagent, is (i) Synthesis of Benzoic Acid from Bromobenzene and (ii) Synthesis of Triphenylmethanol from Benzophenone and Bromobenzene

Exp III: Hydrolysis of Methylsalicylate and Synthesis of Acetylsalicylic acid

The experiment of composed of two parts.  The first involves the hydrolysis of methyl salicylate to produce salicylic acid.  This salicylic will then be used to prepared acetylsalicylic acid, which is aspirin.  

Many esters have familiar odors. Methyl salicylate, an ester derived from the combination of salicylic acid and methanol, is also known as the oil of wintergreen. Methyl salicylate was first isolated in pure form in 1843 by extraction from wintergreen plant (Gaultheria). It was soon found that this compound had analgesic and antipyretic character almost identical to that of salicylic acid when taken internally. This medicinal effect probably results from the ease with which methyl salicylate is hydrolyzed to salicylic acid under the alkaline conditions found in the intestinal tract. Methyl salicylate can be taken internally or absorbed through the skin, hence its use in some liniment preparations. When applied to the skin, it produces a mild burning or soothing sensation, which is probably due to the action of its phenolic hydroxyl group. Methyl salicylate also has a pleasant odor, and it is used as an extract for flavoring purposes.

Esters can be hydrolyzed into their carboxylic acid and alcohol components under either acidic or basic conditions in the presence of heat. In this experiment, methyl salicylate, an ester also known as oil of wintergreen because of its natural source and odor, is treated with aqueous base and heated. Since, in our experiment, hydrolysis occurs in the presence of base (instead of acid), the carboxylic acid and phenolic –OH groups on salicylic acid are ionized and this compound exists as the sodium salt of salicylic acid, sodium salicylate. The reaction mixture is subsequently acidifed using sulfuric acid, which converts this anion into the fully protonated acid, salicylic acid. The alcohol is methanol. The salicylic acid, which is mostly insoluble, is a solid and can be isolated and purified by crystallization.

Exp IV: Williamson Ether Synthesis

Ethers can be produced from two alcohols.  However, unless you want to have symmetrical ethers (e.g., diethyl ether derived from ethanol), ether synthesis from alcohols by themselves will produce a variety of products.  To produce an unsymmetrical ether (e.g., t-butyl methyl ether), you can do this if you have one component as an alkyl halide and the other component is the alkoxide ion. The alkoxide ion can be any alkoxide but the alkyl halide is usually going to be a primary halide.  The reason for this is that a primary halide would have less chance of undergoing elimination, hence you can end with the product you want.  In this experiment we will use either p-cresol and chloroacetic acid (Procedure 1) or iodoethane and β-naphthol (Procedure 2). The alcohol in either case can easily be converted into an alkoxide ion. This procedure is typical for reactions used to produce asymmetrical ethers.  The Williamson Ether Synthesis is one of several organic chemistry reactions referred to as Named Reactions, which employ the name of the scientist who developed it.

Exp V: Aldol Condensation

The aldol condensation is a reaction that is named based on the type of product formed when two aldehydes (or ketones), in the presence of dilute base, yields a molecule having both alcohol and aldehyde functional groups. These products are a β-hydroxyaldehyde (or a β-hydroxyketone). This reaction is used extensively in organic synthesis to form C–C bonds and make bigger molecules. In every case, the product results from the addition of one molecule of an aldehyde (or ketone) to a second molecule in such a way that the α-carbon of the first becomes attached to the carbonyl carbon of the second.

Although a β-hydroxyaldehyde (or a β-hydroxyketone) is produced in an aldol condensation, the ultimate product of these reactions is often a β-unsaturated aldehyde and a separate molecule of water. Upon heating, the β-hydroxy aldehyde products of aldol condensation undergo dehydration to yield a β-unsaturated aldehydes (ketones). Conjugation of the newly formed double bond with the carbonyl group stabilizes the product and provides the driving force for the dehydration process.

Exp VI: Aromatic Side-Chain Oxidation: o-Chlorobenzoic Acid from o-Chlorotoluene

Oxidations are a very important class of reactions in organic chemistry. Most oxidations require either a heteroatom in a reduced state (O in –OH, N in –NH₃, etc.) or a carbon-carbon p-bond (ozonolysis of alkenes and alkynes (and peroxide), formation of oxiranes from alkenes using peroxyacids, etc.). The oxidation of an aromatic side chain does not require any of these factors. All that is needed is a benzylic carbon with at least one hydrogen attached to it.

Exp VII: Amide Synthesis: Preparation of N,N-diethyl-m-toluamide

Carboxylic acid derivatives constitute an important class of organic compounds, both industrially and biologically. In this experiment you will synthesize N,N-diethyl-m-toluamide (DEET), which is a compound that is important commercially because of its biological activity -- it is an insect repellent, and is the active ingredient in  the"Off" and "Jungle Juice" brands.

Exp VIII: Diazonium Coupling Reaction of p-Nitrobenzenediazonium sulfate and N,N -Dimethylaniline: Synthesis of p-(4-nitrobenzeneazo)-N,N-dimethylaniline

Diazonium salts are very useful synthetic intermediates; they can be converted to a large number of functional groups, and, in many cases, are used as the key reaction step in the only practical synthetic route to yield substituted benzene compounds. Another set of important synthetic uses for diazonium salts is the diazonium coupling reaction. The terminal nitrogen of the diazonium cation is used as an electrophile in an EAS reaction.  Most of the products of this type of diazonium coupling reaction are brightly colored, and many of the dyes used in textiles in the past century are made in this way.

Exp IX: Reduction of a Nitro Group: Preparation of m-aminoacetophenone

One of the most generally useful methods of introducing an amimo group into a molecule is to introduce a nitro group first, and then reduce the nitro group to the amine. For instance, the best way to make aniline (and many aniline derivatives) is to make nitrobenzene first, and then reduce nitrobenzene using iron or tin, and hydrochloric acid.  It is also possible to reduce any nitro group using hydrogen and a standard hydrogenation catalyst, such as platinum or palladium.  In this experiment you will reduce an already existing nitro group to the amine, using tin and hydrochloric acid.

Exp X: Multi-step Synthesis -- Coenzyme Catalyzed Synthesis of Benzoin and Derivatives

This experiment is a required conclusion to Chemistry 211.  This experiment must be completed to receive credit for the course.  A formal written lab report for this experiment is also required.  You and your lab partner are responsible for every aspect of this experiment.  

Vitamin B1, thiamine, as its pyrophosphate derivative, thiamine pyrophosphate, is a coenzyme universally present in all living systems. It was originally discovered as a nutrient required to prevent the human disease beriberi, which affects the peripheral nervous system. Symptoms include pain and paralysis of the extremities, emaciation, or swelling of the body. The disease is common in the Far East.

In biological terminology, thiamine functions as a coenzyme, a biological molecule that assists in enzymatic reactions. In most cases, coenzymes are directly involved in the biochemical reaction that the enzyme catalyzes since it binds the substrate. Without the particular coenzyme, no reaction would take place. The enzyme, the biological catalyst, binds the substrate, controlling stereochemistry, energetics, and entropic factors. As indicated above, thiamine is a vitamin (derived from VITal AMINe), and required for many enzymatic reactions. In the current experiment, we will use thiamine to catalyze the reaction of benzaldehyde into benzoin.  Benzoin will be converted into benzil.  Benzil will be converted into benzillic acid.