Lab Reports:

Lab reports entail the turning in of the lab notebook, or copies, for each experiment.  When a formal, written lab report is required, the format changes, and is described here.  This formal lab report must be typewritten and will be graded according to how well it is written as well as on the content.  The table below outlines the information needed for this report.  A sample report is shown as well.  Use this information to put together your report.

Your lab report must follow the pattern described below. The report does not need to be long, but needs to cover the experiment, including protocols and results.  Do not use an outline format.  You do not need to include every detail, because certain techniques, such as extractions, melt point determinations, refluxing, are known to everyone.  Use correct English, in complete sentences.  Your research (data) is always described in past tense (e.g., The refractive index of our product was 1.3456; Our DNA sequence was 5'-AGCTTGT-3').  Established data is described in the present tense (e.g., The refractive index of this chemical is 1.3456; The DNA sequence is 5'-AGCTTGT-3').

	Description of Report Contents by Section
Title	A title which describes your experiments.
Abstract	Brief recap of what you did, why, and your results. No procedures.
Introduction	Explain why you did the experiment. Describe important background information and essential protocols related to your experiment.
Materials and Methods	Describe your experimental protocol and the materials (reagents)  used.  Use complete sentences. Do not use outlines, although tables can be used for reagents.  Do not include every little detail such as, "we used a Pasteur pipette; or we attached tubing to the reflux condensor" since these details are understood and expected.  You should list quantities of important reagents, but only if they are essential to understand how the experiment was performed.
Results and Discussion	Describe your results, including pertinent experimental techniques that are specific for your experiment. Discuss your data and make projections.  State any conclusions.
References	Cite references from the text and handouts.  Reference all established data.

Sample Report:

Electrophilic Aromatic Substitutions: Nitration and Friedel-Crafts Acylation

Author's Name Withheld

ABSTRACT

This is a compilation of Experiment numbers 31, 32 & 33. In these experiments, electron deficient reagents (electrophiles) reacted with electron rich aromatic rings. This type of reaction is known as an electrophilic aromatic substitution. While electrophilic aromatic substitution involves a wide variety of reactions, we used  acid-catalzyed nitration and Friedel-Crafts reactions. These experiments were designed to examine the behavior of the aromatic ring when exposed to an electrophilic reagents, orientation of the product based on attached substituent groups, and practical general organic chemistry synthesis techniques.

INTRODUCTION

The characteristic reactions of benzene involve substitution. The benzene ring has a cloud of electrons above and below its plane which are loosely held and are available to a reagent that is seeking electrons. That is, the benzene ring serves as a source of electrons -- it acts as a base. The electrophilic reagent which reacts with the benzene ring is electron deficient -- it acts as an acid. The reaction of the aromatic ring and the electrophile is characterized as an electrophilic substitution reaction.

The mechanism for electrophilic aromatic substitution via nitration and Friedel-Crafts involves two essential steps. The first is the attack on the ring by an electrophilic reagent to form a carbocation (this is characterized as the rate deteriming or the slow step). It must be noted that the attack generates a carbocation not because of a positive charge on the electrophile, but because electrons are pulled out of the ring to bond to the electrophile. The second step is the abstraction of a proton from the carbocation by some base (characterzied as the fast step). All three experiments follow these principles and mechanisms. These simple mechanisms offer powerful techniques for organic chemistry synthesis.

MATERIALS AND METHODS

Experiment 31: Nitration of Methylbenzoate. In a beaker I combined 6.1g Methylbenzoate with 12 mL conc sulfuric acid. The mixture was cooled to 0C prior to the addition of 8 mL of an equal volume mixture of sulfuric and nitric acids. The reaction mixture was warmed to room temperature and reacted for 15 minutes.

The reaction was stopped when poured over 50g of crushed ice which also precipitated our product. Crystals were isolated using vacuum filtration with a Büchner Funnel. The crystals were washed twice with 25 mL cold water followed by two washes with 10 mL ice cold methanol. The dry product was weighed for recovery.

Experiment 32: p-Nitroaniline

Three grams of acetanilide was mixed with 5 mL of concentrated sulfuric acid. The acetanilide was dissolved swirling and stirring the mixture. After the flask was cooled in an ice bath, a mixture consisting 1.8 mL of concentrated nitric acid and 5 mL of concentrated sulfuric acid was added dropwise using a disposable pipet. The reaction was cooled after each addition of acid by swirling in the ice bath.

After 20 minutes, including the time required for adding the nitric-sulfuric acid mixture, 25 mL of ice water was added. A suspension of nitroacetanilide isomers resulted. To hydrolyze the nitroacetanilides to their corresponding nitroanilines, the mixture was heated. The dilute sulfuric acid already present in the flask served as the hydrolyzing medium. Heating the mixture allows the solids to dissolve. The flask was cooled in an ice bath and 30 mL of concentrated aqueous ammonium hydroxide was added. The nitroaniline isomers precipitated during this step. The precipitated nitroaniline was collected using a Büchner funnel. The solid was washed with small amounts of water (total about 50 mL). The sampe was then air dried.

The dry material was added to hot ethanol and dissolved. After boiling, when the first crystals appeared, the flask was placed in an ice bath to complete the crystallizaiton. Crystals of p-nitroaniline were collect by vacuum filtration. The crystals were wash with a minimum amount of cold ethanol and allowed to dry. Crude p-nitroaniline was dissolved in 15 mL ethanol for each gram of p-nitroaniline and the solution warmed to dissolve the solid. About 0.5g of activated charcoal was added to the solution and swirled for a few minutes. The charcoal was removed by gravity filtration. The filtrate was concentrated to about 1/3 of its original volume by heating on a hot plate. When the solution cooled, and the first crystals appeared, the flask was placed in an ice bath. After the crystals were collected, they were dried in air and weighed.

Experiment 33: Friedel-Crafts Acylation

2.8 g of anhydrous aluminum chloride was added to 5 mL methylene chloride in a 100 mL round bottom flask. After adding all the dichloromethane, the flask was stoppered.The cooled suspension of aluminum chloride and methylene chloride was stirred using a stirring bar. 1.6g of acetyl chloride, along with 4 mL of dichloromethane, was added to the reaction apparatus over a 15 minute period. After addition was complete, 1.4g of toluene was dissolved in 3 mL of dichloromethane. Addition of the toluene mixture occured over 20 minutes. After this addition, reaction was allowed to proceed for 30 minutes, swirling frequently.

The reaction mixture was poured into a mixture of 10g of ice and 5 mL of concentrated hydrochloric. This solution was mixtured thoroughly for 10 to 15 mintues. Using a separatory funnel, the organic layer was collected and saved. The aqueous layer was extracted with 6 mL of dichloromethane. The two organic layers were combined. The organic layers were washed with 10 mL of saturated sodium bicarbonate solution and then dried with anhydrous magnesium sulfate.

RESULTS AND DISCUSSION

Experiment 31: I obtained a yield of 7.83 g of what I believe to be m-nitrobenzoate. I would expect the major product to be the meta isomer since I know that methyl benzoate is electron withdrawing, that is, it is deactivating, and meta directing. I also expect the monosubstituted product for two reasons. First, the experiment was conducted using relatively low temperatures, and, second, the nitro group that was attached to the ring deactivates the ring against further substitution. Crystallization purified my desired product away from the ortho and para isomer.

Experiment 32: I must admit that this particular experiment initially brought about some confusion. At first, I wondered why I couldn't directly nitrate aniline to make p-nitroaniline (it is strongly activating, the para product would seem likely). However the text revealed that since this electrophilic aromatic substitution reaction occurs in acidic media, the basic amino group is converted into the cationic ammonium group (-NH₃⁺) which is electron withdrawing and would be meta not para directing. This is why it was necessary to convert the amino group into the acetamido group which would reduce the reactivity of the amino groups reactivity with acids. I obtained a yield of 0.74g of p-Nitroaniline. Since I knew that acetamido group (-NHCOCH₃) is strongly activating, I expect that I obtained predominately the para product with some ortho isomer. But why mostly para? According to the text, "steric hindrance makes ortho substitution much less likely than para substitution" (Pavia, 237).

Experiment 33: Toluene was used as substrate using the acylating agent acetyl chloride. According to the text, I expected to have a single product, a substituted acetophenone. However, according to lecture, Friedel-Crafts reactions have limitations that must be noted. Namely, these reactions are succeptible to rearrangements and polysubstitution. My refractometer reading was 1.5290 which, according to Dr. Robertson, was well within the range of acceptable values (this value reassured me that my product was the desired product and not a rearranged or polysubstituted product). According to the Acros Organics catalog, the melting point and boiling point for 4-methylacetophenone (95%) are 22-24^oC and 226^oC , respectively. The known refractive index value is about 1.5330.

LITERATURE CITED

1. Introduction to Organic Laboratory Techniques, 3rd ed., pgs. 232-247, Pavia, Lampman, Kriz.

2. Acros Organics 95 & 96 Catalog of Fine Chemicals, Fisher Scientific.