acetanilidelab

acetanilidelab - Experiment 8 Acetaniiide 65 WWW...

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Unformatted text preview: Experiment 8 Acetaniiide 65 WWW Salicylamide Ibuprofen Ketoprofen Naproxen _ —— 00125 g —~ Senozan, N. M. “Methemoglobinemia: An Illness Caused by the Ferric State.” Journal of Chemical Education, 62 (March 1985): 181. . U‘évqw'caq/ 1 a; {.711 4‘ Vt‘ui DAL] E x P E R l M E N T 8 mini/EM. name “their! Acetanilide “We «Cw: my gun Alv bd’b’lfl? iii UM” rwlvzvi‘b Crystallization Gravity filtration (V (0“; Vacuum filtration I . I t ’if Decolorization m (Li/LNW/Wti (1 Wave? (Mom/'5‘“! . . I 0‘ Preparation of an amide MW An amine can be treated with an acid anhydride to form an amide. In this experiment, aniline, the amine, is reacted with acetic anhydride to form acetanilide, the amide, and ace— tic acid. Crude acetanilide contains a colored impurity that is removed by decolorization with charcoal. Acetanilide is purified further by crystallization from hot water. it NH O O NHwC—CH 2 H n ./ 3 C C l + —--> 1 + CH COOI—l / \y / \ ’ 3 / Aniline Acetic anhydride Acetaniiide Acetic acid 66 Part One Introduction to Basic Laboratory Techniques Amines can be acylated in several ways. Among these are the use of acetic anhydride, acetyl chloride, or glacial acetic acid. The procedure with glacial acetic acid is of commer~ cial interest because it is economical. It requires long heating, however. Acetyl chloride is unsatisfactory for several reasons. Principally, it reacts vigorously, liberating HCl; this con~ verts half of the amine to its hydrochloride salt, rendering it incapable of participating in the reaction. Acetic anhydride is preferred for a laboratory synthesis and is used in this ex- periment. Its rate of hydrolysis (reaction with water) is low enough to allow the acetylation of amines to be carried out in aqueous solutions. The procedure gives a product of high pu- Iity and in good yield, but it is not suitable for use with deactivated amines (weak bases) such as orth— and para-nitroanilines. Acetylation is often used to “protect” a primary or a secondary amine functional group. Acylated amines are less susceptible to oxidation, less reactive in aromatic substi— tution reactions (Experiments 42 and 46), and less prone to participate in many of the typ- ical reactions of free amines, because they are less basic. The amino group can be regener~ ated readily by hydrolysis in acid or base (Experiment 46). Required Reading ,. Review: Techniques 5 and 6 Technique 7 Reaction Methods, Section 7.4 Technique 8 Filtration, Sections 8.1—8.5 Technique 9 Physical Constants of Solids: The Melting Point New: Technique 11 Crystallization: Purification of Solids Essay Analgesics Special Instructions Acetic anhydride can cause irritation of tissue, especially in nasal passages. Avoid breathing the vapor and avoid contact with skin and eyes. Aniline is a toxic substance, and it can be absorbed through the skin. Care should be exercised in handling it. You should be care- ful not to stop the experiment at any place where solid has not been filtered from the solution. Suggested Waste Disposai Aqueous solutions obtained from filtration operations should be poured into the con- tainer designated for aqueous wastes. Notes to the Instructor Aniline acquires a black color upon standing due to air oxidation. Because charcoal is very effective in decolorizing the crude acetanilide, it is recommended that students use impure aniline in this experiment. When very dark aniline is used, students can seejust how effective charcoal can be in purifying organic compounds. 4 1 § i ‘1 i r 4 Experiment 8 Acetanilide 67 Procedure Wflw Reaction Mixture. Weigh 2.0 g of aniline into a 125—mL Erlenmeyer flask. To avoid spills or contact with the skin, use a Pasteur pipet to transfer the aniline to the flask. Add 15 mL of water to the flask. Next, swirl the flask gently while slowly adding 2.5 mL of acetic anhydride (density 1.08 g/mL). Note in your laboratory notebook any changes that might occur during this reaction. 66% Once the crude acetanilide precipitates during this reaction, it must be crystal- TJ lized. This crystallization will be accomplished in the same flask as the original reaction. guru} \ Add 50 mL of water, along with a boiling stone, to the flask. Heat the mixture on a gay/‘1 hot plate until all the solid and oily materials have dissolved. After removing the flask U/‘tWi from the hot plate, pour about 1 mL of the hot solution into a small beaker and allow \‘ this material to cool. “‘1‘ WT} for CV“ rule 6/7311! , 6N Caution: The Erlenmeyer flask will be hot, so it is advisable to handle ' it with a paper towel. Do not use a test tube clamp or crucible tongs to remove the flask. Decolorization. Add a small amount of activated charcoal, or Norit, to the Er— lenmeyer flask and bring the mixture to a boil again. About one spatulaful should be enough charcoal. it is important not to add the charcoal to the solution while it is boil- ing vigorously, or violent frothing is likely. Swirl the mixture and allow it to boil gen— tly for a few minutes. Gravity Filtration. While the solution is boiling, assemble an apparatus for grav- ity filtration, equipped with a funnel (stemless, if possible) and fluted filter paper in a 125— or 250~mL Erlenmeyer flask (see Technique 8, Section 8.1, p. 645). Also prepare about 25 mL of boiling water, which will be needed as a washing solvent in the steps that follow. Warm the funnel by pouring about 10 mL of the boiling water through it. Dis— card this warming water, put in the fluted filter paper (Figure 8.3, p. 648), and then filter the acetanilide—charcoal mixture as quickly as possible, but in small portions, through the fluted filter. Keep the solution warm on the hot plate until the solution is poured into the funnel. While pouring the solution through the filter, keep the col— lection flask warmed on the hot plate. The purpose of keeping these flasks on the hot plate is to allow the water vapor to warm the funnel stem and to reduce the likelihood that crystals will form in the funnel, clogging it. if all goes well, the charcoal remains behind on the fluted filter paper, and the aqueous solution containing acetanilide passes through the filter. lf crystallization should begin in the funnel, add some hot water to the funnel to dissolve the crystals. Rinse the flask and the solid materials on the fluted filter paper with a little hot water and set the flask containing the filtrate aside to cool slowly to room temperature. Crystallization and Vacuum Filtration. To complete the crystallization, place the flask in an ice bath for about 15 minutes. Using the instructions given in Section 8.3, ..,,.i._._,.. ., , . . , , ., . ............--i..._w.i.r_. ., . 68 Part One introduction to Basic Laboratory Techniques page 651, prepare a BUchner tunnel with filter paper. Collect the crystals by vacuum filtration and dry them as completely as possible by allowing air to be drawn through them while they remain on the BUChner funnel. Complete the drying by spreading the crystals on a watch glass, covering them with an inverted beaker, and allowing them to dry until the next laboratory period. Collect the crystals that were not treated with charcoal in a Hirsch tunnel or small Bachner funnel and compare the color of these crystals with the color of the crystals that were treated with charcoal. Record the results of the comparison in your labora- tory notebook. Record the weight of the pure crystallized product and calculate the percentage yield. Determine the melting point of both the pure and the impure samples of dried acetanilide. Place each sample of crystals in a separate, labeled vial and submit both samples to the instructor with your laboratory report. QUESTIONS ‘/ 1. Aniline is basic, and acetanilide is not basic. Explain this difference. / 2. If 10 g of aniline are allowed to react with excess acetic anhydride, what is the theoretical yield of acetanilide in moles? in grams? 3. Give equations for the reactions of aniline with acetyl chloride and with acetic acid, to give ac— etanilide. "/ 4. In the introduction to this experiment, the hydrolysis of acetic anhydride is mentioned as a com- peting reaction. Write an equation for this reaction. J 5. During the crystallization of acetanilide. why was the mixture cooled in an ice bath? 6. Give two reasons why the crude product in most reactions is not pure. EXPEREMENT 9 ___________________.___.___.—_—————-——————-—- Acetaminophen Vacuum filtration Decolorization Crystallization Preparation of an amide Preparation of acetaminophen involves treating an amine with an acid anhydride to form an amide. In this case, p—aminophenol, the amine, is treated with acetic anhydride to form acetaminophen ( p—acetamidophenol), the amide. The crude solid acetaminophen contains dark impurities carried along with the p- aminophenol starting material. These impurities, which are dyes of unknown structure, are formed from oxidation of the starting phenol. Although the amount of the dye impurity is small, it is intense enough to impart color to the crude acetaminophen. Most of the colored ...
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acetanilidelab - Experiment 8 Acetaniiide 65 WWW...

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