the microscale laboratory
Tetraphenylpentadienone
In a 13- x 100-mm tegt tube are placed 105mg(O.5 mmol) of bend and 105mg (0.5 mmol) of 1,3-diphenylacetone. One milliliter of w 4 triethylene glycol is used to wash down the sides of the \ test tube.The contents are No, mixed and the test tube is irradiated in the micr* wave for 1 min at 50% power. Ten drops of Mton B are added and mixed with the contents. The test tube is returned to the micmwave and irradiated another minute at 50% power. When the tegt tube has cooled enough to handle, 1 mL of methanol is added and miKed with the contents. ARer further cooling, the dark precipitate is collected in a Hirseh funnel and washed with cnld methanol. The precipitate is dried by drawing air through it and pressing it between filter paper. The average yield is 75%, mp 21&218 OC. Dimethyl tetraphenylphfhalate
In a 50-mL heaker are p l a d 39 mg of tetraphenylcyel* pentadienone (0.1mmol), 3 drops (an excess)of dimethyl acetylenedicahxylate and 11 of triethylene g l p l . These are mixed by swirling,covered with a watch glass and irradiated in the micmwave oven at 50% power for 5 min. During this time the dark color of the tetraphenyleyclopentadienon~ disappears and the solution assumes a golden color. As it m l s slowly to room temperature colorleas crystals of the pmduct separate slowly These are wlleded in a Hirsch funnel and the remaining crystals are washed from the beaker with a little cold 95% ethanol that also is used to wash the oystals in the filter. Recrystallizationin 95%ethanol gave an average yield of 85%, mp 255-257'C. I.BadS.S.;Bme.A.J.;Chau-,A.G.;Msnhaa,M.S.;Rqju,V.S.;Robb,E.W.J. Chrm Edur 1882.69.92&929. 2.la)Fieaor.L. F.;Willisman, K L. OlgonielLartina. 4th cd.; Hcath.Lexir.gtm, 1979: p p n 2 2 1 6 . @ ) Mayo, D. W.; Kke,R. M.; BuWls, S.S.Miemsmlr h g M i e i n b o rotm 2nd 4.; Wiley.Ncw%rh 1989: pp 381*. (cl Pans, D. I*; h p m a n , G. M.;Kri..G. s.;Engel. R G. h ~ ~ i t ooO wnn i e L o l a m t o y Ikhniqw% saun. ders, Philadelphia, 1990; pp 287.290 (dl Wilmr. C . F. E~p.rimontnlO g o e Chonus@y; Maemillan: New York. 1988: pp 3 4 1 4 4 4 . (e) Williamson. K . L. 1989:pp47& M ~ m s m l r ~ d hMg M~i ekE ~ p . r i m n l s ; H c a t hLexinm, : 479.
Direct bromination of aniline produces a variety of polybrominated and oxidized products and direct nitration also leads to oxidized pmducts. Besides this, in acid solution the anilinium ion is formed, and this charged group acts as a deactivator and a meta diredor. By adding the acetyl group, one arrives a t a molecule that does not readily oxidue and substitutes largely at the rrara msition. A second substitution takes place-aithe posiiion okho tn the carbon carrying the acetamido group. Hydrolysis of the amide function pves the desired 4-brome2-nitroaniline. This sequence has been performed by nearly one hum dred students. More than 95%of these have completed the sequence in 3-3 112 h with a reasonable yield of the final pmduct. Procedure
In a 25-mL Erlenmeyer flask is placed 465 mg (5 mmol) of aniline, 12 mL of water, and 0.5 mL of concentrated hydrochloric acid. The mixture is swirled to dissolve the aniline. Asolution of 750 mg of sodium acetate trihydrate in 2 mL of water is prepared for the next step. To the flask containing the aniline, 1.0 mL of acetic anhydride is added with mixing followed immediately by the sodium acetate solution. The.flask is placed in an ice bath and stirred as the product crystallizes. When the reaction seems complete, the solid is collected in a Buchner funnel and washed with a little ice water. The product isdried by. pulling air thmugh the filter cake, and pressing it between fdter papers between paper towels. This material is pure enough to be used in the next step without purification. Bromination
4-Bromo-2-Nitroaniline: A Multistep Synthesis John W. ~lder'and Mark A. Paollllo
Failfield University Failf~eld,CT06430
Multistep organic syntheses often are required when direct methods give undesirable hyprodncts. These multisteo nrocesses are challeneine but freouentlv involve pm&dbes and products unfahTar to students ( j ) .We describe here the svnthesis of a relativelv simnle comwund that can he madeonly indirectly,hut us& methods &at are both easy to perform and familiar to students. '~uthorto w h m correspondence should be addressed. A144
Journal of Chemical Education
I n a 25-mL Erlenmeyer flask, the slightly moist acetanilide is dissolved in 4 mL of glacial acetic acid. ARer the addition of 1.6 g of pyridinium bromide perbromide, the contents are mixed and heated in a 60% water bath for 10 min. FiReen milliliters of water are added along with 2 mL of saturated sodium bisulfite solution. (If the orange color persists, another milliliter of saturated sodium hisulfite solution is added.) ARer being mixed, this is cooled in an ice bath for 5 min. The crystals are collected in a Hirsch funnel, washed with water, and partially dried by pullingair through them and pressing them between filter paper. Final drying is accomplished by heating the crystals on a watch glass over a beaker of boiling water. The crystals must be dry for the followingreaction t o work.
N;tration
The moist 4bmmo-2-nitmacetanilide is in a 20x 150-mm test tube with 2.0 mL of water and 3.0 mL of concentrated hydrochloric acid. Boiling chips are added and mixture i s ~ e n l y refluxed for 10 min. At the end ofthe hydrolysis, thekaction mixture is poured with mixinginto a mixture of 30 mL of ice water and 5 mL of concentrated ammonium hydroxide. If the mixture is not basic, it is made basic by the addition of more concentrated ammonium hydroxide. After being cooled 5 min in an ice bath, the precipitate is collected in a Hirsch funnel, washed with a small amount of ice water, and recrystallized in a minimal amount of 50% ethanol.
flask was filled to the mark with distilled water and set aside. Seven pairs of students prepared three serial dilutions from the stock solution using 10-mL volumetric flasks. The concentration range for the class was 6.758 x lo3 to 6.05798 x lo-' moles&. The experiment was conducted at room temperature. The baseline was determined using distilled water in both cells. The solution cell was drained and rinsed with each solution prior to recording the spectrum. The cell was drained again, and exactly 2.50 mL of the first solution was added to the cell using a pipet graduated in 0.1 mL units. The ceU was stoppered, and the spectrum was recorded. (Cyclohexanone bas an absorption maximum at 277 mu.) (The 2.50-mL volume was the minimum volume required to give the same absorbance obtained with the cell fdled. Smaller volumes gave absorbance values that were too high. Each instructor should fmd this minimum volume prior to the experiment.) After recording the spectrum, the cell was removed and exactlv 1.50 mL of cvclohexane was added to the cell from a p i p i graduated in 0.1 -mL units. The small free volume (0.05 mLl mmainine in the s t o ~ w r e dcell facilitated mixing of the two phages and w"usefu1 for removing any small bubbles that may adhere to the surface of the cell. The cell was shaken for two minutes and allowed to stand for 1min prior to being returned to the spectrophotometer. The spectrum of the extracted aqueous layer wasrecorded. Additional shaking was done as necessaq until the ahsorbance value remained constant. Most samples required 2 min of shaking. The solution cell was washed with acetone and soapy water and rinsed with distilled water after each run and a new baseline was obtained prior to each solution. Student pairs averaged 2 h to complete the experiment.
Literature Cited
Discussion
The dry crystals are weighed. The following directions are f o e mmol(428 mg) ofp-bmmoacetanilide.Pmportionate quantities should he used for different quantities of starting material. In a 25- x 150-mm test tube, thep-bmmoacetanilide is dissolved in 6 mL of concentrated sulfuric acid (with slight heating if necessary). A stirring bar is added and the solution is stirred in an ice bath. A mixture of 12 drops of concentrated nitric add and 20 dmps of concentrated sulfuric acid is prepared and woled in the ice bath. This nitrating mixtule is added to the bromoacetanilide solution at the rate of one drop everv 10 s while the mixture is stirred in the ice bath. ~ & the-addition r is complete the mixture is stirred another 15 min in the ice ba& and poured into 40 mL of ice water with mixing. After 5 min of frequent swirling in an ice bath, the precipitate is collected in a Hirsch funnel, washed with ice water, and partially dried by pulling air through it and pressing it between filter paper between paper towels. This moist pmduct is used directly in the hydrolysis step.
I .a Mayo. 0 W . nkc. R M..Buuhar, Y S Mumrob OwmcLobnmlw, 2nd d.. Wlly New Yark. 1989: pp J57-399. $bl W#llumam.K L Mnrnanb ond Mar r m b O r # a n r r h n w n b Hsalh I m n g n r . 198% pp 52R574
The Distribution of Cyclohexanone between Cyclohexane and Water John D. Worky St. Norbert College DePere, WI 54115
Although microscale experiments have been incorporated into general and organic lab manuals, analytical chemistry and physical chemistry generally have not adopted microscale techniques. This article describes a micmscale emriment that mav be used to demonstrate extraction, s&Arophotometric"analysis, and the determination of a distribution constant in an analvtical or . ~hvsical . laboratory Experimental
The experiment requires reagent grade cyclohexanone, cyclohexane, and distilled water. Measurements were made with a W spectrophotometer (e.g., a double beam Shimadzu Model 160) using matched rectangular 1-cm cells with tighbfitting Teflon stoppers. Astock solution was prepared by weighing to the nearest 0.1 mg a glass-stoppered 100-mLvolumetric flask containing about 15 mL of distilled water. Thirty drops of cyclohexanone were added, and the flask was weighed. The
The system studied is comparatively simple. Cyclohexanone has a large nonpolar moiety and should prefer the organic layer. In the absence of wmpeting equhbria, it can be shown that the distribution wnstant can be determined from the measured absorbance data according to Kd = ((AilA& 1)*(2.5/1.5)
(1)
where Ai and Ar are absorbances for the unextracted (initial) and extracted (final) solutions. resoectivelv. Volumes are incorporated in the constant fa&or at the riiht of eq 1. Cvclohexanone has no sienificant acid or base ~ r o ~ e r t i e s in aqueous solution. 1Cis reasonable to assume that tautomeric forms would be negligible under the conditions of this experiment. A typical student result and calculation follows. A solution with a cyclohexanone concentratim of 5.385 x lo-' M had an initial absorbance of 1.170 and a fmal absorbance of 0.498. The distribution constant as calculated from eq 1 is 2.25. Student values ranged from 1.83 to 2.48 with a mean of 2.22 and a relative standard deviation of 5%. The lowest concentrations of cyclohexanone gave low values (Ka= 1.83,1.91) for the distribution constant and were not included in the average. The standard Gibb's free energy accompanying the transfer of a mole of cyclohexanone from the aqueous phase to the organic phase was calculated using the class mean for the distribution constant. At 23 "C. AGO = -1.96 kJ demonstrating the preference by cyclohexknone for the nonpolar phase. The molar absomtivitv for cvclohexanone (Continued on next page)
Volume 71 Number 6 June 1994
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