denser. Placing the cold finger condenser into a 6-in. side arm test tube forms a sublimation apparatus. Sublimations can be carried out at reduced pressure by sealing the SISATT into position with a rubber washer made by cutting off the top of a 1-mL rubber dropper bulb. See Figure 4. Seatine the cold fineer condenser into a three-wav adapter &es a short path distillation apparatus capabce of handling larger volumes of distillate. See Figure 5. Solvents can be evaporated quickly by attaching an aspirator to the side arm of a SISATT that has a rubber adapter with a Pasteur pipet through it. See Figure 6. An inexoensive drvine tube can be constructed bv olacing a s m i l amountof cotton in the bottom of a S~SATT, adding a section of glass tubing, drying agent and more cotton. See Figure 7. Gas vapors that escape from the top of a reflux condenser can be removed by inverting a SISATT over the top of the glass tubing used as a condenser and attaching the side arm of the SISATT to a n aspirator. The systemis not under any reduction of pressure because there is no seal between the glass tubing and the SISATT. See Figure 8. Amedicine dropper on top of the SISATT may be used to add liquid to a reaction. This apparatus has been used as a mini steam distillation apparatus and to generate acetylene gas. See Figure 9. While not as elegant as a n Abderhalden Drying Apparatus, this setup will serve the same purpose for a small sample and is much cheaper. See Figure 10. The SISATT also can act as a vacuum flask for suction filtrations using a small Hirsch funnel.
vent needed for the chromatographic separation (50-100 mL ligroin, 300 mL methylene chloride and 5&100 mL ethanol) and the time necessary to make the chromatographic column and perform the separation (oRen more than one laboratory period, resultingin poor separations). The method described here overcomes these difficulties while reducing the volume of solvents needed to about 100 mL total for the experiment. Procedure Isolation of the Pigment Mixture
The pigment mixture is obtained by refluxing 0.25 g of paprika in 10 mL of methylene chloride for 20 min using a 10-mL round-bottomed flask and condenser. The solid is removed by vacuum filtration using a Buchner funnel, and the solid is discarded. The filtrate is transferred to a 50-mL Erlenmeyer flask and concentrated to 1-2 mL using a steam cone. Column Preparation
Approximately 50 mL of a methylene ch1oride:ligroin mixture (1:3 by volume) is prepared. An 18gauge hypodermic needle (usually included in the microscale kit) is inserted through a rubber stoooer that will fit a 125- or 250mL vacuum filtration flask ?A drop of mineral oil on the stopper a t the ooint of insertion makes this easier.) The stopper is inserted in the filter flask, and a solid phase extractionfiltration column with a filter frit is placed in the luer fitting of the hypodermic needle. (A 6-mi Bakerbond spe Disposable Filtration Column with a 20-pm frit works Acknowledament well.) Silica gel (1.0-1.5 g) is slurry packet using 10-20 mL of the methylene ch1oride:ligroin mixture. Agentle vacuum The author is grateful to Karen Quaal, Alicia Todaro, may be applied to the filtration flask to pack the column Dale Marko, and Dawd Ferrar for their patience in helping but a 1-cm solvent head should remain on the column. A to incoroorete the use of the SISA'IY' into their laborarorv sections. Additional thanks go to students John ~ e ~ a &layer of sand may be added to the top of the column to protect the sorbent layer. and Keith Perry who tested many of these procedures before their use in our laboratory
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Separation of Pigments
Literature Cited 1. Markowitz, M.;Boryts.D. J C h m . Educ. 196s.40,482.
Microscale Column Chromatographic Isolation of a Red Pigment from Paprika Kevin J. west' and Paul FIauch2 University of Wisconsin-Whitewater Whitewater, WI 53190
The isolation of a red pigment from paprika using a macroscale procedure by Miller and Neuzil (1)was satisfactory with only a few problems. However, the difficulties encountered with the microscale exoeriment oromoted an effort to devise a better microscale version. ' h e p;oblems associated with the procedure included the quantity of sol'Author to whom correspondence should be addressed. %Indergraduateresearch student. Current address: Depaltment of Chemistry, Ohio University, Athens, OH 45701.
The oiement mixture is mixed with 1-2 mL of the mixed solve2 and placed on the column using a Pasteur pipet. A gentle vacuum is aodied and the mixed solvent is added &ti1 the yellow bands are removed. The vacuum is stopped and the contents of the filter flask are transferred to a 125-mL Erlenmeyer flask. The filter flask is rinsed with 1-2 mL of methylene chloride that is added to the flask containing the yellow band solution. The column is reassembled and developed with neat methylene chloride (20-30 mL), using a gentle vacuum if necessary, until the solvent is no longer colored. The two fractions obtained from the column are concentrated to 1-2 mLeach. The concentrated piement fractions may be compared with the original pigmini mixture using thin-layer chromatography (silica gel plate and methylene chloride solvent).The red pigment (mostly fatty acid esters of capsanthin) in the second fraction is analyzed by infrared spectrometry by evaporation of the solvent from the solution on AgCl windows. An ultraviolethisible spectrum (260400 nm)also is obtained by dissolving one drop of the (Continued on page A62)
Volume 71
Number 3 March 1994
A59
the microscale laboratory concentrated pigment solution in 3 mL of 95% ethanol. The yellow pigment in the first fraction may be analyzed in a similar manner. Discussion This procedure is performed easily in a 2.75-h laboratory period with the possible exception of obtaining the IR and UVNis spectra. Care must be taken to prevent the uiament m i t u r e or the fractions wllected frbm going to dr;ness while concentrating them because they may oxidize in air. If storage of the is required, tb;! dissolved pigments may be sealed in a flask with Parafilm. The only difficulty encountered was a tendency for the column to separate if allowed to stand attached to the vacuum filter flask. Application of a gentle vacuum reunites the column without adverse results. This procedure has been well received by the students. It gives results comparable to the macroscale method while requiring less time and smaller amounts of chemicals. Literature Cited 1. Miller, J,A; Neuril, E. F Madern E x p r i m n f o l O w e Chemlatn: D.C. Heath: laxingtan, MA, 1982; pp 270-274.
Salt Bridge Using Soil Moist David W. Brooks and Helen B. Brooks Center for Curriculum & Instruction University of Nebraska-Lincoln Lincoln, NE 68588
Small scale electrochemical experiments are becoming more common. While 24-well and even 48-well plates are hand for setting up most half cells (e.g., Cu/Cu2+; PtiFe me3+)and modern electronics makes high impedance multimeters readily available to teachers, salt hridges remain a problem. Strips of paper or pieces of wettable thread moistened with electrolyte often are inadequate. Recently we attem ted to do a microscale potentiometric titration. The CdCu1;: couple was used as a reference cell. A titration of Fez+with Mn04- with a platinum wire electrode was the reaction cell. (Nichrome is usable over the range of the experiment where Fez+is available.) Under these conditions, salt bridges of paper and thread failed. However, the following procedure worked. A small piece of Soil Moist, a dehydrated polymer (25% hydroxyethyl methacrylate, acrylamide copolymer, crosslinked acrylic homopolymer) that swells in water, was inserted ahout 3 cm into the stem of a plastic transfer pipet. (An unwound paper clip works well.) The pipet was squeezed slowly to expel air, then inserted into a test tube containing 0.5 M Na2S04, to draw the electrolyte solution slowly into the bulb. The pipet was allowed to stand for about 3 min. Changes in the solid were noticeable a t first but, before long, the solid seemed to disappear. The pipet was removed from the solution, and the bulb cut off where it joins the stem. The resulting tube remains filled with electrolyte, conducts well, and is flexible. It readily can be bent to conn e d adjacent or nearby wells. For the purposes of the potentiometric titration, this tube served as a n excellent salt
z
'Soil Moist is a product of JRM Chemical Division, 13900 BroadThe product is way Avenue. Cleveland. OH 44125.800-962-4010. available at garden stores. A62
Journal of Chemical Education
bridge. In addition, it was a practical laboratory use of the Soil Moist product.' The same approach can be used to construct a one-piece bridge-reference cell-stirrer. The tip of a standard plastic transfer pipet is cut to 4 cm. The polymer piece is placed about 2 cm into the stem. The pipet is then filled as above with 1M Na2S04After the gel swells, a small hole is made a t the end of the pipet bulb. A plastic transfer pipet is used to remove excess Na2S04 through the hole. Next 1 M CuS04 is added through the hole, a copper wire is inserted, and the entire piece is used a s a reference cell, salt bridge, and stirrer. When this device is used in the potentiometric titration, readings are remarkably stable aRer reaction in the working cell is complete.
A More Affordable Undergraduate Experiment on the Reduction of Acetophenone by Yeast Moses ~ e eand ' Martha Huntington Furman University Greenville, SC 29613
In a n earlier publication we described an experiment for the synthesis of (-1-(R)-a-deuteriovanillylalcohol by reduction of vanillin with yeast in D20 (11. While the ex~eriment was surcessful in i ~ i u s t r a t i n ~ t enantiomeric he &lecti\ity of the reaction, the expense of D20 may preclude some departments from adopting it. a he current contribution describes the reduction of acetophenone, 1,by yeast, which is more cost-effective in demonstrating the stereochemical control of such reactions. In the described experiment yeast is used to reduce 1to (Continuedon page A64) $C
0
II
H
Y
OH
3(S,S)andior 2(S,R)
Synthesis of I-phenyiethanol 2 give the optically active (-)-1-phenylethanol2 in 5 %yield, and NaBH4 is used to form the racemic alcohol 2 in 73% neld (see reaction below). Althouah the vield of the optically active 2 is not as high as the;eported value (2)sifficient auantities of it are easilv obtained to comolete this exerciie. Also in this study thestructure of 2 can i e readily deduced by IR, 'H-NMR (31, GC-MS, and polarimetric analyses. The chiral and racemic 2 are then reacted with (S)-(-)-methoxytrifluorophenylacetic acid (MTPA), 'Author to whom correspondence should be addressed.
