A simple sublimation apparatus - Journal of Chemical Education (ACS

A simple sublimation apparatus for use in organic chemistry. .... Members · Librarians · ACS Publishing Center · Website Demos · Privacy Policy · Mobi...
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the micro~ccrle Icrborcrtory

The sample dispenser consists of a 13- X 100-mm screw-capped culture tube fitted with a self-sealing, Teflon-lined septum and an open-topped cap. The liquid reagent is introduced via syringe into the culture tuhe after it has been flushed with argon. A small argon-filled halloon is used to maintain the inert atmosphere as students remove samples. (The inflated balloon is slipped over the end of a disposable 2.5-mL syringe body from which the ears have been removed.) The syringe is fitted with a 4-in. 22-gauge needle that extends to the bottom of the tube. The filled tube is then inverted and clamped to a ring stand. In this position the tip of the needle is above the surface of the liquid so that none of the sample enters the balloon. Students remove the &sensitive solution using polypropylenelpolyethylene syring~.~ When theexperimentisdoneon a 1-mmol scale, each student requires about 1.6 mL of 1.4 M methyl lithium. Since the capacity of a 13- X 100-mm culture tube is approximately 8 mL, each apparatus services four or five students. Four such assemblies meet the needs of an entire lab section. When used with a 31s-in., %gauge needle, a balloon/syringe assembly also provides students with a convenient means to maintain an inert atmosphere over their reactions. The argon-filled balloon allown students to flush the air from their apparatus through a vent needle. Without a vent, the balloon expands in response to addition of reagents to the apparatus. This prevents pressure from building up and facilitates the injection of samples. It should be noted that argon is preferable to nitrogen for two reasons. First, organolithium reagents do not react with argon. Second, being more dense than air, argon will displace it from the bottom of a reaction vessel.

Use an Eppendorf pipetter to dispense 1.00 i 0.02 mmol of 3-methyl-2-cyclohexen1-one into a dry 13- X 100-mm screwcapped culture tube. Stopper the tube with aTeflon-lined septum, and vent it witha 26gauge needle. Inject 2.2 0.1 mL of anbydrous ether into the tube. Remove the vent needle. Place 1.00 i 0.02 mmol of copper(1) iodide into a dry, 5-mL conical vial equipped with a spin vane. Seal the vial with a Teflonlined septum. Vent it as you did previously, and flush it with argon from a balloon attached to a 2.5-mL syringe fitted with a % in. %-gauge needle. After 1-2 min, inject 300400 wL of anhydrous ether. Remove the vent needle. Stir the CuIIether slurry in an ice-water bath rapidly for 3 4 minutes before injecting 2.20 i 0.02 mmal of 1.4 M methyl lithium into the reaction vial. Continue to stir the mixture for 5 min. With a 2.5-mL syringe, inject the 3-methyl-2-cyclobexen-1-one solution into the stirred CuIlether slurry over a period of several minutes. Continue to stir the mixture at 0 OC for 5 min and at room temperature for an additional 10 min. Using a Pasteur pipet, squirt the reaction mixture into 2 mL of NH3/NHaCI buffer (pH = 8-9) in a 25-mL Erlenmeyer flask. Swirl the solutions as you mix them. Continue mixing by drawing the sulution into the Pasteur pipet and expelling it back intn the flask several times. Hinae the mini-vial with another 0.5 mL portion of buffer, followed by 0.5 mL of solvent ether. Add these rinses to the Erlenmeyer flask. Transfer the entire sample to a 13- X 100-mm screw-capped culture tuhe. Stopper the tube tightly, and shake it vigorously. Centrifuge the sample for approximately 1min to facilitate separa-


tion of the aqueous and organic phases. Wash the ether layer with 1mL of saturated salt solution. Transfer the bulk of the ether layer into another culture tuhe containing approximately 300 mg of anhydrous sodium sulfate. Rinse the salt solution with 0.5 mL ofsolventether. Combine this rinse with the other ether layer. Cap the tube,and shake it gently. Filter the solution through approximately 100 mg of anhydrous sodium sulfate in a filter pipet. Rinse the culture tube with 0.5 mL of solvent ether, and pass the rinse through the filter pipet, too. Collect the filtrate in a tared 5-mL mini-vial. Evaporate the ether in a sand bath until the mass of the sample decreases by less than 5% between two successive weighings.

' a . Mayo. D. W.: Plke. R. M.: Butcher. S. S. Microscale Organic L a h t a y . 2nd ed.: Wiley: New York. 1989. b. Pavia, D. L.: Lampman, G. L.: Krlz. G. S.: Engel. R. G. lntrcduction to Organic L a h t a y Techniqw: A Microscale Appmach; Saunders: Philadelphia, 1990. a. Willlamson. K. L. Macmcale and Miw+ scab hgsnic Experiments; Heam: Lexington. 1989. b. Rodig, 0. R.; Bell, C. E., Jr.: Clark, A. K. Organic Chemishy Laboram Standardand Miscale Experimentsbunders: Philadelphia. 1990. An experiment h t requires Inert atmosphere ~ondltlonsappeared in J. Chem. Educ. 1990, 67, A232 while this work was In progress. House, H. 0.: Fischer. W. F.. Jr. J. Org. Cham. 1863, 33, 949. These syrlnges are available horn Aldrlch Chemical Co.. 940 W. St. Paul Ave.. Milwaukee. WI 53233. They are suitable for use with organ* llmlurn reagents.

A Simple Sublimation Apparatus Henry Brouwer Redeemer College Ancaster. ON L9G 3N0, Canada With the widespread use of small-scale reactions in organic chemistry, the role of sublimation as a means of purifying compounds is becoming more important. A recent article in this Journal1 described in allglass microsuhlimatar adapter for use witha 5-mL vial fitted with a 14/10 glass joint. To construct such a device would require glassblowing facilities and skills. Although a simpler sublimation apparatus can be made* by test tube with a ruhfitting a large side.her stopper bored to accept a smaller test tube, which serves as a cold-finger, such a device has several disadvantages. First, because the test tube needs to be small, it cannot contain murh ice. Second, it is located too high in the larger test tuhc for good sublimation. Third, it is difficult to bore the (Continued on page A641


Journal of Chemical Education

the microtcole loborotory

rubber stopper. These difficulties can be overcome with the modifications described and illustrated below. A 15- x 125-mm test tube is fitted a t the top with a IO-rnm length of 15-mm-i.d. Tygon tubing or a ring of masking tape thick enough to prevent the small tube from slipping into the Larger one. An O-ring seal, made by cutting about 3 mm from a piece of latex tubing (%-in. i.d. X %a-in. wall), is placed near the top. This should fit snuggly into the side-arm test tube (18 X 150mm) to form a good seal. The sample to be sublimed is placed inside the larger test tube, the inner test tube is filled with crushed ice, the side arm is connected to a water aspirator, and the apparatus is placed in a hot sand or water bath. Compounds that have been found to sublime well are biphenyl, naphthalene, paradichloro-benzene, henzophenone, benzoie acid, and camphor. Additional compounds are listed in the article by Winston.'

The apparatus.

15 mm i.d. Tygon tubing or masking tape O-ring (cut from 4i-in. i.d. X %-in. wall latex tubing)

18 X 150 mm srde-arm test


----- 15 X 125 mm test tube

'Winston. A. J. Chem. Educ 7990, 67, 162. WIICOX. 6.F.. JL Experimental Organic Chem istry; MacMillan: New York, 1988: p 74. bed

Journal of Chemical Education