provocative opinion Down-Scaling Organic Experiments: Another Option H. Raymond Shelden Loma Linda University, Riverside, CA 92515 Recentlv there has been considerable interest in downscaling organic experiments. Most of the discussions have centered around microscale work. leadine to the publication of laboratory books'J and the marketing of chem kits designed specifically for microscale experiments. This article presents a third option, semi-microscale, and, based on three years' experience, shows it to he a viable alternative for down-scaling organic experiments. Typically macroscale organic experiments involve 5 to 20 e of startine material and are done in 125- to 500-mL flasks. khile microwork starts with 0.03 to 0.5 of material and uses 0.1- to 10-mL containers. In contrast to both of these options, semi-micro experiments start with0.3 to 2 g of material and are carried out in 10- to 50-mL flasks. In the past, one of the major impediments to semi-micro work has been the difficulty of finding suitable plassware. Today this problem no longer exists, although a-complete setup does require acquisitions from more than one supplier. hep primary Eomponent of the equipment used is a chem kit produced by Safe-Lab3 that contains all of the items commonlv found in chem kits and emnlovs 14/20 standard-taner joints. The kit was customized slightly for semi-micro work by substituting a 10-mL separatory funnel, a variety of 10mL flasks, and a 25-mL two-neck flask for the standard larger pieces. Safe-Lab glassware is unique in that in addition to the standard taper joint, all male members are threaded, allowing plastic locking nuts to hold the joint tight during use, and facilitating the loosening of a stuck joint. These locking nuts allow several pieces of glassware t o be held together in one secure unit. For example, an entire distillation setup can be locked together and held in position with one clamp, making apparatus setup easy and assuring tight joints, which in turn increases yields. Another source of useful elassware for semi-micro work is Kontes,' which produces l 6 m Erlenmeyer ~ flasks (without standard taoer ioints~and 25-mI. filter flask. Althoueh these items are dekgned a8 the larger pieces of their micro kit, they are available separatelv. Hirsch funnels and 10-ml. beakers are available from a number of suppliers. Add to these items a few moderate-size beakers (for water baths), graduated cylinders, small test tubes, and a spatula, and one has a locker equipped to do a vast number of experiments. Finding a lab book desiglied for semi-micro work is not quite as easy. However, since the techniques used in semimicro work are the same as those used in macroscale. anv common lab hook can be adapted by simply modifying thk amounts of material called for. If need be the down-scaled amounts can be merely written on a laboratory hlackboard. Experience has shown, however, that it is helpful to duplicate a short supplement giving the reduced amounts of ma-
74
Journal of Chemical Education
terial and sizes of glassware to be used. Althoueh this approach is not as iieal as a book designed spec~ficallyfbr semi-micro work, i t does allow the use of experiments that are already familiar and are from a wide variety of sources. Discussions with publishing representatives indicate that semi-microscale books m a r he available soon. Students have had success doing experiments on anywhere from one-fifth to one-twentieth of the amounts commonly called for in popular macroscale lab manuals, depending on the number of steps involved and the amounts originaily listed. Using the &sware described, students can ho ex~erimentssuccessfullvstarting with0.2 p. to 2 p. For example, in the common dehjdration of cyclohe~anol~xperiment, 1.9 g of cyclohexanol leads to 0.75 g of cyclohexene after the final distillation, and 0.3 g of salicylic acid can be converted to 0.18 g of recrystallized aspirin. With liquids of low to moderate boiling points, as little as 1 mL can be distilled, producing a reliable boiling point with 75% recovery. One important variation from macroscale work is the necessity of using pipets to transfer liquids. Semi-microscale experiments provide many advantages over macroscale work, including reduced cost of reagents, reduced waste peneration, reduced vapors in lab, and increased safety. considerable time is saved, particularly in distillations, filtrations, and heating and cooling periods. In situations where a reagent must be added in small amounts, it is often possible safely to add it all a t once. All of these advantaees also anolv to microscale work. However, some additional a d v a c i e s of semi-microscale work are that i t teaches the common, traditional techniques of organic chemistry, including separatory-funnel work and vacuum filtration. Also. this scale is laree enoueh that students really experienceorganic chemist&. e he; can see reflux rings, color changes, and signs of reaction. Sufficient produciis produced t h a t students see it, even smell it, and experience the thrill of having made something. These factois are important in helping students to reaize that the experiments they are doing are part of the real world, that chemistry actually happens!
Presented at me 193rd ACS National Meeting, Divislon of Chemlcal Education. April 1987. ' Mayo, D. W.; Pike, R. M.; Butcher, S. S. Microscale Organic Laboratory: Wiiey: New York, 1986. Williamson, K. L. Mlcroscale Organic Experiments; Heath: Lexington. 1987. Safe-Lab, Inc.. Santee. CA. Kontes, Vineland. NJ.
