reduction occurs mainly by axial attack on the ketone, a stereochemical result typical of cyclohexanones (4). Experimental The ketone isomer ratio is first determined by capillary GC analvsis3 of Aldrich 2.6-dimethvlnrclohexanone. with set from 80 'd to appro%ately 100 'C at 2 C the oer minute. Then 1 uL of ketone mixture is dissolved in 15 h o p s of methanol in a l-dram vial, a tiny granule (not more than a few millierams) of 1 0 4 0 mesh sodium borohydride is added, acd the liquid is swirled until the solid dissolves. About 0.5 mL of saturated aqueous sodium bicarbonate and 1-2 mL of hexanes are then added, and the vial is capped and shaken vigorously for a few seconds. After the layers separate (the organic phase should be clear), a 10-yL syringe is used to sample about 1yL of the upper hexanes phase (not the lower water layer!) for GC analysis using the same conditions as above. Literature Cited 1. Aldtich Chemical Company, Inc. I S 1 9 9 3 Hwdbmk of Fine Chemicals; item X 10,2261. 2. Corey.E. J.;Enders,D. Tobohedmnktt. 19TB.34. 3. Wigfield,D. C.; Phelp, D. J. J.Am. C k m Soc 19T4,96,543-549. orgonie C k m i s w , 3rd d.; Plenum: New 4. Carey, F.A ; Sundkrg, FL J. Ad"& Ymk, 1990;part B, pp 241-244.
3A ketone concentration of about 1 PL in 2-3 mL Of dichloromethane was used, with a 1 pL injection. The instrument used here was a Hewlett-Packard 5890 equipped with a 0.32 mm x 25 m HP-5 (SF54) capillary column and set to a split ratio of approximately 40:l, with helium carrier. Chromatograms were recorded on an HP 3396 integrator. In all cases, half-height peak widths were less than 0.05 min 13 s). - , If~necessarv the initial GC temoerature can be lowered %I0 'C to improve sepa&t/on. \-
Inexpensive Small-Volume Pipeting Travis Henley and Linda Munchausen Southeastern Louisiana University Hammond. LA70402
Manvmicmscale orocedures stioulate the use of a olastic syringi to deliver tLe small volulhes of organic li&ds reauired. These svrinees melt when accidentallv heated. and " the plunger is often incompatible with organic solvents. The following is a n inexpensive method that decreases the need to replace damaged syringes and is comparable to the s use of automatic ~ i ~ eort disoensers. A short length o r ' ~ ~ g oorn rubber tubing (about 2 cm, is cut and olaced uver the needle end of the svrinee. Inco the other end of the tubing is placed a regular &&able Pasteur pipet. The pipet should be positioned snugly against the syringe to minimize flexibility of the apparatus. When the tip of the Pasteur pipet is placed below the surface of the solution to be pipetted and the plunger of the syringe is raised to the desired mark, the volume of liquid pulled into the Pasteur pipet is equal to that specified by the syringe. The reagent is delivered into the reaction vial withoutactually touching the syringe, and the Pasteur pipet can be safely disposed of and replaced by a clean one for the next measurement. Loneer nieces of tubine and "flicking" the pipet tip are to be ivoi'ded because tcey increase the emor in disoensine small volumes. For reoetitive meadesurements madeinour lab, this inexpensive livered volumes that differed by no more than 2.3% from those measured with a Hach Tensette, The standard em the for five repetitive runs was for mL, 0.0023; for 0.2 mL, 0.0°18; for 0.5 mL, 0.0°13; and for
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Circle No. 5 on Readers' lnqulry Card Volume 70 Number 12 December 1993
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