Moisture-Sensitive Reagents in the Student Laboratory While planning experiments on the characterization of alwhols we were confronted with the question of how best to dispense samples of 3,s-dinitrobenzoyl chloride and other moisture-sensitive reagents to a laboratory class of 30 students over a period of 3-4 weeks. During that time each student would need to obtain several accurately measured quantities (20&250 mg each) of these reagents for the purpose of preparing crystalline derivatives of the alcohols. Past experience with such moisture-sensitive substances has taught us that the wntinual opening of stock battles for removal and weighing of samples would saon lead to serious deterioration of the reagents, especially under the usual wnditions prevailing in a n undergraduate laboratory. A satisfactory solution to the problem was developed, involving syringe transfer of the reagents in solution in a n appropriate solvent. This resulted in the maintenance of reagent purity and a t the sametime minimized the lachrymatory effect of these substances. The method described below also avoids the need for multiple puncturing of the rubber serum cap as successive samples are withdrawn. By way of example, a bottle for dispensing 0.25 M 3,5-dinitrobenzoyl chloride in dichloromethane was prepared as follows. Ahmwn 8-oz. reagent bottle was marked at the 200-mL point and charged with 11.53 g (0.050 mol) of 3,5-dinitrobenzoyl chloride. Addition of dichloromethane with swirling and dilution to the mark gave a clear stock solution. A serum cap was put in place and then pierced with a 1%- in., 2-gauge 87ringe needle fastened to a plastic 5-mL syringe barrel. The latter was charged with Drierite and served as a drying tube. The serum cap was then pierced with a &in., 18-gauge needle leading to the bottom of the bottle and connected to a syringe of appropriate size (see figure). For use, the desired volume of solution is drawn up into the syringe, which is then detached from the needle and replaced by a Teflon Luer cap. The reagent is then discharged into the reaction vessel wntaining the alwhol to be derivatized along with Apparatus for dispensing moisture-sensi- a n equivalent of triethylamine. Acid chlorides have been stored in this wav. with freouent withdrawal of tive reagents. aamdes. . ~far neriods ~ ~ un~to five . weeks with no k;idence ofdeterioration of the reagent or s y r i n g ~needle. Hy replacing the drwng ttlhr with a static head of nirmgm, the Jystem can bc adaptcd for use with oxygsn-sensitive reagent* such ns Crignards and alkyllithiums. ~~~~~
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Samuel G. Levine NoRh Carolina State University Raleigh, NC 27695-8204
Volume 69 Number 6 June 1992
501
