A Better Way to Prepare DGI For ahout 20 years we have had undergraduate students prepare samples of DCl(g) far physical chemistry experiments using the usual method of refluxing DzO and benzoyl chloride in a vacuum system connected to a gas cell. This method has serious drawbacks, among which are lack of control of the rate of reaction, formation of solid benzoic acld as a byproduct, possible exposure to a suspected carcinogen, benzoyl chloride, and 1-2 h preparation time. For the past five years we have used a simple alternative method of preparing DC1, with very satisfactory results. The reaction is
D2SOacan be purchased readily at a reasonable price (Sigma Chemical Ca.). Soon after it isreceived, the DzSOa should be transferred in 2- or 3-mL portions into small ampoules, which are sealed. This step prevents exchange of D with H from H10 in the atmomhere. Assumine that reaction (1) eoes to camnletion. 1mL of D8Oa should produce about 0.95 L of &e estimated volum; of the gas cell, reaction flask, and vacuum Gne connecting tubing, it D $ ( ~ ) at 25'C and 1atm. ~ r o m is easy to determine how much D2S04is required. For each liter of DCl(g) to he prepared, or each 1mL of DzS04 used, place a t least 3 g (an excess) of KCl(s) in a 125- or 250-mL three-necked flask. Add a magnetic stirring bar, and connect one neck to the manometer of the vacuum line which is also connected to the gas cell. Place a dropping or separatory funnel in the second neck. The third neck is connected throuah . a stopcock to an aspirator. Close this stopcock. Pump the air from the flask, manometer, and cell, and check for leaks. Open an ampoule of D2S04and add the contents (perhaps 2 mL) to the dropping funnel. Start the magnetic stirrer. Close the sto~cockconnectine the manometer to thevacuum manifold. Carefullv add DISOa dro~wiseto the reaction flask. Ceaw nddina I ) ~ w s h~~ ,nth; manometer shows that rhe rrquirrd prerwre QIDCIga;has'been generated. Whrn the manometer reading has been rerordcd, dose the cell ~toprork.Repeatedly aspirate the reartion flask and manometer to prevent DCI getting into the vacuum system. The reaction goes rapidly and smoothly, making it easy to generate the desired quantity of DCI. Care must he taken to avoid adding d l of the DzS04which would then allow air to enter the reaction flask. Our students often prepare a mixture of HCI and DCI hy using a mixture of H2S04and Dzs0.1. ~~~~~
J. Leland Hollenberg University of Rsdlands Redlands, CA 92373
Volume 82
Number 10
October 1985
897
