the yield up to 30% by carrying out the reaction in the presence of a cataIjrtic amount of triethylamine or pyridine under refluxing conditions. In their synthesis, labeled silver carbonate was prepared from sodium carbonate-C14, which in turn was obtained by liberation of carbon dioxide from barium carbonate-C l 4 followed by absorption in sodium hydroxide solution.We have now found that silver carbonate is obt,ained in about 90% yield by stirring barium carbonate with aqueous silver nitrate. This simplified! the whole procedure very much by eliminating the need of intermediate preparation of labeled sodium carbonate. Silver carbonate and excess of ethyl iodide in dry ether a t room temperature in the dark gave diethyl carbonate in about 40y0 yield based on the barium carbonate used.
EXPERIMENTALSilver ~arbonate-C'~. Since silver carbonate is unstable in the light and darkens when exposed even to diffuse room light for several hours, it had to be prepared and handled in the dark. Silver nitrate (4.3 g.) in 10 cc. of water was added gradually to a stirred suspension of 2.473 g. of barium carbonate-C*4 (0.0538 f 0.0006 mc./mole) in 10 cc. of water.After stirring for 30 min., the pale yellow precipitate formed was filtered off with a sintered-glass filter, and washed with water until silver ion was no more detected, then with ethanol, and finally with dry ether. The dried material weighed 3.4 g. In a preliminary evperiment with ordinary barium carbonate, silver carbonate prepared was analyzed for silver by dissolving it in dilute nitric acid followed by precipitation and weighing of silver chloride (Found: Ag, 70.60. Calcd. for
Diethyl carbonate-(~arbonyl-C~~). Silver carbonate-C14(3.4 g.) , 5.0 g. of ethyl iodide, and 20 cc. of ether were placed in a 100-cc. Erlenmeyer flask, and the mixture was allowed to stand for 50 hr. in the dark with occasional agitation. It was, after addition of 1.405 g. of non-labeled diethyl carbonate, filtered with a sintered-glass filter, and the residue was washed with two portions of 10 cc. of ether. The filtrate and washings were combined and distilled through a Vigreux column, yielding 1.8 g. of diethyl carbonate-(carbonyl-C14), -4 half gram of the diluted labeled ester obtained above and 0.7 g. of hydrazine hydrate were heated at 120' for 6 hr. in an oil bath. The solid precipitate, on 3 crystallizations from ethanol, gave carbohydrazide-C14 of a constant activity of 0.0167 = 0.0006 mc./mole, m.p. 152.0-152.5'. The diluted ester, therefore, had an activity of 0.0167 mc/mole, and this value indicated that 0.630 g. of diethyl carbonate-(carbonyl-(214) had been formed before the dilution corresponding to a yield of 42.8y0 based on the barium carb0nate-0~ used. The total recovery of radioactivity in the product from the active b:trium carbonate was 37.970.Radiocictivity determinations. The carbohydrazide-C14 (40 mg.) was oxidized according to the method of Van Slyke and Folch,3 and the liberated carbon dioxide was converted into barium carbonate and counted on an "infinitely thick" la...
