Determination of organolithiums in hydrocarbons by high-frequency titration with acetone

Abstract

The results of numerous determinations of 0.3-to 10mg quantities of potassium, rubidium, and cesium are summarized in Tables II, III, and IV. With quantities greater than 0.5 mg, the mean error (regard to sign) is -0.3% for potassium, -0.2% for rubidium, and -0.4% for cesium. There is no reason to suspect that these mean errors are small because of fortuitous compensation of errors in the precipitation and coulometric titration. On the contrary, since errors associated with the precipitation certainly will tend to be negative, such compensation would require positive errors in the coulometric titration, which seems very unlikely in view of the results of the assays of the commercial sodium tetraphenylborate (Table I). We conclude that if there is any significant systematic error in the coulometric titration it is not greater than about 0.4%, and very probably is smaller. In other words, the precipitation reaction between tetraphenylborate ion and silver ion is stoichiometrically exact.That potassium tetraphenylborate, wetted with water, decomposes on drying is demonstrated by the data in Table V. In these experiments, 25.00-and 50.00-mg samples of potassium ion were precipitated as described above. The washed precipitates were then dried either in an oven at 105°, oral room temperature in a vacuum desiccator, to constant weight. After weighing, the dried precipitates were dissolved in pure acetone to a known volume, and aliquots were then titrated coulometrically.The gravimetric results are uniformly too high by 1.0 to 1.5% and there is no significant difference in weight by the two drying techniques. In sharp contrast, the coulometric results (which measure the tetraphenylborate content of the dried precipitates) are consistently several per cent too low, and oven drying tends to produce a greater deficiency of tetraphenylborate ion than drying in a vacuum desiccator at room temperature. Presumably, the decomposition reaction is hydrolytic, and the fact that it produces an increase in weight indicates that the products are relatively nonvolatile.

Kinetics and mechanism of the C-S coupling reactions of aryl Grignard reagents with aryl arenesulfonates

“…Phenyl tosylate was prepared according to the published procedure and authentic sample of phenyl p-tolyl sulfone was prepared by our reported sulfone synthesis procedure [30] using phenyl magnesium bromide-phenyl tosylate coupling. Grignard reagent was prepared in THF by standard method and their concentrations were found by titration prior to use [38]. Thermo-Focus gas chromatograph equipped with a ZB-1 capillary column (immobilized with phenyl polydimethylsiloxane) and a flame ionization detector was used for GLC analysis.…”

Stereoselectivity of directed epoxidations of 22-hydroxy-Δ23-sterol side chains

“…Vinylmagnesium bromide was purchased from the Aldrich Chemical Co. 2-Propenyllithium and 2-methyl-I-propenyllithium were titrated with diphenylacetic acid (26), (E)-1-propenylmagnesium bromide was titrated using 1,10 phenanthroline and sec-butyl alcohol (27), and n-butyllithium was titrated with 2,5-dimethoxybenzyl alcohol (28). Aldehyde 2b (29), allylic alcohol 7 (6), and di-(2,4,6-trimethylphenyl) diselenide (30) were synthesized according to literature methods.…”

Sulfonyl transfer mechanism in C–S coupling of phenylmagnesium bromide with phenyl arenesulfonates

“…THF was distilled over sodium benzophenone dianion and toluene was distilled over sodium. Phenylmagnesium bromide 1a was prepared in THF by standard method and its concentration was found by titration prior to use [41]. Phenyl arenesulfonates 2a-e were prepared by the published procedures using arenesulfonyl chlorides and phenol and were confirmed by melting points, IR and 1 H NMR spectroscopy [25,33,[42][43][44] Kinetic procedure for the reaction of phenylmagnesium bromide 1a with phenyl arenesulfonates 2a-e: The kinetics were followed by measuring concentration of remaining phenyl arenesulfonate by GC analysis.…”