ethers are not required for the disulfide cleavage reaction of organolithium compounds and are undesirable in the analysis of alkylaluminum compounds. However, ethyl ether does not react rapidly with organolithium compounds; and the analysis can be completed before the ether decomposition of organolithium compounds is serious. Furthermore in presence of stoichiometric amounts of ether, stable complexes can form which do not decompose the organolithium compounds (22) appreciably. Aliphatic thioethers, RSR, react with butyllithium to give stoichiometric amounts of mercaptide. An excess of thioether could be used in place of the disulfide as an analytical reagent. However, the thioether would be unsatisfactory for analysis of less reactive compounds such as lithium aluminum hydride and organomagnesium compounds. The problem of reaction of thioethers for the analysis of disulfide was handled by Veibel and Wronski (9) by controlling the reaction conditions. This approach could also be used in our analysis, but so far it has been unnecessary. Oxygen, water, and alcohols and the products of their reactions with organolithium compounds do not interfere with the disulfide cleavage procedure except for the destruction of a stoichiometric amount of organometal compound. Actually, the reactions with water (22) and with alcohol (3, 7) are the bases for procedures reported for analyzing organolithium compounds. The reaction product with oxygen has been used in a procedure for analyzing dilithioaromatic compounds (23). The stoichiometry of the water-RLi reaction (24) is being used in these laboratories as a basis for studying the effect of water on various organometal systems, and the results will be reported in the future. Organolithium Compounds. The disulfide cleavage procedure for the analysis of organolithium compounds has been used in these laboratories for several years and has been more convenient than the benzyl chloride coupling reaction and more accurate than the acid-base titration procedure and the vanadium oxide procedure in our hands. Precision is good as is shown by the analysis of a standard solution over a period of time (Table V). The possibility of analyzing methyllithium by this procedure is also worth noting (Table IV). The differences between the manufacturer’s assay of the stock solutions and that found by the disulfide procedure for stored solutions are similar to those reported by others (3,25), Table IV. The procedure can be used for analyzing dilute and concentrated solutions of organolithium compounds. Although the lower limit of sensitivity has not been established, application in different research problems indicates the sensitivity is comparable to that estimated for the most sensitive methods previously reported (5). Other Organometal Compounds. Any compounds capable of cleaving disulfides without side reactions could be analyzed (22) R. Adams, Ed., Org. Reactions, 6 , 353 (1951). (23) A. F. Clifford and R. R Olsen, ANAL. CHEM ,31,1860 (1959). (24) D. K. Polyakov, Polymer Sci. USSR,7 (4), 668 (1965). (25) R. L. Eppley and J. A. Dixon, J. Organometal. Chem., 8, 176 (1967).
by this procedure. Organo-potassium, -calcium, and -aluminum compounds seem to have reacted quantitatively with the disulfide in hydrocarbon solvents at a practical rate. Diethylmagnesium and diethylzinc reacted too slowly in hydrocarbon solvents for analytical purposes, but diethylmagnesium reacted quantitatively in ether at a satisfactory rate. The disulfide procedure seemed unsatisfactory for the analysis of organozinc compounds. Triisobutylaluminum reacted in 30 minutes with 3 moles of disulfide in cyclohexane or in heptane as solvent (Figure 1). The presence of toluene decreased the rate of reaction somewhat, but in the presence of 3377, ether or isoquinoline the organoaluminum reacted too slowly for practical purposes. This slow reaction in the presence of ether is attributed to the formation of complexes with polar solvents (23, 26). Either the complexes react slowly with the disulfide or an unfavorable equilibrium exists and only the free organoaluminum compound cleaves the disulfide. The sensitivity of the disulfide cleavage to the reaction medium indicates this procedure might be a simple means of studying the relative stability and kinetics of alkylaluminum-polar compound complexes. The slow drift of thiol determined in analyses of triisobutylaluminum to a value higher than a stoichiometric amount expected for a quantitative reaction suggests the presence of a side reaction. Hydrides which are known components of commercial alkylaluminum compounds (22, 27) were suspected. Excess lithium aluminum hydride cleaved tolyl disulfide quantitatively without any appreciable side reaction. Thus the presence of hydride could account for the higher than stoichiometric amounts of alkylaluminum if not corrected for. RECEIVED for review September 27, 1967. Accepted November 13,1967. (26) E. B. Baker and H. H. Sisler, J . Am. Chem. SOC.,75, 5193 (1953). (27) Ethyl Corp., Baton Rouge, La., “Technical Information on Aluminum Alkyls and Alkyl Aluminum Halides,” p. 28, 1959.
Correction Colorimetric Determination of Iron in Plutonium Metal Using a Nitrobenzene Extraction Technique In this article by C. E. Plock and C. E. Caldwell [ANAL.
CHEM. 39, 1472 (1967)J there is an error in column 2 of page 1472. The first sentence of the Reagents section should read as follows. “The hydroxylamine hydrochloride solution (2.2 %) was prepared by dissolving 108 grams of NH20H.HCl in water, adding 60 ml of glacial acetic acid, and diluting to 5000 ml with water.”
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