New methylides are stable
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Sulfonium ylides in which the nega tive charge on carbon is stabilized only by sulfonium groups have been iso lated for the first time by two chem ists at the University of Massachusetts, Amherst [/. Am. Chem. Soc, 88, 1560 ( 1966) ]. An ylide is an internal salt of a carbanion and a nonmetal. The university's Dr. C. Peter Lillya and Phillip Miller have prepared the three "strikingly" stable bis(dialkylsulfonium) methylides by treating the corresponding methylene bis(dialkylsulfonium ) difluoroborates with one equivalent of potassium hydroxide in methanol. The alkyl groups are methyl or ethyl groups.
LOTIONS GLOW LIKE LIQUID PEARL Hydrofol Acid 336 in solid form exhibits a glistening needle-like structure. This high-purity eutectic mixture of stearic and palmitic acid adds pearlescent brilliance to lotions and creams. Other advantages: Practically odorless and resists color change for long shelf life, outstanding for pharmaceuticals as well as cosmetics. AGREEMENT. The experimental NMR spectrum (top) of cyclobutane dissolved in pfp'-di-n-hexyloxazoxybenzene, obtained by Dr. Saul Meiboom, agrees with the theoretical spectrum (bottom) computed by Dr. L. C. Snyder. Refinements of the analysis give almost perfect agreement
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tances, and 114.6° for the H - C - H angle. The corresponding values of 1.510 Α., 1.089 Α., and 115.1° were obtained from electron diffraction data by Dr. O. Bastiansen, Dr. F. N. Fritsch, and Dr. Kenneth Hedberg at the University of Oslo (Norway). The Bell workers then went on to study the structure of cyclobutane, a molecule that scientists believe is slightly bent from a planar configura tion. (Dr. Meiboom disclosed the NMR work at the 151st ACS National Meeting. ) After testing various assumptions for the geometry and motion of the cy clobutane molecule, they have found one in which the experimental NMR spectrum agrees quite closely with the calculated spectrum. For cyclobutane, they arrive at a value of 18° ± 1° for the molecule's dihedral angle (between the two planes defined by the carbon atoms) and 6° ± 1° for the angle of tilt of the methylene groups. There are two such equivalent ge ometries. Dr. Meiboom and Dr. Snyder thus conclude that cyclobutane is rapidly flipping between the two. The Bell team now is studying the position of the carbon relative to the protons in cyclobutane using proton NMR spectra of molecules containing carbon-13 in natural abundance. They are also studying the structures of other simple organic molecules.
bis(dialkyl8ulfonium) methylide Dr. Lillya and Mr. Miller launched their attempts to synthesize the bis(dialkylsulfonium)methylides because they anticipated that the compounds would be unusually stable. They also expected that these ylides would react with carbonyl compounds. Thus, they reasoned, the ylides would be useful reagents for organic syntheses. To prepare the bis(dialkylsulfonium ) difluoroborates, the Massachu setts team reacts bis (methylthio) meth ane or bis (ethylthio) methane with triethyl- or trimethyloxonium fluoroborate [/. Am. Chem. Soc, 88, 1559 (1966)]. These bissulfonium salts precipitate from aqueous solution as glistening white crystals when ethanol is added slowly. The bissulfonium salts behave on monobasic acids in aqueous solution and can be titrated potentiometrically with alkali in dilute aqueous solution. These neutralization reactions can be followed by observing the ultraviolet spectra of the bissulfonium salts. A 10-3M. solution of bis(diethylsulfonium) methane difluoroborate in methanol gives an absorption maxi mum at 214 m/i, Dr. Lillya and Mr. Miller find. When they add small amounts of hydrogen chloride to this solution, the absorption at 214 πΐμ, is APRIL 25, 1966 C&EN 53
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reduced to zero. By contrast, addition of one equivalent of sodium methoxide greatly increases absorption. These changes are reversible. From this and the titration data, they suggest the formation of bis(dialkylsulfonium)methylides, which are similar to those formed by the closely related methylenebis ( triphenylphosphonium) salts reported by other workers. Several pieces of evidence support the structure for the sulfonium ylides proposed by the Massachusetts chemists. For example, treating the ylides with aqueous fluoroboric acid regenerates the corresponding bissulfonium salts in high yields. The nuclear magnetic resonance spectra of both the fluoroborates and the tetraphenylboronate derivatives are consistent with the ylide structures. Potentiometric titration curves for the starting methylenebis (dialkylsulfonium) salts indicate the formation of conjugate bases by loss of only one proton. And the UV spectra of the fluoroborate ylides and elemental analyses of the tetraphenylboronates are also consistent with the ylide structures. In contrast to less stable sulfonium ylides, the bis(dialkylsulfonium)methylides do not react with carbonyl compounds. The tetraphenyl boronate ylides can be recrystallized from hot aqueous acetone. None of these ylides react with p-nitrobenzaldehyde, which reacts readily with the stable dimethylsulfoniumfluoroenylide. The nucleophilic character of the bis(dialkylsulfonium)methylides is apparent, however, in their reactions with alkyl and acyl halides. Bis(methylethylsulfonium ) methylide fluoroborate reacts vigorously with benzoyl chloride. The resulting deep-orange oil hydrolyzes at room temperature in the presence of iodide ion to give phenylglyoxal hydrate as one of the products. Dr. Lillya and Mr. Miller view this reaction as a nucleophilic displacement of chloride ion by the ylide, followed by an iodide-catalyzed hydrolysis of the resulting substituted bissulfonium salt.
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