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polystannane
Polystannanes are organotin compounds with the formula (R2Sn)n. These polymers have been of intermittent academic interest; they are unusual because heavy elements comprise the backbone. Structurally related but better characterized (and more useful) are the polysilanes (R2Si)n.
==History==
Oligo- or polystannanes were first described by Löwig in 1852,〔C. Löwig, ''Mitt. Naturforsch. Ges. Zürich'', 1852, ''2'', 556.〕 only 2 years after Edward Frankland's report on the isolation of the first organotin compounds.〔Edward Frankland|, ''Q. J. Chem. Soc.'', 1850, ''2'', 263.〕 Löwig' route involved treating an Sn/K and Sn/Na alloys with iodoethane, in the presence of quartz sand which was used to control the reaction rate. Products with elemental compositions close to those of oligo(diethylstannane)s or poly(diethylstannane) were obtained. Cahours obtained similar products and attributed the formation of the so-called "stannic ethyl" to a reaction of the Wurtz type.〔A. Cahours, ''Ann. Chem. Pharm. (Liebig’s Ann.)'', 1860, ''114'', 227A. Cahours, ''Ann. Chim. Phys., Sér. 3'', 1860, ''58'', 5.〕 Already in 1858, "stannic ethyl" was formulated as a polymeric compound denoted with the composition n(SnC4H5).〔A. Strecker, ''Ann. Chem. Pharm. (Liebig’s Ann.)'', 1858, ''105'', 306.〕 In 1917 Grüttner,〔G. Grüttner, ''Ber. Deutsch. Chem. Gesell.'', 1917, ''50'', 1808.〕 who reinvestigated results on hexaethyl-distannanes(H5C2)3Sn-Sn(C2H5)3 (reported by Ladenburg in 1870) confirmed the presence of Sn-Sn bonds and predicated for the first time that tin could form chain like compounds.〔A. Ladenburg, ''Ber. Deutsch. Chem. Gesell.'', 1870, ''3'', 353.〕 In 1943, it was postulated that “diphenyltin” exists as a type of polymeric material because of its yellow color (), and indeed a bathochromic shift of the wavelength at maximum absorption with increasing number of Sn atoms was found later in the case of oligo(dibutylstannane)s comprising up to 15 Sn atoms.〔L. R. Sita, K. W. Terry, K. Shibata, ''J. Am. Chem. Soc.'', 1995, ''117'', 8049.〕
The Wurtz reaction is still used for the preparation of poly(dialkylstannane)s. Treatment of dialkyltin dichlorides with sodium lead to polystannanes of high molar mass, however, in low yields and with formation of (cyclic) oligomers. (). Other efforts to prepare high molar mass polystannanes by electrochemical reactions〔M. Okano, N. Matsumoto, M. Arakawa, T. Tsuruta, H. Hamano, ''Chem. Commun.'', 1998, 1799. M. Okano, K. Watanabe, ''Electrochem. Commun.'', 2000, ''2'', 471.〕 or by catalytic dehydropolymerization of dialkylstannanes (R2SnH2) were also made ().〔T. Imori, T. D. Tilley, ''J. Chem. Soc., Chem. Commun.'', 1993, 1607; V. Y. Lu, T. D. Tilley, ''Macromolecules'', 2000, ''33'', 2403; H. G. Woo, J. M. Park, S. J. Song, S. Y. Yang, I. S. Kim, W. G. Kim, ''Bull. Korean Chem. Soc.'', 1997, ''18'', 1291; H. G. Woo, S. J. Song, B. H. Kim, ''Bull. Korean Chem. Soc.'', 1998, ''19'', 1161.〕 Unfortunately, frequently, the polymers prepared by those methods were not isolated and typically contained significant fractions of cyclic oligomers.
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