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71.
Alfred Fischer Michael W. Morgan Colin Eaborn 《Journal of organometallic chemistry》1977,136(3):323-332
Rates of cleavage of some picoyl- and (quinolylmethyl)-trimethylsilanes (RSiMe3, where R = PyCH2 or QnCH2SiMe3) have been measured in “90%” aqueous methanolic sodium methoxide at 50°C. Relative reactivities are: 2-PyCH2, 1.0; 3-PyCH2, 0.030; 4-PyCH2, 8.9; 2-QnCH2, 41; 3-QnCH2, 0.161; 4-QnCH2, 37. The rates correlate well with those for base-catalysed hydrogen-exchange in the parent carbon acids RH. Approximate pKa's (based on the scale of ion-pair acidities in CsNHC6H11H2NC6H11, with pKa of 9-phenylfluorene = 18.6) for the carbon acids, RH, can be derived as follows: 2-PyCH3, 29.5; 3-PyCH3, 34; 4-PyCH3, 27; 2-QnCH3, 25; 3-QnCH3, 32; 4-QnCH3, 25.Rates of cleavage of pyridyl- and quinolyl-trimethylsilanes (PySiMe3 and QnSiMe3) by sodium hydroxide in 4 : 1 v/v Me2SO/H2O at 50°C have also been measured; and the relative reactivities are: 2-Py, 1.0; 3-Py, 2.9; 4-Py, 8.4; 2-Qn, 15.9; 3-Qn, 12.7; 4-Qn, 184. The sequence of reactivity differes from that for base-catalysed hydrogen-exchange at the relevant positions of pyridine and quinoline, indicating that the reactivities are not determined in both cases (if in either) solely by the stabilities of the corresponding carbanions. 相似文献
72.
In many technical processes, complex multicomponent mixtures have to be handled, for example, in reaction or separation equipment. High-resolution NMR spectroscopy is an excellent tool to study these mixtures and gain insight in their behavior in the processes. For on-line studies under process conditions, flow NMR probes can be used in a wide range of temperature and pressure. A major challenge in engineering applications of NMR spectroscopy is the need for quantitative evaluation. Flow rates, recovery times, and other parameters of the on-line NMR experiments have to be optimized for this purpose. Since it is generally prohibitive to use deuterated solvents in engineering applications, suitable techniques for field homogenization and solvent signal suppression are needed. Two examples for the application of on-line NMR spectroscopic experiments in process engineering are presented, studies on chemical equilibria and reaction kinetics of the technically important system formaldehyde-water-methanol and investigations on reactive gas absorption of CO(2) in aqueous solutions of monoethanolamine. 相似文献
73.
Dan Veierov Tuvia Bercovici Ernst Fischer Yehuda Mazur Amnon Yogev 《Helvetica chimica acta》1975,58(4):1240-1243
Enol-esters 1a-1e undergo clean Photo-Fries-rearrangements without side reactions. With anthroyl derivatives the reaction is observed only at 254 nm, not at 366 nm. 相似文献
74.
Guibin Ma Andreas Fischer Julius Glaser 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m177-m178
The title compound, bis(dimethyl sulfoxide)triiodothallium(III), [TlI3(C2H6OS)2], was crystallized from equimolar amounts of TlII and I2 in a dimethyl sulfoxide (DMSO) solution. After the initial redox reaction, the thallium(III)–iodo complex forms and precipitates as a DMSO solvate. In the crystal structure, Tl is surrounded by three iodide ligands in the equatorial plane and two O‐coordinated DMSO molecules in the axial positions, forming a slightly distorted trigonal bipyramid. The complex lies on a twofold rotation axis, making the DMSO molecules and two of the I atoms crystallographically equivalent. 相似文献
75.
1,3-Dipolar Addition of 2-Benzonitrilio-2-propanid to 7-Methylthieno[2,3-c]pyridine 1,1-Dioxide and Subsequent Reactions The addition of dipole 2 , generated photochemically from 2,2-dimethyl-3-phenyl-2H-azirine ( 1 ), to 7-methylthieno[2,3-c]pyridine 1,1-dioxide yields the pyrroline derivative 4 as a major product and regioisomer 5 in low yield. Compound 4 can be transformed into the pyrrolidine derivative 11 by ring opening, loss of SO2 and hydrogenation. Bromopyrroline derivative 14 gives either by dehydrohalogenation compound 18 or, by substitution, nitrile 17 or ethoxy derivative 19 . Substitution of 14 and ring opening yields methoxypyrrole derivative 20 , which gives access to the unstable hydroxypyrrole and hydroxypyrrolidine derivative 28 resp. 30 . The vinylsulfone 18 is the starting material for addition-ring-cleavage reactions. Oxidation of pyrroline derivative 4 gives epoxy-substituted N-oxide 39 and di-N-oxide 40 ; and oxidative transformation of pyrrolidine derivative 11 yields the (hydroxymethyl)pyridylpyrrolidine derivative 45 . 相似文献
76.
Julian M. Menter Patricia P. Acin Robert M. Sayre † Isaac Willis 《Photochemistry and photobiology》1992,55(5):705-712
This work provides a dose-response model of UV-induced epidermal-stratum corneum thickening induced by irradiation at wavelength lambda. This model assumes that photobiochemical reaction(s) can give rise to hyperplasia in a manner which is predictable from a simple photochemical kinetic scheme. In this work, we derive an equation which predicts an approximately linear relationship between the logarithm of the increase in optical skin thickening measured at 320 nm (delta OD320) and total cumulative dose (DT) seen by the target cells in or near the basal layer. For each excitation wavelength lambda, the slope R(lambda) of the log delta OD320 vs DT plot is proportional to epsilon(lambda) phi rx, where epsilon(lambda) is the extinction coefficient for the target chromophore at excitation wavelength, and phi rx is the quantum yield for the photochemical reaction(s) leading to hyperplasia. Our data previously obtained from irradiation of SK-1 hairless mice with "monochromatic" UV wavebands at 280, 290, 300, 307 and 313 nm (Menter et al., 1988, Photochem. Photobiol. 47, 225-260.) and data from Sterenborg and van der Leun at 254 and 313 nm (1988, Photodermatology 5, 71-82) are in good agreement with this model, except for 254 and 280 nm excitation, which are greatly attenuated by epidermis-stratum corneum. For excitation at the latter wavelengths, "dark" regressive processes successfully compete with the "light" reaction(s) which lead to (pre)cancerous lesion. This difficulty notwithstanding, the "intrinsic" action spectrum for hyperplasia derived from these measurements indicates that the target chromophore preferentially absorbs in the UV-C region.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
77.
The title amines were pyrolyzed in a stirred-flow reactor at 380–510°C, pressures of 8–15 torr and residence times of 0.3–2.4 s, using toluene as carrier gas. The substrates with an allyl group yielded propene and iminonitriles as reaction products. HCN is formed by decomposition of the iminonitriles. The first-order rate coefficients for propene formation fit the Arrhenius equations
- Allyl cyanomethyl amine:
- Diallyl cyanomethyl amine:
78.
V. V. Burlakov A. V. Letov P. Arndt W. Baumann A. Spannenberg Ch. Fischer L. I. Strunkina M. Kh. Minacheva Ya. S. Vygodskii U. Rosenthal V. B. Shur 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):63-67
Zwitterionic titanoxanes {Cp[η5-C5H4B(C6F5)3]Ti}2O (I) and {(η5-iPrC5H4)[η5-1,3-iPrC5H3B(C6F5)3]Ti}2O (II), which contain two positively charged Ti(IV) centres in the molecule, are able to catalyse the ring-opening polymerization of -caprolactone (-CL) in toluene solution and in bulk. The process proceeds with a noticeable rate even at room temperature and accelerates strongly on raising the temperature to 60 °C. The best results have been obtained on carrying out the reaction in bulk. Under these conditions, the use of I as a catalyst (-CL:I = 1000:1) gives at 60 °C close to quantitative yield of poly--CL with the molecular mass of 197 000. An increase in the -CL:I ratio to 6000:1 increases the molecular mass of poly--CL to 530 000. Tetrahydrofuran (THF) is also polymerized under the action of I albeit with a lesser rate. However, the molecular mass of the resulting poly-THF can reach rather big values under optimal conditions (up to 217 000 at 20 °C and the THF:I ratio of 770:1). A rise in the reaction temperature from 20 to 60 °C results here to a decrease in the efficiency of the process. Titanoxane II is close to I in its catalytic activity in the -CL polymerization but it is much less active in the polymerization of THF. Propylene oxide (PO), in contrast to -CL and THF, gives with I only liquid oligomers in wide temperature and PO:I molar ratio ranges (−30 to +20 °C, PO:I = 500–2000:1). γ-Butyrolactone and 1-methyl-2-pyrrolidone are not polymerized under the action of I at room temperature. The reactions found are the first examples of catalysis of the cationic ring-opening polymerization by zwitterionic metallocenes of the group IVB metals. 相似文献
79.
Microemulsion-based synthesis of CeO(2) powders with high surface area and high-temperature stabilities 总被引:2,自引:0,他引:2
Bumajdad A Zaki MI Eastoe J Pasupulety L 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11223-11233
Pure ceria powders, CeO(2), were synthesized in heptane-microemulsified aqueous solutions of CeCl(3) or Ce(NO(3))(3) stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethylammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO(2). Characterization of the powders by X-ray powder diffractometry, laser-Raman spectroscopy, and Fourier transform infrared spectroscopy revealed that in the presence of surfactants almost-agglomerate-free nanosized crystallites (6-13 nm) of anionic vacancy-free cubic CeO(2) were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO(2) was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N(2) sorptiometry, and high-resolution electron microscopy showed AOT- or (DDAB + Brij 35)-stabilized microemulsions to assist in formation of crystallites exposing surfaces of large specific areas (up to ca. 250 m(2)/g) but of low stability to high-temperature calcination (28-13 m(2)/g at 800 degrees C). In contrast, the double-chained DDAB was found to generate cubic CeO(2) crystallites of lower initial surface areas (144 (microemulsion) to 125 (vesicles) m(2)/g)) but of higher thermal stability (55-45 m(2)/g at 800 degrees C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts. 相似文献
80.
Hans-Rudolf Waespe Heinz Heimgartner Hans Schmid Hans-Jürgen Hansen Henning Paul Hanns Fischer 《Helvetica chimica acta》1978,61(1):401-429
The photochemical reactions of different allyl aryl ethers (Scheme 3) were investigated in hydrocarbons (Chap. 3.1) and in alcoholic solvents (Chap. 3.2). The composition of the photoproducts depended very much on the nature of the solvent. Irradiation (3–95 h) of different methyl substituted allyl aryl ethers ( 1, 3, 5, 7 and 11 ) with a low pressure mercury lamp (λEmiss. = 254 nm; 6 or 15 Watt) under argon (quartz vessel) resulted in the formation of 2-, 3– and 4-substituted phenols, dienones and products of consecutive reactions (Tables 1–4 and 6). The results suggested that all products were formed by homolytic cleavage of the C? O bond in the singlet state of the ethers to intermediate radical-geminates (Scheme 5) followed by radical recombination of the two fragments. No products were formed by concerted processes (Table 5, Schemes 5 and 6). Upon irradiation of allyl aryl ethers lacking alkyl substituents at position 4 ( 1 and 5 ) in protic solvents, mainly 2- and 4-allylated phenols were obtained (Tables 1 and 4); 3-allylated phenols were formed only in small amounts (0.02%). However, in aromatic hydrocarbons or cyclohexane 3-allylated phenols were obtained from 1 , 5 and 11 in significant amounts (3–11%; Tables 1, 4 and 6). E.g., upon irradiation of allyl-2,6-dimethyl-2,4-cyclohexadien-1-one ( 6 ) besides 3- and 4-allyl-2, 6-dimethyl-phenol ( 23 and 24 ). Irradiation of 5 in methanol afforded 23 and 6 only in traces, whereas 24 was the main product. 相似文献