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391.
392.
Steven M. Heilmann Jerald K. Rasmussen Larry R. Krepski Howell K. Smith 《Journal of polymer science. Part A, Polymer chemistry》1986,24(1):1-14
The reaction of polymercaptans and 2-alkenyl azlactones has been further investigated, and several new multiazlactones which are liquids at room temperature have been prepared and characterized. Michael addition yielding the multiazlactones was found to take place slowly in the absence of and rapidly in the presence of acid catalysts. If basic impurities capable of forming mercaptide ion were present, however, the reaction underwent a substantially different course producing primarily ring-opened products. A source of these basic impurities was determined to be the method of preparation of the alkenyl azlactone itself. When the azlactone was prepared from its acyclic N-substituted aminoacid precursor by cyclodehydration by use of ethyl chloroformate and triethylamine, a small amount of triethylamine remained that dramatically altered the course of reaction. Nonbasic cyclodehydration agents such as dicyclohexylcarbodiimide were effective at eliminating this side reaction, as well as was the practice of adding excess acid to the reaction system to neutralize the basic impurities. 相似文献
393.
Vinylidene chloride polymers are prominent in the
barrier plastics packaging industry. They display good barrier to the transport
of oxygen (to prevent spoilage of food items) and flavor and aroma constituents
(to prevent 'scalping' on the supermarket shelf). However, these
polymers undergo thermal dehydrochlorination during processing. This can lead
to a variety of problems including the evolution of hydrogen chloride which
must be scavenged to prevent its interaction with the metallic walls of process
equipment. Such interaction leads to the formation of metal halides which
act as Lewis acids to facilitate the degradation. A potentially effective
means to capture hydrogen chloride generated might be to incorporate into
the polymer a mild organic base. Accordingly, copolymers of vinylidene chloride
and 4-vinylpyridine have been prepared and subjected to thermal aging. Results
suggest that the pyridine moiety is sufficiently basic to actively promote
dehydrochlorination in the vinylidene chloride segments of the polymer. 相似文献
394.
Angela Patti Giovanni Nicolosi James A.S. Howell Kristina Humphries 《Tetrahedron: Asymmetry》1998,9(24):2944-4394
Chiral ferrocenyl aminoalcohols possessing either OH or NR2 functionality to the ferrocenyl ring were prepared and exhibit modest enantioselectivities for the addition of diethylzinc to benzaldehyde. Chiral ferrocenyl aminonitriles exhibit a facile inversion process in protonic solvents. 相似文献
395.
Amy R. Howell W. R. Martin J. W. Sloan Walter T. Smith 《Journal of heterocyclic chemistry》1991,28(4):1147-1151
4-Azanicotine ( 1 ) has been synthesized by the cyclopropylimine rearrangement. A study of several Lewis acids as possible catalysts for the NMF-mediated cyclopropyl imine rearrangement of cyclopropyl-2-pyrazinylmethanone ( 4 ) indicated that both aluminum chloride and magnesium chloride are suitable catalysts, lithium bromide shows only a trace of activity and zinc chloride, titanium tetrachloride, and titanium tetra-isopropoxide show no activity. Compound 1 , in which the aromatic ring is less basic than in nicotine, and 6-aminonicotine ( 5 ), in which the aromatic ring is more basic, have been compared with the binding properties of nicotine in the P2 rat brain preparation. Compound 1 binds with an affinity very similar to that of nicotine at two of the receptor sites, 5 binds at these sites but with a lower affinity. Unlike nicotine, 1 and 5 do not bind at the very high affinity ‘upregulatory’ site. 相似文献
396.
Edwards HG Newton EM Dickensheets DL Wynn-Williams DD 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(10):2277-2290
The vital UV-protective and photosynthetic pigments of cyanobacteria and lichens (microbial symbioses) that dominate primary production in Antarctic desert ecosystems auto-fluoresce at short-wavelengths. A long wavelength (1064 nm) near infra-red laser has been used for non-intrusive Raman spectroscopic analysis of their ecologically significant compounds. There is now much interest in the construction of portable Raman systems for the analysis of cyanobacterial and lichen communities in the field; to this extent, Raman spectra obtained with laboratory-based systems operating at wavelengths of 852 and 1064 nm have been evaluated for potential fieldwork applications of miniaturised units. Selected test specimens of the cyanobacterial Nostoc commune, epilithic lichens Acarospora chlorophana, Xanthoria elegans and Caloplaca saxicola and the endolithic Chroococcidiopsis from Antarctic sites have been examined in the present study. Although some organisms gave useable Raman spectra with short-wavelength lasers, 1064 nm was the only excitation that was consistently excellent for all organisms. We conclude that a 1064 nm Raman spectrometer, miniaturised using an InGaAs detector, is the optimal instrument for in situ studies of pigmented communities at the limits of life on Earth. This has practical potential for the quest for biomolecules residual from any former surface or subsurface life on Mars. 相似文献
397.
The acetic acid-promoted addition of lithium nitropropanate and the Lewis acid-catalyzed [Sc(OTf)3, Cu(OTf)2, or Ti(OiPr)4] addition of trimethylsilyl nitropropanate to a range of heteroaromatic and simple aliphatic aldimines gave anti-rich (approximately 3-19:1) beta-nitroamines in >95% yields as the kinetic products. It was found that a nonpolar N-imine protecting group was essential for reactivity with the o-methoxybenzyl (OMB) group giving better selectivities and yields than p-methoxybenzyl (PMB) or p-methoxyphenyl (PMP) in the Lewis acid-catalyzed addition reactions. Reduction with SmI2, treatment with COCl2, followed by OMB deprotection gave diastereomerically pure cis-imidazolidinones in 55-79% overall yield from imine. Preliminary results have shown that acetic acid can catalyze the reaction of N-OMB-benzylideneamine with nitropropane, used as solvent, to give the thermodynamically more stable syn-beta-nitroamine product. 相似文献
398.
The use of a pigment variously described as caput mortuum, usta or ostrum to provide a deep purple colour in ancient wall-paintings was highly prized, despite the technical difficulties associated with its application. With the Raman spectroscopic characterization of pigments in ancient frescoes and wall-paintings becoming more widespread, it is timely to consider the identification of this material either as a generic haematite alone or in admixture with contemporary blue pigments. Here, Raman and infrared spectroscopic, X-ray diffractometric and scanning electron microscopic structural studies have been undertaken to characterize caput mortuum and to identify a specimen of Roman wall-painting dating from the 3rd century. 相似文献
399.
Kathleen B. Mchugh William M. Howell John J. Doran Michael C. Cann 《Journal of heterocyclic chemistry》1990,27(6):1839-1840
The synthesis of 8H-furo[3,4-d]dibenz[b,f]azepine 8 from 5H-dibenz[b,f]azepine 1a is described. The preparation of 8 represents the synthesis of a new heterocyclic system. 相似文献
400.
James A.S. Howell John C. Kola Denis T. Dixon Philip M. Burkinshaw Marion J. Thomas 《Journal of organometallic chemistry》1984,266(1):83-96
Kinetic data for the exchange of 1,3-cyclohexadiene with (η4-benzylideneacetone)Fe(CO)2L complexes (L = CO, PPh3-xMex (x = 0-2) or P(OPh)3) to give (η4-1,3-cyclohexadiene)Fe(CO)2L derivatives indicate a mechanism involving stepwise competing D and Id opening of the ketonic M-CO π-bond. Rates increase in the order CO ? PPh3 ≈ P(OPh)3 > PPh2Me ? PPhMe2, and both steric and electronic factors appear to be important. (η4-1,3-cyclohexadiene)Fe(CO)2L complexes of potential use in enantioselective synthesis (L=(+)-Ph2P(menthyl) or (+)-Ph2PCH2CH(Me)Et) may be prepared via their (η4-benzylideneacetone)Fe(CO)2L complexes. 相似文献