The photolysis reactions of three compounds commonly used as a sunscreen agents, Parsol 1789 (1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-1,3- propanedione), Oxybenzone ((2-hydroxy-4-methoxyphenyl)phenyl-methanone) and Padimate O (2-ethylhexyl-4-(dimethylamino)benzoate), were investigated to provide a chemical background to aid in the understanding of the photosensitization of the sunscreen agents. Photolysis was carried out in cyclohexane for 70–140 h using a mercury vapor lamp (450W) without excluding oxygen.
Irradation of Parsol 1789 in cyclohexane yielded tert-butylbenzene, p-tert-butylbenzoic acid and p-methoxybenzoic acid; products obtained from the combination of the sunscreen with the solvent included the cyclohexyl esters of p-methoxybenzoic acid, p-tert-butylbenzoic acid and methanoic acid; products obtained from the solvent included cyclohexanol, cyclohexanone and dicyclohexyl ether.
Irradiation of Oxybenzone in the cyclohexane for 100 h produced no detectable products by either gas or liquid chromatographic analysis. Oxybenzone was recovered unchanged and no products were observed from the photoinitiated reaction of oxygen with the solvent.
Irradiation of Padimate O in cyclohexane yielded the ethylhexyl esters of p-aminobenzoic acid, p-monomethylaminobenzoic acid and p-dimethylamino (o/m)-methylbenzoic acid, as well as products from the photoinitiated reaction of oxygen with the solvent. 相似文献
We consider biased random walk on supercritical percolation clusters in ℤ2. We show that the random walk is transient and that there are two speed regimes: If the bias is large enough, the random
walk has speed zero, while if the bias is small enough, the speed of the random walk is positive.
Received: 20 November 2002 / Revised version: 17 January 2003
Published online: 15 April 2003
Research supported by Microsoft Research graduate fellowship.
Research partially supported by the DFG under grant SPP 1033.
Research partially supported by NSF grant #DMS-0104073 and by a Miller Professorship at UC Berkeley.
Mathematics Subject Classification (2000): 60K37; 60K35; 60G50
Key words or phrases: Percolation – Random walk 相似文献
The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control. An emerging strategy to generate coordinatively-unsaturated active sites is through the use of organic linkers that lack a functional group that would usually bind with the metal nodes. To execute this strategy, we synthesize a model MOF, Ni-MOF-74 and incorporate a fraction of 2-hydroxyterephthalic acid in place of 2,5-dihydroxyterephthalic acid. The defective MOF, Ni-MOF-74D, is evaluated vs. the nominally defect-free Ni-MOF-74 with a host of ex situ and in situ spectroscopic and electroanalytical techniques, using the oxidation of hydroxymethylfurtural (HMF) as a model reaction. The data indicates that Ni-MOF-74D features a set of 4-coordinate Ni–O4 sites that exhibit unique vibrational signatures, redox potentials, binding motifs to HMF, and consequently superior electrocatalytic activity relative to the original Ni-MOF-74 MOF, being able to convert HMF to the desired 2,5-furandicarboxylic acid at 95% yield and 80% faradaic efficiency. Furthermore, having such rationally well-defined catalytic sites coupled with in situ Raman and infrared spectroelectrochemical measurements enabled the deduction of the reaction mechanism in which co-adsorbed *OH functions as a proton acceptor in the alcohol oxidation step and carries implications for catalyst design for heterogeneous electrosynthetic reactions en route to the electrification of the chemical industry.The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control.相似文献
Two libraries of alpha-substituted alkynes has been prepared on solid phase using a sequential Sonogashira/Nicholas reaction approach. The scope of nucleophiles in the Nicholas reaction on solid phase has been investigated, including carbon, oxygen, nitrogen, sulfur, fluoride, and hydride nucleophiles. The conditions for the reaction sequence have been optimized in terms of Lewis acid, catalyst for the Sonogashira step, temperature, reaction time, and decomplexation method, enabling the five-step sequence to be performed in 1 day. 相似文献
An on-line method for the analysis of Sb(III), Sb(V) and trimethylstiboxide (TMSbO) is presented. The separation is performed
using ion chromatography (IC) on a strong anion-exchange column with phthalic acid plus 2% acteone at pH 5 as mobile phase.
The chromatographic system is coupled to an ICP-MS as detector. The influence of different complexing agents on the chromatographic
behavior of the antimony species is studied. Rather stable complexes of Sb(III) seem to be formed with citrate and tartrate
under the experimental conditions. TMSbO forms a dianionic species with citrate in contrast to the otherwise monoanionic complex.
Received: 31 Juli 1997 / Revised: 8 December 1997 / Accepted: 11 December 1997 相似文献
The properties of inclusion complexes of 1,4-di-R-bicyclo[2.2.2]octaves (R = H (1), Me (2), Cl (3), Br (4), and OH (5)) with cyclodextrins have been studied by NMR, microcalorimetry, and force-field computations. The compounds2 and3 (but not the other compounds) give dynamically stable 1:2 guest-host complexes with -cyclodextrin. Microcalorimetry of5 in water indicates a moderately strong 1:1 complex with - but weak complexes with - or -cyclodextrin. The behaviour depends on the subtle interplay size, polarity, hydrophobicity and type of solvent. 相似文献
A theoretical and experimental treatment of axial dispersion in coiled tubes is presented. The dispersion, δ, is related to the theoretical plate height divided by four times the radius of the tube (H/4r). This parameter, when plotted against the product of the Reynolds number and the Schmidt number (ReSc), accurately predicts maxima in dispersion curves. Variations in the boundary layer thickness and the velocity profile cause the dispersion to pass through a maximum at a constant value of log (De2Sc1·14) equal to 6.13 for unretained solutes (De is the Dean number). A new measure of dispersion is proposed; the reduced dispersion, ? = 256/(Re0.667Sc), is derived from the experimental behavior of dispersion at values of log (De2Sc1·14) smaller than 6.13. The logarithm of ? is found to be approximately zero for 2.2 < log (De2Sc1·14) < 6.1 and to decrease linearly with log (De2Sc1·14) at higher values. Experiments with four solutes that have a wide range of molecular diffusivities are reported. Results agree with theory. 相似文献
Methods of the preparation of catalysts for alkane skeletal isomerization based on uniform nanoparticles of sulfated zirconia
anchored to different supports were investigated. These catalysts were characterized by using the ICP, HRTEM and BET techniques.
The activities of the catalysts in the reaction of n-butane isomerization were measured and compared with those of bulk catalysts. 相似文献