Medium Pressure Hg Lamp Research Articles

Synthesis, Structure, and Reactivity of a Bis(silylene)carbonylruthenium Complex and a Novel Addition Reaction of Photochemically Generated Dimethylsilylene to Bis(silylene) Complexes Cp(OC)M{SiMe2···O(Me)···SiMe2} (M = Ru, Fe)

Photolysis of CpRu(CO)2SiMe2SiMe3 (1a) with a low- or medium-pressure Hg lamp for a long time caused the loss of a SiMe2 moiety to give CpRu(CO)2SiMe3 (2), perhaps through the photochemical dissociation of a CO ligand. This mechanism was supported by the quantitative formation of the bis(silylene)ruthenium complex Cp(OC)Ru{SiMe2···O(Me)··· SiMe2} (3a) by photolysis of the (methoxydisilanyl)ruthenium complex CpRu(CO)2SiMe2SiMe2OMe (1b). The X-ray crystal structure analysis of 3a revealed that 3a has an almost planar Ru−Si−O−Si four-membered chelate ring with short Ru−Si bonds (2.316(3) and 2.311(3) Å) and long Si···O bonds (1.801(7) and 1.793(7) Å). 3a reacts with MeOH instantaneously to give Cp(OC)Ru(H)(SiMe2OMe)2 (4) quantitatively. Photolysis of CpM(CO)2SiMe2SiMe2OMe (1b, M = Ru; 1c, M = Fe) or Cp(OC)M{SiMe2···O(Me)···SiMe2} (3a, M = Ru; 3b, M = Fe) with the photochemical silylene precursor (SiMe2)6 by means of a low-pressure Hg lamp afforded a mixture of 3a or 3b, disilanyl−silylene complexes Cp(OC)M{SiMe2←O(Me)SiMe2SiMe2} (5a, M = Ru; 5b, M = Fe), and (SiMe2)5. Two possible mechanisms for the addition of dimethylsilylene to 3 to give 5 were proposed.

Photolysis of chlorimuron‐ethyl in benzene

Chlorirauron‐ethyl, a sulfonylurea herbicide was irradiated by ultra violet light from a medium pressure Hg lamp (>290 nm) in benzene solution using a quartz apparatus. Three major and six minor products were identified by spectroscopic methods. These products are formed by cleavage of sulfonylurea bridge, rearrangement, dechlorination etc. The rate of degradation of chlorimuron‐ethyl followed first order kinetics with significant rate constant.

Photochromic behaviour of ozonated and photoirradiated cellulose studied by fluorescence spectroscopy

Samples of ozonated pure cotton cellulose have been subjected to three extended periods of irradiation with monochromatic light at 350 nm, with intervening dark periods. The changes during the treatments were monitored using fluorescence spectroscopy. Photochromic behaviour, comprising a fairly rapid emission intensity decrease during irradiation and a slower recovery of the emission intensity in the dark at ambient temperature, was observed. Starting from the completion of the first irradiation/dark treatment the intervening dark reaction almost completely restored the situation prevailing before irradiation. The photochromism observed for a reference sample of cellulose not pretreated with ozone and for microcrystalline cellulose was similar but differed both in amplitude and in fluorescence recovery during the dark periods. The ozonated sample was also irradiated with the entire spectrum of a medium pressure Hg lamp. This treatment caused a strong increase in the emission intensity and a red-shift of the emission maximum. The changes caused by ozonation and irradiation were also studied by diffuse reflectance FT-IR and UV-visible reflectance spectroscopy.

Photoscissable Hydrogel Synthesis via Rapid Photopolymerization of Novel PEG-Based Polymers in the Absence of Photoinitiators

Branched polyethylene glycol (four arms, MW = 15 000) having a cinnamylidene acetyl moiety as a pendant group was synthesized by an esterification reaction between polyethylene glycol and cinnamylidene acetyl chloride. The photosensitive polymer was irradiated with a 450 W medium pressure Hg lamp (λ > 300 nm) from 5 min to 3 h to produce polyethylene glycol hydrogels. These gels were swollen in water and showed characteristic properties of a hydrogel. The degree of swelling was controlled by the content of cinnamylidene acetyl moiety in the polymer and the time of ultraviolet irradiation. A reduced degree of substitution resulted in increased swellability of the synthesized hydrogel. The photoscission of the gel, which was monitored by its UV spectrum, was performed by irradiating the hydrogel with a 150 W Xenon lamp at 254 nm using a bandpass filter. The biocompatibility of the synthesized gel was also determined. The antithrombogenic behavior (99.6% reduction in platelet deposition) of the synthesized b-PEG-CA hydrogel was demonstrated by measuring platelet adhesion onto coverslips which had been coated with PMMA with a second coating film of b-PEG-CA hydrogel.

Towards the synthesis of amino[ b, e][1,4]dioxin derivatives via cationic ruthenium complexes

Double nucleophilic aromatic substitution reactions between N-substituted ( ν 6-1,2-dichlorobenzene)RuCp + salts and substituted 1,2-benzenediols have been carried out under mild conditions to prepare N-substituted ( ν 6-dibenzo[ b, e][1,4]dioxin)ruthenium(II)) complexes. The dibenzodioxin ligands were subsequently liberated to photolysis, with radiation from a sunlamp or from a medium pressure Hg lamp (300 nm).

Reaction of Singlet Oxygen with Thietane. A Novel Example of a Self-Catalyzed Reaction Which Provides Evidence for a Thiadioxirane Intermediate

Singlet oxygen reacts with thietane, 1, to give the sulfoxide, 1S0, and a trace of sulfone, 1SOz. A mechanism which involves a novel substrate catalyzed interconversion of a persulfoxide and thiadioxirane intermediate is proposed. The data which support the reaction of the persulfoxide with 1 by attack at sulfonium sulfur include the facts that Ph2SO and 1 compete for a common intermediate and physical quenching is suppressed by increasing concentrations of 1. The unique ability of 1 to catalyze its own oxidation is a result of a small C-S-C angle which allows an unencumbered approach to the sulfonium sulfur. In contrast, the larger C-S-C angle in Et2S sterically precludes the catalysis step and forces direct collapse of the persulfoxide to the thiadioxirane intermediate. In 1983, 30 years after the first report of the photooxidation of a dialkyl sulfide,‘ Foote and co-workers2 suggested a mechanism for the reaction of singlet oxygen (‘02) with diethyl sulfide (Et2S) which has served as the prototypical example for sulfide photooxidation reaction surfaces. The unique feature of the Foote mechanism was the suggestion of two intermediates, a persulfoxide which collapsed to the second intermediate in competition with physical quenching, and a thiadioxirane which reacts with a molecule of substrate to give the sulfoxide product. Recently, however, concerns about the viability of the second intermediate on the Foote reaction surface have called into question the generality of this mechanism and have pointed out the need for more detailed kinetic studies with other dialkyl sulfide^.^,^ We report here the first extensive study of the photooxidation of a cyclic sulfide, thietane 1, and compare it to the photooxidation of Et& We also suggest a new mechanism for the photooxidation of 1 which differs from the Foote mechanism for Et2S in that it invokes a novel substratecatalyzed interconversion of persulfoxide 2, and thiadioxirane 4, intermediates. Photooxidations of 1 (0.05-0.2 M) in oxygen-saturated CDC13 solutions containing (2-4) x M TPP (tetraphenylporphyrin) as sensitizer were conducted at room temperature by irradiation with a 650-W tungsten-halogen or a 450-W medium-pressure Hg lamp through a 1-cm NaN02 filter solution. Under these carefully controlled conditions the sulfoxide, 1S0, and a trace of the sulfone, lSOz, were the only products observed at either high or low conversion^.^ Identical results were also obtained in benzene and in acetone-d6 at both room and low temperatures. The experimental evidence which supports the mechanism for this photooxidation as outlined in Scheme 1 includes the following: (1) Cophotooxidations of 1 with diphenyl sulfoxide (Ph2SO) and diphenyl sulfide (Ph2S) produce diphenyl sulfone (Ph2SO2) and Ph2S0, respectively. Control reactions demonstrate that Ph2SO and Ph2S are inert to singlet oxygen under the reaction (1) Schenck, G. 0.; Krausch, C. H. Angew. Chem. 1962, 74, 510. (2)Liang, J.-J.; Gu, C.-L.; Kacher, M. L.; Foote, C. S. J. Am. Chem. (3) Watanabe. Y.: Kuriki. N.: Ishicuro. K.: Sawaki. Y . J. Am. Chem. SOC. 1983, 105, 4717-4721. ‘2 SOC. 1991, 113, 2677-2682. (4) Jensen, F. J. Org. Chem. 1992, 57, 6478-6487. 0002-7863/95/1517-9800$09.00/0 Scheme 1

(1‐PYRENYL)METHYL CARBAMATES FOR FLUORESCENT “CAGED” AMINO ACIDS AND PEPTIDES

AbstractA highly fluorescent 1‐pyrenylmethyloxycarbonyl amino acid (Pmoc‐amino acid) is obtained in moderate yield by the reaction of (1‐pyrenylmethyl)‐4‐nitrophenylcarbonate with an amino acid in the presence of sodium carbonate. The condensation of Pmoc‐amino acid with an amino acid gives Pmoc‐peptide in the presence of 1‐ethyl‐3‐(3‐dimethylaminepropyl)carbodiimide and 1‐hydroxyben‐zotriazole. The amino acid is recovered from an H2O‐dioxane (2:3) solution of Pmoc‐amino acid by irradiation through a Pyrex filter with a medium pressure Hg lamp or at 340 nm. Although the quantum yield of the photolysis is rather low (ca 0.01), the photolysis proceeds fast and efficiently due to the large absorption coefficient of Pmoc‐amino acid at around 340 nm. Thus, the use of Pmoc‐amino acid as a “caged” amino acid is promising.

Surface chemistry of polycarbonate film and adhesion of ultraviolet-cured inks

One of the primary uses of polycarbonate film is in screen-printing applications, with ultraviolet (UV)-cured inks becoming increasingly popular due to environmental concerns. During multicolor printing operations, regions of the polycarbonate film surface are unavoidably exposed to UV irradiation during the cure of adjacent regions. Subtle changes in the polycarbonate surface chemistry affect subsequent printing on the UV-exposed surface, primarily manifest as a decrease in the ink adhesion level. In this study, static secondary-ion-mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), and contact angle measurements were used to show that the surface becomes oxidized and water wettable. The degree of photo-oxidation, nature of the photoproducts, and ink adhesion characteristics were measured as a function of the UV wavelength window. Filtering out the short wavelengths (λ<300 nm) from a medium pressure Hg lamp resulted in significantly less photo-oxidation compared to identical exposures from the unfiltered UV. The ink/polymer interfaces were also examined by transmission electron microscopy (cross section) and by peeling followed by XPS and static SIMS analysis. Based on these results, mechanisms for ink/polycarbonate interface adhesion are proposed.

A spectroscopic study of photoirradiated cellulose

The influence of photoirradiation on cellulose was studied by means of fluorescence, Fourier transform IR and UV—visible reflectance spectroscopy. Samples of cellulose were irradiated with the entire spectrum of a medium pressure Hg lamp, with the light from the Hg lamp filtered through a glass filter, or selectively with monochromatic light of different wavelengths. The emission spectra of untreated cellulose samples and of differently irradiated samples were recorded after various exposure times. Irradiation with the unfiltered radiation from the Hg lamp caused a strong increase in the emission intensity and a gradual shift in the emission maximum to longer wavelengths. After irradiation for 96 h a pronounced band at 1733 cm −1 was seen in the diffuse reflectance IR Fourier transform spectrum of the sample, indicating the formation of carbonyl groups as a result of the treatment. Irradiation with filtered light from the Hg lamp caused a small decrease in the emission intensity and shifted the emission maximum from 445 to 462 nm. Exposure of cellulose to monochromatic light of 350 nm wavelength caused a gradual fading of the fluorescence with increased exposure time and a small shift in the emission maximum to longer wavelengths. After the sample had been allowed to stand in the dark, the emission intensity was almost completely restored to its original value, but the red shift of the emission maximum caused by the irradiation remained unchanged.

Hydrogen photogeneration from aqueous solutions of alcohols by the Fe3+ ion

Fe(III) chlorocomplex ions are found to generate hydrogen from aqueous solutions of aliphatic alcohols on photolysis with a medium pressure Hg lamp. The reaction mechanism is believed to involve the formation of reactive intermediates Cl− and H−, where H− abstracts hydrogen from the alcohol.

Pinching group stabilization. The synthesis and thermal isomerization of 10-Oxapentacyclo[6.3.2.13,6.01,8.02,7]tetradeca-4,12-diene

Sensitized irradiation (benzophenone, 0�, N2, pyrex filter, medium pressure Hg lamp) of dimethyl tricyclo[4.2.1.02,5]nona-3,7-diene-3,4-dicarboxylate (11) in (E)-1,2-dichloroethene yielded a mixture of 1 : 1 adducts (13) and (14) by site selective [2 π+2 π] cycloaddition at the cyclobutene π-bond. Reduction of the (Z)-dichloro isomer(13) with lithium aluminium hydride formed the related diol (16) which is the immediate precursor to the cyclic ether (18). Dechlorination of (18) with zinc in ethanol forms the title diene (19). Thermolysis of the polycyclic diester (20) affords the fragmentation products cyclopentadiene and dimethyl benzene-1,4-dicarboxylate. In contrast, the title compound (19) containing the cyclic ether ring was more stable and yielded the novel isomer (28) as the major product only upon flash vacuum pyrolysis at 560�(1.5 × 10-2 Torr). This difference in behaviour is attributed to a pinching group effect exerted by the cyclic ether present in (19).

Photoproducts of chlorpromazine which cause red blood cell lysis.

AbstractA mechanism for chlorpromazine (CPZ) phototoxicity has been proposed that attributes the response to formation of stable, toxic photoproducts which cause cell membrane disruption. We have characterized these toxic photoproducts as dimers and higher multimers of CPZ. Chlorpromazine solutions (3 or 10 mA/) were irradiated with a medium pressure Hg lamp filtered to exclude λ < 280 nm. Five low mol wt photoproducts were separated by high performance liquid chromatography. Two were identified as CPZ‐sulfoxide and promazine. Higher mol wt photoproducts were separated by Sephadex G‐50 chromatography into 3 broad bands which were characterized by their absorption and fluorescence spectra. Band A (mol wt > 800) had λmaxabs= 263 nm, λmaxfl= 490 nm and Band B (mol wt = 350‐800) had λmaxabs= 255 nm, λmaxfl= 450 nm. Based on the mol wt of CPZ, Band A contained trimers and higher mol wt compounds and Band B was composed of dimeric structures. BandC(λmaxabs= 255,310 nm; λmaxfl= 445 nm) was composed of CPZ (mol wt = 315) and the low mol wt photoproducts. Red blood cell lysis was used as an assay for the ability of photoproducts to cause membrane disruption. Bands A and B, but not Band C, caused cell lysis. These data indicate that the CPZ photoproducts which cause cell membrane disruption are dimers (Band B) and higher multimers (Band A).

Studies of the reactions of lithium atoms with methyl cyanide and methyl isocyanide in inert gas matrices

Linear LiNC is known to be the more stable isomer when isolated in inert gas matrices at low temperatures (4–15K). 1 In an attempt to form the other geometrical isomer, LiCN, studies of the reaction of lithium atoms with CH 3CN and CH 3NC were undertaken. A new absorption in the CN stretching region was observed when lithium atoms were co-condensed with CH 3NC in solid argon and xenon matrices. Photolysis of the matrices with a medium pressure Hg lamp during deposition of Li/CH 3NC seemed to favour the formation of the more stable isomer, LiNC. Reactions of lithium atoms with CH 3CN only led to the formation of LiNC, with or without photolysis.

Photoinduced ionic and free-radical reactions of some organosilicon iodides

U.v. irradiation (medium-pressure Hg lamp) induces reaction of TsiSiPh2l (1a)[Tsi =(Me3Si)3C] with methanol to give both the unrearranged and rearranged methoxides TsiSiPh2OMe and (Me3Si)2C(SiPh2Me)(SiMe2OMe); in the presence of LiNO3some (Me3Si)2C(SiPh2Me)(SiMe2ONO2) is also formed. The analogous solvolysis in PhNH2gives the rearranged anilide (Me3Si)2C(SiPh2Me)(SiMe2NHPh). These reactions are thought to involve the intermediate formation of a silico-cation. On the other hand the exclusive formation of the unrearranged chloride TsiSiPh2Cl upon irradiation in CCl4appears to involve a free-radical process. The photoinduced rearrangement of (1a) to (Me3Si)2C(SiPh2Me)(SiMe2l) in n-C5H12, n-C6H14, Et2O, and PhOMe may involve a cationic intermediate, but a free radical rearrangement cannot be ruled out; the subsequent formation of a disilaindane derivative (6) in PhOMe probably involves cyclization of a free radical. The iodide TsiSiPhMel also undergoes rearrangement to (Me3Si)2C(SiPhMe2)(SiMe2l) upon irradiation in n-C5H12. The methanolysis of TsiSiMe2l is also photo-catalysed, though less effectively than that of (1a).

N-quaternary compounds. Part 52. Photochemically induced valence bond isomerism and rearrangement to pyridinones of thiazolo[3,2-a]pyridinium-8-olate derivatives

Irradiation of derivatives of thiazolo[3,2-a]pyridinium-8-olate with a medium pressure Hg lamp resulted in rearrangement to derivatives of the isomeric thiazolo[3,2-a]pyridin-5-ones. Irradiation at 350 nm of 5-methyl-dihydrothiazolo[3,2-a] pyridinium-8-olate gave the valence isomeric structure 6-methyl-2-thia-5-azatricyclo[4.3.0.01,5]non-7-en-9-one which on further irradiation with the medium pressure Hg lamp yielded the corresponding rearranged dihydrothiazolo[3,2-a]pyridin-5-one.

The photochemical reaction of vinylchloride with oxygen studied by i.r. spectroscopy

The reaction products formed when vinylchloride (chloroethene) at pressures of 6–150 torr and air at room temperature were irradiated by u.v. light from a medium pressure Hg lamp were investigated by the technique of i.r. spectroscopy. Carbon dioxide, carbon monoxide, water, hydrochloric acid, formic acid and acetylene appeared as main reaction products. Various experimental parameters: pressures of vinylchloride and air, irradiation time, frequency region of the irradiating light and the catalytic effects of the alkali halide cell windows affected the reaction rate and their influence was systematically studied. The presence of nitrogen dioxide-nitric oxide (NO 2/NO) in the vinylchloride-air mixture greatly increased the reaction rate. At low nitrogen dioxide concentrations (1–5 torr) the same reaction products were formed as in the absence of NO 2/NO. Under higher concentrations, however, nitrosyl chloride (NOCl) and nitrous oxide (N 2O) were also detected in the spectra. Vinylchloride and air were exposed to sunshine and reacted negligibly in a silica cell with pyrex windows, whereas CsI or KBr windows catalysed the reaction. In the presence of nitric oxide and sunshine, vinylchloride reacted readily with air.

The photochemistry of the matrix-isolated dichloroethylenes

The vacuum ultraviolet photolysis of the three isomers of dichloroethylene has been studied in argon, carbon monoxide, nitrogen and krypton matrices at 13 K. Selective excitation into various regions from 1200 to 2050 Å with resonance line sources and a medium pressure Hg lamp resulted in the formation of HCl and chloroacetylene as the major products detected by infrared spectroscopy. Isomerization among the three dichloroethylenes was also important, while the production of acetylene and dichloroacetylene made only minor contributions to the photochemistry. The chlorovinyl radical was not identified, though several unassigned absorptions were observed. The infrared absorptions of chloroacetylene and HCl produced by photolysis of trans-1,2-dichloroethylene were shifted from those produced from the other isomers, providing evidence for αα elimination of HCl from the trans isomer. The effects of varying the matrix material from Ar to CO, N 2 or Kr show that all the processes, with the exception of the formation of acetylene and Cl 2, arise from triplet states. It is suggested that the αα elimination process observed for the trans isomer is due to the participation of a 3nσ * state in the photochemistry of this isomer.