Medium Pressure Hg Lamp Research Articles

Continuous-Flow Synthesis of Cyclobutenes Using LED Technology

AbstractCyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2] cycloadditions that exploit low-wavelength UV radiation emitted from inefficient medium-pressure Hg lamps. This paper reports on the development of a modern approach using a high-power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous-flow reactor. The resulting flow process renders a series of cyclobutenes from maleimides and various commercial alkynes. This provides a more energy-efficient approach that is readily scalable to access multigram quantities of cyclobutenes in high chemical yields and short residence times. The value of these products is exemplified by flow-based hydrogenations yielding highly substituted cyclobutanes which represent sought after building blocks in modern medicinal chemistry programs.

Generation of 1,2-Difluorobenzene via a Photochemical Fluorodediazoniation Step in a Continuous Flow Mode

A proof-of-concept study for the synthesis of 1,2-difluorobenzene from 2-fluoroaniline via the Balz–Schiemann reaction using HF/pyridine as the fluorinating reagent is reported. Key to success for a fast reaction, a clean reaction profile─and thus high product selectivity─was a photochemically induced fluorodediazoniation of the in situ-generated diazonium salt performed in a continuous flow mode. A high-power 365 nm light-emitting diode provided a more robust and efficient irradiation system compared to a medium-pressure Hg lamp with respect to the reaction performance on scale-out runs and reaction time, allowing the generation of 1,2-difluorobenzene within a 10 min residence time and a product selectivity of ≥95% at full conversion.

Synthesis, bridgehead functionalization, and photoisomerization of 9,10-diboratatriptycene dianions.

9,10-Diboratatriptycene salts M2[RB(μ-C6H4)3BR] (R = H, Me; M+ = Li+, K+, [n-Bu4N]+) have been synthesized via [4 + 2] cycloaddition between doubly reduced 9,10-dihydro-9,10-diboraanthracenes M2[DBA] and benzyne, generated in situ from C6H5F and C6H5Li or LiN(i-Pr)2. [HB(μ-C6H4)3BH]2- reacts with CH2Cl2 to form quantitatively the bridgehead-derivatized [ClB(μ-C6H4)3BCl]2-, while twofold H- abstraction with B(C6F5)3 in the presence of SMe2 leads cleanly to the diadduct (Me2S)B(μ-C6H4)3B(SMe2). Photoisomerization of K2[HB(μ-C6H4)3BH] (THF, medium-pressure Hg lamp) provides facile access to diborabenzo[a]fluoranthenes, a little explored form of boron-doped polycyclic aromatic hydrocarbons. According to DFT calculations, the underlying reaction mechanism consists of three main steps: (i) photoinduced di-π-borate rearrangement, (ii) "walk reaction" of a BH unit, and (iii) boryl anion-like C-H activation.

TiO2 Decorated Sand Grains for Photodegradation of Pollutants: Methylene Blue and Ciprofloxacin Study

This study shows a preparation and evaluation of a new non-expensive TiO2 based photocatalyst built over sand grains surfaces as an alternative green technology for water treatment. The semiconductor covalently bonded to the silica sand grains (sand@TiO2) prepared by hydrolysis of isopropoxide orthotitane over sand grains, showed a high surface area 296 m2 g-1 and a high reaction rate for methylene blue (MB) photodegradation (0.064 min-1), on steady state condition by using 3 g of sand@TiO2 and an MB solution (20 mL, 3 × 10-5 mol L-1) or ciprofloxacin hydrochloride (CIP) solution (20 mL, 1.9 × 10-3 mol L-1). Under UV irradiation with a medium pressure Hg lamp, the total MB removal reached 70% after 7 min and 45% for CIP in 60 min. Further, the photocatalyst showed to be a promising reusable material for removal of ciprofloxacin hydrochloride antibiotic (CIP) on wastewater. This new material appears as a new promising low cost and low impact reusable catalyst for water treatment.

A scalable continuous photochemical process for the generation of aminopropylsulfones.

An efficient continuous photochemical process is presented that delivers a series of novel γ-aminopropylsulfones via a tetrabutylammonium decatungstate (TBADT) catalysed HAT-process. Crucial to this success is the exploitation of a new high-power LED emitting at 365 nm that was found to be superior to an alternative medium-pressure Hg lamp. The resulting flow process enabled the scale-up of this transformation reaching throughputs of 20 mmol h-1 at substrate concentrations up to 500 mM. Additionally, the substrate scope of this transformation was evaluated demonstrating the straightforward incorporation of different amine substituents as well as alkyl appendages next to the sulfone moiety. It is anticipated that this methodology will allow for further exploitations of these underrepresented γ-aminopropylsulfone scaffolds in the future.

Inductive Medium Pressure UV-Source

In this paper, an efficient inductively coupled medium pressure source for ultraviolet radiation (UV-source) is demonstrated. The lamp was operated with powers up to 3 kW while the radiation and the coldest point temperature were measured. In addition, different coil geometries were investigated. Here a symmetrical and asymmetrical winding density were compared. Also the operation pressures and DC to radiation efficiencies are presented. In this work, an operation pressure of one atmosphere and an UV-efficiency (200–380 nm) of 15.5% was achieved. This is comparable to conventional medium pressure Hg-lamp technology. The main advantage of the presented inductive lamp is the electrodeless operation and therefore the longer service life, since an electrode failure is eliminated.

New Photodegradation Products of the Fungicide Fluopyram: Structural Elucidation and Mechanism Identification.

Identifying the fate of agrochemicals is important to understand their potential risk for living organisms. We report here new photodegradation products (PPs) of the fungicide fluopyram. The PPs were produced by irradiating a fluopyram standard in 0.1% acetonitrile aqueous media by a 150-W medium pressure Hg-lamp that emits wavelengths between 200–280 nm. The structural elucidation of PPs was achieved by combining the retention time, isotopic pattern, targeted fragmentation, and accurate mass measurements using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and high resolution-MS (HRMS). In addition to previously known PPs, seven new PPs of fluopyram were identified in this work: mainly dihydroxyl and hydroxylimide fluopyram as well as mono, di, and trihydroxyl lactam. Additionally, two PPs were found to be formed by rearrangement after the loss of H2C=CH2. Hence, the results of the work contribute to extending the current knowledge regarding the photoinduced fate of agrochemicals, and fluopyram in particular.

Simulated sunlight photodegradation of 2-mercaptobenzothiazole by heterogeneous photo-Fenton using a natural clay powder

The efficiency of 2-mercaptobenzothiazole (MBT) degradation by heterogeneous photo-Fenton process using local natural clay powder (NCP) is described. Experiments were conducted at natural pH with a batch reactor equipped with a medium-pressure Hg lamp emitting mainly at 366 nm. The natural clay was characterized by SEM-EDS, UV–vis diffuse reflectance spectroscopy, XRF and XRD analysis. The specific BET surface area of the clay was 30.2 m2 g−1.The photodegradation of MBT follows first order (for direct photolysis) and pseudo-first order kinetics (for photocatalysis). Direct photolysis of MBT showed a negligible effect both upon 254 and 365 nm irradiation, while 42.5% and 62% of MBT was eliminated in three hours under 310 nm irradiation in the presence of H2O2 and under sunlight irradiation (using NCP), respectively. Kinetic runs carried out with 5.0·10−5 M MBT and 0.5 g L−1clay showed both higher MBT conversion and photodegradation rate at basic pH (10) and in oxygen saturated media. The presence of oxalic acid and H2O2 significantly enhanced MBT photodegradation. The photodegradation of MBT is mainly attributed to reaction with HO, leading to different intermediates that have been identified by HPLC–MS. A reaction mechanism is proposed. The highest TOC removals were obtained using UVA at low pHs (2.6), and in the absence of O2 with 68% and 65% TOC removal respectively in two hours, whereas MBT transformation is faster (t½ = 7 min) and higher (90%) at pH = 10. The obtained results strongly support the use of natural clay rich in iron oxides as inexpensive, clean and efficient photocatalysts for water pollutants abatement using heterogeneous photo-Fenton process.

Direct Photolysis of Sulfamethoxazole Using Various Irradiation Sources and Wavelength Ranges-Insights from Degradation Product Analysis and Compound-Specific Stable Isotope Analysis.

The environmental micropollutant sulfamethoxazole (SMX) is susceptible to phototransformation by sunlight and UV-C light which is used for water disinfection. Depending on the environmental pH conditions SMX may be present as neutral or anionic species. This study systematically investigates the phototransformation of these two relevant SMX species using four different irradiation scenarios, i.e., a low, medium, and high pressure Hg lamp and simulated sunlight. The observed phototransformation kinetics are complemented by data from compound-specific stable isotope and transformation product analysis using isotope-ratio and high-resolution mass spectrometry (HRMS). Observed phototransformation kinetics were faster for the neutral than for the anionic SMX species (from 3.4 (LP lamp) up to 6.6 (HP lamp) times). Furthermore, four phototransformation products (with m/z 189, 202, 242, and 260) were detected by HRMS that have not yet been described for direct photolysis of SMX. Isotopic fractionation occurred only if UV-B and UV-A wavelengths prevailed in the emitted irradiation and was most pronounced for the neutral species with simulated sunlight (εC = -4.8 ± 0.1 ‰). Phototransformation of SMX with UV-C light did not cause significant isotopic fractionation. Consequently, it was possible to differentiate sunlight and UV-C light induced phototransformation of SMX. Thus, CSIA might be implemented to trace back wastewater point sources or to assess natural attenuation of SMX by sunlight photolysis. In contrast to the wavelength range, pH-dependent speciation of SMX hardly impacted isotopic fractionation.

Removal of tributyltin from contaminated seawater by combinations of photolytic and TiO2 mediated photocatalytic processes

Harbour sediment contaminated with tributyltin (TBT) is a worldwide problem and treatment of TBT contaminated seawater is an issue during dredging operations. This study presents results from photolytic and photocatalytic treatment experiments where the influence of the seawater matrix, different types of high and low pressure ultraviolet (UV) lamps and different reactor designs have been examined. The study showed that the photolytic rate of degradation in seawater was reduced by 41% compared to the degradation in demineralized water. Moreover, the photocatalytic TiO2 surface was inactivated and produced radicals were scavenged by the relatively high salinity and content of organic matter in the water. Within the same type of lamps, the rate of removal was dependent only on the specific amount of energy supplied to the water regardless of the specific power used. The high power medium pressure Hg lamp was found to be the most efficient compared to the four low-pressure lamps, and the energy consumptions were estimated to be in the 7–8WhL−1 range per log reduction of TBT. This study has demonstrated a feasible method for abatement of TBT in seawater matrix.

Photochemistry of aroyloxiranes: Substituent effect on oxepinones and hydroxyalkenones formation

Abstract The photo-irradiation of some aroyloxiranes with Pyrex filtered UV-light from 125 W medium pressure Hg lamp has been described. These compounds furnished the 2-aryl-4,10-dihydrofuro[3,2- c ][1]benzoxepin-10-ones and the hydroxyalkenones by the photochemical irradiation. The product(s) formation/distribution in terms of oxepinones and the hydroxyalkenones largely depended upon the nature of the substituent: the oxiranes having electron-donating groups in their benzoyl moiety gave the hydroxyalkenones while oxiranes having electron-withdrawing groups furnished the oxepinones as the major products. The formation of oxepinones has been envisaged to occur through the heterolytic C C bond cleavage of epoxide to give carbonyl ylide intermediates followed by the furo-oxepinone ring formation via [3+2] cycloaddition and of hydroxyalkenones through the initial β-H abstraction followed by epoxide ring opening. The structures of all the compounds (substrates and photoproducts) have been determined on the basis of their spectral data (IR, NMR and Mass).

Combined AOPs for potential wastewater reuse or safe discharge based on multi-barrier treatment (microfiltration-H2O2/UV-catalytic wet peroxide oxidation)

The viability of a multi-barrier treatment (MBT) for safe discharge or potential reuse of synthetic industrial wastewater was evaluated in this study. The proposed MBT consists of microfiltration membrane pre-treatment (MF), followed by hydrogen peroxide photolysis (H2O2/UVC) using a medium pressure Hg lamp (MP) and granulate activated carbon (GAC). The synthetic wastewater (SIWW) obtained by addition of different industrial organic pollutant (orange II, phenol, 4-chlorophenol and phenanthrene) to the effluent taken from a municipal wastewater treatment plant was used in this study.At optimal operational conditions complete degradation of added contaminants, about 85% of total mineralization and total disinfection were achieved after MBT treatment. Toxicity tests with Vibrio fischeri and Paracentrotus lividus sea-urchin (fertilization and embryo-larval development assays) were conducted with water after each treatment step and drastic decrease of toxicity was observed after applied process. However, it was demonstrated that after H2O2/UVC step toxicity of water significantly increased and was even higher than that of SIWW. Novel equation for estimation of UVC dose was introduced as one of the most important scaling parameter. The main operational and maintenance cost (O&M) of MBT process was evaluated in this work. Thus, the high quality of the obtained effluent suggests its suitability for water reuse or safe discharge.

Identification of phototransformation products of thalidomide and mixture toxicity assessment: An experimental and quantitative structural activity relationships (QSAR) approach

The fate of thalidomide (TD) was investigated after irradiation with a medium-pressure Hg-lamp. The primary elimination of TD was monitored and structures of phototransformation products (PTPs) were assessed by LC–UV–FL–MS/MS. Environmentally relevant properties of TD and its PTPs as well as hydrolysis products (HTPs) were predicted using in silico QSAR models. Mutagenicity of TD and its PTPs was investigated in the Ames microplate format (MPF) aqua assay (Xenometrix, AG). Furthermore, a modified luminescent bacteria test (kinetic luminescent bacteria test (kinetic LBT)), using the luminescent bacteria species Vibrio fischeri, was applied for the initial screening of environmental toxicity. Additionally, toxicity of phthalimide, one of the identified PTPs, was investigated separately in the kinetic LBT.The UV irradiation eliminated TD itself without complete mineralization and led to the formation of several PTPs. TD and its PTPs did not exhibit mutagenic response in the Salmonella typhimurium strains TA 98, and TA 100 with and without metabolic activation. In contrast, QSAR analysis of PTPs and HTPs provided evidence for mutagenicity, genotoxicity and carcinogenicity using additional endpoints in silico software. QSAR analysis of different ecotoxicological endpoints, such as acute toxicity towards V. fischeri, provided positive alerts for several identified PTPs and HTPs. This was partially confirmed by the results of the kinetic LBT, in which a steady increase of acute and chronic toxicity during the UV-treatment procedure was observed for the photolytic mixtures at the highest tested concentration. Moreover, the number of PTPs within the reaction mixture that might be responsible for the toxification of TD during UV-treatment was successfully narrowed down by correlating the formation kinetics of PTPs with QSAR predictions and experimental toxicity data. Beyond that, further analysis of the commercially available PTP phthalimide indicated that transformation of TD into phthalimide was not the cause for the toxification of TD during UV-treatment.These results provide a path for toxicological assessment of complex chemical mixtures and in detail show the toxic potential of TD and its PTPs as well as its HTPs. This deserves further attention as UV irradiation might not always be a green technology, because it might pose a toxicological risk for the environment in general and specifically for water compartments.

Degradation of lidocaine, tramadol, venlafaxine and the metabolites O-desmethyltramadol and O-desmethylvenlafaxine in surface waters

The photodegradation and biotic transformation of the pharmaceuticals lidocaine (LDC), tramadol (TRA) and venlafaxine (VEN), and of the metabolites O-desmethyltramadol (ODT) and O-desmethylvenlafaxine (ODV) in the aquatic environmental have been investigated. Photodegradation experiments were carried out using a medium pressure Hg lamp (laboratory experiments) and natural sunlight (field experiments). Degradation of the target compounds followed a first-order kinetic model. Rates of direct photodegradation (light absorption by the compounds itself) at pH 6.9 were very low for all of the target analytes (⩽0.0059h−1 using a Hg lamp and ⩽0.0027h−1 using natural sunlight), while rates of indirect photodegradation (degradation of the compounds through photosensitizers) in river water at pH 7.5 were approximately 59 (LDC), 5 (TRA), 8 (VEN), 15 (ODT) and 13 times (ODV) higher than the rates obtained from the experiments in ultrapure water. The accelerated photodegradation of the target compounds in natural water is attributed mainly to the formation of hydroxyl radicals through photochemical reactions. Biotic (microbial) degradation of the target compounds in surface water has been shown to occur at very low rates (⩽0.00029h−1). The half-life times determined from the field experiments were 31 (LDC), 73 (TRA), 51 (VEN), 21 (ODT) and 18h (ODV) considering all possible mechanisms of degradation for the target compounds in river water (direct photodegradation, indirect photodegradation and biotic degradation).

Photolysis of sulfamethoxypyridazine in various aqueous media: Aerobic biodegradation and identification of photoproducts by LC-UV–MS/MS

Sulfonamides are one of the most frequently used antibiotics worldwide. Therefore, mitigation processes such as abiotic or biotic degradation are of interest. Photodegradation and biodegradation are the potentially significant removal mechanisms for pharmaceuticals in aquatic environments. The photolysis of sulfamethoxypyridazine (SMP) using a medium pressure Hg-lamp was evaluated in three different media: Millipore water pH 6.1 (MW), effluent from sewage treatment plant pH 7.6 (STP), and buffered demineralized water pH 7.4 (BDW). Identification of transformation products (TPs) was performed by LC-UV–MS/MS. The biodegradation of SMP using two tests from the OECD series was studied: Closed Bottle test (OECD 301 D), and Manometric Respirometry test (OECD 301 F). In biodegradation tests, it was found that SMP was not readily biodegradable so it may pose a risk to the environment. The results showed that SMP was removed completely within 128min of irradiation in the three media, and the degradation rate was different for each investigated type of water. However, dissolved organic carbon (DOC) was not removed in BDW and only little DOC removal was observed in MW and STP, thus indicating the formation of TPs. Analysis by LC-UV–MS/MS revealed new TPs formed. The hydroxylation of SMP represents the main photodegradation pathway.

Captopril and its dimer captopril disulfide: Photodegradation, aerobic biodegradation and identification of transformation products by HPLC–UV and LC–ion trap-MSn

In some countries effluents from hospitals and households are directly emitted into open ditches without any further treatment and with very little dilution. Under such circumstances photo- and biodegradation in the environment can occur. However, these processes do not necessarily end up with the complete mineralization of a chemical. Therefore, the biodegradability of photoproduct(s) by environmental bacteria is of interest.Cardiovascular diseases are the number one cause of death globally. Captopril (CP) is used in this study as it is widely used in Egypt and stated as one of the essential drugs in Egypt for hypertension. Three tests from the OECD series were used for biodegradation testing: Closed Bottle test (CBT; OECD 301 D), Manometric Respirometry test (MRT; OECD 301 F) and the modified Zahn–Wellens test (ZWT; OECD 302 B). Photodegradation (150W medium-pressure Hg-lamp) of CP was studied. Also CBT was performed for captopril disulfide (CPDS) and samples received after 64min and 512min of photolysis.The primary elimination of CP and CPDS was monitored by LC–UV at 210nm and structures of photoproducts were assessed by LC–UV–MS/MS (ion trap). Analysis of photodegradation samples by LC–MS/MS revealed CP sulfonic acid as the major photodegradation product of CP. No biodegradation was observed for CP, CPDS and of the mixture resulting from photo-treatment after 64min in CBT. Partial biodegradation in the CBT and MRT was observed in samples taken after 512min photolysis and for CP itself in MRT. Complete biodegradation and mineralization of CP occurred in the ZWT.

A Novel Photocatalytic Conversion of Tryptophan to Kynurenine Using Black Light as a Light Source

The photocatalytic conversion of an aqueous solution of l-tryptophan (Trp) to kynurenine (KN) was investigated under the illumination of different light sources. Results show that Trp converted to KN with a selectivity of 64% under the illumination of a medium pressure (MP) Hg lamp. KN selectivity was increased to >90% when black light (BL) was used a light source. The novel use of BL in the photocatalytic conversion of Trp to KN significantly reduces the energy consumption compared with MP light.

Photocatalytic decomposition of phenol by nanocomposite of ZnS nanoparticles and montmorillonite

The nanocomposite of ZnS nanoparticles stabilized by cetyltrimethylammonium ions (ZnS-CTA) and montmorillonite (ZnS-CTA-MMT) was prepared and used as a catalyst for the photodecomposition of phenol under UV irradiation of a medium pressure Hg lamp. The content of ZnS in ZnS-CTA-MMT was about 7 wt.%. For comparison, the photodecomposition was also performed with ZnS-CTA, montmorillonite and with no catalyst, i.e., using only UV irradiation. The photodecomposition efficiency decreased in the order: UV + ZnS-CTA-MMT ≈ UV + ZnS-CTA > UV > UV + MMT. The photodecomposition in the presence of ZnS-CTA-MMT and ZnS-CTA proceeded according to the pseudo-first order reaction kinetics. In other cases, the photodecomposition corresponded to the pseudo-second order reaction of phenol and hydroxyl radicals. Hydroxyl radicals were produced by reactions of dissolved oxygen and electrons released from the ZnS nanoparticles and excited phenol molecules. MMT decreased the photodecomposition reaction rate and no MMT catalytic activity was observed.

ChemInform Abstract: Effects of Methylene Chains on Photoreactions of Diphenylalkanediones and Phenylalkenones.

Upon conventional UV-irradiation of 1,ω-diphenylalkane-1,ω-dione (PhC(O)–(CH2)n–C(O)Ph, n = 5, 6, 7, 8, and 10) in acetonitrile using a medium-pressure Hg lamp, an intramolecular γ-hydrogen abstraction of the triplet ketone (type II photoreaction) occurred to give acetophenone and 1-phenylalk-n-en-1-one (PhC(O)–(CH2)n − 3–CHCH2), respectively, in a 1∶1 product ratio. Type II photoreaction occurred in all the 1,ω-diphenylalkane-1,ω-diones. The product 1-phenylalk-n-en-1-one also underwent a photoreaction to give secondary products under prolonged photoirradiation. The secondary products obtained from 1-phenylalk-n-en-1-one varied with the number of the methylene group n. For instance, no reaction occurred on the photolysis of 1-phenylbut-4-en-1-one obtained from type II photoreaction of 1,7-diphenylheptane-1,7-dione (n = 5). On the other hand, 1-phenylhex-5-en-1-one from the photoreaction of 1,8-diphenyloctane-1,8-dione (n = 6) gave acetophenone, buta-1,3-diene, 1-phenylhex-4-en-1-one, 2-vinyl-1-phenylcyclobutan-1-ol, and 1-phenylcyclohex-3-en-1-ol. Photolyses of other 1,ω-diphenylalkane-1,ω-dione (n = 7, 8, and 10) gave similar secondary products. Consequently, type II photoreaction of 1,ω-diphenylalkane-1,ω-dione occurs in which the number of methylenes between the two benzoyl groups does not affect the products. On the other hand, the length of the methylene group influences the photoreaction of 1-phenylalk-n-en-1-ones.

Reactive photoinduced species in estuarine waters. Characterization of hydroxyl radical, singlet oxygen and dissolved organic matter triplet state in natural oxidation processes

This paper describes the reactive photo-induced species (RPS) hydroxyl radical (HO*), singlet oxygen ((1)O(2)) and chromophoric dissolved organic matter triplet state ((3)CDOM*) in fresh water (Canal Fumemorte) and estuarine water (Vaccarès), sampled in the Camargue region, southern France. Experiments were conducted with a medium-pressure Hg lamp in a glass photoreactor (lambda > 290 nm, 220 W m(-2) irradiance between 290 and 400 nm). Steady-state concentration and initial production rate of RPS were determined for HO* and for (1)O(2). HO* and (1)O(2) were indirectly identified in the presence of benzene and furfuryl alcohol, respectively, as specific probes. The steady-state measured concentration of HO* was (1.72 +/- 0.01) x 10(-16) M and (9.41 +/- 0.12) x 10(-17) M for Vaccarès and Canal waters samples, respectively, and the respective concentrations of (1)O(2) was (2.06 +/- 0.22) x 10(-13) M and (5.44 +/- 0.04) x 10(-14) M. The interference of (3)CDOM* or other species in the determination of (1)O(2) with furfuryl alcohol, and of (1)O(2) in the quantification of (3)CDOM* with 2,4,6-trimethylphenol was also quantitatively assessed. We developed a kinetic model describing the solar photo-transformation of xenobiotic organic compounds induced by the three different photooxidants HO*, (1)O(2) and (3)CDOM*.