Errors in ferrioxalate actinometry

Cobalt-catalyzed synthesis of amides from alkenes and amines promoted by light

Catalytic methods to couple alkene and amine feedstocks are valuable in synthetic chemistry. The direct carbonylative coupling of alkenes and amines holds promise as a perfectly atom-economical approach to amide synthesis, but general methods remain underdeveloped. Herein, we report an alkene hydroaminocarbonylation catalyzed by unmodified, inexpensive cobalt carbonyl under mild conditions and low pressure promoted by light. Silane addition after the reaction enables sequential cobalt-catalyzed amide reduction, constituting a formal alkene hydroaminomethylation. These methods exhibit exceptional scope across both alkene and amine components with high chemo- and regioselectivity and proceed efficiently even in the absence of solvent. The formation of a hydridocobalt through photodissociation of a carbonyl ligand is proposed to enable catalytic activity under mild conditions, which addresses a long-standing challenge in catalysis.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.

4,4'-Dimethylazobenzene as a chemical actinometer

Chemical actinometers are a useful tool in photochemistry, which allows to measure the photon flux of a light source to carry out quantitative analysis on photoreactions. The most commonly employed actinometers so far show minor drawbacks, such as difficult data treatment, parasite reactions, low stability or impossible reset. We propose herewith the use of 4,4'-dimethylazobenzene as a chemical actinometer. This compound undergoes a clean and efficient E/Z isomerization, approaching total conversion upon irradiation at 365 nm. Thanks to its properties, it can be used to determine the photon flux in the UV-visible region, with simple experimental methods and data treatment, and with the possibility to be reused after photochemical or thermal reset.

Singlet Oxygen Quantum Yields in Environmental Waters

Singlet oxygen (¹O₂) is a reactive oxygen species produced in sunlit waters via energy transfer from the triplet states of natural sensitizers. There has been an increasing interest in measuring apparent ¹O₂ quantum yields (Φ_Δ) of aquatic and atmospheric organic matter samples, driven in part by the fact that this parameter can be used for environmental fate modeling of organic contaminants and to advance our understanding of dissolved organic matter photophysics. However, the lack of reproducibility across research groups and publications remains a challenge that significantly limits the usability of literature data. In the first part of this review, we critically evaluate the experimental techniques that have been used to determine Φ_Δ values of natural organic matter, we identify and quantify sources of errors that potentially explain the large variability in the literature, and we provide general experimental recommendations for future studies. In the second part, we provide a qualitative overview of known Φ_Δ trends as a function of organic matter type, isolation and extraction procedures, bulk water chemistry parameters, molecular and spectroscopic organic matter features, chemical treatments, wavelength, season, and location. This review is supplemented with a comprehensive database of Φ_Δ values of environmental samples.

Point-of-use water disinfection using ultraviolet and visible light-emitting diodes

Improvements in point-of-use (POU) drinking water disinfection technologies for remote and regional communities are urgently needed. Conceptually, UV-C light-emitting diodes (LEDs) overcome many drawbacks of low-pressure mercury tube based UV devices, and UV-A or visible light LEDs also show potential. To realistically evaluate the promise of LED disinfection, our study assessed the performance of a model 1.3 L reactor, similar in size to solar disinfection bottles. In all, 12 different commercial or semi-commercial LED arrays (270-740 nm) were compared for their ability to inactivate Escherichia coli K12 ATCC W3110 and Enterococcus faecalis ATCC 19433 over 6h. Five log10 and greater reductions were consistently achieved using the 270, 365, 385 and 405 nm arrays. The output of the 310 nm array was insufficient for useful disinfection while 430 and 455 nm performance was marginal (≈ 4.2 and 2.3-log10s E. coli and E. faecalis over the 6h). No significant disinfection was observed with the 525, 590, 623, 660 and 740 nm arrays. Delays in log-phase inactivation of E. coli were observed, particularly with UV-A wavelengths. The radiation doses required for >3-log10 reduction of E. coli and E. faecalis differed by 10 fold at 270 nm but only 1.5-2.5 fold at 365-455 nm. Action spectra, consistent with the literature, were observed with both indicators. The design process revealed cost and technical constraints pertaining to LED electrical efficiency, availability and lifetime. We concluded that POU LED disinfection using existing LED technology is already technically possible. UV-C LEDs offer speed and energy demand advantages, while UV-A/violet units are safer. Both approaches still require further costing and engineering development. Our study provides data needed for such work.

TiO₂-Mediated Photocatalytic Mineralization of a Non-Ionic Detergent: Comparison and Combination with Other Advanced Oxidation Procedures

Triton X-100 is one of the most widely-applied man-made non-ionic surfactants. This detergent can hardly be degraded by biological treatment. Hence, a more efficient degradation method is indispensable for the total mineralization of this pollutant. Application of heterogeneous photocatalysis based on a TiO₂ suspension is a possible solution. Its efficiency may be improved by the addition of various reagents. We have thoroughly examined the photocatalytic degradation of Triton X-100 under various circumstances. For comparison, the efficiencies of ozonation and treatment with peroxydisulfate were also determined under the same conditions. Besides, the combination of these advanced oxidation procedures (AOPs) were also studied. The mineralization of this surfactant was monitored by following the TOC and pH values, as well as the absorption and emission spectra of the reaction mixture. An ultra-high-performance liquid chromatography (UHPLC) method was developed and optimized for monitoring the degradation of Triton X-100. Intermediates were also detected by GC-MS analysis and followed during the photocatalysis, contributing to the elucidation of the degradation mechanism. This non-ionic surfactant could be efficiently degraded by TiO₂-mediated heterogeneous photocatalysis. However, surprisingly, its combination with the AOPs applied in this study did not enhance the rate of the mineralization. Moreover, the presence of persulfate hindered the photocatalytic degradation.

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV)

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim.

Degradation of industrial surfactants by photocatalysis combined with ozonation

The efficiency of titanium dioxide-mediated photocatalytic degradation of pollutants can be enhanced by combination with another advanced oxidation procedure such as ozonation. Mineralization of hydroxy- and dihydroxybenzenesulfonate based on these methods, both individually and combined, was investigated by monitoring the total organic carbon content, sulfate concentration, pH, high-performance liquid chromatography as well as the absorption spectral changes. The mineralization efficiency of the combined procedure significantly exceeded the sum of those of the individual techniques. The comparison of the disappearance of the starting material and the formation of the sulfate ions indicates that desulfonation is not the primary step of the degradation. Moreover, in the case of the combined method, ring cleavage, and thus, partial mineralization can occur without desulfonation. Efficient degradation of other, widely used industrial surfactants, such as alkylbenzene sulfonates and alkyl ether sulfates, was also achieved by heterogeneous photocatalysis combined with ozonation, offering an applicable method for the removal of these pollutants.

Equilibrium, photophysical and photochemical examination of anionic lanthanum(III) mono- and bisporphyrins: the effects of the out-of-plane structure

Lanthanum(III) ions form kinetically labile complexes with the 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (H(2)TSPP(4-)), the compositions and formation constants of which significantly depend on the presence of potential axial ligands (at 0.01 M). Deviating from the chloride ion, acetate coordinating to the metal center hinders the formation of a bisporphyrin complex. In these lanthanum(III) complexes, the metal center, due to its large ionic radius (103.2 pm), is located out of the ligand plane, distorting it. Accordingly, the absorption and fluorescence spectra of these coordination compounds display special properties characteristic of the so-called sitting-atop (SAT) or out-of-plane (OOP) porphyrin complexes. Metalation significantly decreases the quantum yield of the fluorescence from the S(1) excited state. Quantum chemical calculations (DFT) confirm the considerable OOP displacement of the La(III) center (about 120 pm in the monoporphyrin complexes). The monoporphyrins display efficient fluorescence (Φ ≈ 0.03), while the bisporphyrin does not emit. Differing from the normal (in-plane) metalloporphyrins, the excitation of these lanthanum(III) porphyrins leads to an irreversible ligand-to-metal charge transfer (LMCT) followed by the opening of the porphyrin ring, which is also typical of OOP complexes. Dissociation releasing free-base porphyrin can also be observed upon irradiation of the monoporphyrin in acetate solution, while in the presence of chloride ions interconversions of the mono- and bisporphyrins may also take place beside the irreversible photoredox reaction.

Synthesis, photochemistry, and photophysics of butadiene derivatives: influence of the methyl group on the molecular structure and photoinduced behavior

Novel butadiene derivatives display diverse photochemistry and photophysics. Excitation of 2-methyl-1-(o-vinylphenyl)-4-phenylbutadiene leads to the dihydronaphthalene derivative, whereas photolysis of the corresponding model o-methyl analogue results in the formation of the naphthalene-like derivative, deviating from the nonmethylated analogue of the prior starting compound and producing benzobi- and -tricyclic compounds. The effect of the methyl substituents is even more dramatic in the case of the dibutadienes. The parent unsubstituted compound undergoes photoinduced intramolecular cycloaddition giving benzobicyclo[3.2.1]octadiene, whereas the photochemical reaction of the corresponding dimethylated derivative shows only geometrical isomerization due to the steric effect of the substituents. Methyl groups on the butadiene backbones reduce the extent of conjugation, causing a blue-shift of the characteristic absorption band. The fluorescence efficiency is dramatically decreased, as a consequence of nonplanarity and reduced rigidity of the molecules due to the crowding by the methyl and phenyl groups together. Four molecules of very similar structures show dramatically different photoinduced behavior, revealing how changes of the nature and position of the substituents are valuable in understanding the photophysics and photochemistry of these types of compounds.

Photocatalytic degradation of benzenesulfonate on colloidal titanium dioxide

Titanium dioxide-mediated photocatalyzed degradation of benzenesulfonate (BS) was investigated by monitoring chemical oxygen demand (COD), total organic carbon (TOC) content, sulfate concentration, pH as well as the absorption and emission spectral changes in both argon-saturated and aerated systems. Liquid chromatography-mass spectrometry analysis was utilized for the detection of intermediates formed during the irradiation in the UVA range (λ(max) = 350 nm). The results obtained by these analytical techniques indicate that the initial step of degradation is hydroxylation of the starting surfactant, resulting in the production of hydroxy- and dihydroxybenzenesulfonates. These reactions were accompanied by desulfonation, which increases [H(+)] in both argon-saturated and aerated systems. In accordance with our previous theoretical calculations, the formation of ortho- and meta-hydroxylated derivatives is favored in the first step. The main product of the further oxygenation of these derivatives was 2,5-dihydroxy-benzesulfonate. No decay of the hydroxy species occurred during the 8-h irradiation in the absence of dissolved oxygen. In the aerated system much more efficient desulfonation and hydroxylation, moreover, a significant decrease of TOC took place at the initial stage. Further hydroxylation led to cleavage of the aromatic system, due to the formation of polyhydroxy derivatives, followed by ring fission, resulting in the production of aldehydes and carboxylic acids. Total mineralization was achieved by the end of the 8-h photocatalysis. It has been proved that in this photocatalytic procedure the presence of dissolved oxygen is necessary for the cleavage of the aromatic ring because hydroxyl radicals photochemically formed in the deaerated system too alone are not able to break the C-C bonds.

Photolysis in aqueous aerosols: 300 nm yields of Fe2+ from a ferrioxalate actinometer and of OH radical from nitrate ions

300 nm photolysis yields of Fe(2+) from potassium ferrioxalate and of OH from nitrate ion have been measured in aqueous aerosols, the yield from ferrioxalate in a bulk solution being used to measure the light intensity. Mie theory was used to calculate effective cross-sections for absorption and scattering of light by the aerosol droplets. Yields of OH from nitrate ion have been measured with benzoic acid and carbon monoxide radical scavengers. The photolysis yield of Fe(2+) from ferrioxalate was found to be enhanced in the aerosol by a factor of 48 +/- 17. This enhancement is believed to be real, and is attributed to surfactant behaviour that results in the presence of a high concentration of ferrioxalate in a region of high light intensity near the droplet surface. The experiments with benzoic acid indicate that the yield of OH from nitrate in aerosol droplets is not significantly different from the yield in bulk solution. The CO experiments appear to indicate that the total OH production in the aerosol is enhanced over that in bulk solution by a factor of 10 +/- 3, but this number is not considered reliable.

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(i) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

In aqueous solutions, thallium(I) ions and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin form a kinetically labile metalloporphyrin of 2 : 1 composition (Tl(2)P(4-)). The formation constant of this sitting-atop (SAT) complex is relatively low (beta2/[H+]2= 3.55 x 10(3) M(-2) at pH = 7), due to the large size and rather small charge of Tl+. As a consequence of the considerably weak metal-ligand interaction in this system, the 1 : 1 species does not appear in detectable concentration. Both the absorption and the emission properties of the Tl(2)P(4-) complex are characteristic for the typical SAT metalloporphyrins. Compared to the corresponding values of the free-base porphyrin, the diminished fluorescence quantum efficiency (Qfl= 0.0131 vs. 0.056) of Tl(2)P(4-) can be accounted for by the heavy-atom effect, while the larger Stokes shift (442 vs. 282 cm(-1)) indicates a stronger distortion of the ligand plane. Both Soret- and Q-band irradiations of the Tl(2)P(4-) complex lead to the degradation of the porphyrin with quantum yields of magnitude 3 x 10(-4). The primary photochemical step in this process is ligand-to-metal charge transfer reaction, which is unusual for normal (coplanar) metalloporphyrins. In the case of SAT complexes, the kinetic lability facilitates the separation of the primary redox products, followed by an irreversible ring-opening of the oxidized porphyrin. Photoinduced electron ejection as a considerable step in the degradation mechanism could be ruled out.

Photolysis of naphthenic acids in natural surface water

Naphthenic acids are toxic and corrosive substances in oil sands leachates comprising a group of saturated aliphatic and alicyclic carboxylic acids in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). In the current study, photolysis was applied to naphthenic acid mixtures and individual compounds to determine the efficacy of a variety of UV/vis radiation sources for reducing both concentration and aryl hydrocarbon (Ah) receptor binding as a measure of toxicity. The results show that the concentrations of neither the compounds nor the mixtures were significantly reduced in Athabasca River water, although compositional changes occurred within the mixtures and Ah receptor binding potential was affected by photolysis. Photolysis at UV254 was the most effective radiation source applied in all instances.

Photolysis of atrazine and ametryne herbicides in Barbados sugar cane plantation soils and water

The photodegradation kinetics of atrazine (2-chloro-6-(ethylamino)-4-isopropylamino-1,3,5-triazine) and ametryne (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine), in fresh and coastal salt water from Barbados, were measured under irradiation with artificial solar and UV254-radiation. The first-order rate constants were greater for ametryne than for atrazine, and the rates were reduced in seawater relative to fresh water, and in soil slurries relative to fresh water. However, rates were accelerated in the presence of iron(III) at pH 3 due to photo-Fenton type processes. This rate enhancement was reduced at ambient pH values (pH 7-7.5) representative of surface water in Barbados. These results have important implications for the relative persistence of these contaminants in aquatic environments in tropical areas.

The photolysis of dichlorotriphenylbismuth(V) in chloroform

Under 254 nm irradiation in chloroform, Bi(C6H5)3Cl2 reacts to yield HBiCl4 and H2BiCl5, in contrast to its behavior in acetonitrile, in which bismuth metal appears to be the eventual product, unless anhydrous HCl is present, in which case H2BiCl5 is also formed. The photolysis in CHCl3 is not significantly solvent-initiated. The rate depends directly on the light intensity absorbed by the metal complex, and the quantum yield is 0.026. In CCl4 a portion of the reaction occurs through absorption of light by the solvent.

Degradation of surfactants by hydroxyl radicals photogenerated from hydroxoiron(iii) complexes

The Fe(III)-photoinduced oxidation of anionic lauryl sulfate (LS-) and cationic cetyltrimethylammonium (CTA+) surfactants has been investigated in aqueous solution. Competition experiments using 2-propanol showed that the initial rate of disappearance is proportional to the concentration of the photogenerated HO* radicals scavenged by the surfactants (the degradation of lauryl sulfate involves attack by HO* only) and no direct photoinduced charge-transfer reaction occurs between the Fe(III) species and the surfactant ions. Ageing of the Fe(III) solution did not significantly influence the efficiency of photodegradation in air-saturated systems. Conversion of Fe(III) to Fe(II) in aerated solution reached a steady-state level of ca. 50% after 2 h irradiation. In nitrogen-saturated systems, the rate of surfactant oxidation decreased due to the total reduction of Fe(III). Addition of H2O2 doubled the quantum yield of the disappearance of both detergents as a result of the photo-Fenton reaction. The photoinduced oxidation of both surfactants was most efficient in acidic solutions of pH 2-3, without H2O2, and for the photo-Fenton system; the quantum yields are phi(NaLS) = 0.011, phi(CTAB) = 0.012 without H2O2, and phi(NaLS) = 0.024, phi(CTAB) = 0.027 in the photo-Fenton system with irradiation at 366 nm. For the disappearance of 4 x 10(-4) M detergent, due to the first oxidation step, 4 h of irradiation (at pH 2.6) is sufficient, whereas 100% mineralization of the total organic carbon content requires prolonged photolysis for at least 10 h. The formation of carbon dioxide dramatically accelerated after a 2 h induction period (1 h in the photo-Fenton system), indicating the cleavage of the long hydrocarbon chains to shorter intermediates in the first stage of the mechanism. The following step is total mineralization of these smaller compounds, which were identified as mostly hydroxy acids via GC-MS.

Liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry determination of N-methylpyrrolidinone in riverine biofilms

A rugged procedure utilizing reversed-phase liquid chromatography with positive-ion electrospray ionization mass spectrometry (LC-MS) along with tandem MS is described for the quantification and confirmation of N-methylpyrrolidinone (NMP) in methanolic extracts of riverine biofilm. The LC-MS method provided a 100-fold improvement in detection limits (2 ng g(-1) with a repeatability of 80-95% based on triplicate analyses) compared to a conventional LC-UV detection procedure and was applicable to quantitative analysis of biofilm samples with little or no clean up. Under low-energy collision induced dissociation (CID) conditions (17 V, laboratory frame of reference, with argon as the collision gas), two product-ions of the [M+H]+ ion were formed at m/z 69 [MH-CH3NH2]+ and m/z 58 [MH-CH3NCH]+ with relative abundances of 30% and 5%, respectively. These CID transitions were used to demonstrate that biofilm uptake of a photocatalytically-generated mixture of NMP was rapid once acclimation was achieved.