EFFECT OF SULFACETAMIDE ON THE COMPOSITION OF CORROSION PRODUCTS FORMED ONTO CARBON STEEL SURFACE IN HYDROCHLORIC ACID

IUPAC name N- [(4-aminophenyl) sulfonyl] acetamide (APSA) on the corrosion of carbon steel in 1.0 M HCl solution has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and XPS analysis. The electrochemical measurements indicated that the presence of APSA in 1.0 M HCl solution decreases the corrosion current (i corr ) and increases the polarization rezistance (R p ). XPS surface analysis showed at this stage, in the absence of APSA, that the main product of corrosion is a non-stoichiometric Fe 3+ oxide/oxidehydroxide, consisting of a mixture of Fe 2 O 3 and FeO(OH), where FeO(OH) is the main phase. Moreover, in presence of inhibitor the surface layer consists of FeO(OH) rather than pure oxide, adsorbed molecules of sulfacetamide and inorganic compounds such as: sulfides, carbonates, sulphates, nitrates, which were obtained by electrochemical degradation of APSA. UV-Vis spectrophotometry and HPLC technique were performed to determine the medium composition before and after corrosion. The results showed a decrease of the inhibitor concentration in 1.0 M HCl solution after carbon steel corrosion, indicating an adsorption process between organic compound molecules from aqueous phase and the electrode surface and/or the electrochemical degradation of APSA

Formation mechanisms and yields of small imidazoles from reactions of glyoxal with NH4+ in water at neutral pH

SSCI-VIDE+ATARI+AMX:BNO:HMEInternational audienceImidazoles have numerous applications in pharmacology, chemistry, optics and electronics, making the development of their environmentally-friendly synthetic procedures worthwhile. In this work, the formation of imidazole, imidazole-2-carboxaldehyde, and 2,2-bis-1H-imidazole was investigated in the self-reaction of glyoxal and its cross-reactions with each of these compounds in aqueous solutions of inorganic ammonium salts at pH = 7. Such conditions are relevant both as cheap and environmentally-friendly synthetic procedures and for the chemistry of natural environments where NH4+ is abundant, such as in atmospheric aerosols. These reactions were investigated both by H-1-NMR and UV-Vis absorption spectroscopy at room temperature with the objective to determine the formation pathways of the three imidazoles and the parameters affecting their yields, to identify the optimal conditions for their synthesis. The results show that only the simplest imidazole is produced by the self-reaction of glyoxal and that imidazole-2-carboxaldehyde and 2,2-bis-1H-imidazole are produced by cross-reactions of glyoxal with imidazole and imidazole-2-carboxaldehyde, respectively. The yields of imidazole-2-carboxaldehyde and 2,2-bis-1H-imidazole formed by the cross-reactions were close to unity, but the yield of imidazole formed by the self-reaction of glyoxal, Y-Im, was small and varied inversely with the initial glyoxal concentration, [G](0): Y-Im > 10% only for [G](0) < 0.1 M. The latter result was attributed to the kinetic competition between the imidazole-forming condensation pathway and the acetal/oligomer formation pathway of the glyoxal self-reaction and constitutes a bottleneck for the formation of higher imidazoles. Other parameters such as pH and the NH4+ concentration did not affect the yields. Thus, by maintaining small glyoxal concentrations, high imidazole yields can be achieved in environmentally-friendly aqueous ammonium solutions at neutral pH. Under the same conditions, higher yields are expected expected from substituted carbonyl compounds, regardless of their concentration, as they produce less acetals

iminium-catalysed hydrolysis of epoxides by nh4+ in water: importance for atmospheric and green chemistry

SSCI-VIDE+ATARI+AMX:BNO:LFI:CFEInternational audienceIminium catalysis, which was known for a long time to be mediated by amines and amino acids, was also recently shown to be mediated by inorganic ammonium ions, NH4+. Iminium catalysis by NH4+ is potentially of great interest both for green chemistry in water and in atmospheric aerosols where these ions are abundant. In this work we investigate the hydrolysis of epoxides such as 1,2-epoxybutane, cis-2,3-epoxybutane, 2,3-dimethyl-2,3-epoxybutane, and the âisoprene-derivedâ cis- and trans-(2-methyloxirane-2,3-diyl)dimethanol (or âIEPOXâ 3 and 4, respectively) in aqueous solutions at pH = 5-8 in the presence of NH4+. The products and kinetics of each reaction have been studied with a combination of GC/MS, GC/FID and 1H-NMR and by comparison with authentic standards. The results showed that each epoxide produced the expected diol or tetrol in large yield and that the reaction rate was much larger than when catalyzed by base or acid, confirming that NH4+ is an efficient catalyst for the hydrolysis of epoxides. Iminium catalysis by NH4+ thus provides a cheap and green alternative for the manufacturing of diols and glycols in water. In tropospheric aerosols, the hydrolysis of epoxides by NH4+ catalysis should be much faster than by acid catalysis for pH 3-4, thus in many regions except the most polluted ones

The hydrolysis of epoxides catalyzed by inorganic ammonium salts in water: kinetic evidence for hydrogen bond catalysis

International audienceNaturally-occurring inorganic ammonium ions have been recently reported as efficient catalysts for some organic reactions in water, which contributes to the understanding of the chemistry in some natural environments (soils, seawater, atmospheric aerosols, …) and biological systems, and is also potentially interesting for green chemistry as many of their salts are cheap and non-toxic. In this work, the effect of NH4+ ions on the hydrolysis of small epoxides in water was studied kinetically. The presence of NH4+ increased the hydrolysis rate by a factor of 6 to 25 compared to pure water and these catalytic effects were shown not to result from other ions, counter-ions or from acid or base catalysis, general or specific. The small amounts of amino alcohols produced in the reactions were identified as the actual catalysts by obtaining a strong acceleration of the reactions when adding these compounds directly to the epoxides in water. Replacing the amino alcohols by other strong hydrogen-bond donors, such as trifluoroethanol (TFE) or hexafluoroisopropanol (HFIP) gave the same results, demonstrating that the kinetics of these reactions was driven by hydrogen-bond catalysis. Because of the presence of many hydrogen-bond donors in natural environments (for instance amines and hydroxy-containing compounds), hydrogen-bond catalysis is likely to contribute to many reaction rates in these environments

Quantifying the ionic reaction channels in the Secondary Organic Aerosol formation from glyoxal

International @ AIR+AMX:BNO:SRS:CGOInternational audienceGlyoxal, a common organic gas in the atmosphere, has been identified in recent years as an important Secondary Organic Aerosol (SOA) precursor (Volkamer et al., 2007). But, unlike with other precursors, the SOA is largely produced by particle-phase reactions (Volkamer et al., 2009) and equilibria (Kampf et al. 2013) that are still not entirely characterized. Since 2009 series of smog chamber experiments have been performed within the Eurochamp program at the Paul Scherrer Institute, Switzerland, to investigate SOA formation from glyoxal. In these experiments, glyoxal was produced by the gas-phase oxidation of acetylene in the presence of seeds, the seed composition and other conditions being varied. The 2011 campaign resulted in the identification of salting processes controlling the glyoxal partitioning in the seeds (Kampf et al. 2013). This presentation will report results of the 2013 campaign focusing on the identification of the various reactions (ionic or photo-induced) contributing to the SOA mass. In particular, the contribution of the ionic reactions, i.e. mediated by NH4+, were investigated by quantifying the formation of imidazoles (imidazole, imidazole-2-carboxaldehyde, 2,2-biimidazole) from the small condensation channel of glyoxal with ammonia. For this, the SOA produced were collected on quartz filters and analyzed by Orbitrap LC/MS (Q-Exactive Thermo Fisher). The formation of other products such as organic acids was also investigated to determine potential competing reactions. Time-resolved MOUDI sampling coupled with nano-DESY/ESI-MS/MS analysis was also used to identify nitrogen- and sulphur-containing products from all the reactions. The results obtained for a range of conditions will be presented and compared with recent mechanistic information on the ionic reaction channels (Nozičre et al., in preparation, 2013). The implementation of all this new information into a glyoxal-SOA model will be discussed