Bis-(hydroxyamino)triazines: highly stable hydroxylamine-based ligands for iron(III) cations.

Bis-(hydroxyamino)triazines (BHTs) constitute a new, general and highly versatile group of tridentate iron(III) chelating agents exhibiting higher affinity to iron(III) than other tridentate iron(III) chelators and superior iron(III) over iron(II) selectivity compared to desferrioxamine-B (DFO), EDTA as well as other tridentate ligands.

Quantitative evaluation of tracers for quantification of wastewater contamination of potable water sources.

Quantitative criteria for selection of tracers for assessment of mixing of wastewater and pristine water are proposed and evaluated for leakage from a wastewater effluent recharge system to nearby pristine water wells and the dilution of the effluents in a reclamation well by pristine water from the surrounding aquifer. Two molecular tracers were compared: carbamazepine, an organic drug whose refractory behavior was evaluated on-site, and chloride, a widely used conservative tracer. The mixing ratios and the corresponding uncertainty levels in their calculation were evaluated using actual field data. Uncertainty level analysis illuminates the effects of the analytical errors in the determination of trace micropollutants on one hand and the high level of chloride in the background on the other. Uncertainty level calculations revealed that chloride is a somewhat better tracer for the estimation of the dilution of wastewater by flow from a pristine aquifer, whereas carbamazepine is a much better tracer for the calculation of wastewater contamination of nearby drinking water wells. Surprisingly, we show that even when carbamazepine degrades to a large and unknown extent, it can still be used to estimate accurately the probability that a site is contaminated by a wastewater stream.

Bis(hydroxyamino)triazines: versatile and high-affinity tridentate hydroxylamine ligands for selective iron(III) chelation.

A new versatile family of chelating agents based on bis(hydroxyamino)-1,3,5-triazines, BHTs, is described. The properties of different BHT ligands are determined by electrochemistry, spectroscopy and titrimetry revealing high redox stability, transparency in the visible range, and diprotic acid-like behaviour in the 5-9 pH range. The iron(III) and iron(II)-BHT complexes were studied revealing high affinity of BHTs to iron(III). Electrochemical studies show exceptional preference of the BHT ligands to iron(III) over iron(II), this, in addition to their small size and their fast and reversible electrochemistry makes them potentially useful electrochemical redox couples for the low end of the aqueous potential window (<0.6 V, vs. NHE). The synthetic versatility of the new ligands allows easy tuning of the hydrophobicity, redox potential, and to some extent the stability constant of the complexes by alteration of the peripheral groups appended to the BHTs.

Selective esterifications of alcohols and phenols through carbodiimide couplings.

Esterification of carboxylic acids capable of forming ketene intermediates upon treatment with carbodiimides permits the selective acylation of alcohols in the presence of phenols lacking strong electron-withdrawing groups. The selectivity of acylations involving highly acidic phenols could be reversed through the addition of catalytic amount of acid. Esterification of other carboxylic acids was found to proceed through the formation of symmetric anhydrides and provide the opposite chemoselectivity. In both cases the relative acylation rates of substituted phenols are consistent with a reaction mechanism involving an attack of phenolate anions on electrophilic intermediates such as ketenes and symmetric anhydrides, with the carbodiimides serving both as an activating reagent and as a basic catalyst.

Acylation through Ketene Intermediates.

Carboxylic acids possessing a strong electron-withdrawing group in the alpha-position undergo facile dehydration upon reaction with carbodiimides to form the corresponding substituted ketenes that can react in situ with alcohols providing esters in a high yield. The ketene formed by the treatment of ethyl 2-methylmalonate with DCC was trapped in situ by a [4+2] cycloaddition with a second DCC molecule. The chemoselectivity of the acylation through the ketene intermediates was found to be substantially different from that of conventional acylation reagents showing a very low sensitivity toward the steric bulk of alcohols. A comparison of the sensitivity of the acylation to the steric bulk of alcohols supports the presence of a pseudopericyclic pathway for the nucleophilic addition of alcohols to ketenes derived from ethyl malonic and diethylphosphonoacetic acid.