The conversion of glycerol selectively to lactic acid has been accomplished in high yields (ca. 90 %) by a NNN pincer-Ru catalyst. DFT explains the role of Ru-P bond and...

The synthesis and characterization of a pincer-nickel complex of the type ( iPr2NNN)­NiCl2(CH3CN) is reported here. We have demonstrated the utility of this pincer-nickel complex (0.02 and 0.002 mol %) for the catalytic N-alkylation of amines using various alcohols. Under solvent-free conditions, while the highest yield (ca. 90%) was obtained for the alkylation of 2-aminopyridine with naphthyl-1-methanol, excellent turnovers (34000 TONs) were observed for the alkylation of 2-aminopyridine with 4-methoxybenzyl alcohol. To demonstrate the synthetic utility of these systems, high-yield reactions (up to 98%) have been probed for representative substrates with a higher loading of the pincer-nickel catalyst (4 mol %). DFT studies indicate that while β-hydride elimination is the RDS for alcohol dehydrogenation, the N-alkylated product can be formed either via hydrogenation with a rate-determining σ-bond metathesis or by alcoholysis that has imine insertion as the RDS. All of the corresponding resting states have been observed by HRMS (ESI) analysis. The labeling experiments are also complementary to DFT studies and show evidence for the involvement of the benzylic C–H bond in the RDS with a k CHH/k CHD value of about 2.5. This method has been applied to accomplish efficient (2000 TONs) dehydrogenative coupling leading to various benzimidazoles.

A series of NNN pincer‐ruthenium complexes (R2NNN)RuCl2(PPh3) (R=Cyclohexyl (Cy), t‐butyl (tBu), i‐propyl (iPr) and phenyl (Ph)) have been synthesized and characterized. These pincer‐ruthenium complexes have been used to catalyse the Kharasch addition or atom transfer radical addition (ATRA) of carbon tetrachloride to styrene. Among the pincer‐ruthenium catalysts screened for the Kharasch addition, the catalytic activity followed the order (Cy2NNN)RuCl2(PPh3)>(iPr2NNN)RuCl2(PPh3)≫(Ph2NNN)RuCl2(PPh3). The oxidation of Ru(II) is easier with (Cy2NNN)RuCl2(PPh3) and (iPr2NNN)RuCl2(PPh3) in comparison with RuCl2(PPh3) as indicated by cyclic voltammetry studies. The catalyst precursor (R2NNN)RuCl2(PPh3) itself is the resting state of the reaction. The rate determining step involves the generation of the five‐coordinate 16‐electron ruthenium(II) species (R2NNN)RuCl2. Owing to weaker binding of triphenyl phosphine to ruthenium, the generation of catalytically active 16‐electron species (Cy2NNN)RuCl2 and (iPr2NNN)RuCl2 are more favourable. The complex (Cy2NNN)RuCl2(PPh3) demonstrates very high productivity (5670 turnovers after 48 h at 140 °C) in the absence of any co‐catalyst radical initiator. To the best of our knowledge, our turnovers (ca. 5670) are much higher than that reported hitherto. Quantum mechanical calculations demonstrate that the path involving the activation of carbon tetrachloride by (Cy2NNN)RuCl2 is more favoured than the path where carbon tetrachloride is activated by (Cy2NNN)RuCl2(η2‐styrene). Density functional theory (DFT) and kinetic studies are in accord with the widely accepted mechanism involving the single electron transfer (SET) from ruthenium(II) to chloride radical with concomitant generation of a benzyl radical which is trapped by the resulting ruthenium(III) species.magnified image

No abstract

Pyrolysis oil is a renewable resource derived from biomass and can be viewed as a potential crude oil substitute or extender. Pyrolysis oil has several undesirable properties, including very high acid and water contents. Because of the high acid content, pyrolysis oil will likely be blended with conventional crude oil for processing into transportation fuel, lowering the overall acid content of the mixture and mitigating the corrosivity toward refining units. Pyrolysis oil contains polar and nonpolar organics, water, and particulates. These components can be difficult to homogenize and, if left standing, may separate again. Additionally, pyrolysis oil will thicken with time as components react to form higher molecular weight products. ASTM D664 "Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration" is often used for determining the acid content of pyrolysis oils. However, ASTM D664 was developed specifically for petroleum-based lubricants. The ASTM D664 solvent system is unsuited for use with pyrolysis oil, failing to completely solubilize the pyrolysis oil and yielding unreliable results. This work addresses two related problems with pyrolysis oil. The first is obtaining and maintaining a stable, homogeneous sample for analysis that is representative of the material to be analyzed. The second issue is the development of a reliable method for the measurement of the acid concentration by titration, which is necessary to calculate the amount of pyrolysis oil that can be mixed with a crude oil and safely processed in existing refinery equipment. A simple solvent system based on ethylene glycol (ethane-1,2-diol) has been devised that produces stable, homogeneous solutions and allows for highly repeatable acid numbers on pyrolysis oil. The accuracy and precision for the modified method are both satisfactory.■ EXPERIMENTAL SECTION ASTM D664: "Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration". 6 The ASTM D664 test method A acid number titration was developed to measure the acidic properties of petroleum products and lubricants. In 2009, the method was extended to biodiesel and blends of biodiesel with the