Atmospheric pressure photoionization mass spectrometry as a tool for the investigation of the hydrolysis reaction mechanisms of phosphite antioxidants

The hydrolysis reaction mechanism of phosphite antioxidants is investigated by liquid chromatography-mass spectrometry (LC/MS). The phosphites were chosen because they differed in chemical structure and phosphorus content. Dopant assisted-atmospheric pressure photoionization (DA-APPI) is chosen as the ion source for the ionization of the compounds. In our previous work, DA-APPI was shown to offer an attractive alternative to atmospheric pressure chemical ionization (APCI) since it provided background-ion free mass spectra and higher sensitivity [M. Papanastasiou, et al., Polymer Degradation and Stability 91 (11) (2006) 2675–2682]. In positive ion mode, the molecules are generally detected in their protonated form. In negative ion mode, the phosphites are unstable and only fragment ions are observed; these however, are characteristic of each phosphite and may be used for the identification of the analytes in complex mixtures.The analytes under investigation are exposed to accelerated humid ageing conditions and their hydrolytic pathway and stability is investigated. Different substituents around the phosphorus atom are shown to have a significant effect on the stability of the phosphites, with phenol substituents producing very hydrolytically stable structures. Alkanox P24 and PEP-36 follow a similar hydrolytic pathway via the scission of the first and then the second PO_phenol bonds, eventually leading to the formation of phenol, phosphorous acid and pentaerythritol as end products. HP-10 exhibits a rather different structure and the products detected suggest scission of either the PO_hydrocarbon or one of the PO_phenol bonds. A phenomenon similar to that of autocatalysis is observed for all phosphites and is attributed to the formation of dialkyl phosphites as intermediate products.     

A convenient method to reduce hydroxyl-substituted aromatic carboxylic acid with NaBH4/Me2SO4/B(OMe)3

The reduction of hydroxyl-substituted aromatic carboxylic acid with NaBH₄/Me₂SO₄/B(OMe)₃ is described. Borane is generated by the reaction of NaBH₄ with Me₂SO₄ in THF, which is as efficient as the commercial one. B(OMe)₃ has been successfully applied to increase the reactivity and selectivity of this reaction. The optimum ratio of borane/B(OMe)₃/acid is studied, and a variety of hydroxyl-substituted aromatic acids are reduced in good yields.     

Excess molar enthalpies for binary mixtures of trimethyl phosphate with alkanols {CH3(CH2)nOH, n = 0–3} at 298.15 K

The excess molar enthalpies () for the binary mixtures of trimethyl phosphate (TMP) with alkanols {CH₃(CH₂)_nOH, n = 0–3} have been measured with an isothermal calorimeter at 298.15 K and atmospheric pressure. The values are positive for all the mixtures over the whole composition range. The values increase in the order methanol < ethanol < 1-propanol < 1-butanol. The experimental results have been correlated with the Redlich–Kister equation.     

Synthesis of novel cyclohexanediol-derived chiral phosphite ligands and their application in the Cu-catalyzed conjugate addition of organozinc to cyclic enones

A series of novel chiral diphosphite ligands have been synthesized from (1R,2R)-trans-1,2-cyclohexanediol, (1S,2S)-trans-1,2-cyclohexanediol, racemic trans-1,2-cyclohexanediol and chlorophosphoric acid diary ester, and were successfully employed in the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to cyclohexenone with up to 99% ee. It was found that ligand 1,2-bis[(R)-1,1'-binaphthyl-2,2'-diyl]phosphitecyclohexanediol 6a derived from racemic diol skeleton can show similar catalytic performance compared with ligand (1R,2R)-bis[(R)-1,1'-binaphthyl-2,2'-diyl]phosphitecyclohexanediol 6a' derived from enantiopure startingmaterial. A significant dependence of stereoselectivity on the type of enone and the ring size of the cyclic enone was observed. Moreover, the configuration of the products was mainly determined by the configuration of the binaphthyl moieties of diphosphite ligands in the 1,4-addition of cyclic enones.     

硼酸三甲酯为探针红外光谱定量研究氧化镁的路易斯碱性

采用硼酸三甲酯(BATE)作为探针分子对MgO的路易斯碱性进行了红外光谱定量研究。MgO对硼酸三甲酯的吸附使硼酸三甲酯在1360cm-1的谱峰分裂成1410cm-1和1300cm-1两个峰,1036cm-1的谱峰紫移到1060cm-1。低压下吸收峰高与硼酸三甲酯压力成正比,与MgO含量成正比。结果表明MgO有一定的路易斯碱强度,与硼酸三甲酯之间的吸附是单分子层化学吸附。     

The development of iodide-based methods for batch and on-line determinations of phosphite in aqueous samples

Recent developments in the field of microbiology and research on the origin of life have suggested a possible significant role for reduced, inorganic forms of phosphorus (P) such as phosphite [HPO₃²⁻, P(+III)] and hypophosphite [H₂PO₂⁻, P(+I)] in the biogeochemical cycling of P. New, robust methods are required for the detection of reduced P compounds in order to confirm the importance of these species in the overall cycling of P in the environment. To this end, we have developed new batch and flow injection (FI) methods for the determination of P(+III) in aqueous solutions. The batch method is based on the reaction of P(+III) with a mixed-iodide solution containing tri-iodide (I₃⁻) and penta-iodide (I₅⁻). The oxidation of P(+III) consumes free I₃⁻ and I₅⁻ in solution. The remaining I₃⁻ and I₅⁻ subunits are then allowed to react with the amylose content in starch to form a blue complex, which has a λ_max of 580 nm. The measurement of this blue complex is directly correlated with the concentration of P(+III). The on-line FI method employs the same reaction between P(+III) and mixed-iodide producing phosphate [P(+V)] that is determined spectrophotometrically by the molybdenum blue method employing ascorbic acid at a λ_max of 710 nm. The linear range for both the batch and FI determination of P(+III) was 1.0–50 μM with detection limits of 0.70 and 0.36 μM, respectively. Interference studies for the batch method show that arsenite [As(+III)] and sulfite [S(+IV)] can also be determined by this technique; however, these interferences can be circumvented by oxidizing As(+III) and S(+IV) using KMnO₄ which is an ineffective oxidant for P(+III). Both methods were applied to P(+III) determinations in ultra-pure water and simulated creek water. Results and analytical figures of merit are reported and future work is considered.     

Palladium-catalyzed cross-coupling of trimethoxysilylbenzene with aryl bromides and chlorides using phosphite ligands

Phosphites were employed as ligands in palladium-catalyzed Hiyama coupling reactions. The optimized reaction conditions were equimolar amounts (5 mol % each) of Pd(acac)₂ and phosphite 1 in p-xylene at 80 °C with TBAF as an additive. This catalyst system exhibited high activities in the reactions with trimethoxysilylbenzene and aryl bromides that have electron-donating or electron-withdrawing groups. In the case of aryl chlorides, substrates possessing electron-withdrawing groups gave the coupled products in high yields.     

Hydrolytic stability and hydrolysis reaction mechanism of bis(2,4-di-tert-butyl)pentaerythritol diphosphite (Alkanox P-24)

The excellent processing stability afforded by the commercial phosphate antioxidant, Alkanox P-24 is well known in the literature. However, it is known that Alkanox P-24 is hydrolytically unstable. Enhancement of its hydrolytic stability is therefore a key objective in this work and some binary and ternary blends were developed using other additives that are often used for polymer stabilisation, including the primary antioxidant tetrakis[methylene-3-(3′,5′-di-tert-butyl-4-hydroxyhyphenyl)propionate]methane (Anox 20), acid scavengers calcium stearate (DW) and the hydrotalcite like compound (DHT-4A). An improvement in the hydrolytic stability of Alkanox P-24 was found when it was blended with these additives. A comparison with different physical forms of blends (traditional powders versus recently introduced Non-Dust Blends) was undertaken. Better performance was observed with NDB relative to the free flowing mixed powders. Spectroscopic studies (FTIR, and mass spectrometry) were also undertaken to elucidate the hydrolysis mechanism of the phosphite antioxidant Alkanox P-24. Mechanistic schemes were devised and interpreted. Hydrolysis products of Alkanox P-24 are believed to be involved in the mechanism of stabilisation. In this programme of work, the role of the hydrolysis products was investigated by controlled thermomechanical degradation in an extruder and stabilisation activity evaluated by following the yellowness index and the melt flow rate. The influence of partially hydrolysed Alkanox P-24 on polymer processing was studied. It was found that some active hydrolysis products showed significant antioxidant activity and retarded polymer degradation during processing. Mechanisms for their formation and identity are elucidated.     

Crystal Structure And Magnetic Property of the Complex of Hydrogen-bonded Two-dimensional Layer Copper(Ⅱ) Acrylate with Trimethyl Phosphate

Coopper carboxylate complexes play an important role in catalysing the enzymatic activi-ties[1— 4] ,and the phosphate has an especial use in DNA recognition[5] .Indeed the reportabout copper carboxylate complexes with phosphate ligands is rare. A chain structuresupramolecule [Cu2 (CH2 CH— COO) 4 (H2 O) 2 ] n has been reported recently[6] ,in which aCu2 (CH2 CH—COO) 4 (H2 O) 2 unitislinked by four O(water)—H…O(carboxyl) hydrogenbonds with two adjacentunits(Fig.1 ) .In this work …