Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction

Polymer additives often show many side reactions during the ageing of polymers which change the useful life-time of the materials. In this regard nano-grade titanium dioxide additives with high surface areas and nano-particle sizes appeared in recent years to be used in polymers where the side reactions have been found to markedly influence mechanisms of ageing. The interaction between titanium dioxide pigments and stabilizers therefore is proposed as a field of great importance.In this paper the influence of nano and micron particle grade anatase and rutile titanium dioxide pigments on the efficiency of a hindered amine stabilizer, Chimassorb 119FL and Chimassorb 119 has been investigated in the system comprising the model radical reaction of cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation. This model reaction was designed to simulate the thermo-oxidative processes in polymers.Kinetic measurements of oxidation rates in the absence of the pigments showed strong retarding activity of the stabilizers under conditions of the model experiments. The rates depend linearly on the reciprocal square root of the concentration of the stabilizers over a sufficiently wide range thereby fitting the mechanism of addition of cumylalkyl R radicals to the Chimassorb molecules. The rate constants for the addition of cumyl R radicals to Chimassorb 119FL and Chimassorb 119 were determined to be k_(333 K) = (1.4 ± 0.2) × 10⁸ and (1.2 ± 0.2) × 10⁸ M⁻¹ s⁻¹, respectively. Hence the Chimassorb 119 family is relatively powerful retarders of thermal oxidation.Further measurements of oxidation rates in the presence of titanium dioxide particles showed that there is a significant reduction in the retarding action of the stabilizers in the presence of titanium dioxides. It occurs as a result of the initiating action of titanium additives producing an additional concentration of free radicals and inducing an additional oxidation rate which may weaken the initial inhibiting efficiency of the added hindered piperidine stabilizers. The titanium nano-samples added at a 1-wt.% into the oxidized condensed system are able to completely decrease the initial inhibiting efficiency of the stabilizers. In terms of the degree of the sensitising action the titanium dioxides can be ordered as: nano-rutile > nano-anatase treated hydroxyapatite > nano-anatase untreated > micro-anatase > micro-rutile.The behaviour of titanium dioxide particles incorporated with hindered piperidine HAS stabilizers in condensed systems may thus be used for the assessment of their performance during the thermo-oxidative degradation of polymers.     

Radical scavenging efficiency of different fullerenes C60-C70 and fullerene soot

This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C₆₀ and C₇₀ in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C₆₀ and C₇₀ and fullerene soot. All fullerenes - C₆₀ of gold grade, C₆₀/C₇₀ (93/7, mix 1), C₆₀/C₇₀ (80 ± 5/20 ± 5, mix 2) and C₇₀ operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C₆₀ and C₇₀ the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k_(333K) = (1.9 ± 0.2) × 10⁸ (C₆₀); (2.3 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 1); (2.7 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 2); (3.0 ± 0.3) × 10⁸ (C₇₀), M⁻¹ s⁻¹. The increasing C₇₀ constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C₆₀−soot] = (2.0 ± 0.1) × 10⁻⁴ mol g⁻¹ and k_inh = (6.5 ± 1.5) × 10³ M⁻¹ s⁻¹ respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.     

Pressurized solvent extraction followed by gas chromatography tandem mass spectrometry for the determination of benzotriazole light stabilizers in indoor dust

A novel and sensitive method for the determination of five benzotriazole compounds (commonly used as light stabilizers) in indoor dust is presented. Pressurized liquid extraction (PLE) and gas chromatography followed by tandem in time mass spectrometry (GC–MS/MS) were used as sample preparation and determination techniques, respectively. Extraction and clean-up were integrated on-line and, after an evaporative concentration step, the extract provided by the PLE instrument was injected directly in the GC–MS/MS system. Parameters affecting the performance of the sample preparation process were evaluated using experimental factorial designs. Under optimized conditions, analytes were recovered from 0.5 g samples in 3 static extraction cycles of 10 min, using a hexane:dichloromethane (7:3) mixture, at 90 °C. Silica (1 g) was placed in the bottom of the extraction cells as clean-up sorbent. The recoveries of the method varied from 82 to 122%, with standard deviations below 13. The inter-day precision ranged from 9 to 12%, and the limits of quantification (LOQs) remained below 10 ng g⁻¹ for all species. For the first time, four of the five investigated species were found in dust from indoor environments. Their mean concentrations ranged from 71 to 780 ng g⁻¹.     

Synergistic effect of maleimido phenyl urea derivatives mixed with some commercial stabilizers on the efficiency of thermal stabilization of PVC

Four novel antimicrobial maleimido phenyl urea stabilizers 1–4 were synthesized from N-[4-(chlorocarbonyl) phenyl] maleimide with phenyl urea and its derivatives (p-methyl, o-chloro and p-carboxy). The effect of mixing maleimido phenyl urea stabilizer 2 with each of the reference stabilizers, dibasic lead carbonate (DBLC), cadmium-barium-zinc stearate (Cd-Ba-Zn stearate) or n-octyltin mercaptide (n-OTM), on the stabilization efficiency in thermal degradation of rigid PVC at 180 °C in air, has been investigated. Mixing was effected in the range of 0–100 wt% of stabilizer 2 relative to each of the reference stabilizers. The stabilizing efficiency was evaluated by measuring the length of the thermal stability period (Ts), the period during which no detectable amount of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination, and by the extent of discoloration of the degraded polymer samples. The results show a true synergistic effect from the combination of stabilizer 2 with any of the reference stabilizers. Mixing of the stabilizers improves the Ts values, decreases the rate of dehydrochlorination and lowers the extent of discoloration of the polymer. The maximum synergism was attained when stabilizer 2 is mixed with either of the three reference stabilizers in equivalent weight ratio (50%/50%). The observed synergism may be attributed to the different mechanisms by which the investigated and the reference stabilizers work.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XI: Anthraquinone derivatives

Anthraquinone and 1-aminoanthraquinone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide. Blending these organic stabilizers with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate.A probable mechanism for the stabilizing mode of these derivatives has been proposed. The stabilizing efficiency is attributed partially to the stabilizers' ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

三吡啶胺Zn(II)配合物作为碳酸酐酶模拟物的研究

The protonation constant of TPA and, in its 1:2 (Zn(II):L) complex, the deprotonation constant of H2O coordinated to Zn(II) have been determined by pH titration at 25±0.1℃, I=0.1 mol•dm-3 KNO3. They are 4.29 and 7.8, respectively. It is worthy to be noted that the H2O bound to Zn(II) could deprotonate easily near physiology pH. A kinetic study of 4-nitrophenyl acetate(NA) hydrolysis by Zn(II)(TPA)2•H2O complex in 10%(v/v) CH3CN at 25±0.1℃, I=0.1 mol•dm-3 NaClO4, and pH range 6~9(20mmol•dm-3 Tris buffer)，has been carried out. The maximum value of second-order rate constant k((mol•dm-3)-1•s-1) obtained is 3.32×10-2. Thus, Our present model study shows that, like the Zn(II)-enzymes, the Zn(II)-bound OH- in complex can act as a good nucleophile agent to the carbonyl carbons, the Zn(II) complex of TPA is a good model for carbonic anhydrase.     

氮化硼催化低碳烷烃氧化脱氢的活性起源探讨（英文）

页岩气的急速开采推动了以天然气替代石油的资源革命.除主组分甲烷外,天然气、页岩气中还包含大量乙烷、丙烷等低碳烷烃资源,将这些储量丰富的碳资源直接转化为烯烃等基础化学品有望革新以原油为基础的化学工业.现有烷烃催化脱氢制烯烃工艺中,直接脱氢过程吸热、热力学受限,且存在催化剂迅速失活的难题;而氧化脱氢是放热过程、无平衡限制,也无积碳等引发催化剂失活的问题,有利于提高反应效率、降低能耗,代表了更为高效和经济的新路线.但作为一个热力学爬坡过程,目前金属氧化物催化剂上烯烃产物很容易深度氧化到CO_2,选择性仍有待提高.非金属氮化硼能够有效活化低碳烷烃中的C-H键,促进烷烃氧化脱氢,并能够有效抑制深度氧化产物的生成,解决低碳烷烃临氧脱氢过程中产物易深度氧化的固有难题.本文综述了近期氮化硼在乙烷、丙烷、丁烷等低碳烷烃氧化脱氢制烯烃反应中的研究进展.以丙烷氧化脱氢为例,通过比较文献报道的几种氮化硼材料的氧化脱氢性能,发现羟基化氮化硼显示了最高的烯烃选择性和时空收率,以20.6%的丙烷转化率为基准,烯烃选择性超过90%,而时空收率可达6.8 golefin gcat~(-1) h~(-1).在此基础上,本文重点讨论了对于氮化硼材料催化活性起源的认识.主要实验事实和结论包括:氮化硼自身几乎没有氧化脱氢活性,而在烷烃氧化脱氢反应条件下存在活性诱导期;活性诱导期伴随着氮化硼边沿氧官能团化过程;氮化硼边沿B-O官能团没有脱氢活性,而B-OH官能团参与了氧化脱氢过程,辅助分子氧引发低碳烷烃脱氢反应;分子氧在羟基氮化硼边沿解离活化,反应过程中与边沿结构氧存在动态交换;氮化硼边沿羟基化定向合成过程可显著增强氧化脱氢反应活性.氮化硼作为一类新型烷烃氧化脱氢催化剂,目前正处于研究的初始阶段.因此,本文最后总结了一些关于氮化硼烷烃脱氢催化体系仍需深入研究的科学问题.     

三吡啶胺Zn(Ⅱ)配合物作为碳酸酐酶模拟物的研究

利用pH电位滴定法，在25±0.1℃，I＝0.1mol·dm-3KNO3条件下，测定了三吡啶胺（TPA）的质子化常数和三吡啶胺Zn（II）配合物中配位水的解离常数.结果表明，该配合物中与Zn（II）配位的H2O分子的电离常数显著下降，测得pKa为7．8．在25±0．1℃，I＝0．1mol·dm－3NaClO4条件下，pH＝6～9（三羟甲基氨基甲烷缓冲溶液，20mmol·dm-3）范围内，用紫外-可见分光光度法考察了该配合物催化对硝基苯酚乙酸酯（NA）水解的动力学行为，得到了配合物催化酯水解的二级反应速率常数kNP，其最大值为3．32×10－2（mol·dm-3）-1·s－1热力学、动力学的研究结果均说明，三吡啶胺Zn（II）配合物中与Zn（II）配位的OH-是较好的亲核试剂，该配合物是一个较好的碳酸酐水解酶的模拟物．     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol)

Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide.Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers.A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

Development of a new equipment for applying the constant rate thermal analysis (CRTA) to temperature programmed oxidation (TPO) of catalysis

A new equipment has been developed in order to apply the constant rate thermal analysis method (CRTA) to Temperature Programmed Oxidation (TPO) processes. The exhausted gases flow through an electrochemical oxygen sensor after leaving the reactor in order to monitor the oxygen consumption in the reaction. The control of the sample temperature is carried out by interfacing both the furnace and the electrical signal of the oxygen sensor to a PID controller that allows to monitor the sample temperature in such a way that the consumption of oxygen is a constant value previously selected by the user.

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Zusammenfassung Es wurde eine neue Apparatur zur Anwendung der Konstantgeschwindigkeits-Thermoanalyse (CRTA) auf temperaturprogrammierte Oxidationsprozesse (TPO) entwickelt. Die abgesaugten Gase strömen nach Verlassen des Reaktors zur Bestimmung der während der Reaktion verbrauchten Sauerstoffmenge durch einen elektrochemischen Sauerstoffsensor. Die Überwachung der Probentemperatur erfolgt, indem sowohl das Ofen-als auch das elektrische Signal des Sauerstoffsensors an einen PID-Regler weitergeleitet wird, der die Probentemperatur wiederum so regelt, daß der Sauerstoffverbrauch auf einem zuvor vom Anwender wählbaren Wert konstant gehalten wird.

     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XII: N-phenyl-3-substituted-5-pyrazolone derivatives

N-phenyl-3-substituted-5-pyrazolone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (T_s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate, calcium-zinc soap and n-octyl tin mercaptide. Blending these derivatives with some of the reference stabilizers in different ratios had a synergistic effect on both the induction period and the dehydrochlorination rate.A probable mechanism for the stabilizing mode of N-phenyl-3-substituted-5-pyrazolone derivatives has been proposed. The stabilizing efficiency is attributed at least partially to the ability of the organic stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation.     

Evaluation of antioxidants using oxidation reaction rate constants

An evaluation method for the capacity of antioxidants to protect drugs against oxidation is presented. As a new viewpoint, to determine the priority of the competitive oxidations between the antioxidant and the protected drug, and to compare the drug-protection capacity of antioxidants, it is important to determine their oxidation rate constants using chemical kinetics instead of standard oxidation (or reduction) potentials. Sodium sulfite, sodium bisulfite and sodium pyrosulfite were used as models for the determination of oxidation reaction rate constants in aqueous solutions. In the experiments, sufficient air was continually infused into the solution to keep the concentration of dissolved oxygen constant. The residual concentrations of the antioxidants were determined by iodimetry, and the concentration of dissolved oxygen by oxygen electrode. The data were fitted by linear regressions to obtain the reaction rate constants. It was found that the degradation of sodium sulfite, sodium bisulfite or sodium pyrosulfite obeyed pseudo zero-order kinetics in the buffer solutions. Because of the ionization equilibrium, these three antioxidants have the same ion form in solutions at a definite pH value and therefore their apparent rate constants were essentially the same. The average apparent rate constants of the three antioxidants at 25°C are (1.34 ± 0.03) × 10⁻³ at pH 6.8, (1.20 ± 0.02) × 10⁻³ at pH 4.0 and (6.58 ± 0.02) × 10⁻³ mol·L⁻¹·h⁻¹ at pH 9.2, respectively. Translated from Acta Chimica Sinica, 2006, 64(6): 496–500 (in Chinese)     

Antioxidant capacity of novel amine derivatives of buckminsterfullerene: Determination of inhibition rate constants in a model oxidation system

The radical scavenging efficiency of fullerenes can be significantly activated by means of a connection with hydrogen donating groups of antioxidants such as phenolic, amine and sulfhydryl. The developed system of conjugated σ–π bonds arranged in the fullerene molecule in a closed shape can promote a strong resonance effect on the grafted units and increase the hydrogen atom abstraction efficiency. In this case the known ability of fullerene to trap alkyl radicals might be combined with the strong chain breaking functionality to afford a new class of antioxidants with bimodal action. Explorations in the field of fullerene derivatives on their antioxidant performance provide novel information on the potential stabilization properties of this type of molecular structure. A series of amine derivatives of buckminsterfullerene (C₆₀) with tethered aliphatic chain, cycloaliphatic and aromatic fragments were synthesized and their antioxidant activity was determined. The antioxidant activity of the investigated derivatives was studied by measuring the inhibition rate constants for their reaction with alkyl and peroxy radicals in a model cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation experiments and compared to that recorded under identical experiments for buckminsterfullerene itself and commercial primary aromatic amine stabilizers. The results indicate that linking the amine moieties groups directly to the fullerene core gives rise to a new chain breaking antioxidant mode for the buckminsterfullerene while cyclic fragments containing the same but distant amine group do not reveal this ability. The inhibition rate constants for trapping of peroxy radicals by the amine derivatives were found to be higher than that of known aromatic amine antioxidants Neozone-D and Naugard 445. In addition the C₆₀ part of these molecules acts synergistically by trapping alkyl radicals with inhibition rate constants which exceed that of underivatised fullerene. The amine derivative containing sterically hindered piperidine and pyrrolidine fragments also heighten the inherent rate constant of buckminsterfullerene for scavenging alkyl radicals due to the additional antioxidant contribution promoted by the radical-quenching ability of the formed nitroxyl intermediates. These novel C₆₀–amine conjugates may be considered as promising molecules for broad-spectrum radical scavenging antioxidants.     

超高效液相色谱/静电场轨道阱高分辨质谱法同时测定塑料食品接触材料中光稳定剂和抗氧化剂的特定迁移量

建立了超高效液相色谱/静电场轨道阱高分辨质谱同时测定塑料食品接触材料中多种光稳定剂和抗氧化剂特定迁移量的方法。采用30 g/L乙酸、体积分数分别为10%、20%、50%的乙醇和油类模拟物(异辛烷)这5种食品模拟物对塑料食品接触材料进行处理,对处理液进行超高效液相色谱/静电场轨道阱高分辨质谱分析,外标法定量。该方法测定的40种目标化合物在相应的范围内均具有良好的线性关系,相关系数均大于0.998,定量限为0.01~1.00μg/L。考察了上述5种食品模拟物中光稳定剂和抗氧化剂的特定迁移量,平均加标回收率为81.46%~94.53%,相对标准偏差为3.25%~9.99%。应用该方法对市售塑料食品接触材料进行了测定,结果在部分样品中检出了不同含量的光稳定剂和抗氧化剂。该方法灵敏度高,定量限低,满足塑料食品接触材料中光稳定剂和抗氧化剂特定迁移量的检测要求。