The Reaction of Sulfenic Acids with Peroxyl Radicals: Insights into the Radical‐Trapping Antioxidant Activity of Plant‐Derived Thiosulfinates

Sulfenic acids play a prominent role in biology as key participants in cellular signaling relating to redox homeostasis, in the formation of protein‐disulfide linkages, and as the central players in the fascinating organosulfur chemistry of the Allium species (e.g., garlic). Despite their relevance, direct measurements of their reaction kinetics have proven difficult owing to their high reactivity. Herein, we describe the results of hydrocarbon autoxidations inhibited by the persistent 9‐triptycenesulfenic acid, which yields a second order rate constant of 3.0×10⁶ M ^?1 s^?1 for its reaction with peroxyl radicals in PhCl at 30 °C. This rate constant drops 19‐fold in CH₃CN, and is subject to a significant primary deuterium kinetic isotope effect, k_H/k_D=6.1, supporting a formal H‐atom transfer (HAT) mechanism. Analogous autoxidations inhibited by the Allium‐derived (S)‐benzyl phenylmethanethiosulfinate and a corresponding deuterium‐labeled derivative unequivocally demonstrate the role of sulfenic acids in the radical‐trapping antioxidant activity of thiosulfinates, through the rate‐determining Cope elimination of phenylmethanesulfenic acid (k_H/k_D≈4.5) and its subsequent formal HAT reaction with peroxyl radicals (k_H/k_D≈3.5). The rate constant that we derived from these experiments for the reaction of phenylmethanesulfenic acid with peroxyl radicals was 2.8×10⁷ M ^?1 s^?1; a value 10‐fold larger than that we measured for the reaction of 9‐triptycenesulfenic acid with peroxyl radicals. We propose that whereas phenylmethanesulfenic acid can adopt the optimal syn geometry for a 5‐centre proton‐coupled electron‐transfer reaction with a peroxyl radical, the 9‐triptycenesulfenic is too sterically hindered, and undergoes the reaction instead through the less‐energetically favorable anti geometry, which is reminiscent of a conventional HAT.     

Chemical reaction fouling: A review

Recent research on fouling of organic fluids is renewed. Fouling in organic mixtures can be caused by numerous reactions, including autoxidation, polymerization and thermal decomposition. Understanding of autoxidation processes and their link to fouling has developed markedly in the past few years. By contrast, for fouling under non-oxidative conditions, the chemical and physical processes have not been adequately explored.     

高超音速推进用吸热型烃类燃烧的热稳定性研究 Ⅱ．添加剂的合成与评价

结合燃料的自氧化机理，指出了抗氧剂，金属减活剂以及清净分散剂三种单元添加剂在燃烧自氧化过程中的抗沉积原理，自行合成了一种新型清净分散剂－聚异丁烯硫磷酸的季戊四醇酯PETPA，对酯化产物用FT－IR和NMR进行了结构分析，给出了合成过程中硫磷化，水解，及本经化阶段的反应历程，考察了三种单元添加剂抗氧剂A，清净分散剂D和金属减活剂M，以及由单元添加剂组成的添加剂包的抗沉积效果，结果表明，抗沉积效果AMD＞MD＞AD＞AM＞D＞M＞A，其中清净分散剂为主要添加剂，三种单元添加剂组成的添加剂包的抗沉积效果最为明显，在RT－3，MCH及THDCPD燃料体系中，沉积量分别减少了87．10％，90．91％和89．12％，PETPA无论是单独还是复合使用其效果均优于聚异丁烯丁二酰亚胺T154。     

Biomimetic Synthesis of Complex Flavonoids Isolated from Daemonorops “Dragon's Blood”

The dragonbloodins are a pair of complex flavonoid trimers that have been isolated from the palm tree Daemonorops draco, one of the sources of the ancient resin known as “dragon's blood”. We present a short synthesis that clarifies their relative configurations and sheds light on their origin in Nature. This synthesis features biomimetic cascade reactions that involve both ionic and radical intermediates. The biogenetic relationships between dracorhodin, the dracoflavans C, and the dragonbloodins A1 and A2 are discussed.     

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol⁻¹ above the hydroperoxide substrate and around 15 kJ mol⁻¹ below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O−O bond homolysis is coupled with a C−H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule-induced radical formation (MIRF) process is significantly lower than that of the unimolecular O−O bond cleavage. The same type of reaction is also possible in the self-reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co-products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen-bonding interactions.     

低温常压氧气液相氧化邻硝基甲苯的表观动力学研究

文章讨论了低温常压条件下氧气液相氧化邻硝基甲苯的表观动力学。在确定了邻硝基苯甲醛和邻硝基苯甲酸为主要产物的基础上，建立了连串反应模型，根据不同温度下的实验数据，确立了首步一级，第二步二分之一级的反应级数，进而求得了两步反应的速率参数k1、k2，并将实验数据与理论计算值相比较，表明在较低温度(0℃以下)下，拟合的级数与使用符合较好。     

超氧化物歧化酶模型化合物--N,N-二(2-苯并咪唑亚甲基)苄胺Cu(Ⅱ)配合物的晶体结构及量子化学计算

以N,N-二(2-苯并咪唑亚甲基)苄胺(BN 3)为配体合成了Cu2(BN 3)2.(C6H5COO)2.(C lO4)2.2C2H6O的拟CuZn-SOD模型配合物,采用X射线衍射方法对在乙醇溶液中得到的蓝色透明单晶的晶体结构进行了测定,晶体学参数为:Mr=1 372.20,三斜晶系,a=1.474(8)nm,b=1.526(8)nm,c=1.595(9)nm,α=76.118(13)o,β=77.917(13)o,γ=71.090(11)o,V=3.262(10)nm3,Dc=1.397M g/cm3,Z=2,F(000)=1 418,空间群为p,ī并对其进行了紫外、红外表征及元素分析.利用G 98量子化学程序包,在HF/LanL 2DZ基组水平上对配合物进行了从头计算.利用经典的邻苯三酚自氧化法对配合物的生物活性进行了测定.     

甾酮类化合物的碱催化自氧化反应的研究

酮类化合物的碱催化自氧化反应受底物的结构和反应条件的影响较大。不同的底物或不同的反应条件,可得不同类型的产物。在油菜甾醇内酯 B 环的合成中,曾探索了用该反应来合成内酯环。本文报道一些与三元环共     

Syntheses and rearrangements of tris(hydroxymethyl)phosphine and tetrakis(hydroxymethyl)phosphonium salts

Abstract

Tetrakis(hydroxymethyl)phosphonium (HOCH₂)₄P⁺ salts, particularly the chloride (THPC) and sulfate (THPS), are among the most accessible organophosphorus compounds that can be made quantitatively from PH₃ and formaldehyde in aqueous media under ambient conditions. These phosphonium salts are air-stable, and are widely used as reactants in organic syntheses, as well as in textile or oil industries. Synthesis of tris(hydroxymethyl)phosphine (THP), an active component of the salts, is more complicated because direct synthesis from PH₃ and CH₂O requires either pressure and high temperature, at which THP rearranges into bis(hydroxymethyl)methylphosphine oxide, CH₃P(O)(CH₂OH)₂, or a metal catalyst that is usually difficult or impossible to recover. Syntheses of THP based on neutralization of the salts are more convenient but require pH control and additional steps to separate THP from CH₂O. This review summarizes literature data on syntheses and purification of the salts and THP, and side reactions such as thermal rearrangement and oxidation.