Catalytic Dimerization of Alkyl Acrylates

The review deals with the chemistry of dimerization of acrylic esters in the presence of various catalysts. The article covers literature from 1963 through early 1995. The dimerization reactions are divided into three categories depending on the type of catalyst used, namely, phosphine-catalyzed, metal-catalyzed, and miscellaneous catalysts. Phosphine catalyzed dimerization leads to branched or head—tail dimers. Metal catalyzed dimerization deals with the reactions that take place in the coordination sphere of the transition metals (Ni, Pd, Ru, and Rh) complexes and are aimed at linear or tail—tail dimers. The tail—tail dimers, dialkyl hexenedioates, have a commercial potential as precursors of adipic acid, which is a raw material in the manufacture of nylon-6,6. Various strategies involved in designing the transition metal catalysts for tail—tail dimerization are highlighted. A miscellaneous catalyst section deals with systems that are not covered under the above two categories. It describes catalyst systems comprised of organic and/or inorganic compounds leading to head—tail or tail—tail dimers. The hydrodimerization reactions, which directly give dialkyl adipate from acrylic ester, are discussed separately. The mechanisms of the important dimerization reactions are outlined at appropriate places.     

乙烯二聚反应条件探讨

简述了乙烯二聚反应的机理,指出影响反应的因素除ＩＦＰ提及的催化剂、温度、压力外,还有停留时间、返混、溶解等、并分析了中原石化Ｕｎｉｐｏｌ聚乙烯装置１９９９年初静电产生的原因。     

异戊二烯的二聚及衍生物

本文介绍了异戊二烯在精细化学品生产中的应用,主要是异戊二烯环状和链状二聚的反应,以及由异戊二烯衍生的精细化工产品的途径,提出了适合C5分离装置的异戊二烯下游产品的发展方向。     

末端炔烃二聚反应的研究进展

末端炔烃二聚反应是一类构建碳碳键的重要反应,其相应的产物-共轭二炔广泛存在于天然产物、药物、有机合成、材料化学等领域。介绍了近年来末端炔烃二聚生成对称和不对称共轭二炔以及相关机理的研究进展,指出在发展新颖的催化体系的同时,也要不断加深末端炔烃二聚反应的绿色化研究。     

乙烯二聚合成丁烯-1的研究

<正> 随着石油化工的迅速发展,丁烯-1作为一个重要的有机合成单体,其地位正在与日俱增。它不仅可以合成许多基本有机合成原料,而且使丁烯-1聚合或和其它单体共聚合,可以制备具有各种优良性能的塑料。丁烯-1的主要用途详见图1。制备丁烯-1的方法有丁醇脱水、丁烷脱氢、醋酸丁酯和氯丁烷的高温分解、从裂解气C_4馏分中分离以及乙烯的热二聚或催化二聚等。目前工业上采用的主要是从C_4馏分中分离和乙烯的催化二聚这两种方法。毫无疑问,从C_4馏分中分离以制备丁烯-1是我们首先     

Dimerization of protegrin-1 in different environments

The dimerization of the cationic β-hairpin antimicrobial peptide protegrin-1 (PG1) is investigated in three different environments: water, the surface of a lipid bilayer membrane, and the core of the membrane. PG1 is known to kill bacteria by forming oligomeric membrane pores, which permeabilize the cells. PG1 dimers are found in two distinct, parallel and antiparallel, conformations, known as important intermediate structural units of the active pore oligomers. What is not clear is the sequence of events from PG1 monomers in solution to pores inside membranes. The step we focus on in this work is the dimerization of PG1. In particular, we are interested in determining where PG1 dimerization is most favorable. We use extensive molecular dynamics simulations to determine the potential of mean force as a function of distance between two PG1 monomers in the aqueous subphase, the surface of model lipid bilayers and the interior of these bilayers. We investigate the two known distinct modes of dimerization that result in either a parallel or an antiparallel β-sheet orientation. The model bilayer membranes are composed of anionic palmitoyl-oleoyl-phosphatidylglycerol (POPG) and palmitoyl-oleoyl-phosphatidylethanolamine (POPE) in a 1:3 ratio (POPG:POPE). We find the parallel PG1 dimer association to be more favorable than the antiparallel one in water and inside the membrane. However, we observe that the antiparallel PG1 β-sheet dimer conformation is somewhat more stable than the parallel dimer association at the surface of the membrane. We explore the role of hydrogen bonds and ionic bridges in peptide dimerization in the three environments. Detailed knowledge of how networks of ionic bridges and hydrogen bonds contribute to peptide stability is essential for the purpose of understanding the mechanism of action for membrane-active peptides as well as for designing peptides which can modulate membrane properties. The findings are suggestive of the dominant pathways leading from individual PG1 molecules in solution to functional pores in bacterial membranes.     

Intensification of Cyclopentadiene Dimerization by Ultrasound Irradiation

Cyclopentadiene and isoprene are produced in large quantities by the steam cracking of naphtha and gas oils to produce ethylene. At room temperature, cyclopentadiene slowly dimerizes in a Diels‐Alder reaction to give dicyclopentadiene. This work presents a new method for accelerating the Diels‐Alder reaction in the presence of ultrasonic irradiation under ambient conditions. The effects of various reaction conditions such as ultrasonic reaction time and reaction temperature on cyclopentadiene dimerization and oligomerization of cyclopentadiene and isoprene were investigated. The results showed that the two reactions could be significantly enhanced by ultrasonic irradiation. The kinetic results revealed that the introduction of ultrasonic irradiation lowered the activation energy of both reactions, but not to the same degree. The increased difference in activation energy between the two reactions is the driving force to produce more dicyclopentadiene in the presence of ultrasonic irradiation.     

Dimerization of 9-isopropenyl phenanthrene by TiCl4

Summary 9-isopropenyl phenanthrene was dimerized by reaction with TiCl₄, in CH₂Cl₂ and the structure of the dimer studied by ¹H NMR spectroscopy. The structure results from the attack of carbocation on carbon 9.     

Dimerization of 1-isopropenyl anthracene by TiCl4

Summary 1-isopropenyl anthracene was dimerized by reaction with TiCl₄ in CH₂Cl₂ and the structure of the dimer studied by ¹H NMR spectroscopy. The spectrum was assigned and is in agreement with simulation. The structure results from the attack of carbocation on carbon 9.     

Solid State Dimerization of a Styryl Disperse Dye

During an investigation into structure-property relationships of a series of ethyl-α-cyano-4-aminocinnamate disperse dyes, the 4-(N-β-cyanoethyl-N-β-acetoxyethyl) amino derivative showed anomalous behaviour on attempts to purify it. This compound was shown to be susceptible to dimerization to a colourless cyclobutane derivative, the structure of which was established by nmr spectroscopy. The dimerization is interpreted in terms of ‘Topochemical’ factors. Typical nmr spectra characteristics of some monomeric styryl disperse dyes are also indicated.     

Photosensitized Dimerization of Thymine and Cytosine in DNA

Thymine and cytosine homo- and heterodimers ate produced when E. coli DNA is irradiated at wavelength > 300 mμ in the presence of acetone as photosensitizer. Employing acetophenone as sensitizer only thymine containing dimers are obtained. In heat denatured DNA photosensitized dimerization of thymine occurs in a higher proportion of the TT dinucleotide sequences than in native DNA and the trans-syn thymine dimer isomer is formed as a minor photoproduct.     

Dimerization of Hexadecene with Acid Mesoporous Silica-Alumina Catalysts

Catalytic dimerization of 1-hexadecene is shown to be a promising path to make high quality base oil. The base oil is produced by hexadecene dimerization with acid mesoporous silica-alumina catalyst, followed by distillation and hydrogenation. The base oil stock had a high viscosity index (typically 140–150) and a low volatility (Noack typically less than 8 %). The best performance in hexadecene dimerization was achieved with the MCM-22 zeolite embedded MCM-41 catalyst within the silica-alumina catalysts compared. Commercial mesoporous silica-alumina catalysts behaved similarly to a non-commercial MCM-41 catalyst. Y-zeolite and ion exchange resin Amberlyst-35 deactivated fast.     

Dimerization determines substrate specificity of a bacterial prenyltransferase

We have identified the native dimer interface of heptaprenylglyceryl phosphate synthase PcrB from the bacterium Bacillus subtilis and analyzed the significance of oligomer formation for stability and catalytic activity. Computational methods predicted two different surface regions of the PcrB protomer that could be responsible for dimer formation. These bona fide interfaces were assessed both in silico and experimentally by the introduction of amino acid substitutions that led to monomerization, and by incorporation of an unnatural amino acid to allow cross-linking of the two protomers. The results showed that, in contrast to previous assumptions, PcrB uses the same interface for dimerization as the homologous geranylgeranylglyceryl phosphate synthase from Archaea. Thermal unfolding demonstrated that the monomeric proteins are only slightly less stable than wild-type PcrB. However, activity assays showed that monomerization limits the length of accepted polyprenyl pyrophosphates to three isoprene units, whereas the native PcrB substrate contains seven isoprene entities. We provide a plausible hypothesis as to how dimerization determines substrate specificity of PcrB.     

叔丁醇对异丁烯二聚反应选择性的影响

以强酸性阳离子交换树脂为催化剂,在高压釜内考察了加入叔丁醇(TBA)前后异丁烯(IB)二聚反应工艺条件对二异丁烯(DIB)选择性的影响.结果表明.在加入TBA后.降低了IB二聚速率.但提高了DIB选择性.当反应温度为90℃、原料中IB质量分数为17%～20%、TBA质量分数为0.6%、搅拌速率750r/min、反应3.5h后,IB的转化率约为60%,DIB的选择性可达80%左右。     

A CNDO/2 Study of Dimerization of Methylene

The CNDO/2 Molecular Orbital method has been used to investigate the energetically favoured path in the dimerization of methylene in the singlet state.     

Influence of Polar Components in the Dimerization of Isobutene

Isooctane is seen as a potential replacement for methyl tert-butyl ether (MTBE) in gasoline. Isooctane can be produced via the indirect alkylation route in two steps. Isobutene is first dimerized to isooctenes, which are then further hydrogenated to isooctane. In the dimerization a polar component is used to enhance the selectivity for diisobutenes. In this study the effects of tert-butyl alcohol (TBA), methanol and MTBE in the dimerization reaction were compared on the basis of experimental results. All the oxygenates studied induced similar effects: higher selectivity for diisobutenes and lower isobutene conversion as the oxygenate content increased and temperature decreased. The different polarity of the components causes the need for more methanol or MTBE than TBA to get the same conversion and selectivity.     

Role of Polyamine-Induced Dimerization of Antizyme in Its Cellular Functions

The polyamines, spermine (Spm) and spermidine (Spd), are important for cell growth and function. Their homeostasis is strictly controlled, and a key downregulator of the polyamine pool is the polyamine-inducible protein, antizyme 1 (OAZ1). OAZ1 inhibits polyamine uptake and targets ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis, for proteasomal degradation. Here we report, for the first time, that polyamines induce dimerization of mouse recombinant full-length OAZ1, forming an (OAZ1)₂-Polyamine complex. Dimerization could be modulated by functionally active C-methylated spermidine mimetics (MeSpds) by changing the position of the methyl group along the Spd backbone—2-MeSpd was a poor inducer as opposed to 1-MeSpd, 3-MeSpd, and Spd, which were good inducers. Importantly, the ability of compounds to inhibit polyamine uptake correlated with the efficiency of the (OAZ1)₂-Polyamine complex formation. Thus, the (OAZ1)₂-Polyamine complex may be needed to inhibit polyamine uptake. The efficiency of polyamine-induced ribosomal +1 frameshifting of OAZ1 mRNA could also be differentially modulated by MeSpds—2-MeSpd was a poor inducer of OAZ1 biosynthesis and hence a poor downregulator of ODC activity unlike the other MeSpds. These findings offer new insight into the OAZ1-mediated regulation of polyamine homeostasis and provide the chemical tools to study it.     

离子液体中裂解C5馏分二烯烃聚合反应动力学

用离子液体1-丁基-3-甲基咪唑六氟磷酸盐作为裂解C5馏分中混合二烯烃的反应介质和催化剂,考察了其对混合二烯烃二聚反应的影响。在温度303.15—343.15 K、离子液体质量分数0.3—0.8范围内,采用封管实验方法测定了C5混合二烯烃的动力学数据。在相同温度范围内,测定了离子液体介质中环戊二烯无限稀释状态下的动力学数据。将催化剂影响因数引入Arrhen ius方程,确定了离子液体介质中二烯烃聚合反应动力学模型。用墨森数值积分和非线性最小二乘法拟合求取了各反应速率常数,得到了模型参数和各聚合反应对于催化剂质量分数的反应级数,动力学模型预测值与实验值吻合良好。     

Dimerization of isobutene over nickel modified zeolites to obtain isooctene

Ni/H Zeolites catalysts were prepared by impregnation, starting from HY-Zeolite, Hβ-Zeolite and H-mordenite with nickel precursor salts, NiCl₂, NiSO₄ and NiCO₃. The total number, NTSA, and the acid strength were found dependent on the nickel precursor salt. High catalytic activity, selectivity and stability of the modified zeolites in isobutene dimerization was attributed to the acidic properties of nickel modified zeolites. HY-Zeolite modified with NiCO₃ resulted more active and selective to dimerization reaction. The prepared catalysts were characterized by EDSX, SEM, and Adsorption/Desorption of N₂ at 77 K, NH₃ chemisorption and Ammonia Temperature-Programmed-Desorption (NH₃-TPD) and FT-IR of adsorbed pyridine. NH₃-TPD and isobutene adsorption revealed an acid sites a new distribution and apparition of acid sites not present in the protonated zeolites. Catalytic activity and reactor behavior were studied in a continuous downstream fixed bed reactor at 298 K, 27.6 kPa (4 psig), and WHSV = 0.27 h⁻¹.