Kinetics terminal double bond

Stein166 has indicated that the reactivity of the terminal double bond of the macromonomer (112) is 80% that of VAc monomer. The kinetics of incorporation of 112 have also been considered by Wolf and Burchard175 who concluded that 112 played an important role in determining the time of gelation in VAc homopolymerization in bulk. 

The detailed composition, referring to classes of compounds, is shown for C6 in Figure 9.3 with and without precolumn hydrogenation. In addition to paraffins, there are olefins—mainly with terminal double bond—and small amounts of alcohols (and aldehydes). The low detection limit of gas chromatography (GC) analysis allows precise determination even of minor compounds and provides exhaustive composition data also for use in kinetic modeling. Because of the short sampling duration of ca. 0.1 s,8 time-resolved selectivity data are obtained. 

The three papers just referred to share a further assumption, namely that a steady state is set up in the continuous reactor, so that all time derivatives in the kinetic equations may be equated to zero. Graessley (91) considered the unsteady state during the start-up of a continuous stirred reactor and found that Mw may in certain cases increase without bound instead of reaching a steady state this will occur if a branching parameter exceeds a critical value. His reaction scheme is restricted to mono-radicals, and the effect of loss of radicals from the reactor is not taken into account. If a steady state is set up, the MWD obtained is Beasley s, when termination by combination and branching by copolymerization of terminal double bonds are absent. Since there is reason (92) to doubt the validity of Beasley s conclusions, as discussed above, the same doubt must apply to this work of Graessley s. 

Since the formation of the terminal double bonds is kinetically favored, short reactions times favor high amounts of vinylidene moieties. 

The nickel-catalyzed hydrocyanation of butadiene is a two-step process (Figure 3.32). In the first step, HCN is added to butadiene in the presence of a nickel-tetrakis(phosphite) complex. This gives the desired linear product, 3-pente-nenitrile (3PN), and an unwanted branched by-product, 2-methyl-3-butenenitrile (2M3BN). The products are separated by distillation, and the 2M3BN is then isomerized to 3PN. In the second step, 3PN is isomerized to 4PN (using the same nickel catalyst), followed by anti-Markovnikov HCN addition to the terminal double bond. The second step is further complicated by the fact that there is another isomerization product, CH3CH2CH=CHCN or 2PN, which is thermodynamically more stable than 4PN. In fact, the equilibrium ratio of 3PN/2PN/4PN is only 20 78 1.6. Fortunately, the reaction kinetics favor the formation of 4PN [95],... 

Instability of the polymer is responsible for the primary step in decomposition and is attributed either to fragments of initiator or to branched chains or to terminal double bonds. The appearance of branching is the result of reactions of chain transfer through the polymer, while that of unsaturated terminal groups results from reaction of disproportionation and chain transfer through the monomer. During thermal and thermo-oxidative dehydrochlorination of PVC, allyl activation of the chlorine atoms next to the double bonds occurs. In this volume, Klemchuk describes the kinetics of PVC degradation based on experiments with allylic chloride as a model substance. He observed that thermal stabilizers replace the allylic chlorine at a faster ratio than the decomposition rate of the allylic chloride. 

In order to predict the stereochemical outcome of a cyclization, some rules have been proposed based on a model for the attack of an electrophile, under kinetic control, to an alkene containing an internal nucleophile. The selectivity is determined by the relative affinity of the diastereotopic face of the double bond towards a proton syn to H in an OH-in-plane-conformer, or syn to OH in a H-in-plane-conformer, and the cyclization involves a probable intramolecular attack on a 7i-compIex. In fact, when a hydroxy or an alkoxy group is present, the electrophile preferentially attacks the OH-in-plane-conformer from the face of the double bond syn to the allylic hydrogen 22. Thus, starting from terminal double bonds, the ci.v-diastereomer is prevalent in the reaction mixture. 

The ring-closure mechanism of 2-chloroethanol has been studied on the basis of kinetic and equilibrium chlorine isotope effects. Epoxidation of the terminal double bond of farnesyl acetate has been achieved via the bromohydrin, obtained with NBS. A stereospecific method has been elaborated for the preparation of 1-alkynyloxiranes, starting from the monotosylate ester of acetylenic diols. 1-Alkynyloxiranes are also formed from a-hydroxy quaternary ammonium salts in alkaline medium (Eq. 57). ... 

Albers et al. [77] analyzed the pressure effect on the hydroformylation of 1- and 4-octene with [Rh(COD)(PPh3)2]BF,j (COD = 1,5-cyclooctadiene) at 70 °C (Table 5.2). As expected, with the terminal olefin as a substrate at low pressure, n- and iso-aldehyde 1 and 2 were formed in the ratio 1.6 1. Because of some isomerization, also the other branched aldehydes 3 and 4 were detected in decreasing amounts. Extremely high syngas pressure of 500 MPa completely suppressed double bond migration, and -nonanal and 2-methyl-octanal were formed in almost equal quantities. This result illustrates nicely the poor ability of the catalyst to discriminate between the 1- and 2-position of the terminal double bond. With 4-octene as a substrate, at low pressure, isomerization also played a significant role. The highest yield of 4-formyl-octane (4), which derives from the C-C bond formation in C4/C5 position of 4-octene, was observed at 500 MPa. Noteworthy, also aldehydes 2 and 3 were obtained. These products require the prior isomerization of 4-octene into the less thermodynamically stable olefins, which accounts for a kinetic control. This result is in contrast to the reaction with 1-octene under the same conditions. 

As a first approach, we studied the epoxidation of the exocychc double bond of 1 by weto-chloroperbenzoic acid (mCPBA) in dichloromethane. IR spectra provided evidence for a fluorescent epoxide [94]. Eater on, surface-catalyzed epoxidation was ascribed to the formation of further fluorescent BODIPY derivatives [54]. The bimolecular rate constant had been determined beforehand, and pointed to the concentration range of mCPBA for maintaining useful pseudo-first-order kinetics. Immobilization turned out to be a major issue because, while the oxidizing species should have free access to the double bond, the translational mobility of the substrate must be widely suppressed. Introduction of a further terminal double bond permitted subsequent immobilization on polymeric sihcone [102-104]. 

The PDF of Eq. (178) expresses the probability of an insertion of a chain with Ni branch points under the condition that a polymer with N branch points and a terminal double bond is formed. This formula is symmetrical by definition. It turns out that this PDF (apart from round-off errors) is identical to the PDF defined in Eq. (177). This is due to the kinetics of the system, which allows the concentration of polymers with a terminal double bond to be written as a fraction of the concentration of polymers without terminal double bonds [35], as formulated in ... 

Kinetic studies of alkene-phosphorus pentachloride reactions in benzene show the effects of substituents when the double bond is terminal.88 When the alkene is conjugated, the standard work-up conditions (using sulphur dioxide) produce alk-1-enylphosphonyl dichlorides (103), instead of 2-chloroalkylphosphonyl dichlorides (104).87... 

Spontaneous polymerization of 4-vinyl pyridine in the presence of polyacids was one of the earliest cases of template polymerization studied. Vinyl pyridine polymerizes without an additional initiator in the presence of both low molecular weight acids and polyacids such as poly(acrylic acid), poly(methacrylic acid), polyCvinyl phosphonic acid), or poly(styrene sulfonic acid). The polyacids, in comparison with low molecular weight acids, support much higher initial rates of polymerization and lead to different kinetic equations. The authors suggested that the reaction was initiated by zwitterions. The chain reaction mechanism includes anion addition to activated double bonds of quaternary salt molecules of 4-vinylpyridine, then propagation in the activated center, and termination of the growing center by protonization. The proposed structure of the product, obtained in the case of poly(acrylic acid), used as a template is ... 

Fig. 6. The characteristic behavior of the propagation kinetic constant, kp, and the termination kinetic constant, k as a function of double bond conversion for a multifunctional monomer polymerization...

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