Alkenes short-chain

The aromatic hydrocarbons are used mainly as solvents and as feedstock chemicals for chemical processes that produce other valuable chemicals. With regard to cyclical hydrocarbons, the aromatic hydrocarbons are the only compounds discussed. These compounds all have the six-carbon benzene ring as a base, but there are also three-, four-, five-, and seven-carbon rings. These materials will be considered as we examine their occurrence as hazardous materials. After the alkanes, the aromatics are the next most common chemicals shipped and used in commerce. The short-chain olefins (alkenes) such as ethylene and propylene may be shipped in larger quantities because of their use as monomers, but for sheer numbers of different compounds, the aromatics will surpass even the alkanes in number, although not in volume. 

As early as 1990, Chauvin and his co-workers from IFP published their first results on the biphasic, Ni-catalyzed dimerization of propene in ionic liquids of the [BMIM]Cl/AlCl3/AlEtCl2 type [4]. In the following years the nickel-catalyzed oligomerization of short-chain alkenes in chloroaluminate melts became one of the most intensively investigated applications of transition metal catalysts in ionic liquids to date. 

Hou CT, R Patel, AI Laskin, N Barnabe, I Barist (1983) Epoxidation of short-chain alkenes by resting-cell suspensions of propane-grown bacteria. Appl Environ Microbiol 46 171-177. 

Coenzyme M was shown to function as the central cofactor of aliphatic epoxide carboxylation in Xanthobacter strain Py2, an aerobe from the Bacteria domain (AUen et al. 1999). The organism metabolizes short-chain aliphatic alkenes via oxidation to epoxyalkanes, followed by carboxylation to p-ketoacids. An enzyme in the pathway catalyzes the addition of coenzyme M to epoxypropane to form 2-(2-hydroxypropylthio)ethanesulfonate. This intermediate is oxidized to 2-(2-ketopropylthio)ethanesulfonate, followed by a NADPH-dependent cleavage and carboxylation of the P-ketothioether to form acetoacetate and coenzyme M. This is the only known function for coenzyme M outside the methanoarchaea. 

Intermolecular hydride transfer to polymer probably accounts for the short-chain branching found in the polymerizations of 1-alkenes such as propene. The propagating carbocations are reactive secondary carbocations that can abstract tertiary hydrogens from the polymer... 

In practice, short-chain alkanes and alkenes are normally used as feedstock for shape-selective catalytic formation of isooctanes at relatively low temperatures. Until the 1980s, lead alkyls (Section 18.1) were added to most automotive fuels to help suppress engine knock, but they have been phased out in North America because of the chronic toxicity of lead and lead compounds. The most commonly used nonlead antiknock additive is now methyl tert-butyl ether [MTBE CH30C(CH3)3], which is made by the reaction of methanol with 2-methylpropene, (CHs C—CH2 (see Section 7.4). The latter is obtained by catalytic cracking of petroleum fractions to give 1-butene, which is then shape-selectively isomerized on zeolitic catalysts. 

The distribution of volatile products of low molar mass from the irradiation of poly (olefin) s is strongly dependent on the nature of substituents (short-chain branches) on the backbone chain. Hydrogen is the main volatile product with smaller quantities of alkanes and alkenes. 

We have studied the alkane and alkene yields from the radiolysis of copolymers of ethylene with small amounts of propylene, butene and hexene. These are examples of linear low density polyethenes (LLDPE) and models for LDPE. Alkanes from Ct to C6 are readily observed after irradiation of all the polymers in vacuum. The distribution of alkanes shows a maximum corresponding to elimination of the short-chain branch. This is illustrated in Figure 8 for the irradiation of poly (ethylene-co-1-butene) containing 0.5 branches per 1,000 carbon atoms at 20 C. 

Alkenes are only produced in significant amounts above ca. 80 C. Ethylene is produced with the highest yield, which may be comparable to that for alkanes from short-chain branches after irradiation above 150 C (15). Typical results for the increasing yields of alkanes and alkenes with irradiation temperature are shown in Figure 10. Closer examination of the butane and butene produced has shown that they include considerable proportions of isobutane and isobutene. Typical G values for the formation of the butenes at... 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

The short chain length is due to the high water concentration the intermediate carbocation loses a proton to water before it can react with another alkene molecule. 

Excellent enantioselectivity is observed in the CP0/H202-catalyzed epoxidation of short-chain (Z)-alkenes with a chain length of nine of fewer carbon atoms, except for monosubstituted alkenes, which often function as reversible suicide inhibitors of the enzyme [266-271]. (E)-Alkenes are highly unreactive substrates and are converted to epoxides in yields below 5%. A number of functionalized (Z)-2-alkenes have been successfully epoxidized by CPO using tert-butyl hydroperoxide as the terminal oxidant [272]. This procedure appears to be more effective, especially in large-scale reactions, due to the fairly high sensitivity of CPO to hydrogen peroxide. 

The catalyst + aliphatic n-alkene system, for all of the olefins from propene to 1-decene, give almost 40,000 possible conformations. The most stable conformations for each of the olefins were selected (around 1,700) and their transition states were optimized at IMOMM level. The calculated enantiomeric excesses are shown in Fig. 13. Calculations are able to reproduce the observed increase in ee for short chains, and the presence of a ceiling value after which the increase in enantioselectivity is much smaller, in excellent agreement with experiment. 

The polymerisation of ethylene in the presence of an Ni(II) complex containing a ligand originating from aminobis(imino)phosphorane leads to short-chain branched polyethylene [182]. This is due to the copolymerisation of ethylene with short-chain 1-alkenes formed in such a system. 

Copolymerizations of BD with 1-alkenes such as 1-octene and 1-dodecene aim at short chain branching of BR. Kaulbach et al. used the ternary catalyst system NdO/TIBA/EASC (htiba/ Nd = 25, nci/nNd = 3) for the respective copolymerizations of BD/l-octene and BD/l-dodecene [508]. These authors showed that only small amounts of 1-alkenes are incorporated and that no neighboring 1-alkene moieties are present in the copolymer. The copolymerization parameters have been determined by the method of Kelen-Tiidos rBD = 25 and ri-octene 0 rBD = 18 and r dodecene = 0.1. With increasing amounts of 1-alkene in the monomer feed catalyst activity decreases drastically. The cis- 1,4-contents of the BD units in the copolymer were around 90% and were barely affected by increases of the 1-alkene content in the monomer feed. 

Incomplete combustion of gasoline and other motorfuels releases significant quantities of volatile organic compounds (VOCs) into the atmosphere. VOCs are composed of short-chained alkanes, alkenes, aromatic compounds, and a variety of other hydrocarbons. VOCs are components of air pollution and contribute to cardiac and respiratory diseases. 

For reasons of symmetry the resulting acids are identical when a symmetrically substituted alkcne is oxidized. For the preparation of short-chain fluorinated acids, such as trifluoroacetic acid. this method is more economical than the oxidation of an alkene with a terminal C = C bond (see Table 1). Oxidation of polyfluorinated dienes and polyenes gives fluorinated dicar-boxylic acids. 

Perfluorinated alkanes, alkenes or cycloalkanes show a high thermal stability, heating to temperatures over 1000 C results in radical cleavage to give short chains or alkenes.However, C C bonds which contain quaternary and tertiary carbons are cleaved at lower temperatures than those between secondary carbons. In the presence of bromine, chlorine or toluene, cleav age products are isolated, e.g.Rp—Rp - 2 RpBr Other examples involve pyrolyses. ... 

One of the first mechanistic proposals for the hydrocarboxylation of alkenes catalyzed by nickel-carbonyl complexes came from Heck in 1963 and is shown in Scheme 24. An alternate possibility suggested by Heck was that HX could add to the alkene, producing an alkyl halide that would then undergo an oxidative addition to the metal center, analogous to the acetic acid mechanism (Scheme 19). Studies of Rh- and Ir-catalyzed hydrocarboxylation reactions have demonstrated that for these metals, the HX addition mechanism, shown in Scheme 24, dominates with ethylene or other short-chain alkene substrates. Once again, HI is the best promoter for this catalytic reaction as long as there are not any other ligands present that are susceptible to acid attack (e g. phosphines). 

Branching can resnlt from the chain-growth process or from branching gronps in the monomers. For example, ethylene can be polymerized by a radical process to a highly branched low-density polyethylene (LDPE) or copolymerized with small amounts of a-alkenes like 1-hexene or 1-octene nsing a metal-mediated catalyst the resnlt is a linear polyethylene punctuated by short-chain branches and known as linear-low-density polyethylene (LLDPE). 

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