OLEFINS, HIGHER

A number of more complex olefins have been studied, and the results of this miscellaneous group are given in Table 7. Many of the rate coefficients are, of course, obtained from competition reactions rather 

Hydrogen atom addition to various higher alkenes 

None of this is unexpected. Where we do see some slight fall-off in reactivity is in some of the highly substituted compounds such as 

3-dimethyl-2-butene (tetramethylethylene). The expected increase in reactivity with increased substitution in this compound does not occur the reactivity observed is not very different from that of 2-butene. While no new hyper-conjugative resonance stabilization of the initial intermediate radicEil is possible as compared with a terminal olefin, one does acquire a statistical factor of two in the equivalence of reaction sites. Polarization of the double bond in the transition state is reduced, however, by this symmetry, and steric problems, too, may play a role in the approach of the H atom and achievement of tetrahedral character at the carbon atom attacked. However, none of these considerations can be evaluated with the current data. 

Cycloalkenes probably present no special problems in the prediction of their behaviour in reactions with H atoms. No recent data have been reported, but early work by Melville and co-workers [15, 38] gives values of the rate for cyclohexene which are suspiciously high when compared with simpler olefins (log k = 8.76, 8.90 at 298°K and 9 Torr for cyclohexene, as compared with 8.60 for c/s-2-butene). The high reactivity and low selectivity of the H atom ought to produce rates comparable with those for simple olefins of comparable structure. No studies on more highly strained rings seem to have been carried out. 

Some cross-metathesis reactions of higher olefins are collected in Table 9.3 also see Kawai (1989). 

The reaction of 2,4,4-trimethylpent-2-ene with 4-vinylcyclohexene, eqn. (16), proceeds with a selectivity of 75% in the presence of Rc207/Al203 if the catalyst is pretreated with Cu(N03)2 to suppress side reactions (Lyons 1988). 

16% PhCH2CH=CHCH2Ph formed at equilibrium 2-C4 not a primary product 

Pinazzi 1977a Karan 1989 Kiipper 1975, 1976 Woerlee 1984 Warwel 1982a 

Cross-metathesis of stilbene with symmetrical olefins is only possible at 100°C with the Rc207/Al203 catalyst when it is activated with Bu Sn. With equimolar amounts of the reactants an equilibrium mixture (50% conversion) is obtained (Warwel 1985). 

Since the review of Voge and Adams [343], not much kinetic research has been carried out on the selective oxidation of olefins with more than four carbon atoms. This is unexpected because isopentenes can be selectively oxidized to isoprene, which is an important material in the production of thermoplastic rubbers. Isopentenes are available from hydrocarbon-conversion operations. 

Maissant et al. [194] used a Bi203 Mo03 = 1 2 catalyst at 450°C to convert l-methyl-2-butene and 2-methyl-2-butene into isoprene. A selectivity of 37% was reached with an activity about 10 times as large as the dehydrogenation of butene with the same catalyst under comparable conditions. Trimethyl-2,2,3-butene-l gave 75% of ferf-butylacrolein. 

Investigating a bismuth molybdate catalyst with Bi Mo = 1 oxidizing pentenes to isoprene, Watanabe and Echigoya [344] found that isomers of pentenes were less reactive than those of the corresponding butenes in flow experiments, but the reverse was true in pulse experiments. Heat of adsorption measurements make it clear that the active sites are not uni- 

Higher selectivities were obtained by Rennard et al. [263] by using MgCrFe04 and ZnCrFe04 catalysts. At temperatures above 350°C 2-methyl-2-butene and 2,3-dimethyl-2-butene are converted at a level of about 30% to diolefins with a selectivity of 90%. Molecules with conjugated bonds are favoured. 

Pichler et al. [255] report the conversion of monomethylbutenes to isoprene on a catalyst containing 9.8 wt. % V2Os, 19.4 wt. % Mo03 and 0.8% P205 on a Ti02 carrier. At a temperature of 335°C, the selectivity is maximal (30%) at a residence time of 0.2 sec. 

1-Pentene can be obtained by co-dimerization of ethylene with propene [41]. 1-Hexene is manufactured by SHOP (shell higher olefins process) [42] or via trimerization of ethylene [11,43] and, on a much smaller scale, by dehydration of corresponding alcohols [44]. 

The hydroformylation of mixtures of Cg-olefins is a process with huge economic importance. A typical example is di-n-butene, consisting of isomeric -octenes, methylheptenes, and dimethylhexenes. The mixture is produced from Raffinate II, in which isomeric butenes are dimerized (e.g., by IFP Dimersol [47] or Octol process [48]). Hydroformylation of di- -butene produces linear and alkyl-branched Cg-aldehydes, which are converted to diisononyl phthalate (DINP), another additive for flexible PVC with immense industrial relevance. For this application, the use of terminal aldehydes is preferred. 

Alternatively, 1-undecanal can be converted by aldol condensation with formaldehyde and subsequent hydrogenation into 2-methyl-undecanal (methyl-nonylacetaldehyde = MNA) [58]. This is a technically feasible alternative to the Darzens reaction of 2-undecananone with methyl chloroacetate. MNA is a sought-after principal ingredient in perfumery (see also Section 6.1.3.1.2). 

Because of decomposition problems of Rh catalysts during the separation of high-boiling products, most commercial plants for long-chain aldehydes ( Cjo) operate with Co catalysts. These approaches are based on unmodified catalysts under rather severe conditions (30 MPa, 200 C) [59]. Besides alcohols, alkanes are also formed. Through modification of the Co catalyst with phosphines, the pressure can be lowered ( 10MPa) and, as a result, selectivity toward the formation of the linear alcohols is enhanced [60]. A suitable feedstock of higher olefins (up to C20) can be derived from Fischer-Tropsch feed (Sasol), or it is produced by SHOP. Products are commonly used for the production of surfactant alcohols. 

For example, hydroformylation of 1-dodecene has been carried out with a phosphabicyclononane-modified Co catalyst at 8.5 MPa syngas pressure (CO/H2 = 1 2) at 120 °C with a Co/P ratio of 1 2 to produce 55% isomeric Cj g alcohols [61]. RhClj immobilized on trioctylmethylammonium chloride operating in a multiphase Uquid system together with isooctane and water was developed for the conversion of tetradecene [62]. In more sophisticated approaches, phosphorus-modified Rh catalysts have been screened in biphasic systems, sometimes containing surface-active compounds [63]. Even internal olefins, such as (Z)-2-tridecene, have been used as substrates. Thus, by using a mixed, homogeneous Rh/Ru catalyst in a hydroformylation-hydrogenation protocol, 1-tetradecanol was obtained with a yield of 83% and with an Hb selectivity of 12 (see Section 5.2) [64]. 

Evidence as to the mechanism of decomposition of the excited homologues of ethylene has been provided bythe mass-spectrometric studies ofLossing et They find, for example, that the following reactions occur 

The main processes thus involve the breaking of a bond p to the double bond, with formation of resonance-stabilized allylic radicals. 

Work on the mercury-photosensitized reactions of acetylene has been carried out by Bates and Taylor , lungers and Taylor , Melville , Le Roy and Stea-cie , Shida et al , Mains et Sherwood and Gunning , Tsukuda and Shida , and LeRoy . The system offers an interesting contrast to that with ethylene, in that a primary energy-transfer process appears to be imimportant the main steps are probably 

The radicals C4H3 and C2H3 produced in this way then add on to acetylene molecules, with the formation of benzene and other polymeric material, viz. 

The mercury-photosensitized decomposition of benzene has been investigated by Scott and Steacie . The main initiation step appears to involve energy transfer, viz. 

The desired a-alkenes in the C10-C20 range are used as feedstock in the production of detergent alcohols and in the synthesis of lubricants, the C6-Q0 alkenes are used as plasticizer alcohols in phthalates for PVC, and as comonomers in low-density polyethylene, and a variety of other products. The internal by-products are mainly used for the production of alcohols via a cobalt-catalyzed hydroformylation. 

The typical size of the Shell process plant described here is 250,000 tons per year. The total production of higher olefins includes several alternative routes 

Higher alkenes can be obtained from thermal cracking of wax, and although a thermodynamic mixture of internal alkenes might have been expected, the wax-cracker product contains a high proportion of 1-alkenes, the kinetically controlled product. For the cobalt-catalyzed hydroformylation the nature of the alkene mixture is not relevant, but for other derivatizations the isomer composition is 

The oligomerization catalyst is a homogeneous nickel complex of a phosphi-nocarboxylic acid. The other catalysts are fixed bed catalysts a Co/Mo oxide for the metathesis reaction and a solid catalyst for the isomerization. 

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