IsoButene, hydrogenation

The photolysis of neopentane has been studied by Lias and Ausloos at 1236 and 1470 A. The two main processes which occur are molecular methane elimination from, and fragmentation of, the excited neopentane. The products of photolysis are methane, isobutene, hydrogen, ethane, and propene, with smaller amounts of isobutane, ethylene, propane, acetylene and 2,2-dimethylbutane. The suggested reactions are... 

Cortright RD, Levin PE, Dumesic JA (1998) Kinetic studies of isobutane dehydrogenation and isobutene hydrogenation over Pt/Sn-based catalysts. Ind Eng Chem Res 37 1717... 

Diisobutyl sulfide Di-t-butyl sulfide t-Butyl isobutyl sulfide isoButyl mercaptan isoButene Hydrogen sulfide Non-volatile residue... 

Isobutene hydrogenation has presumably a different reaction mechanism. Although 2-isobutyl groups and 7t-bonded isobutene were the dominant surface species under reaction conditions, the hydrogenation rate of 2-isobutyl was much slower than that of 1-isobutyl. As a... 

Figure 9. Suggested reaction pathways for ethylene, propylene and isobutene hydrogenation on Pt(lll).

The reaction of isobutylene and methanol is assumed to go to 98% equilibrium without side reactions. The dehydrogenation reaction produces isobutene, hydrogen, propylene, and methane. 

The energy transferred during methane-, isobutene-, hydrogen-, water-, and methanol-CI is 68, 4, 99, 33, and 18 kcal/mol, respectively. Because fi ag-mentation is proportional to the energy transferred, the [225]/[243] ratio increases in the order isobutene < methanol < water < methane < hydrogen. 

Happel, J., and Mezaki, R., (1973), "Thermodynamic Equilibrium Constants for the Isobutane-Isobutene-Hydrogen System", J. of Chemical and Engineering Data, Vol, p. 152. 

Cyclodimerhation of isoprene to 1,5-dimethylcycloocta-1,5-diene and disproportion with a rhenium oxide catalyst and isobutene produce 2,6-dimethyUiepta-l,5-diene. The diene is hydroformylated to citroneUal, which after hydrogenation produces citroneUol (137). 

Some types of reactions involving gases that have been studied in IFs are hydrogenations [16, 25-37 ], oxidations [38, 39], and hydroformylations [25, 40 5]. In addition, some dimerizations and allcylations may involve the dissolution of condensable gases (e.g., ethylene, propylene, isobutene) in the IF solvent [46-50]. 

FCC after removal of C5 olefins via selective hydrogenation step passes to the isomerization unit. It has been proposed that after the formation of a hutyl carhocation, a cyclopropyl carhocation is formed which gives a primary carhenium ion that produces isobutene ... 

Di-f-butyl sulfone is different from the other dialkyl sulfones in that RH is mainly alkene and not alkane [G(isobutene) = 3.2 and G(isobutane) = 1.2]. The preference for isobutene over isobutane means that the formation of the alkene cannot be due to disproportionation of two t-butyl radicals but is due to a hydrogen atom expulsion as suggested by Bowmer and O Donnell70... 

The condensation of methanol with isobutene and the highly chemoselective hydrogenation of dienes and alkynes are independently promoted by the active acidic sites (-SO3H) and by the active metal. 

Because hydrogen can easily be removed from a reaction stream, many dehydrogenations have been studied. These include dehydrogenation of methane to carbon,326 ethane to ethene,327,328 propane to propene,329 n-butane to butenes,330 isobutane to isobutene,331,332 cyclohexane to benzene,332-334 meth-ylcyclohexane to toluene 335 n-heptane to toluene,336 methanol to formaldehyde,330 and ethanol to acetaldehyde.337... 

Attempts to polymerise isobutene by free radical catalysis have all failed [16,17] and copolymerisation experiments show that the t-butyl radical has no tendency to add to isobutene. The reasons for these facts are not at all obvious. Evidently, they cannot be thermodynamic and therefore they must be kinetic. One factor is probably that the steric resistance to the formation of polymer brings with it a high activation energy [17], and that the abstraction by a radical of a hydrogen atom from isobutene, to give the methallyl radical, has a much smaller activation energy. This reaction will also be accelerated statistically by the presence of six equivalent hydrogen atoms. 

A ubiquitous co-catalyst is water. This can be effective in extremely small quantities, as was first shown by Evans and Meadows [18] for the polymerisation of isobutene by boron fluoride at low temperatures, although they could give no quantitative estimate of the amount of water required to co-catalyse this reaction. Later [11, 13] it was shown that in methylene dichloride solution at temperatures below about -60° a few micromoles of water are sufficient to polymerise completely some decimoles of isobutene in the presence of millimolar quantities of titanium tetrachloride. With stannic chloride at -78° the maximum reaction rate is obtained with quantities of water equivalent to that of stannic chloride [31]. As far as aluminium chloride is concerned, there is no rigorous proof that it does require a co-catalyst in order to polymerise isobutene. However, the need for a co-catalyst in isomerisations and alkylations catalysed by aluminium bromide (which is more active than the chloride) has been proved [34-37], so that there is little doubt that even the polymerisations carried out by Kennedy and Thomas with aluminium chloride (see Section 5, iii, (a)) under fairly rigorous conditions depended critically on the presence of a co-catalyst - though whether this was water, or hydrogen chloride, or some other substance, cannot be decided at present. 

Propane was selected as solvent for the isobutene for experiments down to -145° the aluminium chloride was dissolved in ethyl chloride, for the work at lower temperatures a mixture of ethyl chloride and vinyl chloride was used. Although these catalyst solutions were made up at -78° they were yellow, and as stated above, they probably contained some hydrogen chloride and other catalytically active decomposition products. The polymerisations were carried out by running the cooled catalyst solution into the monomer solution. Polymer was formed, and came out of solution, almost immediately, and the reaction was very fast even at the lowest temperature (-185°) and lowest monomer concentration (0.6 mole/1). After the reaction was over, propanol at the reaction temperature was added to the reaction mixture to deactivate the catalyst. 

With ethyl bromide as solvent a brief, exploratory study [77] showed that the rates and DPs were more irreproducible than with other alkyl halides, and this was ascribed, at least partly, to the relatively high dissociation constant of ethyl bromide to ethylene and hydrogen bromide. No evidence was obtained whether ethyl bromide itself is a co-catalyst, and the putative co-catalyst in the reaction was residual water and possibly traces of t-BuBr formed from HBr and isobutene. Experiments with [C4H8] = 0.11-0.92 mole/1, [TiCl4] (2.7-11.2) x 103 mole/1, T = -38° to -103° showed that EDP = 5.5 0.5 kcal/ mole that below about -60° the DP is almost independent of monomer concentration and that kjkp = 2 x 10 4 at -63° and 8 x 10"5 at -71°. 

Linalool is an important fragrance and fragrance precursor (esters) with an annual production of over 15 000 t. Some 50% is made by semi-synthesis from a- and / -pinene, the other part is made synthetically starting from isobutene via 6-methylhept-5-en-2-one (9). Addition of an acetylene fragment followed by partial hydrogenation (Pd) leads to linalool. 

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