Isobutylene Isobutene

Isobutylene has had a tremendous increased production in the last few years because of the dynamic growth of the gasoline additive MTBE. About two thirds of it is made from isobutane by dehydrogenation in thermal cracking. 

The other third comes from t-butyl alcohol by dehydration, with the t-butyl alcohol being made available as a by-product by oxidation of isobutane followed by epoxidation of propylene with t-butyl hydroperoxide. 

The epoxidation of propylene is discussed in Chapter 10, Section 2. Some isobutane can be made by isomerizing -butane. The isomerization of -butenes to isobutylene is also being commercialized. 

The major uses of isobutylene are estimated in Table 8.5. Much of isobutylene is a captive market used by refineries in alkylation or polymerization of gasoline. The remainder goes into the octane enhancer MTBE, polyisobutylene, and butyl rubber. Some is burned for fuel. 

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Melbylpropene, isobutylene, isobutene, Me2C CH2 Prepared by heating r-butanol with oxalic acid. 

Butenes or butylenes are hydrocarbon alkenes that exist as four different isomers. Each isomer is a flammable gas at normal room temperature and one atmosphere pressure, but their boiling points indicate that butenes can be condensed at low ambient temperatures and/or increase pressure similar to propane and butane. The 2 designation in the names indicates the position of the double bond. The cis and trans labels indicate geometric isomerism. Geometric isomers are molecules that have similar atoms and bonds but different spatial arrangement of atoms. The structures indicate that three of the butenes are normal butenes, n-butenes, but that methylpropene is branched. Methylpropene is also called isobutene or isobutylene. Isobutenes are more reactive than n-butenes, and reaction mechanisms involving isobutenes differ from those of normal butenes. 

MTBE is made by reacting methanol (methyl alcohol CH3OH) with isobutylene (isobutene CH3C(CH3)=CH3). The... 

Isobutanethiol. See 2-Methyl-1-propanethiol Isobutanoic acid. See Isobutyric acid isobutanol HP, Isobutanol. See Isobutyl alcohol Isobutanolamine Isobutanol-2 amine. See Aminomethyl propanol Isobutene. See Isobutylene Isobutene homopolymer Isobutene polymer. See Polyisobutene Isobutene trimer. See Triisobutylene Isobutenol. See Methallyl alcohol Isobutenyl chloride. See 3-Chloro-2-methylpropene... 

Ethylene, propylene Isoprene, pentenes, methyl butenes, c/5-piperylene, trans-piperylene, cyclopentadiene Diisobutylene Isobutylene Isobutylene Isobutene... 

Polybutenes. Polybutenes are produced by controlled polymerization of butenes and isobutene (isobutylene) (see Butylenes). A typical polyisobutylene stmcture is... 

In commercial extraction operations, the fractions that contain butadiene, isobutene, and 1- and 2-butenes usually first go through a butadiene extraction unit in which the butadiene is removed. This may be followed by isobutylene removal via reaction between isobutylene and methanol to form methyl /-butyl ether [1634-04-4] (MTBE). The butenes are then distilled from the MTBE. 1-Butene may then be separated from 2-butene by distillation. 

The reaction between isobutylene (separated from C4 fractions from cracking units or from cracking isobutane to isobutene) and formaldehyde produces a cyclic ether (dimethyl dioxane). Pyrolysis of dioxane gives isoprene and formaldehyde. The formaldehyde is recovered and recycled to the reactor. 

Common Name 2-Methylpropene Synonym isobutene, isobutylene Chemical Name 2-methylpropene CAS Registry No 115-11-7 Molecular Formula C4H8 CH3C(CH3)CH2 Molecular Weight 56.107 Melting Point (°C) ... 

Alkenes are like alkanes less two hydrogens, giving them a double bond somewhere in the chain, making them an olefin. They have the formula, CnH2n. such as butene (more often called butylene), isobutene (isobutylene), and propene (usually called propylene). 

The isomerization of light olefins is usually carried out to convert -butenes to isobutylene [12] with the most frequently studied zeolite for this operation being PER [30]. Lyondell s IsomPlus process uses a PER catalyst to convert -butenes to isobutylene or n-pentenes to isopentene [31]. Processes such as this were in larger demand to generate isobutene before the phaseout of MTBE as a gasoline additive. Since the phaseout, these processes often perform the reverse reaction to convert isobutene to n-butenes which are then used as a metathesis feed [32]. As doublebond isomerization is much easier than skeletal isomerization, most of the catalysts below are at equilibrium ratios of the n-olefins as the skeletal isomerization begins (Table 12.5). 

Synonyms y-Butylene CCRIS 2281 1,1-Dimethylethene u/35// -Dimethylethylene EINECS 204-066-3 Isobutene Isobutylene Methylpropene 2-Methyl-l-propene 2-Methylpropylene UN 1055. 

Indenopyrene, see Indeno[l,2,3-crf pyrene l//-Indole, see Indole Indolene, see Indoline Inexit, see Lindane Inhibisol, see 1,1,1-Trichloroethane Insecticide 497, see Dieldrin Insecticide 4049, see Malathion Insectophene, see a-Endosulfan, p-Endosulfan Intox 8, see Chlordane Inverton 245, see 2,4,5-T lodomethane, see Methyl iodide IP, see Indeno[l,2,3-crf pyrene IP3, see Isoamyl alcohol Ipaner, see 2,4-D IPE, see Isopropyl ether IPH, see Phenol Ipersan, see Trifluralin Iphanon, see Camphor Isceon 11, see Trichlorofluoromethane Isceon 122, see Dichlorodifluoromethane Iscobrome, see Methyl bromide Iscobrome D, see Ethylene dibromide Isoacetophorone, see Isophorone a-Isoamylene, see 3-Methyl-l-butene Isoamyl ethanoate, see Isoamyl acetate Isoamylhydride, see 2-Methylbutane Isoamylol, see Isoamyl alcohol Isobac, see 2,4-Dichlorophenol Isobenzofuran-l,3-dione, see Phthalic anhydride 1,3-Isobenzofurandione, see Phthalic anhydride IsoBuAc, see Isobutyl acetate IsoBuBz, see Isobutylbenzene Isobutane, see 2-Methylpropane Isobutanol, see Isobutyl alcohol Isobutene, see 2-Methylpropene Isobutenyl methyl ketone, see Mesityl oxide Isobutyl carbinol, see Isoamyl alcohol Isobutylene, see 2-Methylpropene Isobutylethylene, see 4-Methyl-l-pentene Isobutyl ketone, see Diisobutyl ketone Isobutyl methyl ketone, see 4-Methyl-2-pentanone Isobutyltrimethylmethane, see 2,2,4-Trimethylpentane Isocumene, see Propylbenzene Isocyanatomethane, see Methyl isocyanate Isocyanic acid, methyl ester, see Methyl isocyanate Isocyanic acid, methylphenylene ester, see 2,4-Toluene-diisocyanate... 

Besides ethylene and propylene, the steam cracking of naphtha and catalytic cracking in the refinery produce appreciable amounts of C4 compounds. This C4 stream includes butane, isobutane, 1-butene (butylene), cis- and trans-2-hutene, isobutene (isobutylene), and butadiene. The C4 hydrocarbons can be used to alkylate gasoline. Of these, only butadiene and isobutylene appear in the top 50 chemicals as separate pure chemicals. The other C4 hydrocarbons have specific uses but are not as important as butadiene and isobutylene. A typical composition of a C4 stream from steam cracking of naphtha is given in Table 8.3. 

In this work, the performance of two green acid catalysts, a Ti02 synthesized by the sol-gel method and sulfated in situ was compared with a traditional NiY zeolite in the trimerization of isobutene. The reaction was carried out at mild conditions atmospheric pressure and 40°C of temperature. The results obtained in the catalytic evaluation showed higher conversion and stability as well as a better selectivity to tri-isobutylene for the sulfated titania catalyst with respect to the NiY zeolite. 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

There is one last experimental result arguing for a high activation energy for internal ft—C—H abstraction. When Steps 11" and 12 compete, epoxidation (Step 11") always seems to be faster than olefin formation (Step 12). This is true in the HC1 catalyzed, chain decomposition of ter -Bu202 which produces isobutylene oxide and negligible isobutene (2) via a peroxyalkyl radical. Similar behavior is observed from the addition of H02 and R02 to olefins, which produce mainly ethers or epoxides at rapid rates (12). Note that although we estimate A12 — 1013 4 sec."1 and An" -— 10115 sec. 1, Step 12 is endothermic by -— 11 to 13 kcal., while Step 11" is exothermic by 10 to 17 kcal. A reasonable estimate for Ei2 is 20 kcal., while En" has an upper limit of 16 kcal., and some data (12) point to a value closer to 10 kcal. 

An important intermediate for synthetic p-ionone (36) is the C8 building block methyl heptenone (37). In addition to the synthesis shown above, two further processes are known for its industrial production. In the process of Rhodia INC 36), the starting material is isoprene, and methyl heptenone (37) is obtained via prenyl chloride. At BASF, methyl heptenone (37) is produced, for economic reasons, in the form of its double bond isomer (37 a) by thermal condensation of isobutylene, formaldehyde and acetone 37) (see page 13). By suitable choice of the reaction conditions, various side-reactions, such as the Cannizzarro reaction of formaldehyde, the oligomerization of isobutene and aldol condensation between formaldehyde and acetone, can largely be suppressed. 

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