Isobutylene dimerization

Typical isobutylene, as suppHed to the butyl mbber process, has a purity in the range of 95—99%, and includes varying amounts of propene, 1-butene, 2-butene, isobutylene dimer, and tert-huty alcohol, and trace quantities of a variety of oxygen-containing compounds, depending on the process employed. 

When high purity isobutylene is not required, the acid extract from the rich stage may be heated for a few minutes to 250-300°F, and then quickly cooled. Under these conditions the isobutylene dimerizes to form largely 2,4,4, trimethyl pentene-1. This is known as the dimer process and may be used to concentrate i-butenes for dehydrogenation feed, the isobutylene dimer being added to the motor gasoline pool. Trimers, as well as codimers with normal butenes are also produced. 

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. 

With the increased use of catalytic cracking, large quantities of fight olefins become available. Utilization of these reactive, cheap streams for gasoline production became the object of much petroleum research. One of the processes arising out of this work was the catalytic poljnnerization of Cs and C4 olefins to gasoline. The first unit for polymerization of olefins to motor fuel went on stream in 1935. A year before, the cold-acid process for isobutylene dimerization was announced. This was followed shortly by the hot-acid process for copolymerization of all C4 olefins. 

Saipem S.p.A./CDTech Iso-octene Mixed C hydrocarbons Isobutylene dimerization to produce isooctene in presence of catalytic distillation tower NA NA... 

Saipem S.p.A./Ecofuel S.p.A. Iso-octene/lso-octane C streams containing isobutylene Multipurpose plant. Flexibility, Isobutylene dimerization and hydrogenation of produced Iso-OctEne 2 2006... 

The National Bureau of Standards indicates that average Hydrocodimer (hydrogenated isobutylene dimer) contains about 0.7 per cent hexanes, 3.2 per cent heptanes, 85.8 per cent octanes, and 10.3 per cent nonanes or heavier. 

The strong catalytic activity of anhydrous hydrogen fluoride results from the abiUty to donate a proton, as in the dimerization of isobutylene (see Butylenes) ... 

Propjiene (qv) [115-07-1] is the predominant 0x0 process olefin feedstock. Ethylene (qv) [74-85-1J, as well as a wide variety of terminal, internal, and mixed olefin streams, are also hydroformylated commercially. Branched-chain olefins include octenes, nonenes, and dodecenes from fractionation of oligomers of C —C olefins as well as octenes from dimerization and codimerization of isobutylene and 1- and 2-butenes (see Butylenes). 

Since a carbocation can add to an alkene to form a larger cation, under acidic conditions isobutylene can dimerize to form 2,4,4-trim ethyl -1 -pen ten e [107-39-1] and 2,4,4-trimethyl-2-pentene [107-40-4J, which can then be hydrogenated in the presence of nickel to form isooctane [540-84-1]. This reaction is no longer of commercial significance. 

Alkylation of isobutylene and isobutane in the presence of an acidic catalyst yields isooctane. This reaction proceeds through the same mechanism as dimerization except that during the last step, a proton is transferred from a surrounding alkane instead of one being abstracted by a base. The cation thus formed bonds with the base. Alkylation of aromatics with butylenes is another addition reaction and follows the same general rules with regard to relative rates and product stmcture. Thus 1- and 2-butenes yield j -butyl derivatives and isobutylene yields tert-huty derivatives. 

Di- and Triisobutylcncs. Diisobutylene [18923-87-0] and tnisobutylenes are prepared by heating the sulfuric acid extract of isobutylene from a separation process to about 90°C. A 90% yield containing 80% dimers and 20% trimers results. Use centers on the dimer, CgH, a mixture of 2,4,4-trimethylpentene-1 and -2. Most of the dimer-trimer mixture is added to the gasoline pool as an octane improver. The balance is used for alkylation of phenols to yield octylphenol, which in turn is ethoxylated or condensed with formaldehyde. The water-soluble ethoxylated phenols are used as surface-active agents in textiles, paints, caulks, and sealants (see Alkylphenols). 

This process produces polymer gasoline with a high octane. Dimerization was first used (1935) to dimerize isobutylene to diisobutylene, constituted of 2,4,4-trimethyl-1-pentene (80%) and 2,4,4-trimethyl-2-pentene (20%). Both phosphoric and sulfuric acid were used as catalysts. 

Isobutylene could be dimerized in the presence of an acid catalyst to diisobutylene. The product is a mixture of diisobutylene isomers, which are used as alkylating agents in the plasticizer industry and as a lube oil additive (dimerization of olefins is noted in Chapter 3). 

Model experiments with 2,4,4-trimethyl-l-pentene (C8H16, TMP) and H20 / AlBr3/MeBr at —80 °C, ia, with a conventional Lewis acid system which would give AEjjv = —6.6 kcal/mole in isobutylene polymerization, gave exclusively a dimer (C16H32) by proton elimination, ia, by a mechanism which mimics transfer in polymerization ... 

The acetoacetyl group may be supplied as ketene dimer (p T277), leaving alcohol (31). You may have considered chlorinating ketone (32) or adding CCl to aldehyde (33) to make (31) but you probably did not see the disconnection to chloral and isobutylene (3lb),... 

Complicating aspects of the reactions include the solvent dependence of the dimerization of cyclopentenone, the head-to-head ratio increasing with polarity of solvent ".ioo)( and the plethora of products from the reaction cyclohexenone-isobutylene, where several olefinic products are not shown in Eq. 30. 97> The complicated features of these reactions are so well-described in a recent review article 94> that no furhter outline will be provided here. Biradical mechanisms can account for a great... 

With propene, n-butene, and n-pentene, the alkanes formed are propane, n-butane, and n-pentane (plus isopentane), respectively. The production of considerable amounts of light -alkanes is a disadvantage of this reaction route. Furthermore, the yield of the desired alkylate is reduced relative to isobutane and alkene consumption (8). For example, propene alkylation with HF can give more than 15 vol% yield of propane (21). Aluminum chloride-ether complexes also catalyze self-alkylation. However, when acidity is moderated with metal chlorides, the self-alkylation activity is drastically reduced. Intuitively, the formation of isobutylene via proton transfer from an isobutyl cation should be more pronounced at a weaker acidity, but the opposite has been found (92). Other properties besides acidity may contribute to the self-alkylation activity. Earlier publications concerned with zeolites claimed this mechanism to be a source of hydrogen for saturating cracking products or dimerization products (69,93). However, as shown in reaction (10), only the feed alkene will be saturated, and dehydrogenation does not take place. 

In Experiment C9 (circular points in Figure 7) 0.75 mol of isobutylene was added at -80 °C to 3.3 mmol of aluminium bromide in 40 ml of methyl bromide over ca. 1.5 h. According to the ratio (kc - k /Kj, which was ca. 103, the initiator solution was very pure. No polymerisation took place the isobutylene was shown by GLC analysis to be unchanged and this showed no dimers. 

Therefore, the base-catalyzed reaction of isobutylene yields the same dimer as the acid-catalyzed reaction although the mechanisms are completely different. Since olefin isomerizations are also catalyzed under these conditions, an equilibrium distribution of products is expected for example, the reaction of isobutylene yields 78% of 2,4,4-trimethyl-l-pentene and 22% of 2.4,4-trimethyl-2-pentene. 

In polymerization an olefin can react with another olefin to generate dimers, trimers, and tetramers of the olefin. As a simple example, isobutylene reacts to give a highly branched Cg olefin. 

The /-butyl alcohol can be used to increase the octane of unleaded gasoline or it can be made into methyl /-butyl ether (MTBE) for the same application. The alcohol can also be dehydrated to isobutylene, which in turn is used in alkylation to give highly branched dimers for addition to straight-run gasoline. 

Dimerization of propylene is also used to produce isoprene. Several steps are involved. Initially, dimerization of propylene to 2-methyl-1-pentene occurs. Then isomerization to 2-methyl-2-pentene is effected. Finally, the 2-methyl-2-pentene is pyrolyzed to isoprene and methane. Another multistep synthesis starts with acetylene and acetone. Perhaps the most attractive route involves formaldehyde and isobutylene (equation 17.42). 

The thermal polymerization of isobutylene (at 370-460° and 540-5350 p.s.i.) is of particular interest because it yields 1,1,3-trimethyl-cyclopentane rather than 2,4,4-trimethyl-l- and -2-pentene (McKinley et al., 11). This cyclic dimer amounted to as much as 45.9% of the total liquid product when the reaction was carried out at 400° and 540 p.s.i. It was suggested that its formation might involve one of three mechanisms ... 

The complex, XLYI, may add to another molecule of isobutylene to yield a higher polymer complex or eliminate aluminum chloride to yield the dimer in the latter case intramolecular migration (a 1,5-shift 1) of hydrogen must be postulated in order to form an olefin. On the other hand, cyclization may readily occur (particularly after a 1,2-shift of a proton from a methyl group) with the resultant formation of a naphthene. 

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

Schoenmakers et al. [72] analyzed two representative commercial rubbers by gas chromatography-mass spectrometry (GC-MS) and detected more than 100 different compounds. The rubbers, mixtures of isobutylene and isoprene, were analyzed after being cryogenically grinded and submitted to two different extraction procedures a Sohxlet extraction with a series of solvents and a static-headspace extraction, which entailed placing the sample in a 20-mL sealed vial in an oven at 110°C for 5,20, or 50 min. Although these are not the conditions to which pharmaceutical products are submitted, the results may give an idea of which compounds could be expected from these materials. Residual monomers, isobutylene in the dimeric or tetrameric form, and compounds derived from the scission of the polymeric chain were found in the extracts. Table 32 presents an overview of the nature of the compounds identified in the headspace and Soxhlet extracts of the polymers. While the liquid-phase extraction was able to extract less volatile compounds, the headspace technique was able to show the presence of compounds with low molecular mass... 

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