Isobutylene

Isobutylene (CH2=C(CH3)2) is a reactive C4 olefin. Until recently, almost all isobutylene was obtained as a by-product with other C4 hydrocarbons from different cracking processes. It was mainly used to produce alkylates for the gasoline pool. A small portion was used to produce chemicals such as isoprene and diisobutylene. However, increasing demand for oxygenates from isobutylene has called for other sources. 

The following section reviews the chemistry of isobutylene and its important chemicals. 

Experiments have been carried out to substantiate the comprehensive closed-loop model described in Sect. 2. The experiments included the determination of kc and kp under various conditions including a study of the effect of temperature on these parameters, an examination of the effect of experimental conditions on M and Mw/M together with an analysis of the GPC traces obtained. The raw data are shown in Tables 2-8 in the Appendix. 

In the presence of insufficient [ED] chain transfer may occur thus with increasing time (conversion), kc calculated by Eq. (27) may increase, suggesting a higher than true cationation rate. (See. Sects. 2.2.1, 2.3). 

The kp is also decreasing with increasing [ED] indicating the conversion of highly reactive cationic chain ends to less reactive living species by MtX ED complexes. Since the contribution of kpC to the overall kp is decreasing, the latter must also decrease (see Eq. (32)). 

According to the data shown in Fig. 17A, B, kc and kp are increasing with increasing solvent polarity at — 80 °C. Evidently, the higher the polarity the higher the solvation of the ionic chain ends which explains the higher overall kpS. 

Thus the series of experiments have been carried out in which first the solvent-initiator-electron donor and TiCl4 in this order, were premixed, and 

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Example 2.5 tert-Butyl hydrogen sulfate is required as an intermediate in a reaction sequence. This can be produced by the reaction between isobutylene and moderately concentrated sulfuric acid ... 

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

Derivatives of polyisobutylene (6. in Figure 9.1) offer the advantage of control over the molecular weight of the polyisobutylene obtained by cationic polymerization of isobutylene. Condensation on maleic anhydride can be done directly either by thermal activation ( ene-synthesis reaction) (2.1), or by chlorinated polyisobutylene intermediates (2.2). The condensation of the PIBSA on polyethylene polyamines leads to succinimides. Note that one can obtain mono- or disuccinimides. The mono-succinimides are used as... 

The organophilic part of commercial dispersants is obtained by cationic oligomerization of isobutylene. 

Alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Conventional paraffin-olefin (alkane-alkene) alkylation is an acid-catalyzed reaction, such as combining isobutylene and isobutane to isooctane. 

Alkylation of isoalkanes with alkenes is of particular significance. The industrially used alkylation of isobutane with isobutylene to iso-... 

The reaction of trivalent carbocations with carbon monoxide giving acyl cations is the key step in the well-known and industrially used Koch-Haaf reaction of preparing branched carboxylic acids from al-kenes or alcohols. For example, in this way, isobutylene or tert-hutyi alcohol is converted into pivalic acid. In contrast, based on the superacidic activation of electrophiles leading the superelectrophiles (see Chapter 12), we found it possible to formylate isoalkanes to aldehydes, which subsequently rearrange to their corresponding branched ketones. 

With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. 

The oxidative coupling of alkenes which have two substituents at the 2 posi-tion, such as isobutylene, styrene, 2-phenylpropene, 1,1-diphenylethylene, and methyl methacrylate, takes place to give the 1,1,4.4-tetrasubstituted butadienes 285 by the action of Pd(OAc)2 or PdCF in the presence of sodium acetate[255-257]. Oxidation of styrene with Pd(OAc)2 produces 1.4-diphenylbutadiene (285, R = H) as a main product and a- and /3-acetoxystyrenes as minor pro-ducts[258]. Prolonged oxidation of the primary coupling product 285 (R = Me) of 2-phenylpropene with an excess of Pd(OAc)2 leads slowly to p-... 

Alkenes are hydrocarbons that contain a carbon-carbon double bond A carbon-carbon double bond is both an important structural unit and an important func tional group m organic chemistry The shape of an organic molecule is influenced by the presence of this bond and the double bond is the site of most of the chemical reactions that alkenes undergo Some representative alkenes include isobutylene (an industrial chemical) a pmene (a fragrant liquid obtained from pine trees) md fame sene (a naturally occurring alkene with three double bonds)... 

Figure 3.4 is a display of data which confirms the predictions of Eq. (3.46). For T and a constant-the case in these experiments—Eq. (3.46) predicts that a plot of Uj versus 1 /M should yield a straight line with an intercept proportional to 1/M(,. The elastomers on which the experiments were conducted were copolymers of isobutylene containing a small amount of isoprene. The polymers... 

In cationic polymerization the active species is the ion which is formed by the addition of a proton from the initiator system to a monomer. For vinyl monomers the type of substituents which promote this type of polymerization are those which are electron supplying, like alkyl, 1,1-dialkyl, aryl, and alkoxy. Isobutylene and a-methyl styrene are examples of monomers which have been polymerized via cationic intermediates. 

Use the values determined in Example 7.6 for the vinylidene chloride (M )-isobutylene (M2) systemf to calculate for various values of fi according to the terminal mechanism. Prepare a plot of the results. On the same graph, plot the following experimentally measured values of fi and ... 

Some additional dyad fractions from the research cited in the last problem J are reported at intermediate feedstock concentrations (M = vinylidene chloride M2 = isobutylene) ... 

Isobutyl alcohol [78-83-1] forms a substantial fraction of the butanols produced by higher alcohol synthesis over modified copper—zinc oxide-based catalysts. Conceivably, separation of this alcohol and dehydration affords an alternative route to isobutjiene [115-11 -7] for methyl /-butyl ether [1624-04-4] (MTBE) production. MTBE is a rapidly growing constituent of reformulated gasoline, but its growth is likely to be limited by available suppHes of isobutylene. Thus higher alcohol synthesis provides a process capable of supplying all of the raw materials required for manufacture of this key fuel oxygenate (24) (see Ethers). 

NR, natural mbber CR, chloroprene SRs, synthetic mbbers IR, natural isoprene SBR, styrene—butadiene mbber BR, butadiene EPDM, ethylene—propjiene-diene EPM, ethylene—propylene polymer HR, isobutylene—isoprene NBR, nitrile—butadiene. 

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

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