Isobutylene, oligomerization

Table 3 Isobutylene Oligomerization Catalyzed by Nafion Blends...

Table 4 Isobutylene Oligomerization Catalyzed by Heterogeneous Sulfonic Acids...

Table 6 compares activity of three catalysts Nafion on CSC with 100% SO3H group. Catalyst B on CSC with 79% SO3H groups and bulk Nafion . Activity was again measmed by isobutylene oligomerization. 

Lapidus, A. L., Slenkin, L. N., Rudakova, X N., Myshankova, M. 1., Loktev, X S., Papko, Ya., and Eidus, X, Effect of the composition of catalyst system NiC-SiOz-AI2O3 on its catalytic properties in ethylene and isobutylene oligomerization reaction, Izv. Akad. Nauk. SSSR, Ser. Khim., 1974, 1956 (Russian). 

Lapour, P, and Marek, M., Isobutylene oligomerization in the presence of Friedel-Crafts catalysts, Makromol. Chem., 134, 23, 1970. 

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

Hydrocarbons with up to 16 carbon atoms are detected in a typical alkylate (82). With the liquid acids, it was found that the oligomerization rate is higher for isoalkenes than for linear alkenes (49). The same is true for solid acids (14,83). Because of their tertiary carbon atoms, isobutylene and isopentene obviously react more easily with carbenium ions. This point can be inferred from the reverse reaction, (3-scission (see below), which is fastest for reactions of tertiary cations to give tertiary cations. In oligomerization experiments, the following pattern of... 

Because of their very similar boiling points and azeotrope formation, the components of the C4 fraction cannot be separated by distillation. Instead, other physical and chemical methods must be used. 1,3-Butadiene is recovered by complex formation or by extractive distillation.143-146 Since the reactivity of isobutylene is higher than that of n-butenes, it is separated next by chemical transformations. It is converted with water or methyl alcohol to form, respectively, tert-butyl alcohol and tert-butyl methyl ether, or by oligomerization and polymerization. The remaining n-butenes may be isomerized to yield additional isobutylene. Alternatively, 1-butene in the butadiene-free C4 fraction is isomerized to 2-butenes. The difference between the boiling points of 2-butenes and isobutylene is sufficient to separate them by distillation. n-Butenes and butane may also be separated by extractive distillation.147... 

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

The reaction is also called hydrocarboxylation. According to a later modification, the alkene first reacts with carbon monoxide in the presence of the acid to form an acyl cation, which then is hydrolyzed with water to give the carboxylic acid.97 The advantage of this two-step synthesis is that it requires only medium pressure (100 atm). Aqueous HF (85-95%) gave good results in the carboxylation of alkenes and cycloalkenes.98 Phosphoric acid is also effective in the carboxylation of terminal alkenes and isobutylene, but it causes substantial oligomerization as well.99 100 Neocarboxylic acids are manufactured industrially with this process (see Section 7.2.4). The addition may also be performed with formic acid as the source of CO (Koch-Haaf reaction).101 102 The mechanism involves carbocation formation via protonation of the alkene97 103 [Eq. (7.10)]. It then reacts with carbon monoxide... 

It seems certain that acid-catalyzed true oligomerization occurs via a carbocatio-nic mechanism as first suggested by Whitmore.5 Thus, the formation of diisobutylenes by dimerization of isobutylene in the presence of acidic catalysts occurs according to the following equation ... 

Since isobutylene is a very reactive olefin, its oligomerization can be promoted by almost any electrophilic catalyst. More recently fluorinated alumina,6 cation-exchange resins,7 benzylsulfonic acid siloxane,8 pentasil zeolites,9 and perfluori-nated resinosulfonic acids10 were studied. Some of these catalysts may bring about improved oligomerization. 

Conjunct polymerization involves hydride abstraction from an olefin or oligomer by a carbocation. For example, during the oligomerization of isobutylene by dissolving it in 96% sulfuric acid, octene products may react with carbocation 1 [Eq. (13.4)] before they eliminate a proton to form trimethylpentenes 11... 

There are other commercial processes available for the production of butylenes. However, these are site or manufacturer specific, eg, the Oxirane process for the production of propylene oxide the disproportionation of higher olefins and the oligomerization of ethylene. Any of these processes can become an important source in the future. More recendy, the Coastal Isobutane process began commercialization to produce isobutylene from butanes for meeting the expected demand for methyl-tert-buty ether (40). 

A comparative study of nanocomposites (16% Nafion-silica and commercial SAC-13) has been performed by Hoelderich and co-workers169 in the alkylation of isobutane and Raffinate II. Raffinate II, the remaining C4 cut of a stream cracker effluent after removal of dienes, isobutane, propane, and propene, contains butane, isobutylene, and butenes as main components. High conversion with a selectivity of 62% to isooctane was found for Nafion SAC-13 (batch reactor, 80°C). Both the quality of the product and the activity of the catalysts, however, decrease rapidly due to isomerization and oligomerization. Treating under reflux, the deactivated catalysts in acetone followed by a further treatment with aqueous hydrogen peroxide (80°C, 2 h), however, restores the activity. 

Extracting the isobutylene with sulfuric acid and distilling the 1-butene away from butane and butadiene is used for separation of the 1-butene. It is also made by Ziegler (or non-Ziegler) oligomerization of ethylene (Fig. 1). 

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. 

Isobutylene is present as 20-30% of the C4 fraction from the naphtha cracking process. A number of different upgrading reactions with isobutylene have been carried out industrially (with and without prior separation from the C4 fraction). One of these includes the acid-catalyzed oligomerization... 

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