Isobutene intermediate

Methyl tert-Butylluther Methyl /-butyl ether (MTBE) is an increasingly important fuel additive. Platinum—tin and other PGM catalysts are used for the dehydrogenation of isobutane to isobutene, an intermediate step in MTBE manufacture. 

Citral is prepared starting from isobutene and formaldehyde to yield the important C intermediate 3-methylbut-3-enol (29). Pd-cataly2ed isomeri2ation affords 3-methylbut-2-enol (30). The second C unit of citral is derived from oxidation of (30) to yield 3-methylbut-2-enal (31). Coupling of these two fragments produces the dienol ether (32) and this is followed by an elegant double Cope rearrangement (21) (Fig. 6). 

The three isomers constituting n-hutenes are 1-hutene, cis-2-hutene, and trans-2-hutene. This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene (Chapter 2). The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same intermediates and hence the same products. Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis-and trans-2-butene mixture. Each stream produces specific chemicals. Approximately 70% of 1-butene is used as a comonomer with ethylene to produce linear low-density polyethylene (LLDPE). Another use of 1-butene is for the synthesis of butylene oxide. The rest is used with the 2-butenes to produce other chemicals. n-Butene could also be isomerized to isobutene. ... 

The catalytic asymmetric cyclopropanation of an alkene, a reaction which was studied as early as 1966 by Nozaki and Noyori,63 is used in a commercial synthesis of ethyl (+)-(lS)-2,2-dimethylcyclo-propanecarboxylate (18) by the Sumitomo Chemical Company (see Scheme 5).64 In Aratani s Sumitomo Process, ethyl diazoacetate is decomposed in the presence of isobutene (16) and a catalytic amount of the dimeric chiral copper complex 17. Compound 18, produced in 92 % ee, is a key intermediate in Merck s commercial synthesis of cilastatin (19). The latter compound is a reversible... 

The first example of chemically induced multiplet polarization was observed on treatment of a solution of n-butyl bromide and n-butyl lithium in hexane with a little ether to initiate reaction by depolymerizing the organometallic compound (Ward and Lawler, 1967). Polarization (E/A) of the protons on carbon atoms 1 and 2 in the 1-butene produced was observed and taken as evidence of the correctness of an earlier suggestion (Bryce-Smith, 1956) that radical intermediates are involved in this elimination. Similar observations were made in the reaction of t-butyl lithium with n-butyl bromide when both 1-butene and isobutene were found to be polarized. The observations were particularly significant because multiplet polarization could not be explained by the electron-nuclear cross-relaxation theory of CIDNP then being advanced to explain net polarization (Lawler, 1967 Bargon and Fischer, 1967). 

This conclusion is not in complete agreement with theoretical calculations (p. 224), which imply that the ionic intermediate derived from isobutene closely resembles an open jS-bromocarbocation, whereas those from cis- or trans-2-butenes would be bromonium ions. This difference between experiment and calculations is not fully understood, but could be attributed to some... 

Highly alkylated l-chloro-2-(trimethylsilyl)cyclopentenes 44, which are of interest as possible cyclopentyne precursors, were prepared by reacting 3-chloro-3-methyl-l-(trimethylsilyl)but-l-yne (45) with 1,1-dialkylated or 1,1,2-trialkylated ethylenes in the presence of titanium tetrachloride35. Because of the low S/v 1 reactivity of 45, the yields of the products were moderate. The stepwise [3 + 2]-cycloaddition mechanism discussed above was proven by the isolation of the intermediate acyclic adduct (in 74% yield) when 45 and isobutene were reacted in the presence of BCI3. Under these conditions, the intermediate 46 could be trapped by Cl since BCI4 is more nucleophilic than TiC.15 (equation 16). 

C4 Butesom [Butene isomerization] A process for isomerizing linear butenes to isobutene, catalyzed by a zeolite. The isobutene is intended for use as an intermediate in the production of ethers for use as fuel additives. Developed by UOP in 1992. See also C5 Pentesom. 

Escambia (1) A process for oxidizing isobutene to a-hydroxy-isobutyric acid (HIBA), for use as an intermediate in the manufacture of methacrylates. The oxidant was dinitrogen tetroxide, N204. Operated by the Escambia Chemical Corporation, FL, in 1965 before its destruction by an explosion in 1967. It has not been used again. 

Hydride transfer from alkenes was also proposed to occur during sulfuric acid-catalyzed alkylation modified with anthracene (77). Then the butene loses a hydride and forms a cyclic carbocation intermediate, yielding—on reaction with isobutene—trimethylpentyl cations. This conclusion was drawn from the observation of a sharp decrease in 2,2,3-TMP selectivity upon addition of anthracene to the acid. 

Tebbe and co-workers reported the first olefin metatheses between titanocene-methyli-dene and simple terminal olefins [13]. They showed cross-metathesis between isotopically labeled isobutene and methylenecyclohexane to be catalyzed by titanocene-methylidene. This process is referred to as degenerate olefm metathesis as it does not yield any new olefin (Scheme 14.6). The intermediate titanacyclobutane has been isolated and characterized [14], and its stability [15] and mechanism of rearrangement [16] have been investigated. 

Although the reaction of a titanium carbene complex with an olefin generally affords the olefin metathesis product, in certain cases the intermediate titanacyclobutane may decompose through reductive elimination to give a cyclopropane. A small amount of the cyclopropane derivative is produced by the reaction of titanocene-methylidene with isobutene or ethene in the presence of triethylamine or THF [8], In order to accelerate the reductive elimination from titanacyclobutane to form the cyclopropane, oxidation with iodine is required (Scheme 14.21) [36], The stereochemistry obtained indicates that this reaction proceeds through the formation of y-iodoalkyltitanium species 46 and 47. A subsequent intramolecular SN2 reaction produces the cyclopropane. 

Above we have mentioned several heterogeneous applications such as the OCT process and SHOP. Neohexene (3,3-dimethyl-1-butene), an important intermediate in the synthesis of fine chemicals, is produced from the dimer of isobutene, which consists of a mixture of 2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl- 1-pentene. Cross-metathesis of the former with ethene yields the desired product. The catalyst is a mixture of W03/Si02 for metathesis and MgO for isomerisation at 370 °C and 30 bar. The isobutene is recycled to the isobutene dimerisation unit [48],... 

We also note that some 2,2-disubstituted oxiranes have toxicological significance, as exemplified by 2,2-dimethyloxirane (2-methyl-l, 2-epoxypropane, 10.43, R = Me). This compound is the toxic metabolite of 2-methyl-prop-1-ene (isobutene), a gaseous alkene widely used as a monomer in the industrial production of adhesives, plastics, and other polymers. Interestingly, detoxification of this epoxide catalyzed by liver epoxide hydrolase was high in the human, intermediate in the rat, and low in the mouse [125], These activities were inversely correlated with the epoxide levels measured in vitro in liver tissue of these species. 

If the initial intermediate or the original fuel is a large monoolefin, the radicals will abstract H from those carbon atoms that are singly bonded because the CH bond strengths of doubly bonded carbons are large (see Appendix D). Thus, the evidence [12, 32] is building that, during oxidation, all nonaromatic hydrocarbons primarily form ethene and propene (and some butene and isobutene) and that the oxidative attack that eventually leads to CO is almost solely from these small intermediates. Thus the study of ethene oxidation is crucially important for all alkyl hydrocarbons. 

In the oxidation of f-butanol, acetone and isobutene appear [46] as intermediate species. Acetone can arise from two possible sequences. In one,... 

In the second scheme, the alkane is transformed to the olefin by oxidehydro-genation, and the outlet stream is sent to the second oxidation reactor without any intermediate separation." Isobutane and isobutene are recycled, together with oxygen, nitrogen, and carbon oxides. Finally, the third scheme differs from the first one in that hydrogen is separated from propane/propylene after the dehydrogenation step, and oxygen is preferably used instead of air in the oxidation reactor." ... 

The reaction network for isobutane selective oxidation catalyzed by POMs consists of parallel reactions for the formation of methacrolein, methacrylic acid, carbon monoxide, and carbon dioxide. Consecutive reactions occur on methacrolein, which is transformed to acetic acid, methacrylic acid, and carbon oxides. ° Methacrylic acid undergoes consecutive reactions of combustion to carbon oxides and acetic acid, but only under conditions of high isobutane conversion. Isobutene is believed to be an intermediate of isobutane transformation to methacrylic acid, but it can be isolated as a reaction product only for very low alkane conversion. ... 

Glycine <-butyl ester is a valuable intermediate for the preparation of peptides of glycine, since the labile /-butyl group can readily be removed by add under conditions which do not affect the blocked amino grouping. The present method using /-butyl chloroacetate is superior to that using the bromo derivative, since chloride is cheaper to prepare, less lachrymatory and more easily separated, by fractional distillation, from the /-butyl azidoacetate. The method is also less cumbersome than the procedure using isobutene. 

The first reactions concerned (Simons and Archer, 27) alkylation of benzene with propylene to form isopropylbenzene, with isobutene to form f-butylbenzene and di-f-butylbenzene, and trimethylethylene to form amylbenzene. Later on (Simons and Archer, 28) studied these and other reactions in more detail and showed that high yields could be obtained and that the product was not contaminated with tars or other obnoxious impurities. It was shown that the products obtained with trimethylethylene were mono- and di-f-amylbenzene, that phenyl-pentane resulted from the use of pentene-2, and that cyclohexene produced cyclohexylbenzene. Cinnamic acid reacted with benzene (Simons and Archer, 29) to form /3-phenylpropionic acid and allyl benzene reacted with benzene to form 1,2-diphenylpropane. It is interesting to note that although allyl alcohol reacted with benzene to form 1,2-diphenylpropane, the intermediate in the reaction, allylbenzene, was isolated and identified. This shows that in this case the hydroxyl reacted at a more rapid rate than the double bond. Both di- and triisobutylene reacted with phenol (Simons and Archer, 30) at 0°, when using hydrogen fluoride containing only relatively small quantities of water, to form f-butyl-benzene, but diisobutylene with 70% hydrogen fluoride produced p-f-octylphenol. Cyclohexene reacted with toluene to form cyclohexyl-toluene and octene-1 rapidly reacted with toluene to form 2-octyltoluene (Simons and Basler, 31). 

Treatment of 7-chloroamine 363 with potassium /i t/-butoxide in refluxing THE gave rise to a mixture of (Z-tert-butyl)-5,5-dimethyl-5,6-dihydro-4f/-l,3-oxazine 366 and 1-pivaloylazetidine 367 (Scheme 67). The heterocycles 366 and 367 were formed through generation of the Favorskii intermediate 364 by dehydrocyanation, which was followed by opening of the cyclopropylideneamine by /r-rt-butoxide with the subsequent loss of isobutene and a subsequent intramolecular N-alkylation or O-alkylation of the amide anion 365 <1999EJ0239>. 

For many reactions the type of intermediate that is involved may be deduced from a study of a family of reactants. For example, by noting that in allylic oxidation the order of reactivity is isobutene > trans-2-butene > cis-2-butene > 1-butene one may deduce that an allyl radical or cation is an intermediate. For other oxidations, if the reaction rate order is primary > secondary > tertiary, then an anionic intermediate is implicated. However, care must be taken that the formation of the intermediate is involved in the ratedetermining step and that there are no adsorption equilibrium effects. To rule out the latter, the reaction should be carried out at conditions of low coverage. 

The isobutene oligomerization is a highly exothermic reaction, carried out via the carbenium ion mechanism, which is thermodynamically favoured at low temperature. The kind of products obtained as well as the conversion and stability at constant temperature and pressure will depend on the reaction GHSV, which determine the intermediate carbenio ion formed during the first steps. 

The main chemistry generates some products (HCrO ) reminiscent of the Craq002+/CH3CH0 reaction, but there is clearly another path, responsible for the formation of C02 and isobutene. The latter was formed in comparable yields in air- and 02-saturated solutions, which rules out the disproportionation of tert-butyl radicals (formed by decarbonylation) as the source of this product. It is much more likely that the initially formed intermediate branches into two sets of products, Craq03++ CMe3C(0)0H and (Cr3++ C02 +isobutene, as shown in Scheme 8. 

The obvious candidates for the two competing reactions are those shown in Eqs. (24) and (25). The mechanisms of the two reactions are probably similar, although it was not possible to show whether reaction 25 produced isobutene. The expected chemistry is shown in more detail in Eq. (32). In a less appealing possibility, the tentative peroxo intermediate would cleave homolytically to yield alkyl and alkoxyl radicals, a route that is thermodynamically much less favorable than reaction 32. 

The acidity of a clay can be either of the Brpnsted (H+ donor) or Lewis (electron pair acceptor) type. Even at temperatures below 100 °C, tertiary carbocation intermediates can be generated on clays with high Brpnsted acidity through protonation of the C=C double bond in secondary alkenes, as in the clay-catalyzed formation of MTBE from methanol and isobutene ... 

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