Butene-1 and isobutene

Studies on the photolysis of butene-1 at 1849 A have been made by Harumiya et and by Borrell and Cashmore . Ethane and 1,5-hexadiene are the most important products. Borrell and Cashmore report a total of twenty-five products which in addition to the ethane and 1,5-hexadiene include methane, ethylene, acetylene, propene, propane, allene, cis- and franj-butene-2, 3-methylbutene, n- and isopentane, cis- and fra j-pentene-2, pentene-1, as well as various Cg, C and Cg compounds. The following reactions explain these products. 

Both studies lead to the conclusion that the main mode of decomposition is the rupture of a bond p to the double bond, with the C-C bond rupture in reaction (2) being about 6 times more important than the C-H bond rupture of reaction (3). Inert gases are found to decrease the yield of all products. Oxygen completely eliminates certain products, which are presumably formed by free-radical proces- 

The photolysis of isobutene was first examined by Kieffer and Howe and has been examined in more detail recently by BorrelP . Fewer molecular products are formed compared with the photolysis of the other butenes. The main decomposition mode is the rupture of the C-H bond J3 to the double bond, viz. 

It should be noted that in the photolysis of all the butenes the breaking of the bond p to the double bond is the most important primary process. 

The photolysis of higher olefins has not received a lot of attention. The reader is referred to the original literature for the following compounds m-pentene-2, Borrell and Cashmore cw-hexene, Chesick .  

---

Dialkylhalonium ions are known to be effective alkylating agents for arranatic compounds and their reactions with olefins have also been studied Dimethylbromonium hexa-fluoroantimonate has been shown to initiate the cationic polymerisation of butene-1 and isobutene in liquid SOj ... 

It is important to remove all oxygen, dienes and acetylenes from the feed to the metathesis reactor. Furthermore, the C4 stream needs to contain the minimum practical level of butene-1 and isobutene to minimize the metathesis reaction of the C4 hydrocarbons, which results in the formation of C5 and Ce olefins. The higher olefins lead to polymer formation and catalyst deactivation. An excess of ethylene normally suppresses the C4 reactions. A typical steam cracker C4 stream, which has been subjected to selective hydrogenation to remove impurities and fractionation to provide a suitable butene-2 rich raffinate-2, or the butene-2 rich efflnent from an MTBE unit, can provide a suitable feed for the metathesis reactor. The catalyst operating cycle with a rhenium catalyst is usually fairly long. Regular catalyst regeneration may be necessary and the catalyst can last for several years. 

Depending on the method used to separate isobutene or butene-1, and in accordance with the deared application for the remainiag components the Q cuts initially available, supplonentary treatments may exhibit a range of complexity. Hence it may or may not be possible, both for technical and ecopomic reasons, to incorporate them in the extraction facilities that ser e as a basis for the upgrading schemes selected. In certain cases, in fact, one of the primary separation processes already examined can be used as an auxiliary for another technology, that is also designed as an initial step. 

Summarising the essentials, two sub-mechanisms appear to operate in the oxidation of the four alkenes just discussed. With butene-1 and butene-2, the mechanism is sharply dependent on HO2/H2O2 chemistry, whereas with the unique cases of and isobutene, [HO2] is relatively low, and the kinetics of allyl and methylallyl reactions through radical-radical processes are of key importance. The recombination products HDE and DMHDE are responsible through homolysis and reaction with O2 for the striking autocatalysis observed (Fig. 1.17). 

Polybutenes are produced by polymerisation of a hydrocarbon stream containing isobutene, other butene olefins (butene-1 and butene-2) and butanes. The main... 

The currently practiced process is a two-step process, comprising -butane isomerization and successive isobutane dehydrogenation. The n-butane dehydroisomerization (Reaction 5.3) involves the dehydrogenation of n-butane (Reaction 5.1) and successive isomerization to isobutene (Reaction 5.2). The main products measured were normal butene, isobutane, and isobutene ... 

The chromium complexes are CrCl3L3 and CrCl2L2(NO)2, wherein the ligand L are pyridine and tri-n-butylphosphine in conjunction with ethylaluminum dichloride, effect simple dimerization of ethylene at 50°C [133-135]. A conversion of 4700 g butenes per g of chromium complex is achieved with the catalyst CxCX i -Etpy),. The butene fraction consists of 1-butene (50%), trans-2-butene (32%), ds-2-butene (18%), and isobutene (0.1%). Cr or Cr species may be involved in the reaction. Here chromium atoms are probably associated with the organoalu-minum halides to form bridged chromium-halogen-aluminum species. 

Xl.l Butenes—Butene-1, butene-2, and isobutene may be avetaged Vi, Vi, Vi. However, when a straight average is applied, limit the butenes total to 10 to 15 mole % to hold maximum error of lighter components to 0.5 mole % and limited to 5 mole % to keep maximum error of lighter components to 0.1 mole %. For a more accurate determi-... 

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. 

Ethyl-methyl 1-Butene, (Z)- and (E)-butene, methylcyclopropane (E)-Butene, isobutene, methylcyclopropane... 

The industrial reactions involving cis- and trans-2-butene are the same and produce the same products. There are also addition reactions where both 1-butene and 2-butene give the same product. For this reason, it is economically feasible to isomerize 1-butene to 2-butene (cis and trans) and then separate the mixture. The isomerization reaction yields two streams, one of 2-butene and the other of isobutene, which are separated by fractional distillation, each with a purity of 80-90%. Table 2-3 shows the boiling points of the different butene isomers. 

Other olefins that are commercially alkylated are isobutene and 1- and 2-butenes. Alkylation of isobutene produces mainly 2,2,4-trimethylpen-tane (isooctane). 

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). 

The reactions of Y with four butene isomers, namely 1-butene, cis-2-butene, trans-2-butene, and isobutene, were studied at a collision energy (/ ycoii) of 26.6kcal/mol (see Table 2). In reactions with 1-butene and cis- and trans-2-butene, four processes were observed ... 

Fig. 41. Proposed mechanisms for the reactions (a) Y + propene, (b) Y + cis-2-butene, (c) Y + 1-butene, (d) Y + isobutene. Note that the mechanism for Y + trans-2-butene is similar to that for Y + cis-2-butene and so is not shown. Double-sided arrows indicate resonance structures. See text for details.

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

Several review articles [37-40] have been written discussing the use of molecular sieves for the isomerization of light olefins, especially butene. The major driving force was the requirement in the 1990 amendments to the Clean Air Act in the United States that required the addition of oxygenates to gasoline in amounts up to 2.7wt% oxygen in the final gasoUne product [37]. The primary additive chosen to meet these requirements was MTBE, with lesser amounts of the ethyl ether (ETBE) or tert-amyl methyl ether (TAME) as supplements. One major possible route to meet these requirements was the isomerization of linear butenes (1-butene, cis-2-butene and trans-2-butene) into isobutene (2-methyl-l-propene). 

The crude C4 fraction is extracted with acetone, furfural, or other solvents to remove alkanes such as -butane, isobutane, and small amounts of pentanes, leaving only 1- and 2-butenes and isobutene. The isobutene is removed by reaction with sulfuric acid and water because it reacts more easily, being able to form a tertiary carbocation. 

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. 

There is evidence that both ionic and free radical species are involved in the degradation and depolymerization of poly (olefin sulfone) s by high energy radiation (70). Thus, the yields of olefins from poly (1-butene sulfone) at 30 °C (the sample was heated to 70 °C during removal of the gaseous products) are shown in Table II. The butene is not solely 1-butene, but comprises significant proportions of all three isomers, 1-butene, 2-butene and isobutene. 

Butadiene is available commercially as a liquefied gas underpressure. The polymerization grade has a minimum purity of 99%, with acetylene as an impurity in the parts-per-million (ppm) range. Isobutene, 1-butene, butane and cis-l- and Zrc//7.s-2-butcnc have been detected in pure-grade butadiene (Miller, 1978). Typical specifications for butadiene are purity, > 99.5% inhibitor (/c/V-butylcatecliol). 50-150 ppm impurities (ppm max.) 1,2-butadiene, 20 propadiene, 10 total acetylenes, 20 dimers, 500 isoprene, 10 other C5 compounds, 500 sulfur, 5 peroxides (as H2O2), 5 ammonia, 5 water, 300 carbonyls, 10 nonvolatile residues, 0.05 wt% max. and oxygen in the gas phase, 0.10 vol% max. (Sun Wristers, 1992). Butadiene has been stabilized with hydroquinone, catechol and aliphatic mercaptans (lARC, 1986, 1992). 

The reaction of CH2 with cyclopropane1617 46177 gives excited methyl-cyclopropane which is deactivated or undergoes structural isomerization to butene-1, butene-2 (m and trans), and isobutene. The lifetime of methylcyclopropane wa6 found to depend on the CH2 source. 

The addition of HX to alkenes proceeds according to the Markownikoff rule, i.e. the halogen is attached to the more substituted carbon atom [321—323], The reactivity order of butenes was found to be dependent on the nature of the catalyst. Over MgS04, the order was isobutene > trans-2-butene > 1-butene > cis-2-butene but with CaCl2, the reactivity decreased in the order isobutene > m-2-butene > 1-butene > trans-2-butene [321], Propene is more reactive than ethylene [318], Earlier reports that tert-butylchloride is formed from 1-butene and hydrogen... 

In the case of propylene and 1,3-butadiene the lifetimes can be readily evaluated from the trends in Figures 1 and 2. In doing this, it is assumed that sufficient energy is removed in a single collision to prevent decomposition of the hot molecule. The values obtained in this manner are given in Table I. For isobutene and butene-1 approximate values... 

Sato and Cvetanovi6 (88) studied in some detail the photooxidation of 1-butene and isobutene at 3660 A. The 1-butene exhibited all the features of the olefin reactions with oxygen atoms produced by the N2O technique. The addition products, a-butene oxide, n-butyraldehyde, and... 

---