Isobutane formation

Isobutane formation is accounted for by alkylation to form C8+ surface intermediate species followed by P scission.300,305 One possible pathway is depicted as follows ... 

Cs2,s indicates CS25H05PW12O40. The rate for isobutane formation moi g 1 s l. 1-C4, C, C2, C3, C4 =, and C5 indicate isobutane, methane, ethane, propane, butenes, and pentanes. dM1F = 41 ghmol"1. MIF = 18ghmor, where M is the catalyst mass and F is the total flow rate. 

The coexistence of metal and HPA reveals a unique catalytic bifunctionality. For Pt-Cs2.5Ho.sPWi204o, the activity of the -butane isomerization is remarkably enhanced in the presence of H2. The rate of isobutane formation at 573 K is comparable with or higher than those of Pt-H-ZSM5 and Pt-SC>4 /ZrC)2 while the selectivity of HPA is much higher [100, 101]. 

Table 2 gives the yields of the various products in Co radiolysis of gaseous cyclopropane obtained by the several workers. It shows a good agreement of the yields of the main products obtained in the various studies. However, there are some disagreements, e.g. for propane or isobutane formation. The controversy concerning the G-value for propane formation can be explained if von Bunau and Kuhnert s system included small amounts of alkanes which were found to increase the yield of propane from 0.5 to 1.0. 

The yields of propane and propene were found to be linearly dependent on the concentration of tritium. Temperature has no effect on the initial rate of formation of propane or propene. NO inhibits completely the formation of propane, but only partly that of propene. Propane can still be formed by hot labeling, through ring-opening and subsequent abstraction of hydrogen—a process which is inhibited by a radical scavenger. Isobutane formation was independent of tritium concentration and temperature and was completely inhibited by the addition of nitric oxide. In the presence of NO, the yield of... 

Increasing the constant for n-butane adsorption onto S2 (1<2) also leads to a significant increase of 111% in the isobutane formation rate. 

Figure 6. Turnover frequency for isobutane formation (filled circles) and n-butane formation (open circles) vs. oxygen coverage.

Thus the secondary and primary deuterium isotope effects determined in this study also indicate that entropy and zero-point energy factors associated with breaking of the C—D bond and migration in the activated complexes are important for the structural isomerization to yield butene-1 and butene-2, and reaction path B (equation 197) must be included in the mechanistic considerations concerning the cyclopropane isomerization. But the higher activation energy for isobutane formation (g = 64.3 kcal mol" ) than that for butene-2 or butene-1 (Q = 62.0 0.6 kcal mol" ) indicates also that the rupture of... 

Solve the same problem for propane and isobutane (2-methylpropane). The bond matrix is the same as it is for n-butane, but the enthalpy of formation is somewhat different (n-butane) = —127.1 kJ mol vs. (isobutane) = —134.2... 

When usiag HF TaF ia a flow system for alkylation of excess ethane with ethylene (ia a 9 1 molar ratio), only / -butane was obtained isobutane was not detectable even by gas chromatography (72). Only direct O -alkylation can account for these results. If the ethyl cation alkylated ethylene, the reaction would proceed through butyl cations, inevitably lea ding also to the formation of isobutane (through /-butyl cation). 

Acetone is a coproduct of butane LPO. Some of this is produced from isobutane, an impurity present in all commercial butane (by reactions 2, 13, 14, and 16). However, it is likely that much of it is produced through the back-biting mechanisms responsible for methyl ketone formation in the LPO of higher hydrocarbons (216). 

Autoxidation of alkanes generally promotes the formation of alkyl hydroperoxides, but d4-tert-huty peroxide has been obtained in >30% yield by the bromine-catalyzed oxidation of isobutane (66). In the presence of iodine, styrene also has been oxidized to the corresponding peroxide (44). 

Isomerization. Isomerization of any of the butylene isomers to increase supply of another isomer is not practiced commercially. However, their isomerization has been studied extensively because formation and isomerization accompany many refinery processes maximization of 2-butene content maximizes octane number when isobutane is alkylated with butene streams using HF as catalyst and isomerization of high concentrations of 1-butene to 2-butene in mixtures with isobutylene could simplify subsequent separations (22). One plant (Phillips) is now being operated for this latter purpose (23,24). The general topic of isomerization has been covered in detail (25—27). Isomer distribution at thermodynamic equiUbrium in the range 300—1000 Kis summarized in Table 4 (25). 

Di-f-butyl sulfone is different from the other dialkyl sulfones in that RH is mainly alkene and not alkane [G(isobutene) = 3.2 and G(isobutane) = 1.2]. The preference for isobutene over isobutane means that the formation of the alkene cannot be due to disproportionation of two t-butyl radicals but is due to a hydrogen atom expulsion as suggested by Bowmer and O Donnell70... 

It was shown that no rearrangement of isobutyl radical to tert-butyl radical (which would involve the formation of a more stable radical by a hydrogen shift) took place during the chlorination of isobutane. 

Several of the lower molecular weight aliphatic compounds, in a mixture, are part of the roasted coffee aroma. A nine-compound mixture with roasted coffee aroma contained isopentane, n-hexane, acetaldehyde, dimethyl sulfide, propanal, isobutanal, isopentanal, methanol, and 2-methylfuran.20 In addition, the freshness of aroma and taste has been correlated with 2-methylpropanal and diacetyl. When the concentration of these falls off, so does the taste.21 Other aliphatic compounds that are steadily lost from ground roasted coffee, unless it is vacuum packaged, include methyl formate, methyl acetate, methyl thioacetate, and acetone.22 The concentrations in roast coffee for four compounds whose contribution to the fresh flavor have long been known are dimethyl sulfide (4 ppm), methyl formate (12 ppm), isobutanal (20 ppm), and diacetyl (40 ppm). The taste thresholds are 0.1, 0.5, 0.5, and 1.0 ppm, respectively, in the brew made with 5 g coffee per 100 ml water.15... 

The reaction of tert-butyl esters with Et3SiH/TFA results in the reductive deprotection of the ester and formation of isobutane. The yields of the isobutane are not recorded, but the acids are obtained nearly quantitatively (Eq. 150).307 In a similar manner, the lactone shown in Eq. 151 is converted into the acid in good yield.308 In like manner, the reductive deprotection of allyl esters provides the carboxylic acids in high yields.270... 

Blatter, F., Sun, H. and Frei, H. (1996). Highly selective formation of tert-butyl hydroperoxide from the reaction of isobutane and 02 in a zeolite under visible light. Chem. Eur. J. 2, 385-389... 

Alkylation of isobutane with C3-C5 alkenes in the presence of strong acids leads to the formation of complex mixtures of branched alkanes, called alkylate, which are excellent blending components for gasoline. Alkylate has a high octane... 

Theoretically, even the direct alkylation of carbenium ions with isobutane is feasible. The reaction of isobutane with a r-butyl cation would lead to 2,2,3,3-tetramethylbutane as the primary product. With liquid superacids under controlled conditions, this has been observed (52), but under typical alkylation conditions 2,2,3,3-TMB is not produced. Kazansky et al. (26,27) proposed the direct alkylation of isopentane with propene in a two-step alkylation process. In this process, the alkene first forms the ester, which in the second step reacts with the isoalkane. Isopentane was found to add directly to the isopropyl ester via intermediate formation of (non-classical) carbonium ions. In this way, the carbenium ions are freed as the corresponding alkanes without hydride transfer (see Section II.D). This conclusion was inferred from the virtual absence of propane in the product mixture. Whether this reaction path is of significance in conventional alkylation processes is unclear at present. HF produces substantial amounts of propane in isobutane/propene alkylation. The lack of 2,2,4-TMP in the product, which is formed in almost all alkylates regardless of the feed (55), implies that the mechanism in the two-step alkylation process is different from that of conventional alkylation. 

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