Isobutene in sulfuric acid

If du Vigneaud and Bodanszky had wanted a carboxylic-acid-protecting group that was more stable towards attack by nucleophiles, they could have made a t-butyl ester with isobutene in sulfuric acid. 

Deckwer,W.-D. "Absorption and reaction od isobutene in sulfuric acid". Chem.Engng.Sci. 32 (1977) 51. 

In contrast to the low activation barrier for the protonation of isobutene in sulfuric acid, the computed activation energies for isobutene protonation in a zeolite using comparable models are much higher, namely 70 kJ/mol. In Chapter 4, the formation of protonated isobutene in mordenite is considered in more detail. It is concluded that protonation is an activated process with respect to the adsorbed rr-complex and that the protonated isobutene forms an alkoxy complex. This chemistry is very similar to that discussed here for protonation of isobutene with (112804)2 (Fig. 5.13a). 

The applicability of model <23> as formulated here with consideration of gas flow and pressure variations has been demonstrated by Deckwer [34] for absorption and hydration of isobutene in sulfuric acid and by Deckwer et a1. [35, 36] for CO2 mass transfer. The physical absorption of CO2 in water proved to be a very useful tool to simulate conditions which often prevail in chemical processes, i.e. large amounts of gas are absorbed in a liquid under drastic changes of gas volume flow. As an example Fig. 11 shows CO2 gas phase profiles measured in a BC of 20 cm diameter and 7.2 m height. As shown in Fig. 11, the profiles computed on the basis of model <23> excellently describe the measured data. It is understood that... 

Deckwer, W.-D. Absorption and Reaction of Isobutene in Sulfuric Acid III. Considerations on the Scale up of Bubble Columns. 

When the absorption and reaction of isobutene in sulfuric acid was studied in a tall bubble column it was found that the conversions measured at the column exit could be explained reasonably only on the base of this improved model ( ) However, the comparison of experimental and predicted concentration profiles would present a better mean to prove the validity of a parti-... 

A combination of the thermal polymerization process and the U.O.P. catalytic process was introduced in 1937 at the Shamrock Oil and Gas Co., Sunray, Tex. (28). In 1934 the Shell Development Co. introduced the cold acid process (18), which selectively polymerizes isobutene, using sulfuric acid as catalyst. The hot acid process was also developed by them and differed from the cold acid process in polymerizing all C4 olefins. Both products are predominantly the dimer. The cold acid process produces a large pro-... 

Derivation Absorption of isobutene from cracking petroleum or natural gas in sulfuric acid with subsequent hydrolysis by steam. 

BHT can be produced by direct dialkylation of p-cresol with isobutene with sulfuric acid catalysis at 50 to 80 °C, or by monobutylation of m-/p-cresol mixtures. In the latter method, it is necessary to separate the monobutylated m-/p-mixture and further butylate the 2-tert-butyl-p-cresol to 2,6-di-tert-butyl-p-cresol. 

Isobutene is separated from C4 crack fractions by absorption and reaction in sulfuric acid solutions [34] ... 

An alternative method for separating the hutenes is hy extracting isobutene (due to its higher reactivity) in cold sulfuric acid, which polymerizes it to di- and triisohutylene. The dimer and trimer of isobutene have high octane ratings and are added to the gasoline pool. 

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. 

Alkylation (Figure 4.11) combines low-molecular-weight olefins (primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst, either sulfuric acid or hydrofluoric acid. The product, called alkylate, consists of... 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

C12H15N3O6, Mr 291.21, mp 114°C, does not occur in nature. It forms yellow crystals with a persistent musk odor. Musk xylol is prepared by alkylation of m-xylene with isobutene and subsequent nitration with a sulfuric acid nitric acid... 

Most butenes are produced in the cracking process in refineries along with other C-4 fractions such as the butanes. Butenes are separated from other compounds and each other by several methods. Isobutene is separated from normal butanes by absorption in a sulfuric acid solution. Normal butenes can be separated from butanes by fractionation. The close boiling points of butanes and butenes make straight fractional distillation an inadequate separation... 

Butenes are used extensively in gasoline production to produce high-octane gasoline compounds. In alkylation reactions, butenes combine with isobutane to produce branched gasoline-range compounds (see Butane). Isooctane can be produced by dimerization of isobutene in the presence of sulfuric acid. Dimerization is the combination of a molecule with itself to produce a molecule called a dimer. The dimer has exactly twice the number of atoms in the original molecule. Therefore the dimerization of isobutene produces two dimers with the formula C H,... 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

Friedel-Crafts alkylation of benzo[6]thiophene has received little attention. The published results, which deserve reexamination, indicate that exclusive 3-substitution occurs in some cases, whereas in others, 2-substitution predominates. Benzo[6]thiophene is alkylated with isopropyl chloride, isopropanol, or propene in the presence of various acid catalysts under a variety of reaction conditions to give a mixture of 2- and 3-isopropylbenzo[6]thiophene in which the 2-isomer predominates (78-92%).358 410 In contrast, alkylation with isobutene in the presence of either 80% sulfuric acid415 or 100% phosphoric acid416 is said to afford exclusively 3-/er<-butylbenzo[6]thiophene in yields of 100 and 75%, respectively. In neither case was the structure of the product rigorously confirmed. Likewise, 3-Jeri-amylbenzo [63-thiophene is the exclusive product of alkylation with tert-amyl alcohol in the presence of stannic chloride414 alkylation with pent-l-ene, hex-l-ene, and a Ci8 propylene polymer is also claimed to give... 

R-Bromo-5-methylpentanoic acid (123.0 g, 0.63 mol) was dissolved in DCM (400 ml) and the solution cooled to -40°C while isobutene was condensed in to roughly double the volume. Maintaining the temperature at -40°C concentrated sulfuric acid (4 ml) was added dropwise. When the addition was complete the reaction was allowed to warm to room temperature overnight. The resultant solution was concentrated to half the volume by removing the solvent at reduced pressure, then the DCM was washed twice with an equal volume of 10% sodium bicarbonate solution. The organic layer was dried over magnesium sulfate and the solvent removed under reduced pressure to leave the t-butyl 2R-bromo-5-methylpentanoate as a yellow oil (148.1 g, 0.59 mol, 94%). 

In the process (Fig. 1), the crude C4 fraction is extracted with acetone, furfural, or other solvents to remove alkanes such as n-butanc, iso-butane, and small amounts of pentanes, leaving only 1- and 2-butenes and isobutene. The isobutene is removed by extraction with sulfuric acid because it oligomerizes more easily. 

Similarly, zeolites can catalyze the addition of ammonia to an olefinic double bond, as is exemplified by the BASF process for the production of tert-butylamine by reaction of isobutene with ammonia, in the vapor phase, over a rare earth exchanged ZSM-5 or Yzeolite (Fig. 2.20) [58, 59]. This process has an atom efficiency of 100% and replaced a conventional synthesis via a Ritter reaction, which employs HCN and sulfuric acid and generates formate as a coproduct. 

The traditional method for preparing (m-butyl ethers involves reacting a large excess of isobutene with a solution of the alcohol in dichloromethane in the presence of concentrated sulfuric acid, p-toluenesulfonic acid or phosphoric acid and the method is effective for protecting the side chain hydroxyl functions of serine, threonine [Scheme 4.123], and tyrosine.223 224 A more convenient method involving use of Amberlyst H-15 resin in hexane as the acid catalyst deserves wider attention.217... 

The classical method for making tert-butyl esters involves mineral acid-catalysed addition of the carboxylic acid to isobutene but it is a rather harsh procedure for use in any but the most insensitive of substrates [Scheme 6.33].80-82 Moreover, the method is hazardous because a sealed apparatus is needed to prevent evaporation of the volatile isobutene. A simpler procedure [Scheme 6.34] involves use of tert-butyl alcohol in the presence of a heterogeneous acid catalyst — concentrated sulfuric acid dispersed on powdered anhydrous magnesium sulfate. 3 No interna] pressure is developed during the reaction and the method is successful for various aromatic, aliphatic, olefinic, heteroaromatic, and protected amino acids. Also primary and secondary alcohols can be converted into the corresponding /erf-butyl ethers using essentially the same procedure (with the exception of alcohols particularly prone to carbonium ion formation (e.g. p-... 

The 9-fluorenylmethoxycarbonyl group is another distinguished contribution from the Carpino laboratory198199 to the solution-phase synthesis of peptides and latterly it has been adapted to solid-phase peptide synthesis too.200 The Fmoc group is exceptionally stable towards acid thus, carboxylic acids can be converted to acid chlorides with thionyl chloride201 or terf-butyl esters using sulfuric acid and isobutene.202 Furthermore, Fmoc groups are unscathed by HBr in... 

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