Olefins, alkylation with

As hydrogen fluoride functions with equal ease in alkylation with olefins, alkyl halides, or alcohols, and in acylation with acids, acid anhydrides as well as acyl halides, a wide choice of reagents is possible and a separate operation of the reconversion of them is often saved. With aluminum chloride the alkyl halides and acyl halides are the preferred reagents and frequently must be made from more plentiful, cheaper, and readily available substances. 

Protic acids are usually used as catalysts for alkylation with olefins rather than with alkyl halides. Anhydrous hydrogen chloride, in the absence of metal halides, is a catalyst for the alkylation of benzene with terf-butyl chloride only at elevated temperatures96 where an equilibrium with isobutylene may exist. Other alkyl halides and cyclohexene were also reacted with benzene and toluene using this catalyst. 

Desorption Influence on Benzene Alkylation with Olefins over Y Zeolites... 

The skeletal isomerization of straight-chain paraffins is important for the enhancement of the octane numbers of light petroleum fractions. The isomerization of H-butane to isobutane has attracted much attention because isobutane is a feedstock for alkylation with olefins and MTBE synthesis. It is widely believed that the low-temperature transformation of n-alkanes can be catalyzed only by superacidic sites, and this reaction has often been used to test for the presence of these sites. 

Both of these facts do explain the nickel effect. The first finding is the basis for the syntheses of Wilke s nickel(0)-olefin complexes (1 and 2) [Eq. (3)] 10), while the second reflects the fact that 1, 2, and (C2H4)3Ni(0) (3), which is obtained from 1 and ethylene 11, 12), are highly active catalysts for the transalkylation of aluminum alkyls with olefins as, for example in Eq. (4) 11, 13). 

Transfer of two hydride ions and one proton would result in DMH. Since the methyl groups could migrate on the chain, DMH s other than 2,5-DMH could be produced. Some t-butyl cations dissociate into isobutylene and protons hence this method could occur during alkylation with olefins other than isobutylene. Reaction N is probably only of minor Importance in most cases, however, since only small concentrations of free isobutylene are thought to occur at the acid-hydrocarbon interface most isobutylene quickly protonates to form t-butyl cations. 

Olefinic malonic esters are obtained directly by alkylation with olefinic halidesor by alkylation of alkylidenemalonic esters obtained from the Knoevenagel condensation (method 37). 

Lithium butoxides increase the rate of reaction of lithium alkyls with olefins in cyclohexane or hexane but decrease it in benzene. The propagation rate is, however, decreased in both types of solvent [77, 78] according to information presently available. In fact, as far as is known, butoxides reduce rates where the mechanism has been suggested to be dissociative and increase them in the other cases. More data are still required to confirm that this always happens. The experiments with polystyryllithium [77] show that the polymer dimers in solution are not dissociated by lithium fert.-butoxide as would be expected if mixed aggregates of the type (PstLi. BuOLi ) were formed. In this case, at least, the rate effect appears to be caused by addition of butoxide to the polystyryllithium dimers. The reaction still shows half order characteristics, and the rate depression is almost complete at a 1 1 ratio of butoxide to polymer chains. The major species present in solution would seem to be (PstLi. BuOLi)2 at this point. Similar results have been obtained with polyisoprenyllithium in cyclohexane [78]. The nature of... 

In aromatic alkylation with olefins, the solid acid catalyst based process has instead largely substituted the homogeneous acid catalysis process. This evidences that the change of substrate (isobutane vs. aromatic) could change completely the applicability of one technology with respect to another. 

Aromatic fractions can be alkylated with olefins to produce products which are used as synthetic lubricants.An aromatic fraction boiling between 160 and 210°C is generally alkylated with Cm to Cw olefins in a ratio of about 2 1. A higher-boiling aromatic fraction (boiling between 210 and 260°C) is reacted with Cs to Cw olefins in a ratio of 1 3. Aluminum chloride promoted with hydrogen chloride is the catalyst normally used. When the alkylated aromatics are blended with thickeners such as polyisobutylene, the mixture obtained is an excellent lubricant with a good viscosity index, stability, and pour point. 

Mechanisms for Liquid-phase Alkylations of Hydrocarbons. Either Friedel-Crafts or protonic acid catalysts are often used when liquid isoparaffins or aromatic hydrocarbons are alkylated with olefins. These catalysts are generally considered to be proton donators which form carbonium ions. The basic reactions are probably similar for all catalysts, and the reaction temperatures are all relatively close to room temperature, about —40 to 30°C. 

Svlfuric Add Alkylation. Despite some disadvantages, such as acid-reGOLYery expense and refrigeration to minimize oxidation, about four fifths of the alkylate produced for motor fuels is based on sulfuric acid as a catalyst. As with HF alkylation, isobutane is alkylated with olefins (other than ethylene), and a flow diagram for such a process is ven in Fig. 14-5. 

The following mechanism, analogous to that suggested for alkylation with olefins, explains the experimental observations. 

Alkylaromatics-Alkylation with Olefins.- The base catalysed alkylation of alkyaromatics with olefins results in selective addition of an olefin to the side chain. These reactions have... 

Fluorinated silica and alumina have also been used for isobutane alkylation with olefins in a batch reactor at 0°C. The fluorinated alumina was active only when mixed with BF3 H2O, but the fluorinated silica was active by itself The selectivity to trimethylpentanes obtained with these catalysts is much lower than that obtained with H2SO4 as a catalyst (48). At 80°C, however, F/AI2O3 catalysts are active for isobutane/2-butene alkylation, though relatively low butene conversions (27% for the most active catalyst containing 1.3% F) are obtained (49). As expected, octenes are the predominant hydrocarbons in the Cg fraction at such a low conversions. The F/AI2O3 catalysts contained both Bronsted and Lewis acid sites in a proportion that depends on the F loading. A good correlation between... 

For the alkylation with olefins, a rhenium complex proved to be the best catalyst, which provided only monoalkylated products, even in the presence of a surplus of the reagent (see 444). With sterically hindered olefins, the para-alkylated compounds (see 446) turned out to be by far the main reaction product [152]. 

Phenols can also be alkylated with olefins. The alkylation of m-cresol with propylene to produce thymol (2-isopropyl —5-methylphenol) was studied with metal sulfates and alumina as catalysts.A 90% selectivity to thymol was obtained at the phenol conversion of 63% from a 1 1 mixture of phenol and propylene at 673 K. 

The aromatics alkylation with olefins is a well-known technology, especially in the case of ethylbenzene (a Mobil-Badger process [109]) and cumene production [110], Ethylbenzene synthesis can be catalyzed by diverse modified HZSM-5, BEA, rare-earth Y, and MCM-22 zeohtes. In most cases, the selectivity is pretty high (99%), but the process must be carried out at a large excess of benzene and the conversion of the latter typically does not exceed 20-25% at 400°C and WHSV= 3 h . For cumene production, a few commercial processes have been developed by CD-Tech (Y zeolite), Lummus-Unocal (Y zeolite), Enichem (H-BEA), Mobil-Raytheon (MCM-22), Dow Chemical (dealuminated mordenite (MOR)), and UOP (a Q-Max process with MgSAPO-31). 

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