Isobutylene alkylation with

Gas chromatography (gc) has been used extensively to analyze phenoHc resins for unreacted phenol monomer as weU as certain two- and three-ring constituents in both novolak and resole resins (61). It is also used in monitoring the production processes of the monomers, eg, when phenol is alkylated with isobutylene to produce butylphenol. Usually, the phenoHc hydroxyl must be derivatized before analysis to provide a more volatile compound. The gc analysis of complex systems, such as resoles, provides distinct resolution of over 20 one- and two-ring compounds having various degrees of methylolation. In some cases, hemiformals may be detected if they have been properly capped (53). 

A tertiary carbonium ion is more stable than a secondary carbonium ion, which is in turn more stable than a primary carbonium ion. Therefore, the alkylation of ben2ene with isobutylene is much easier than is alkylation with ethylene. The reactivity of substituted aromatics for electrophilic substitution is affected by the inductive and resonance effects of a substituent. An electron-donating group, such as the hydroxyl and methyl groups, activates the alkylation and an electron-withdrawing group, such as chloride, deactivates it. 

Methylphenol is converted to 6-/ f2 -butyl-2-methylphenol [2219-82-1] by alkylation with isobutylene under aluminum catalysis. A number of phenoHc anti-oxidants used to stabilize mbber and plastics against thermal oxidative degradation are based on this compound. The condensation of 6-/ f2 -butyl-2-methylphenol with formaldehyde yields 4,4 -methylenebis(2-methyl-6-/ f2 butylphenol) [96-65-17, reaction with sulfur dichloride yields 4,4 -thiobis(2-methyl-6-/ f2 butylphenol) [96-66-2] and reaction with methyl acrylate under base catalysis yields the corresponding hydrocinnamate. Transesterification of the hydrocinnamate with triethylene glycol yields triethylene glycol-bis[3-(3-/ f2 -butyl-5-methyl-4-hydroxyphenyl)propionate] [36443-68-2] (39). 2-Methylphenol is also a component of cresyHc acids, blends of phenol, cresols, and xylenols. CresyHc acids are used as solvents in a number of coating appHcations (see Table 3). 

Di-tert-butyipbenoi (2,6-DTBP) OI 2,6-bis(l,l-dimethylethyl)phenol is pioduced fiom phenol by alkylation with isobutylene under aluminum... 

Ritter Reaction (Method 4). A small but important class of amines are manufactured by the Ritter reaction. These are the amines in which the nitrogen atom is adjacent to a tertiary alkyl group. In the Ritter reaction a substituted olefin such as isobutylene reacts with hydrogen cyanide under acidic conditions (12). The resulting formamide is then hydroly2ed to the parent primary amine. Typically sulfuric acid is used in this transformation of an olefin to an amine. Stoichiometric quantities of sulfate salts are produced along with the desired amine. 

Dehydiation with POCl, followed by N-alkylation with isobutylene, gives the cyano ester intermediate, which on treatment with methylamine yields (64), a compound having good herbicidal activity (eq. 15). 

Toluenesulfonic Acid. Toluene reacts readily with fuming sulfuric acid to yield toluene—sulfonic acid. By proper control of conditions, /)i7n7-toluenesulfonic acid is obtained. The primary use is for conversion, by fusion with NaOH, to i ra-cresol. The resulting high purity i7n -cresol is then alkylated with isobutylene to produce 2 (i-dii-tert-huty -para-cmso (BHT), which is used as an antioxidant in foods, gasoline, and mbber. Mixed cresols can be obtained by alkylation of phenol and by isolation from certain petroleum and coal-tar process streams. 

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). 

With propene, n-butene, and n-pentene, the alkanes formed are propane, n-butane, and n-pentane (plus isopentane), respectively. The production of considerable amounts of light -alkanes is a disadvantage of this reaction route. Furthermore, the yield of the desired alkylate is reduced relative to isobutane and alkene consumption (8). For example, propene alkylation with HF can give more than 15 vol% yield of propane (21). Aluminum chloride-ether complexes also catalyze self-alkylation. However, when acidity is moderated with metal chlorides, the self-alkylation activity is drastically reduced. Intuitively, the formation of isobutylene via proton transfer from an isobutyl cation should be more pronounced at a weaker acidity, but the opposite has been found (92). Other properties besides acidity may contribute to the self-alkylation activity. Earlier publications concerned with zeolites claimed this mechanism to be a source of hydrogen for saturating cracking products or dimerization products (69,93). However, as shown in reaction (10), only the feed alkene will be saturated, and dehydrogenation does not take place. 

Table III provides a comparison of alkylate compositions for both the liquid acid-catalyzed reactions with various feed alkenes. The data show that H2SO4 produces a better alkylate with 1-butene, whereas HF gives better results with propene or isobutylene. The products from 2-butene and also from pentenes (not shown in Table III) are nearly the same with either acid.

Cycloalkanes possessing a tertiary carbon atom may be alkylated under conditions similar to those applied for the alkylation of isoalkanes. Methylcyclopentane and methylcyclohexane were studied most.5 Methylcyclopentane reacts with propylene and isobutylene in the presence of HF (23-25°C), and methylcyclohexane can also be reacted with isobutylene and 2-butene under the same conditions.20 Methylcyclopentane is alkylated with propylene in the presence of HBr—AlBr3 (—42°C) to produce l-ethyl-2-methylcyclohexane.21 C12H22 bicyclic compounds are also formed under alkylation conditions.21 22 Cyclohexane, in contrast, requires elevated temperature, and only strong catalysts are effective. HC1—AICI3 catalyzes the cyclohexane-ethylene reaction at 50-60°C to yield mainly dimethyl- and tetra-methylcyclohexanes (rather than mono- and diethylcyclohexanes). The relatively weak boron trifluoride, in turn, is not active in the alkylation of cyclohexane.23... 

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. 

Alkylation with isobutylene under similar conditions167 and alkylation with propylene catalyzed by perfluorosulfonic acids,168 in turn, lead to 2-substituted naphthalenes. As was shown by Olah and Olah,169 the kinetic alkylation of naphthalene, even in case of rm-butylation, gives preferentially the 1-isomers, which, however, isomerize very fast to the thermodynamically preferred 2-alkylnaphthalenes. Great care is therefore needed to evaluate kinetic regioselectivities. 

Further improvements in alkylation can be achieved when an MTBE unit (acid-catalyzed addition of methanol to isobutylene to form tert-butyl methyl ether) is added before the alkylation unit.299 The MTBE unit removes the lowest-octane-producing isomer, isobutylene, from the C4 stream (and produces a very-high-octane number component, MTBE). The H2S04 alkylation unit then can be operated under better conditions to produce an alkylate with a somewhat increased octane number (0.75-1). Higher acid consumption, however, may be experienced as a result of methanol, MTBE and dimethyl ether impurities in the olefin feed. The combination of MTBE with HF alkylation offers no apparent advantages. 

The acidity dependence of the isobutane-isobutylene alkylation was studied using triflic acid modified with trifluoroacetic acid (TFA) and water in the range of acidity... 

In the petroleum industry, catalytic cracking units provide the major source of olefinic fuels for alkylation. A feedstock from a catalytic cracking units is typified by a Ci/C 4 charge with an approximate composition of propane, 12.7% propylene, 23.6% isobmaiie, 25.0% n-bulane, 6.9% isobutylene, 8.8% 1-butylene, 6.9% and 2-butylene, 16.1%. The butylenes will produce alkylates with octane numbers approximately three units higher than those from propylene. 

Superacid-catalyzed alkylation of adamantane with lower alkenes (ethene, propene, isomeric butenes) has been investigated by Olah et al.151 in triflic acid and triflic acid-B(0S02CF3)3. Only trace amounts of 1 -ferf-butyladamantane (37) were detected in alkylation with 1- and 2-butenes, whereas isobutylene gave consistently relatively good yield of 37. Since isomerization of isomeric 1-butyladamantane under identical conditions did not give even traces of 37, its formation can be accounted for by (r-alkylation, that is, through the insertion of the ferf-butyl cation into the C—H bond (Scheme 5.22). This reaction is similar to that between ferf-butyl cation and isobutane to form 2,2,3,3-tetramethylbutane discussed above (Scheme 5.21). In either case, the pentacoordinate carbocation intermedate, which may also lead to hydride transfer, does not attain a linear geometry, despite the unfavorable steric interactions. 

Two reports demonstrate that Bronsted (Olah et al., 1999) or Lewis acids (Oakes et al., 1999) may be more reactive in sc C02 than in organic solvents. The isobutane-isobutylene alkylation (eq. 2.2), which is used commercially to increase the octane numbers in automotive fuels, has been demonstrated to occur in sc C02 with several liquid acid catalysts (Olah et al., 1999). Increased selectivity for Cg-alkylates is observed in sc C02 relative to neat acid media when anhydrous HF, pyridine poly(hydrogen fluoride) (PPHF),... 

The surface active cations also improve product quality when alkylating with a typical refinery feed. Table V contains a list of additives studied with a feed containing 94 percent Isobutane and 6 percent butenes. The butenes contained 42 percent isobutylene and an equilibrium mixture of 1- and 2-butene. 

If acid-olefin reactions which occurred in this investigation at -10 C or lower also occur during conventional alkylations at 10 C or higher, some if not all of the significant differences in the type of alkylations with n-butenes and with isobutylene can be explained, as will be discussed later (10). 

More than 20 runs were made to Investigate the reaction between Isobutane and the products of first-effect reactions with Isobutylene. Alkylate was not produced until excess acid was used and larger amounts of excess acid were needed for runs at -30°C as compared to runs at -10 c (3). An acld-to-olefin ratio of about 1.0 was required at -10 C to obtain TMP s whereas a 7 1 ratio was needed at -30 C. 

The Importance of Reaction 1-2 has not yet been proved however, some as yet unidentified acid-soluble hydrocarbons (formed from Isobutylene) react with Isobutane to form alkylate (6). 

Main Olefin Reactions. Although some olefins react to form t-butyl cations, i.e. to initiate the alkylation steps as shown in Table I, most olefins react by Reactions G through K, as summarized in Table II. Reaction G-1 is the reaction in which either 2-butene or Isobutylene reacts with a t-C Hn to form a TMP . This reaction is of major importance, and it is widely accepted as being a key step in alkylation (9,10). It should be emphasized, however, that the reaction as postulated here can be but is not necessarily part of a chain sequence of reactions. 

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. 

One possible advantage of the HF process in propylene/ butylene alkylation is the production of isobutylene from isobutane effected by the hydride-ion transfer to propylene. Isobutylene is the C4 olefinic isomer which produces a significantly higher octane alkylate with HF. This shift, however, converts as much as 22% of the propylene to propane and is a debit. 

Some normal butane is also produced from butylenes but this is estimated at only 4-6%. The higher octane isobutylene alkylate and a claimed yield increase must be contrasted with normal paraffin production from olefins and a higher isobutane requirement. The typical mixed 03 = 704= feed can be made to produce a high octane alkylate with either acid catalyst by the optimization of other variables. The highest alkylate octane numbers reported are produced with sulfuric acid catalyst, alkylating with a typical cat cracker butylene olefin. 

Supplemental processes which can be operated in conjunction with alkylation and/or sulfuric acid production can influence the overall economics. Examples are (1) the integration of normal butane-to-isobutane isomerization with alkylation, utilizing common fractionation equipment and (2), utilizing 65% sulfuric acid extraction of isobutylene or isoamylene from olefins fed to alkylation, justified by monetary return on sale of the high purity iso-olefin as a petrochemical feedstock, which reduces quantity of alkylate produced and reduces isobutane required while producing still higher quality alkylate with sulfuric acid catalyst. 

Several processes are used to upgrade the C4 fraction. The isobutydene contained in the C4 cut is removed by reaction with methanol to produce MTBE. The remaining n-butenes in the C4 cut can be alkylated with isobutane catalyzed by liquid HE or H2SO4 or isomcrized into isobutylene in the presence of acid catalysts. 

SEPARATION OF META-, PARA-CRESOLS VIA ALKYLATION WITH ISOBUTYLENE... 

In the above process, usually 2 mol of isobutylene react with each mole of cresol in the presence of acidic catalyst. Dilute H2SO4 is the most popular catalyst for both alkylation and dealkylation process. Some of the plants use p-toluene sulfonic acid or even a mixture of sulfuric acid and p-toluene sulfonic acid. It is reliably learnt that at least one plant has been using some quantities of a very strong Friedel Crafts alkylation catalyst—Triflic acid or trifluoromethane... 

Ethylene is the largest volume carbon-based chemical produced in the United States. Moreover, ethylene can be converted directly to transportable fuels (ethanol or high-octane gasoline) or high-volume petrochemicals, such as ethylene glycol. Similarly, methanol is a liquid and can be used directly as a turbine or transportation fuel. It can also be converted to MTBE (methyl tertiary butyl ether) by alkylation with isobutylene. Oxyhydrochlorination of methane includes production of methylchloride as an intermediate to the production of gasoline. 

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