Isomerization Friedel-Crafts reaction

Ruthenium/Br0nsted Acid System The tandem isomerization/Friedel-Crafts reaction of aUylamides reported by Sorimachi and Terada was another early example of a cascade catalysis procedure using Brpnsted acid and metal salts as catalysts (Scheme 2.93) [127]. With the promotion of the ruthenium catalyst 342, the aUylamides isomerized to enamide X32, which was then tautomerized by a Brpnsted acid (343 or 344) to form imine X33 then the electron-enriched aromatic substrates 341 attacked the Brpnsted acid-activated imine intermediates to afford Friedel-Crafts products 345 in up to 91% yield. 

Oxazol-5(2H)-one, 2-benzylidene-4-methyl-tautomerism, 6, 186 Oxazol-5(2ff)-one, 2-methylene-isomerization, 6, 226 Oxazol-5(2H)-one, 2-trifluoromethyl-acylation, 6, 201 Oxazol-5(4ff)-one, 4-allyl-thermal rearrangements, 6, 199 Oxazol-5(4H)-one, 4(arylmethylene)-Friedel-Crafts reactions, 6, 205 geometrical isomerism, 6, 185 Oxazol-5(4ff)-one, 4-benzylidene-2-phenyl-configuration, 6, 185 photorearrangement, 6, 201 Oxazol-5(4ff)-one, 4-benzyl-2-methyl-Friedel-Crafts reactions, 6, 205 Oxazol-5(4ff)-one, 4-methylene-in amino acid synthesis, 6, 203 Oxazol-5(4ff) -one. 2-trifluoromethyl-hydrolysis, 6, 206 Oxazolones... 

A good deal of experimental care is often required to ensure that the product mixture at the end of a Friedel-Crafts reaction is determined by kinetic control. The strong Lewis acid catalysts can catalyze the isomerization of alkylbenzenes, and if isomerization takes place, the product composition is not informative about the position selectivity of electrophilic attack. Isomerization increases the amount of the meta isomer in the case of dialkylbenzenes, because this isomer is thermodynamically the most stable. ... 

It should be noted that Scheme 5.1-44 shows idealized Friedel-Crafts allcylation reactions. In practice, there are a number of problems associated with the reaction. These include polyalkylation reactions, since the products of a Friedel-Crafts alkylation reaction are often more reactive than the starting material. Also, isomerization and rearrangement reactions can occur, and can result in a large number of products [74, 75]. The mechanism of Friedel-Crafts reactions is not straightforward, and it is possible to propose two or more different mechanisms for a given reaction. Examples of the typical processes occurring in a Friedel-Crafts alkylation reaction are given in Scheme 5.1-45 for the reaction between 1-chloropropane and benzene. 

Aromatic hydrocarbons substituted by alkyl groups other than methyl are notorious for their tendency to disproportionate in Friedel-Crafts reactions. This tendency has previously limited the application of the isomerization of para- or ortho-) m ky -benzenes to the corresponding meta compounds. At the lower temperature of the present modification, disproportionation can be minimized. 

Room temperature ionic liquids have been found to be excellent solvents for a number of reactions [50b] such as the isomerization [51], hydrogenation [52] and Friedel-Crafts reactions [53]. A number of Diels-Alder reactions were recently investigated in these systems. 

Room temperature ionic liquids (RTILs), such as those based on A,A-dialkylimidazolium ions, are gaining importance (Bradley, 1999). The ionic liquids do not evaporate easily and thus there are no noxious fumes. They are also non-inflammable. Ionic liquids dissolve catalysts that are insoluble in conventional organic chemicals. IFP France has developed these solvents for dimerization, hydrogenation, isomerization, and hydroformylation reactions without conventional solvents. For butene dimerization a commercial process exists. RTILs form biphasic systems with the catalyst in the RTIL phase, which is immiscible with the reactants and products. This system is capable of being extended to a list of organometallic catalysts. Industrial Friedel-Crafts reactions, such as acylations, have been conducted and a fragrance molecule tra.seolide has been produced in 99% yield (Bradley, 1999). 

The isomeric benzo[l,2-A4,3- ]dithiophene-4,5-quinone is prepared in reasonable yields by a one-step Friedel-Crafts reaction of 3,3 -bithienyl with oxalyl chloride in refluxing 1,2-dichloroethane over 7-10 days (Equation 85) <2001JA11899>. 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

Synthesis (Tull et al. (Merck Co.), 1975 1976) Friedel-Crafts reaction of fluorobenzene and a-bromoisobutyryl bromide gives 5-fluoro-2-methylindan-1-one, which is treated with 4-methylthiobenzylmagnesium chloride to yield 5-fluoro-2-methyl-1-(4-methylthiobenzyl)indene. Condensation with glyoxylic acid in the presence of N-benzyltrimethyl ammonium hydroxide (Triton B) gives 3-carboxy methylene-5-fluoro-2-methyl-1 -(4-methylthio-ben-zyl) indene, which is isomerized in acid to 5-fluoro-2-methyl-1-(4-methylthiobenzylidene)indene-3-acetic acid. Oxidation with hydrogen peroxide affords sulindac. 

Koch Chemical Company is the only U.S. supplier of all PMBs (except hexamethylbenzene). Its process has the flexibility of producing isodurene, prehnitene, and pentamethylbenzene, should a market devdop. Koch s primary process (20) is based on isomerization, alkylation, and disproportionation conducted in the presence of a Friedel-Crafts catalyst. For the synthesis of mesitylene and hemimellitene, pseudocumene is isomerized. If durene, isodurene, or prehnitene and pentamethylbenzene are desired, pseudocumene is alkylated with methyl chloride (see Alkylation Friedel-Crafts reactions). 

Some of the organic reactions performed in ILs are hydroformylation, hydrogenation, isomerization, oligomerization, polymerization, C—C bonding, and acid-catalyzed Friedel-Crafts reactions. 

MF5 and MCI5 are strongly electrophilic see Electrophile and Electrophilic Reaction) and catalyze Friedel-Crafts reactions. The HF/TaFs system is a superacid catalyst and has been used in the selective acid-catalyzed isomerization and hydrogenolysis of cycloalkanes. Oligomerization and polymerization of alkynes with Nb and Ta halides as catalysts have been reported see Oligomerization Polymerization by Homogeneous Catalysis) ... 

The acidic salts of heteropolyacids, in which the protons are partially substituted with Cs+, are active for acid-catalyzed reactions such as Friedel Crafts reactions, Ritter-type reactions, and skeletal isomerization of alkanes. The... 

Another application that demonstrates the advantages of using NPC for the separation of analytes prone to hydrolysis is the reaction monitoring for the formation of 9,10-anthraquinone [29]. Anthraquinone is an important intermediate in the manufacturing of various dye products but also is used as a catalyst in the isomerization of vegetable oils. It is produced in large amount by Friedel-Crafts reaction of phthaUc anhydride with benzene in the presence of AICI3 catalyst. 

The application of the ideas of Lewis on acids, which correlate a wide range of phenomena in qualitative fashion, has as yet led to very few quantitative studies of reaction velocity but has led to detailed speculations as to mechanisms (Luder and Zuffanti, 118). Friedel-Crafts reactions are considered to be acid-catalyzed, the formation of a car-bonium ion being the first step. The carbonium ion then acts as an acid relative to the base benzene which, upon loss of a proton, yields the alkylated product. Isomerizations of isoparaffins can be explained in similar fashion (Schneider and Kennedy, 119). An alkyl halide yields a carbonium ion on reaction with acids such as boron trifluoride, aluminum chloride, and other metal halides. 

Next ask yourself, What is an immediate precursor ofp-bromotolueneT Perhaps toluene is an immediate precursor because the methyl group would direct bromination to the ortho and para positions, and the isomeric products could be separated. Alternatively, bromobenzene might be an imme ate precursor because we could carry out a Friedel-Crafts methylation li obtain para product. Both answers are satisfactory, although, in view of 1 difficulties often observed with polyalkylation in Friedel-Crafts reactions, bromination of toluene may be the better route. ... 

For some time the main emphasis of Friedel-Crafts reactions was chiefly on aromatic compounds. The development of aliphatic Friedel-Crafts chemistry was of minor importance until World War 2, when isomerization of alkanes and cycloalkanes, preparation of high-octane aviation gasoline and synthetic rubber, and polymerization of alkenes achieved considerable importance these contributed to the growth of aliphatic Friedel-Crafts chemistry. 

Anhydrous Lewis acids themselves are suitable catalysts for Friedel-Crafts reactions of compounds containing n-donor groups. However, they are generally insufficient as acceptors in reactions of alkenes or alkynes or isomerization of hydrocarbons. These reactions generally require a cocatalyst, such as a hydrogen halide or other cationic species. 

More stable catalysts are obtained by using fluorinated graphite or fluorinated alumina as backbones and Lewis acid halides, such as SbFs, TaFs and NbFs, which have a relatively low vapor pressure. These Lewis acids are attached to the fluorinated solid supports through fluorine bridging. They show high reactivity in Friedel-Crafts reactions including the isomerization of straight chain alkanes such as n-hex-ane. 

J. W. Cook introduced the method of cyclizing an o-aroylbenzoic acid to an anthraquinone by heating the keto acid with phosphorus pentoxide in nitrobenzene at 150-165 . For example, the isomeric acids (3) and (4) resulting from the Friedel-Crafts reaction of 1,2-naphthalic anhydride with thiophene are cyclized to the same quinone (5). ... 

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