Friedel-Crafts alkylation, of aromatic

We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

Vinylchlorosilanes react with aromatic compounds in the presence of Lewis acid to give the alkylation products 2-(chlorosilyl)ethylarenes. In the Friedel-Crafts alkylation of aromatic compounds, the reactivity of vinylchlorosilanes is slightly lower than that of allylchlorosilanes.Friedel-Crafts alkylation of benzene derivatives with vinylsilanes to give 2-(chlorosilyl)ethylarenes was first reported by the Andrianov group (Eq. (5))." The reactivity of vinylsilanes in the... 

The Friedel-Crafts alkylation of aromatic compounds with alkyl halides in the presence of Lewis acid is well defined in organic chemistry. However, alky-... 

Among the Friedel-Crafts alkylations of aromatic compounds with (chlorinated alkyl)silanes, the alkylation of benzene with (tt>-chloroalkyl)silanes in the presence of aluminum chloride catalyst was generally affected by two factors the spacer length between the Cl and silicon and the electronic nature of substituents on the silicon atom of (w-chloroalkyl)silanes. As the spacer length between the C—Cl and silicon increases from (chloromethyl)silane to (/i-chloroethyl)silane to (/-chloropropyl)silane, the reactivity of the silanes increases. As the number of chloro-groups on the silicon decreases from (chloromethyl)trichlorosilanes to (chloromethyl)methyldichlorosilanes to (chloromethyl)trimethylsilanes, the... 

Scheme 6.6 Products resulting from 9-catalyzed Friedel-Crafts alkylation of aromatic and heteroaromatic N-containing substrates performed in toluene and without solvent.

The Friedel-Crafts alkylation of aromatic compounds by oxetanes in the presence of aluminum chloride is mechanistically similar to the solvolyses above, since the first step is electrophilic attack on the ring oxygen by aluminum chloride, followed by a nucleophilic attack on an a-carbon atom by the aromatic compound present. The reaction of 2-methyloxetane and 2-phenyloxetane with benzene, toluene and mesitylene gave 3-aryl-3 -methyl-1-propanols and 3-aryl-3-phenyl-l-propanols as the main products and in good yields (equation 27). Minor amounts of 3-chloro-l-butanol and 4-chloro-2-butanol are formed as by-products from 2-methyloxetane, and of 3-phenyl-l-propanol from 2-phenyloxetane (73ACS3944). 

Supercritical hydrogenation is just one example of continuous reactions which can be carried out in SCCO2 solution. Other reactions which have been carried out successfully include Friedel-Crafts alkylation of aromatics by alcohols [64], the dehydration of alcohols to form ethers [65] (using acid catalysts), and the hydroformylation of alkenes [52] (using rhodium catalysts immobilized on Si02). In each of these reactions, it is possible to obtain a selectivity which is at least as good, and often better, than with conventional solvents. However, the precise role of the scCC>2 in these reactions is not as obvious as in supercritical hydrogenation. 

The third case shows the immobilisation of Lewis-acidic ionic liquids. The resulting catalysts, named Novel Lewis-Acidic Catalysts (NLACs), are highly active in the Friedel-Crafts alkylation of aromatic compounds with dodecene. Conversions and selectivities to the desired monoalkylated products were excellent. No leaching of the catalytically active component could be observed. The isomer distribution of the monoalkyated products is very similar to that obtained over pure aluminum(III)chloride. The main drawback of the NLACs is that thy are very sensitive towards water, which leads to irreversible deactivation. A second problem is the deactivation after long reaction times. The most likely cause is olefin oligomerisation. 

It should be noted that an active form of magnesium chloride, formed during the reaction of magnesium with alkyl chlorides, may catalyse Friedel-Crafts alkylation of aromatic solvents [1]. 

Friedel-Crafts alkylation of aromatic compounds involves the formation of a carbocation that acts as electrophile (see section 2.1.3). 

The procedure described here is typical for the catalytic alkylation of aromatic ketones at the ortho position by alkenes. Aromatic ketones are readily available by Friedel-Crafts acylation and many other methods, and many of these ketones are suitable substrates for the present catalytic alkylation with alkenes affording the corresponding ortho-alkylated ketones. The present method provides a direct way to alkylate aromatics with olefins. Moreover, the C-C bond formation takes place with exclusive ortho selectivity, while mixtures of 0-, m-, p-isomers are usually obtained in the conventional Friedel-Crafts alkylation of aromatic compounds. 

Boron halides can also act as halide ion acceptors when they serve as catalysts— for example, in the Friedel-Crafts alkylation of aromatic hydrocarbons ... 

Friedel-Crafts alkylation of aromatics with a wide variety of alkenes has led to many useful applications in organic synthesis. Particularly, much effort has been devoted to choosing appropriate catalysts... 

Tab. 8.28 Reductive Friedel-Crafts alkylation of aromatics with carbonyl compounds...

The Friedel-Crafts alkylation of aromatic compounds is of great importance in laboratory synthesis and industrial production. For example, the industrial processes for ethylbenzene, cumene and linear alkylbenzenes, etc., are on the base of this kind of reaction. It is well known that the drawbacks of the traditional acid catalysts such as A1Q3, H SO, and HF do great harm to the equipment and the environment, and these catalysts cannot be reused after the usual aqueous work-up besides, most of the reactions are carried out in the harmful and volatile organic solvents which can cause the environmental pollution aU of these problems need the replacement of the solvents or the acid catalysts. In this context, room-temperature ionic liquids have been iuCTeasingly employed as green solvents. 

Song s group [25] has developed a novel and recyclable catalytic system for Friedel-Crafts alkylation of aromatic compounds with alkenes. The Sc(OTf)j was immobilized in the ionic Uquids, to obtain quantitatively the desired alkylated products in the reaction of Ihe allqrlation of benzene with hex-l-ene, in which the ionic liquids containing 20 mol% ScCOTl) such as [EMIM][SbFg] ([EMIM] is denoted as... 

Figure 6.7 Microflow system for Friedel-Crafts alkylation of aromatic compounds with an N-acyliminium ion (M, micromixer R, microtube reactor)...

Yoshida et al. [36] have studied the effect of fast mixing of miscible systems by measuring the selectivity towards mono-alkylation in the Friedel-Crafts alkylation of aromatics. They observed a 20-fold increase in the relative selectivity of the mono-alkylate over the di-alkylated system when using a micromixer instead of a conventional batch reactor. In the cycloaddition of the N-acyHminium ion to styrene [36], 50-80% of the cycloadduct is typically lost towards polymeric byproducts. Using an interdigital micromixer, the yield to the cycloadduct increased from 20-50% to almost 80%. 

Laszlo and co-workers have reported that K10 montmorillonites ion-exchanged with various transition metal cations are effident catalysts for Friedel-Crafts alkylation of aromatics with a wide range of alkylating agents such as alcohols, alkenes and alkyl halides.25... 

Early research on hydrothermal reactions was also carried out by Charles Friedel, an instructor at the Ecole Normale Supdrieure [108], the same institution where Paul Villard received his education. Over many years Charles, and later his son Georges Friedel, published a series of papers on the reaction of minerals in H2O at temperatures and presumably also pressures far above critical, starting with the preparation of quartz in 1879 [109,110]. Charles Friedel is more famous for his discovery of the Friedel-Crafts alkylation of aromatics. The works of de LaTour, Daubr6e and the Friedels together ensured that the first experimental reactions of and in SCFs were those of H2O, as reviewed in great detail by Morey [111]. 

Another important application of Friedel-Crafts alkylation of aromatic hydrocarbons includes the production of ethylbenzene via alkylation of benzene with ethylene. 

The boron trihalides, BXj, are Lewis acids (Chapter 6). These compounds are monomeric and planar—unlike diborane, B2H5, and the aluminum halides, AI2X5 (Section 3.1.4). As Lewis acids, boron trihalides can accept an electron pair from a halide to form tetrahalobo-rate ions, BX4. Boron halide catalysts act as halide ion acceptors, as in the Friedel-Crafts alkylation of aromatic hydrocarbons (in margin). 

Friedel-Crafts alkylation of aromatics with CMF to give rise to benzyl derivatives 34a and 34b was first demonstrated in 1909 [139] and reprised by Rauchfuss and co-worker in 2013 to provide feedstock 34c for hydrodeoxygenation to diesel-range hydrocarlxMis [140]. Similar reactions have been used to produce a range of novel monomers and polymers. Thus, Szmant et al. reported as far back as 1981 the application of CMF to the synthesis of polymeric building blocks 35 and 36, among others (Fig. 1) [141]. 

The Friedel-Crafts alkylation of aromatics with ro-haloalkyl fluorides always favors the formation of ru-haloalkylarenes (9, 10). Symbiosis determines the selective C—X bond severance. Similarly, the indene synthesis by alkylation of benzene with 1-bromo-l-fluorocyclopropanes is shown to proceed via an electrocyclic ionization of the hard F (11). This behavior is opposite to the trend of the uncatalyzed thermal heterolysis of halocyclopropanes (see Chapter 11, Section 11.4). 

For the sake of completeness, it should be mentioned that the use of microreactors and miniaturized flow reactors for the Friedel-Crafts alkylation of aromatic compounds has also been documented by other authors. For example, the Friedel-Crafts alkylation ofbenzenewithcydohexene using H2SO4 as a catalyst has been described [7]. The reaction was conducted in a static micromixer giving 58% cyclohexylbenzene. PoUakofi and coworkers have carried out the Friedel-Crafts alkylation of anisole with n-propanol in supercritical CO2, testing five different Bronsted solid acid catalysts under systematic variation of process conditions such as temperature and pressure [8]. 

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