Friedel-Crafts Benzylation Research Articles

Development of Fe‐, Sb‐, Bi‐ and Al‐impregnated silica catalysts using rice husk silica as a support for Friedel–Crafts benzylation of arenes

AbstractThe milling by‐product of rice, rice husk, constitutes a major waste of the agricultural industry. It is mainly used as a fuel additive for various purposes, leaving behind residual ash which is rich in silica (Biogenic silica). In the present project, rice husk silica was impregnated with Fe3+, Sb3+, Bi3+ and Al3+ from both their aqueous and organic solutions. The resultant catalysts were activated at 120 °C and 550 °C and used for the Friedel–Crafts benzylation of benzene using benzyl chloride. Copyright © 2003 Society of Chemical Industry

A convenient and improved montmorillonite K-10 catalysed Friedel-Crafts benzylation and allylation with activated esters

Benzyl benzoate and cinnamyl acetate has been effectively used respectively as alkylating and allylating substrates in Friedel–Crafts reaction catalysed by montmorillonite K-10 clay.

Friedel–Crafts Benzylation and Phenethylation Reactions Using Benzyl and Phenethyl Benzothiazol-2-yl Carbonate Derivatives

Abstract Friedel–Crafts benzylation and phenethylation reactions of several aromatic compounds with benzyl and phenethyl benzothiazol-2-yl carbonate derivatives were carried out in the presence of scandium triflate (Sc(OTf)3) as a catalyst. Suitable combinations of the leaving group of carbonates and acid promoters that generate cationic alkyl species were examined.

Study of catalytic activity of free and K10 -supported iron oxyhydroxides and oxides in the Friedel–Crafts benzylation reaction using benzyl chloride/alcohol to understand their role in the catalysis by the Fe-exchanged/impregnated K10 catalysts

α-Fe 2O 3, γ-Fe 2O 3 and Fe 3O 4 were prepared in the free form and also supported on montmorillonite K10 in situ. The resultant catalysts were activated at 120 °C (except for Fe 3O 4) and were used for the Friedel–Crafts benzylation of different arenes using benzyl chloride. The catalysts were characterised using FTIR and XRD. The reactions were carried out at different temperatures. Exceptional activity was found to be associated with K10-γ-Fe 2O 3 the catalyst was reusable. K10-Fe 3+ and FeCl 3 impregnated K10 were also prepared and activated at 550 °C; their activities were compared with the above catalysts. All the forms of iron(III) oxyhydroxides and oxides were used for benzylation reaction using benzyl alcohol to study the decreasing in acidity on calcination of FeCl 3-exchanged and impregnated K10.

Divalent Transition Metal Ion‐Exchanged Faujasites as Mild, Efficient, Heterogeneous Friedel—Crafts Benzylation Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of 2-Benzylphenols: Transformation of the Baylis-Hillman Adducts Derived from 2-Cyclohexen-1-one

an extension of the reaction, we intended to prepare acridine skeleton from the Baylis-Hillman adducts of 2-cyclohexen1-one as shown in Scheme 1. However, we could not prepare the desired compounds via the reaction scheme (vide infra). Instead, we could obtain 2-benzylphenol derivatives in good yields as shown in Scheme 2 and wish to report herein the results. The Friedel-Crafts alkylation reaction is one of the most powerful methods to form the carbon-carbon bond in organic reactions. The Friedel-Crafts benzylation reaction is of great synthetic significance in industrial processes. 3 However, synthesis of 2-benzylphenols regioselectively from phenols or benzyl phenyl ethers is difficult due to the formation of ortho-/para- mixtures. 4 Synthesis of these compounds by Fries rearrangement of phenyl phenylacylates also suffers from the formation of mixtures. 5 Ortho-specific alkylation of phenols via 1,3,2-benzodioxaborins was known. 6 1,3,2-Benzodioxaborins can be reduced to orthoalkyl phenols with tert-butylamine borane in the presence of aluminum chloride. The Baylis-Hillman reaction of 2-fluorobenzaldehyde (1a) and 2-cyclohexen-1-one (2) was carried out in aqueous THF with the aid of DMAP at room temperature to give the corresponding adduct 3a in 58% yield as reported previously. 7 Acetylation of 3a with Ac2O/DMAP gave 4a in 91% yield. Initially, we examined the reaction of 4a and ptoluenesulfonamide in the presence of K 2CO3 in DMF. However, 2-(2-fluorophenyl)methylphenol (5a) was isolated in 74% yield, unexpectedly. The formation of 5a occurred well without tosylamide. Actually, the yield of 5a was improved up to 94% without tosylamide as shown in Table 1 (entry 1). Thus, we prepared some Baylis-Hillman acetates of 2cyclohexen-1-one and examined their conversion to 2arylmethylphenols and the results are summarized in Table 1. As mentioned previously, the Baylis-Hillman reaction of 1 and 2 was carried out in aqueous THF in the presence of 0.1 equiv. of DMAP. 7 The corresponding adducts 3a-h were obtained in reasonable yields (41-64%) at room temperature. Following conversion to their acetate 4a-h was excellent in all cases (CH2Cl2, Ac2O/DMAP, rt, 90-98%). The reaction of 4a-f in DMF in the presence of K 2CO3 (1.0 equiv) gave 5a-f in good yields (89-96%) in short time (1-2 h) at 60-70 o C. 8 The formation of 5g, the quinoline derivative, was carried out at room temperature. The reaction is believed to occur as depicted in Scheme 2: potassium carbonate assisted elimination of acetic acid and the following keto-enol tautomerization and 1,5-hydrogen transfer. 9 We could not obtain the corresponding phenol derivative from the analogous reaction with 4h, derived from hexanal. Intractable mixtures were observed on tlc at 60-70 o C. Instead, we could isolate cyclohexenone derivative 6 in 40% yield at room temperature. 10 The structure of 6 was determined by 1 H, 13 C, and 1 H- 1 H COSY. 8 In conclusion we disclosed unusual transformation of the Baylis-Hillman acetates of 2-cyclohexen-1-one into 2arylmethylphenols. Further chemical transformation of the products to xanthene derivatives via the nucleophilic aromatic substitution strategy and the synthesis of acridines are underway.

Divalent Transition Metal Ion-Exchanged Faujasites as Mild, Efficient, Heterogeneous Friedel–Crafts Benzylation Catalysts

Ni2+-, Cu2+-, and Zn2+-exchanged faujasite (MY) zeolites efficiently catalyze the Friedel–Crafts benzylation of arenes in a clean and simpler method.

Friedel-Crafts benzylation of benzene derivatives catalyzed by silica and alumina-supported polytrifluoromethanesulfosiloxane

Friedel-Crafts benzylation of benzene derivatives catalyzed by silica and alumina-supported polytrifluoromethanesulfosiloxane

Room temperature synthesis of diphenylmethane over MCM-41 supported AlCl 3 and other Lewis acids

The catalytic properties of MCM-41 activated with AlCl 3, ZnCl 2 and other Lewis acids, such as FeCl 3, NiCl 2 and CuCl 2 were investigated for room temperature Friedel–Crafts benzylation in the liquid phase. The catalysts were studied under batch-wise as well as continuous operation conditions. AlCl 3/MCM-41 showed higher activity than ZnCl 2/MCM-41, while FeCl 3/MCM-41, CuCl 2/MCM-41 and NiCl 2/MCM-41 were inactive under identical conditions. ZnCl 2 offered some advantages due to reduced hydrolytic sensitivity and better selectivity. The optimized ZnCl 2 loading of ZnCl 2/MCM-41 was 4 mmol g −1. For AlCl 3/MCM-41, the pore size of MCM-41 did not affect the activity nor the selectivity in the benzylation of benzene. Very low selectivity was observed in the benzylation of substituted aromatics using AlCl 3/MCM-41 as catalyst due to a tendency for migration or transfer of the substituent group. With its inherently lower activity, ZnCl 2/MCM-41 did not catalyze this reaction. In a continuous trickle bed reactor, sustained activity of the AlCl 3/MCM-41 catalyst could be demonstrated. Hence, MCM-41 supported with AlCl 3 or ZnCl 2 may be promising candidates to replace AlCl 3 in the industrial manufacture of diphenylmethanes.

The enhanced activity of Sb after supporting on K10 in the benzylation of benzene using benzyl chloride and benzyl alcohol

K10 was modified under aqueous and non-aqueous conditions using SbCl 3 and the resultant catalysts were used for the Friedel–Crafts benzylation of benzene with benzyl chloride (BzCl) and benzyl alcohol (BzOH). Effect of activation temperature on the activity of the catalysts was also studied. The catalysts activated at 120°C in both the cases were found to be more active. The outstanding observation of this investigation was the significant catalytic activity associated with Sb(III), particularly in view of the fact that SbCl 3 is known to be the least active Lewis acid under homogeneous conditions.

ChemInform Abstract: Indium Catalyzed Friedel—Crafts Benzylation of Aromatic Compounds with Benzyl Halides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Lithium Tetrakis(pentafluorophenyl)borate-Catalyzed Friedel–Crafts Benzylation Reactions

Abstract Lithium tetrakis(pentafluorophenyl)borate [LiB(C6F5)4], a neutral salt, effectively catalyzed Friedel–Crafts benzylation reactions of aromatic compounds with benzyl chloride or mesylate and their substituted derivatives. The LiB(C6F5)4-catalyzed reactions proceeded more efficiently in the coexistence of magnesium oxide.

Solid superacid, silica-supported polytrifluoromethanesulfosiloxane catalyzed Friedel–Crafts benzylation of benzene and substituted benzenes

A new inorganic polymer, silica-supported polytrifluoromethanesulfosiloxane solid superacid (SiO 2–Si–SCF 3), has been prepared. The acid strength of superacid (Ho<−13.76) is higher than that of 100% H 2SO 4 (Ho=−11.9). It was found that SiO 2–Si–SCF 3 could catalyze Friedel–Crafts benzylation of benzene and substituted benzenes with benzyl alcohol under relatively mild experimental conditions. Reactions are very clean, water is the only by-product of the reaction. The yields amounted to 97–100%, respectively. The selectivity was influenced by catalyst concentration, reaction time and toluene/benzyl alcohol molar ratios.

The Reactivity-Selectivity principle and the electrophilic substitution of aromatic compounds

The application of the Reactivity-Selectivity principle (RSP) to the Friedel-Crafts alkylation reaction has been reinvestigated using the N-nitrosoamide decomposition as the source of electrophiles. Plots of p f vs σ + for 4-methylbenzyl, benzyl, 4-chlorobenzyl, and 4-nitrobenzyl cations] yielded ϱ values of −3.4, −2.5, −2.4, and −1.2, resp. The data indicate that the Reactivity-Selectivity Principle is applicable to the electrophilic substitution of aromatic compounds contrary to a claim in the literature. A claim that a reactivity reversal should occur in Friedel-Crafts benzylation is also shown to be in question.

Superacid-Catalyzed Reductive Friedel-Crafts Reaction of Arenes Using Arenecarbaldehyde Acetals.

Reaction of 2-aryl-1,3-dioxane with arenes in the presence of a catalytic amount of trifluoromethanesulfonic acid gave the corresponding diarylmethanes in good to excellent yields. The acid-catalyzed Friedel-Crafts benzylation of arenes could altenatively be carried out using arenecarbaldehyde and 1,3-propanediol. The reaction was assumed to proceed through a redox process involving hydride shift from the cyclic acetal moiety to the benzylic carbon. The hydride shift was confirmed by the reaction with 5-ethyl-2-phenyl-4,4,6,6-tetradeuterio-1,3-dioxane, wherein more than 90% deuterium was incorporated into the benzylic carbon of the diphenylmethane. Diphenylmethyl ether Ph(2)CHOCH(2)CH(2)CH(2)OH also reacted with benzene to afford diphenylmethane under the same reaction conditions, suggesting that the ether should be the plausible intermediate that underwent the hydride shift.

Role of benzyl ether in the inversion of reactivities in Friedel-Crafts benzylation of toluene by benzyl chloride and benzyl alcohol

In the inversion in the reactivities and selectivities of benzyl chloride (BnCl) and benzyl alcohol (BnOH) in a single pot Friedel-Crafts benzylation with toluene, there is not only a preferential adsorption of benzyl alcohol on the solid acid catalyst but also a second preference to the adsorption of benzyl ether (BE) formed in-situ. The order of prefential adsorption is BnOH > BE > BnCl.

Scandium(III) trifluoromethanesulfonate-catalysed reductive Friedel–Crafts benzylation of aromatic compounds using arenecarbaldehydes and propane-1,3-diol

Scandium(III) trifluoromethanesulfonate catalyses the Friedel–Crafts benzylation of aromatic compounds with arenecarbaldehydes and propane-1,3-diol to produce, through a clean redox process, diarylmethanes in high to excellent yields.

Convenient Preparation of 1,4-Dibenzylbenzene using Zinc Chloride in the Presence of Polar Solvents

Abstract 1,4-Dibenzylbenzene was successfully synthesized by the Friedel-Crafts benzylation of benzene with 1,4-bis(chloromethyl)benzene using zinc chloride in the presence of polar solvents. In particular, zinc chloride dissolved in primary alcohols or ketones with a molar ratio of 1 was a highly effective catalytic system in the reaction.

Activation of Clayzic and its effect on the relative rates of benzylation of aromatic substrates

The effects of the activation of K10 montmorillonite supported zinc chloride (‘Clayzic’) by different methods on the reactivity of the catalyst in the Friedel–Crafts benzylation of benzene and halo-benzenes have been investigated. There is an optimum temperature for thermal activation in air at which point a rate enhancement, compared to unactivated Clayzic, in the benzylation of benzene of greater than 30 has been achieved. The rate limiting factor for these reactions is believed to be the ability of the aromatic substrate to enter the polar mesopores containing the active zinc ions in Clayzic, causing unexpected and activation-dependent rate trends to be observed. Activation of Clayzic is believed to reduce the polar nature of the pores, so aiding partitioning of the substrate into the catalyst.

アルミナ担持塩化銅（ＩＩ）触媒によるＦｒｉｅｄｅｌ‐Ｃｒａｆｔｓベンジル化反応

Alumina-supported copper (II) chloride efficiently catalyzed Friedel-Crafts benzylation of aromatic hydrocabons and phenols with benzyl chloride under mild conditions. The recovered catalyst can be readily regenerated and reused without a decrease in catalytic activity. The reaction of benzene with bis (chloromethyl) benzenes gave dibenzylbenzenes in high yields, and the formation of by-products such as polybenzylbenzenes was depressed in contrast to that in the reaction catalyzed by AlCl3, AlCl3CH.NO2 or FeCl3.