Friedel-Crafts alkylation solvent effect

Neither Friedel-Crafts acylation nor alkylation reactions can be earned out on mtroben zene The presence of a strongly deactivating substituent such as a nitro group on an aromatic ring so depresses its reactivity that Friedel-Crafts reactions do not take place Nitrobenzene is so unreactive that it is sometimes used as a solvent m Friedel-Crafts reactions The practical limit for Friedel-Crafts alkylation and acylation reactions is effectively a monohalobenzene An aromatic ring more deactivated than a mono halobenzene cannot be alkylated or acylated under Friedel-Crafts conditions... 

In chemistry, the term complex can mean many things. The belief, which I shared, that complexes of the metal halides with monomers or with alkyl halides are important in CP induced me to undertake several difficult but fruitful investigations. Complexes between RX and MtXn were well known [see References in [24]] and they were being studied at about that time by several workers, such as H. C. Brown at Purdue University with regard to the A1 halides and Fairbrother at Manchester University was concerned with similar systems and with the ionisation of trityl halides by metal halides. I was concerned with TiCl4, my then favourite catalyst , and its interaction with the alkyl chlorides which were used as solvents for CP. The theory first suggested by Pepper [46] and adopted by us was that if a CP was initiated in an alkyl chloride RC1, and there was no evident effect of water, then the initiation was most likely akin to a Friedel-Crafts alkylation. This was represented by the equations (7) and (8) ... 

Alternatively the alkylated aromatic products may rearrange. -Butylbenzene [104-57-8] is readily isomerized to isobutylbenzene [538-93-2] and j Abutyl-benzene [135-98-8] under the catalytic effect of Friedel-Crafts catalysts. The tendency toward rearrangement depends on the alkylatiag ageat and the reaction conditions (catalyst, solvent, temperature, etc). 

The most selective 4-substitution is obtained in the Friedel-Crafts isopropylation of 2-acetylthiophene, which under certain conditions gives as much as 99% of this isomer and 1% of the 5-isomer. An--other case of selective 4-substitution is the bromination of 2-thienyl alkyl ketones using the swamping catalyst effect (i.e., brominating in the presence of excess AlCb without solvent), which yields 43-63% of apparently isomer-free 4-bromo-2-thienyl alkyl ketones. Gold-farb et al. also have applied this method to the chloromethylation of... 

Highly Lewis-acidic chloroaluminate ionic liquids (ILs) are well known to be both versatile solvents and effective catalysts for Friedel-Crafts reactions [1,2]. Tailoring the physical and chemical properties of the ILs to the needs of a specific reaction allows for a high diversity of applications [3,4]. We could show that immobilising these ILs on inorganic supports yields very active catalysts for alkylation reactions. The immobilisation of ionic liquids leads to novel Lewis-acidic catalysts (NLACs). The methods presented include the method of incipient wetness (method 1, further on called NLAC I), which has been introduced in detail by Hoelderich et al. f5], but focus of this presentation lies on the methods 2 (NLAC II) and 3 (NLAC III). 

Uses. Tetramethylene sulfone has high solvent power for aromatics and has been used extensively by Olah and co-workers for Friedel-Crafts type nitrations and for studies of the mechanism of nitronium tetrafluoroborate nitration of alkyl-benzenes and halobenzenes in homogeneous solution. It is a superior solvent for quaternization of tertiary amines with alkyl halides, since it has a high dielectric constant and does not enter into side reactions observed with nitrobenzene and dimethylformamide. For example in the synthesis of the acridizinium salt (3), Bradsher and Parham effected quaternization of (1) with benzyl bromide in tetramethylene sulfone at room temperature in excellent yield. Several other salts analagous to (2) were obtained in good yield and in crystalline form with use of tetramethylene sulfone, whereas with other solvents the products were colored... 

The Friedel-Crafts reaction involves an electrophilic aromatic substitution that facilitates the alkylation or acylation of arenes (135) and heterocyclic compounds catalyzed by acidic catalysts. Zinc oxide has been found to be an effective catalyst for the Friedel-Crafts acylation of activated and nonactivated aromatic compounds (135) (Hosseini-Sarvari and Sharghi 2004) under solvent-free and room temperature conditions (Scheme 9.44). The catalyst provides a large surface area for the reaction. This Friedel-Crafts reaction is a safe and environmentally benign method which requires simple workup, mild reaction conditions and a short reaction time. 

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