Carbon dioxide Friedel-Crafts alkylation

Now let s draw the forward scheme. Benzene is converted into isopropyl benzene upon treatment with 2-chloropropane and a Lewis acid (via a Friedel-Crafts alkylation). Benzylic bromination replaces the benzylic hydrogen atom with a bromine atom. Conversion to a Grignard reagent, followed by reaction with carbon dioxide and subsequent acidification, gives the desired carboxylic acid. 

Thomas Swan and Co. Ltd. built a 1000-tonne/annum multipurpose supercritical carbon dioxide demonstration plant at its Consett site to explore hydrogenation and Friedel-Crafts type acylations and alkylations, inter alia. 

Alternative catalysts for this reaction are polymer-supported alkyl sulfonic acids [231], even if they show lower performances than the zeolite. Two of the problems in the reactions are the need to vaporize the reactant and the periodic regeneration of the rapidly deactivating zeolite catalysts. It was thus proposed recently that continuous catalytic Friedel-Crafts acylation can be performed in the biphasic medium of an ionic liquid and supercritical carbon dioxide [232]. 

Indoxyls are normally prepared from anthranilic acids via alkylation with a haloacetic acid followed by a cyclising condensation with loss of carbon dioxide. " Indoxyl itself is best prepared by Friedel-Crafts type ring closure of iV-phenylglycine activated with triphenylphosphine oxide/triflic anhydride in the presence of triethylamine at room temperature. " ... 

Huorous compounds are also potentially useful as additives to promote organic reactions in carbon dioxide. For example, a fluorous alcohol RfCH20H assists asymmetric hydrogenations with non-fluorous ruthenium BINAP catalysts, and a fluorous aryl alkyl ether (C8F17C6H4-P-OC12H25) does so in scandium-triflate-catalyzed aldol and Friedel-Crafts reactions. These additives are presumed to act as solubilizers or emulsifiers to promote contact among the various reaction components. Since they are fluorous, they can be readily recovered from the otherwise organic reaction mixtures for reuse. 

Supercritical carbon dioxide (SCCO2) is a well-known and important medium for organic transformations and it has considerable value to the chemical industry. It was shown that SCCO2 is capable of ionizing alkyl halides and related substrates to carbocations (Scheme 14). For example, 1-bromoadamantane (55) ionizes to the 1-adamantyl cation (56). The Friedel-Crafts product (57) is formed (88% yield) in the presence of 1,3-dimethoxybenzene and the reduced product (58, X = H) is formed by... 

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