Aromatic hydrocarbons with alkyl halides

The alkylation of aromatic hydrocarbons with alkyl halides RX in the presence of AICI3 (according to Friedel—Crafts) also proceeds through the intermediate R and, hence, is accompanied by the isomerization of the carbocation, due to which a mixture of alkylated aromatic hydrocarbons is formed. For example, in the alkylation of benzene with n-propyl chloride (AICI3,255 K) two hydrocarbons are formed... 

Considerable progress has been made on C02 fixation in photochemical reduction. The use of Re complexes as photosensitizers gave the best results the reduction product was CO or HCOOH. The catalysts developed in this field are applicable to both the electrochemical and photoelectrochemical reduction of C02. Basic concepts developed in the gas phase reduction of C02 with H2 can also be used. Furthermore, electrochemical carboxyla-tion of organic molecules such as olefins, aromatic hydrocarbons, and alkyl halides in the presence of C02 is also an attractive research subject. Photoinduced and thermal insertion of C02 using organometallic complexes has also been extensively examined in recent years. 

Fittig s synthesis org chem The synthesis of aromatic hydrocarbons by the condensation of aryl halides with alkyl halides, using sodium as a catalyst. fid-iks, sin-tho-s3s ... 

Alkylation with Alkanes. Alkylation of aromatic hydrocarbons with alkanes, although possible, is more difficult than with other alkylating agents (alkyl halides, alkenes, alcohols, etc.).178 This is due to the unfavorable thermodynamics of the reaction in which hydrogen must be oxidatively removed. 

Alkylation is a very broad reaction type and it can, depending on the nature of the alkylating agent, proceed either as a substitution or as an addition reaction. The alkylation by substitution of, for example, aromatic hydrocarbons, phenols or amines is based on the reaction with alkyl halides or alcohols. Some evidence indicates that, at least partly, the alkylation proceeds through the intermediate formation of alkenes from the alkylating agent when the reaction is conducted at atmospheric pressure and at high temperature. 

Sulfonylation of aromatic hydrocarbons in the presence of a Lewis acid and the reaction of sodium benzenesulfinate with alkyl halides proved to be particularly easy and useful to prepare starting materials for the Julia olefination procedure (see Section 4.3.2). 

The results obtained in the gas-phase isopropylation of various aromatic hydrocarbons with isopropyl chloride over Nafion-H catalyst showed only a relatively small variation of reactivity in going from fluorobenzene to xylenes.235 Therefore, it has been assumed that the reaction rate is controlled by the formation of a reactive electrophilic intermediate (possibly, protonated alkyl halide 61, or some form of incipient alkyl cation) rather than by cr-complex formation between the electrophile and the aromatic nucleus [Eq. (5.89)]. 

According to Hugel and Lerer324 the organosodium compounds obtained from polycyclic aromatic compounds such as naphthalene and anthracene in liquid ammonia or other media also react with alkyl halides, and especially with isopentyl and isobutyl chloride they yield doubly substituted hydrocarbons. The experimental conditions are briefly illustrated as follows ... 

An important reaction which enabled many new aromatic compounds to be prepared was that discovered in 1877 by Charles Friedel (1832-1899) and James Mason Crafts (1839-1917). They found that an alkyl or acyl group could be substituted into a benzene ring by the reaction of the aromatic hydrocarbon with an alkyl or acyl halide in the presence of aluminium chloride catalyst. The reaction proved to be of wide application and is particularly useful in the preparation of aromatic ketones and in the formation of a new ring by an intramolecular process (Figure 10.11). 

The Friedel-Crafts Reaction, in which an aromatic hydrocarbon reacts with an alkyl halide under the influence of aluminium chloride ... 

Friedel and Crafts reaction. alkyl halide condenses with an aromatic hydrocarbon in the presence of anhydrous aluminium chloride to yield, in the first instance, a hydrocarbon in accordance with the following scheme —... 

Sodium (metal). Used as a fine wire or as chips, for more completely drying ethers, saturated hydrocarbons and aromatic hydrocarbons which have been partially dried (for example with calcium chloride or magnesium sulfate). Unsuitable for acids, alcohols, alkyl halides, aldehydes, ketones, amines and esters. Reacts violently if water is present and can cause a fire with highly flammable liquids. 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

The mechanism of the chemiluminescent reactions between alkyl halides and electrogenerated aromatic hydrocarbon radicals (cf. p. 119) has been elucidated in more detail 213>. The proposed general mechanism is consistent with the observed experimental results ... 

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