Iodination of aromatic compounds

The effect of micromixing in the iodination reaction is smaller than that observed for the Friedel-Crafts alkylation using N-acyliminium ions. The smaller effect seems to be ascribed to the smaller rate of iodination, because computational fluid dynamics simulation indicated that the effect of the micromixing on the product selectivity of a competitive consecutive reaction increases with an increase in the reaction rate. Therefore, the electrochemically generated I seems to be less reactive than the N-acyliminium ions. 

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This case is related to the acid-catalyzed de-iodination of aromatic compounds which proceeds via its conjugate acid,... 

Cyanogen Iodide (ICN) has been used extensively for the cyanation of alkenes and aromatic compounds [12], iodination of aromatic compounds [13], formation of disulfide bonds in peptides [14], conversion of dithioacetals to cyanothioacetals [15], formation of trans-olefins from dialkylvinylboranes [16], lactonization of alkene esters [17], formation of guanidines [18], lactamization [19], formation of a-thioethter nitriles [20], iodocyanation of alkenes [21], conversion of alkynes to alkyl-iodo alkenes [22], cyanation/iodination of P-diketones [23], and formation of alkynyl iodides [24]. The products obtained from the reaction of ICN with MFA in refluxing chloroform were rrans-16-iodo-17-cyanomarcfortine A (14)... 

Radioiodination involves the substitution of radioactive iodine atoms for reactive hydrogen sites in target molecules. The process usually involves the action of a strong oxidizing agent to transform iodide ions into a highly reactive electrophilic iodine II compound (typically I2 or a mixed halogen species such as IC1). Formation of this electrophilic species leads to the potential for rapid iodination of aromatic compounds... 

Earlier investigations reported on the gas-phase bromination and iodination of aromatic compounds of the type C6H5X (X = F, Cl, Br, Me) with Br+ and I+ produced by a radiolytic method44. It was proposed that the reaction with Br+ involves, as the first step, the exothermic charge exchange of equation 1045. 

Ogata reports iodination of aromatic compounds in fair yield by reaction with iodine and peracetic acid in acetic acid solution the effective reagent may be acetyl hypoiodite, CH3COOI. The reagent reacts with cyclohexene to give l-iodo-2-acetoxycyclohexane, but in low yield." The Provost reaction Is far better. 

The electrochemically generated serves as a powerful iodinating reagent for direct iodination of aromatic compounds. Miller and co-workers reported that the electrochemical oxidation of iodine (I2) in acetonitrile gives CH3CNI (equivalent of I ) (Scheme 8.9) and that this... 

Scheme 8.10 Product selectivity of iodination of aromatic compounds with electro-chemically generated 1 ...

The same reagent, F-TEDA, in the presence of iodine in imidazolium and pyri-dinium ionic liquids has also been used [63] for the regioselective iodination of aromatic compounds. The reaction is para-directed when possible. Otherwise, it occurs in the ortho-position. In addition, competitive experiments (kmesiiyiene kdurene) suggest a polar mechanism for this process, in agreement with the behavior in molecular solvents. 

The iodination of aromatic compounds using the electrophilic fluorinating agent l-(chloromethyl)-l,4-diazabicyclo[2,2,2]octane tetrafluoroborate and iodine was carried out in a range of [BF4] and [PFe]" ionic liquids and generally gave high yidds [106]. Trihalide-based ionic liquids have been synthesised and the structure of the... 

It has been demonstrated that tosyloxybenziodoxole 97 (Section 2.1.8.1.3) can be used as an effective reagent for the oxidative iodination of aromatic compounds [111, 112]. Treatment of various aromatic compounds 96 with reagent 97 and I2 gives the corresponding iodinated compounds 98 in good yields (Scheme 3.39). As compared with other divalent iodine compounds, the tosylate 97 shows the best reactivity as an oxidant for oxidative halogenation [112]. 

Additional examples of synthetic application of periodic acid as an oxidant include the oxidative iodination of aromatic compounds [1336-1341], iodohydrin formation by treatment of alkenes with periodic acid and sodium bisulfate [1342], oxidative cleavage of protecting groups (e.g., cyclic acetals, oxathioacetals and dithioacetals) [1315, 1343], conversion of ketone and aldehyde oximes into the corresponding carbonyl compounds [1344], oxidative cleavage of tetrahydrofuran-substituted alcohols to -y-lactones in the presence of catalytic PCC [1345] and direct synthesis of nitriles from alcohols or aldehydes using HsIOe/KI in aqueous ammonia [1346],... 

Oxidative iodination of aromatic compounds by the combination of a hypervalent iodine reagent with iodine is a synthetically important reaction (Section 3.1.4) [34]. Polymer-supported diacetate 4 is a particularly convenient reagent for oxidative iodination since it can be regenerated and reused many times. Reagent 4 gives the best results for the iodination of electron-rich arenes 13, with predominant formation of the para-substituted products 14 (Scheme 5.8) [12,21]. 

Kataoka K, Hagiwara Y, Midorikawa K et al (2008) Practical electrochemical iodination of aromatic compounds. Org Process Res Dev 12 1130-1136... 

Halogenations of aromatic compounds have been investigated using different types of midostructured readors. A good overview comprising the gas-liquid processes of fluorinations and chlorinations and also liquid-phase brominations has been presented [26]. However, in this section only liquid-phase brominations and iodinations of aromatic compounds are considered. 

Amination under palladium-catalysis is possible using hydroxylamines as electrophiles.Bromination and chlorination can be performed with N-halosuccinimides or PhICb, while iodine can be used directly. In case of PhICl2, the catalytic cycle involves palladium(III) intermediates.A diastereoselective method for the iodination of aromatic compounds was used by the Yu group (Scheme 5-196). 

Like Friedel-Crafts reactions, halogenation such as bromination and iodination of aromatic compounds are classified as electrophilic aromatic substitution reactions. Bromine and iodine substituents are weakly electron-withdrawing groups, and introduction of such substituents causes a decrease in reactivity, and therefore, the first halogenation is faster than the second halogenation. However, the reactions in batch macroreactors suffer from the problem of disguised chemical selectivity, i.e, the formation of dihalogenated products. 

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