Iodine complex with aromatic hydrocarbons

The highest conductivities thus far observed in organic molecules are found among the donor-acceptor complexes. The activation energies for conduction are small, on the order of 0.1 eV ( 2 kcal) or less. Examples are the complexes of aromatic hydrocarbons with iodine and complexes of amines with chloranil or related quinones. The best conductors have a high free-radical content and are usually not of simple stoichiometry. The complex salts of TCNQ ° (I) are the best of the known organic conductors. The... 

Bhowrmk, B.B. and Chattopadhyay, S.P. (1981) Charge-transfer complexes of iodine with aromatic hydrocarbons. Spectrvchim. Acta, Part A, 37A, 135-139. 

In the presence of heptakis(6-bromo-6-deoxy-(3-CD) ((3-CD7Br), Femia and Cline Love observed the room-temperature phosphorescence of phenanthrene and other polynuclear aromatic hydrocarbons in N2-purged N,N-dimethylfol-mamide (DMF)-water mixtures [24], On the other hand, Hamai and Monobe observed room-temperature phosphorescence of 2-chloronaphthalene from a deaerated solution containing a 1 1 complex of 6-iodo-6-deoxy-(3-CD ((3-CDI) and 2-chloronaphthalene [25], This result indicates that even only one iodine atom on the (3-CD rim can accelerate the intersystem crossing rate of 2-chloronaphthalene included in the CD cavity. The room-temperature phosphorescence of 6-bromo-2-naphthol and 3-bromoquinoline was also observed for the complexes with (3-CDI [26],... 

The parallels observed between CM) solubility and electrophilic substitution products are regular if C6o dissolution in aromatic hydrocarbons is considered as acid-base relationships. According to the theoretical research and experimental results, double bonds of aromatic hydrocarbons with mobile Tt-electrons are Lewis base. Consequently, they react with acids and Lewis acids to form complexes. It has been established that these complexes cannot be to a marked extent electrostatic. It has been found that they are often colored. Complexes with iodine (Lewis acid) give absorption bands at 300 nm in the UV region. These complexes are not true chemical compounds. According to Dewar, all the above facts are due to the formation of Tt-complexcs between an acid or Lewis acid and the entire Ji-electron system of an unsaturated compound which should be considered as Lewis base. Because in these complexes a double bond is an electron donor and Lewis acid is an electron acceptor, they are known as donor-acceptor complexes. The decrease in energy in complexing is conditioned by quantum-mechanical reasons. 

Fluorescence quenching of fluorene, dibenzofuran, and dibenzothiophens by aromatic nitriles and aliphatic amines is the result of electron transfer with exciplex formation,177 and ion-pair formation in pyromellitic dianhydride-ethylbenzene is followed by dissociation into separated ion pairs in their highly excited states.178 Photochemical iodination of aromatic hydrocarbons may proceed by way of an electronically excited Ia-aromatic charge-transfer complex.179 Modulation excitation spectrophotometry has been used to analyse the nature of some complexes between polycyclic aromatic hydrocarbons and chloranil.180... 

Table 1 Data for charge-transfer complexes of polynuclear aromatic hydrocarbons with iodine...

Hypervalent iodine species were demonstrated to have a pronounced catalytic effect on the metalloporphyrin-mediated oxygenations of aromatic hydrocarbons [93]. In particular, the oxidation of anthracene (114) to anthraquinone (115) with Oxone readily occurs at room temperature in aqueous acetonitrile in the presence of 5-20 mol% of iodobenzene and 5 mol% of a water-soluble iron(llI)-porphyrin complex (116) (Scheme 4.57) [93]. 2-ferf-Butylanthracene and phenanthrene also can be oxygenated under similar conditions in the presence of 50 mol% of iodobenzene. The oxidation of styrene in the presence of 20 mol% of iodobenzene leads to a mixture of products of epoxidation and cleavage of the double bond. Partially hydrogenated aromatic hydrocarbons (e.g., 9,10-dihydroanthracene, 1,2,3,4-tetrahydronaphthalene... 

The proposed mechanism for these catalytic oxidations includes two catalytic redox cycles (i) initial oxidation of iodobenzene with Oxone, producing hydroxy(phenyl)iodonium ion and hydrated iodosylbenzene and (ii) the oxidation of iron(III)-porphyrin to the oxoiron(IV)-porphyrin cation-radical complex by the intermediate iodine(III) species (Scheme 4.58) [93]. The oxoiron(IV)-porphyrin cation-radical complex acts as the actual oxygenating agent toward aromatic hydrocarbons. The presence of the [PhI(OH)]+ and PhI(OH)2 species in solutions containing Phi and Oxone has been confirmed by ESI mass spectrometry [93]. 

The donor-acceptor complexes formed between electron acceptors (such as iodine or tetracyanoethylene) and electron donors (such as aliphatic amines or aromatic hydrocarbons) have, been extensively studied from various points of view -spectroscopic 5 structural and thermodynamic (3). Kinetic investigation has lagged behind, because the reactions are extremely fast and the equilibrium constants small the rate constant of one such reaction had been measured by means of our microwave apparatus (without the recent improvements), at -83 C (U). We have now determined rate constants, in 1-chlorobutane, as solvent for the reactions of zinc tetraphenyl-porphyrin with pyridine and 2-methyl pyridine, which have been well characterised by spectrophotometric methods (5, 6). They are less than the diffusion-controlled value by an order of magnitude. Further investigations are in progress. 

Among other polycyclic hydrocarbons, apparently diphenyl does not enter into the reaction. A benzo analog of diphenyl, namely, 2,2-binaphthyl 132 reacts with MA in the presence of iodine to give anhydride 133 as the main product in a complex mixture.Note that the diene unit is generated by participation of two aromatic rings. The fate of the ring hydrogen was not clear. 

---