8-Hydroxyquinolines, complexation reactions

N-Arylation of pyridones. The Cu-mediated ChanLam reaction <1999T12757> can be used for N-arylation of pyridones or pyridazinones. Alternative methods use Pb(OAc)4ZnCl2 <2004TL8781> or catalytic amounts of a copper(II) hydroxyquinolinate complex under standard UllmannGoldberg reaction conditions <2006TL149>. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

The five-coordinate complexes Ir(CO)(PPh3)2L, where HL = /3-diketone, A-benzoyl-A-phenyl-hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone, 2-hydroxy-8-methoxybenzophenone, were prepared from [Ir(CO)(PPh3)2Cl].632 The resulting compounds all underwent oxidative addition reactions with Br2. Reaction of [(cod)2IrCl]2 with N-substituted 3-hydroxy-2-methyl-4-pyridine gives the bichelated complex (389). 33... 

In a molecule of 2-phenyl-l-boraadamantane there are two markedly different types of B-C bonds two of them are boron-alkyl and one is boron-benzyl. On treatment of THF complex 34 with 8-hydroxyquinoline at 20 °C, mpture of the 1-boraadamantane core takes place, resulting in a mixture of boron chelates 52-54 (Scheme 16). When trimethylamine adduct 16 is used as the starting compound, reaction takes place only in boiling toluene. Interestingly, all the products result from the protolysis of B-CH2 bonds only <2006UP1>. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

When a metal atom donates electron density to a bound ligand, usually by means of Ji-back bonding, electrophilic substitution reactions may be promoted. This is observed then usually with metals in low oxidation states and is therefore prevalent with organometallic complexes - and less with those of the Werner-type, where the metals are usually in higher oxidation states. Nevertheless there have been detailed studies of electrophilic substitution in metal complexes of P-diketones, 8-hydroxyquinolines and porphyrins. Usually the detailed course of the reaction is unaffected. It is often slower in the metal complexes than in the free ligand but more rapid than in the protonated form. 

Extrinsic fluors are produced via a chemical reaction where the added reagent either enhances emission of a weak emitter through association or the analyte is derivatized with a fluor tag. 8-Hydroxyquinoline (HQS) is an example of an extrinsic complexing reagent (Reaction 11.1) where the native ligand is a marginal fluorophore but forms intense emitting metal chelates. This approach affords sensitive detection of... 

Another synthetic approach to the octahedral complexes of type (252) is provided by the thermal decomposition of the hydrido complex [ReH7(PPh3)2] in the presence of 2-mercapto-quinoline or 2-hydroxyquinoline in 1,2-dichloroethane solutions. The solvent is source of the chloro ligands and, thus, essential for the formation of the rhenium(III) products. Comparable reactions in THF afford hydridorhenium(V) complexes (see Section 5.3.2.11). 

General Order of Rate Constants. The rate constants of electrophilic reactions of aromatic ligands and their metal complexes fall in the order fo, > kML > kffL. The difference between these rate constants becomes greater as the activity of the attacking reagent decreases. When L is a phenolate, HL is the phenol when L is an amine, HL is the corresponding ammonium derivative. The possible synthetic applications of this sequence can be appreciated from the fact that 8-hydroxyquinoline is usually sulfonated with 15 to 30% oleum, while its copper (II) complex can be readily sulfonated in 70% sulfuric add (5). 

The unavailability of suitable starting materials has hindered work in this area, but the reaction of cyclopentadienylindium(I) in Et20/benzene mixtures with 4,4,4-trifiuoro-l-(thien-2 -yl)butane-l,3-dionate (ttaH) gave the extremely hygroscopic In(tta), and similar derivatives of other bidentate ligands were obtained by this same process.14 The reactions of the analogous In(oxine) (oxine = 8-hydroxyquinoline anion) show that such InL species are easily oxidized to indium(III) complexes (see Section 25.2.4.8). The insolubility of the product in the reaction mixture is presumably an important factor in this method. 

Complexes of 8-hydroxyquinoline and chromium(III) have been known for many years.1139 Complexes have been mercurated and the deuterated quinoline isolated.1139 The bromination of chelated 8-hydroxyquinoline proceeds about thirty-five times faster than that of the free ligand.1140 Tris(8-hydroxyquinolinato)chromium(III) absorbs large amounts of hydrochloric, hydrobromic and hydrofluoric acids. Chemical reaction with the complex was considered a more likely explanation than solid solution or clathrate formation, even though more than one mole of acid was absorbed per mole of complex.1141... 

The reaction of 8-hydroxyquinoline with silver(I) ions to give metal chelates is well established.429-430 Complexes of the type AgOx-HOx and Ag(HOx)2 have been isolated, with... 

The possibility of forming a five-membered ring through N and O shown by 8-hydroxyquinoline (7) is shared by quinaldinic acid (2) which forms well defined complexes Cu(C oH6N02)2 H20 from relatively acid solutions whence the more soluble complexes of Cd and Zn can be separated. Like oxine it is unselective and reacts with very many cations so that pH and other reaction conditions must be carefully controlled. Anthranilic acid (8) is so unselective that its use is confined to the quantitative precipitation of a single cation from a solution containing only Cd, Co, Cu, Ni or Zn. 

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