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A great variety of monosubstituted nitrobenzene derivatives has been reduced in good yield to the corresponding anilines with hydrazine hydrate in the presence of an iron oxide hydroxide catalyst prepared by precipitation from an aqueous iron(III) solution with sodium hydroxide. The dependence of the rate of reduction on the nature and the position of additional substituents other than the nitro group was determined by measuring the reaction kinetics. The rate is enhanced by electron- attracting substituents and decreased by electron- donating groups, which results in a positive slope of ρ =0.546 for the Hammett plot. Competitive reduction experiments with mixtures of two differently substituted nitrobenzene derivatives revealed that the nitro compound with the more electron- attracting substituent is reduced first.

The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.

The cyclopalladation of two different types of aniline derivatives is described: the acetylated anilines N-(3-methylphenyl)acetamide (2a), 3-(acetylamino)-4-chlorobenzoic acid (2c), and N-(2-chlorophenyl)acetamide (2d) are cyclometalated easily with palladium(II) acetate and trifluoroacetic acid to yield the corresponding complexes 4a, 4c, and 4d, respectively, whereas the acetylated meta-toluidine N-(2-chloro-5-methylphenyl)acetamide (2b) cannot be metalated at the only accessible site between the acetylamino and the methyl group. This aromatic CH bond can be activated, however, with the second type of meta-toluidine derivatives: the 2-chloro-5, N-dimethyl-N-nitrosoaniline (3b) readily undergoes cyclopalladation to yield the corresponding PdII complex di-μ-trifluoro-acetato-bis[3-chloro-6-methyl-2-(N-methyl-N- nitrosoamino)phenyl-C,NO]dipalladium(II) (5b) containing a five-membered palladacycle with coordination of PdII at the nitroso N-atom, which is established by 15N-NMR spectroscopy.

The syntheses of 1-phenylazonaphthalene (1a) and its [3′-methyl- (1b), 4′-methoxy- (1c), 3′-methoxy- (1d)] derivatives are described. Cyclopalladation of these azo ligands with Pd(II) acetate or Na2PdCl4 leads to complexes with Pd(II) coordinated on the azo Nβ-atom and a PdC σ-bond at C(2) in the naphthalene moiety. The preference of Pd(II) for this type of metalation at C(2) over the palladation at the ortho positions of the phenyl ring or at the peri position of the naphthyl ring is believed to be largely due to steric effects and the different reactivities of the two arene moieties. Substitution of the acetato-bridge with bromide or iodide allows the syntheses of the corresponding bromo- and iodo-bridged complexes, and a chloro-bridged dimer complex can be converted to a monomeric ethylenediamino-Pd(II)-azo species with ethylenediamine. Cyclopalladation of sulfonated azo ligands leads to water-soluble Pd(II) complexes with a Pd-C σ-bond at C(2).

A simple mixing-reaction model has been developed [1] which allows a description and simulation of the coupling of the mass diffusion with the chemical reaction during the mixing process of two miscible reactant solutions. For competitive, consecutive as well as for competitive, parallel second-order reactions the general behaviour and the dependence of the product distribution on diffusion effects are calculated for semi-continuous reaction conditions using various simplifying assumptions. The usefulness of these assumptions is discussed with reference to the calculated predictions of two versions of the mixing-reaction model.

The influence of mass diffusion on substrate and positional selectivities is discussed. A simple model is developed which allows a description and simulation of the coupling of the mass diffusion with the chemical reaction during the mixing process of two reactant solutions. For competitive, consecutive reactions and competitive, parallel reactions the general behaviour and the dependence of the product selectivity on diffusion effects is demonstrated.

A variety of cyclopalladated 1-arylazonaphthalenes is described, where ortho-palladation occurs at C(2) in the naphthyl ring or at C(2′ or 6′) in the phenyl moiety. Two examples of Peri-cyclopalladation at C(8) in the naphthyl ring are presented. The electronic and steric-influences of substituents at either arene moiety on the relative basicities of the azo-N-atoms and the relative nucleophilicities of the potential palladation sites C(2), C(2′ or 6′), and C(8) are discussed qualitatively in order to rationalize the observed regioselectivity.

The reaction of a cyclopalladated 1-arylazonaphthalene with tetrabutylammonium cyanide leads to an ortho-cyano-1-arylazonaphthalene and a 3-amino-aryl-benzo[g]indazole, depending upon whether triphenylphosphine or 1,2-bis(diphenyl-phosphino)ethane (DIPHOS) is used to monomerize the binuclear Pd(II)-complex. In a similar insertion reaction with cyclohexyl isocyanide the corresponding 3-(N-cyclohexyl)-aminoindazole is formed. A Pd(II)-isocyano complex is shown to be a possible intermediate in that conversion.

The results of this study show that three parameters are sufficient to describe the selectivity behaviour of nitrations influenced by mixing as long as a fast combination of the reactant solutions takes place and fast agitation is employed. This is in full agreement with the prediction of the mixing-reaction model developed previously [1]. Furthermore, the results show clearly that in nitromethane the formation rate of nitronium ions from nitric acid is slower than the mixing rate and the rate of the electrophilic substitution proper. From the mixing-disguised selectivity curves for the nitrations of durene and prehnitene with nitronium hexafluorophosphate in nitromethane the ratio of the rate constants k2 for the second nitrations can be estimated to be 1:2. For the two aromatic compounds the k1/k2 ratios are ≥ 104. Finally it could also be shown that small impurities in the solvent (e.g. water) can influence strongly the selectivity curves, depending on the method used for mixing.

In mixing-disguised azo coupling reactions the protons which are released during the electrophilic substitution steps cause a pH-gradient in the reaction zone. Since, owing to the acid-base pre-equilibria, these pH-gradients also determine the local concentrations of the reactants in the reaction zone, they also have an influence on the measured product distribution of such fast reactions. In the present work, the product distribution of the azo coupling of 1-naphthol with 4-sulfophenyldiazonium ion was experimentally measured and the results were compared with the distributions predicted from our mixing-reaction model developed previously [1]. Furthermore, some experimental evidence for the existence of isoselectivity points are presented, at which a change of the initial pH-value has no influence on the product distribution.

A mixing-reaction model ‘MIRE-CSTR’ is developed to describe the selectivity behaviour mixing-disguised reactions in continuous stirred tank reactors (CSTR). For competitive, consecutive reactions the general behaviour is demonstrated and a comparison with the behaviour in discontinuous operation is made. Furthermore, the start-up process of the CSTR is discussed with the help of a model similar to the model ‘MIRE-CSTR’.

1-Arylazonaphthalenes with all the potential cyclopalladation sites (one peri- and three ortho-positions) substituted by methyl or ethyl groups react with stoicheiometric or catalytic amounts of sodium tetrachloropalladate(II) to the corresponding 2-arylbenzo[g]indazoles. Possible mechanisms for the catalytic cyclization reaction are proposed.

The results of this study show that, for given initial and boundary conditions, four parameters are sufficient to describe the final product distribution of azo coupling reactions influenced by mixing. This is in agreement with the prediction of the mixing-reaction model developed previously [4] [5]. In order to explain the pH-dependence of the measured mixing-disguised product distribution, it is necessary to assume that a selectivity-determining, local pH-gradient exists even though the solution is macroscopically buffered.

The first acidity constants (pK1) and the zinc complex formation constants (pKzn) of 9 dyes of the type 1-(2-hydroxy-4′-X-5′-Y-phenylazo)-2-naphthol 1 were measured potentiometrically. The sorption behaviour of these dyes on zinc oxide in toluene demonstrates that first a Langmuir-type pseudo-equilibrium of the dye with a monomolecular edge-on adsorption (11) can be observed. The more acidic the dyes, the more is this equilibrium disguised by a faster dissolution of zinc ions from the surface to form (practically irreversibly) the polymeric 1:1 zinc-dye complex 10. This complex is detectable in electron micrographs. The discharge kinetics of dye-sensitized zinc oxide-binder layers in the dark and under irradiation by visible light (10 interference filters) was determined. Substituents X and Y have no detectable influence on the intrinsic discharge kinetics; however, they influence the formation of the polymer complex 10 which is contrast to 11 is not a good sensitizer.

A procedure is described which allows a quantitative determination of the enantio-differentiating chirospecificity of chiral solid materials. It enables the chiral recognition to be studied by analysing the sorption kinetics and isotherms of enantiomers onto such solids. The procedure is exemplified using polystyrene-bound chiral phosphine oxides as chiral solids and the enantiomers of mandelic acid. In addition, a model for the description of the competitive sorption of enantiomers onto a chiral porous solid is presented. With the aid of this model some surprising experimental observations can be rationalized.