Alkoxy anilines, hydrogenation

Hydrogenation of alkoxy anilines takes place over a rhodium catalyst at 60°C and 3.5 atmospheres (Eqn. 17.14). /0> Hydrogenation over a ruthenium catalyst occurs at 80°-90°C and 75-100 atmospheres ofhydrogen. The amount of alkoxy group hydrogenolysis observed under these conditions decreased from about 35% in methanol to about 10% in tert-butyl alcohol. 

An excellent route to cyclohexylamines is by hydrogenation of the corresponding aniline over rhodium or ruthenium (17,18,19 2 36,63,64). Rhodium has proved especially useful in saturation of alkoxyanilines with minimal hydrogenolysis of the alkoxy function (45), The extent of hydrogenol ysis occurring in saturation of alkoxyanilines depends also on the solvent. Hydrogenolysis of p-methoxyaniline over Ru(OH)2 fell with alcohol solvent in the order methanol (35%) > ethanol (30%) > propanol (26%) > butanol (22%) > isopropanol (16%) > r-butanol (8%) (43). 

Hydrogenation of aryl amines. Rhodium-alumina appears to be the catalyst of choice for the low-temperature hydrogenation of anilines, particularly alkoxy derivatives, to cyclohexylamines. " Hydrogenolysis is not extensive, and usually secondary amines are formed in only small amounts. 

Special multicomponent catalysts were necessary for N-aUcylation of sterically hindered anilines with alkoxy alcohols [9]. Doping Cu-chromite with Pd accelerated the hydrogenation of the imine intermediate this was found to be the rate-limiting step for all the catalysts. Alkali cations (Na and Ba ) increased the activity whereas acidic centers (e. g. Cr " " and Al ) favored hydrogenolysis of the ether bond. For N-alkylation with secondary alkoxy alcohols a Pt/Si02 catalyst doped with Sn + and Ca ions afforded the best performance. Yields of mono-alkylated anilines varied in the range 22-93 % depending on the steric hindrance in the reactants. 

Once interest in polyaniline as a most suitable conducting polymer was established, several strategies were worked out to induce solubility and processability in polyaniline [115-35]. One method to achieve solubility is by substituting one or more hydrogens by an alkyl, an alkoxy, an aryl hydroxyl, an amino group or a halogen in an aniline nucleus. We will briefly consider these aspects in this chapter. 

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