Adams catalyst acid-base reactions

Phenylethylamine has been made by a number of reactions, many of which are unsuitable for preparative purposes. Only the most important methods, from a preparative point of view, are given here. The present method is adapted from that of Adkins,1 which in turn was based upon those of Mignonac,2 von Braun and coworkers,3 and Mailhe.4 Benzyl cyanide has been converted to the amine by catalytic reduction with palladium on charcoal,5 with palladium on barium sulfate,6 and with Adams catalyst 7 by chemical reduction with sodium and alcohol,8 and with zinc dust and mineral acids.9 Hydrocinnamic acid has been converted to the azide and thence by the Curtius rearrangement to /3-phenyl-ethylamine 10 also the Hofmann degradation of hydrocinnamide has been used successfully.11 /3-Nitrostyrene,12 phenylthioaceta-mide,13 and the benzoyl derivative of mandelonitrile 14 all yield /3-phenylethylamine upon reduction. The amine has also been prepared by cleavage of N- (/3-phenylethyl) -phthalimide 15 with hydrazine by the Delepine synthesis from /3-phenylethyl iodide and hexamethylenetetramine 16 by the hydrolysis of the corre-... 

The presence of the epoxide moiety at C-3 and C-4 in excelsine explained the interesting chemical reactions observed earlier. On treatment with acetic anhydride and p-toluenesulfonic acid, excelsine yielded a triacetate derivative, while treatment with acetyl chloride afforded a tetraacetate derivative. On reduction with Raney nickel in methanolic base, excelsine yielded lapaconidine (92), but was inert toward other reducing agents, e.g., lithium aluminum hydride, sodium borohydride, and Adams catalyst. Treatment of excelsine with boiling aqueous hydrochloric acid yielded an epimeric mixture of chlorohydrins with molecular formula C22H34NO6CI. These epimers were hydrolyzed to the crystalline compound C22H33NO6 when treated with aqueous sulfuric acid. This compound formed a tetraacetate derivative for which structure 105 was proposed on the basis of spectral data. 

Adams catalyst (Pt02/H+) reductions of the substituted benzoic acids are generally rapid but usually give product ratios characteristic of kinetic controlled reactions. Reductions in strong base with Raney nickel catalyst appear to give the equilibrated (thermodynamic) product. 

A first test was carried out in deuterated methanol as solvent and in the presence of the catalyst employing the raw material obtained after the transmethylation step shown in Figure 12. To this mixture, D2O was slowly added by mean of a dropping fuimel. Both the Adam s catalyst (Pt02) and 10% Pd over charcoal resulted to be efficient, but the first is preferable due to the easier removal of the catalyst and work-up of the reaction. After this crucial step, the free acid was obtained by base-catalyzed hydrolysis followed by acidification of the carboxylate, as shown in Figure 12. 

---