Hydrogenolysis amine effect

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

Tertiary amines are effective promoters in hydrogenolysis of hindered benzyl esters that otherwise may undergo cleavage only with difficulty (187). 

It was found in the case of O-benzyl systems that palladium oxide is much more effective than palladium metal. No such effect was observed with the N-benzyl system.8 It is possible that the N-compounds can poison the electrophile metal ions, and the hydrogenolysis of the N-benzyl bond can take place only by the hydrogenolytic cleavage instead of the insertion mechanism. This is supported by the experimental finding that the product amine can inhibit the catalyst, and this can be minimized by buffering at a pH less than 4. 

The triphenylmethyl function, also known as trytil (Trt), is a valuable bulky protecting group for peptide chemistry. Trytil groups confer acid-labile protection onto amines, but effective removal can also be achieved by catalytic hydrogenolysis. 

Protection of amines homobenzyloxycarbonyl (hcbo) group.2 In contrast to the Cbo group, the homoCbo group is stable to HBr in HO Ac at 25° and to HC1 in ether. It is also less susceptible to hydrogenolysis, but deblocking can be effected by catalytic transfer hydrogenolysis with a Pd/C catalyst in the presence of ammonium formate. Best results are obtained with a catalyst freshly prepared from Pd(OAc)2. 

TABLE 11.17 Effects of Solvents on Hydrogenation-Hydrogenolysis of Aromatic Amines over Ruthenium Catalyst ... 

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