Catalysis of Organic..

Gőbölös et al. 49noteworthy that, in contrast to ref. (11), no isomerization was observed in theabsence of catalyst (see experiments No. 12 and No. 13 in Table 3). In the catalyticisomerization of pure cis isomer the yield of the trans isomer estimated from TLCresults are listed in see Table 3. It is noteworthy that upon increasing the reactiontemperature and the amount of Raney® nickel catalyst (Metalyst, 35 % nickelcontent) the yield of trans isomer increases (compare experiments No.1 - No.11 inTable 3). For clarity, some experiments were listed and grouped twice in Table 3.Theyield of trans isomer increases, indeed, with the amount of catalyst (see experimentsat the bottom of Table 3). Careful analysis of data given in Table 3 suggests that 120-130°C is required to reach 45-55% trans isomer yield on the Metalyst Raney® nickelcatalyst. The H 2 pressure had also an influence on the trans isomer yield. However,the highest yield was obtained at 1 MPa and 120°C (experiment No. 16 in Table 3).It is worth to remind that the trans-isomer was probably formed via olefinicintermediates on the surface of Raney® nickel catalyst (5). This suggests that thehydrogen pressure should have an optimum value.Table 4 Isomerization of cis-4-aminocyclohexane carboxylic acid on Raney® nickelcatalyst (B 113 W). Effect of the amount of catalysts, temperature and H 2 pressureNo. m catalyst , mg T, °C P MPa trans- isomer,%1 150 100 1 452 150 120 1 703 150 140 1 704 150 100 2 455 a 150 120 2 506 150 140 2 607 150 100 4 408 150 120 4 509 150 140 4 6010 100 100 1 4011 100 140 1 7012 100 100 4 3013 100 140 4 5014 200 100 2 4515 200 120 2 5516 200 140 2 60Reaction condition: Solvent: 2 %NaOH-H 2 O, V=6ml; Substrate: 0.15g; t=5h.In the catalytic isomerization of pure cis isomer the yield of the trans isomerestimated from 1 H-NMR results are listed in Table 4. Results obtained on Raney®nickel catalyst (B 113 W, nickel content 90%) indicate that the yield of the transisomer significantly increases with the temperature and also affected by the hydrogenpressure (compare experiment No. 1 – No. 9 in Table 4). However the highest yieldof the trans isomer was reached at 1 MPa H 2 pressure (see experiments No. 10 – No.13 in Table 4). Upon increasing the amount of catalyst from 100 to 150 mg the yieldof the trans isomer slightly increased.The 1 H-NMR spectrum of pure cis-4-aminocyclohexane carboxylic acid ethylester is seen in Figure 1. Signals with chemical shift at δ=1.2-1.3 ppm can beassigned to the protons of the methyl group, whereas the signals of the -CH 2 - protons