Hydrogenation cyclooctadiene, selective

Transfer hydrogenation of dienes to monoenes 1,5-Cyclooctadiene is selectively reduced to cyclooctene by transfer hydrogenation with isopropanol catalyzed by this metal carbonyl cluster. The first step is isomerization to conjugated diene isomers. 1,5-Hexadiene is reduced under these conditions to frms-3-hexene (19%), os-2-hexene (21%), trans-2-, and cw-3-hexene (56%). Ru3(CO)i2, Os3(CO)12, and Ir4(CO)i2 catalyze isomerization of 1,5-cyclooctadiene, but are less active than Rh6(CO)i6 for transfer hydrogenation. 

Figure 4.1.13 COD conversion (A) and COE selectivity (B) at different hydrogen pressures, 50°C, and ccoD.cr 0.41 mol/L. Simulation (lines) and experimental data (symbols). Unchanged figure adapted from [16], Reprinted from Industrial Engineering Chemistry Research, Yol. 46, A. Schmidt and R. Schomacker, Kinetics of 1,5-cyclooctadiene hydrogenation on Pd/a-AI2O3,103-110, Copyright (2007), with permission from Elsevier via the Copyright Clearance Center.

Although the hydrogenation rate of 1,5-cyclooctadiene is lower in ethanol and 1-propanol than in methanol, the selectivity is the same [43]. The PVPD-Pd catalyst is insoluble in ethyl acetate and tetrahydrofuran and shows low activity. The rate of 1,3- and 1,5-cyclooctadiene hydrogenation is expressed by the following equation ... 

Figure 14.5 Hydrogenation of cyclooctadiene (COD) selectivity to the intermediate cyclooctene (COE) versus conversion of cyclooctadiene (COD) for the coated and uncoated Ni catalyst (conditions see Figures 14.7 and 14.8). (Data from [52, 53]).

Cyclooctadiene isomers (i.e., 1,5-cod or 1,3-cod) are selectively hydrogenated by [Ru(/74-cod)(/76-C8H1o)] (51) to produce exclusively cyclooctene in THF, under ambient temperature (20 °C) and 1 bar H2 pressure [64]. Again, cyclooctane is only detected when the diene substrate is completely transformed to the monoene. The rate of hydrogenation is higher in case of the conjugated 1,3-cycloocta-diene substrate, whereas isomerization of the non-conjugated 1,5-cyclooctadiene... 

Table 14.4 Selective hydrogenation of 1,3-cyclooctadiene to cyclooctene with various palladium complexes.

Scheme 14.21 Selective hydrogenation of 1,3-cyclooctadiene catalyzed by [Pd (1 -Me-allyl) PPh3CI] (70) [88],...

For hydrogenation in water with an inexpensive catalyst, solutions containing cobalt salts and excess cyanide are useful10,11. The catalysts are selective for conjugated C=C bonds and are relatively unreactive with unconjugated dienes such as 1,5-cyclooctadiene. 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

The selective hydrogenation of 1,5-cyclooctadiene (1,5-COD) and 1,5,9-cyclodode-catriene (1,5,9-CDT), cyclic oligomers of 1,3-butadiene, to the corresponding monoenes has been the subject of considerable interest, since the hydrogenation may constitute one of the steps leading to the synthesis of C8 and C12 lactams, dicarboxylic acids, and their derivatives. 

Compared to cyclopentadiene, 1,3-cyclooctadiene appears to be more selectively hydrogenated to cyclooctene, since hydrogenation of the cyclooctene produced may be depressed almost completely over selective palladium catalysts such as Pd-PVP-MeOH/NaOH74 and PAA- or CO-poisoned palladium.75 The maximum yields of cy-cloalkene obtained were higher with 1,3-cyclooctadiene than with cyclopentadiene or with 1,4- and 1,5-cyclooctadiene, as seen from the results in Table 3.13. The yields of cyclooctene were lower with a commercial 5% Pd-C or unpoisoned palladium. Over these unpoisoned catalysts the cyclooctene formed was further hydrogenated to cyclooctane, although in slower rates than the cyclooctadiene. 

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