Hydrogenation of Pentadiene

For C5 alkylation, or for TAME production, removal of petandiene is required as it increases the acid consumption in alkylation and fouling in the TAME unit. The simple hydrogenation catalyst is quite sensitive to the presence of mercaptans present in this stream from cat crackers and cokers, and mercaptan removal also becomes necessary for effective hydrogenation. However, the technology of CR L for pentadiene removal achieves both goals hydrogenation of pentadiene and removal of mercaptans in the same unit. The mercaptans react with olefins in the... 

Energy level diagram for the hydrogenation of 1,3- and 1,4-pentadiene. The difference in these energies, 28 ... 

Does the delocalized tt system of 1,3-pen tadiene stabilize the molecule relative to 1,4-pentadiene Each molecule reacts with two molecules of H2 to give a common product, pentane. Thus, a comparison of their energies of hydrogenation allows us to determine the relative stabilities of two delocalized tt bonds compared with two isolated tt bonds. The hydrogenation of 1,4-pentadiene releases 252 kJ/mol, but the hydrogenation of... 

Isomerization versus Reduction Reaction Pathways in the Hydrogenation of 3-Buten-2-ol and l,4-Pentadien-3-ol on Pd-Black... 

Figure 2 Time-dependent composition data is shown for the hydrogenation of aqueous l,4-pentadien-3-ol for both (a) ultrasound irradiated and (b) magnetically stirred systems. The symbols correspond to experimental measurements (l,4-pentadien-3-ol 14PD30L-solid circles l-penten-3-ol lP30L-open hourglass 3-pentanone 3PONE-open triangles 3-pentanol 3POL-crossed squares). The lines in the ultrasound experiment simply connect the data points, whereas for the stirred experiment the lines correspond to a modeled fit (see text).

The third member of the tandem inter [4+2]/intra [3+2] cycloaddition family is classified as the bridge mode, in which the dipolarophile is attached to the dienophile. Simple, 1,4-pentadi-enes as well as 2-alkoxy-l,4-pentadienes can function effectively as dienophiles and dipolarophile combinations with excellent chemical selectivity and regio- and diastereoselectivity. Hydrogenation of the bridged nitroso acetals produces hydroxymethylated derivatives in high diastereo- and enantioselectivity (Eq. 8.116).185... 

The simplest nonconjugated, acyclic diene is 1,4-pentadiene (1), with its enthalpy of formation of 105.6 kJmol-1. The obvious question is whether the two double bonds are truly independent. If they are, then the enthalpy of hydrogenation of one double bond as in (the identical) reactions 4a and 4b would be precisely one half of that of the hydrogenation of both as in reaction 5. 

Levulinic acid is highly reactive and moreover is capable of assuming a lacl one form (XXXII). Valeric y-lactone (XXXIII) can be obtained in very high yield by hydrogenation of levulinic acid, and this compound is a good solvent and may well find extensive uses as such. Moreover it may be hydrogenated to 1,4-pentandiol (XXXIV),which on dehydration yields 1,3-pentadiene (piperylene) (XXXV). Piperylene is... 

Certain monohydride catalysts exhibit high selectivity toward hydrogenation of conjugated dienes and polyenes to give monoenes. Potassium pentacyanocobaltate prepared from CoCl2 and KCN is one of the most active catalysts, but reduces only conjugated double bonds. The reduction of dienes with nonequivalent double bonds follows the usual substitution trend noted for monoenes. 1,3-Pentadiene, for example, is converted selectively to trans-2-pentene via 1,2 addition 134... 

This step has been shown to be stereospecific in the case of hydrogenation (deuteration) catalyzed by dicyclopentadienylmolybdenumdihydride (dideuteride) (62) with cis addition of the metal hydride to the double bond (70). In these systems there is spectral evidence for the initial formation of cr- and 7r-electron donor-acceptor complexes between the catalyst and substrate prior to 7r-complex formation and n-a- rearrangement (70, 71). This catalyst (62) has also been used for the selective homogeneous hydrogenation of 1,4- or 1,3-dienes to monoenes, for example, cyclo-pentadiene (63). The reactions are run at elevated temperature (72). 

All-trans-perhydrotriphenylene (PHTP) (cf. insert in Figure 14) is the product of exhaustive hydrogenation of triphenylene. It belongs to one of ten stereoisomers of PHTP. The chiral compound of high rotational symmetry (D3 — C3 -h 3 C2) forms inclusion complexes. The stereoselective polymerization via 7-radiation of the prochiral diolelin 1,3-pentadiene within the chiral nano channels of (.R)-(-)-all-trans-PHTP led to an optically active 1,4-trans-isotactic polymer (Nattaand Farina, 1976) (cf. Figure 13). 

Intermolecular cycloaddition reactions constitute an important and convergent route to piperidines and related compounds. The research group of Franklin Davis at Temple University published a novel route to optically active piperidines that proceeded through an imino Diels-Alder reaction with enantiomerically enriched compound 84 (Scheme 16) <02OL655>. On reaction with ftww-l,3-pentadiene, intermediate 85 was produced as a single diastereomer in 89% yield. Hydrogenation of this strained intermediate yielded the 2,6-disubstituted piperidine 86 in 75% yield. 

---