Propanediols, hydrogenolysis

Boro nophenyl) alanine (BPA) is a practical boron compound which is clinically used for the treatment of not only malignant melanoma but also of brain tumors, in neutron capture therapy (Scheme 1-40) [105, 152, 153]. Although (pinacolato)di-boron (82) is an excellent reagent to afford the corresponding boronate in 88% yield, it strongly resists the hydrolysis to arylboronic acids. Alternatively, the 1,3-diphenyl-propanediol ester (85) is more convenient to deprotect the diol moiety by catalytic hydrogenolysis [105]. 

In conclnsion, it was shown that the hydrogenolysis of glycerol in the presence of heterogeneous rhodium-based catalysts yielded mainly either 1,2-, or 1,3-propane diol. Many parameters influenced the activity and the selectivity of the catalysts, particnlarly the presence of metal additives and the initial pH value. 1,2-propanediol can be obtained nearly quantitatively at high pH. Further woik is currently under progress in order to optimize this reaction. 

Many systems have been described for the hydrogenolysis of glycerol, yielding mainly 1,2-propanediol. Copper chromite-based catalysts seem to be the better performing ones. Unfortunately, most of the data available is of a descriptive nature and a fundamental understanding of the catalyst is often missing. 

TABLE 2. Yields of polyols and oses hydrogenolysis (1,2-propanediol + glycerol). 

In contrast, selective hydrogenolysis of glycerol to 1,3-propanediol by means of chemo catalysis is still a challenging task. Although several attempts do exist with, for example, Pt/W03/Zr02 or Ir-ReOx/Si02 catalysts [48, 49], the enzyme-catalyzed route using bacterial strains is more efficient [42] and has been commercialized (see Table 2.2.1). 

Amada Y, Shinmi Y, Koso S, Kubota T, Nakagawa Y, Tomishige K. Reaction mechanism of the glycerol hydrogenolysis to 1,3-propanediol over Ir-ReOx/SiC>2 catalyst. Appl Catal B Environ. 2011 105 117-27. 

Primary 2-phenyl- or 2-(l-pyridyl)ethanols may undergo hydrogenolysis between the C1-C2 bond of the side chain on treatment with Raney Ni in refluxing ethanol.308 Thus, 2-phenyl-1,2-propanediol yields ethylbenzene as a main product, along with lesser amounts of cumene and 2-phenyl-1-propanol (eq. 13.163). Similarly, 2-(l-pyridyl)ethanol gives 1-methylpyridine as the predominant product. 

Hydrogenolysis of lactose at a pressure of about 300 atmospheres with a copper-chromium oxide catalyst gave, amongst other products, methanol, ethanol, 1,2-propanediol, and three other compounds (that were tentatively identified as tetrahydro-4-hydroxyfurfuryl alcohol, 1,2,5-hexanetriol, and 1,2,5,6-hexanetetrol. ... 

The chiral glycerol derivative 355 was prepared by lipase-catalyzed asymmetric /ran5-esterification. Tosylation of 355 followed by hydrolysis gave 356. Hydrogenolysis of 356 gave 3-tosyloxy-l,2-propanediol (357). After... 

Hydrogenolysis of glycerol to 1,2- and 1,3-propanediols (PrD) seems to be simple judging from the reaction formula as below (1, 2) because the hydrogenolysis of C-O bonds apparently means the dissociation of C-O bonds and insertion of hydrogen atoms. 

Fig. 3 Comparison of the catalytic the performances in the glycerol hydrogenolysis over modified Rh/Si02 [33]. Reaction conditions glycerol 4 g, water 16 g, Rh-M0 j/Si02 (M/Rh = 0.25) 0.15 g, F(H2) = 8 MPa, r = 393 K, / = 5 h. Re/Rh = 0.5, r = 1 h. PrD propanediol, PrOH propanol. Degradation ethylene glycol + ethanol + methanol + methane. Reprinted with permission from...

Amada Y, Koso S, Nakagawa Y, Tomishige K (2010) Hydrogenolysis of 1,2-propanediol for the production of biopropanols from glycerol. ChemSusChem 3 728-736... 

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