Selective deoxygenation

Deoxygenation is sensitive lo solvent and structure. Alcohols lend lo favor loss of oxygen, as illustrated in selected data of Accrombessi et al. (/). Additionally, methanol and ethanol may give substantial amounts of solvolysis products, in this case methoxy- and ethoxycyclohexanols. 

Ethyl 3-methyl-2-quinoxalinecarboxylate 1-oxide (249) from the corresponding 1,4-dioxide (250) [(MeO)3P, PrOH, reflux, 2.5 h 81% this selective 4-deoxygenation was not obtained with PCI3 or Na2S204]. ° ... 

The success of dibekacin prompted worldwide attention to the removal of selected OH groups in aminoglycoside antibiotics susceptible to modification by resistant bacteria, and the chemical deoxygenation procedure of D. H. R. Barton was found particularly useful. 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Selectivity could be accomplished by this method in deoxygenation of primary and secondary alcohol groups,[2] as well as effective deoxygenation of hindered secondary hydroxyl groups, especially in the carbohydrate series. ... 

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

The selective reduction of the D-ring olefin in 106 using a partially poisoned catalyst (Pd/C, 0.25 % pyridine) provided intermediate 107 (83 %), which was epimerized at -78 °C with sodium methoxide (HOAc quench at -78 °C, 89 %) (Scheme 10.9). Deoxygenation by means of tosyl hydrazone 108 and subsequent treatment with catechol borane and tetrabutylammonium acetate gave pentacyclic... 

The deoxygenation of simple unfunctionalized epoxides has already been investigated with titanocene [17-20] and samarium [27] reagents. Usually both metal complexes give mixtures of the isomers with low selectivity. Epoxide 7 investigated here is mechanistically more interesting because the... 

Numerous chemical intermediates are oxygen rich. Methanol, acetic acid and ethylene glycol show a O/C atomic ratio of 1, as does biomass. Other major chemicals intermediates show a lower O/C ratio, typically between 1/3 and 2/3. This holds for instance for propene and butene glycols, ethanol, (meth)acrylic acids, adipic acid and many others. The presence of some oxygen atoms is required to confer the desired physical and chemicals properties to the product. Selective and partial deoxygenation of biomass may represent an attractive and competitive route compared with the selective and partial oxidation of hydrocarbon feedstock. 

The potential of combining a lower need for deoxygenation and a higher product value is illustrated in Fig. 2.15. It shows that the selective incorporation of oxygen into a hydrocarbon, as done in the petrochemical industry, is very expensive. In contrast, the bio-based alternative enjoys two advantages. Firstly, the feedstock is cheaper than crude oil, even on an energy and carbon base, as discussed above. Secondly, its selective deoxygenation has been proven to cheaper than the petrochemical route in a few cases, e.g., for ethanol and furfural. The same can be expected for other biomass derivates in the future. 

Deoxygenation by full decarboxylation is the best route to make fuel precursors from bio-oil, because paraffin is produced and expensive hydrogen is not required. Decarboxylation of bio-oil has been tried over zeolites, yielding an aromatic product with a too low yield and excessive coke formation (Section 6.9.3). Selective decarboxylation of organic acids makes the bio-oil less acidic and corrosive. If acids can be removed selectively as CO2, it would also improve the energy... 

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