Deoxygenation, catalytic with

Table 2. Barton-McCombie deoxygenation of phenyl thionocarbonate esters comparison of the catalytic with the stoichiometric reaction [25].

P3o-idine-I-oxides are comparatively resistant to reduction because of resonance stabilization by the aromatic system. Typical reagents that have been used for the formation of pyridones and pyridinols are Raney Nickel in methanol, palladium-on-charcoal, phosphorous trichloride, or phosphorus oxychloride in ethyl acetate. The N-oxides of pyridoxine, pyridoxal, and pyridoxamine have been deoxygenated catalytically. 4-Alkoxy-3-halopyri-dine-1-oxides are A-deoxygenated by phosphorous trichloride in chloroform. 2-Amino-3-pyridinol can be prepared ffom2-nitro-3-pyridinol-l-oxide (X1I450) in acetic acid by treatment with iron and mercuric chloride and then with zinc. 2-Halo-3-pyridinols can be prepared from XII-450 by treatment with phosphorous trihalides in chlorofiMm ... 

Reduction. Just as aromatic amine oxides are resistant to the foregoing decomposition reactions, they are more resistant than ahphatic amine oxides to reduction. Ahphatic amine oxides are readily reduced to tertiary amines by sulfurous acid at room temperature in contrast, few aromatic amine oxides can be reduced under these conditions. The ahphatic amine oxides can also be reduced by catalytic hydrogenation (27), with 2inc in acid, or with staimous chloride (28). For the aromatic amine oxides, catalytic hydrogenation with Raney nickel is a fairly general means of deoxygenation (29). Iron in acetic acid (30), phosphoms trichloride (31), and titanium trichloride (32) are also widely used systems for deoxygenation of aromatic amine oxides. 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

Co(TPP) has been demonstrated to act as a catalyst for the electrocarboxylation of benzyl chloride and butyl bromide with CO - to give PhCHiCfOiOCH Ph and Bu0C(0)C(0)0Bu, respectively. The propo.sed mechanism involved Co(TPP)R and [Co(TPP-N-R) as intermediates (the latter detected by spectroscopy) in the catalytic production of free R or R-, which then reacted directly with Co(TPP) precipitated on graphite foil has been successfully used for the determination of organic halides, including DDT and 1,2,3,4,5,6-hexachlorocyclohexane (lindane), to sub-ppm level in aqueous solution. Deoxygenation of the solutions is not required, and the technique is moderately insensitive to the ionic composition of the solution. ... 

The bicyclic ozonides 12 23) and thiaozonides 13 2S) afford on catalytic hydrogenation (Pd-C) the expected 1,4-diones 61 (Eq. 47). Alternatively, deoxygenation of 12 or desulfurization of 13 with triphenylphosphine led to the same products essentially quantitatively. Both reductions served for the chemical characterization of these... 

Pyrolysis of pine wood biomass was conducted at 400°C followed by catalytic deoxygenation at 450°C. The yield of the different product phases was gravimetrically determined. The gas yield was calculated by the difference. The water content of the bio oil was measured by Karl Fischer titration. The yield of the different product phases is given in Table 3, calculated from the pyrolyzed biomass. The non-catalytic experiment was carried out in the same way as the catalytic ones with the exception that the upper catalyst bed was empty. 

Nitric oxide and nitrite react with other peroxidase enzymes such as horseradish peroxidase (HRP) (138a,139), lactoperoxidase (138a) and eosinophil peroxidase (140) similarly. The rate constants for reaction of NO with compounds I and II in HRP were found to be 7.0 x 105M 1s 1 and 1.3 x 106M 1s 1, respectively (139). Catalytic consumption of NO as measured by an NO sensitive electrode in the presence of HRP compounds I and II is shown in Fig. 5 where accelerated consumption of NO is achieved even in deoxygenated solutions (140). 

Deoxygenation reactions are catalyzed by acids and the most studied are solid acids such as zeolites and days. Atutxa et al. [61] used a conical spouted bed reactor containing HZSM-5 and Lapas et al. [62] used ZSM-5 and USY zeolites in a circulating fluid bed to study catalytic pyrolysis (400-500 °C). They both observed excessive coke formation on the catalyst, and, compared with non-catalytic pyrolysis, a substantial increase in gaseous products (mainly C02 and CO) and water and a corresponding decrease in the organic liquid and char yield. The obtained liquid product was less corrosive and more stable than pyrolysis oil. 

The JV-oxide of (l,4-benzodiazepin-2-ylidene)malonate (503, R = H, n = 1) was deoxygenated by catalytic hydrogenation over Raney Nickel in a mixture of methanol and THF at atmospheric pressure for 5 hr (83USP4401597) and by treatment with phosphorus trichloride in methylene chloride at ambient temperature overnight (75JOC153 83USP-4401597). 

A further advantage of this catalytic system is that the organic cycloadducts can be easily separated from the aqueous phase, allowing the catalyst solution to be isolated and directly reused. The catalyst retains its activity for the cycloaddition through several separate uses. As illustrated for the conversion of 108 to 109, the yield of the cycloaddition remained approximately constant for five reuses of the catalyst and decreased only with the sixth use (Tab. 13.9). With alkynoate substrate 94, the experiment was repeated with rigorous deoxygenation (by freeze-pump-thaw cycles) of the catalyst solution between uses, and it was found to function cleanly after eight uses (Tab. 13.8, entry 4). 

Another method of functionalizing 72 was initiated by catalytically hydrogenating 78 to 79. Thermolysis of 79 at 220 °C under vacuum resulted in an ethylene extrusion to generate furan 80. Diels-Alder reaction of 80 with dimethyl acetyle-nedicarboxylate (DMAD) provided endoxide 81, which on subsequent deoxygenation with low-valent titanium gave ester 82 (Scheme 17). ... 

Intramolecular McMurry olefmation was realized by Furstner et al., who achieved synthesis of indol derivatives with a catalytic amount of TiCls. They employed zinc metal as a reductant and Me3SiCl as a deoxygenating agent... 

The deoxygenative ring expansion of nitrobenzene with tri-n-butylphosphine in butanol (77BCJ2013), or with phosphorus trichloride and di-n-butylamine in hexane, followed by catalytic reduction and hydrolysis of the resulting 2-butoxy- or 2-butylamino-3//-azepines have been patented as methods for the production of caprolactam (78JAP(K)78132586, 77GEP2647936 respectively). 

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