In deoxygenation reaction

Complex (J) was crystallographically characterised in the case of Ar = 3,4-dichlorophenyl and shown to have the structure schematically reported in the scheme. Note that the CO2 molecule formed in the first deoxygenation of the nitro compound has not left the coordination sphere of the metal, but has remained included into a metallacyclic structure. Tliis is the earliest intermediate ever isolated in deoxygenation reactions of nitro compounds, though complexes having the same metallacyclic structure had been earlier obtained by interaction of a nitrosoarene complex with CO2 [106-108, 195]. 

Various proton and Fe-modified zeolites, for example, ferrierite, Y and p The yield of bio-oil ranged from 43.5 to 52.7 wt. %. The water yield and formation of CO increased over all zeolites, while COj production increased only to certain extent. P-zeolite was most active in deoxygenation reactions followed by Y and ferrierite. Aho et al. (2010)... 

The standard reduction potential of Cr " (Table 2) shows that this ion is a strong reducing agent, and Cr(II) compounds have been used as reagents in analytical chemistry procedures (26). The reduction potential also explains why Cr(II) compounds are unstable in aqueous solutions. In the presence of air, the oxidation to Cr(III) occurs by reaction with oxygen. However, Cr(II) also reacts with water in deoxygenated solutions, depending on acidity and the anion present, to produce H2 and Cr(III) (27,28). 

The duration of these reactions appears to be extremely important as longer reaction times resulted in deoxygenation of the thiophene derivative. 

Deoxygenative autoaromatization was reported to occur in the reaction of 3-amino-1,2,4-triazine 2-oxides 42 with alcohols in the presence of HCl or acetyl chloride. In this case the intermediate cr -adducts undergo elimination of water or acetic acid, resulting in 6-alkoxy-3-amino-l,2,4-triazines 75 (77JOC3498). 1,2,4-Triazine 1-oxides do not react with alcohols under these conditions (77JOC3498). 

The reactor is loaded with a solution of emulsifier in an organic solvent and the aqueous monomer solution (20-60%) is dispersed in the organic phase by stirring. The obtained emulsion is deoxygenated by purging dry nitrogen or by multiple evacuation and thermostated at 30-60°C. Then, an initiator solution is introduced in the reaction mixture and the process is carried out at 30-60°C for 3-6 h, after which the reaction mixture is aged for 1-5 h. 

Unexpectedly, neither direct complexation nor the deoxygenated complexes 95 or 96136,137 were observed in the reaction of diphenylthiirene oxide (18a) with iron nonacarbonyl. Instead, the red organosulfur-iron complex 97138 was isolated12, which required the cleavage of three carbon-sulfur bonds in the thiirene oxide system (see equation 33). The mechanism of the formation of 97 from 18a is as yet a matter of speculation. 

Rajanikanth and Ravindranath44 have recently published a deoxygenation reaction for sulphoxides that uses metallic lithium in refluxing dimethoxyethane. Dialkyl and alkyl phenyl sulphoxides were reduced cleanly in yields around 70%, even if sterically hindered, but benzyl sulphoxides gave mixtures of products. For example, benzyl phenyl sulphoxide gave frans-stilbene (33%), benzyl phenyl sulphide (20%) and diphenyl disulphide (47%). These products can be rationalized by reaction pathways such as in equation (17) ... 

Figure lb shows the transient absorption spectra of RF (i.e. the difference between the ground singlet and excited triplet states) obtained by laser-flash photolysis using a Nd Yag pulsed laser operating at 355 nm (10 ns pulse width) as excitation source. At short times after the laser pulse, the transient spectrum shows the characteristic absorption of the lowest vibrational triplet state transitions (0 <— 0) and (1 <— 0) at approximately 715 and 660 nm, respectively. In the absence of GA, the initial triplet state decays with a lifetime around 27 ps in deoxygenated solutions by dismutation reaction to form semi oxidized and semi reduced forms with characteristic absorption bands at 360 nm and 500-600 nm and (Melo et al., 1999). However, in the presence of GA, the SRF is efficiently quenched by the gum with a bimolecular rate constant = 1.6x10 M-is-i calculated... 

Scheme 7 Barton-McCombie deoxygenation reaction in the presence of (Me0)2P(0)H...

Deoxygenation by NO proceeds rather slowly, and nitrile oxides take part simultaneously in two other reactions (a) dimerization to furoxans 23 and (b) interaction with NO2 which is formed in the reaction, to give aryltrini-tromethanes. The most unstable of the known arenecarbonitrile oxides, benzonitrile oxide, owing to its fast dimerization gives no phenyltrinitromethane but only furoxans. Products similar to both cited reactions are formed with N2O3 because of its known equilibrium with NO and NO2 (112). 

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). 

Another interesting application of the deoxygenation reaction is shown in Scheme 12.6. Sharpless epoxides are transformed to enantiomerically pure allylic alcohols [14]. It should be noted that the disadvantage of the loss of one-half of the allylic alcohol, as in the case of kinetic resolutions of allylic alcohols, is not a problem when this protocol is employed. 

Care must also be taken to obtain the correct reaction conditions deoxygenation reactions of sulfoxides have been known to occur during relatively simple preparative procedures (see Section IV,C). In addition, displacement of other ligands can easily occur, as, for example, in Eqs. (12) and (13). 

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. 

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