Oxidative dehydration

Propylene-Based Routes. The strong acid-catalyzed carbonylation of propylene [115-07-1] to isobutyric acid (Koch reaction) followed by oxidative dehydration to methacrylic acid has been extensively studied since the 1960s. The principal side reaction in the Koch reaction is the formation of oligomers of propylene. Increasing yields of methacrylic acid in the oxydehydration step is the current focus of research. Isobutyric acid may also be obtained via the oxidation of isobutyraldehyde, which is available from the hydroformylation of propylene. The -butyraldehyde isomer that is formed in the hydroformylation must be separated. 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

Acetonides are quite stable to base, and to oxidation, dehydration and acylation reactions carried out in pyridine. They are cleaved by acid hydrolysis. The 17,21-acetonides of 17a,21-dihydroxy-20-keto steroids and related acetals are split by very mild acid conditions. ... 

Rosenow, M. A., Huffman, H. A., Phail, M. E., and Wachter, R. M. (2004). The crystal structure of the Y66L variant of green fluorescent protein supports a cyclization-oxidation-dehydration mechanism for chromophore maturation. Biochemistry 43 4464 1472. 

In view of the use of glycerol as a chemical commodity for the production of chemical intermediates, an overview will be made of existing catalytic knowledge. More specifically, glycerol oxidation, dehydration, hydrogenolysis, oligomerization/polymerization, polyol formation, and formation of a few miscellaneous products will be dealt with. 

Jansson et al. [189] used the conventional approach of blending the solid particles with solvent after which an aliquot was taken to determine the volatile compounds (e.g., phenols and chlorobenzenes). A second fraction was taken after the lipid removal for determination of compounds sensitive to concentrated sulfuric acid. The bulk lipids were removed by oxidative dehydration with Si02 /H2S04 and further cleaned-up with GPC. The chloroparaffins were isolated at this stage. Separation on silica isolated the OCPs, and the organochlorines and organobromines were finally fractionated on active charcoal. 

Preparation of Manganese(ll) Oxide. Dehydrate 1 g of manganese oxalate by heating in a porcelain bowl at not over 200 °C. Transfer the salt into a porcelain boat and roast it in a tubular furnace in a stream of dry hydrogen at 300-400 °C (see Fig. 115). Preliminarily check the tightness of the apparatus and the purity of the hydrogen ... 

Let us consider some examples, such as conjugated oxidative dehydration of acetic acid [7] 2CH3COOH(lq) (CH3C0)20(lq) + H20(lq), (3.11)... 

The final process represents a new reaction type—oxidative dehydration accompanied by free energy loss. Contrary to usual dehydration, this process may be performed under soft conditions at almost room temperature ... 

Sulfuric acid (oil of vitriol, H2S04) is a colorless, oily liquid, dense, highly reactive, and miscible with water in all proportions. Heat is evolved when concentrated sulfuric acid is mixed with water and, as a safety precaution, the acid should be poured into the water rather than water poured into the acid. Anhydrous, 100% sulfuric acid, is a colorless, odorless, heavy, oily liquid (boiling point 338°C with decomposition to 98.3% sulfuric acid and sulfur trioxide). Oleum is excess sulfur trioxide dissolved in sulfuric acid. For example, 20% oleum is a 20% sulfur trioxide-80% sulfuric acid mix. Sulfuric acid will dissolve most metals and the concentrated acid oxidizes, dehydrates, or sulfonates most organic compounds, sometimes causing charring. 

The compound (70) by epoxide ring-opening with hydrogen fluoride, followed by photocatalysed addition of acetylene to the A16-bond and lithium aluminium hydride reduction, gave (71). Protection of the 1,2-diol system in (71) as the acetonide followed by oxidation, dehydration, and regeneration of the diol grouping produced... 

When 125 was subjected to a two-step sequence, reductive cleavage of the 0-0 bond and subsequent oxidative dehydration, by treatment with zinc in AcOH, the allylic diol 135 and the 1,2-oxazocine 126, as minor product, were isolated. Oxidation of the diol 135 under several different reaction conditions (pyridinium chlorochromate (PCC), 2-iodoxybenzoic acid (IBX)/EtOH, IBX/DMSO, Pyr/SOj) gave 126 in high yield (68-92%), while with tetrapropylammonium perruthenate/Wmethylmorphaline Ar-oxidc (TPAP/NMO) as oxidizing agent 126 was the minor product and the a,/3-unsaturated 7-butyrolactone 136 was obtained in 68% yield (Scheme 28) <2005JOC6995>. 

The body image on the cloth is the result of an oxidation-dehydration reaction of the cellulose material of the cloth itself rather than the result of an applied pigment, stain, or dye. 

In this case study, we have carried out further investigation into the structure of VO, supported on alumina under both oxidized (dehydrated) and reduced environments using both UV- (244 nm) and visible- (488 nm) excited Raman spectroscopy. Special attention has been directed towards the structure of supported VO at extremely low surface density (down to 0.01 Vnm ). 

Wood burns because the cell wall polymers undergo hydrolysis, oxidation, dehydration, and pyrolysis reactions with increasing temperature to give off volatile, flammable gases. The lignin component contributes more to char formation than do the cellulose components, and the charred layer helps insulate the wood from further thermal degradation see Chapter 13). 

Contrary to the case of olefins, homogeneous catalytic oxidations of light alkanes occur at temperatures similar to those of the catalytic reaction. This certainly led to misinterpretation of supposedly catalytic data in certain cases. Two examples will illustrate the role of homogeneous reaction the oxidative dehydration of propane and the reactions of pentane with oxygen. 

The processes responsible for most of the reactions Identified are oxidation, dehydration, sulfur fixation, solid-state interactions and vaporization. Isolating specific reactions occurring in a multi-component system is difficult the use of model systems was helpful in tracing mineral transformations. Additional work planned in this area includes research on non-equilibrium systems and experiments in reducing atmospheres. 

Gel-permeation chromatography" is used to compare the pore structure of jute, scoured jute and purified cotton cellulose. Both native and scoured jute have shown greater pore volumes than cotton. The effects of alkali and acid treatment on the mechanical properties of coir fibers are reported." Scanning electron micrographs of the fractured surfaces of the fibers have revealed extensive fibrillation. Tenacity and extension-at-break decrease with chemical treatment and ultraviolet radiation, whereas an increase in initial modulus and crystallinity is observed with alkali treatment. FTIR spectroscopy shows that the major structural changes that occur when coir fibers are heated isothermally in an air oven (at 100, 150 and 200 °C for 1 h) are attributable to oxidation, dehydration and depolymerization of the cellulose component. 

Process simplification such as oxidative dehydration of ethane to ethylene without a steam cracker and without the release of carbon dioxide and nitric oxides. 

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