Maleic anhydride formation

Beneficial Micro Reactor Properties for Maleic Anhydride Formation... 

As indicated, in this scheme maleic anhydride is formed both directly and from benzoquinone. The latter route, however, contributes only 2—10% to the maleic anhydride formation. 

The suitability of this model, at least for a non-too-wide conversion range, has been confirmed by several authors. However, a correct description of the maleic anhydride production obviously demands splitting of kB into individual rate coefficients for maleic anhydride formation and for combustion, while in fact a separate equation should be added for maleic anhydride combustion. Such multi-step redox models have not been reported in the literature. Sets of first-order rate equations, however, are widely used,... 

Both reactions are exothermic and essentially irreversible. The maleic anhydride formation occurs only at the catalyst surface while its degradation takes place in the gas phase W It is therefore expected that the selectivity and the conversion will be equally important in the operation of fluidized bed reactor. 

More imeresiing is the analysis of ihe peaJc shape which reflects both the rate of formation and the rate of desorption. Assuming the latter constant for MA (a reasonable assumption, because the rate of desorption depends primarly on the nature of the moiecule), the shift in the maAtmum and especially the mictal slope deviation indicate a decrease in the turnover number of the specific sites (or cluster of sites) responsible for maleic anhydride formation. In these conditions, in fact, no iiuemiediate products desorb from the catalyst surface. Probably, this derives frc m the inhibition in the availability of neighboring oxygen sites as discussed above. 

While our studies for identification of the active/selective phase continues, in a parallel effort, we have conducted some experiments to assess the role of dicyclopentadiene, one of the intermediates proposed in the literature [7]. The objective behind this phase of the study was to examine the routes that originate from dicyclopentadiene and result in phthalic anhydride versus maleic anhydride formation. The catalyst used in this set of experiments was vanadium pentoxide that was pre-reduced in situ at 400 °C with hydrogen. 

Many grafting reactions can be considered as multicomponent reactions that are diffusion limited. Good mixing is indispensable for the product quality, because otherwise homopolymerization of the monomer and cross-linking or chain scission of the polymer can occur. This is connected to the fact that the grafting reaction competes with different side reactions like homopolymerization or, as in the case of maleic anhydride, formation of excimers. 

Addition of steam to the reaction feed proves to be crucial for obtaining high yields of maleic anhydride by modifying the physico-chemistry of the VPO catalyst improved overall crystallinity, decreased ratio of V +ZV ", enhanced Brpnsted acidity, but decreased acidic strength. It has been determined that the rate of maleic anhydride formation is proportional to the decay of V " species [28]. 

Acid Chloride Formation. Monoacid chlorides of maleic and fumaric acid are not known. Treatment of maleic anhydride or maleic acid with various reagents such as phosgene [75-44-5] (qv), phthaloyl chloride [88-95-9] phosphoms pentachloride [10026-13-8] or thionyl chloride [7719-09-7] gives 5,5-dichloro-2(5JT)furanone [133565-92-1] (4) (26). Similar conditions convert fumaric acid to fumaryl chloride [627-63-4] (5) (26,27). NoncycHc maleyl chloride [22542-53-6] (6) forms in 11% yield at 220°C in the reaction of one mole of maleic anhydride with six moles of carbon tetrachloride [56-23-5] over an activated carbon [7440-44-4] catalyst (28). 

Hydration and Dehydration. Maleic anhydride is hydrolyzed to maleic acid with water at room temperature (68). Fumaric acid is obtained if the hydrolysis is performed at higher temperatures. Catalysts enhance formation of fumaric acid from maleic anhydride hydrolysis through maleic acid isomerization. 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Polyester resins can also be rapidly formed by the reaction of propylene oxide (5) with phthaUc and maleic anhydride. The reaction is initiated with a small fraction of glycol initiator containing a basic catalyst such as lithium carbonate. Molecular weight development is controlled by the concentration of initiator, and the highly exothermic reaction proceeds without the evolution of any condensate water. Although this technique provides many process benefits, the low extent of maleate isomerization achieved during the rapid formation of the polymer limits the reactivity and ultimate performance of these resins. 

Today, the air oxidation of toluene is the source of most of the world s synthetic benzaldehyde. Both vapor- and Hquid-phase air oxidation processes have been used. In the vapor-phase process, a mixture of air and toluene vapor is passed over a catalyst consisting of the oxides of uranium, molybdenum, or related metals. High temperatures and short contact times are essential to maximize yields. Small amounts of copper oxide maybe added to the catalyst mixture to reduce formation of by-product maleic anhydride. 

Benzo[Z)]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z)]furan and 2- and 3-vinylindoles give adducts involving the exocyclic double bond. In contrast, the benzo[c]-fused heterocycles function as highly reactive dienes in [4 + 2] cycloaddition reactions. Thus benzo[c]furan, isoindole (benzo[c]pyrrole) and benzo[c]thiophene all yield Diels-Alder adducts (137) with maleic anhydride. Adducts of this type are used to characterize these unstable molecules and in a similar way benzo[c]selenophene, which polymerizes on attempted isolation, was characterized by formation of an adduct with tetracyanoethylene (76JA867). 

Blends based on polyolefins have been compatibilized by reactive extrusion where functionalized polyolefins are used to form copolymers that bridge the phases. Maleic anhydride modified polyolefins and acrylic acid modified polyolefins are the commonly used modified polymers used as the compatibilizer in polyolefin-polyamide systems. The chemical reaction involved in the formation of block copolymers by the reaction of the amine end group on nylon and anhydride groups or carboxylic groups on modified polyolefins is shown in Scheme 1. 

One of the earliest references on compatibilizing a nylon-6-polypropylene blend using maleic anhydride grafted PP (PP-g-MAH) was the work of Ide and Hase-gawa published in 1974 [35]. In their study, the formation of a graft copolymer was confirmed by DSC after solvent extraction of the PP component. Blends with PP-g-MAH... 

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. 

A common reaction sequence is shown in the schemes printed above. The sulfosuccinate monoesters are produced by a two-step reaction. In the first step 1 mol of maleic anhydride is reacted with a hydroxyl group-bearing component. In the second step the monoester is reacted with sodium sulfite (or sodium bisulfite) to form the disodium alkyl sulfosuccinate. At the so-called halfester stage, there are two possibilities for an electrophilic attack [61] (Michael-type reaction) at the double bond (Scheme 6). Reactivity differences between the two vinylic carbons should be very small, so that probably an exclusive formation of one single regioisomer can be excluded. 

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