Dehydration methacrylate

Purification. The dehydrated methacrylic add is purified in a series of three vacuum distillation columns, with the separations the top in succession of acetic add by-product and light ends (40 to 50 trays), 99.9 per cent weight methacrylic add (10 to 50 trays) and residual amounts entrained in the heavy compounds. 

The methyl a-hydroxyisobutyrate produced is dehydrated to MMA and water in two stages. First, the methyl a-hydroxyisobutyrate is vaporized and passed over a modified zeoHte catalyst at ca 240°C. A second reactor containing phosphoric acid is operated at ca 150°C to promote esterification of any methacrylic acid (MAA) formed in the first reactor (74,75). Methanol is co-fed to improve selectivity in each stage. Conversions of methyl a-hydroxyisobutyrate are greater than 99%, with selectivities to MMA near 96%. The reactor effluent is extracted with water to remove methanol and yield cmde MMA. This process has not yet been used on a commercial scale. 

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). 

Isobutjiene [115-11-7] or tert-huty alcohol can be converted to methacrylic acid in a two-stage, gas-phase oxidation process via methacrolein as an intermediate. The alcohol and isobutjiene may be used interchangeably in the processes since tert-huty alcohol [75-65-0] readily dehydrates to yield isobutjiene under the reaction conditions in the initial oxidation. Variations of this process have been commercialized by Mitsubishi Rayon and by a joint venture of Sumitomo and Nippon Shokubai. Nippon Kayaku, Mitsui Toatsu, and others have also been active in isobutjiene oxidation research. 

The handling of toxic materials and disposal of ammonium bisulfate have led to the development of alternative methods to produce this acid and the methyl ester. There are two technologies for production from isobutylene now available ammoxidation to methyl methacrylate (the Sohio process), which is then solvolyzed, similar to acetone cyanohydrin, to methyl methacrylate and direct oxidation of isobutylene in two stages via methacrolein [78-85-3] to methacryhc acid, which is then esterified (125). Since direct oxidation avoids the need for HCN and NH, and thus toxic wastes, all new plants have elected to use this technology. Two plants, Oxirane and Rohm and Haas (126), came on-stream in the early 1980s. The Oxirane plant uses the coproduct tert-huty alcohol direcdy rather than dehydrating it first to isobutylene (see Methacrylic acid). 

The first methacrylic esters were prepared by dehydration of hydroxyisobutyric esters, prohibitively expensive starting points for commercial synthesis. In 1932 J. W. C. Crawford discovered a new route to the monomer using cheap and readily available chemicals—acetone, hydrocyanic acid, methanol and sulphuric acid— and it is his process which has been used, with minor modifications, throughout the world. Sheet poly(methyl methacrylate) became prominent during World War II for aircraft glazing, a use predicted by Hill in his early patents, and since then has found other applications in many fields. 

Dehydration of the acid produces 95% yield of methacrylic acid ... 

Uses Solvent for nitrocellulose, ethyl cellulose, polyvinyl butyral, rosin, shellac, manila resin, dyes fuel for utility plants home heating oil extender preparation of methyl esters, formaldehyde, methacrylates, methylamines, dimethyl terephthalate, polyformaldehydes methyl halides, ethylene glycol in gasoline and diesel oil antifreezes octane booster in gasoline source of hydrocarbon for fuel cells extractant for animal and vegetable oils denaturant for ethanol in formaldehyde solutions to inhibit polymerization softening agent for certain plastics dehydrator for natural gas intermediate in production of methyl terLbutyl ether. 

Tissue Preparation for Electron Microscopy. Tissues were fixed in 2% paraformaldehyde, 2.5% glutaraldehyde in phosphate buffer (0.1 M, pH 7.4) and 0.02% picric acid. They were then dehydrated in glycol methacrylate monomer and embedded in glycol methacrylate (GMA) (24). 

Other polymers undergo cyclization, but there are no commercial applications. Poly (methacrylic acid) cyclizes by anhydride formation and poly(methyl vinyl ketone) by condensation (with dehydration) between methyl and carbonyl groups. 

For some years acetone has been converted to ketene (CH2 CO) by high temperature decomposition. The ketene is reacted with acetic acid to give acetic anhydride. Since the mid-1930 s acetone has also been one of the basic raw materials for methacrylate plastics. The first step in this process involves the addition of hydrocyanic acid to acetone to produce acetone cyanohydrin (CH3)2CO + HCN(CHs)2C(OH)CN. The methacrylate ester monomers are then made by reacting with methanol or another alcohol in the presence of sulfuric acid or some other dehydrating agent. 

The hydroxy ester was dehydrated with phosphorus pentoxide to produce ethyl methacrylate... 

Major markets as solvents and intermediates have made the ketones important commercial products lor many years. Acetone and mcthylethyl ketone have had the most impact on the chemical industry Acetone Is used s an intermediate In methyl isobutyl ketone, methyl methacrylate, diucelonc alcohol. ketone. hisphenol-A. phiwnc. and mesityl oxide Acetone is largely produced by dehydration of isopropyl alcohol In the production of phenol from cumene, acetone is produced as a by-product This mute to acetone has tended to control its price. 

Dehydration of the cyanohydrin followed by hydrolysis of the nitrile group and esterification of the resulting carboxylic acid yields methyl methacrylate. 

When the fractional drug release from an initially dehydrated hydrogel sheet is plotted as a function of square root of time as shown in Figure 1 for thiamine HC1 release from a poly(2-hydroxyethyl methacrylate) sheet, linearity in the plot is observed only at large times. This illustrates the non-Fickian and time-dependent nature... 

The polymer of methyl methacrylate (MMA) is known as Perspex. It is a clear transparent glasslike material with high hardness, resistance to fracture, and chemical stability. The conventional route, as shown by reaction 4.10, involves the reaction between acetone and hydrocyanic acid, followed by sequential hydrolysis, dehydration, and esterification. This process generates large quantities of solid wastes. An alternative route based on a homogeneous palladium catalyst has recently been developed by Shell. In this process a palladium complex catalyzes the reaction between propyne (methyl acetylene), methanol, and carbon monoxide. This is shown by reaction 4.11. The desired product is formed with a regioselectivity that could be as high as 99.95%. 

In many cases the organic to be dehydrated (e.g., acetic acid) attacks the ether linkage in the PVA membrane. Indeed, the PVA membrane has very limited fife in the presence of most acids. Ray et al. [14] used the concept of copolymer membranes to dehydrate acetic acid over the entire range of concentration from 0% to 100%. These investigators prepared copolymers of acrylonitrile (AN) with different hydrophUic monomers like hydroxy ethyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid. These copolymers have carbon-carbon bonds, which unlike the ether linkage in the cross-hnked PVA membrane are stable to the attack by carboxyhc acids. The acrylonitrile part is not sufficiently hydrophihc but imparts mechanical strength while the other monomers improve the hydrophilicity. The overall result is an efficient yet stable membrane. Variation of the ratio of AN to (the other) monomer allows freedom of adjusting the hydrophUicity of the membrane to achieve certain... 

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