Oxidation of Isobutylene

Much like the oxidation of propylene, which produces acrolein and acrylic acid, the direct oxidation of isobutylene produces methacrolein and methacrylic acid. The catalyzed oxidation reaction occurs in two steps due to the different oxidation characteristics of isobutylene (an olefin) and methacrolein (an unsaturated aldehyde). In the first step, isobutylene is oxidized to methacrolein over a molybdenum oxide-based catalyst in a temperature range of 350-400°C. Pressures are a little above atmospheric  

In the second step, methacrolein is oxidized to methacrylic acid at a relatively lower temperature range of 250-350°C. A molybdenum-supported compound with specific promoters catalyzes the oxidation. 

Methacrylic acid is esterified with methanol to produce methyl methacrylate monomer. 

Methacrylic acid and methacrylates are also produced hy the hydrocya-nation of acetone followed hy hydrolysis and esterification (Chapter 8). 

Ammoxidation of isobutylene to produce methacrylonitrile is a similar reaction to ammoxidation of propylene to acrylonitrile. However, the yield is low. 

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With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. 

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). 

Because of limitations on the ready availability of HCN, particularly in Japan, processes involving the oxidation of C4 intermediates have been developed and are now replacing the older route developed by Crawford. One important process is based on the two-stage oxidation of isobutylene or -butyl alcohol to methacrylic acid, which is then separated and esterified Figure 15.5a). 

One disadvantage of this process is the waste NH4HSO4 stream. Methacrylic acid (MAA) is also produced by the air oxidation of isobutylene or the ammoxidation of isobutylene to methacrylonitrile followed by hydrolysis. These reactions are noted in Chapter 9. 

Direct non-catalytic liquid-phase oxidation of isobutylene to isobutylene oxide gave low yield (28.7%) plus a variety of oxidation products such as acetone, ter-butyl alcohol, and isobutylene glycol ... 

Isobutylene glycol may also be produced by a direct catalyzed liquid phase oxidation of isobutylene with oxygen in presence of water. The catalyst is similar to the Wacker-catalyst system used for the oxidation... 

Liquid-phase oxidation of isobutylene glycol produces othydroxyisohu-tyric acid. The reaction conditions are 70-80°C at pH 2-7 in presence of... 

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

Methacrylic acid has been used for the synthesis of polyfmethyl methacrylate). It has been synthesized industrially via a reaction of acetone with hydrogen cyanide (12, 17, 330, 331). However, the process produces ammonium bisulfate and uses the toxic hydrogen cyanide. Recently, an alternative, a two-step oxidation of isobutylene, has been developed. The first step is the oxidation of isobutylene to methacrolein, and the second is the oxidation of methacrolein to methacrylic acid ... 

Because of the problems with disposal of the bisulfate waste and the handling of HCN, much research has been devoted to alternative processes. The new processes range from using new feedstocks such as isobutylene / t-butyl alcohol, ethylene, isobutane or methylacetylene to techniques for recycling the HCN and / or ammonium bisulfate279 28°. In 1998 Asahi replaced 60,000 tonnes per year of MMA capacity based on direct oxidation of isobutylene with a new process that also starts with isobutylene. However the new direct oxidative esterification (DOE) process makes MMA by the simultaneous oxidation and esterification of methacrolein, which eliminates the intermediate production of methacrylic acid298. 

Shashkin et al. (1991) Shashkin et al. (1993) IR Multiple promoted iron molybdates Vanadium molybdates Phase formation Active phase identification Identification of hex M0O3 as active phase + + + Partial oxidation of isobutylene C3, C4 olefin partial oxidation... 

Feuer H, editor. The chemistry of the nitro and nitroso groups. New York Wiley 1969. Shoenbrunn E. F, Gardner J. H. Oxidation of isobutylene with dinitrogen tetroxide. J. Am. Chem. Soc. 1960 82 (9) 4905-8. 

The oxidation of isobutylene with thallium triacetate gives 82% of isobutylene oxide [412]. The oxidation of 1-pentene with peroxytrifluo-roacetic acid yields 81% of propyloxirane [283]. The electrooxidation of... 

Derivation Reaction of acetone cyanohydrin and dilute sulfuric acid oxidation of isobutylene. 

Another process used in Japan for making methyl methacrylates is the Escambia process. Methyl methacrylate is made by nitric acid oxidation of isobutylene to methacrylic acid and esterification with methanol [40]. 

Vinyl compounds are widely used in the industry in manufacture of various resins and polymers and the like. Methacrylic acid and methyl methacrylate are especially attractive as row materials of polymethyl methacrylate that is an important polymer so-called "organic glass." Until a new process consisting of two-step oxidation of isobutylene was commercially practiced in 1982, methyl methacrylate had been produced by the "Acetone Cyanohydrine Process," which uses acetone, hydrogen cyanide, methanol, and sulfuric acid as raw materials. Technical and economical drawbacks of this process have spurred a considerable industrial research effort to develop an alternate route to methacrylic acid and methyl methacrylate. Therefore, many attempts have been focused on the production of these compounds by aldol-type condensation using HCHO. 

Oxidation of isobutylene glycol Pt/C a-Hydroxybutyric acid, an intermediate Chemtech (1975)... 

The technical routes of the commercialized processes of PMMA could be categorized by (i) the direct oxidation process which consists of catalytic oxidation of isobutylene or tert-butanol to methacrylic acid (MAA) in two steps (ii) the methacrylonitrile (MAN) route by ammoxidation of tert-butanol (iii) the BASF s method which employs ethylene, carbon monoxide, and formaldehyde as raw materials (iv) the new ACH process by Mitsubishi Gas Chemical Co. Inc., which does not generate acid waste and (v) the direct oxidative esterification of methacrolein by Asahi Chemical Co. Ltd.[l] For most of the newly developed processes, efforts have been made to minimize the impact of the production on the environment. 

These few examples show an advantage of anaerobic oxidations for selected reactions, to minimize CO2 formation. A few other opportunities for further study should include the oxidation of o-xylene to phthalic anhydride, oxidative dehydrogenation of ethylbenzene to styrene, oxidation of isobutylene to methacrolein and methacrylic acid, and oxidative dehydrogenation of paraffins to olefins. 

Acrylates can be made by a single-step process from acetylene or a two-step process from ethylene oxide. Methacrylates can be made by selective oxidation of isobutylene followed by esterification or a two-step process starting with acetone. 

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