Maleic-fumaric acid isomerization

The most ambitious investigation of an isotope effect of this kind is Seltzer s (107) study of the maleic-fumaric acid isomerization in water, catalyzed by thiocyanate ion. Here, AAF" " varies from —100 cal. at 15°C. to —85 cal. at 80°C., and is thus just in the 10-15% range observed by Denny and Tunkel (102) for their reactions with stilbene. The temperature dependence yields an experimental activation energy difference of —125 cal. 

Colourless prisms m.p. 130 C. Manufactured by treating maleic anhydride with water. It is converted to the anhydride by heating at By prolonged heating at 150 "C or by heating with water under pressure at 200 C, it is converted to the isomeric (trans) fumaric acid. Reduced by hydrogen to succinic acid. Oxidized by alkaline solutions of potassium permanganate to mesotartaric acid. When heated with solutions of sodium hydroxide at 100 C, sodium( )-malate is formed. Used in the preparation of ( )-malic acid and in some polymer formulations. 

Both acids 3deld succinic acid, m.p. 185°, upon catalytic reduction (see Section 111,150), thus establishing their structures. Maleic and fumaric acids are examples of compounds exhibiting cis-trans isomerism (or geometric isomerism). Maleic acid has the cm structure since inter alia it readily 3delds the anhydride (compare Section 111,93). Fumaric acid possesses the trans structure it does not form an anhydride, but when heated to a high temperature gives maleic anhydride. 

Fum ric Acid. Eumaric acid [110-17-8] C H O, is unique in its low solubiUty in cold water and slow rate of solution, making it ideal for use in chilled biscuit leavening systems and for dry pudding mixes and beverage powders. It is also used for gelatin desserts, pie filling, fmit juices, and wine. Eumaric acid is produced by the acid-catalyzed isomerization of maleic acid (8,9) (see Maleic anhydride, maleic acid, and fumaric acid). 

Maleic anhydride and the two diacid isomers were first prepared in the 1830s (1) but commercial manufacture did not begin until a century later. In 1933 the National Aniline and Chemical Co., Inc., installed a process for maleic anhydride based on benzene oxidation using a vanadium oxide catalyst (2). Maleic acid was available commercially ia 1928 and fumaric acid production began in 1932 by acid-catalyzed isomerization of maleic acid. 

Maleic and fiimaric acids have physical properties that differ due to the cis and trans configurations about the double bond. Aqueous dissociation constants and solubiUties of the two acids show variations attributable to geometric isomer effects. X-ray diffraction results for maleic acid (16) reveal an intramolecular hydrogen bond that accounts for both the ease of removal of the first carboxyl proton and the smaller dissociation constant for maleic acid compared to fumaric acid. Maleic acid isomerizes to fumaric acid with a derived heat of isomerization of —22.7 kJ/mol (—5.43 kcal/mol) (10). The activation energy for the conversion of maleic to fumaric acid is 66.1 kJ/mol (15.8 kcal/mol) (24). 

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. 

Maleic acid can be thermally dehydrated to maleic anhydride (69) or dehydrated through azeotropic distillation. Solvents such as xylenes (70) or dibutyl phthalate [84-74-2] (71) are preferred but conditions must be carefully adjusted to avoid isomerization to fumaric acid. 

Isomerization. Maleic acid is isomerized to fumaric acid by thermal treatment and a variety of catalytic species. Isomerization occurs above the 130 to 140°C melting point range for maleic acid but below 230°C, at which point fumaric acid is dehydrated to maleic anhydride. Derivatives of maleic acid can also be isomerized. Kinetic data are available for both the uncatalyzed (73) and thiourea catalyzed (74) isomerizations of the cis to trans diacids. These data suggest that neither carbonium ion nor succinate intermediates are involved in the isomerization. Rather, conjugate addition imparts sufficient single bond character to afford rotation about the central C—C bond of the diacid (75). 

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

The presence of a hot spot is known to generate free radicals. Thus, reactions that are initiated by the presence of free radicals can be carried out with less or no catalyst, as has been discovered in the case of isomerization of maleic acid to fumaric acid with an 3 to 16 fold increase in the isomerization rates at reduced catalyst (thiourea) concentrations (Muzumdar, 1988). 

Figure 8 Separation of isomeric acids (maleic and fumaric acid) by controlled surface porosity anion exchange chromatography. Column Sulfonated fluoropolymer coated onto a 50-p glass bead. Average pore size about 1000 A. Flow rate 2.73 ml/min. Eluant 10 mM HN03. Temperature 60°C. Detection absorbance. (Reproduced from Kirkland, J. J., J. Chromatogr. Sci., 7,361,1969. By permission of Preston Publications, A Division of Preston Industries, Inc.)...

Whereas in benzene and in its derivatives the six substituents lie in the same plane, namely, that of the ring, they are distributed in cyclohexane in two planes parallel to that of the ring. Hence there results a special type of spatial isomerism when two hydrogen atoms united to different carbon atoms are replaced. The isomerism is caused by the position of the two substituents, for they may lie in the same plane (m-form), or one in each plane (iraws-form). The phenomenon is closely related to the cis-trans isomerism of the ethylenes, of which the best-known example is that of maleic and fumaric acids. 

In a model the isomerism is seen to be of the same kind as that of maleic and fumaric acids. 

Fumaric acid, a metabolite of many fungi, lichens moss and some plants, and mainly used as the diacid component in alkyd resins, is produced commercially to some extent by fermentation of glucose in Rhizopus arrhizus yet productivity improvements appear essential for the product to be an option for replacing its petrochemical production by catalytic isomerization of maleic acid. 

In geometric isomerism, the isomeric relationship can be explained in terms of two dimensions—as shown by the relationship of the two isomers, maleic acid and fumaric acid ... 

Fumaric Acid, Fumaric acid for commerce is derived from maleic acid through catalytic isomerization. Purified maleic anhydride is Ihc main source of maicic acid. High purity fumaric acid is produced through crystallization of the aqueous mixture, washing, and drying. Decolorizing and crystallization techniques arc used to treat impure maleic solutions. 

Displacement of equilibria in adsorbed layers. In cases of cis-trans isomerism, usually one isomer is much more easily adsorbed than another, and sometimes one isomer can be effectively separated from the other by suitable choice of solvent and adsorbing surface.1 Thus fumaric acid is much more strongly adsorbed than maleic, from aqueous solution, on to charcoal aVazobenzene is much the more strongly adsorbed from petroleum ether by alumina, while the trans form is far more adsorbed than the cis, from methyl alcohol, by charcoal. 

When these are cooked together, maleic anhydride isomerizes to fumaric acid, and they condense to form low-molecular-weight propylene fiimarate phthalate copolyester oligomers. These are mixed with styrene monomer, reinforced by glass fibers, usually extended with low-cost fillers, and cured by peroxide to form rigid strong products which are very resistant to impact and heat (Table 15.20). 

Fumaric Acid or Butanedionic Acid, HOOC.CH CH.COOH mw 116.07, colorless prisms, mp 286—87°(in sealed tube), bp 290° si sol in w in eth sol in ale. Can be prepd by fermentation of molasses isomerization of maleic acid or catalytic oxidation of benz. 

Another instance of a reaction catalyzed by small concentrations of free radicals is the interconversion of geometrical isomers. The cis-trans isomerization of maleic to fumaric acids... 

Geometric Isomerism.—The theory was applied by vanT Hoff and Wislicenus to the present case of the isomeric crotonic acids, and other compounds of similar character, viz., maleic acid and fumaric acid (p. 290). If two carbon atoms, instead of being linked by one bond, become directly linked by a double bond, as in the case of crotonic acid and iso-crotonic acid, the relation of the two carbon atoms, and of the two groups containing them, becomes fixed in space, because the double... 

Maleic Acid HOOC—CH = CH—COOH Fumaric Acid S3mthesis from Succinic Acid.—Two isomeric acids are known oi the constitution of di-carboxy ethene, or bulen-di-oic acid. They are named maleic acid and fumaric acid. Their synthesis from succinic acid establishes their constitution. Mono-brom succinic acid when... 

The reverse of these reactions viz., the conversion of maleic and fumaric acids, by the addition of hydrogen bromide, into mono-brom succinic acid by the addition of two bromine atoms, into di-brom succinic acid and also by the addition of two hydrogen atoms, into succinic acid itself all show these same relations of maleic and fumaric acids to succinic acid and its bromine substitution products and establish the constitution of these isomeric di-basic unsaturated acids as given. The two acids may also be prepared from malic acid which is, in fact, the chief method by which they are prepared. This reaction will be considered later when malic acid itself is studied. 

Isomerism of Maleic and Fumaric Acids.—The isomerism of maleic and fumaric acids is stereo-isomerism of the geometric type. It is exactly like that of the two crotonic acids (p. 177). 

Isomerism.—Cinnamic acid occurs as geometric stereo-isomers, as cis and trans forms like maleic and fumaric acids (p. 291) and crotonic and iso-crotonic acids (p. 177). This is apparent as it is... 

---