Fumaric acid hydrogenation

The ruthenium cluster [Ru2(i76-C6H6)H6]C12 is a catalyst for fumaric acid hydrogenation in aqueous solutions, with a turnover frequency of 35 h 1 at 50°C (86). 

In contrast to the case of maleic and fumaric acids, hydrogenation of crotonic acid was sharply inhibited by an excess of TPPMS - again, behavior analogous to that of [RhCl(PPh3)3] in hydrogenation of alkenes. 

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. 

Racemic acid, ( )-tartaric acid, is a compound of the two active forms. M.p. 273 C (with IHjO), m.p. 205°C (anhydrous). Less soluble in water than (-t-)-tartaric acid. Formed, together with mesotartaric acid, by boiling (4-)-tartaric acid with 30% NaOH solution, or by oxidation of fumaric acid. Potassium hydrogen racemate is very insoluble. 

Description of Method. Salt substitutes, which are used in place of table salt for individuals on a low-sodium diet, contain KCI. Depending on the brand, fumaric acid, calcium hydrogen phosphate, or potassium tartrate also may be present. Typically, the concentration of sodium in a salt substitute is about 100 ppm. The concentration of sodium is easily determined by flame atomic emission. Because it is difficult to match the matrix of the standards to that of the sample, the analysis is accomplished by the method of standard additions. 

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). 

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). 

Succinic anhydride [108-30-5] (3,4-dihydro-2,5-furandione butanedioic anhydride tetrahydro-2,5-dioxofuran 2,5-diketotetrahydrofuran succinyl oxide), C H O, was first obtained by dehydration of succinic acid. In the 1990s anhydride is produced by hydrogenation of maleic anhydride and the acid by hydration of the anhydride, by hydrogenation of aqueous solutions of maleic acid, or as a by-product in the manufacture of adipic acid (qv) (see Maleic ANHYDRIDE, MALEIC ACID, AND FUMARIC ACID). 

Succinic acid can also be produced by catalytic hydrogenation of aqueous solutions of maleic or fumaric acid in the presence of noble metal catalysts, ie, palladium, rhodium, mthenium, or their mixtures, on different carriers (135—139) or on Raney nickel (140). 

Figure 6-18 shows a bell-shaped pH-rate profile for the hydrolysis of monomethyl dihydrogen phosphate. Other examples are the hydrolysis of o-carboxyphenyl hydrogen succinate and the hydration of fumaric acid. ... 

An example of intramolecular hydrogen bonding is provided by the cis- and trans- forms of the acid HOOC—CH=CH—COOH. The trans- form, fumaric acid, has a higher melting point than the cis- form, maleic acid. In addition to the general effect of molecular shape (mentioned earlier in this chapter), another reason for... 

This intramolecular bonding in maleic acid, (8), halves its ability to form intermolecular bonds. In fumaric acid, on the other hand, all of the hydrogen bonds form between molecules (intermolecular bonds) to give a stronger, interlinked crystal structure. 

The potassium salt of tartaric acid, potassium bitartrate or potassium hydrogen tartrate, is weakly acidic, and is known as cream of tartar. Since it is a dry acid, cream of tartar is used in baking powders (along with sodium bicarbonate) to produce carbon dioxide gas when added to water. Other acids used in baking powder are fumaric acid and phosphoric acid. 

Detailed studies of 1 1 complex formation between and maleic and fumaric acids, which precedes reduction to succinic acid, cis-trans isomerisation and exchange of the double bond hydrogens, are relevant to the complex kinetics (A = substrate)... 

Buffers are necessary to adjust and maintain the pH. Buffering agents can be salts of a weak acid and a weak base. Examples are ammonium, potassium, sodium carbonates (caustic soda), bicarbonates, and hydrogen phosphates [1345]. Weak acids such as formic acid, fumaric acid, and sulfamic acid also are recommended. Common aqueous buffer ingredients are shown in Table 17-8. 

Elving, Rosenthal, Hayes and Martin 41> studied the electrochemical reduction of bromofumaric acid(27) and bromomaleic acid(28)in aqueous solution over a wide pH range. It was claimed that reduction of 27 proceeds stereo-specifically to fumaric acid, and that reduction of 28 affords mixtures of maleic and fumaric acids. Because of the polar and hydrogen-bonding properties of the carboxyl groups in 27 and 28, the relation of these results to those of Fry and Mitnick l6) is unclear. 

The effect is very pronounced, but falls off sharply as soon as the carboxyl groups are separated by more than one saturated carbon atom. C/ s-butenedioic(maleic) acid (5, pKal = 1-92) is a much stronger acid than trans-butenedioic(fumaric) acid (6, pX,1 = 3-02), due to the intramolecular hydrogen bonding that can take place with the former, but not with the latter, leading to relative stabilisation of the cis (maleate, 7) mono-anion (cf. o-hydroxybenzoic acid above) ... 

Ethyl fumarate has been prepared from fumaric acid and ethyl alcohol, with or without sulfuric acid as catalyst,4 from silver fumarate and ethyl iodide,5 from silver maleate and ethyl iodide plus a trace of iodine,6 from ethyl maleate by the action of iodine,6 from ethyl maleate and phosphorus pentachloride,7 and by passing hydrogen chloride into a boiling absolute alcohol solution of malic acid.8... 

Hydrogen. The Synthesis and Oxidation of Fumaric Acid. J. Amer. chem. Soc. 64, 948 (1942). 

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. 

The hydrogen transfer photosensitization has been applied to the diastereo-selective alkylation of chiral fumaric acid derivatives, where again the mild conditions of the photochemical method are advantageous (Figure 3.8). ... 

At 87 °C and pH 2.5, malathion degraded in water to malathion a-monoacid and malathion P-monoacid. From the extrapolated acid degradation constant at 27 °C, the half-life was calculated to be >4 yr (Wolfe et al., 1977a). Under alkaline conditions (pH 8 and 27 °C), malathion degraded in water to malathion monoacid, diethyl fumarate, ethyl hydrogen fumarate, and QO-dimethyl phosphorodithioic acid. At pH 8, the reported half-lives at 0, 27, and 40 °C are 40 d, 36 h, and 1 h, respectively. However, under acidic conditions, it was reported that malathion degraded into diethyl thiomalate and 0,0-dimethyl phosphorothionic acid (Wolfe et al, 1977a). 

In aqueous hydrochloric acid solutions, mthenium(II) chloride catalyzed the hydrogenation of water-soluble olefins such as maleic and fumaric acids [6]. After learning so much of so many catalytic hydrogenation reactions, the kinetics of these simple Ru(II)-catalyzed systems still seem quite fascinating since they display many features which later became established as standard steps in the mechanisms of hydrogenation. The catalyst itself does not react with hydrogen, however, the mthenium(II)-olefin complex... 

Let us consider now the origin of the effect of varying solvent composition on the hydrogenation rate in diglyme-water mixtures. The key to the explanation comes from the study of the effect of pH on the rate of hydrogenation of maleic and fumaric acids in homogeneous aqueous solutions. Fig. 3.2.a and 3.2.b show these rates as a function of pH together with the concentration distribution of the undissociated (H2A), half dissociated (HA ) and fully dissociated (A ) forms of the substrates [86]. 

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