Maleic acid, dihydroxy

Magnesium perchlorate, as catalyst in acetylation of starch, I, 289 Maleic acid,.dihydroxy-, II, 96 III, 149 Malic acid, III, 238, 241 IV, 85 labelled with isotopic C, III, 140, 249 Malonic acid, II, 155 III, 238 protection of enzyme by, V, 54 Maltamylase. See under Amylases. Maltase, IV, 25, 30. See also a-Glucosi-dase. 

For catalase and peroxidase there is no direct evidence that a valency change of the iron atom occurs except when azide is added to catalase, and peroxidase is acting as an oxidase in the autoxidation of dihydroxy-maleic acid, when both systems can be poisoned by carbon monoxide. The normal absence of such poisoning cannot be taken as proof that the... 

Gatet and Genevois (1941) reported 10 to 20 mg. per liter of dihydroxy-maleic acid in wines containing 3 to 7 mg. per liter of iron, and 60 to 100 mg. in wine containing 20 to 40 mg. of iron. They explained its formation on the basis of oxidation of tartaric acid by ferric salts. Apparently dioxytartaric acid accumulates first and is converted to carboxy glyoxal acid by the action of ferric salts. Rodopulo (1951) has also studied the... 

The peroxidases, in the type of reactions described above, remain in the ferric state. They are for instance not inhibited by carbon monoxide. However, the peroxidases may function as aerobic oxidases on dihydroxy-maleic acid (88). This reaction is inhibited by carbon monoxide, and the inhibition is reversed by light. This fact shows that a reversible oxidation-reduction of the peroxidase is involved in this case. Hydrogen peroxide must be formed in traces as a necessary intermediate product, since the oxygen uptake can be promptly stopped by the addition of catalase. 

Unsaturated polyesters are prepared through a classical esterification process. Typically, a dihydroxy compound, or mixtures of dihydroxy compounds, are treated with maleic anhydride and/or together with other dicarboxylic acids such as aromatic or aliphatic dicarboxylic acids under elevated temperature to remove the water produced during esterification process. Although various catalysts will catalyze this esterification reaction, there is enough carboxylic acid in the mixture so that it is not necessary to add extra catalyst. 

The pnndpal unsaturated acids used are maleic and fumaric. Saturated acids, usually phthahe and adipic, may also be included. The function of these acids is to reduce the amount of unsaturation in the final resin, making it tougher and more flexible. The acid anhydrides are often used if available and applicable. The dihydroxy alcohols most generally used are ethylene, propylene, diethylene, and dipropylene glycols. Styrene and diallyl philialate are the most common cross-linking agents, Polyesters are resistant to corrosion, chemicals, solvents, etc. 

Osmium tetroxide is also a catalyst in the oxidation of the double bond by chlorates. Cis addition of hydroxyl groups takes place as is shown by the preparation of cis-l,2-cyclohexanediol from cyclohexene and the formation of the proper diastereoisomeric dihydroxy derivatives of maleic, fumaric, and 4-halocrotonic acids. Silver chlorate is preferred to potassium chlorate in the hydroxylation of crotonic acid. ... 

For the synthesis of (69), the enol ether (71) from the indanone (70) was carboxylated with COa-n-butyl-Iithium in THF at —70 C to yield (72). The methyl ester (73) was converted into (75) via the maleic anhydride adduct (74), essentially as described in earlier work. Lithium aluminium hydride reduction followed by oxidation with dicyclohexylcarbodi-imide afforded the aldehyde (76). This was condensed with excess (77) to yield a mixture of the diastereomers (78). Oxidation with chromium trioxide-pyridine in methylene dichloride gave (79), which could be converted into the diketone (80) by treatment with excess benzenesulphonylazide. The diketo-lactam (81) was prepared from (80) as described for the synthesis of the analogous intermediate used in the synthesis of napelline. Reduction of (81) with lithium tri-t butoxyaluminohydride gave the desired dihydroxy-lactam (82). Methylation of (82) with methyl iodide-sodium hydride gave (83). Reduction of this lactam to the amine (84) with lithium aluminium hydride, followed by oxidation with potassium permanganate in acetic acid, gave (69). 

Polyesters are macromolecules made by reacting a diacid or dianhydride with a dihydroxy compound (diols). To make unsaturated polyesters, maleic anhydride or fumeric acid is used in addition to a saturated acid, which provides unsaturation in the structure. The most commonly used anhydrides are maleic anhydride (unsaturated) and phthalic anhydride (saturated). The commonest diols are ethylene glycol or propylene glycol. Use of an unsaturated anhydride is very critical to provide unsaturation in the structure, which is utilised to cure the resin by free-radical polymerisation. The chemical reaction for the synthesis of UPE is shown in Figure 2.13. 

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