Anhydride and Citraconic Acid

Citraconic Anhydride Two hundred and fifty grams of itaconic anhydride (Note r) is distilled rapidly at atmospheric pressure in a 500-cc. modified Claisen flask with a 15-cm. (6-in.) fractionating column (Note 2). The receivers for the distillate must be changed without interrupting the distillation. The distillate passing over below 200° consists of water and other decomposition products. The fraction which distils at 200-2150 consists of citraconic anhydride and is collected separately. The yield is 170-180 g. (68-72 per cent of the theoretical amount) of a product melting at 5.5-6°. On redistillation under reduced pressure there is obtained a yield of 155-165 g. (62-66 per cent of the theoretical amount based on the itaconic anhydride used) of a product which boils at io5-iio°/22 mm. and melts at 7-8° (Note 3). 

Citraconic Acid To 22.4 g. (0.2 mole) of pure citraconic anhydride in a 100-cc. beaker is added from a pipette exactly 

22 mole) of distilled water. The mixture is stirred on a hot plate until a homogeneous solution is formed, then covered with a watch glass and allowed to stand for forty-eight hours. At the end of this time the mixture has solidified completely. The yield is 26 g. of a product melting at 87-89°. For further purification it is finely ground in a mortar, washed with 50 cc. of cold benzene, dried in the air, and then dried for twenty-four hours in a vacuum desiccator over phosphorus pentoxide. The yield is 24.4 g. (94 per cent of the theoretical amount) of a product which melts at 92-93°. 

The crude itaconic anhydride obtained as described on page 70 was used. Itaconic acid may be substituted for the anhydride. 

The success of the preparation depends upon a rapid distillation and changing the receivers without interrupting the distillation. The best yields are obtained when the heating period is of short duration. 

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Condensation with Aldehydes and Ketones. Succinic anhydride and succinic esters in the presence of different catalysts react in the gas phase with formaldehyde to give citraconic acid or anhydride and itaconic acid (94—96). Dialkyl acyl succinates are obtained by reaction of dialkyl succinates with C 4 aldehydes over peroxide catalysts (97). 

Since the best results were obtained with the W and W-based oxide catalysts, the reaction was studied in more detail using 20 g portions of these catalysts. The reaction was performed at 230°C, with feed rates of pyruvic acid, air, and water = 10.5, 350, and 480 mmol/h. The contact time defined as volume of catalyst (ml)/rate of gaseous feed (ml/s) was about 5.2 s. The main products were citraconic anhydride and CO2. The amount of acetic acid was very small. No other products were detected except for very small amounts of CO, acetone, and acetaldehyde. A relatively large discrepancy was observed between the amount of consumed pyruvic acid and that of the sum of produced citraconic anhydride and acetic acid. This discrepancy was defined as "loss". 

The product distributions are shown in Figure 1 as a function of the time-onstream. At the begining of reaction, that is in the first 1 h on stream, the conversion of pyruvic acid reached 92% and the yields of citraconic anhydride and acetic acid were 61 and 5 mol%, respectively. The amount of loss was about 26 mol%. 

The reaction was studied using the iron phosphate catalyst at 230°C with feed rates of pyruvic acid, air, and water = 10.5, 350, and 480 mmol/h. The main products were citraconic anhydride, acetic acid, and CO2. When the amount of catalyst used was lOg, that is, when the contact time is about 2.6 s, the conversion of pyruvic acid reached 95% and the yields of citraconic anhydride and acetic acid were 50 and 28 mol%, respectively the loss was about 17 mol%. The selectivity to citraconic anhydride is clearly lower and that to acetic acid is higher than in the case of the W-based oxide catalysts. However, the catalytic activity was very stable. No clear change in the yield of citraconic anhydride was observed during the reaction for 10 h. 

The reaction was then performed using different amounts of catalyst from 1 to 20g. The yields of citraconic anhydride and acetic acid and the loss are plotted as a... 

It should also be noted that the selectivities remain unchanged with a large variation in the extent of reaction. This indicates that the citraconic anhydride and acetic acid produced are stable enough under the reaction conditions used. 

The crude citraconic anhydride contains a small amount of water, acetone and citraconic acid. Vacuum distillation allows the removal of these impurities without materially decreasing the yield. 

Among the carboxylic acid and anhydride functional monomers that have been employed in the synthesis of these thickener polymers are acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, crotonic acid, maleic anhydride, and citraconic anhydride. The copolymers containing maleic and citraconic anhydride monomers are either hydrolyzed or partially esterified to obtain the required carboxyl functionality. Among these carboxylic monomers, maleic anhydride and particularly methacrylic acid are most frequently favored. Carboxylic homopolymers, where they can be formed, might be considered the simplest examples of ASTs were it not for the fact that they are not copolymers as defined, and some are water soluble in their un-ionized states. Examples of carboxylic homopolymers are the un-ionized free-radical-polymerized atactic forms of polyacrylic acid (i) and polymethacrylic acid (2), which are both readily soluble in water. 

During the manufacture of phthalic anhydride from naphthalene and 6>-xylene, small amounts of MA, citraconic anhydrides, and benzoic acid are coproduced.MA comprises 6% of the product.In some cases, after removal of phthalic anhydride by condensation, the exhaust gases are scrubbed with water. In many cases, the aqueous solution of maleic acid is recovered in the form of fumaric acid. Koppers in the United States recovers 10 MM lb of MA from the phthalic plant. ... 

Depending on heating rate, citric acid monohydrate loses hydration water in the 70-100 °C temperature range and melts from 135 to 152 °C. Decomposition of citric acid starts above 175 °C. Early description of the decomposition process is given in 1877 by Fittig and Landolt [56] who during rapid distillation of anhydrous citric acid obtained as main products itaconic, citraconic and mesaconic acids and anhydrides. This observation was supported in 1880 by Anschutz [57] who detected itaconic and citraconic anhydrides. These compounds were formed between 200 and 215 °C and identified after distillation under reduced pressure. Shriner et al. [58] performed syntheses of itaconic anhydride and itaconic acid from citric acid... 

C. is a strong acid and forms salts (citrates) and water-soluble complexes, which are responsible for the use of c. to inactivate metal ions. At 175 C, various dehydration and decarboxylation reactions take place under formation of aconitic, itaconic and citraconic acid and their anhydrides. Only - itaconic acid is commercially important. 

The major by-products of this process are maleic anhydride, benzoic acid, and citraconic anhydride (methylmaleic anhydride). Maleic anhydride could be recovered economically. ... 

Since formation of citraconic anhydride from pyruvic acid is one of "acid to acid type" transformations, such as reactions from isobutyric acid to methacrylic acid and from lactic acid to pyruvic acid, the required catalysts must be acidic [11). If the catalysts are basic, it may be impossible to obtained acidic products, because basic catalysts activate selectively acidic molecules and, as a result, they show a very high activity for the decomposition of acidic products [11]. 

As for the reaction path from pyruvic acid to citraconic anhydride, it is considered that a condensation reaction first takes place by a reaction between an oxygen atom of carbonyl group and two hydrogn atoms of methyl group in another molecule, followed by oxidative decarboxylation to form citraconic acid. The produced citraconic acid is dehydrated under the reaction conditions used. The proposed reaction path is shown in Figure 7. 

Acid Curing. Urea-formaldehyde resins and resol-phenol-formaldehyde resins can be acid-cured by wastes from the production of maleic anhydride [1902]. The waste from the production of maleic anhydride contains up to 50% maleic anhydride, in addition to phthalic anhydride, citraconic anhydride, benzoic acid, o-tolulic acid, and phthalide. The plugging solution is prepared by mixing a urea-formaldehyde resin with a phenol-formaldehyde resin, adding the waste from production of maleic anhydride, and mixing thoroughly. 

Part 24 Determination of maleic acid and maleic anhydride in food simulants Ion pair HPLC of maleic acid with cetyl trimethyl ammonium chloride and UV detection (245 nm) with citraconic acid as internal standard... 

Citraconic anhydride (or 2-methylmaleic anhydride) is a derivative of maleic anhydride that is even more reversible after acylation than maleylated compounds. At alkaline pH values (pH 7-8) the reagent effectively reacts with amine groups to form amide linkages and a terminal carboxylate. However, at acid pH (3-4), these bonds rapidly hydrolyze to release citraconic acid and free the amine (Figure 1.86) (Dixon and Perham, 1968 Habeeb and Atassi, 1970 Klapper and Klotz, 1972 Shetty and Kinsella, 1980). Thus, citraconic anhydride has been used to temporarily block amine groups while other parts of a molecule are undergoing derivatization. Once the modification is complete, the amines then can be unblocked to create the original structure. 

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