**3.4. Glutaric acid**

336 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

synthesis of pyrimidines and other nitrogen heterocycles.

completely insoluble in benzene.

above 130 °C (Bolton, 1995).

tomatoes), and in many lignites.

**3.3. Succinic acid** 

feature of malonic acid and its derivatives is the high reactivity of the central methylene group. Due to the increasingly electron-withdrawing character of the substituents, the acidity of the hydrogen atoms in the 2-position increases in the order malonates < cyanoacetates < malononitrile. Therefore, all these compounds undergo reactions typical of 1,3-dicarbonyl compounds. For example they are easily alkylated or arylated, undergo aldol and Knoevenagel condensations, and they can be used for the

**Physical Properties:** Important physical properties of malonic acid (propanedioic acid, methanedicarboxylic acid) are listed in Table 1. Its p*K*a values are 2.83 and 5.70. Malonic acid forms a colorless hygroscopic solid which sublimes in vacuum with some decomposition. It's really soluble in the water; but slightly soluble in ethanol and diethyl ether, and is

**Chemical Properties:** Malonic acid is found in small amounts in sugar beet and green wheat, being formed by oxidative degradation of malic acid. Reaction with sulfuryl chloride or bromine gives mono- and dihalogenated malonic acid, whereas treatment with thionyl chloride or phosphorus pentachloride leads to mono- or diacyl chloride. When heated with phosphorus pentoxide, malonic acid does not form an anhydride but rather carbon suboxide, a toxic gas that reacts violently with water to reform malonic acid. On heating the free acid above 130 °C, or an aqueous solution above 70 °C, decomposition to acetic acid and carbon dioxide takes place. The mono- and dianion of malonic acid are more stable. In aqueous solution the monosodium salt decomposes above 90 °C and the disodium salt

Succinic acid is found in amber, in numerous plants (e.g., algae, lichens, rhubarb, and

**Production***:* A large number of syntheses are used to manufacture succinic acid. Hydrogenation of maleic acid, maleic anhydride, or fumaric acid produces good yields of succinic acid; the standard catalysts are Raney nickel, Cu, NiO, or CuZnCr, Pd – Al2O3, Pd – CaCO3, or Ni – diatomite. 1,4-Butanediol can be oxidized to succinic acid in several ways: (1) with O2 in an aqueous solution of an alkaline-earth hydroxide at 90 – 110 °C in the presence of Pd – C; (2) by ozonolysis in aqueous acetic acid; or (3) by reaction with N2O4 at low temperature. Succinic acid or its esters are also obtained by Reppe carbonylation of ethylene glycol, catalyzed with RhCl3 – pentachlorothiophenol; Pd-catalyzed methoxycarbonylation of ethylene; and carbonylation of

Acid mixtures containing succinic acid are obtained in various oxidation processes. Examples include the manufacture of adipic acid; the oxidation of enanthic acid and the ozonolysis of palmitic acid. Succinic acid can also be obtained by phase-transfer-catalyzed reaction of 2-haloacetates, electrolytic dimerization of bromoacetic acid or ester, oxidation of

acetylene, acrylic acid, dioxane, or β- propiolactone (Bolton, 1995).

3-cyanopropanal, and fermentation of *n*-alkanes.

Glutaric acid occurs in washings from fleece and, together with malonic acid, in the juice of unripened sugar beet.

**Production:** Glutaric acid is obtained from cyclopentane by oxidation with oxygen and cobalt (III) catalysts or by ozonolysis; and from cyclopentanol – cyclopentanone by oxidation with oxygen and Co(CH3CO2)2, with potassium peroxide in benzene, or with N2O4 or nitric acid. Like succinic acid, glutaric acid is formed as a byproduct during oxidation of cyclohexanol – cyclohexanone. Other production methods include reaction of malonic ester with acrylic acid ester, carbonylation of *Υ*-butyrolactone, oxidation of 1,5-pentanediol with N2O4, and oxidative cleavage of *Υ*-caprolactone.

**Uses:** The applications of glutaric acid, e.g., as an intermediate, are limited. Its use as a starting material in the manufacture of maleic acid has no commercial importance.
