Maleates

Maleates are chemical compounds that are salts or esters of maleic acid, the cis-butenedioic acid. They include metal salts such as sodium maleate and calcium maleate, and alkyl or aryl diesters such as dimethyl maleate and diethyl maleate. In industry, the term often refers to the anionic forms derived from maleic acid and its derivatives.

Structure and properties: The parent molecule features a cis-configured carbon–carbon double bond with two adjacent carboxyl groups. In salts, the carboxyl groups are deprotonated, while in esters they are converted to ester functionalities. The maleate system is conjugated, influencing reactivity in polymerization and addition reactions. The acid–base behavior is governed by the two pKa values of maleic acid (approximately pKa1 ≈ 1.92 and pKa2 ≈ 6.23), which informs how different forms predominately exist at given pH levels.

Production and occurrence: Dimethyl maleate and other alkyl maleates are typically prepared by esterification of maleic anhydride with alcohols. Metal salts are obtained by neutralization of maleic acid with bases or by direct reaction of maleic anhydride with metal bases. Maleates are primarily industrial intermediates and do not occur naturally in significant quantities.

Applications: Maleates are used as monomers in unsaturated polyester resins and alkyd resins, where they act as reactive crosslinkers. Alkyl and aryl maleates serve as solvents, plasticizers, or intermediates in organic synthesis. Some maleate derivatives function as dienophiles in Diels–Alder reactions, enabling access to cycloaddition products.

Safety: Handling of maleates and maleic acid requires standard chemical hygiene; they can be irritants to skin, eyes, and the respiratory system. Proper ventilation, gloves, and eye protection are recommended. Environmental considerations include typical inorganic/organic salt handling and biodegradability profiles depending on the derivative.