Alpha-hydroxycarboxylic acids

Portanova, R. Lajunen, L.H.J. Tolazzi, M. Piispanen, J. Critical evaluation of stability constants for alpha-hydroxycarboxylic acid complexes with protons and metal ions and the accompanying enthalpy changes. Part II. Aliphatic 2-hydroxycarboxylic acids. Pure Appl. Chem. 2003, 75 (4), 495-540. 

To further understand the synthesis mechanism used in this work, which uses gelatin instead of ethylene glycol, it is necessary to review the traditional polymeric precursor method proposed by Pechini (Pechini, 1967). The Pechini method involves the formation of stable metal-chelate complexes with certain alpha-hydroxycarboxyl adds, such as dtric acid, and polyesterification in the presence of a polyhydroxy alcohol, such as ethylene glycol, to form a polymeric resin. The metal cations are homogeneously distributed in the polymeric resin, which is then calcined to yield the desired oxides. The most common materials used as source of cations are nitrate salts since they can be fully removed at low temperatures (400 - 500 °C). The synthesis mechanism of the modified Pechini method used in this work can be explained in three basic steps, as shown in Fig. 2. It stands out by its simplicity and low cost, using only citric acid, gelatin and metal nitrates as reagents. 

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