Preparation and characterization of yellow materials derived from the decomposition of magnesium tartrate crystals

Abstract

Magnesium tartrate (Mg-TA) is a green, nontoxic, sustainable and dense organic–inorganic hybrid material. In this study, three Mg-TA crystals were prepared under mild conditions using a low-cost magnesium source of MgCl₂·6H₂O. A series of yellow Mg-TA derivatives were obtained by pyrolyzing the Mg-TA crystals under an air atmosphere. The thermal decomposition of Mg-TA is a multistep process that results in the formation of a dicarbonyl compound with a yellow colouration. Initially, the loss of water of crystallization occurs, which does not result in any change in colour. As the temperature continues to rise, the colour begins to turn yellow and deepens. Finally, MgO is formed at approximately 400 °C. In comparison to racemic Mg-TA, chiral Mg-TA exhibits a narrower range of colour change temperatures, and a similar conclusion was reached for the tartrates of different cationic Ca²⁺. Only one yellow product (Mg (d,l-TA)₂₅₀) resulting from the thermal decomposition of racemic Mg-TA could be completely dissolved in water. It is anticipated that this new colourant would be utilized as a green, environmentally friendly alternative to traditional toxic yellow colourants in the preparation of a variety of yellow materials. The generation mechanism and chemical structures of the yellow derivatives have been elucidated through Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–Vis spectrophotometer and ¹H&¹³C NMR spectroscopy.