Oxidation of Organic Compounds in Molten Salts

Abstract

The objective of this research was the oxidation of organic compounds in molten alkali metal nitrates containing manganates. It has been shown that controlled oxidation can be readily achieved with high specificity to give products in high yield with very short reaction times. In order to monitor concurrent changes in the melt, a novel vibrating platinum indicator electrode has been successfully developed. The electrode was operated with a vibrational frequency of 50Hz and an amplitude of approximately 1mm. Using the simple metal/metal ion couple Ag/Ag⁺ in molten (sodium-potassium) nitrate at 523K, the vibrating electrode has been practically and theoretically tested. The electrochemistry of manganates in molten (sodium-potassium) nitrate at 523K has been studied using the vibrating platinum electrode. Voltammetric waves with E half values of -0.05V and -0.60V vs Ag/Ag⁺ (0.07m) reference electrode have been shown to be due to the reaction of Mn(VII)/(VI) and Mn(V)/(IV) respectively. The existence of the species Mn(VII), Mn(VI), and Mn(V) has been studied in the nitrate melt containing periodate, hydroxide, and peroxide respectively. The stability of Mn(VII) and Mn(VI) with time was monitored at various OH:Mn molal ratios in molten (sodium-potassium) nitrate at 523K. A minimum OH:Mn molal ratio of 3:1 has been found, below which Mn(VI) is unstable. A range of organic chemicals has been passed through molten (sodium-potassium) nitrate at 523K containing stabilized Mn(VI) or Mn(VII) without any violent reactions. Ethanol, 2-propanol, benzyl alcohol, and benzaldehyde were oxidized by Mn(VI) and Mn(VII); toluene was only oxidized by Mn(VII), and n-hexane, cyclohexane, and ethene were unchanged by both Mn(VI) and Mn(VII). Detailed experiments have been performed on the reactions of 2-propanol, benzyl alcohol, and benzaldehyde in molten (sodium-potassium) nitrate containing stabilized Mn(VI).