Synthesis and Application of Tetramethylammonium hydroxide pentahydrate

Tetramethylammonium hydroxide pentahydrate is a colorless crystalline compound containing five molecules of water of crystallization. It is hygroscopic and absorbs carbon dioxide from the air. At 130°C, it decomposes into methanol and trimethylamine. The compound is soluble in water.

Figure1: Picture of Tetramethylammonium hydroxide pentahydrate

Synthesis

Tetramethylammonium hydroxide pentahydrate was initially prepared via the reaction of tetramethylammonium chloride with silver oxide. Since the 1970s, this method has been replaced by an electrochemical process, which offers higher product purity and lower production costs.

Raman study on molecular motion

The Raman spectrum as well as conductivity and differential‐thermal‐analysis (DTA) thermogram of tetramethylammonium hydroxide pentahydrate was observed at various temperatures in order to investigate molecular motion in relation to conductivity and a phase transition. It was clarified that different stepwise protonation processes become effective for relaxation in the O–H stretching of hydroxide ions as temperature is increased. The activation energy was 6.1 and 16.0 kJ/mol in 130≤T<210 and 210≤T≤250 K, respectively, whereas the activation energy in conductivity was 41.1 kJ/mol below 250 K. This discrepancy was discussed according to a reorientational motion of water molecules. The Raman band shape of the NM4 asymmetric stretching of tetramethylammonium ions was analyzed on the basis of the reorientational motion about the C3 and C2 axes on the ion, and the activation energies were 8.7 kJ/mol (about the C3 axis) and 14.5 kJ/mol (about the C2 axis). [1]

Application

Tetramethylammonium hydroxide pentahydrate is primarily used as a catalyst in the production of materials such as silicone resins and silicone rubber, leaving no residue after decomposition. It also serves as a polarographic analysis reagent, as well as a cleaning and etching agent in the electronics industry.

Solid-state metal hydride batteries

A novel solid electrolyte, Tetramethylammonium hydroxide pentahydrate, was applied to a nickel oxyhydroxide–metal hydride (NiOOH/MH) battery and a manganese dioxide–metal hydride (MnO₂/MH) battery, both fabricated by impregnating the melted solid electrolyte into the battery components. The NiOOH/MH and MnO₂/MH batteries remained dischargeable even at current densities of 10 mA·cm⁻² and 2 mA·cm⁻², respectively. No appreciable decrease in discharge capacity was observed for either battery over up to 200 cycles. However, both batteries exhibited poor charge retention performance, attributed to the reduced density of oxidized metal ions near the surface of active material particles on their positive electrodes, which resulted from proton diffusion and electron conduction. [2]

Removal of heavy metal ions from heavy oils

The researchers examined the efficiency of Tetramethylammonium hydroxide pentahydrate in removing heavy metal ions from heavy oils derived from Nigerian oil sands using the Soxhlet‑extraction technique. The metals were extracted from the heavy oils at various temperatures by employing Tetramethylammonium hydroxide pentahydrate. Elemental analysis was performed with atomic absorption spectrophotometry (AAS), yielding a recovery percentage of 92.85%, which confirms the reliability of the results. The total metal concentrations followed the order: Ni > Pb > Mn > Cu > Cr > Cd. Analysis of variance showed that F < Fcritical (0.01 < 3.68), supporting the acceptance of the null hypothesis. Cluster analysis revealed three major inter‑elemental clusters, suggesting chemical affinity and/or common origins, while the T‑test indicated statistically significant differences among groups. Metal removal efficiency decreased with rising temperature, consistent with an exothermic process. Negative values of the thermodynamic parameters further confirmed the exothermic nature of the reactions. Additionally, negative ΔS values indicated reduced randomness at the solid‑liquid interface during extraction, and negative ΔG values demonstrated that the extraction was feasible and spontaneous. In conclusion, the distribution of metals in the analyzed heavy oils exhibited a similar pattern, attributable to comparable geological activity, source rock type, maturation history, and depositional environment. The thermodynamic parameters collectively indicated that the extraction process using Tetramethylammonium hydroxide pentahydrate was exothermic, feasible, and spontaneous, thereby proving its efficiency in metal extraction. [3]

Reference

[1] Kanesaka I, Iwaki M, Uezawa C, et al. Raman study on molecular motion in tetramethylammonium hydroxide pentahydrate[J]. The Journal of chemical physics, 1991, 95(12): 8693-8696.

[2] Kuriyama N, Sakai T, Miyamura H, et al. Solid-state metal hydride batteries using tetramethylammonium hydroxide pentahydrate[J]. Solid state ionics, 1992, 53: 688-693.

[3] Adebiyi F M, Yoade R O. Thermodynamic study of the removal of heavy metal ions from heavy oils using tetramethyl ammonium hydroxide pentahydrate ionic liquid[J]. Petroleum Research, 2022, 7(4): 545-550.

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