## LSU Historical Dissertations and Theses

1997

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

Robert J. Gale

#### Abstract

Room temperature molten salts have been of interest because of their unique properties such as aprotic nature and excellent Lewis acid-base adjustability. They provide a novel medium for fundamental studies and constitute a promising electrolyte for metal plating and secondary batteries. In the present study, the room temperature N-Butyl-pyridinium chloride (BPC)-boron trichloride (BCl$\sb3)$ and mixed BCl$\sb3$-AlCl$\sb3$-BPC melts have been prepared and characterized using reaction stoichiometries, electrochemistry and secondary ion mass spectrometry (SIMS). At normal atmosphere and room temperature, even when excess BCl$\sb3$ was added, BCl$\sb3$-BPC melts have a constant composition of 52:48 mole ratio BCl$\sb3$:BPC. SIMS studies confirmed previous Raman results, that is, speciation of boron in the BCl$\sb3$-BPC melts is mainly involved in forming boron tetrachloride anion (BCl$\sb4\sp-).$ Polyboron species were not detected. The excess boron chloride in the melts is dissolved as molecular BCl$\sb3.$ In the BCl$\sb3$ saturated chloroborate and mixed chloroborate-chloroaluminate melts, an irreversible wave has been assigned to the formation of a passive boron film. The mixed chloroborate-chloroaluminate melts can not go beyond neutral melts since $\rm Al\sb2Cl\sb6$ or acidic species such as $\rm Al\sb2Cl\sb7\sp-$ ion reacts with existing boron tetrachloride anion in the melt to form BCl$\sb3$ which is volatile at room temperature. Results from SIMS indicate that, aluminum chloride anions in BPC-based chloride melts are more surface active than boron chloride anions. Speciation of sulfur in nonaqueous media has been of interest for fundamental studies and secondary battery development. In an attempt to prepare organic sulfides, which could find applications for the development of room temperature organic molten salt battery electrolytes, it was found that in acetonitrile, sodium sulfide reacts very fast with BPC to form a dark brown solution. The reaction products were characterized by UV, HPLC, NMR, and GC-MS. A reaction mechanism was proposed with the initial step occurring via N-substituted pyridinyl radicals and monosulfur anion radicals. The monosulfur anion radical has not been characterized in liquid phases and this reaction provides a means for its generation and study.

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