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NEW HORIZONS IN PERCHLORATE CHEMISTRY – IONIC LIQUIDS

Despite their reputation as reactive components in propellant composites and some chemical systems, the use of perchloric acid and perchlorate salts in novel process chemistries as well as industrial and academic research is a well-documented activity. The promotion of organic reactions by ether solutions of anhydrous lithium perchlorate and similar reagents has grown from a laboratory curiosity in the 1980's to a world-wide quest for more efficient and effective synthetic methodologies. Some of the advantages to using perchlorates in this capacity are striking: • Reaction mechanisms can be realized that are not possible using other schemes • Dramatic improvement of reaction rates and selectivities are common • Interesting chemistries can be developed apart from the use of diethyl ether • The concept of "naked ion" Li+ chemistries in organic media has broad synthetic implications Not surprisingly, many of the properties that allow the successful use of perchlorate salts in organic synthesis (and as electrolytes in battery/fuel cell applications) can easily be incorporated into Ionic Liquid systems. GFS founder G. Frederick Smith would not have been surprised that the unusual affinity of LiClO4 for organic solvents could be translated into such a 21st century technology that was unimagined when the original data were gathered in the 1920's.

Traditionally customer driven, GFS is now actively addressing the needs of the Ionic Liquid community for cleaner, less sensitive, and more effective Room Temperature Ionic Liquid (RTIL) formulations. Those needs intersect with unique properties demonstrated by perchlorate chemistries built upon nearly 100 years of research and development. The character of the anion is critical to an RTIL's effectiveness.

Advantages to an RTIL Perchlorate Formulation

•ClO4- does not hydrolyze to toxic or corrosive by-products •ClO4- is non-coordinating and chemically inert at RT •ClO4- is highly ionic in both salt and parent acid form •ClO4- salts are less sensitive to moisture than complex halide salts •ClO4- compounds are not susceptible to halide contamination •ClO4- salts are less expensive than most complex halide salts

Perchloric acid itself is an Ionic Liquid, best formulated as H3O+ClO4-•H2O (ca. 72% concentration), with a pKa of ?1.6, and a dissociation constant of 1014. Temperatures of well over 100 deg C are required before any perchlorate enters the vapor phase. The table below compares the properties of anhydrous lithium perchlorate with a variety of lithium salts of other anions actively used in Ionic Liquid or battery/fuel cell technologies.

Properties of LiClO4 vs. other "Energetic" Lithium Salts

CRITERIA LiClO4 LiPF6 LiBF4 LiAlCl4 LiOTf*

1. Mfg. acid-base high-temp high-temp solid state acid-base method corrosive corrosive 2. Mfg. scale ton multi-ton small batch small batch larger batch

3. Drying dry ton lots difficult to very hard any moisture dries to factors to 99% moisture <1000 ppm solvent hydrolysis purity

4. Material free-flowing powder may packed driest solid is powder may handling fine powder clump when powder derived from clump wet molten salt 5. Hydrolysis minimal corrosive corrosive rapid attack moisture tendencies moisture hydrolysis hydrolysis by moisture sensitive sensitivity products products 6. Cost (for lowest moderate moderate highest moderate research) (* triflate)

Perchlorate salts such as lithium perchlorate can be manufactured in ton lots having a moisture content <100 parts per million. Perchlorates currently see active use in mature industrial technologies as catalysts and process reagents, especially in overseas markets. Catalytic effects of LiClO4 in organic synthesis have been researched for over 15 years.

Technical Precedent

The suggested incorporation of perchlorate ion into Ionic Liquid formulations is supported by recently reported research. Work performed at Edwards AFB by Gregory Drake et al. (2003) described successful one-step, high-yield syntheses of three triazolium perchlorates: •1,2,3-triazolium perchlorate (85% yield as [C2H4N3+][ClO4-] •1,2,4-triazolium perchlorate (93% yield as [C2H4N3+][ClO4-] •4-amino-1,2,4-triazolium perchlorate (98.1% yield as [C2H5N4+][ClO4-]

Differential Scanning Calorimetry helped characterize the 1,2,4-triazolium perchlorate as having good thermal stability at elevated temperatures as well as "reasonable" impact sensitivity. The 1,2,3-triazolium compound was more impact sensitive than the 4-amino-derivative. Since the imidazolium ion substitutes a third carbon atom for a nitrogen (see structures), it is reasonable to expect that a properly substituted imidazolium perchlorate would exhibit significantly enhanced stability over the triazolium anlalogs. This technology will benefit from a partnership between GFS and academic institutions and consortia dedicated to the commercialization of novel Ionic Liquids. Work is underway to accelerate that process; your questions, suggestions and comments are welcome.

For the complete Powerpoint presentation, visit our website at: http://www.gfschemicals.com/TechnicalLibrary/Ionic.Liquid.ppt