Tetra-''n''-butylammonium iodide (TBAI) is a

quaternary ammonium salt In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure , where R is an alkyl group, an aryl group or organyl group. Unlike the ammonium ion () and the primary, secondary, ...

with an

iodide An iodide ion is I−. Compounds with iodine in formal oxidation state −1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine deficiency ...

counterion 160px, cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion. In chemistry, a counterion (sometimes written as "counter ...

. It is used for synthesizing tetra-''n''-butylammonium triiodide by mixing with

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

. TBAI is also commonly used as a catalyst for the protection of alcohols as benzyl ethers with benzyl bromide.

Properties

The solid crystal of tetra-''n''-butylammonium iodide is in the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

crystal system. It has

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

''C''2/''c''. The

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

has dimensions a=14.2806 b=14.1864 c=19.5951 β=111.149. There are eight formulae in the unit cell (Z=8), which has volume 3702.4 Å³. The enthalpy of formation Δ_fH⁰ of tetra-''n''-butylammonium iodide is −499 kJ/mol, which is lower than that for the bromide or chloride (−540, −564 kJ/mol). At lower temperatures with water tetra-''n''-butylammonium iodide forms a

clathrate hydrate Clathrate hydrates, or gas hydrates, clathrates, or hydrates, are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped ins ...

. The tetra-''n''-butylammonium cation is large and hydrophobic. The absolute enthalpy of hydration (from gas phase) is −260 kJ/mol. The He(I) photoelectron spectrum of tetra-''n''-butylammonium iodide contains a peak at 11 eV due to the tetra-''n''-butylammonium cation, and at 7 and 8 eV due to iodide.

References

{{reflist Iodides Tetrabutylammonium salts

Properties

See also

References