Rubidium iodide

Rubidium iodide is a salt of rubidium and iodine, with the chemical formula RbI. It is a white solid with a melting point of 642 °C.

Preparation
Rubidium iodide can be synthesized in several ways. One is to use a mixed reaction of rubidium hydroxide and hydriodic acid/hydrogen iodide:


 * RbOH + HI → RbI + H2O

Another method is to neutralize rubidium carbonate with hydriodic acid:


 * Rb2CO3 + 2HI → 2RbI + H2O + CO2

Another method is to use rubidium metal to react directly with iodine, but because rubidium metal is very expensive, it is the least commonly used method. In addition, rubidium reacts violently with halogens and burns:


 * 2Rb + I2 → 2RbI

Properties
Rubidium iodide forms colorless crystals, and has a red-violet flame color. The refractive index of the crystals is nD = 1.6474. It reacts with halogens to form polyhalides: RbI3, RbICl2, RbICl4. It is easily soluble in water, liquid ammonia, sulfuric acid, RbI·6NH3 and RbI·3SO2. Rubidium iodide is soluble only in the following solvents:

The standard enthalpy of formation of rubidium iodide is ΔfH0298 = −328.7 kJ mol−1, the standard free enthalpy of formation ΔG0298 = −325.7 kJ mol−1, and the standard molar entropy S0298 = 118.11 J K−1·mol−1.

Rubidium iodide has a sodium chloride structure; its lattice constant is a = 7.326 Å, and the Rb–I bond length is 3.66 Å.

Applications
Rubidium iodide is used as a component of eye drops, in which it is sold in Romania under the name Rubjovit® (containing 8 mg/ml RbI). Another product is Polijodurato®. However, there are studies that show that rubidium iodide has allergy-triggering and inflammation-causing side effects. Homeopathic products containing rubidium iodide are available under the name 'Rubidium iodatum'. In the past, towards the end of the 19th century, it was used to treat syphilis.

It found isolated use in organic synthesis, for example for the targeted saponification of a polymethylated phosphate.