Rubidium iodide explained

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:^[1]

Another method is to neutralize rubidium carbonate with hydriodic acid:^[1]

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:^[1]

Properties

Rubidium iodide forms colorless crystals, and has a red-violet flame color. The refractive index of the crystals is n_D = 1.6474.^[2] 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:

Solubility of RbI in organic solvents^[3]
(given in g RbI in 100 cm³ saturated solution)!Solvent!0 °C!25 °C

	1.478	1.350
	0.274	0.305
	0.567	0.518
	0.960	0.674
		4,930

The standard enthalpy of formation of rubidium iodide is Δ_fH⁰₂₉₈ = −328.7 kJ mol⁻¹,^[4] 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.^[5]

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).^[6] Another product is Polijodurato^®. However, there are studies that show that rubidium iodide has allergy-triggering^[7] and inflammation-causing^[8] 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.^[9]

It found isolated use in organic synthesis, for example for the targeted saponification of a polymethylated phosphate.^[10]

Bibliography

• CRC Handbook of Chemistry and Physics, 77th edition

Notes and References

1. Web site: WebElements . 23 February 2006 . 2008-04-18 . https://web.archive.org/web/20080418211628/http://www.webelements.com/webelements/compounds/text/Rb/F1Rb1-13446747.html . live .
2. Book: Ans, Jan d' . Elemente, anorganische Verbindungen und Materialien . Ans . Jan d' . 1998 . Publisher not known . 978-3-540-60035-0 . 4., neubearb. u. rev. Aufl . Taschenbuch für Chemiker und Physiker / D'Ans . Location not known.
3. Book: Aterton Seidell . Solubilities Of Organic Compounds Vol - I . 1940 . D.Van Nostrand Co. . Carnegie-Mellon University Hunt Library, N.Sathyanarayanan.
4. Book: Prinzipien der Chemie . 1988 . de Gruyter . 978-3-11-009969-0 . Dickerson . Richard E. . 2., bearb. und erw. Aufl . Berlin . Sichting . Hans-Werner.
5. 『Japanese: 化学大辞典』　共立出版、1993年
6. Jurja, Sanda, et al. "Correlation between effectiveness and antioxidant activity of some anti cataract eye drops." Rev Chim (Bucharest) 67 (2016): 1004-1007.
7. Web site: Allergen Rubidium Allergie enthalten Allergologie . 2023-09-16 . www.alles-zur-allergologie.de.
8. Cameli . N. . Bardazzi . F. . Morelli . R. . Tosti . A. . Nov 1990 . Contact dermatitis from rubidium iodide in eyedrops . Contact Dermatitis . en . 23 . 5 . 377–378 . 10.1111/j.1600-0536.1990.tb05182.x.
9. Paschalis . C. . Jenner . F. A. . Lee . C. R. . May 1978 . Effects of rubidium chloride on the course of manic-depressive illness . Journal of the Royal Society of Medicine . 71 . 5 . 343–352 . 10.1177/014107687807100507 . 0141-0768 . 1436619 . 349155.
10. Turhanen . Petri A. . 2014-07-03 . Synthesis of Triple-Bond-Containing 1-Hydroxy-1,1-bisphosphonic Acid Derivatives To Be Used as Precursors in "Click" Chemistry: Two Examples . The Journal of Organic Chemistry . en . 79 . 13 . 6330–6335 . 10.1021/jo500831r . 0022-3263.