Palladium
[CAS# 7440-05-3]

Identification

• Classification: Inorganic chemical industry >> Simple substance
• Name: Palladium
• Synonyms: Palladium on activated carbon
• Molecular Formula: Pd
• Molecular Weight: 106.42
• CAS Registry Number: 7440-05-3
• EC Number: 231-115-6
• SMILES: [Pd]

Properties

• Density: 12.02 g/mL (Expl.)
• Melting point: 1554 °C (Expl.)
• Boiling point: 2970 °C (Expl.)
• Water solubility: INSOLUBLE

Safety Data

• Hazard Symbols: GHS02;GHS07 Danger
• Risk Statements: H228-H315-H319-H335-H413
• Safety Statements: P210-P240-P241-P261-P264-P264+P265-P271-P273-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P370+P378-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable solids	Flam. Sol.	1	H228
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Flammable solids	Flam. Sol.	2	H228
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413
Respiratory sensitization	Resp. Sens.	1	H334
Skin sensitization	Skin Sens.	1	H317
Self-heating substances or mixtures	Self-heat.	1	H251
Pyrophoric solids	Pyr. Sol.	1	H250
Flammable liquids	Flam. Liq.	1	H224
Self-heating substances or mixtures	Self-heat.	2	H252
Oxidising solids	Ox. Sol.	2	H272
Gases under pressure (compressed)	Press. Gas (Comp.)		H280
Oxidising solids	Ox. Sol.	1	H271
Acute toxicity	Acute Tox.	3	H301
Specific target organ toxicity - single exposure	STOT SE	1	H370
Eye irritation	Eye Irrit.	2A	H319
Reproductive toxicity	Repr.	2	H361

Discovery and Applications

Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare, lustrous silvery-white metal belonging to the platinum group of metals. Palladium was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas. It is primarily found in ores containing other platinum group metals and is extracted through complex refining processes.

Palladium is valued for its exceptional catalytic properties, corrosion resistance, and ability to absorb large amounts of hydrogen. These characteristics make it highly useful in various industrial and scientific applications.

One of the most significant uses of palladium is as a catalyst in chemical reactions. It is widely employed in catalytic converters for automobiles, where it facilitates the conversion of toxic gases such as carbon monoxide, nitrogen oxides, and hydrocarbons into less harmful substances like carbon dioxide, nitrogen, and water vapor. This application has had a major impact on reducing air pollution from vehicle emissions.

In organic chemistry, palladium catalysts play a crucial role in cross-coupling reactions, which are methods used to form carbon-carbon bonds. Reactions such as the Suzuki, Heck, and Sonogashira couplings rely on palladium complexes to efficiently create complex molecules. These reactions are essential in the synthesis of pharmaceuticals, agrochemicals, and advanced materials.

Palladium is also used in electronics for plating components due to its excellent conductivity and resistance to oxidation. It finds application in the manufacture of multilayer ceramic capacitors and in connector plating in electronic devices.

Jewelry is another important area where palladium is employed. It is used as a white metal alloy with gold to create white gold, valued for its durability and tarnish resistance. Palladium’s hypoallergenic properties make it suitable for sensitive skin.

Hydrogen storage and purification is an emerging field benefiting from palladium’s ability to absorb hydrogen up to 900 times its own volume. This property is exploited in hydrogen sensors, purification membranes, and potential energy storage systems.

In dentistry, palladium is used in dental alloys for crowns and bridges due to its biocompatibility, strength, and corrosion resistance.

Palladium’s physical properties include a melting point of 1555 °C and a density of 12.02 g/cm³. It crystallizes in a face-centered cubic lattice. The metal is soft and ductile but can be hardened by alloying.

Handling palladium generally poses low toxicity risks; however, exposure to palladium compounds should be minimized as they may cause allergic reactions or respiratory sensitization in some individuals.

Overall, palladium’s unique combination of catalytic activity, chemical stability, and physical properties has established it as a vital material across multiple industries, from environmental technology and organic synthesis to electronics and jewelry. Its applications continue to expand with ongoing research into advanced materials and sustainable technologies.

References

2006. New Class of Nucleophiles for Palladium-Catalyzed Asymmetric Allylic Alkylation. Total Synthesis of Agelastatin A. Journal of the American Chemical Society, 128(15).
DOI: 10.1021/ja061105q

2008. Palladium-Catalyzed Highly Regioselective [3 + 2] Cycloaddition Reactions of Alkylidenecyclopropa[b]naphthalenes with Alkenes or Alkynes. Organic Letters, 10(22).
DOI: 10.1021/ol8023083

2010. Mechanism of Escherichia coli inactivation on palladium-modified nitrogen-doped titanium dioxide. Biomaterials, 31(29).
DOI: 10.1016/j.biomaterials.2010.06.032