Sodium aluminium hydride
[CAS# 13770-96-2]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Hydride, nitride, azide >> Hydride
• Name: Sodium aluminium hydride
• Synonyms: Sodium tetrahydroaluminate; Sodium tetrahydroaluminate; Sodium tetrahydroaluminate(1-)
• Molecular Formula: NaAlH₄
• Molecular Weight: 54.00
• CAS Registry Number: 13770-96-2
• EC Number: 237-400-1
• SMILES: [Na+].[AlH4-]

Properties

• Density: 1.24 g/mL

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS07 Danger
• Hazard Statements: H260-H261-H302-H314
• Precautionary Statements: P223-P231+P232-P260-P264-P270-P280-P301+P317-P301+P330+P331-P302+P335+P334-P302+P361+P354-P304+P340-P305+P354+P338-P316-P321-P330-P363-P370+P378-P402+P404-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin corrosion	Skin Corr.	1B	H314
Substances or mixtures which in contact with water emit flammable gases	Water-react.	2	H261
Substances or mixtures which in contact with water emit flammable gases	Water-react.	1	H260
Skin corrosion	Skin Corr.	1A	H314

Discovory and Applicatios

Sodium aluminium hydride, also known by its chemical formula NaAlH₄, is a white to grey solid that belongs to the class of complex metal hydrides. It is composed of sodium (Na⁺) cations and tetrahydridoaluminate (AlH₄⁻) anions. The compound is well known in inorganic and organometallic chemistry for its role as a reducing agent and has been widely studied for its potential in hydrogen storage systems due to its high hydrogen content and reversible decomposition behavior under suitable conditions.

The discovery of sodium aluminium hydride dates back to the early developments in hydride chemistry during the mid-20th century, particularly through the work of researchers exploring the reactivity of aluminium with alkali metals and hydrogen. It was synthesized by reacting sodium hydride (NaH) with aluminium chloride (AlCl₃) or aluminium hydride (AlH₃) under anhydrous and inert conditions. The resulting NaAlH₄ is sensitive to moisture and air, requiring handling in dry, inert environments such as glove boxes or under a blanket of inert gas like nitrogen or argon.

In synthetic chemistry, sodium aluminium hydride has been employed as a powerful reducing agent, similar in function to lithium aluminium hydride (LiAlH₄), though generally less reactive. It is capable of reducing a variety of functional groups including esters, carboxylic acids, aldehydes, and ketones to their corresponding alcohols. In some cases, its lower reactivity is advantageous, offering more controlled reductions and better selectivity under milder reaction conditions. The compound is used in both academic research and industrial processes where specific reductions are required with minimal side reactions.

One of the most important and well-documented applications of sodium aluminium hydride is in the field of hydrogen storage. Because it contains about 7.4% hydrogen by weight, NaAlH₄ has been studied as a candidate for solid-state hydrogen storage in fuel cell technologies. When heated in the presence of a suitable catalyst, such as titanium-based compounds, sodium aluminium hydride undergoes reversible dehydrogenation reactions that release molecular hydrogen. These reactions proceed through intermediate hydrides such as Na₃AlH₆ and eventually to sodium hydride (NaH) and aluminium metal, with the overall process being reversible under specific temperature and pressure conditions. This reversibility makes it attractive for applications where hydrogen must be stored safely and released on demand.

Catalytic doping, particularly with titanium or other transition metals, has been shown to significantly improve the kinetics of hydrogen release and uptake in sodium aluminium hydride. These studies have led to deeper understanding of the reaction mechanisms and facilitated the development of composite materials with enhanced performance. However, challenges related to operating temperature, reversibility under practical conditions, and material stability have limited its widespread adoption in commercial hydrogen storage systems.

In materials science, sodium aluminium hydride has been examined for its structural properties, thermal behavior, and phase transitions. It is known to decompose at elevated temperatures, typically above 180 °C, which releases hydrogen gas and forms solid decomposition products. These thermal properties are central to its role in hydrogen storage and are critical in designing systems that utilize NaAlH₄ safely and efficiently. Detailed studies using X-ray diffraction, thermal analysis, and spectroscopy have contributed to a robust understanding of its behavior under various conditions.

Safety considerations are essential when handling sodium aluminium hydride. It reacts violently with water and alcohols, releasing hydrogen gas, which is flammable and may form explosive mixtures with air. The compound should be handled in a dry, inert atmosphere with proper protective equipment. Exposure to moisture or air can also degrade the compound, reducing its effectiveness and posing safety hazards due to gas evolution. Decomposition of the material under inappropriate conditions can result in high internal pressures or ignition if not properly managed.

Despite its limitations, sodium aluminium hydride remains an important reagent and material in modern chemistry. Its applications in organic synthesis and potential in energy-related technologies continue to drive research efforts to improve its performance, stability, and usability. The fundamental knowledge gained from its study has also contributed significantly to the broader understanding of complex hydrides and their role in sustainable energy systems.

References

1964. Reduction of aromatic nitriles to aldehydes with sodium aluminum hydride. Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science, 13(8).
DOI: 10.1007/bf00850347

2023. Hydrogenation of S6-C60(CF3)12. Russian Journal of Physical Chemistry A, 97(9).
DOI: 10.1134/s0036024423090200

2024. Single Ti atoms coupled with Ti�O clusters enable low temperature hydrogen cycling by sodium alanate. Rare Metals, 43(6).
DOI: 10.1007/s12598-023-02608-2