Lithium Aluminum Hydride (LiAlH4) is a powerful reducing agent used in organic chemistry to convert carbonyl compounds to alcohols. It reacts vigorously with water.
| IUPAC Name | Lithium Aluminum Hydride |
| Molecular Formula | LiAlH4 |
| CAS Number | 16853-85-3 |
| Synonyms | Lithium tetrahydridoaluminate(III), Aluminium(III) lithium hydride |
| InChI | InChI=1S/Al.Li.4H |
Lithium Aluminum Hydride (LiAlH4) Properties
Lithium Aluminum Hydride (LiAlH4) Formula
The formula of lithium tetrahydridoaluminate (LiAlH4) represents its composition. It consists of one lithium (Li) atom, one aluminum (Al) atom, and four hydrogen (H) atoms. The formula is written as LiAlH4, indicating the presence of these elements.
Lithium Aluminum Hydride (LiAlH4) Molar Mass
The molar mass of lithium tetrahydridoaluminate (LiAlH4) is the sum of the atomic masses of its constituent elements. It is calculated as follows:
- Lithium (Li) has a molar mass of approximately 6.94 g/mol.
- Aluminum (Al) has a molar mass of around 26.98 g/mol.
- Hydrogen (H) has a molar mass of about 1.01 g/mol.
By adding up these values, the molar mass of LiAlH4 is approximately 37.95 g/mol.
Lithium Aluminum Hydride (LiAlH4) Boiling Point
Lithium tetrahydridoaluminate (LiAlH4) does not have a distinct boiling point because it decomposes before reaching the boiling point of any of its individual components. Upon heating, LiAlH4 undergoes a decomposition reaction, releasing hydrogen gas.
Lithium Aluminum Hydride (LiAlH4) Melting Point
Lithium tetrahydridoaluminate (LiAlH4) has a relatively low melting point. It melts at around 150-160°C (302-320°F). At this temperature, the solid LiAlH4 converts into a liquid state, allowing it to participate in chemical reactions.
Lithium Aluminum Hydride (LiAlH4) Density g/mL
The density of lithium tetrahydridoaluminate (LiAlH4) is approximately 0.917 g/mL. This density value indicates the mass of LiAlH4 present in a specific volume, with the unit of grams per milliliter.
Lithium Aluminum Hydride (LiAlH4) Molecular Weight
The molecular weight of lithium tetrahydridoaluminate (LiAlH4) is calculated by summing the atomic weights of all its constituent elements. The molecular weight of LiAlH4 is approximately 37.95 g/mol.
Lithium Aluminum Hydride (LiAlH4) Structure
Lithium tetrahydridoaluminate (LiAlH4) has a tetrahedral structure. The aluminum atom is at the center, surrounded by four hydrogen atoms. The lithium atom is also connected to the aluminum atom, completing the structure.
Lithium Aluminum Hydride (LiAlH4) Solubility
Lithium tetrahydridoaluminate (LiAlH4) is insoluble in most organic solvents such as ethers and hydrocarbons. However, it is highly reactive with water, undergoing a vigorous exothermic reaction and producing hydrogen gas. Therefore, LiAlH4 is typically handled and stored in anhydrous conditions to avoid any unwanted reactions with moisture.
| Appearance | White powder |
| Specific Gravity | 0.917 g/mL |
| Color | Colorless |
| Odor | Odorless |
| Molar Mass | 37.95 g/mol |
| Density | 0.917 g/mL |
| Melting Point | 150-160°C |
| Boiling Point | Decomposes |
| Flash Point | Not applicable |
| Water Solubility | Reacts vigorously with water |
| Solubility | Insoluble in organic solvents such as ethers and hydrocarbons |
| Vapour Pressure | Not applicable |
| Vapour Density | Not applicable |
| pKa | Not applicable |
| pH | Not applicable |
Lithium Aluminum Hydride (LiAlH4) Safety and Hazards
Lithium tetrahydridoaluminate (LiAlH4) poses significant safety hazards and must be handled with extreme caution. It is a highly reactive compound that reacts violently with water, releasing flammable hydrogen gas. LiAlH4 is pyrophoric, meaning it can ignite spontaneously in air. It should be stored away from moisture and kept in tightly sealed containers. Direct contact with LiAlH4 can cause severe burns and irritation to the skin, eyes, and respiratory system. Inhalation of its dust or fumes can lead to respiratory distress. Proper personal protective equipment, such as gloves and goggles, should be worn when working with LiAlH4, and it should only be handled in well-ventilated areas with appropriate safety measures in place.
| Hazard Symbols | F, C |
| Safety Description | Highly flammable. Reacts violently with water. Handle with extreme caution. |
| UN IDs | UN 1410 |
| HS Code | 2850.00.00 |
| Hazard Class | 4.3 |
| Packing Group | I |
| Toxicity | Highly toxic, can cause severe burns and respiratory distress. |
Note: The hazard symbols used are “F” for flammable and “C” for corrosive. The safety description highlights the reactivity with water and emphasizes the need for extreme caution. UN IDs and HS Code are specific identification codes used for transportation and trade purposes. The hazard class indicates the classification of the substance based on its characteristics. The packing group represents the level of danger during transportation. Lithium tetrahydridoaluminate (LiAlH4) is highly toxic and can cause severe burns and respiratory distress upon contact or inhalation.
Lithium Aluminum Hydride (LiAlH4) Synthesis Methods
Various methods allow the synthesis of Lithium tetrahydridoaluminate (LiAlH4).
One common method for synthesizing Lithium tetrahydridoaluminate (LiAlH4) involves heating AlCl3 and combining it with lithium hydride (LiH) in a solvent like diethyl ether. The reaction proceeds in the presence of heat, resulting in the formation of LiAlH4.
Another method entails mixing powdered Al metal with lithium hydride, followed by heating the mixture. The reaction occurs, leading to the formation of LiAlH4.
To synthesize LiAlH4 using a different approach, combine lithium aluminum deuteride (LiAlD4) with LiH in a solvent such as tetrahydrofuran (THF). Heat the mixture, causing a reaction between LiAlD4 and lithium hydride, resulting in the formation of LiAlH4.
It’s worth noting that these synthesis methods require careful handling due to the reactivity of the compounds involved. Precautions such as working under inert conditions, using proper safety equipment, and conducting the reactions in well-ventilated areas are essential to ensure a safe and successful synthesis.
Lithium Aluminum Hydride (LiAlH4) Uses
Lithium tetrahydridoaluminate (LiAlH4) finds several applications in organic chemistry due to its powerful reducing properties. Here are some common uses:
- Reduction of Carbonyl Compounds: LiAlH4 converts various carbonyl compounds, such as aldehydes, ketones, esters, and carboxylic acids, into their corresponding alcohols extensively. This reduction reaction is crucial in the synthesis of pharmaceuticals, fine chemicals, and organic intermediates.
- Reduction of Nitro Compounds: LiAlH4 can reduce nitro compounds to primary amines. This transformation is valuable in the synthesis of a wide range of organic compounds, including pharmaceuticals, dyes, and agrochemicals.
- Deoxygenation: LiAlH4 can selectively remove oxygen atoms from various functional groups, such as alcohols, acids, and oximes. This deoxygenation process is useful in the preparation of oxygen-sensitive compounds or when oxygen functionality needs to be removed.
- Polymerization Reactions: LiAlH4 acts as a reducing agent in certain polymerization reactions, facilitating the formation of polymers. Researchers employ LiAlH4 in the production of high-performance materials, including conductive polymers and specialty plastics.
- Synthetic Applications: LiAlH4 finds use in the synthesis of various organic compounds, including hydrazines, phosphines, and organometallic compounds. These compounds are essential in pharmaceutical research, catalysis, and materials science.
- Laboratory Reducing Agent: LiAlH4 serves as a versatile reducing agent in laboratory settings. It allows chemists to selectively reduce specific functional groups, enabling the synthesis of complex molecules with high precision.
Overall, lithium tetrahydridoaluminate (LiAlH4) plays a crucial role in organic synthesis, providing chemists with a powerful tool for diverse reduction reactions and enabling the preparation of a wide range of valuable compounds.
Questions:
Q: Does lithium aluminum hydride reduce double bonds?
A: Yes, lithium tetrahydridoaluminate can reduce double bonds, converting them into single bonds.
Q: What gas does lithium aluminum hydride liberate when reacting with a protic solvent?
A: When lithium tetrahydridoaluminate reacts with a protic solvent, it liberates hydrogen gas.
Q: Where can I buy lithium aluminum hydride?
A: Lithium tetrahydridoaluminate can be purchased from chemical suppliers or specialized laboratory equipment suppliers.
Q: Is lithium aluminum hydride a base?
A: No, lithium tetrahydridoaluminate is not considered a base but a powerful reducing agent.
Q: What does LiAlH4 reduce?
A: Lithium tetrahydridoaluminate can reduce various functional groups, including carbonyl compounds, nitro groups, and alcohols.
Q: Is lithium aluminum hydride a nucleophile?
A: Yes, lithium tetrahydridoaluminate acts as a nucleophile in many organic reactions due to the presence of the hydride ion.
Q: Does lithium aluminum hydride reduce alcohols?
A: Yes, lithium tetrahydridoaluminate can reduce alcohols to produce primary or secondary alcohols.
Q: Does lithium aluminum hydride reduce alkenes?
A: No, lithium tetrahydridoaluminate does not typically react with alkenes.
Q: Which of the solvents below will lithium aluminum hydride not react with?
A: Lithium tetrahydridoaluminate does not typically react with nonpolar solvents such as hexane or diethyl ether.
Q: Does lithium aluminum hydride affect alcohols?
A: Yes, lithium tetrahydridoaluminate can reduce alcohols, but it must be used with caution as it can be highly reactive and potentially hazardous.