What are the key physical and chemical properties of Formamidine acetate for lab use?

2026-05-27 09:30:15

Formamidine acetate, with the CAS registry number 3473-63-0, is a widely used chemical reagent in laboratory settings, particularly in pharmaceutical synthesis, organic chemistry research, and materials science applications such as perovskite solar cell development. Understanding its physical and chemical properties is essential for safe handling, accurate experimental design, and optimal performance in lab workflows. This article outlines the core characteristics of formamidine acetate relevant to laboratory use, drawing on verified technical data to support researchers and technicians in working with this compound effectively.

Basic Identification and Molecular Characteristics

Formamidine acetate is the acetate salt of formamidine, a simple amidinium compound. Its molecular formula is consistently reported as C₃H₈N₂O₂, with a molecular weight of 104.11 g/mol. Alternative sources may list a closely related formula of C₃H₇N₃O₂ with a molecular weight of 105.10 g/mol, reflecting minor variations in structural representation, but the former is the most widely accepted for standard laboratory-grade material. It is also known by synonyms including formamidine acetic acid salt, iminoformamide acetate, and FAA, which are useful for cross-referencing in chemical databases and supplier catalogs. The compound’s EINECS number is 222-442-5, and its InChIKey (XPOLVIIHTDKJRY-UHFFFAOYSA-N) provides a unique identifier for digital chemical libraries.

Physical Properties

Appearance and Odor

In its pure form, formamidine acetate typically presents as a white to light yellow crystalline powder or clear colorless to light yellow liquid, depending on processing and storage conditions. Laboratory-grade material is often supplied as a crystalline solid to enhance stability, with a characteristic acetic acid odor due to its salt structure. The color may shift slightly toward yellow with prolonged exposure to moisture or heat, serving as a visual indicator of potential degradation.

Melting Point and Thermal Stability

The compound exhibits a melting point range of 158–161°C (with decomposition) under standard laboratory conditions, as reported in multiple technical datasets. Some sources note a slightly higher range of 162–164°C for highly purified crystalline batches, while others report 182–185°C for material with specialized processing. Decomposition occurs simultaneously with melting, meaning the compound does not exist as a stable liquid at temperatures above its melting point. This thermal sensitivity requires careful temperature control during experiments involving heating, such as recrystallization or reaction steps exceeding 150°C.

Density and Solubility

Formamidine acetate has a density of 1.124 g/cm³ at room temperature, a key parameter for calculating solution concentrations and reaction volumes. Its solubility is a critical property for lab use: it is freely soluble in water at a rate of 832 g/L (21°C), making it easy to prepare aqueous solutions for biological or chemical reactions. It shows slight solubility in ethanol but is poorly soluble in non-polar organic solvents such as benzene, toluene, and hexane, aligning with the behavior of polar salt compounds. This solubility profile makes it ideal for aqueous-based synthesis, such as the preparation of formamidinium lead triiodide (FAPbI₃) perovskites, where high water solubility ensures uniform precursor mixing.

Hygroscopicity and Storage Stability

A defining physical property of formamidine acetate is its hygroscopic nature, meaning it readily absorbs moisture from the air. Unlike its hydrochloride counterpart, the acetate salt is less prone to caking but still requires protection from humid environments. Recommended storage conditions include temperatures below +30°C (with some sources advising -20°C for long-term stability) in airtight, moisture-resistant containers. Proper storage prevents hydrolysis, which can degrade the compound and reduce its reactivity in sensitive reactions.

Chemical Properties

pH and Aqueous Behavior

Aqueous solutions of formamidine acetate are mildly basic, with a pH of 8 at 400 g/L concentration (20°C), reflecting the dissociation of the acetate ion and the weak basicity of the formamidinium cation. This pH range is compatible with many biological and organic reactions that require neutral to slightly alkaline conditions, such as peptide coupling or heterocycle synthesis. The compound’s high water solubility also supports its use as a buffer additive in specific lab protocols, though its primary role remains as a reactive intermediate rather than a pH regulator.

Reactivity and Functional Group Behavior

Formamidine acetate acts as a versatile condensing agent and intermediate in organic synthesis, owing to the reactive amidinium group (-C(=NH)NH₂⁺) in its structure. It participates in nucleophilic substitution reactions to form heterocyclic compounds, including pyrimidines, imidazoles, and triazoles, which are core scaffolds in pharmaceutical and agrochemical research. For example, it is used to synthesize 4-hydroxyl-5-fluoropyrimidine, an antineoplastic drug precursor, and cyclohexapeptide antifungal agents. The acetate counterion is relatively labile, allowing the formamidinium cation to be released under mild reaction conditions, making it suitable for sensitive substrates that cannot withstand harsh reagents.

Stability and Degradation Pathways

While stable under dry, cool conditions, formamidine acetate is prone to hydrolysis in moist air over time, breaking down into formamide and acetic acid derivatives. This degradation is accelerated by high temperatures and alkaline pH, so lab users should avoid storing solutions for extended periods and prepare fresh stock when possible. It is also incompatible with strong oxidizing agents, which can trigger exothermic reactions, and should be stored separately from such reagents in the lab. The compound has a low fire hazard (autoignition temperature of 565°C) but is classified as a combustible solid (storage class 11), requiring standard flammable material precautions.

Purity and Quality Standards

Laboratory-grade formamidine acetate typically has a purity of ≥98.5% (HPLC), with strict limits on impurities: heavy metals ≤10 ppm, loss on drying ≤0.5%, and residue on ignition ≤0.1%. These standards ensure consistent reactivity and minimize side reactions in sensitive syntheses, such as pharmaceutical intermediate production or perovskite thin-film fabrication. Lower-purity material may contain residual acetic acid or unreacted formamidine, which can alter reaction yields or contaminate final products.

Safety and Handling Considerations for Lab Use

While not a direct physical or chemical property, safety characteristics are integral to lab workflows. Formamidine acetate is labeled with a GHS warning signal word, with hazard statements including H317 (may cause allergic skin reaction). It has a low acute toxicity profile: oral LD₅₀ in rabbits is 2510 mg/kg, and dermal LD₅₀ in rats exceeds 2000 mg/kg, but it can cause skin and eye irritation (risk phrases 36/37/38). Lab users should wear nitrile gloves, safety goggles, and lab coats when handling the compound, and work in a well-ventilated area or fume hood to avoid inhaling dust or vapors. Spills should be contained with inert absorbent material and disposed of as non-hazardous chemical waste per local regulations.

Conclusion

Formamidine acetate’s key physical and chemical properties—including its crystalline appearance, high water solubility, hygroscopicity, thermal decomposition at 158–161°C, mild basicity, and reactivity as a condensing agent—make it a valuable tool in laboratory settings. Its stability under dry, cool storage and compatibility with aqueous reaction systems support its use in pharmaceutical synthesis, materials science, and organic chemistry research. By understanding these properties, lab personnel can optimize experimental conditions, ensure safe handling, and achieve reliable results in applications ranging from heterocycle synthesis to perovskite device fabrication. Adhering to storage guidelines (below 30°C, airtight containers) and purity standards (≥98.5%) further enhances its performance, making formamidine acetate a consistent and effective reagent for diverse lab workflows.