Introduction

Chemists know methyl acetoacetate (MAA, CAS 105-45-3) as a remarkably versatile player in synthetic chemistry. This clear liquid, also called acetoacetic acid methyl ester or methyl 3-oxobutanoate (C₅H₈O₃, MW 116.12 g/mol), serves as a foundational building block across pharmaceuticals, agrochemicals, and polymer science. Its secret lies in the dual reactivity of the ester and keto functional groups – a combination that opens doors to diverse transformations like condensation and cyclization reactions, making it indispensable in the lab and plant.

Key Properties at a Glance

Understanding MAA’s behavior starts with its physical profile. Industry experience shows it typically appears as a colorless to very pale yellow liquid (APHA ≤20). Practical handling requires noting its density (1.076 g/mL at 25°C) and especially its low melting point (–80 °C) combined with a boiling point around 169–170 °C under reduced pressure (70 mmHg). Safety sheets rightly highlight its flash point of 158 °F as an important consideration. For long-term stability, manufacturers consistently recommend storing MAA between 2–8 °C in tightly sealed containers. This combination of low-temperature fluidity and moderate volatility makes it particularly useful for precise reaction control and specific solvent roles.

Where It Shines: Applications

Pharmaceutical & Agrochemical Synthesis: 

Methyl acetoacetate truly excels as a key intermediate. Production lines rely on it for crafting fungicides like hymmezol, dimethylsulfurol, and ethylsulfurol. Its reactivity also underpins the synthesis of established insecticides (think diazinon, pyrifos) and herbicides such as imidazoleetinic acid, alongside certain rodenticides. Furthermore, MAA steps into more complex medicinal chemistry, contributing to structures like pyrimidine oxyphosphorus derivatives.

Organic Synthesis Powerhouse:

Beyond pharma, MAA’s keto-ester functionality earns its keep as a go-to scaffold. Synthetic chemists leverage it extensively as a building block for manufacturing dyes, various agrochemicals, and polymer stabilizers. Its inherent ability to undergo condensation, cyclization, and substitution reactions provides remarkable flexibility.

Practical Solvent Uses: 

Equally important is MAA's role as a solvent. It finds practical application in dissolving cellulose ether and frequently acts as a component in mixed solvent systems tailored for cellulose resins. This solvent compatibility proves valuable in formulating resins and other polymer-related processes.

Conclusion

In essence, methyl acetoacetate (CAS 105-45-3) delivers impressive versatility. Its reactive structure, defined physical properties (notably that very low -80°C melting point and specific boiling range), and usefulness as a reactive intermediate *and* solvent cement its status as a staple chemical. Whether synthesizing life-saving drugs, crop protection agents, or advanced polymers, MAA remains a fundamental tool, requiring only straightforward refrigerated storage to maintain its performance.