Dimethylacetamide
N,N-Dimethylacetamide (DMAc), with the molecular formula C₄H₉NO, is a colorless liquid organic compound serving as a polar aprotic solvent in chemical synthesis and industrial manufacturing.[1][2] It exhibits high solvency for a wide range of organic and inorganic compounds, a boiling point of approximately 165 °C, and miscibility with water and most organic solvents, accompanied by a faint ammonia-like odor.[3] Industrially produced through the reaction of dimethylamine with acetic acid or acetic anhydride, DMAc finds extensive use in dissolving polymers for fiber production (such as polyacrylonitrile and spandex), formulating pharmaceuticals and agrochemicals, and manufacturing coatings, adhesives, and photoresists.[4][5][6] Despite its effectiveness, DMAc poses significant health risks, including developmental toxicity, male reproductive effects, and potential carcinogenicity as recognized under California's Proposition 65; animal studies indicate hepatotoxicity and fetotoxicity at occupational exposure levels.[1][2] Exposure occurs primarily via skin absorption or inhalation, prompting regulatory limits such as OSHA's permissible exposure limit of 10 ppm over 8 hours.[5] Its environmental persistence and bioaccumulative potential further underscore the need for substitution efforts in sensitive applications like electronics and membrane production.[6]Chemical and Physical Properties
Molecular Structure and Basic Characteristics
Dimethylacetamide, systematically named N,N-dimethylacetamide, has the molecular formula CH₃CON(CH₃)₂ (or C₄H₉NO) and a molecular weight of 87.12 g/mol.[1][7] This compound features a tertiary amide functional group, characterized by a carbonyl (C=O) bonded to a nitrogen atom substituted with two methyl groups, which restricts rotation around the C–N bond due to partial double-bond character from resonance delocalization of the nitrogen lone pair into the carbonyl π-system.[8][9] The amide structure confers significant polarity, with a dipole moment of approximately 3.72 D, arising from the electronegative oxygen and the electron-rich nitrogen.[10] As a polar aprotic solvent, dimethylacetamide solvates ions and polar species effectively through its electronegative oxygen acceptor site but lacks acidic protons on nitrogen, preventing hydrogen bond donation and enhancing its utility in reactions sensitive to proton activity.[11] Relative to analogous solvents, dimethylacetamide displays polarity comparable to N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP), evidenced by its polarity index of 6.5—marginally above DMF's 6.4 but below NMP's 6.7—stemming from similar dielectric constants around 37–38 that support dissolution of diverse substrates without protic interference.[12][13] This intrinsic molecular architecture underpins its role as a versatile medium for solvation-driven processes.Thermodynamic and Solubility Properties
Dimethylacetamide (DMAc) is a polar aprotic solvent existing as a colorless liquid under ambient conditions, with a melting point of -20 °C and a boiling point of 166 °C at standard pressure.[14][11] Its density measures 0.942 g/cm³ at 20 °C, while the dynamic viscosity is 0.92 mPa·s at 25 °C, contributing to its flow characteristics in industrial applications.[11][15]| Property | Value | Conditions |
|---|---|---|
| Heat of vaporization | 53.2 kJ/mol | 25 °C |
| Octanol-water log P | -0.77 | 25 °C |