Dimethyl malonate
Dimethyl malonate, chemically known as propanedioic acid dimethyl ester, is a diester of malonic acid with the molecular formula C₅H₈O₄ and a molecular weight of 132.11 g/mol.[1][2] It appears as a clear, colorless liquid at room temperature, characterized by a melting point of -62 °C, a boiling point of 180–181 °C, a density of 1.156 g/mL at 25 °C, and miscibility with alcohols but limited solubility in water (143 g/L at 20 °C).[3] This compound is primarily synthesized through the direct esterification of malonic acid with methanol under azeotropic conditions, often in the presence of an acid catalyst like sulfuric acid.[2] Alternative industrial methods include the reaction of chloroacetic acid derivatives with carbon monoxide and methanol, though esterification remains the most common route.[4] Dimethyl malonate plays a crucial role in organic chemistry as a key intermediate in the malonic ester synthesis, enabling the preparation of mono- and di-substituted acetic acid derivatives via alkylation, decarboxylation, and hydrolysis steps.[2][5] It serves as a precursor for synthesizing pharmaceuticals such as barbiturates, chloroquine, and butazolidin, as well as vitamins B1 and B6.[2] Additionally, it finds applications in the production of fragrances, artificial flavorings, dyes, pesticides, and laboratory chemicals, with annual U.S. production volumes ranging from 1 to 10 million pounds (as of 2016-2019).[1] Naturally occurring as a volatile component in fruits like pineapples, bananas, and blackberries, it contributes to their aroma profiles.[1] From an environmental and safety perspective, dimethyl malonate is readily biodegradable (87% degradation in 7 days) with low bioaccumulation potential (log Kow of -0.09) and low acute toxicity (oral LD50 > 2000 mg/kg in rats). It has been designated by the U.S. EPA as a low-priority substance for risk evaluation under the Toxic Substances Control Act due to its minimal hazard profile.[6]Chemical identity
Names and identifiers
Dimethyl malonate is the common name for the dimethyl ester of malonic acid.[1] The preferred IUPAC name is dimethyl propanedioate.[1] Other names include malonic acid dimethyl ester.[1] The CAS Registry Number is 108-59-8.[7] The molecular formula is C₅H₈O₄.[1] The SMILES notation isCOC(=O)CC(=O)OC.[1]
The InChI is InChI=1S/C5H8O4/c1-8-4(6)3-5(7)9-2/h3H2,1-2H3.[1]
Molecular structure
Dimethyl malonate features a central methylene group (CH₂) bonded to two ester groups (-COOCH₃), forming the structure CH₂(COOCH₃)₂. This diester derivative of malonic acid exhibits a linear carbon backbone with the methylene carbon (sp³ hybridized) connected to two adjacent carbonyl carbons.[1] The bond lengths, determined from gas-phase electron diffraction studies, approximate 1.50 Å for the C-C bonds between the methylene and carbonyl carbons, 1.20 Å for the C=O double bonds, 1.33 Å for the carbonyl C-O bonds, and 1.45 Å for the ester O-CH₃ bonds.[8] The ester moieties are planar, owing to resonance stabilization that delocalizes the oxygen lone pairs into the carbonyl π-system, resulting in partial double-bond character for the C-O linkage and a slight elongation of the C=O bond relative to simple ketones.[9] Conformational flexibility arises around the central C-C bonds, with low-energy barriers (<2 kJ mol⁻¹) separating minima on the potential energy surface. Quantum chemical calculations and spectroscopic data identify two primary conformer groups: a C₂-symmetric form where the ester groups are symmetrically crossed relative to the O=C-CH₂-C=O plane (anticlinal orientations), and C₁-symmetric gauche forms with asymmetric orientations of the carbonyls. In the gas phase, a mixture predominates with ~69% anticlinal-anticlinal and ~31% synperiplanar-anticlinal; in solution, gauche and anti conformations are similarly favored.[8][9] The absence of hydrogen-bond donor groups precludes intermolecular hydrogen bonding, influencing packing in the condensed phase.[9]Physical properties
Thermodynamic properties
Dimethyl malonate appears as a colorless to pale yellow liquid at room temperature, consistent with its role as a low-viscosity ester suitable for organic synthesis.[2][10] Its density is 1.154 g/cm³ at 20°C, reflecting the compact molecular packing influenced by the symmetric structure of the malonate ester.[11] The compound exhibits a low melting point of -62°C, attributable to the molecular formula C₅H₈O₄, which features flexible methylene and ester groups that reduce intermolecular forces.[2][12] The boiling point is 180–181°C at 760 mmHg, indicating moderate thermal stability under standard pressure.[2][12] Vapor pressure is approximately 0.11 mmHg at 20°C, signifying low volatility at ambient conditions.[2] The refractive index is 1.413 at 20°C, a value typical for aliphatic diesters.[2] The heat of vaporization is 57.5 ± 0.3 kJ/mol over the temperature range 278–314 K, highlighting the energy required for phase transition due to dipole-dipole interactions in the liquid state.[12]| Property | Value | Conditions | Source |
|---|---|---|---|
| Appearance | Colorless to pale yellow liquid | Room temperature | ChemicalBook |
| Density | 1.154 g/cm³ | 20°C | Sigma-Aldrich |
| Melting point | -62°C | - | ChemicalBook; NIST |
| Boiling point | 180–181°C | 760 mmHg | ChemicalBook; NIST |
| Vapor pressure | 0.11 mmHg | 20°C | ChemicalBook |
| Refractive index | 1.413 | 20°C (n_D) | ChemicalBook |
| Heat of vaporization | 57.5 ± 0.3 kJ/mol | 278–314 K | NIST |