Sodium methoxide (CH3ONa) and sodium ethoxide (C2H5ONa) are two important alkoxide catalysts. The alcohol group of sodium methoxide is methyl, while the alcohol group of sodium ethoxide is ethyl. The chemical properties of the two are also different, and there are certain differences in their application fields. Based on a comprehensive analysis of physical and chemical properties, alkaline strength, and application scenarios, the core differences are compared as follows:
1、 Physical properties and forms
1. Property parameters:
Sodium methoxide: melting point of 127 ℃, boiling point of 65 ℃ (methanol solution), density of 0.945 g/mL (20 ℃), flash point of 11 ° C (highly flammable), corrosive.
Ethanol sodium: Melting point is 260-270 ℃ (decomposition temperature), boiling point is 91 ℃, density is 0.868g/mL (25 ℃), flash point is 22 ℃, it quickly hydrolyzes with water to produce sodium hydroxide and ethanol.
2. Form and appearance:
Sodium methoxide: It is usually a colorless or slightly yellow viscous liquid (in the form of methanol solution) at room temperature, and the pure product is a white solid powder. It is sensitive to oxygen and flammable and explosive; The solid sodium methoxide content is ≥ 99%, and the liquid sodium methoxide content is ≥ 30%.
Ethanol sodium: mainly composed of white to slightly yellow hygroscopic powder (solid), can also be made into ethanol solution, which easily decomposes and turns black in air. The solid sodium ethoxide content is ≥ 99%, and the liquid sodium ethoxide content is ≥ 20%, and different contents can also be prepared.
3. Solubility and stability:
Both are soluble in the corresponding anhydrous alcohol (sodium methoxide is soluble in methanol/ethanol, and sodium ethoxide is soluble in ethanol), but they quickly hydrolyze in water to produce sodium hydroxide and alcohol.
Sodium methoxide decomposes in air above 126.6 ℃, while sodium ethoxide decomposes at high temperatures (approximately 260 ℃).
2、 Chemical properties
1. Alkaline strength:
Ethanol sodium is more alkaline: due to the weaker electron pushing effect of ethyl than methyl, the conjugated acid (ethanol) of ethanol sodium is less acidic than methanol, making its alkoxy group more easily hydrolyzed and more alkaline.
*Due to the weaker electron pushing effect of ethyl (- C ₂ H ₅) compared to methyl (- CH3), and the weaker acidity of ethanol (pKa ≈ 15.9) compared to methanol (pKa ≈ 15.5), its conjugate base (sodium ethoxide) is more easily dissociated and has a stronger alkalinity.
*Alkaline order: Sodium tert butoxide>Sodium ethoxide>Sodium methoxide>NaOH (alkalinity in water is masked).
*Experimental basis: The pKb of sodium ethoxide is approximately 3, and the pKb of sodium methoxide is approximately 4 (the lower the value, the stronger the alkalinity).
Both are more alkaline than sodium hydroxide, but the pKb (≈ 3) of sodium ethoxide is lower.
2. Reaction activity:
The nucleophilicity of sodium methoxide is slightly stronger than that of sodium ethoxide (due to the small volume of methyl groups), but the difference in alkalinity has a greater impact on the selectivity of catalytic reactions.
3、 Main application areas
1. The use of sodium methoxide:
Pharmaceutical industry: Sodium methoxide is an important raw material for the synthesis of various drugs. In addition, it is also used in the production of sulfonamide drugs and other drugs.
Organic synthesis: Sodium methoxide is used as an alkaline condensing agent and catalyst in organic synthesis for the synthesis of fragrances and dyes. It can also be used in esterification reactions, addition reactions, and dehydrogenation reactions, and has a wide range of chemical reaction applications.
Biodiesel industry: Sodium methoxide is also used in the production of biodiesel.
Edible catalyst: Sodium methoxide is also used as a catalyst for processing edible fats and oils, especially when processing lard, to change the fat structure, suitable for artificial butter, etc., but must be removed from the final food.
Analytical reagent: Sodium methoxide can also be used as an analytical reagent in various chemical analyses
2. The use of sodium ethoxide:
Pharmaceutical raw materials: Sodium ethoxide is mainly used in the synthesis of pharmaceuticals and is an important raw material for various drugs such as sulfonamides.
Organic synthesis: Sodium ethoxide is used as a strong alkaline catalyst and ethoxylate in organic synthesis, for the synthesis of various organic compounds and surfactants
Pesticide intermediates: used as synthetic raw materials for herbicides and insecticides.
Rubber industry: used as a polymerization regulator and vulcanization rate controller in synthetic rubber production to enhance rubber performance.
Analytical reagents: used for acid-base titration and specific metal ion detection in chemical analysis.
