Epichlorohydrin(ECH) is an organic compound with the formula CH2OCHCH2Cl. It is a colorless liquid with a pungent odor. It is mainly used as a precursor for the synthesis of epoxy resins, which are widely used as adhesives, coatings, and plastics.
Hydrolysis of ECH
One of the reactions of epichlorohydrin is hydrolysis with sodium hydroxide. This reaction produces glycerol and sodium chloride as the main products. The reaction can be represented by the following equation:
CH2OCHCH2Cl + NaOH -> CH2OHCHOHCH2OH + NaCl
The hydrolysis of epichlorohydrin is a step-growth polymerization that can produce linear or crosslinked polymers depending on the concentration of sodium hydroxide, the reaction temperature, and the dropping method . The lower the concentration of sodium hydroxide, the higher the yield of glycerol. The maximum yield of glycerol was reported to be 85% for 1% sodium hydroxide solution .
Synthesis of epoxy resins from epichlorohydrin
Another important reaction of epichlorohydrin is the synthesis of epoxy resins from bisphenols. Bisphenols are aromatic compounds with two hydroxyl groups attached to the same carbon atom. The most common bisphenol is bisphenol A (BPA), which is derived from phenol and acetone.
The synthesis of epoxy resins from bisphenols and ECH involves two steps: (1) the formation of bisphenol A diglycidyl ether (DGEBA) and its condensed forms by the reaction of BPA and ECH in the presence of sodium hydroxide; and (2) the curing of DGEBA with co-monomers or hardeners to form crosslinked polymers .
The structure of DGEBA and its condensed forms depends on the stoichiometry of the reactants. The average number of epoxy groups per molecule (n) can vary from 0.03 to 10. The epoxy resins are crystalline solids for n values close to zero, liquids for n values up to 0.5, and amorphous solids for higher n values .
The curing of DGEBA can be done by various co-monomers or hardeners, such as amines, anhydrides, phenols, thiols, or acids. The curing mechanism can be either step-growth or chain-growth polymerization, or a combination of both. The properties of the cured epoxy resins depend on the type and amount of co-monomer or hardener, the curing temperature and time, and the presence of catalysts or additives .
Data on epichlorohydrin and its derivatives
The following table summarizes some data on ECH and its derivatives:
| Compound | Molecular formula | Molecular weight | Boiling point | Melting point |
|---|---|---|---|---|
| Epichlorohydrin | C3H5ClO | 92.52 g/mol | 116 °C | -57 °C |
| Glycerol | C3H8O3 | 92.09 g/mol | 290 °C | 18 °C |
| Sodium chloride | NaCl | 58.44 g/mol | 1413 °C | 801 °C |
| Bisphenol A | C15H16O2 | 228.29 g/mol | 220 °C (sublimes) | 158 °C |
| DGEBA (n=0) | C21H24O4 | 340.41 g/mol | 210 °C (decomposes) | 40-45 °C |
| DGEBA (n=0.5) | C24H28O5 | 396.48 g/mol | – | – |
Extended Reading
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