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clear slightly colored liquid
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Methacryloyl chloride is the clear to slightly colored acid chloride of methacrylic acid. It appears as a liquid of density 1.07g/cm3, boiling point 95-96°C, and flash point 55°F. Highly toxic. Supplied in technical grades of varying purity. Monomethyl ether hydroquinone is added as a stabilizer to prevent auto polymerization. Reaction with diisopropyl ether in presence of metal salts is rigorous.
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Highly flammable. Reacts with water to produce gaseous hydrogen chloride (corrosive and toxic).
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Methacryloyl chloride is incompatible with strong oxidizing agents, alcohols, bases (including amines). Can polymerize violently; but the polymerization reaction can be inhibited by the addition of phenolthiazine. May react vigorously or explosively if mixed with diisopropyl ether or other ethers in the presence of trace amounts of metal salts [J. Haz. Mat., 1981, 4, 291].
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Flammable and corrosive liquid.
Synthesis
Using α-methacrylic acid as a raw material, it is reacted with liquid phosgene (trichloromethyl chloroformate) or solid phosgene (bis(trichloromethyl) carbonate) in the presence of a catalyst, followed by the addition of a polymerization inhibitor and distillation to obtain the target product. The specific method is as follows: 0.5–2 wt% of an organic basic catalyst and 0.1–1 wt% of a polymerization inhibitor are added to α-methacrylic acid. Solid or liquid phosgene is added dropwise over 1 hour at room temperature. After the addition is complete, the reaction is carried out at 20–75°C for 4–10 hours. Then, distillation is performed under atmospheric pressure, and the fraction collected at 95–98°C yields methacryloyl chloride.
Purification Methods
Purify the ester by fractional distillation. If it contains the acid (OH bands in the IR) then add redistilled SOCl2 (with cooling) and cuprous chloride (ca to 2%), reflux the mixture gently for 1hour and fractionate it through a 1metre column packed with glass helices. Redistillation then provides the acid chloride in high purity as a colourless liquid. It is necessary to keep the apparatus moisture free (use CaCl2 tubes), Stabilise it with 0.05% of 2,6-di-tert-butyl-4-methylphenol. [Lal & Green J Org Chem 20 1032 1955, Beilstein 2 IV 1537.]
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