Acid Chlorides. Chlorination of Carboxylic Acids

Various chlorinating agents have been used to convert carboxylic acids or their anhydrides into acid chlorides. The most commonly reported methods employ thi-onyl chloride, phosphorus trichloride, or phosphorus pentachloride. However, the unsatisfactory degree of purity of the final acid chlorides, due to inherent contamination with sulfur or phosphorus by-products, has stimulated a search for new reagents and catalysts. 

Typical procedure. Lauroyl chloride 1331 [1002]. Equipment A 500-mL, round-bottomed flask was fitted with a paddle stirrer, a gas inlet tube, a thermowell, and a 

Several phosgene equivalents have been reported to bring about clean and efficient activation of the carboxylic group as an add chloride. 

Pure 2-cyanoacryloyl chloride, which is useful for the preparation of esters suitable for contaminant-free adhesives, is manufactured by reacting 2-cyanoacrylic add with a chlorinating agent under conditions inhibiting side reactions and polymerization. Oxalyl chloride, thionyl chloride, trifluoroacetyl chloride, and phosgene, 

Typical procedure. 2-Cyanoacryloyl chloride [1008] 2-Cyanoacrylic acid (2.0 g) was dissolved in hot p-xylene (250 mL) containing y-propanesultone (1 mg). Some 50 mL of the xylene was then removed by distillation, and the concentrated solution was filtered and cooled to 40 °C. Me2NCHO (5 mg stock solution in benzene) was added, and then oxalyl chloride (6 mL) was added dropwise with stirring under a continuous flow of Ar. The mixture was stirred for 12 h at room temperature, then ethyl furfurylidenecyanoacetate (5 mg) was added and the volatiles (along with a part of the solvent) were removed in vacuo to give 100 mL of a clear yellow solution of 2-cyanoacryloyl chloride in xylene. 

---