CaCl2-Catalyzed Functionalization of Saturated Hydrocarbons with CO to Carboxylic Acids and Esters

The functionalization of saturated hydrocarbons such as ethane, propane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane with CO by CaCl2 catalyst in the presence of K2S2O8 and CF3COOH was studied. In this reaction carboxylic acids were formed as dominant products and alkyl trifluoroacetates were formed as by-products. In the reaction of propane, isobutyric acid was the main product and n-butyric acid and isopropyl trifluoroacetate were the by-products in 95% total yield based on propane when 1 bar of propane reacted with 30 bar of CO in the presence of CaCl2 (0.5 mmol), K2S2O8 (5 mmol), and CF3COOH (5 ml) at 80°C for 24 h. Ethane gave about 88% total yield; however, in that case 23% acetic acid was formed by the oxidation of ethane. Cyclopentane, cyclohexane, and cycloheptane underwent reaction, giving about 44, 33, and 12% total yields, respectively. However, cyclooctane did not undergo this reaction. The activation parameters for the reaction of propane (5 bar) with CO (30 bar) have been determined to be Ea=130.3, 138.0, and 153.8 kJ/mol; A=7.14×1013, 5.83×1014, and 5.80×1016 s−1; ΔH‡=128.0, 134.7, and 150.5 kJ/mol; ΔS‡=10.3, 28.6, and 66.8 J/mol K; and ΔG353‡=124.4, 123.9, and 126.9 kJ/mol for the products isobutyric acid, n-butyric acid, and isopropyl trifluoroacetate, respectively.