1. A new reaction, the direct non-catalytic, addition of hydrogen fluoride to alkynes giving a series of difluoroparaffins, of the formula RâCF2âCH2âR', has been described. 2. With the exception of acetylene the alkynes studied, namely, propyne, butyne-1, butyne-2, pentyne-1, hexyne-1, hexyne-3, and heptyne-1, all reacted at temperatures around -70° to give good yields of a difluorinated paraffin. 3. The properties of 2,2-difluoro-propane, -butane, -pentane, -hexane, -heptane and 3,3-difluoro-hexane are described. 4. The hydrofluorination of acetylene was accomplished by contacting it with liquid hydrogen fluoride in an autoclave under pressure. 1,1-Difluoro-ethane and vinyl fluoride were the reaction products isolated. © 1942, American Chemical Society. All rights reserved.