Eleven compounds of general structure RCON=NC(CN)R2′, where R = C6H5, CH3, C6H5CH2, and R2′ = (CH3)2, (CH2)4, (CH2)5, (CH2)6, have been found to decompose in a first-order manner in dilute toluene solution in the temperature range 60–100°. The N-acetyl compounds decompose ca. four times faster than the corresponding N-benzoyl cases. Variation in R2′ causes changes in rate parallel to those observed by Overberger for the analogous bis-α-cyanoalkyl diimides but of smaller magnitude. The products are those expected from homolytic cleavage, and intermediate N-acylketenimines have been trapped by added water in two cases.