Prepn by a modified Willgerodt reaction: Jelinek, US 2572809; US 2572810 (both 1951 to GAF); from butyryl chloride: Philbrook, J. Org. Chem. 19, 623 (1954); from butyraldoxime: Huber, US 2721199 (1955 to du Pont); from butyric acid: Rahman, Rec. Trav. Chim. 79, 188 (1960); from butyronitrile: Gilbert, Rumanowski, US 3062883 (1962 to Allied Chem.).