Acylphosphine oxide compounds their preparation and use

An acylphosphine oxide compound of the formula ##STR9## where R.sup.1 is straight-chain or branched alkyl of 1 to 6 carbon atoms cyclohexyl, cyclopentyl, phenyl or naphthyl which is unsubstituted or substituted by halogen, alkyl of 1 to 6 carbon atoms or alkoxy of 1 to 6 carbon atoms, or a fully aromatic S-containing or N-containing five-membered or six-membered heterocyclic radical having one hetero atom, selected from pyridyl or thienyl,

• R.sup.3 is an at least disubstituted phenyl, pyridyl, furyl or thienyl radical which carries, at least at the two carbon atoms adjacent to the linkage point of the carbonyl group, the substituents A and B, which may be identical or different, and each of which is alkyl, alkoxy or alkylthio of 1 to 6 carbon atoms, cycloalkyl of 5 to 7 carbon atoms, phenyl or halogen, or R.sup.3 is .alpha.-naphthyl substituted by A and B at least in the 2- and 8-positions or is .beta.-naphthyl substituted by A and B at least in the 1- and 3-positions and
• R.sup.2 has one of the meanings of R.sup.1 (but R.sup.1 and R.sup.2 may be identical or different with the proviso that R.sup.1 and R.sup.2 do not stand simultaneously for alkyl of 1 to 5 carbon atoms or alkoxy of 1 to 5 carbon atoms if R.sup.3 is phenyl which carries the substituents A and B, in the same positions as defined above, but in which the meanings of A and B are restricted to alkoxy of 1 to 5 carbon atoms or halogen) or is alkoxy of 1 to 6 carbon atoms, phenoxy, methylphenoxy or benzyloxy, or R.sup.1 and R.sup.2 may be joined together to form a five- or six-membered P-containing ring.