compounds of the class of acetals of 6 - phenyl - 4h - s - triazolobenzodiazepine - 1 - carboxaldehyde and the 5 - oxides and pharmaceutically acceptable acid addition salts thereof have valuable pharmacological properties , in particular anticonvulsant effectiveness . further , they show central depressant and muscle - relaxing activity and are active ingredients for therapeutic preparations . specific embodiments are 6 - phenyl - 8 - chloro - 4h - s - triazolobenzodiazepine - 1 - carboxaldehyde - diethylacetal , 6 -- 8 - chloro - 4h - s - triazolobenzodiazepine - 1 - carboxaldehyde - diethylacetal and 6 - benzodiazepine - 1 - carboxaldehyde - diethylacetal .