A method of determining the number of methoxy (–OCH3) groups in an organic compound. The compound is heated wih excess hydriodic acid, forming an alcohol and iodomethane:R-O-CH3+HI → ROH+CH3I The iodomethane is distilled off and led into an alcoholic solution of silver nitrate, where it precipitates silver iodide. This is filtered and weighed, and the number of iodine atoms and hence methoxy groups can be calculated. The method was developed by S. Ziesel in 1886.
R-O-CH3+HI → ROH+CH3I