The Rosenmund reduction of acid chlorides to the corresponding aldehydes was discussed in volume 4 of this series. There are a number of other less direct methods by which carboxylic acids can be converted into aldehydes and the purpose of this chapter is to consider the more useful of these procedures. Three of these methods, the hydrolytic decomposition of Reissert’s compounds, the method of Grundmann, and the reductive desulfurization of thiol esters require acid chlorides as intermediates and in the respect are competitive with the Rosenmund reduction of acid chlorides. In the fourth method method, the McFadyen and Stevens synthesis, acid chlorides may be used for the preparation of the intermediate acyl hydrazides. Two additional methods, (Sonn and Muller, and Stephen) are based on the intermediate imido chlorides. These methods listed appear to be the one ones developed to the point where further discussion is profitable.