disclosed are improved procedures for preparing pinacolone from compounds of general formula ## str1 ## wherein , either adjacent two of a , b , c and d form a single bond between them and the remaining two are hydrogen atoms , or both a and d are hydrogen atoms and one of b and c is a hydrogen atom and the other represents oh , cl , br , hso 4 , h 2 po 4 or clo 4 , and a new procedure which enables preparing pinacolone from a compound of general formula ## str2 ## wherein , both w and y are each hydrogen atoms and x and z are the same or different and each represents oh , cl , br , hso 4 , h 2 po 4 , clo 4 or rcoo wherein r is a hydrogen atom or an alkyl group of 1 to 3 carbon atoms , or one of w and y is a hydrogen atom and the other forms a single bond together with x , and z represents oh , cl , br , hso 4 h 2 po 4 , clo 4 or rcoo where r is defined as above . in the process of preparing pinacolone from compounds of formula by reacting them with formaldehyde in the presence of a strong inorganic acid , the process can be improved by adding a salt of a strong inorganic acid , or a compound of formula . pinacolone can also be produced by heating a compound of general formula in the presence of a strong inorganic acid and this reaction , too , can be improved by the addition of a salt of a strong inorganic acid . the use of a salt of a strong inorganic acid according to the invention makes it possible to reduce the concentration and the amount of strong acid normally required , and to improve the yield of pinacolone .