Ruthenium-phenol catalysts and method of preparing menthone from isopulegol

A method for preparing menthone comprising conducting a transfer hydrogenation reaction in the presence of a liquid medium that includes isopulegol, a ruthenium precursor and a phenol derivative,

• wherein the phenol derivative:isopulegol is present at a weight ratio of 1:10, and the transfer hydrogenation reaction is carried out at a temperature in range from 150 to 200° C., and the phenol derivative is of the formulae (Ia) or (Ic)
• wherein
• R1, R2, R3, R4 independently are hydrogen, alkyl, or hydroxy, or
• R3, R4 together with the carbon atoms to which they are bound form an anellated aromatic ring;
• R5a is hydrogen, alkyl, or hydroxy;
• R6, R7, R8, R9 independently are hydrogen or alkyl, or
• R6, R7 together with the carbon atoms to which they are bound form an anellated aromatic ring;
• R10 is hydrogen or hydroxy, and
• X is a chemical bond;
• alkylene optionally substituted by 1, 2 or 3 substituents which are independently selected from the group consisting of halogen, alkyl, substituted alkyl, cycloalkyl, aryl, and OH;
• or arylene optionally substituted by 1, 2, 3 substituents which are independently selected from the group consisting of halogen, alkyl, substituted alkyl, alkoxy and OH;
• —O—;
• and —S—;
• and the ruthenium precursor does not possess nitrogen or phosphorous donor ligands.