The invention relates to an improved process for the preparation of 2,2-dimethyl-5-(2,5-dimethylphenoxy)-pentanoic acid of Formula (I) ##STR1## which comprises reacting an ester of the general Formula (X) ##STR2## wherein X represents halogen and Z stands for a straight or branched chain C.sub.1-8 alkylene group optionally substituted by one or two 2,2-dimethyl-5-halopentanoyloxy group(s), wherein halo represents chlorine or bromine, and in which alkylene group one or two methylene group(s) may be optionally replaced either by hetero atom(s) or by a bivalent heterocyclic group--with an alkali salt of 2,5-dimethylphenol of Formula (II) ##STR3## or with an ester of the latter formed with a lower alkanoic acid, and hydrolizing the aryloxy-substituted ester of the general Formula (XI) thus obtained. ##STR4## Furthermore the invention relates to intermediate compounds of the general Formula (X), wherein X and Z are as stated above, and to a process for the preparation thereof.