Improved process for the acid-catalyzed conversion of a reactant into a reaction product wherein the improvement comprises contacting said reactant with an acid catalyst represented by general formula (I), wherein X is selected from the group consisting of oxygen, sulfur or represents 2 hydrogen atoms; Z is selected from the group consisting of the anions of strong acids, e.g. chloride, bromide, bisulfate, nitrate or dihydrogen phosphate; R1 is hydrogen or a lower alkyl having one to four carbon atoms; R is hydrogen or a methyl radical; m is an integer of from 2 to 6; n is 0 or 1; and o is 0 or an integer of from 1 to 17, at reaction conditions, and recovering a reaction product. Reactants which may be converted into reaction products in the process of this invention include hydrocarbons and heteroatom-substituted hydrocarbons, wherein said heteroatoms may be selected from the group consisting of nitrogen, oxygen, sulfur, phosphorus and halogen atoms. For example, in the present inventive process, olefins may be reacted with tertiary alkanes to provide alkylated products; olefins may be reacted with carboxylic acids to obtain esters; alcohols may be dehydrated to obtain olefins or ethers or reacted with carboxylic acid to obtain an alkylated product or an ester, respectively; anhydrides may be reacted with an aromatic or an olefinic compound to obtain acetylated derivatives thereof; epoxides may be reacted to the corresponding glycols, etc.