TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The heterogeneous acid catalyst is heterogeneous heteropolyacid, natural clay mineral, cation exchange resin, metal oxide, mixed metal oxide including zeolite, metal sulfide, metal sulfate, metal sulfonate, metal nitrate, metal phosphate, metal phosphonate, metal molybdate, metal tungstate and/or metal borate and the metal is Groups I, IIa, IIIa, VIIa, VIIIa, Ib and IIb of the periodic table of the elements, aluminum, chromium, tin, titanium or zirconium.The heterogeneous catalyst has an Ho of less than or equal to4 and comprises heterogeneous heteropolyacid of Formula XaMbOcq-.The heterogeneous catalyst is supported on a catalyst support, selected from carbon, alumina, silica, silica-alumina, silica- titania, silica-zirconia, titania, titania-alumina, zirconia, barium sulfate, calcium carbonate, strontium carbonate and/or their compounds and is a heteropolyacid.X=phosphorus, silicon, boron, aluminum, germanium, titanium, zirconium, cerium, cobalt or chromium;M=at least one transition metal selected from tungsten, molybdenum, niobium, vanadium, or tantalum;q,a,b,c=whole numbers or their fractions.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The heterogeneous acid catalyst is heterogeneous heteropolyacid, natural clay mineral, cation exchange resin, metal oxide, mixed metal oxide including zeolite, metal sulfide, metal sulfate, metal sulfonate, metal nitrate, metal phosphate, metal phosphonate, metal molybdate, metal tungstate and/or metal borate and the metal is Groups I, IIa, IIIa, VIIa, VIIIa, Ib and IIb of the periodic table of the elements, aluminum, chromium, tin, titanium or zirconium.The heterogeneous catalyst has an Ho of less than or equal to4 and comprises heterogeneous heteropolyacid of Formula XaMbOcq-.The heterogeneous catalyst is supported on a catalyst support, selected from carbon, alumina, silica, silica-alumina, silica- titania, silica-zirconia, titania, titania-alumina, zirconia, barium sulfate, calcium carbonate, strontium carbonate and/or their compounds and is a heteropolyacid.X=phosphorus, silicon, boron, aluminum, germanium, titanium, zirconium, cerium, cobalt or chromium;M=at least one transition metal selected from tungsten, molybdenum, niobium, vanadium, or tantalum;q,a,b,c=whole numbers or their fractions.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The temperature and the pressure of the reaction are 1 - 300 (preferably 80-150)degreesC and 0.1-15 (preferably 0.1-5) MPag respectively. The content of the acid catalyst is 0.1-50 wt.% of the solution comprising the reactants and the heterogeneous acid catalyst is an ion exchange resin. EXAMPLE - A pressure vessel was charged with a solution (700 mg) consisting of ethanol (70%), alpha-angelica lactone (30%) and a Amberlyst 15 (RTM; acid catalyst) (50 mg). The reactor was pressurized with nitrogen (5.52 MPag) and heated at 100degreesC for 1 hour. The vessel was then cooled, vented and the products of ethyl levulinate were analyzed. The % of the lactone conversion was 99.29% and the selectivity of ethyl levulinate was 95.63%.