Reaction (1) suffers somehow of the competition with the production of diethyl ether (DEE):equation(2)2C2H5OH→C2H5OC2H5+H2OΔH298=-25.1kJ/molwhich is exothermic, also favored at low or moderate temperature. Over most catalysts, reaction (2) occurs very selectively at low temperature and conversion while reaction (1) occurs at higher temperature and very high conversion. Different opinions are reported concerning the path involved in these reactions. The reaction (1) performed in the liquid phase with concentrated sulfuric S Tag as a catalyst at ca. 450 K is supposed to occur with a “monomolecular” mechanism, either with an E2 (bimolecular elimination) concerted elimination mechanism, while reaction (2) occurring at lower temperature (410 K) is reported to occur with a SN2 (bimolecular nucleophilic substitution) bimolecular mechanism from a protonated form of ethanol and an non-protonated one  and . According to DFA (density functional analysis) computational studies, the E2 mechanism should be the most favored also on alumina for reaction (1) . Roca et al. working on silica alumina concluded that DEE and ethylene are produced by parallel reactions . Also DeWilde et al. concluded that the bimolecular mechanism producing DEE and the unimolecular mechanism producing ethylene are parallel on alumina, both being inhibited by water . According to these authors, two ethanol undissociatively adsorbed “dimer” species react together forming DEE, while ethylene is formed by decomposition of ethoxy- groups. Other authors believe that DEE can be formed by reaction of an adsorbed ethanol molecule with an ethoxide group  or of two ethoxide groups . Several authors , , , , ,  and  also suggest that diethyl ether might be an intermediate in the dehydration of ethanol to ethylene.