The kinetics and mechanism of dichlorocarbene addition to C=C bond under liquid/liquid (l/l) and solid/liquid (s/l) phase-transfer catalysis conditions are discussed. In the s/l system reaction kinetics is strongly influenced by the formation of a crust of solid NaCl on the NaOH surface. In the l/l system the reaction is significantly slower and occurs in a liquid border film. The influence of physical factors in both s/l and l/l systems is shown. (C) 2002 Elsevier Science B.V. All rights reserved.