3-Methyl-4'-nitro-diphenyl ether, an important agrochemical. is normally synthesized by employing aprolic polar solvents, or Ullmann reaction at elevated temperatures leading to a number of by-products and the process is costly The current paper presents a cost effective and simpler process of synthesis of 3-methyl-4'-nitro-diphenyl ether from sodium salt of in-cresol and p-chloronitrobenzene (PCNB) by using o-xylene as a solvent under solid-liquid phase transfer catalysis (S-L PTC). at 120 C. which is 10014, selective. The liquid-liquid (L-L) PTC process does not work at the same conditions due to poor reactivity of the ion-pair. A novel mathematical model is developed to determine simultaneously the rate constant and anion exchange equilibrium constant from the same set of data This will he helpful in reactor design and scale up. The activation energy and Gibb's free energy for a combined ion exchange and partitioning of ion pairs is are also calculated. The reactivity of sodium salts of o- and p-cresol with PCNB is also tested, (c) 2005 Elsevier B.V. All rights reserved.