Determination of Hammett Equation Rho Constant for the Hydrolysis of p-Nitrophenyl Benzoate Esters
Sheue L. Keenan, Karl P. Peterson, Kelly Peterson, and Kyle Jacobson
Department of Chemistry, University of Wisconsin–River Falls, River Falls, WI 54022
Seven p-nitrophenyl benzoate esters (p-nitrophenyl benzoate, p-nitrophenyl m-anisate, p-nitrophenyl p-anisate, p-nitrophenyl m-chlorobenzoate, p-nitrophenyl p-chlorobenzoate, p-nitrophenyl m-toluate, p-nitrophenyl p-toluate) were synthesized and characterized by students in a second-semester organic laboratory course. In a subsequent laboratory period, the rate constants for the base hydrolysis of these esters were measured by monitoring the formation of the p-nitrophenoxide ion by UV-vis spectrophotometry. The Hammett equation rho (ρ) constant for this hydrolysis reaction was then determined. The two-experiment sequence was developed to demonstrate structure–reactivity relationships and pseudo-first-order reaction kinetics. The students gained experience in organic synthesis and characterization, performing kinetics studies by spectrophotometry, and carrying out data analysis using spreadsheet software.
Supplement
List of the chemicals; Instructor notes, including IR and NMR spectra; Student handouts
Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
Our Secondary School editors work hard to distill all the JCE materials to produce a fraction of particular interest to high school teachers. We call it CLIC.
In recent years we have worked hard to better match our advertisers with our readers. When shopping for chemistry education materials, visit our advertisers' WWW sites first.
Take JCE along on your outreach missions. Copies of the Journal, guest access to JCE Online, our publications catalog, and more are available for your participants.
Caution! 
