A Conductometric Study of the Reaction Velocities of 2, 4-Dinitrochloro, Bromo, and Iodobenzene with Piperidine in Dimethylsulfoxide at Various Concentrations and Temperatures

Abstract

The problem. C. O. Frank and T. R. Berkland have followed the kinetics of the reaction of 2,4-dinitrohalobenzene with piperidine in ethanol using a conductometric method. L. E. Youngberg concluded that this method permits greater precision than either the titrimetric or spectrophotometric techniques which involve quenching of reaction aliquots. Significant reaction rate increases have been observed for certain reaction types when protic solvents are replaced with dipolar aprotic solvents, which are not readily explainable in terms of such physical properties as dielectric constant. Since data in dipolar aprotic solvents is random, the above system was studied in dimethyl sulfoxide to determine the applicability of the conductometric method, rate constants, activation energies and entropies, and halogen reactivity series. Procedure: After checking the chloro analog in ethanol, piperidine and 2,4-dinitrochloro, bromo, and iodobenzene were reacted in dimethyl sulfoxide at three temperatures and two temperatures. Findings. The revised average rate for the chloro analog in ethanol was 1.691 1 mol-1 min-1 ± .094. The average rate constants for the chloro, bromo, and iodo analogs in dimethylsulfoxide at 25.0°C were 142.2 ± 11.9, 111.2 ± 8.7, and 20.04 1 mol-1 min-1 ± 0.48, and at 35.0°C the average rate constants were 195.2 ± 20.0, 165.7 ± 19.2, and 30.62 1 mol-1 min-1. There are no comparable data by other methods. Conclusions. The 2,4-dinitrohalobenzene series reacts 50 to 90 times faster in dimethylsulfoxide than in ethanol. This is in agreement with the increases reported for the 4-nitrohalobenzene series. However, the iodo analog of the latter series increased 350 times. The halogen reactivity series is Cl>Br>>I and Cl>>Br>I in terms of rate constants and activation energies respectively. Recommendations. The design of an automated system of data collection could be investigated. The application of this technique to quantitative determinations and analysis of amine mixture also offers an area for study.