Kinetic Study of the Substitution Reactions of Benzyl Halides and Halide Ions in Acetone

Abstract

Key Word Index-Eenzyl halides; halide ions; Finkelstein reactions.The kinetics of the FinkeIstein reactions of benzyl halides and halide ions in dry acetone was studied by using the GC and HPLC methods. The method of conductivity is used to measure the degree of dissociation of alkali halide in acetone. The dissociation of the salt and the common-ion effect were used to correct the halide ion concentration, Let K,,and K,,+ represent the corrected second-order rate cansfant and equilibrium constant for the PhCH,X-X'reaction, respectively, then a t 2 5 O kc,l--1.83X10-3 M-Is-1, &-,l-=4.48x104; R B ,~~-= O .~I ? M -~ s-l, 24.5"C) were identified by 'H NMR, IR, and GC/MS. Both NMR and IR data showed that the products contained a negligible amount of water. The mass spectrum of benzyI iodide gave m/e (%> (at 70eV): 91 (loo), 65 (lo), 92 (7), 89 (4), 218 (3.25), 127 (as), 77 (0.1), InstrumentsThe following instruments were used in t h i s work: (1) Shimadzu GC-4C with Hewlett Packard 3390 integrator, (2) Varian GC-3300 with Varian SP-4290 integrator, (3j Hewlett Parkard 1084B LC with 79850B LC terminal, (4) Hitachi 260-30 IR spectrometer, (5) Hitachi M-52 Mass spectrometer, (6) Bruker WP lOOFT NMR spectrometer, (7) Tokyo Toa Omnimeter model OM-l A, Japan, (8) Yokogawa YEW 2575 Digital Thermometer, Japan, (9) Colora Thermostat WK-5, (10) Mel-Temperature, Laboratory Devices. ProceduresMeasured volumes of reactant solutions of known concentrations were mixed under stirring to start a kinetic run (e,g., 5 m L ) 0.44 !I11 PhCH,Cl added to 25 nzL 0.088rl.l NaI). The mixing time was within 5 secoizds.

Kinetic Study of the Substitution Reactions of Triphenylphosphine with Chlorobenzyl Chlorides, Dimethylbenzyl Chloride, and Methylbenzyl Bromides in Various Two‐Phase Organic Solvent/Water Media

“…To avoid the interference of the SN 1 reaction, the S N2 reaction is frequently studied in aprotic solvents such as CH 2Ch, CHCb, C6H6, and Me£O. Similar to the substitution reactions of benzyl halides and halide ions in ace tone, 17 a preliminary study showed that the substitution reactions of triphenylphosphine (TP, Ph3P) with benzyl halides (BnX = CDC, DMBC, and MBB) in aprotic organic solvents followed the SN2 mechanism (reaction (R4».…”