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Dediazoniation of Arenediazonium Ions. Part XX. Secondary deuterium isotope effects in reactions of benzenediazonium tetrafluoroborate
Author(s) -
Szele Ivanka,
Zollinger Heinrich
Publication year - 1981
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19810640832
Subject(s) - chemistry , deuterium , kinetic isotope effect , tetrafluoroborate , ion , isotope , medicinal chemistry , reaction rate constant , photochemistry , kinetics , organic chemistry , catalysis , atomic physics , nuclear physics , ionic liquid , physics , quantum mechanics
Secondary deuterium isotope effects were measured for the dediazoniation of [2,4,6‐ 2 H 3 ]‐benzenediazonium tetrafluoroborate ([ 2 H 3 ]‐ 1 ), and were found to be ( k H / k D3 ) s = 1.46 in 2,2,2‐trifluoroethanol (TFE) and 1.51 in 1, 1, 1, 3, 3, 3‐hexafluoro‐2‐propanol (HFIP), respectively. These values are in agreement with the previously proposed rate determining formation of the phenyl cation ( Eqn. 1 ), and are similar to the results obtained by Swain et al. in other solvents. The N α ‐N β rearrangement Eqn. 2 ) of β‐ 15 N labelled 1 was studied in TFE. The percent of rearrangement after 70% dediazoniation was found to be 8.18, which corresponds to a rate constant for the rearrangement k r =4.02 · 10 −6 S −1 . Thus the secondary deuterium isotope effect in the rearrangement in TFE ( k H / k D3 )r was calculated to be 1.42. The fact that the isotope effect in the rearrangement is, within experimental error, the same as that observed during dediazoniation, definitely excludes the formation of benzenespirodiazirine cation 3 , which has repeatedly been discussed as an intermediate in the rearrangement. The size of the deuterium isotope effect in the rearrangement is in accordance with the rearrangement proceeding via a phenyl cation/N 2 molecule pair ( 2 ).