SPECTRAL EVIDENCE FOR THE EXISTENCE OF THE ALIPHATIC CARBONIUM ION

Author Institution: The University of TexasThe addition of an olefin containing three or more carbon atoms to 96% sulfuric acid produces an absorption band at 300 mu with an oscillator strength of .08 [$\epsilon_{\max}\sim 3000$]. The addition of the compounds ROH, ROR, $ROSO_{3}H, RCl$, and $ROCOCF_{3}$ to surfuric acid produces a similar band. It is postulated that the similarity in the spectrum is due to the production of the identical species $R^{+}[HSO_{4}]^{-}$ in all reactions. {C}_{n}{H}_{2{n}}+{H}_{2}{SO}_{4}\rightarrow {C}_{n}{H}^{+}_{2{n}+1}[{HSO}_{4}]^{-}{C}_{n}{H}_{2{n}+1}{X}+{H}_{2}{SO}_{4}\rightarrow {C}_{n}{H}^{+}_{2{n}+1}[{HSO}_{4}]^{-}+{HX} The peak appears only in acid of strength greater than 70%. The peak also appears in methane sulfonic acid [$H_{0}\sim 9$] but not in trifluoracetic acid [$H_{0}\sim 7$]. It is of interest to note that alkylation which is postulated to proceed via a carbonium ion mechanism occurs under the same conditions that produce a 300-mu peak. Conduction and freezing point determinations in sulfuric acid indicate that the species $R^{+}[HSO_{4}]^{-}$ is dissociated. A discussion of the spectrum and stability of the species $R^{+}[HSO_{4}]^{-}$ is given based on a charge-transfer-complex and on a protonated-double bond