H/D exchange between light alkanes and deuterated strong acids. Competition between regiospecific isotope exchange and skeletal rearrangement: an H-1/H-2 NMR study

The deuterium distribution observed in 3-ethylpentane when it is in contact with D2O-exchaned USY zeolite at temperatures as low as 70 degrees C shows that for some alkanes the skeletal rearrangement of the intermediate terti ary carbenium ion can be much faster than the de- and reprotonation reactio n which is at the origin of the observed, generally regiospecific, isotope exchange. This behavior is notably increased when the solid acid is replace d by D2SO4 in which the hydride transfer is less efficient. (C) 1999 Elsevi er Science B.V. All rights reserved.