THE GAS-PHASE PYROLYSIS OF SEVERAL ALIPHATIC 1,3-DIOLS - THE KINETIC AND MECHANISM OF 2,4-DIMETHYL-2,4-PENTANEDIOL

Satisfactory kinetic determinations of several aliphatic 1,3-diols wer e difficult to obtain. Moreover the product distributions from each of these substrates suggest complex parallel mechanisms. However, the el imination kinetic of 2,4-dimethyl-2,4-pentanediol has been measured ov er the temperature range of 419.7-459.9 degrees C and pressure range o f 47-115 torr. The reaction carried out by employing a static system, in seasoned vessel, and in the presence of the free-radical inhibitor propene, proved to be homogeneous, unimolecular, and follows a first-o rder rate law. The products are acetone, isobutene, and H2O. The rate coefficient is expressed by the following Arrhenius equation: log k(1) (s(-1)) = (12.53 +/- 0.58) - (217.3 +/- 8.0) kr mol(-1) (2.303 RT)(-1) . The pyrolytic elimination of this substrate is believed to proceed t hrough a concerted six-membered cyclic transition-state type of mechan ism. (C) 1997 John Wiley & Sons, Inc.