Baldwin-Walker Scheme

In order to model the oscillatory waveform and to predict the p-T locus for the (Hopf) bifurcation from oscillatory ignition to steady flame accurately, it is in fact necessary to include more reaction steps. Johnson et al. [45] examined the 35 reaction Baldwin-Walker scheme and obtained a number of reduced mechanisms from this in order to identify a minimal model capable of semi-quantitative p-T limit prediction and also of producing the complex, mixed-mode waveforms observed experimentally. The minimal scheme depends on the rate coefficient data used, with an updated set beyond that used by Chinnick et al. allowing reduction to a 10-step scheme. It is of particular interest, however, that not even the 35 reaction mechanism can predict complex oscillations unless the non-isothermal character of the reaction is included explicitly. (In computer integrations it is easy to examine the isothermal system by setting the reaction enthalpies equal to zero this allows us, in effect, to examine the behaviour supported by the chemical feedback processes in this system in isolation... 

Baldwin and Walker (1974) observed that N-benzyl and N-allyl benzothiazolium salts form bis benzothiazolidine (106) on treatment with triethylamine in DMF at 0 °C. These dimers were found to imdergo 1,3 or 3,3 sigmatropic rearrangements (scheme-31) depending upon the reaction conditions and the nature of the N-alkyl group to provide the more stable 2,3-dialkyl-2-(benzothiazol-2-yl)benzothiazoline (107) (Scheme-30) (Baldwin Walker 1974). 

In 1973, Baldwin and Walker [19] described the Claisen rearrangement of the allylic and acetylenic esters of a-bromo carboxylic acids with zinc at higher temperatures through the Reformatsky procedure. Though the method was better, it was severely restricted as it becomes mandatory to prepare the corresponding bromo-ester from the system of interest before the rearrangement could be effected (Scheme 5.1.7). 

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