Alkene carboxylic acids, pyrolysis

Rearrangements and other side-reactions are rare. The ester pyrolysis is therefore of some synthetic value, and is used instead of the dehydration of the corresponding alcohol. The experimental procedure is simple, and yields are generally high. Numerous alkenes have been prepared by this route for the first time. For the preparation of higher alkenes (> Cio), the pyrolysis of the corresponding alcohol in the presence of acetic anhydride may be the preferable method." The pyrolysis of lactones 9 leads to unsaturated carboxylic acids 10 ... 

Ester Pyrolysis is a syn-elimination yielding an alkene, similar to the Cope Elimination, for which -hydrogens are needed. The carboxylic acid corresponding to the ester is a byproduct.The cyclic transition state can only be achieved if the steric environment is not too demanding. 

Pyrolysis of Carboxylic Acid Esters. The second stage of our proposed ethylene/propylene synthesis (eq. 21) has been demonstrated also for typical intermediate ethyl/propyl esters. Pyrolysis of acyclic, aliphatic carboxylic acid esters to alkenes and the parent acid is well documented (72-74) and in our work C1-C3 alkyl propionates, prepared by the synthesis techniques of Table VI (expt. 1 and 11) and isolated by fractional distillation, were pyrolyzed to ethylene, propylene and propionic acid by the homogeneous gas phase method (see Table VIII). In the initial experimental series, 98+% ethyl propionate is passed over pyrex helices at 460 C (expt. 16). Ethyl propionate conversion averages ca. 30% per pass selectivity to propionic acid is 95-97% ethylene comprises 92% of the light gas fractions. 

Ester pyrolysis to form an alkene and a carboxylic acid is another common thermal elimination (Eq. 10.94). At temperatures between 400 and 450 °C, these reactions can be very efficient. The reactions are first order, and show only syn elimination products, indicating that... 

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