Solid state reactions decarboxylation

While much attention has been paid to the chemistry of cyclodextrin complexes in solution, there have been relatively few studies of their solid-state reactions. One such reaction is the decarboxylation of phenylethylmalonic acid, 155. In solution this is catalyzed by fj-cyclodextrin, and yields racemic 2-phenylbutyric acid, 156 (230). The malonic acid forms a crystalline 1 1 complex with p-cyclodextrin in which decarboxylation occurs at a much lower temperature than in the crystalline diacid. Interestingly, the product formed in the clathrate reaction is nonracemic, the optical yield being 7%. 

Decarboxylation of p-lactones (see 17-27) may be regarded as a degenerate example of this reaction. Unsymmetrical diacyl peroxides RCO—OO—COR lose two molecules of CO2 when photolyzed in the solid state to give the product RR. Electrolysis was also used, but yields were lower. This is an alternative to the Kolbe reaction (11-37). See also 17-29 and 17-40. 

Kaeriyama et al. [15] reported the Ni(0)-catalyzed coupling of 1,4-dibromo-2-methoxycarbonylbenzene to poly(2-methoxycarbonyl-l,4-phenylene) (4) as a processable PPP precursor. The aromatic polyester PPP precursor, 4, is then saponified to carboxylated PPP (5) and thermally decarboxylated to 1 with CuO catalysts. However, the reaction conditions of the final step are quite drastic and cannot be carried out satisfactorily in the solid state (film). 

Recently, it has been reported that the reaction of hydrazine hydrate with supercritical carbon dioxide forms a stable solid that is a 1 1 adduct of hydrazine and CO2 [26]. Its single-crystal structure (Figure 1.10) shows it to be as a zwitterion (NH3 NHCOO ). Its reactivity is similar to that of liquid hydrazine as it produces anhydrous hydrazine locally via the decarboxylation process. Owing to its zwitterionic form, carbazic acid exhibits better selectivity. It also shows excellent reactivity toward carbonyl compounds in the solid state and has been found to be a valuable alternative to liquid hydrazine [27]. 

The thermal decomposition of a number of organic acids has been studied by DTA by Wendlandt and Hoiberg (60,6l). Since ihe acids were decomposed in an argon atmosphere, only endothermic peaks were observed in the DTA curves. These peaks were caused by such reactions as dehydration, decarboxylation. sublimation, decomposition, and phase transitions from the solid to the liquid state. The maximum peak temperatures for the phase transitions were 10 to 30 higher than the reported melting-point temperatures. The DTA curves for some of the acids are given in Figure 7.33. 

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