1.3- Dioxolane-4-methanol, 2-phenyl

The Hammett p-value for cleavage of the exocyclic bond of 2-methoxy-2-substituted-phenyl-l,3-dioxolans (—1.58 + 0.06) is a little larger than that for cleavage of the endocyclic C— bond of 2-hydroxy-2-substituted-phenyl-l,3-dioxolans (—1.24 + 0.04) (Table 9) (Chiang et al., 1983). A direct comparison between the p-values for C—OMe bond cleavage of trimethyl orthobenzoates and dimethyl hemiorthobenzoates is not possible at present since they have not been measured in the same solvent. However, that based on H+ for the breakdown of the hemiorthobenzoates (— 1.58) is less than that based on the equilibrium constants for their conversion into methyl benzoates and methanol which is —1.9 (derived from the equilibrium constants for formation of the hemiorthobenzoates, McClelland and Patel, 1981b). This implies that the development of positive charge in the transition state is less than in the final product, the ester. 

A mixture of l-(4-hydroxyphenyl)-4-(l-methylethyl)piperazine, cis-[2-(2,4-dichloro-phenyl)-2-(lH-l,2,4-triazol-l-ylmethyl)-l,3-dioxolan-4-ylmethyljmethanesulfonate, potassium carbonate and N,N-dimethylformamide is stirred and heated overnight at 120°C. The reaction mixture is cooled and poured onto water. The product is extracted twice with dichloromethane. The combined extracts are washed twice with a potassium carbonate solution, dried, filtered and evaporated. The residue is taken up in methanol and a sodium methanolate solution 30% are added. The whole is stirred and refluxed for 1 h. The mixture is poured onto water and the layers are separated. The organic phase is dried, filtered and evaporated. The cis-l-(4-((2-(2,4-dichlorophenyl)-2-(lH-l,2,4-triazol-l-ylmethyl)-l,3-dioxolan-4-yl)methoxy)phenyl)-4-(l-methylethyl)piperazine was obtained, melting point 116.3°C. 

The solventless reaction in the presence of diallq ltin(iv) complexes led to a conversion of 42% with 78% selectivity to diphenyl carbonate. Starting from phenyl acetate, total conversion was obtained at 220 "C with higher selectivity to diphenyl carbonate (95%). Transesterification with higher alcohols was also examined, giving better conversion due to higher nucleophilicity compared to phenol. However, a steric effect was evidenced as fert-butanol was unreactive. Transesterification of ethylene carbonate (l,3-dioxolan-2-one) with methanol to dimethyl carbonate was also reported early. " Today, both transesterifications with methanol and phenol are integrated into the value chain of bisphenol-A polycarbonate production and commercialised by Asahi Kasei Corporation (Scheme 21.12). ... 

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