Diphenyl ester synthesis process

Diphenols are scarcely reactive towards aromatic diacids (2) and only low molecnlar weight polymers can be achieved through their direct reaction. To increase the reactivity and promote the polycondensation, at least one of the monomers has to be properly activated. Thus, two processes have been conceived for polyarylate synthesis interfacial polycondensation (preferred over the solution process) between diacyl chlorides and alkali metal diphenate, and the high temperature metal-catalyzed melt polycondensation between either diphenol acetates and aromatic diacids, or diphenols and diacid diphenyl esters. 

The general process used to synthesise aromatic polybenzimidazoles (PBIs) is presented in Section 4.3.3. More detailed information can be found in previously published books [87,88]. During 1960-1970 a number of publications, comparable to those on polyimides, reported the synthesis and properties of all aromatic and aryl-aliphatic polybenzimidazoles. Most of these polymers were prepared by the two-step process illustrated in Fig. 14 with the reaction of 1,3-benzenedicar-boxylic acid diphenyl ester 27 and [l,l -biphenyl]-3,3, 4,4 -tetramine 11 yielding ultimately PBI 29. All the applications - laminates and filament winding resins, adhesives, fibres and foams - used polymer 29, which was produced in semicommercial quantities by the Whittaker Corporation (Narmco Division) under the generic trade mark Imidite . Currently, forty years later, this polymer is manufactured by Hoechst-Celanese and its only commercial success is in the area of heat resistant fibres and fabrics. It is, however, worth noting the adhesive properties of this polymer and the reasons explaining the major obstacles to the development of PBIs as heat-resistant adhesives. 

M.E. Jung and co-workers have developed a synthesis of selectively protected L-Dopa derivatives from L-tyrosine via a Reimer-Tiemann reaction followed by the modified Dakin oxidation. The formyl group introduced by the Reimer-Tlemann reaction had to be converted to the corresponding phenol. After trying many sets of conditions, the Syper process was chosen, which uses arylselenium compounds as activators for the oxidation. Treatment of the aromatic aldehyde with 2.5 equivalents of 30% hydrogen peroxide in the presence of 4% diphenyl diselenide in dichloromethane for 18h gave the aryl formate in excellent yield. This ester was cleaved by treatment with methanolic ammonia for 1h to afford the desired phenol in good yield. 

Sulfonic (-SO3H) and Sulfinic (-SO2H) Acid-Based Nonsalt Photoinitiators Photosensitive tosylate esters of nitrobenzyl [65] and benzoin [73], sulfonyl ketones [67,68], and diphenyl disulfones [68] can be employed in cationic photopolymerization, especially in photolithography and chemical amplification processes. The advantages of these photoinitiators are the ease of synthesis, the absorption wavelengths suitable for deep-UV curing and the high yield of acid formation [65]. 

In order to avoid the need for DCC, a number of activated derivatives of IV-hydroxysuccinimide itself have been developed which react directly with, for example, an oi-amino acid to provide the required activated oi-amino acid esters. These include the commercially available carbonate (1), a stable crystalline solid obtained from HOSu and Trichloromethyl Chloroformate or from 0-trimethylsilyloxysuccinimide and Phosgene and the related phosphate (2) derived from HOSu and Diphenyl Phosphorochlo-ridate under Schotten-Baumann conditions. Another alternative (also commercially available) is the oxalate (3), formed from HOSu and Oxalyl Chloride In general, these intermediates react rapidly with an iV -protected a-amino acid, usually in the presence of a mild base such as pyridine, to provide excellent yields of the required hydroxysuccinimide esters, generally with less racemization than is sometimes associated with the HOSu-DCC method. It is also possible to cany out the entire process of peptide synthesis in one pot using these reagents. 

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