Replacing phthaloyl with

In view of the utility of the aromatic polyesters and the demonstrated effectiveness of the aromatic polyphosphonates as flame retardants, the combination of these two polymers was chosen for this study. In addition, this system provided a composition in which both copolymers and polymer blends could be prepared with identical chemical compositions. The polyesters were prepared from resorcinol with an 80/20 m/m ratio of iso-phthaloyl and terephaloyl chlorides while the polyphosphonates were resorcinol phenylphosphonate polymers. Copolymerized phosphorus was incorporated by replacement of a portion of the acid chloride mixture with phenylphosphonic dichloride. 

Phthaloyl dichloride from phthalic anhydride and PC15 1039 Phthalic anhydride (1 mole sublimed) and pure PC15 (1.06 moles) are heated in a 500-ml round-bottomed flask fitted with a reflux condenser and a CaCl2 tube and placed in an oil-bath at 150°. After 12 h the reflux condenser is replaced by a downward water-condenser and the bath-temperature is raised gradually to 250°. Most of the POCl3 formed distils off. The residual crude dichloride, when distilled, has b.p. 131-133°/9-l 0 mm, the yield being 92%. The product contains a little phthalic anhydride. 

Lastly, phthaloyl-protected (R)-alanine 112 is formed in high yield by reaction of 2 with phthalimide [40]. Recently, polystyrene-supported methyl azodicarboxylate has been used as a replacement for the soluble dialkyl azodicarboxylates in the Mitsunobu reaction [41]. Yields generally are not as high as in the classical reaction (e.g., 2 112, 45% yield), but, purification can be expedited simply by filtration of the nonexplosive resin. 

The classical method for removal of the phthaloyl function is treatment with aqueous or ethanolic hydrazine hydrate. The hydrazide by-product separates out by precipitation. Hydrazine is a good nucleophile (so-called a-effect) which will attack the anhydride-like phthaloyl function under conditions that will not affect peptide linkages. However, there is a danger of hydrazinolysis of any ester linkages, if present. Other protecting groups will not be affected by the hydrazinolysis. The use of hydrazine in hydroxylic solvents may be replaced by phenylhydrazine in organic solvents, in which... 

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