Chlorocyclophosphazenes

One of the most significant developments in phosphazene chemistry during the past year has been the reported application of alkoxycyclophos-phazenes, [NP(OR)2l3,4, as flame retardants in rayon. This development has, in turn, provided a stimulus for improvements to be made in the large-scale production of chlorocyclophosphazenes. Interest in the properties of the monophosphazenes has again increased considerably. 

The traditional and most extensively used method of synthesis of chlorocyclophosphazenes [NPCl2] involves the reaction of finely ground ammonium chloride with phosphorus pentachloride in a high boiling solvent such as sym-tetrachloroethane. This reaction affords a mixture of cyclic and linear products from which the individual products have to be separated, usually by fractional distillation in high vacuum (1, 5,17,18,35-39), (Eq. 1) ... 

Reactions of thiolates with chlorocyclophosphazenes are found to proceed in an exclusive geminal pathway (14). 

The reactions of chlorocyclophosphazenes with difunctional reagents such as diamines, diols, or amino alcohols can in principle lead to the formation of several products. These are shown in Fig. 19. The reactions of these reagents with the chlorocyclophosphazenes are discussed below. 

The reactions of the six-membered chlorocyclophosphazene were studied with a number of aliphatic diamines (169 175), aromatic diamines (176), aliphatic diols (177-179), aromatic diols (180,181) and compounds containing amino and hydroxyl functional groups (169,170,182). This subject has been reviewed (11,16,20). There are at least five different reaction products that are possible (Fig. 19). Replacement of two chlorine atoms from the same phosphorus atom produces a spirocyclic product. Replacement of two chlorine atoms from two different phosphorus atoms in the same molecule produces an ansa product. Reaction of only one end of the difunctional reagent, resulting in the substitution of only one chlorine atom, leads to an open-chain compound. Intermolecular bridged compounds are formed when the difunc-... 

The chemistry of chlorocyclophosphazenes continues to be of great interest. Many of the mechanistic features involving the aminolysis reactions are now understood. However, rigorous kinetic studies on reactions of chlorocyclophosphazenes with other types of nucleophiles are quite rare. The most promising utility of the chlorocyclophosphazenes is their reactive periphery combined with a robust framework. It... 

Advances in the Chemistry of Chlorocyclophosphazenes Vadapalli Chandrasekhar and Venkatasubbaiah Krishnan... 

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