Substituent Exchange Reactions of Linear Oligomeric Aryloxyphosphazenes with Sodium 2,2,2-Trifluoroethoxide

Abstract

Side-group-exchange reactions have been studied for short-chain linear oligomeric phosphazenes, (RO)(4)P[N═P(OR(2))](n)OR (n = 6, 10, 20, and 40) as models for the corresponding linear high polymers (n ~ 15000). Specifically, the exchange behavior of oligomers where OR = OCH(2)CF(3), OC(6)H(5), OC(6)H(4)CHO-p, OC(6)H(4)CN-p, and OC(6)H(4)NO(2)-p with sodium trifluoroethoxide was examined. The ease of aryloxy group replacement by trifluoroethoxy increased with the electron-withdrawing character in the order OR = OC(6)H(5) ≪ OC(6)H(4)CHO-p < OC(6)H(4)CN-p < OC(6)H(4)NO(2)-p, but the reaction was efficient only if the phosphazene contained no more than 20 repeating units. However, attempts to force slower reactions by the use of excess sodium trifluoroethoxide induced secondary reactions at the trifluoroethoxy units already introduced to produce CF(3)CH(2)OCH(2)CF(3) and generate -O(-)Na(+) units in their place. The longest chain model underwent side-group-exchange reactions preferentially at the end units. These results are significant for the synthesis of phosphazene high polymers with fluoroalkoxy and aryloxy side groups.

Linear 2-Ethylhexyl Imidophosphoric Esters as Effective Rare-Earth Element Extractants

“…The molar ratio of phosphazene salt to H2O was 1:2 in order to replace one chlorine atom in the cation and to neutralize the counterion (Scheme 4). It should be noted that along with the PPR, short linear oligophosphazenes are susceptible to an adverse reaction of an attacking agent with α-carbon atoms of organic substituents, mainly those located at terminal units, resulting in the elimination of the side ether R-O-R and the formation of -O − Na + fragments [43]. The subsequent replacement of the sodium atom by hydrogen during purification leads to the formation of -N=(RO) 2 P-OH groups, which proceeds further with PPR to yield the aminophosphonyl form -NH-(RO) 2 P=O.…”

Generation of structural diversity in polyphosphazenes

“…A third method involves the exchange of organic side groups present on a poly(organophosphazene) by exposure to the sodium salt of another alcohol. This is a more restricted process that those based on halogen replacement but one that utilizes an air‐stable organophosphazene starting point rather than a hydrolytically sensitive halogenophosphazene substrate The relationship between this approach and the normal halogen replacement method is illustrated in Fig.…”

“…One of the limitations of this process is that the aryloxy side groups in poly(diphenoxyphosphazene) resist the exchange reaction, probably for steric reasons, although aryloxy side groups with electron‐withdrawing substituents such as nitro or cyano can be replaced by trifluoroethoxy groups . These exchange processes take place at the small‐molecule level as well as for the high polymer Secondary chemistry carried out on organic side groups .…”

Inorganic and organometallic polymers

“…A similar study was conducted with short-chain linear oligomeric PPNs. 28 Amphiphilic PPNs with diisopropylamino (DPA) substituents were synthesised and its cell membrane permeability in a certain pH range was recently evaluated. PPNs with a high DPA content inhibited P-glycoprotein activity in cells and are currently being investigated for applications for the treatment of drug-resistant tumors.…”