Phosphonium salts hazards

It should be mentioned that phosphonium salts with anions such as perchlorate, picrate, permanganate and other oxidizing anions may be very sensitive to decomposition (dangerous hazards)137. 

A selection of commercially available phosphonium salts suitable for the activation of carboxylic acids in the presence of amines is sketched in Figure 13.5. Phosphonium salts such as those shown in Figure 13.5 do not react with amines, and are well suited for preparing amides on insoluble supports, with either the amine or the acid linked to the support (Table 13.5). Solutions of these reagents in dry DMF are quite stable and can be used even after standing at room temperature for several days [84]. BOP, one of the first phosphonium salts used for peptide synthesis [85], leads to the formation of mutagenic HMPA, and should therefore be replaced by the less hazardous PyBOP [86],... 

Hazardous Decomp. Prods. Heated to decomp., emits highly toxic fumes of phosphine and POx Uses Organic synthesis phosphonium salts ... 

In general, the decomposition of phosphonium-based ILs is accompanied by an endothermic temperature the only exceptions to date are the hexafluorophosphate salts. At a heating rate of 5 °C min a 510 J g exotherm beginning at 310 °C and with a maximum at 337 °C was noted [62]. In addition to the possible evolution of HF, the exothermic decomposition of hexafluorophosphate salts presents an added hazard when operating at or near the upper temperature limit. This is especially important to note when large volumes of such solvents are in service. 

Ionic liquids are salts that form a stable fluid at or near room temperature and are expected to replace hazardous and volatile organic solvents because they have low vapor pressure, non flammability, high polarity and relative inertness. Most ionic liquids consist of bulky organic cations, for example Af,Af-dialkylimidazolium, A-alkylpyridinium, quaternary ammonium, quaternary phosphonium, and common weakly coordinating anions such as AlCU", Bp4 , PP6 , CFsSOs", TfO , (CP3S03)2N and some of them, such as Af,Af-dialkylimidazolium salts, show excellent conductivity [222]. Typical chemical structures of cations and anions are reported in Fig. 1.19. 

The wastes from the synthesis of dibromosilane and phosphonium dibromide salt were hazardous wastes. Residue from KCs was treated with isopropanol before subjecting the residue to flammable hazardous waste. 

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