Polymeric poison

Most commercial palladium scavengers are designed for use after a reaction - thus at low temperatures. Is the solid poison being considered stable at the temperatures of the reaction Many Heck couplings are used at well over 100°C and some polymeric poisons may bre down under these conditions. This could lead to ineffective poisoning of solution species as well as unwanted interaction of small molecule degradation products with supported palladium species. 

Cyanogen chloride, CICN. Colourless liquid, m.p. — C,b.p. 13 C(aqueousCN plusCl2). Linear molecule, polymerizes to cyanuric chloride (CICN),. Extremely poisonous. 

Table 3 provides typical specifications for isoprene that are suitable for Al—Ti polymerization (89). Traditional purification techniques including superfractionation and extractive distillation are used to provide an isoprene that is practically free of catalyst poisons. Acetylenes and 1,3-cyclopentadiene are the most difficult to remove, and distillation can be supplemented with chemical removal or partial hydrogenation. Generally speaking distillation is the preferred approach. Purity is not the main consideration because high quaUty polymer can be produced from monomer with relatively high levels of olefins and / -pentane. On the other hand, there must be less than 1 ppm of 1,3-cyclopentadiene. 

Phosphorus(III) Oxide. Phosphoms(III) oxide [12440-00-5] the anhydride of phosphonic acid, is formed along with by-products such as phosphoms pentoxide and red phosphoms when phosphoms is burned with less than stoichiometric amounts of oxygen (62). Phosphoms(III) oxide is a poisonous, white, wax-like, crystalline material, which has a melting point of 23.8°C and a boiling point of 175.3°C. When added to hot water, phosphoms(III) oxide reacts violentiy and forms phosphine, phosphoric acid, and red phosphoms. Even in cold water, disproportionation maybe observed if the oxide is not well agitated, resulting in the formation of phosphoric acid and yellow or orange poorly defined polymeric lower oxides of phosphoms (LOOP). 

Other Uses. Other appHcations for sodium nitrite include the syntheses of saccharin [81-07-2] (see Sweeteners), synthetic caffeine [58-08-2] (22), fluoroaromatics (23), and other pharmaceuticals (qv), pesticides (qv), and organic substances as an inhibitor of polymerization (24) in the production of foam blowing agents (25) in removing H2S from natural gas (26) in textile dyeing (see Textiles) as an analytical reagent and as an antidote for cyanide poisoning (see Cyanides). 

In all of the ethylene polymerization processes, the catalyst is sensitive to feed impurities and is poisoned by most polar compounds. Many of the properties of the polymer are determined by polymerization conditions, but catalyst composition and condition are critical determinants as well. 

Polymerization processes are characterized by extremes. Industrial products are mixtures with molecular weights of lO" to 10. In a particular polymerization of styrene the viscosity increased by a fac tor of lO " as conversion went from 0 to 60 percent. The adiabatic reaction temperature for complete polymerization of ethylene is 1,800 K (3,240 R). Heat transfer coefficients in stirred tanks with high viscosities can be as low as 25 W/(m °C) (16.2 Btu/[h fH °F]). Reaction times for butadiene-styrene rubbers are 8 to 12 h polyethylene molecules continue to grow lor 30 min whereas ethyl acrylate in 20% emulsion reacts in less than 1 min, so monomer must be added gradually to keep the temperature within hmits. Initiators of the chain reactions have concentration of 10" g mol/L so they are highly sensitive to poisons and impurities. 

Install automatic or manual activation of bottom discharge valve to drop batch into a dump tank with diluent, poison, or inhibitor, or to an emergency containment area (May not be effective for systems such as polymerization reactions where there is a significant increase in viscosity.)... 

In the feed preparation section, those materials are removed from the reactor feed which would either poison the catalyst or which would give rise to compounds detrimental to product quality. Hydrogen sulfide is removed in the DBA tower, and mercaptans are taken out in the caustic wash. The water wash removes traces of caustic and DBA, both of which are serious catalyst poisons. Also, the water wash is used to control the water content of the reactor feed (which has to be kept at a predetermined level to keep the polymerization catalyst properly hydrated) and remove NH3, which would poison the catalyst. Diolefins and oxygen should also be kept out of poly feed for good operation. 

Chemical Reactivity - Reactivity with Water Reacts vigorously with water, generating phosphine, which is a poisonous and spontaneously flammable gas Reactivity with Common Materials Can react with surface moisture to generate phosphine, which is toxic and spontaneously flammable Stability During Transport Stable if kept dry Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Washing light hydrocarbons with water is a common refinery practice. It finds application on the feed to catalytic polymerization plants. It is used to remove any entrained caustic from the mercaptan removal facilities as well as any other impurities such as amines which tend to poison the polymerization catalyst. Another use for water wash is in alkylation plants to remove salts from streams, where heating would tend to deposit them out and plug up heat exchanger surfaces. Water washing can be carried out in a mixer- settler, or in a tower if more intimate contacting is necessary. 

In line with the conclusions derived in the model study10), the effect of solvent on initiator reactivity can also be explained on the basis of halogen polarizability in MeX. A detailed discussion of these trends is given in Section VIII. Mel is a poison in isobutylene polymerization. The poisoning activity of Mel will be discussed in Section VII. 

Similarly to Et2 A1C1 and Et2 AlBr systems, polymerization did not occur with Et2 All using Mel. Surprisingly, however, MeBr was also a poison and polymer did not form in MeBr. These observations are further discussed in Section VII. 

Mel poisoning in isobutylene polymerization with r-BuX/Me3Al systems was studied using mixed solvent systems containing various proportions of MeG and Mel. Results, together with experimental details and materials used are reported in Fig. 2. 

This study shows that Mel, and, for some systems, MeBr are potent poisons in isobutylene polymerization. The extent of poisoning increases in the presence of less reactive initiator and by decreasing temperatures. The mechanism of poisoning is discussed in Section VIII. 

The absence of polymerization using Mel and using MeBr for Et2 All system has been further investigated using mixtures of MeCl and Mel or MeBr. This had led to the proposition that poisoning by Mel or MeBr is due to the formation of propagation-inactive halonium ions. 

CO poison can probably allow observation of the v(CH2) modes of the first products of the polymerization. 

As an example, consider the use of PVPy as a solid poison in the study of poly(noibomene)-supported Pd-NHC complexes in Suzuki reactions of aryl chlorides and phenylboroiuc acid in DMF (23). This polymeric piecatalyst is soluble under some of the reaction conditions employed and thus it presents a different situation from the work using porous, insoluble oxide catalysts (12-13). Like past studies, addition of PVPy resulted in a reduction in reaction yield. However, the reaction solution was observed to become noticeably more viscous, and the cause of the reduced yield - catalyst poisoning vs. transport limitations on reaction kinetics - was not immediately obvious. The authors thus added a non-functionalized poly(styrene), which should only affect the reaction via non-specific physical means (e.g., increase in solution viscosity, etc.), and also observed a decrease in reaction yield. They thus demonstrated a drawback in the use of the potentially swellable PVPy with soluble (23) or swellable (20) catalysts in certain solvents. 

Not all solid poisons will likely be nseful in all media. Many polymeric resin-based poisons swell differently in various solvents. In one solvent, all the sites may be accessible, whereas in others, as little as a 1% of the sites, those on the external surface, for example, may be available. 

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