Alfin catalyst

Alfernol A112Fe3Si A19Fe2Si2 Alfin catalysts Alfonic... 

Sodium is a catalyst for many polymerizations the two most familiar are the polymerization of 1,2-butadiene (the Buna process) and the copolymerization of styrene—butadiene mixtures (the modified GRS process). The alfin catalysts, made from sodium, give extremely rapid or unusual polymerizations of some dienes and of styrene (qv) (133—137) (see Butadiene Elastomers, synthetic Styrene plastics). 

Alfin Catalysts. Alfin catalysts (44,45) give polyisoprenes of high /ram-1,4 microstmcture (46). For example, a typical Alfin catalyst gives polyisoprene of 52% /ram-1,4, 27% cis-1,4, 16% 3,4, and 5% 1,2 content (ir analysis) (46). One type of Alfin catalyst consists of aHylsodium, sodium isopropoxide, and sodium chloride (47,48). Because of the mixed microstmcture polyisoprene produced, Alfin catalysts are not used commercially. 

The "Alfin" catalyst (Morton 1964 Reich 1966) is made up to a suspension, in an inert solvent like pentane, of a mixture of an alkylenyl sodium compound (such as allyl sodium), an alkoxide of a secondary alcohol (such as sodium isopropoxide), and an alkali halide (such as sodium chloride). The catalyst is highly specific for the polymerisation of dienes into the 1, 4-forms. 

Smith (29) showed that the polymerization of styrene by sodium ketyls with excess sodium produced low yields of isotactic polystyrene. Smith also believed that sodium ketyls initiated the styrene polymerization in the same way as the anionic alfin catalyst. Das, Feld and Szwarc (30) proposed that the lithium naphthalene polymerization of styrene occured through an anionic propagating species arising from the dissociation of the alkyllithium into ion pairs. These could arise from the dimeric styryllithium as a dialkyllithium anion and a lithium cation... 

M. Kinoshita Polymerization of vinyl monomers with alfin catalysts. J. Chem. Soc. Japan, Ind. Chem. Sect. 61, 452—454 (1958). 

Using Alfin catalysts, butadiene polymers were already obtained in the 1940s. The Alfin catalytic system consists of three components (formed in statu nascendi from alkyl chloride, metallic sodium, alcohol and olefin) sodium salt of secondary alcohol (e.g. sodium isopropoxide), alkenylsodium (e.g. allyl-sodium) and finely dispersed sodium chloride (the name Alfin originates from a/cohol + olefin) [2,3], Since the molecular weight of polybutadiene obtained with Alfin catalysts is very high (it can reach a value of a few millions), 1,4-dihydronaphthalene is often added to the polymerisation system for the regulation of molecular weight [1],... 

With these catalysts, the cation complexes with the monomer so weakly that a solid surface and low polymerization temperatures are required to achieve sufficient orientation for stereospecificity. Braun, Herner and Kern (217) have shown that lower polymerization temperatures are required (in n-hexane diluent) to obtain isotactic polystyrene as the alkyl metal becomes more electropositive (RNa, —20° C. RK, —60° to —70° C. and RRb, —80° C.). They correlate isotacticity with the polymerization rate as a function of catalyst, temperature or solvent. However, with Alfin catalysts, stereospecific polymerization of styrene is unrelated to rate (226). A helical polymerization mechanism as proposed by Ham (229) and Szwarc (230) is also inadequate for explaining the temperature effects since the probability for adventitious formation of several successive isotactic placements should have been the same at constant temperature in the same solvent for all catalysts. 

Although Morton (228) has proposed a free radical-type mechanism for Alfin catalysts, Natta and Danusso (231) believe the mechanism is anionic. 

Morton and Taylor (226) found that Alfin catalysts which produce 1,4-polybutadiene are poor catalysts for making isotactic polystyrene and vice versa. They concluded that the monomer is adsorbed or com-plexed and oriented at the surface of the insoluble catalyst. 

It is known from the work of Morton, on polymerization with Alfin catalysts, that the inorganic constituent of the catalysts (NaCl) plays an important part in the special effectiveness of these initiators. Hence, the question had to be examined if, likewise, the presence of inorganic substances is necessary for stereospecific polymerization with organosodium and -potassium compounds. As a result, it has been established that all the organometallic compounds derived as indicated in the above preparative methods facilitate the stereospecific polymerization of styrene in n-heptane. In addition, the nature and chain length of the residue R have no significant influence on the initiators. In fact, R can be linear or branched or aryl-aliphatic. Also, phenyl or triphenylmethylsodium yields isotactic polystyrene. 

Other types of complex catalysts that have received attention for stereospecific polymerization are the reduced metal oxides and the alfin catalysts (prepared from compounds of sodium). All three types are mainly used in heterogeneous polymerization, although some homogeneous processes are also commercially important. 

It has an NiAs-type structure (Fig. 15-5), and the isolated methyl groups are presumably in the lattice as the pyramidal CHJ ion.35 Sofiium amd potasstuirralkyl5 can be used for metallation reactions- for example, in eq. 6-2. They can also be prepared from Na or K dispersed on an inert support material, and such solids act as carbanionic catalysts for the cyclization, isomerization or polymerization of alkenes. The so-called alfin catalysts for copolymerization of butadiene with styrene or isoprene to give rubbers consist of sodium alkyl (usually allyl) and alkoxide (usually isopropoxide) and NaCl, which are made simultaneously in hydrocarbons.33... 

Naphthylmethylsodium does not itself induce Alfin polymerization but can act as a support or extender for an Alfin reagent. When mixed in equal quantities (1 mole of allylsodium to 1 mole of naphthylmethylso-dium), the capacity of the reagent is doubled or tripled (9). Polymerization does not spread to the naphthylmethylsodium but remains the same as for the Alfin catalyst alone. That is to say, the viscosity and the ratio of trans-... 

H. E. Diem B. F. Goodrich Co., BrecksviUe, Ohio) I should like to point out that the highly specific character of the alfin reagent for the polymerization of butadiene, which Dr. Morton s many papers have demonstrated (Lecture 75), suggest that the monomer is adsorbed in a specific oriented fashion on the catalyst surface. If this is true, it seems unlikely that the structure of the poljuner (% 1,4- vs. % 1,2- addition) can serve to distinguish the mechanism of the reaction. That is, the fact that the structure of the polymer butadiene from the alfin catalyst is very similar to that obtained from free radical catalysts is only a coincidence. 

On the other hand, changes in the recipes of alkali metal polymerizations frequently make appreciable changes in the microstructures of the resultant polymers (2, 10, 12). Thus, sodium polybutadiene, or sodium polyisoprene, has a microstructure different from that of the corresponding potassium-catalyzed polymer. It also has been established that promoters or modifiers like dioxane or dimethoxytetraglycol affect the microstructure in these alkali metal catalyzed systems. One further example is afforded by the Alfin catalyst, which is apparently related to alkali metal catalysts but which gives a polybutadiene or polyisoprene with a microstructure very different from that of the corresponding alkali metal polymers. 

Closely related to the Wurtz reaction is the synthesis of organosodium compounds, such as amylsodium (25) and phenylsodium (13). These can be prepared from sodium and the organic halide by using an excess of sodium and keeping the temperature low in order to minimize the Wurtz reaction. The promising alfin catalyst for the polymerization of butadiene is prepared by a reaction of this type (24). The catalyst consists essentially of allylsodium, mixed with sodium chloride and a sodium alkoxide. 

Next in importance is the polymerization of butadiene, if the use of sodium is ignored in the production of such inorganic compound as sodium cyanide, sodium peroxide, and titanium. Buna rubber, prepared by the sodium-catalyzed copolymerization of butadiene and styrene, was of considerable importance during World War II, especially in Germany. More recently, Morton s alfin catalyst has caught the attention of the rubber industry because of the exceptional quality of polybutadiene prepared by his techniques. 

Describe initiations and propagation processes by Alfin catalysts. 

At high conversions, cationic polymerizations of isoprene result in formations of some crosslinked material. The soluble portions of the polymers are high in tram A A structures. Alfin catalysts yield polymers that are higher in trans-lA structures than free-radical emulsion polymerizations. ... 

The long-known alfin polymerization of butadiene recently has also become important industrially. The alfin catalyst is so called because it originally resulted from the transformation of an alcohol and an olefin (e.g., sodium isopropylate and alkyl sodium). Commercially, the best means of producing the catalysts is to proceed from isopropanol, sodium, and w-butyl chloride ... 

The real alfin catalyst is then produced by the addition of propylene to this suspension, causing the butyl sodium to become converted to allyl sodium ... 

The alfin catalyst is probably a complex of allyl sodium, sodium isopropionate, and NaCl ... 

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