Halide catalysts

Polystyrene produced by free-radical polymerisation techniques is part syndio-tactic and part atactic in structure and therefore amorphous. In 1955 Natta and his co-workers reported the preparation of substantially isotactic polystyrene using aluminium alkyl-titanium halide catalyst complexes. Similar systems were also patented by Ziegler at about the same time. The use of n-butyl-lithium as a catalyst has been described. Whereas at room temperature atactic polymers are produced, polymerisation at -30°C leads to isotactic polymer, with a narrow molecular weight distribution. 

The 17-ethylene ketal of androsta-l,4-diene-3,17-dione is reduced to the 17-ethylene ketal of androst-4-en-3,17-dione in about 75% yield (66% if the product is recrystallized) under the conditions of Procedure 8a (section V). However, metal-ammonia reduction probably is no longer the method of choice for converting 1,4-dien-3-ones to 4-en-3-ones or for preparing 5-en-3-ones (from 4,6-dien-3-ones). The reduction of 1,4-dien-3-ones to 4-en-3-ones appears to be effected most conveniently by hydrogenation in the presence of triphenylphosphine rhodium halide catalysts. Steroidal 5-en-3-ones are best prepared by base catalyzed deconjugation of 4-en-3-ones. ... 

Copolymerization of methacrylic acid with butadiene and isoprene was photoinitiated by Mn2(CO)io without any halide catalyst [28,29]. The po]ymerization system is accompanied by a Dieis-Alder additive. Cross propagation reaction was promoted by adding trieth-y]aluminum chioride. 

Brown and Jensen395 suggested that the rate equation (194) for the reaction of benzene with excess benzoyl chloride could be interpreted according to the mechanisms given by the reactions (201) and (202), (203) and (204) and (205) and (206) which refer to nucleophilic attack of the aromatic upon the polarised acyl halide-catalyst complex, upon the free acylium ion, and upon an ion pair derived from the acyl halide-catalyst complex, viz. 

An explanation for the effect of excess catalyst has been offered by Corriu et al. 16, who measured the rates of the aluminium chloride-catalysed reaction of benzoyl chloride with benzene, toluene, and o-xylene. The observed rate coefficients were analysed in terms of a mixture of second- and third-order reactions (the latter being second-order in the halide-catalyst complex), the following results being obtained benzene (40 °C), k2 = 2.5 xlO-5, fc3 = 3.3 xlO-5 toluene (2.5 °C), k2 = 0.75 xlO"4, k3 = 3.83 xlO-4 o-xylene (0 °C), k2 = 1.83 x 10-3, k3 = 4.50 x 10-3. They suggest the equilibrium... 

In contrast to bulk polymerization, solution polymerization provided soluble polymers with high molecular weights using low FeCl3 concentration at 120-140 C.31 A major disadvantage of the above approaches is that all the metal-halide catalysts need to be removed, since the catalyst residue will deteriorate die thermal stability and electrical and other properties. 

The reaction on unactivated halides can also be done with copper halide catalysts (the Hurtley reaction), and with palladium complex catalysts. 

Such a mechanism is open to serious objections both on theoretical and experimental grounds. Cationic polymerizations usually are conducted in media of low dielectric constant in which the indicated separation of charge, and its subsequent increase as monomer adds to the chain, would require a considerable energy. Moreover, termination of chains growing in this manner would be a second-order process involving two independent centers such as occurs in free radical polymerizations. Experimental evidence indicates a termination process of lower order (see below). Finally, it appears doubtful that a halide catalyst is effective without a co-catalyst such as water, alcohol, or acetic acid. This is quite definitely true for isobutylene, and it may hold also for other monomers as well. 

Derivatization (GC) 848 alkylating reagents 861 alkyl halide/catalyst 861 dialkyl acetals 863 diazoalkanes 862 extractive alkylation 863 pyrolytic alkylation 865 al) ldimethylsilyl reagents 855... 

They find that heating cyclotri- and cyclotetrasilazanes with ammonium halide catalysts at temperatures of 160°C for 6-8 h results in a condensation polymerization process that evolves ammonia and leads to the formation of waxy polysilazanes. Analytical results suggest that these polysilazanes consist of rings linked by silyl bridges as illustrated by the following structure ... 

Acidic gases, limestone reaction with, 15 33 Acidic halide catalysts, 12 167 Acidic hydrolysis, 10 502. See also Acid hydrolysis... 

It is useful to note here a fundamental distinction between cationic and anionic polymerizations (including Ziegler-Natta systems). In the latter, residual water merely inactivates an equivalent quantity of catalyst, whereas in the former water may be a cocatalyst to the metal halide catalyst in excess it may decrease the rate by forming catalytically inactive higher hydrates and in very many systems it, or its reaction product(s) with a metal halide, act as extremely efficient chain-breakers, thus reducing the molecular weight of the polymers (see sub-section 5.4). 

Methanol can be hydroformylated with syngas (CO and H2) in the presence of a copper or nickel halide catalyst to give acetaldehyde. Reaction conditions are 350-400°F and 4000-6000 psi. 

The metal halide catalysts include aluminum chloride, aluminum bromide, ferric chloride, zinc chloride, stannic chloride, titanium tetrachloride and other halides of the group known as the Friedel-Crafts catalysts. Boron fluoride, a nonmetal halide, has an activity similar to that of aluminum chloride. 

With halide catalysts of the Friedel-Crafts type (e.g., aluminum chloride or boron fluoride) in the presence of hydrogen halide the formation of the carbonium ion results in the addition of the proton from the promoter to the pi electrons ... 

The halide catalysts are electron acceptors, and, in the absence of hydrogen halide promoter, the active complex is presumably formed by the addition of the catalyst to the olefin (Hunter and Yohe, 17 cf. Whitmore, 18) ... 

The metal halide thus functions in similar manner to the proton and may be considered to be an acidic catalyst (cf. Luder and Zuffanti, 19). The catalyst-olefin complex differs in one significant respect from the product formed by the addition of the proton (or the corresponding acid) to the olefin the halide catalyst is a neutral but electronically deficient molecule and combines with the pi electrons of the double bond to form a coordinate bond between the carbon atom and the aluminum or boron. On the other hand, the addition of the positive proton to the double bond results in the formation of a true (covalent) link between carbon and hydrogen. In other words, the complex, while it contains an electron-deficient (hence, positive) carbon atom, is in itself electronically neutral the product of the addition of a proton to the alkene contains a similar carbon atom but is itself electrically positive. It has been suggested (Whitmore and Meunier, 20) that this difference is related to the fact that metal halide catalysts tend to yield much higher polymers than do the acid (proton) catalysts. 

It seems questionable, however, that the geometry of all metal halide catalysts would be such as to permit the formation of the carbon-halogen coordinate bond. 

Fluorinated and Chlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The literature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl halides, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal halide catalysts, such as... 

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