Promoters boron fluoride

The principal use of the alkylation process is the production of high octane aviation and motor gasoline blending stocks by the chemical addition of C2, C3, C4, or C5 olefins or mixtures of these olefins to an iso-paraffin, usually isobutane. Alkylation of benzene with olefins to produce styrene, cumene, and detergent alkylate are petrochemical processes. The alkylation reaction can be promoted by concentrated sulfuric acid, hydrofluoric acid, aluminum chloride, or boron fluoride at low temperatures. Thermal alkylation is possible at high temperatures and very high pressures. 

Aluminum chloride, boron fluoride and certain other Friedel-Crafts catalysts catalyze the polymerization of isobutylene, at temperatures below about —70° recent work has indicated that the presence of a promoter such as water is usually necessary (see Section V). A rubberlike polymer is obtained. 

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 polymerization of olefins in the presence of halides such as aluminum chloride and boron fluoride but in the absence of hydrogen halide promoter may also be described in terms of the complex carbonium ion formed by addition of the metal halide (without hydrogen chloride or hydrogen fluoride) to the olefin (cf. p. 28). These carbonium ions are apparently more stable than those of the purely hydrocarbon type the reaction resulting in their formation is less readily reversed than is that of the addition of a proton to an olefin (Whitmore, 18). Polymerization in the presence of such a complex catalyst, may be indicated as follows (cf. Hunter and Yohe, 17) ... 

Unlike boron fluoride, titanium tetrachloride does not catalyze the liquid phase polymerization of isobutylene under anhydrous conditions (Plesch et al., 83). The addition of titanium tetrachloride to a solution of the olefin in hexane at —80° failed to cause any reaction. Instantaneous polymerization occurred when moist air was added. Oxygen, nitrogen, carbon dioxide, and hydrogen chloride had no promoting effect. Ammonia and sulfur dioxide combined with the catalyst if these were added in small quantity only, subsequent addition of moist air permitted the polymerization to occur. Ethyl alcohol and ethyl ether, on the other hand, prevented the polymerization even on subsequent addition of moist air. They may be regarded as true poisons. 

This method is safe on condition that it is conducted as described below, by adding the reactants to the previously warmed acetic anhydride. Otherwise, the exothermic nature of the reaction may cause an explosion. It is therefore inadmissible to mix the reactants and heat up the mixture, since this causes too violent a reaction. Addition of boron fluoride to the mixture promotes the initiation of reaction and increase its safety. 

Conceivably, therefore, epoxides could form their own co-catalysts or alternatively, any trace of water could promote the formation of further hydroxyl groups. In the case of oxacyclobutane (trimethylene oxide) however the polymerization appears to involve oxonium ions yet the completely dry mixture of monomer and boron fluoride is stable, reacting only on addition of co-catalyst. It seems probable, therefore, that the formation of oxonium ions is catalysed by protons and if so, then the work of Klages and Meuresch (5) is pertinent to the present discussion. These workers found that the ether complexes of acids such as HBF4 and HSbClfi react rapidly and quantitatively with diazomethanes to yield oxonium salts... 

The catalytic alkylation of saturated hydrocarbons with olefins was discovered and developed by Ipatieff and his co-workers in the laboratories of the Universal Oil Products Company (Ipatieff, 1). Experiments were carried out in June, 1932, by Ipatieff and Pines, using aluminum chloride as the catalyst, hydrogen chloride as a promoter, and hexane and ethylene as the reactants. These experiments having given positive results, they were repeated by Komarewsky, who then also investigated the alkylation of naphthenes. The alkylation of hexane was studied quantitatively by Grosse, who extended the reaction to other paraffins and catalysts, particularly boron fluoride. 

The alkylation of paraSins with olefins to yield higher molecular weight branched-chain paraffins may be carried out thermally or catalyt-ically. The catalysts for the reaction fall into two principal classes, both of which may be referred to as acid-acting catalysts (1) anhydrous halides of the Friedel-Crafts type and (2) acids. Representatives of the first type are aluminum chloride, aluminum bromide, zirconium chloride, and boron fluoride gaseous hydrogen halides serve as promoters for these catalysts. The chief acid catalysts are concentrated sulfuric acid and liquid hydrogen fluoride. Catalytic alkylations are carried out under sufficient pressure to keep at least part of the reactants in the liquid phase. 

Halide catalysts of the Friedel-Crafts type. The most important catalysts of this class are anhydrous aluminum chloride and boron fluoride promoted by small amounts of hydrogen chloride and hydrogen fluoride, respectively. It has been suggested that a function of the hydrogen halide is to convert the aluminum or boron halide to a more active acidic form. For example ... 

The probable function of hydrogen halides as promoters for the metal halides and boron fluoride in the alkylation of isoparaffins seems to be to initiate and maintain the formation of f-alkyl halide by the reaction of step 1. Also, it may convert the metal halide to the more active form, such as, for example, hydrogen aluminum tetrachloride or an ester thereof. 

Boron fluoride, promoted by a minor amount of hydrogen fluoride or water, seems to catalyze the alkylation of isoparaffins with ethylene at lower temperatures than does aluminum chloride (Grosse and Ipatieff, 25). The reaction of isobutaiie with ethylene to —30 to —40° and 6 atmospheres pressure yielded a liquid produet, 20% of which was hexanes, to the extent of 180% by weight of the ethylene charged. At 0-5° and 10 atmospheres pressure, a 224% yield of alkylate, 45% of which was hexanes, was obtained. Like the aluminum chloride product formed at 25-35°, the hexanes consisted of 70-90% of 2,3-dimethylbutane, l( -25% of 2-methyl-pentane, and 3% of 2,2-dimethylbutane. 

Alkylation of isobutane with isobutylene at 25° in the presence of boron fluoride promoted by water yielded an alkylate which contained 32% octanes and 15% dodecanes (Ipatieff and Grosse, 37). 

Although in the recent years the stereochemical control of aldol condensations has reached a level of efficiency which allows enantioselective syntheses of very complex compounds containing many asymmetric centres, the situation is still far from what one would consider "ideal". In the first place, the requirement of a substituent at the a-position of the enolate in order to achieve good stereoselection is a limitation which, however, can be overcome by using temporary bulky groups (such as alkylthio ethers, for instance). On the other hand, the ( )-enolates, which are necessary for the preparation of 2,3-anti aldols, are not so easily prepared as the (Z)-enolates and furthermore, they do not show selectivities as good as in the case of the (Z)-enolates. Finally, although elements other than boron -such as zirconium [30] and titanium [31]- have been also used succesfully much work remains to be done in the area of catalysis. In this context, the work of Mukaiyama and Kobayashi [32a,b,c] on asymmetric aldol reactions of silyl enol ethers with aldehydes promoted by tributyltin fluoride and a chiral diamine coordinated to tin(II) triflate... 

Numerous Lewis acids promote the formation of nitronium ions when in the presence of nitric acid. Nitric acid-boron trifluoride, and the nitric acid-hydrogen fluoride-boron trifluoride reagents described by Olah are practical nitrating agents the latter provides a convenient preparation of nitronium tetrafluoroborate. Olah reports that nitric acid-magic acid (FSOsH-SbFs) is extremely effective for the polynitration of aromatic substrates. 

The use of additional substances to increase the activity of a catalyst is a well known phenomenon. Hydrogen chloride or traces of water are known to promote aluminum chloride catalyzed reactions. In the same way the reaction of isoparaffins with olefins has been shown to be catalyzed by boron trifluoride in the presence of nickel powder and with water as the promoter (Ipatieff and Grosse, 76). Hydrogen fluoride can take the place of the water and thus serve as the promoter. 

Thienylboronic acids are useful building blocks for preparing biaryls and heterobiaryls employing the Suzuki reaction. In one case, a Suzuki coupling between thiophene-3-boronic acid and iodocyclopropane 99 was promoted by cesium fluoride to furnish the adduct 100 with retention of configuration [74]. In another example, the union between thiophene-3-boronic acid and 5-bromo-2,2-dimethoxy-l,3-mdandione (101) provided ninhydrin derivative 102 [75]. 

---