Alkylation boron fluoride

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form ethyUdene diacetate [542-10-9], boron fluoride also catalyzes the reaction (78). Ethyfldene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutfyene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-y -dioxanes 2,4,4,6-tetramethyl-y -dioxane [5182-37-6] is produced in yields up to 90% (82). 

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. 

A ubiquitous co-catalyst is water. This can be effective in extremely small quantities, as was first shown by Evans and Meadows [18] for the polymerisation of isobutene by boron fluoride at low temperatures, although they could give no quantitative estimate of the amount of water required to co-catalyse this reaction. Later [11, 13] it was shown that in methylene dichloride solution at temperatures below about -60° a few micromoles of water are sufficient to polymerise completely some decimoles of isobutene in the presence of millimolar quantities of titanium tetrachloride. With stannic chloride at -78° the maximum reaction rate is obtained with quantities of water equivalent to that of stannic chloride [31]. As far as aluminium chloride is concerned, there is no rigorous proof that it does require a co-catalyst in order to polymerise isobutene. However, the need for a co-catalyst in isomerisations and alkylations catalysed by aluminium bromide (which is more active than the chloride) has been proved [34-37], so that there is little doubt that even the polymerisations carried out by Kennedy and Thomas with aluminium chloride (see Section 5, iii, (a)) under fairly rigorous conditions depended critically on the presence of a co-catalyst - though whether this was water, or hydrogen chloride, or some other substance, cannot be decided at present. 

It might be thought that the question whether a particular alkyl halide is a co-catalyst for a particular monomer-catalyst combination could be settled easily, by adding some of the compound in question to a non-reacting mixture of monomer and catalyst. This approach has been used [36, 44], but it must be carried out in a polar solvent which is itself not a co-catalyst, or only a very weak one. The ideal solvent for this kind of work remains to be found it may be that S02 or even CS2 (which behaves like a polar solvent) will provide the answer. If one wants to use alkyl chloride solvents without being troubled by the possibility of solvent co-catalysis, boron fluoride should be used as catalyst, since the ion BF3C1 is not formed under the conditions generally used for polymerisations. 

The initiation reaction in the polymerization of vinyl ethers by BF3R20 (R20 = various dialkyl ethers and tetrahydrofuran) was shown by Eley to involve an alkyl ion from the dialkyl ether, which therefore acts as a (necessary) co-catalyst [35, 67]. This initiation by an alkyl ion from a BF3-ether complex means that the alkyl vinyl ethers are so much more basic than the mono-olefins, that they can abstract alkylium ions from the boron fluoride etherate. This difference in basicity is also illustrated by the observations that triethoxonium fluoroborate, Et30+BF4", will not polymerise isobutene [68] but polymerises w-butyl vinyl ether instantaneously [69]. It was also shown [67] that in an extremely dry system boron fluoride will not catalyse the polymerization of alkyl vinyl ethers in hydrocarbons thus, an earlier suggestion that an alkyl vinyl ether might act as its own co-catalyst [30] was shown to be invalid, at least under these conditions. 

Paushkin and Topchiev also used H3P()4-BF3 at room temperature to alkylate benzene with olefins (287,402). For alkylation of benzene with alcohols, temperatures of 90-97° and a feed mole ratio of 0.5 alcohol 1.0 benzene 0.5 catalyst were recommended (394). In a recent study (400a) these authors supplemented their previously published views (396) concerning the properties of boron fluoride complexes with phosphoric acid, alcohols, and sulfuric acid as catalysts. Data on the electroconductivity of these catalysts was correlated with their activity in alkylation of isobutane and it was concluded (400a) that the acid ion concentration did not affect the alkylation or polymerization reactions over these catalysts, and therefore the carbonium ion mechanism was not applicable. 

Cleavage of a carbon-fluorine bond can be induced by reaction with a Lewis acid (see Chapter 4, Section VIC). In Friedel-Crafts alkylations, aUcyl fluorides are more reactive than the chlorides [37] with, for example, aluminium halides or boron halides as catalysts (Figure 5.17). 

Kennedy et al. recently reported a survey on the role of numerous alkyl and aralkyl chlorides in the polymerisation of isobutene by boron fluoride, boron chloride... 

BORON FLUORIDE (7637-07-2) Reacts with moist air, water, steam, producing hydrogen fluoride, boric acid, and fluoboric acid. Violent reaction with allyl chloride, alkyl nitrate, benzyl nitrate, calcium oxide, ethyl ether, iodine, magnesium tetrahydroaluminate, active metals (except magnesium). Used as a polymerization catalyst contact with monomers may cause explosions. Corrodes most metals in the presence of moisture. 

Catalysis. An apparent characteristic of many alkylation and dealkylation reactions is their initial slowness, and it has been necessary to resort to catalysis to make the reactions proceed at a rate that will be commercially feasible. Mineral acids, such as sulfuric, phosphoric, hydrochloric, and hydrofluoric, are widely employed as are aluminum chloride, ferric chloride, boron fluoride, etc. With a wide variety of catalysts and alkylating agents to choose from, the choice of agents to use will depend on the relative costs and the reaction rates which will result. 

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. 

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). 

BORON ISOTOPE EXCHANGE BETWEEN BORON FLUORIDE AND ITS ALKYL HALIDE COMPLEXES. II. INFRARED SPECTRUM OF BORON FLUORIDE-METHYL FLUORIDE COMPLEX. 

Precaution Flamm. uel 21.3%, lei 5.5% may form explosive mixts. in air incompat. with oxidizers can react violently with hydrogen chloride alkyl boron/alkyl hyponitrite compds. initiate polymerization forms peroxides with pure oxygen heat-sensitive Hazardous Decomp. Prods. CO, CO2, hydrogen fluoride heated to decomp., emits toxic fluoride fumes emits toxic fumes underfire conditions... 

Phosphoric acid-boron fluoride C-Alkylation of arenes with ethylene derivatives... 

Several reaction mechanisms were also proposed to explain stereospecific placement with insoluble catalysts. Furukawa [46] suggested that here the mechanism for cationic polymerization of vinyl ethers depends upon multicentered coordinations. He felt that coordinations of the polymeric chains and monomers with the catalysts are possible if the complexed counteranions have electrically positive centers. This can take place in the case of aluminum alkyl and boron fluoride ... 

It is of interest to note that in several instances the effect of a catalyst such as aluminum chloride or boron fluoride is enhanced by the presence of an acidic assistant. Alkylation by olefins with aluminum chloride as a catalyst is favored by the presence of anhydrous hydrogen chloride, and the condensation of primary alcohols with benzene uting boron fluoride is possible only with the aid of an. assistant such as phosr phoric anhydride, benzenesulfonic acid, or sulfuric acid. It has been foimd also that chlorides of tin, silicon, or titanium increase the catalytic activity of aluminum chloride, whereas ferric chloride decreases the... 

Although boron fluoride or hydrogen fluoride will catalyze allQ lation by means of alkyl halides, these catalysts are much more effective and useful with olefins or alcohols. Reactions carried out with either of these catalysts are distinguished by the lack of colored and resinous byproducts which so generally accompany the use of aluminum chloride. 

The catalyst may also influence the fate of the alkyl group. Normal alcohols, for example, usually alkylate without rearrangement in the presence of aluminum chloride, but rearrangement does occur when sulfuric acid or boron fluoride is used as a catalyst. 

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