Boron trifluoride, Table

The reactivity of halogenated alkenes in the electrophilic hydrofluorination reaction decreases with an increasing number of halogen atoms. Thus polyhaloalkenes are rather resistant to the electrophilic addition of hydrogen fluoride.Therefore, the hydrofluorination needs catalysis, with boron trifluoride(Table 6), tantalum(V) fluoride (Table 5), antimony(V) chloride, niobium(V) fluoride,titanium(IV)chloride or molybdenum(V) chloride. ... 

The d.r. value is influenced by the type and amount of catalyst added. Note that the induced effect by zinc(II) chloride and 4-toluenesulfonic acid is opposite to that of aluminum trichloride or boron trifluoride (Tables 4 and 5). 

The Diels-Alder reaction has been shown to be subject to catalysis by a wide range of solid catalysts (see Chapter 4 for some examples). Acidic mesoporous aluminosilicates can be used to catalyse selective Diels-Alder reactions such as that between cyclopentadiene with methyl acrylate. The zinc-exchanged version of the material is particularly effective and compares well to other more established solid acids such as the ion-exchanged clay Zn2+-K10 as well as homogeneous catalysts such as boron trifluoride (Table 2.7).50... 

From these results it appears that the 5-position of thiazole is two to three more reactive than the 4-position, that methylation in the 2-position enhances the rate of nitration by a factor of 15 in the 5-position and of 8 in the 4-position, that this last factor is 10 and 14 for 2-Et and 2-t-Bu groups, respectively. Asato (374) and Dou (375) arrived at the same figure for the orientation of the nitration of 2-methyl and 2-propylthiazole Asato used nitronium fluoroborate and the dinitrogen tetroxide-boron trifluoride complex at room temperature, and Dou used sulfonitric acid at 70°C (Table T54). About the same proportion of 4-and 5-isomers was obtained in the nitration of 2-methoxythiazole by Friedmann (376). Recently, Katritzky et al. (377) presented the first kinetic studies of electrophilic substitution in thiazoles the nitration of thiazoles and thiazolones (Table 1-55). The reaction was followed spec-trophotometrically and performed at different acidities by varying the... 

Chemical Properties. In addition to the reactions Hsted in Table 3, boron trifluoride reacts with alkali or alkaline-earth metal oxides, as well as other inorganic alkaline materials, at 450°C to yield the trimer trifluoroboroxine [13703-95-2] (BOF), MBF, and MF (29) where M is a univalent metal ion. The trimer is stable below — 135°C but disproportionates to B2O2 and BF at higher temperatures (30). 

Table 4. Boron Trifluoride Adducts with Oxygen-Containing Compounds...

Compounds containing fluorine and chlorine are also donors to BF3. Aqueous fluoroboric acid and the tetrafluoroborates of metals, nonmetals, and organic radicals represent a large class of compounds in which the fluoride ion is coordinating with trifluoroborane. Representative examples of these compounds are given in Table 5. Coordination compounds of boron trifluoride with the chlorides of sodium, aluminum, iron, copper, 2inc, tin, and lead have been indicated (53) they are probably chlorotrifluoroborates. 

Table 5. Boron Trifluoride Adducts with Compounds Containing Chlorine and Fluorine...

Cationic polymerization of coal-tar fractions has been commercially achieved through the use of strong protic acids, as well as various Lewis acids. Sulfuric acid was the first polymerization catalyst (11). More recent technology has focused on the Friedel-Crafts polymerization of coal fractions to yield resins with higher softening points and better color. Typical Lewis acid catalysts used in these processes are aluminum chloride, boron trifluoride, and various boron trifluoride complexes (12). Cmde feedstocks typically contain 25—75% reactive components and may be refined prior to polymerization (eg, acid or alkali treatment) to remove sulfur and other undesired components. Table 1 illustrates the typical components found in coal-tar fractions and their corresponding properties. 

Table 3. Synthesis of ort/io-Substituted Fluoroaromatics from Nitrite Esters, Boron Trifluoride, and Hydrogen Fluoride [26]...

Table 8-11. Enthalpy Change for Boron Trifluoride Complex Formation with Donors al 25°C...

A solution of 3 g of the nitrile, water (5 moles per mole of nitrile), and 20 g of boron trifluoride-acetic acid complex is heated (mantle or oil bath) at 115-120° for 10 minutes. The solution is cooled in an ice bath with stirring and is carefully made alkaline by the slow addition of 6 A sodium hydroxide (about 100 ml). The mixture is then extracted three times with 100-ml portions of 1 1 ether-ethyl acetate, the extracts are dried over anhydrous sodium sulfate, and the solvent is evaporated on a rotary evaporator to yield the desired amide. The product may be recrystallized from water or aqueous methanol. Examples are given in Table 7.1. 

Addition of 15-crown-5 to the higher-order cuprate led to a reagent that is totally unrcac-tive towards 2-phenylpropanal even at room temperature18. If, however, boron trifluoride-diethyl ether complex was added as additional ingredient, the reactivity was restored and, furthermore, the Cram selectivity increased to 90 10 (Table 4). Analogous results could be obtained by placing the crown-ether effect within the cuprate itself, as in reagent 10. 

Benkeser et a/.431 measured the relative rates of acetylation of alkylferrocenes using acetic anhydride catalysed by boron trifluoride etherate, in dichloromethane at 0 and 25 °C. The relative reactivities are given in Table 115, and are interesting... 

Shatenshtein et a/.S19 have also measured the effect of boron trifluoride as a catalyst for hydrogen exchange in acetic acid and have compared it with stannic chloride (Table 157). The logarithm of the rate coefficient was linearly related to... 

The role of Lewis acids in the formation of oxazoles from diazocarbonyl compounds and nitriles has primarily been studied independently by two groups. Doyle et al. first reported the use of aluminium(III) chloride as a catalyst for the decomposition of diazoketones.<78TL2247> In a more detailed study, a range of Lewis acids was screened for catalytic activity, using diazoacetophenone la and acetonitrile as the test reaction.<80JOC3657> Of the catalysts employed, boron trifluoride etherate was found to be the catalyst of choice, due to the low yield of the 1-halogenated side-product 17 (X = Cl or F) compared to 2-methyI-5-phenyloxazole 18. Unfortunately, it was found that in the case of boron trifluoride etherate, the nitrile had to be used in a ten-fold excess, however the use of antimony(V) fluoride allowed the use of the nitrile in only a three fold excess (Table 1). 

C21-0097. Construct a table of bond lengths that supports the existence of 7r bonding in boron trifluoride and boric acid. The relevant data can be found in the text. Label your table thoroughly. 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

The reactivity of acylzirconocene chlorides towards carbon electrophiles is very low, and no reaction takes place with aldehydes at ambient temperature. In the reaction described in Scheme 5.12, addition of a silver salt gave the expected product, albeit in low yield (22—34%). The yield was improved to 79% by the use of a stoichiometric amount of boron trifluoride etherate (BF3OEt2) (1 equivalent with respect to the acylzirconocene chloride) at 0 °C. Other Lewis acids, such as chlorotitanium derivatives, zinc chloride, aluminum trichloride, etc., are less efficient. Neither ketones nor acid chlorides react with acylzirconocene chlorides. In Table 5.1, BF3 OEt2-mediated reactions of acylzirconocene chlorides with aldehydes in CH2C12 are listed. 

In a more practical sence, treatment of ethyl diazoacetate and boron trifluoride etherate transformed the cyclobutanone (154) to (155) (Table 5) 55). 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

Epoxytrichloroacetimidates 153 also undergo oxazoline ring formation in the presence of a catalytic amount of Lewis acids.Diethylaluminum chloride was found to be superior to boron trifluoride, which tends to further hydrolyze the oxazoline 154 to the trichloroacetamide. Generally, formation of the six-membered ring oxazine 155 is not favored, but it can be a serious side reaction if the epoxide contains substituents that stabilize the incipient cation generated prior to ring closure. Examples from this study are summarized in Table 8 19 (Fig 8 8 Scheme 8.45). 

Volatile boron compounds, especially boranes, are usually more toxic than boric acid or soluble borates (Table 29.9) (NAS 1980). However, there is little commercial production of synthetic boranes, except for sodium borohydride — one of the least toxic boranes (Sprague 1972). Boron trifluoride is a gas used as a catalyst in several industrial systems, but on exposure to moisture in air, it reacts to form a stable dihydride (Rusch etal. 1986). Eor boric oxide dusts, occupational exposures to 4.1 mg/m (range 1.2 to 8.5) are associated with eye irritation dryness of mouth, nose and throat sore throat and cough (Garabrant et al. 1984). 

The olefins formed under these conditions using other tertiary alcohols tend to follow the Hofmann rule [6a]. However, tertiary alcohols and phenols [6b] can be made to react with isocyanates to give urethanes when they are catalyzed by acids or bases such as pyridine [6b], triethylamine, sodium acetate, boron trifluoride etherate, hydrogen chloride, or aluminum chloride [7]. Table I indicates the results of preparing phenylurethanes of tertiary alcohols... 

Pure isomerizations have been observed in Lewis acid catalyzed thermal1,2 7 and photochemical3 4 rearrangements, but incorporation of the electrophile occurs with acid fluoride-boron trifluoride.5 6 Examples are collected in Table 2. 

Table 5. Fluorination of Aromatic Compounds with l-Fluoro-4-(4-pyridyl)pyridinium Boron Trifluoride Tetrafluoroborate (31) and l-Fluoro-l -methyl-4,4 -bipyridinium Ditriflate (32)67...

Thus, the ring-opening reaction of l,2-epoxy-l-(4-nitrophenyl)cyclohexane (1) with boron trifluoride diethyl ether complex exhibits a pronounced solvent dependence as shown in Table 4.31... 

Table 4. Product Composition in the Reactions of Epoxide 1 with Boron Trifluoride-Diethyl Ether Complex...

Investigation of the reaction of xenon difluoride and difluoroiodobenzene with aliphatic 1,3-dienes in the presence of boron trifluoride-diethyl ether complex has shown that under mild conditions this reaction proceeds with kinetic control, to form mainly the products of 1,2-addition of fluorine atoms. The ratio of product is reported in Table 5. 

---