Ammonia with boron trifluoride

At first glance, neither the reactants nor the product appears to be an acid or base, but the reactants are revealed as a Lewis acid-base pair when drawn as Lewis dot structures as in Figure 16-1. Ammonia donates its lone pair of electrons to the bond with boron trifluoride, making ammonia the Lewis base and boron trifluoride the Lewis acid. 

Before the synthesis, displace air from the apparatus with a strong stream of ammonia. Next pass the ammonia and boron trifluoride through the apparatus at the same rate. (If excess boron trifluoride is introduced, it evolves in the form of white smoke from discharge opening 5.)... 

Lewis acids and bases, because of their complexity, shall be examined briefly. Consider the structure of ammonia with its free pair of electrons. If the free pair of electrons were to make a bond with boron trifluoride, which substance is labeled as an acid and which one is the base Because the boron accepted a pair of electrons it is considered to be the Lewis acid. Ammonia is the substance that donated the electron pair and is classified as the Lewis base. (See Figure 9.3.)... 

This is the case, for example, with boron trifluoride and ammonia ... 

Ammonia (NH ) can bond with boron trifluoride (BF ). For the bond formation, the electrons are most likely supplied by ... 

Ammonia gas (NH3) reacts with boron trifluoride gas (BF3) to give a colourless molecular solid, H3NBF3. This can be explained by adding a further postulate to 1-9 above ... 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

Adberabibty of the film may be enhanced by its treatment with flame, electric discharge, boron trifluoride gas, activated gas plasma, dichromate sulfuric acid, and a solution of alkab metal ia Hquid ammonia (84—87). A coating of polyurethane, an alkyl polymethacrylate, or a chlotinated adhesive can be apphed to PVF surfaces to enhance adhesion (80,88,89). 

AHylestrenol (37) is prepared from (32), an intermediate in the synthesis of norethindrone. Treatment of (32) with ethanedithiol and catalytic boron trifluoride provides a thioketal. Reduction with sodium in Hquid ammonia results in the desired reductive elimination of the thioketal along with reduction of the 17-keto group. Oxidation of this alcohol with chromic acid in acetone followed by addition of aHyl magnesium bromide, completes the synthesis... 

Preparation. Hexagonal boron nitride can be prepared by heating boric oxide with ammonia, or by heating boric oxide, boric acid, or its salts with ammonium chloride, alkaU cyanides, or calcium cyanamide at atmospheric pressure. Elemental nitrogen does not react with boric oxide even in the presence of carbon, though it does react with elemental boron at high temperatures. Boron nitride obtained from the reaction of boron trichloride or boron trifluoride with ammonia is easily purified. 

In another approach to analogs, nortestosterone is first converted to the thioketal by treatment with ethylene dithiol in IUe presence of boron trifluoride. (The mild conditions of this reaction compared to those usually employed in preparing the oxygen ketals probably accounts for the double bond remaining at 4,5.) Treatment of this derivative with sodium in liquid ammonia... 

The boron atom in BF5 can complete its octet if an additional atom or ion with a lone pair of electrons forms a bond by providing both electrons. A bond in which both electrons come from one of the atoms is called a coordinate covalent bond. For example, the tetrafluoroborate anion, BF4 (31), forms when boron trifluoride is passed over a meral fluoride. In this anion, the formation of a coordinate covalent bond with a fluoride ion gives the B atom an octet. Another example of a coordinate covalent bond is that formed when boron trifluoride reacts with ammonia ... 

The reactions of boron trifluoride adducts of ammonia,and primary, secondary, and tertiary amines with phosphorus pentachloride have been studied and in the first two cases acyclic phosphazenes were obtained. With the ammonia-adduct, a previously characterized phosphazene salt was obtained ... 

In the presence of boron trichloride or trifluoride (Lewis acids), ammonia is likely to detonate. In contact with boron, it causes incandescence. 

A. Nortricyclyl acetate. A mixture of 156 g. (1.70 moles) (rf bicyclo[2.2.l]hepta-2,5-diene (Note 1), 105 g. (100 ml., 1.75 moles) of glacial acetic acid, and 3 ml. of boron trifluoride ether- ate (Note 2) is placed in a 500-ml. flask attached to a condenser equipped with a drying tube. The mixture is heated on a steam bath for 6 hours, cooled to room temperature, and diluted with 250 ml. of ether. The ethereal solution is washed successively with two 50-ml. portions of 3A ammonia and 50 ml. of water and dried over magnesium sulfate. The ether is removed by distillation through a short column of glass helices, and the dark... 

Being an electron deficient compound, boron trifluoride forms complexes with Lewis bases and compounds that have unshared pair(s) of electrons. With ammonia, it forms boron trifluoride ammonia. Similar coordination compounds are formed with monoethylamine, BF3-NH2C2H5 diethyl ether, CH3CH20(BF3)CH2CH3 and methanol, BF3—OHCH3. It forms a sohd complex HNO3-2BF3 with concentrated nitric acid. 

The halogen derivatives of boron unite with ammonia, forming ammines. Boron trifluoride combines with ammonia, forming the substances BFj.NIIg, BF3.2NFI3, BF3.8NIT3 the two latter are liquid, and easily lose ammonia with formation of the monannnine. 

Monammino-boron Fluoride, BF3.NH3, is a white solid which may be sublimed without decomposition in a closed tube. The vapour of the substance is stated by Mixtcr 1 to attack glass it is decomposed on exposure to moist air, and dissolves in water with formation of oxy-fluoborate. It is probable that these compounds of boron trifluoride and ammonia are mixtures of the same type as those formed from boron trichloride described by Joannis. 

Such a bond, in which the donor molecule (or anion) provides both bonding electrons and the acceptor cation provides the empty orbital, is called a coordinate or dative bond. The resulting aggregation is called a complex. Actually, any molecule with an empty orbital in its valence shell, such as the gas boron trifluoride, can in principle act as an electron pair acceptor, and indeed BF3 reacts with ammonia (which has a lone pair, NH3) to form a complex H3N ->BF3. Our concern here, however, is with metal cations, and these usually form complexes with from 2 to 12 donor molecules at once, depending on the sizes and electronic structures of the cation and donor molecules. The bound donor molecules are called ligands (from the Latin ligare, to bind), and the acceptor and donor species may be regarded as Lewis acids and Lewis bases, respectively. 

Preparation of Boron Trifluoride Ammine. Assemble an apparatus as shown in Pig. 113. Place flask 1 into a bath with ice. To produce ammonia, spill solid granulated sodium or potassium hydroxide into bottle 2. Pour a concentrated ammonia solution into the dropping funnel. 

There are some molecules in which the fourth orbital of boron is used for formation of another bond and is not available to permit double-bond character to be assumed by the B—X bonds. In these molecides the bond lengths should approximate the values calculated for B—X single bonds (Table 9-1 column 2). An example is ammonia-boron trifluoride, with the structure... 

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