Bronsted-Lewis equation

More recent work in our " and other groups has shown that the use of Lewis (Equation 11) and Bronsted acid (Equation 12) catalysts can significantly reduce the reaction times for these allylboration reactions. Furthermore, the reaction temperature can be lowered, which allows for sensitive functional groups to be present on the aldehyde and allylboronate. It is also important to mention that even in the presence of the catalyst, the diastereospecificity of the reaction is maintained. 

Write the balanced chemical equation for (a) the thermal decomposition of potassium chlorate without a catalyst (b) the reaction of bromine with water (c) the reaction between sodium chloride and concentrated sulfuric acid, (d) Identify each reaction as a Bronsted acid—base, Lewis acid—base, or redox reaction. 

A) In addition to the more modem Bronsted and Lewis theories, it is important not to forget the classic Arrhenius theory in its modern form, the so-called solvents theory, where it can be applied, i.e., with solvents that undergo self-dissociation in this form it was originally formulated in 1949 by Jander3 in Germany and is illustrated by the following reaction equations ... 

With reference to a solvent, this term is usually restricted to Brpnsted acids. If the solvent is water, the pH value of the solution is a good measure of the proton-donating ability of the solvent, provided that the concentration of the solute is not too high. For concentrated solutions or for mixtures of solvents, the acidity of the solvent is best indicated by use of an acidity function. See Degree of Dissociation Henderson-Hasselbalch Equation Acid-Base Equilibrium Constants Bronsted Theory Lewis Acid Acidity Function Leveling Effect... 

At about the same time that Bronsted proposed his acid-base theory, Lewis put forth a broader theory, A base in the Lewis theory is the same as in the Brpnsted one, namely, a compound with an available pair of electrons, either unshared or in a tt orbital. A Lewis acid, however, is any species with a vacant orbital.1115 In a Lewis acid-base reaction the unshared pair of the base forms a covalent bond with the vacant orbital of the acid, as represented by the general equation... 

Gay and Liang also found large changes in 13C chemical shifts when amines interacted with Bronsted acid sites, and smaller ones when the interaction involved Lewis acid sites. They suggested therefore that fractional coverage of the surface of the amine could be calculated from the magnitude of the 13C chemical shift, based on wo assumptions (1) that chemical shifts are average values from protonated and unprotonated amine molecules and (2) that the shift for a protonated molecule is the same as for the acid solution of the amine. Experiments showed that both assumptions were well founded. It follows that the fraction, /B, of amine molecules bonded to the Bronsted sites can be derived from the equation... 

Balance each equation and classify the reaction as Bronsted acid-base, Lewis acid-base, or redox. 

Figure 1.14 a Equation for the cyclization of geraniol, and b possible mechanism in the presence of zeolite Y, a solid acid catalyst that has both Bronsted and Lewis acid sites. 

According to the Lewis definition, an acid is an electron pair acceptor and a base is an electron pair donor. All Bronsted-Lowry bases are also Lewis bases. However, Lewis acids include many species that are not proton acids instead of H+, they have some other electron-deficient species that acts as the electron pair acceptor. An example of a Lewis acid-base reaction is provided by the following equation. In this reaction the boron of BF3 is electron/deficient (it has only six electrons in its valence shell). The oxygen of the ether is a Lewis base and uses a pair of electrons to form a bond to the boron, thus completing boron s octet. 

Although the 3a,4,5,6a-tetrahydrofuro[3,2-fiQisoxazoles are unstable in the presence of Bronsted acids (e.g., Equation (58)), they are relatively stable to mild Lewis acids. As exemplified in Scheme 35, the combination of an organolithium and lithium bromide facilitates alkylative conversion of the isoxazoline nucleus (207) to the bicyclic isoxazolidines (208) and (209) <89CL1079>. A similar transformation was also reported for the tetrahydrofuro[3,4-fiQisoxazole (210) (Equation (59)). 

A vast generalization beyond the Bronsted—Lowry acids and bases concepts is the concept of a Lewis29 base (an electron pair donor) and a Lewis acid (an electron pair acceptor). This concept has been used extensively in all branches of chemistry. In physical organic chemistry, quantities of the type pA = —logio[A] have used extensively to study reactivities—for example, in the Hammett equation. 

One definition of a metal complex or coordination compound is "a compound formed from a Lewis acid and a Bronsted base a Lewis acid being an electron pair acceptor and a Bronsted base a proton acceptor. Thus the interaction of the Lewis acid metal centre in Ni(C104)2 with the Bronsted base ammonia to form a complex according to equation 4.1... 

Isomerization of phenols 137 over sUica gel in the solid phase furnishes the corresponding 2,3-dihydro-4-oxo-4//-l-benzopyrane derivatives 138 (equation 60) ° . The cascades of the charge-accelerated rearrangements of the ortl o-(l,l-dimethylpropenyl)phenol 139 catalyzed by Bronsted acid (e.g. trifluoroacetic acid, equation 61) as well as by Lewis acids (anhydrous AICI3 or TiCLj, equations 62 and 63) proceed via the common intermediate 140 . 

The Claisen rearrangement can be effectively catalyzed by Lewis acids, Bronsted acids, bases, Rh(I) and Pt(0) complexes as well as by silica . Several reviews were published recently in which the application of zeolites and acid-treated clays as catalysts for the Claisen rearrangement was described Thus, it was shown that the rearrangement conditions for phenolic allyl ethers can be dramatically milder if this reaction is carried out by thermolysis of a substrate immobilized on the surface of previously annealed silica gel for chromatography. For example, the thermolysis of ether 159 on silica gel (in a 159 Si02 ratio of 1 10 w/w) at 70°C gives the phenol 160 in 95% yield after 3.5 hours (equation 70). An additional example is shown in equation 71. ... 

Thus, water functions both as an acid (donor of or proton) and as a base (acceptor of H+ or proton). This description of an acid and a base follows from the Bronsted-Lowry theory. According to the Lewis theory, acids are electron pair acceptors and bases are electron pair donors. The equilibrium constant, K, for the dissociation reaction in Equation (1.1) is... 

Solutions of EB may be also readily doped with a range of metal salts and Lewis acids in a process (Equation 4.2) reminiscent of the Bronsted acid doping of EB described earlier. Similar to protonic doping, binding of the metal ions to imine N sites on the EB chains is believed to occur, leading to conducting PAn products of the general type 14. 

Allylations of aldehydes and imines also constitute important carbon-carbon bond-forming reactions [14]. A range of metal-based Lewis acid catalysts have been reported. Hall and co-workers described the Bronsted acid-catalyzed allylation of aldehydes with allyl boronate (Equation 10.8) [15]. 

The CeY zeolite is utilized for the preparation of 4-methylcoumarin by the reaction of phenol with AAN. The formation of PA represents the first step the subsequent acylation at the ortho position, followed by an intramolecular aldol-like condensation, affords the final 4-methylcoumarin in 75% yield (Scheme 5.8). In the entire process, the cerium-catalyst shows a bifunctional character the active centers in the supercage of CeY zeolite, the Ce + ions, act as Lewis acid catalysts, whereas the acid centers H+, formed by the dissociation of water according to the equation Ce + + H2O [Ce(OH)]2+ + H+, act as Bronsted catalysts. 

The mass of pyridine remaining adsorbed on the sample at the two (or three) adsorption temperatures, in combination with the integrated areas underneath the bands due to the 19b ring vibrations of pyridine adsorbed at Lewis and Bronsted sites (ca. 1450 and 1540 cm, respectively) at the corresponding temperatures allowed calculation of the Bronsted and Lewis absorption coefficients. The number of Lewis and Bronsted sites could be calculated by fitting this data to the equation (1) ... 

For example, five types of hydroxyl groups are predicted to occur on the (100), (111), and (110) surfaces of aluminas, as depicted in Figure 1. The relative concentration and distribution of these groups depends on the exposed faces. Dehydroxylation of the surface, according to equation (1), yields surface oxo groups and exposes aluminum cations. The surface hydroxyl groups have Bronsted acidity, while exposed metal cations behave as Lewis acids. Alumina surfaces with Lewis acidity can be prepared from aluminum alkoxides under mild conditions by protecting the incipient Lewis acid site with... 

Zinc hydroxide is an amphoteric substance. Write equations that describe Zn(OH)2 acting as a Bronsted-Lowry base toward H and as a Lewis acid toward OH . 

Recently the Lewis acid-catalysed oxidation of isobutane has been re-examined with the rigorous exclusion of any Bronsted acid and stoichiometric volumes of hydrogen were collected. When the temperature of a solution of isobutane in SbF5/S02ClF was raised to — 30 °C, hydrogen evolved and the t-butyl cation was produced quantitatively. Analysis of a white precipitate showed SbF3 to have been formed (equation 9). When the reaction was carried out in the presence of acetone, then only traces of hydrogen were detected and equimolar quantities of the t-butyl cation and protonated acetone formed (equation 10). 

As G. N. Lewis said, We frequently define an acid or a base as a substance whose aqueous solution gives, respectively, a higher concentration of hydrogen ion or hydroxide ion than that furnished by pure water. This is a very one-sided definition. In 1923, Bronsted and Lowry expanded the definitions of acids and bases to include species that do not involve solvent participation. According to the Bronsted-Lowry definition, an acid is any proton donor, whereas a base is any proton acceptor. This broader definition expanded acid-base theory to include gaseous species, such as HCI (g) and NH3 (g). It also allowed for the inclusion of acid-base reactions occurring in nonionizing solvents, such as benzene, as shown by Equation (14.6) ... 

In 1923, Gilbert Newton Lewis defined an acid as an electron pair acceptor and a base as an electron pair donor. This definition is even more inclusive than the previous one because it includes all Bronsted-Lowry acids and bases as a subset and provides the foundation for the field of coordination chemistry. A coordination compound is the product of a Lewis acid-base reaction, such as the one shown in Equation (14.11) and Figure 14.5, in which the metal ion (Lewis acid) and ligand (Lewis base) are held together by a coordinate covalent bond. 

For each acid-base theory referred to in Question 7, write an equation illustrating the neutralization of an acid with a base. Write the Lewis structure for the (a) bromide ion, (b) hydroxide ion, and (c) cyanide ion. Why are these ions considered to be bases according to the Bronsted-Lowiy and Lewis acid-base theories ... 

Write a chemical equation using Lewis structures for the reaction of water with ammonia. Identify the Bronsted-Lowry add and base in the reaction. 

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