Boron-aluminum

In addition, boron, aluminum, and gallium tris(triduoromethanesulfonates) (tridates), M(OTf)2 and related perduoroalkanesulfonates were found effective for Friedel-Crafts alkylations under mild conditions (200). These Lewis acids behave as pseudo haUdes. Boron tris(tridate) shows the highest catalytic activity among these catalysts. A systematic study of these catalysts in the alkylation of aromatics such as benzene and toluene has been reported (201). 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thaHous) and trivalent (thaUic) forms. There are numerous thaHous compounds, which are usually more stable than the corresponding thaUic compounds. The thaUium(I) ion resembles the alkaU metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkaU metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other haUdes are insoluble. Thallium (ITT) ion resembles aluminum, gallium, and indium ions in properties. 

A. N. Nesmeyanov and R. A. SokoUk, The Organic Compounds of Boron, Aluminum, Gallium, Indium and Thallium, North-HoUand Publishing Co., Amsterdam, the Netherlands, 1967. 

Lewis acids are defined as molecules that act as electron-pair acceptors. The proton is an important special case, but many other species can play an important role in the catalysis of organic reactions. The most important in organic reactions are metal cations and covalent compounds of metals. Metal cations that play prominent roles as catalysts include the alkali-metal monocations Li+, Na+, K+, Cs+, and Rb+, divalent ions such as Mg +, Ca +, and Zn, marry of the transition-metal cations, and certain lanthanides. The most commonly employed of the covalent compounds include boron trifluoride, aluminum chloride, titanium tetrachloride, and tin tetrachloride. Various other derivatives of boron, aluminum, and titanium also are employed as Lewis acid catalysts. 

Historically, polymer-matrix composite materials such as boron-epoxy and graphite-epoxy first found favor in applications, followed by metal-matrix materials such as boron-aluminum. Ceramic-matrix and carbon-matrix materials are still under development at this writing, but carbon-matrix materials have been applied in the relatively limited areas of reentry vehicle nosetips, rocket nozzles, and the Space Shuttle since the early 1970s. 

Let s address the issue of nonlinear material behavior, i.e., nonlinear stress-strain behavior. Where does this nonlinear material behavior come from Generally, any of the matrix-dominated properties will exhibit some degree of material nonlinearity because a matrix material is generally a plastic material, such as a resin or even a metal in a metal-matrix composite. For example, in a boron-aluminum composite material, recognize that the aluminum matrix is a metal with an inherently nonlinear stress-strain curve. Thus, the matrix-dominated properties, 3 and Gj2i generally have some level of nonlinear stress-strain curve. 

The reactions of nitrones constitute the absolute majority of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions. Boron, aluminum, titanium, copper and palladium catalysts have been tested for the inverse electron-demand 1,3-dipolar cycloaddition reaction of nitrones with electron-rich alkenes. Fair enantioselectivities of up to 79% ee were obtained with oxazaborolidinone catalysts. However, the AlMe-3,3 -Ar-BINOL complexes proved to be superior for reactions of both acyclic and cyclic nitrones and more than >99% ee was obtained in some reactions. The Cu(OTf)2-BOX catalyst was efficient for reactions of the glyoxylate-derived nitrones with vinyl ethers and enantioselectivities of up to 93% ee were obtained. 

Unsolvated organomagnesium compounds have been recommended for the synthesis of organometallic derivatives of mercury, boron, aluminum, silicon, germanium, tin, phosphorus, arsenic, and antimony6-8 and have been used in procedures for the alkylation of aromatic rings and for the production of various polymerization catalysts.4 9... 

Metallic elements with low ionization energies commonly form basic ionic oxides. Elements with intermediate ionization energies, such as beryllium, boron, aluminum, and the metalloids, form amphoteric oxides. These oxides do not react with or dissolve in water, but they do dissolve in both acidic and basic solutions. 

Describe the major uses of hydrogen, sodium, potassium, beryllium, magnesium, boron, aluminum, carbon, and silicon. 

Boron has high neutron absorption and the boron-aluminum composites are being investigated for nuclear applications. Single-ply boron-epoxy composites have microwave polarization properties with potential applications in antenna and radome designs. 01... 

Group IIIB (13). Boron, Aluminum, Gallium, Indium, Thallium... 

Chaper on Boron, Aluminum, Scandium Wiley New York, 1976. 

The reader will no doubt have realized that the y-hetero rearrangement is well-known, being none other than the familiar neighboring group effect. The a-hetero rearrangement is known for all of the elements mentioned but boron, aluminum, and silicon. Perhaps a suitably constituted boron compound would rearrange to a zwitterionic product as follows ... 

Boron-aluminum-magnesium alloys, 4 137 Boron analysis, of water, 26 39 Boronate affinity chromatography, 6 403 04... 

Almond, M. J. Group 13 boron, aluminum, gallium, indium and thallium. J. Organomet. Chem. 2002, 30, 128-158. 

Since the alpha-ray impacts shattered only a minute proportion of the total number of atoms of boron, aluminum, or magnesium, the chemical identification of the products was extremely difficult. These indefatigable workers, however, accomplished even this. Although it would have been impossible to identify the products simply by ordinary chemical means, the Joliots were able to take advantage of the radioactive nature of the products formed. Since they had good reason to believe that the boron atom had captured a helion and ejected a neutron and that the new element was therefore probably an isotope of nitrogen, they heated some bombarded boron nitride with caustic soda and found that the liberated... 

Several new effective Friedel-Crafts catalysts have been developed. These include triflate93 (trifluoromethanesulfonate) derivatives of boron, aluminum, and gallium [M(0S02CF3)3]. Trichlorolanthanides have also been proved to be active reusable catalysts in benzylation.94 Superacids as catalysts are also very efficient in many Friedel-Crafts alkylations.95... 

Triflates of boron, aluminum, and gallium were found to be efficient catalysts in Friedel-Crafts acylations.46 However, these are water-sensitive materials and were required to be used in equimolar quantities to be effective. More recently various water-tolerant and recyclable triflate salts, which were also tested in alkylation, were found to exhibit similar good characteristics in Friedel-Crafts acylations. Although benzene cannot be acylated, Sc triflate,47 48 lanthanum triflates,48-51 and Hf triflate52 usually give high yields of aryl ketones in acylation with acid anhydrides. In many cases, Li perchlorate was found to accelerate the reactions.48 52... 

Pyridine readily forms stable coordination compounds. Thus, boron, aluminum and gallium trihalides react at 0°C in an inert solvent to give 1 1 adducts (cf. 85). Steric factors are important, and a-substituents decrease the ease of reaction. This is illustrated by the heats of reaction of pyridine, 2-methylpyridine and 2,6-dimethylpyridine with boron trifluoride which are 101.3, 94.1 and 73.2 kJ mol-1, respectively. The marked decrease in exothermicity here should be contrasted with the small steric requirement of the proton as shown by the pA., values of substituted pyridines (see Section 3.2.1.3.4). 

Metallic elements with low ionization energies commonly form ionic oxides. As remarked in Section 10.1, the oxide ion is a strong base, so the oxides of most of these metals form basic solutions in water. Magnesium is an exception because its oxide, MgO, is insoluble in water. However, even this oxide reacts with acids, so it is regarded as basic. Elements with intermediate ionization energies, such as beryllium, boron, aluminum, and the metalloids, form amphoteric oxides. These oxides do not react with water, but they do dissolve in both acidic and basic solutions. 

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