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The Borate Minerals are minerals which contain a borate anion group. The borate (BO 3) units may be polymerised similar to the SiO 4 unit of the silicate mineral class. This results in B 2 O 5, B 3 O 6, B 2 O 4 anions as well as more complex structures which include hydroxide or halogen anions. [2] The [B(O,OH) 4] − anion exists as well.
An important synthetic application using such dialkylboranes, such as diethylborane, is the transmetallation of the organoboron compounds to form organozinc compounds. [9] [10] Some diaryl and dialkylboranes are well known. Dimesitylborane is a dimer (C 6 H 2 Me 3) 4 B 2 H 2). It reacts only slowly with simple terminal alkenes.
Borate ions occur, alone or with other anions, in many borate and borosilicate minerals such as borax, boracite, ulexite (boronatrocalcite) and colemanite. Borates also occur in seawater, where they make an important contribution to the absorption of low frequency sound in seawater. [1] Borates also occur in plants, including almost all fruits. [2]
Trimethyl borate is a popular borate ester used in organic synthesis. Borate esters form spontaneously when treated with diols such as sugars and the reaction with mannitol forms the basis of a titrimetric analytical method for boric acid. Metaborate esters show considerable Lewis acidity and can initiate epoxide polymerization reactions. [4]
Sodium borate is a generic name for any salt of sodium with an anion consisting of boron and oxygen, and possibly hydrogen, or any hydrate thereof. It can be seen as a hydrated sodium salt of the appropriate boroxy acid , although the latter may not be a stable compound.
Borates are formed when boron bearing solutions, caused from the leaching of pyroclastic rocks, flow into isolated basins where evaporation then takes place. Over time, borates deposit and form into stratified layers. Ulexite occurs in salt playas and dry saline lakes in association with large-scale gypsum deposits and Na-Ca borates. [8]
Calcium borate (Ca 3 (BO 3) 2). It can be prepared by reacting calcium metal with boric acid. The resulting precipitate is calcium borate. A hydrated form occurs naturally as the minerals colemanite, nobleite and priceite. [citation needed] One of its uses is as a binder in some grades of hexagonal boron nitride for hot pressing.
The α form consists of infinite chains of trigonal planar metaborate anions [BO 2 O −]n. The γ form is stable at 15 kbar and 950 °C. It has a polymeric cation consisting of a tridimensional regular array of [B(O−) 4] − tetrahedra sharing oxygen vertices, alernating with lithium cations, each also surrounded by four oxygen atoms.