Borate formation

To immobilize such anions as borate, organoboron polymers were reacted with aryllithium reagents.31,32 The reaction of alkylborane polymers with n-BuLi was examined first however, the ionic conductivity of the resulting material was very low. Moreover, complicated peaks were observed in the H-NMR spectrum. Conversely, selective lithium borate formation was observed in the nB-NMR spectrum when PhLi was employed (scheme 6). An ionic conductivity of 9.45 X 10 7Scm 1 was observed at 50°C. The observed ionic conductivity was relatively low because of the decreased number of carrier ions compared with dissolved salt systems. However, the lithium transference number of this polymer was markedly high (0.82 at 30°C). 

The reaction of silylborane with 1-halo-l-lithio-l-alkenes yields 1-boryl-l-silyl-l-alkenes via borate formation followed by 1,2-migration of silyl group (Equation (90)).76,240 The mechanism seems to be closely related to that proposed for the silaboration of isocyanide (Figure 2). Vinyl-substituted carbenoids, l-chloro-l-lithio-2-alkenes, react with silylpinacolborane to give l-boryl-l-silyl-2-alkanes in good yield (Equation (91)).241 This methodology is applied to the synthesis of l-boryl-l-silyl-2-cyclobutene.2 2 Similar reactions are carried out with other carbenoid... 

It appears that the first example of deprotonation to give a boron-stabilized carbanim was that shown in equation (9). In general, however, early attempts to deprotonate organoboranes (equation 10) foundered because borate formation (equation 11) was favored. 

The production of boron-stabilized caibanions using steric hindrance on the borane to inhibit borate formation was first demonstrated as part of a study of the properties of dimesitylboryl derivatives. Unlike the situation with dialkoxyboryl derivatives, it was possible to carry out the deprotonation with only one boron atom present and with no extra stabilizing groups. Either LDA or lithium dicyclohexylami may be used as base, the latter being rather more efficient (equation 17). The initial study showed that the reaction with MeS2BCHR R was successful with R, R = H R = H, R = Me R = H, R = Ph and R, R = Me. 

The R3AI can be substituted by R Li or R MgX, although the yields are lower (borate formation, ether cleavage). Moderate yields of cyclic triorganoboranes R2BR are obtained from the reaction between R BX2 (X = F, Cl) and dimetallated hydrocarbons (M = Li, MgX) ... 

With allowances for the actual metal content of zirconium (a small correction is also necessary for the hafnium content of about 2 /2%) and postulation of barium zirconate formation (see Table 27), reasonable accord between calculated and measured caloric output is established. However, the situation is more complex with boron mixtures where one encounters increase of heat output with increase of the percentage of boron in the mixtures much beyond the amounts of Equation (la). Thus, even with the reasonable assumption of secondary barium borate formation, the stoichiometry and heat output of the mixtures with more than about 10% of technical boron theoretical 8%) is obscure. Chromium boride formation may be a fector. 

Boron surpasses in heat output every element except hydrogen and beryllium. By itself it burns only partially, even under pure oxygen at higher pressure, forming a glassy, low-melting oxide that envelops the unburnt residue. Reactivity in mixtures, however, is complete and borate formation may contribute significantly to heat output. 

Fig. 13 (a) Simplified mechanism for the magnesium-catalyzed hydroboration of carbonyls (b) Borate formation during group 2-mediated hydroboration chemistry... 

Ion exchange Silica or polymer grafted with anionic groups (—SO3",—C02, etc.) cationic groups (-NH3+,-N(CH3)3+, etc.) Water and ionic salt anionic (phosphates, acetate, borate, formate, carbonates, etc.) cationic (hydronium, pyridinium, ammonium, etc.) Organic and inorganic ions... 

Byrne, R.H. and Thompson, S.W. (1997) Ferric borate formation in aqueous solution. J. Solution Chem., 26, 729-734. 

Allylation with allyl borates takes place smoothly under neutral conditions. Allylic alcohols are also used for allylation in the presence of boron oxide by in situ formation of allylic borates[125]. Similarly, arsenic oxide is used for allylation with allylic aleohols[126]. In addition, it was claimed that the allyl alkyl ethers 201. which are inert by themselves, can be used for the allylation in the presence of boron oxide[127]. 

Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

P-Hydroxy acids lose water, especially in the presence of an acid catalyst, to give a,P-unsaturated acids, and frequendy P,y-unsaturated acids. P-Hydroxy acids do not form lactones readily because of the difficulty of four-membered ring formation. The simplest P-lactone, P-propiolactone, can be made from ketene and formaldehyde in the presence of methyl borate but not from P-hydroxypropionic acid. P-Propiolactone [57-57-8] is a usehil intermediate for organic synthesis but caution should be exercised when handling this lactone because it is a known carcinogen. 

The equihbrium shown in equation 3 normally ties far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is compHcated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequently, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

From Boric Oxide and Alcohol. To avoid removing water, boric oxide, B2O3, can be used in place of boric acid. The water of reaction (eq. 4) is consumed by the oxide (eq. 5). Because boric acid reacts with borates at high temperatures, it is necessary to filter the reaction mixture prior to distillation of the product. Only 50% of the boron can be converted to ester by this method. In cases where this loss can be tolerated, the boric oxide method is convenient. This is particularly tme for methyl borate and ethyl borate preparation because formation of the undesirable azeotrope is avoided. 

Electrochemical Process. Several patents claim that ethylene oxide is produced ia good yields ia addition to faradic quantities of substantially pure hydrogen when water and ethylene react ia an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized ia the ethylene oxide formation are ethylene, water, and electrical energy. The electrolyte is regenerated in situ ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkah metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemicalprocessing). 

Catechols can be protected as diethers or diesters by methods that have been described to protect phenols. However, formation of cyclic acetals and ketals (e.g., methylenedioxy, acetonide, cyclohexylidenedioxy, diphenylmethylenedioxy derivatives) or cyclic esters (e.g., borates or carbonates) selectively protects the two adjacent hydroxyl groups in the presence of isolated phenol groups. 

Sodium borate (decahydrate, hydrated borax) [1303-96-4] M 381.2, m 75 (loses 5H2O at 60 ), d 1.73. Crystd from water (3.3mL/g) keeping below 55° to avoid formation of the pentahydrate. Filtered at the pump, washed with water and equilibrated for several days in a desiccator containing an aqueous solution saturated with respect to sucrose and NaCl. Borax can be prepared more quickly (but its water content is somewhat variable) by washing the recrystd material at the pump with water, followed by 95% EtOH, then Et20, and air dried at room temperature for 12-18h on a clock glass. 

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