Borate ions reactions

Ionophoresis of Carbohydrates. Part III. Behaviour of Some Amylosaccharides and their Reaction with Borate Ions, A. B. Foster, P. A. Newton-Heam, and M. Stacey, J. Chem. Soc., (1956) 30-36. 

In equation 7.1. a 4-chloropyridine was coupled with diethyl(3-pyridyl)borane.3 The reaction was run in aqueous THF in the presence of potassium carbonate. The role of the base is to facilitate the transmetalation step through the formation of a borate ion, as organoboranes are usually not nucleophilic enough to transfer their organic moiety onto the palladium. An alternate function of the base is to increase the electrophilicity of the palladium through exchange of the halide to carbonate. 

In recent years visible photoinitiators for the formation of polymers via a radical chain reaction have also been developed. These absorb light which is blue, green, or red and also cause the polymerization of polyolacrylates, in some instances, such as encapsulated systems, with speed which is near photographic. Some of these photoinitiators provide the photochemical backbone of the nonsilver, near-photographic speed, imaging processes such as the Cycolor processes invented by the Mead Corporation. Cycolor initiators are cyanine dye, borate ion salts (4)—so-called ( +, —) ion pair... 

This question is essentially a mechanistic one in which the two candidates reaction with the diol mechanism are in rapid equilibrium with each other. Such mechanistic questions can be more properly answered by studying the kinetics of the reaction. A kinetic study of the reaction boric acid and tartaric acid has been reported (17). It was found that tartaric acid reacts with boric acid and not the borate ion. Also, the relaxation time for this reaction is near 20 msec. 

The conversion of methanol to ethanol with carbon monoxide and hydrogen has attracted considerable attention. Further carbonylation to higher alcohols occurs much more slowly, but acetic acid formation is a competing reaction and this leads to ester formation. Using CoI2 in presence of PBu 3 as catalyst, the selectivity to ethanol was improved by addition of the borate ion B4072. 399 This was attributed to an enhanced carbene-like nature of an intermediate cobalt-acyl complex by formation of a borate ester (equation 76). This would favour hydrogenolysis to... 

Since this reaction, unlike the reactions in Secs. A and B, cannot be overrun, it is often convenient to use the evaporated filtrate residues from A and B and reflux them in excess pyrazole for 2 to 3 days, thus converting all incompletely pyrazolylated species to tetrakis(l-pyrazolyl)borate ion. 

Reaction of [RuC12(C6H6)]2 (la), in acetonitrile, with pyrazole, 3,5-dimethylpyrazole, or potassium tris(3,5-dimethylpyrazolyl)borate, K[HB-(Me2pz)3], proceeds by substitution of all chlorides and affords complex 16 (Scheme 1), resulting from the coupling of acetonitrile with pyrazole (22). The reaction of la with tetrakis(l-pyrazolyl)borate ion in boiling acetonitrile, however, led to the trisubstituted derivative 17, the structure of which was established by an X-ray diffraction study (26). 

In addition to substitution of the carbonyl groups, changes in the cyclopentadienyl ring have also been extensively studied. The use of pentamethylcyclopentadiene led to formation of some of the first organometallic multiply bonded complexes as discussed in Section 4.8. The tris(pyrazolyl)borate ion (Tp , see Tris(pyrazolyl)borates) is a Cp analog." It reacts with Mo(CO)6 to yield the TpMo(CO)3 anion. Oxidation yields the paramagnetic radical that shows no tendency to form a single metal-metal bond. Decarbonylation yields a triply bonded stracture. These reactions are summarized in equation (16). 

Acetylneuram nic acid. The yield and stereoselectivity of the aldol condensation of 2-acetamido-2-dc.soxy-r>-manno.sc (1) with oxalacetic acid (2) to give N-acetyl-ncuraminic add (3) are improved by adding sodium tetraborate to (he reaction, which is carried out in aqueous solution at pH 10. Thus in the absence of borate ion, yields of (3) ofl 1.5 % have been reported, whereas addition of borate improves the yield to 21.6%. I he borate ion inhibits the alkaline cpimerization of various 2-acylamino-2-desoxy-aldoses. 

Xanthone (34) and thioxanthone (35) are smoothly reduced with diborane in tetrahydrofuran at 0 °C to give the correspxjnding xanthenes (36 and 37). The ease of this reaction is explained by the formation of a stable xanthonium ion (38), generated by elimination of the borate ion (Scheme 11). ... 

The boron cation, B, exists in aqueous solution as undissociated boric acid B(OH)3 and as the borate ion B(OH)4. Formation waters with pH values lower than 9 favor B(OH)3 as the predominant species, because the pK values for reaction (1)... 

Recently, fluoride salts have been found to effect the cross-coupling reactions of 1-alkenyl- and arylboronic acids [53]. The species that undergoes transmetallation is assumed to be the organo(trifluoro)borate ion, RBp3 (Scheme 2-19). 

In 1952, a number of publications appeared which showed that, in the presence of alkaline borate, a wide variety of neutral carbohydrates migrate toward the anode in zone electrophoresis. It is of interest to note that Coleman and Miller, in 1942, had observed the migration of n-glu-cose and maltose toward the anode when a potential was applied across their solution in aqueous borax. The reaction of polyhydric alcohols with borate ions has long been knowrf and it has been suggested that the following equilibria occur. 

A limitation of zone electrophoresis in the field of methylated sugars is the non-reaction of several polymethylated derivatives with borate ions, but, as the results in Table II testify, in the mono- and di-O-methyl series there is a much wider variation in Ma values than in Ro values. 

The similar Mg values of the anomeric methyl u-galactopyranosides and the anomeric methyl u-arabinopyranosides indicate that their reactions with borate ions are independent of configuration at the glycosidic center. 

The structures allocated on the basis of the reaction of the anomeric methyl n-fructopyranosides with borate ions (as reflected in the Mg values) are consistent with the structures allocated on the basis of their optical rotations. It is interesting to note that methyl a-n-fructopyranoside (V) and methyl /3-n-gulopyranoside (VI), which have a closely related disposition of their hydroxyl groups, have closely similar Mg values. 

Polyhydric Alcohols.—Using a borate buffer at pH 9.2, Frahn and Mills have studied the zone-electrophoretic behavior of a number of diols (see Table VII). Thus 1,4-butanediol and 1,5-pentanediol were found not to react with borate ions, indicating that borate complexes involving 7- and 8-membered rings have little tendency to be formed. The more ready reaction of comparison with the erythro isomer, is not unexpected, since the 5-membered ring in the borate complex of the latter (but not the former) would possess eclipsed methyl groups at C2 and C3. The relative reactivity of the 2,3-butanediols toward borate... 

Arenediazonium ion reactions often are complex.61 Benzenediazonium fluoro-borate in 2,2,2-trifluoro ethanol (TFE), for example, decomposes by first-order kinetics to give a mixture consisting largely of the ether (62%) formed by solvolysis and fluorobenzene (34%) resulting from reaction with fluoroborate ion. Addition of pyridine changes the kinetic order and gives rise to additional products.62 The same diazonium ion solvolyzes faster in TFE than in water. Because water is a better nucleophile than TFE, it is likely that a nucleophile is not involved in the rate limiting step of the reaction.63 ... 

Initially 1 + IO3 were in an alkaline medium. In the range pH < pH iodine was stable and in the range pH > pH I- + IO3 were stable. The initial pH-value was determined by the starting concentration of borate ions and the final pH-value by the addition of acid. If both pH-values are greater than pH, then the solution of I + IO3 remained stable and no iodine was formed. If iodine was observed, then this could only mean that segregation was present which produced a local excess of acid. The task of the boric acid was to maintain a pH > 9 at which the second reaction could not in practice take place. In a local excess of acid, iodine was produced, which was immediately complexed with I to triiodide I3, which could be measured spectrophotometrically at 353 nm. 

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