Boric ester complex

The BF2 chelates are hydrolytically stable (the majority of them may be recrystallized from water) whereas the BC12 chelates are easily hydrolyzed. The boric acid ester complex triptych boroxazolidines are also stable towards hydrolysis as are other aminoalcohol esters.83 A great number of the boron chelates are colored several spectrophotometric methods are based on chelate formation81 84 for the analytical determination of boric acid, organoboric acids and chelating organic compounds. The boron chelates are remarkable for their pharmacological properties as well.84 Various aspects of the boron chelates have been reviewed.81,83-86... 

Among the many hydroborating agents developed over the years,337 catecholbor-ane, a boric ester derivative, exhibits decreased reactivity359 It has since been observed, however, that the addition can be greatly accelerated by transition-metal complexes.360,361 Most of the studies focused on Rh(I) catalysts 361... 

Hydroboration. Although hydroboration seldom requires a catalyst, hydrobora-tion with electron-deficient boron compounds, such as boric esters, may be greatly accelerated by using transition-metal catalysts. In addition, the chemo-, regio- and stereoslectivity of hydroboration could all be affected. Furthemore, catalyzed hydroboration may offer the possibility to carry out chiral hydroboration by the use of catalysts with chiral ligands. Since the hydroboration of alkynes is more facile than that of alkenes the main advantage of the catalytic process for alkynes may be to achieve better selectivities. Hydroboration catalyzed by transition-metal complexes has become the most intensively studied area of the field.599... 

The direct oxidation of paraffin by atmospheric oxygen is a non-selective reaction which yields a complex mixture of alcohols, ketones, acids and esters. It was used in Germany during the Second World War to manufacture fatty acids. The orientation of this reaction towards the production of alcohols results from research by the Japanese Nobori and Kawai f1943) and the Russian Bashkirov 1956). Alcohol selectivity in relation to the other oxidation products derives from the use of boric acid which withdraws the secondary alkyl hydroperoxides from any subsequent oxidation by converting them to stable boric esters. ... 

Boric acid forms ester complexes with hydroxyl groups of organic compounds preferably occurring when the hydroxyl groups are adjacent and cis (Hunt 1998). The importance of the proper hydroxyl arrangement is demonstrated by the fact that poly-... 

Xylitol reacted with boric acid under reduced pressure to give mixtures of boric esters and polymeric xylitol-borate complexes, and a cryoscopic study of the borate complexes formed by pentaerythritol has been reported. N.m.r. spectroscopic studies have confirmed that borax complexes with HO-1 and -2 and with HO-3, -5, and -6 of D-glucose in the a-furanose form to give bidentate and terdentate complexes, respectively. Only those D-glucobioses that are (1 3)- or (1 6)-linked formed complexes with borax. 

The "allyl shift" in accordance with an Sf2 process is typical for all 2-alkenylborane or -boronate reactions with electrophiles unless ate complexes get involved. This also holds for protodeborylations. The metalation of a 2-alkene or cycloalkene with a superbase followed by condensation with a boric ester or fluorodimethoxyborane and acidification results in the "counterthermodynamic" transformation of an internal into a terminal olefin (Scheme 1-19). ... 

Methylation of Inorganic oxyarsenic anions occurs in organisms ranging from microbial to mammalian methylated and products include arsenocholine, arsenobetaine, dimethylarsinic acid, and methylarsonic acid arsenite methyltransferase and monomethylarsonic acid methyltransferase use S-adenosylmethionine for the methyl donor Boron biochemistry essentially that of boric acid, which forms ester complexes with hydroxyl groups, preferably those adjacent and cis, in organic compounds. Five naturally occurring boron esters (all antibiotics) synthesized by various bacteria have been characterized Exists as Br Ion in vivo, binds to proteins and amino acids... 

Alcohols react with boric acid with elimination of water to form borate esters, B(OR)3. A wide variety of borate salts and complexes have been prepared by the reaction of boric acid and inorganic bases, amines, and heavy-metal cations or oxyanions (44,45). Fusion with metal oxides yields... 

Figure 17-14. Formation of complexes of boric acid with glycerol. Three hydroxyl units form an ester and one unit forms a complex bond. Here a proton will be released that lowers the pH. The scheme is valid also for polyhydroxy compounds. In this case, two polymer chains are connected via such a link.

When aldehydes, with or without a hydrogen, are treated with aluminum ethoxide, one molecule is oxidized and another reduced, as in 9-69, but here they are found as the ester. The process is called the Tishchenko reaction. Crossed Tishchenko reactions are also possible. With more strongly basic alkoxides, such as magnesium or sodium alkoxides, aldehydes with an a hydrogen give the aldol reaction. Like 9-69, this reaction has a mechanism that involves hydride transfer.751 The Tishchenko reaction can also be catalyzed752 by ruthenium complexes.753 by boric acid,754 and, for aromatic aldehydes, by disodium tetracarbonylferrate Na2Fe(CO)4,755 OS I, 104. 

At equilibrium the diol-boric acid ester or complex can have a diol to boron ratio of 1 to 1, 2 to 1, or both. 

If it is true that the structural form of D-glucose which reacts with boric acid is the a-D-pyranose form, then that form probably exists in a boat or twist conformation in the complex. This implies that the study of the stability constants of sugar borate ester might give information about the ability of various carbohydrates to form such boat or twist conformations (10, 21). 

The constitution of the fairly strong complex acids formed from alkyl borates and alcohol and of esters of boric acid with polyalcohols with hydroxyl groups in the cis position (Boese-ken) must be similar ... 

Poly(vinyl alcohol) is utilized as a component of starch-based adhesives.11121114 Other patents report the use of partially oxidized starch,1115 dextrins,1116 dextrins and urea,1117 borax,1118 boric acid,1119 and vinyl methyl ether-maleic acid copolymers.1120 Other patents indicate the use of poly (vinyl alcohol) with partially hydrolyzed poly(vinyl acetate),1121 nonhy-drolyzed poly(vinyl acetate),1122 and poly(vinyl chloride).1123 A few patents have reported such poly acrylic additives as poly (acrylic acid)1124 and its salts,1125 poly(acrylamide),1126 1127 A-methylacrylamide or poly(A-acryl-amide),1128 and polyethyleneimine.1129 Polystyrene has also been used,1130 as well as more complex copolymers such as a maleic acid monobutyl ester-methyl vinyl ether copolymer, together with dextrin and polyacrylamide),1131 carboxylated ethyl acrylate-styrene zinc salt copolymer,1132 ethylene-methyl acrylate-vinyl acetate copolymer,1133 vinyl acetate-vinyl pyr-rolidone copolymer,1134 and ethylene-vinyl acetate copolymer.1135 Some adhesives are compounded with SBR latex1136 1138 and phenol-formaldehyde resins.1139... 

Ebelman and Bouquet prepared the first examples of boric acid esters in 1846 from boron trichloride and alcohols. Literature reviews of this subject are available. B The general class of boric acid esters includes the more common orthoboric acid based trialkoxy- and triaryloxyboranes, B(0R)3 (1), and also the cyclic boroxins, (ROBO)3, which are based on metaboric acid (2). The boranes can be simple trialkoxyboranes, cyclic diol derivatives, or more complex trigonal and tetrahedral derivatives of polyhydric alcohols. Nomenclature is confusing in boric acid ester chemistry. Many trialkoxy- and triaryloxyboranes such as methyl, ethyl, and phenyl are commonly referred to simply as methyl, ethyl, and phenyl borates. The lUPAC boron nomenclature committee has recommended the use of trialkoxy- and triaryloxyboranes for these compounds, but they are referred to in the literature as boric acid esters, trialkoxy and triaryloxy borates, trialkyl and triaryl borates or orthoborates, and boron alkoxides and aryloxides. The lUPAC nomenclature will be used in this review except for relatively common compounds such as methyl borate. Boroxins are also referred to as metaborates and more commonly as boroxines. Boroxin is preferred by the lUPAC nomenclature committee and will be used in this review. 

The macrocyclization has been accelerated by heating the reaction mixture in a flask fitted with a reflux condenser. With alkoxy-containing complexes, care must be taken since upon inefficient cooling low-boiling boric acid esters can be distilled off, whereby the product yield is drastically reduced. In some cases, an appreciable effect has been observed when the water from the reaction mixture has been distilled off as azeotrope [47]. The preformed FeDm3(BOH)2 complex has undergone esterification in alcohol medium to give alkoxyboron-capped macrobicyclic compounds. Compounds of this type can also arise from transesterification of preformed complexes (Scheme 6) [47]. 

The reaction of alkenes with borane, monoalkyl and dialkylboranes leads to a new organoborane (see 15-16). Treatment of organoboranes with alkaline H2O2 oxidizes trialkylboranes to esters of boric acid." This reaction does not affect double or triple bonds, aldehydes, ketones, halides, or nitriles that may be present elsewhere in the molecule. There is no rearrangement of the R group itself, and this reaction is a step in the hydroboration method of converting alkenes to alcohols (15-16). The mechanism has been formulated as involving initial formation of an ate complex when the hydroperoxide anion attacks the electrophilic boron... 

Unprotected aldoses and ketoses can be reduced to afford alditols while aldonolactones can be reduced to give either aldoses or alditols. The reagent of choice for reduction to alditols is sodium borohydride since it is both cheap and convenient to use. The reduction is carried out under mild conditions at room temperature in an aqueous solution. Sodium borohydride is stable in water at pH 14 while it reacts with the solvent at neutral or slightly acidic pH, but at a slower rate than the rate of carbonyl reduction. In some cases, the product will form esters with the generated boric acid. These borate complexes can be decomposed by treatment with hydrochloric acid or a strongly acidic ion-exchange resin and the boric acid can be removed in the work-up as the low boiling trimethyl borate by repeated co-evaporation with methanol at acidic pH [155]. 

Few medicines based on boron are known, in general boric acid or a boronic acid serve to esterify an a-diol or an ortho-diphenol. This is the case for the emetic antimony borotartrates of the ancient pharmacopoieas, for the injectable catecholamine solutions, for tolboxane " , that is close to meprobamate and that was commercially available as a tranquilhzer some decades ago, or also for the phenylbo-ronic esters of chloramphenicol. " Boromycine was the first natural product containing boron isolated. " It is a complex between boric acid and a polyhydroxylated tet-radentate macrocycle. " Another natural product is aplas-momycin with antibiotic properties. " " ... 

D-mannopyranose), as demonstrated by paper electrophoresis, and (c) boric acid.106,114 Levoglucosan (6) does not itself show any tendency to form either similar anionic complexes392-395 or complexes with boric acid and its derivatives106,301,394,396,397 nevertheless, complexes with methanolic sodium acetate and potassium398 or sodium iodide,387 and with alkali hydroxides have been described.397,399,400 A zinc-ferric complex of levoglucosan of undefined structure,401,402 and complexes of levoglucosan esters with Lewis acids, have been prepared. 

Most esters and complexes between boric acid and borate ions, respectively, and polyhydroxy compounds can be formulated as follows ... 

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