Boron halides hydrolysis

Analysis for boron, halide, free halogen, and silicon is carried out by standard methods following hydrolysis of BX3 (11,79). Specifications for BC13 and BBr3 supplied by Kerr-McGee Corp. are given in Table 2. 

It must be mentioned, however, that the order of activity of a series of initiators or coinitiators may differ depending on the identity of the other component, monomer, solvent, or the presence of competing reactions. For example, the activity of boron halides in isobutylene polymerization is observed to be BF3 > BCI3 > BBrs with water as the initiator, while the order of acidity is BBra > BCI3 > BF3. This is due to hydrolysis of the boron halides to inactive products increasing in the same order as their acidities. 

Boric Acid.9 Hydrolysis of boron halides, hydrides, etc., affords the acid, B(OH)3, or its salts. The acid forms white, needle-like crystals in which B(OH)3 units are linked together by hydrogen bonds to form infinite layers of nearly hexagonal symmetry the layers are 3.18 A apart, which accounts for the pronounced basal cleavage. 

Group III.—Boron. It has only recently been conclusively shown that the stoicheiometry of the boric acid-tartaric acid complex is 1 1. Kinetic results from T-jump experiments indicate attack by an alcohol-oxygen lone-pair at the electron-deficient boron. Other references to reaction mechanisms of three-co-ordinate boron compounds deal with hydrolysis and methanolysis of boron halides, with disproportionation of boranes, and with Sh2 radical reactions of alkylboranes. ... 

Main group dithiocarbamate complexes are generally prepared by reaction of the appropriate metal halide with the parent (hydrated) group 1 (I A) metal or ammonium dithiocarbamate salt. Few dithiocarbamate complexes of boron and aluminum have therefore been reported aluminum and boron halides are susceptible to hydrolysis, and hydroxide substitution is generally unfavorable. 

As an example of the selective reactivity of borazirconocene alkenes, their hydrolysis was examined [1]. The carbon—zirconium bond is more reactive than the carbon—boron bond towards various electrophiles, and so hydrolysis can be expected to occur with preferential cleavage of the former bond. Since hydrolysis of alkenylzirconocenes is known to proceed with retention of configuration [4,127—129], a direct utility of 45 is the preparation of (Z)-1-alkenylboronates 57 (Scheme 7.17) [12]. Though the gem-dimetalloalkenes can be isolated, in the present case it is not necessary. The desired (Z)-l-alkenylboronates can be obtained in a one-pot procedure by hydrozirconation followed by hydrolysis with excess H20. The reaction sequence is operationally simple and is compatible with various functional groups such as halides, acetals, silanes, and silyloxy protecting groups [12]. 

In general terms Suzuki coupling refers to the reaction of organic halides with boronic acids and boronates (Scheme 6.8). These compounds are fairly stable to hydrolysis, so application of aqueous solvents [7-11] is quite straightforward. 

Alkoxides are usually more difficult to hydrolyze than halides, although hydrolysis can be rapid in activated systems. Pyrimidinethiones can sometimes be hydrolyzed directly to pyrimidinones, but it is often better to convert the thiones into alkylsulfenyl, alkylsulfmyl, or alkylsulfonyl derivatives before hydrolysis <1994HC(52)1, 1996CHEC-II(6)93>. The formation of 5-hydroxypyrimidines is not normally performed using hydrolytic procedures, although it can be achieved by the oxidation of boronate species in aqueous solution <1996CC2719, 2006TL7363>. 

An alternate approach to the formation of pyridylboronic acids is the cross-coupling of a halopyridine with a diboronate ester (usually bis(pinacolato)diboron, 7.7.)9 The analogous reaction of 2-chloropyridine led to pyridine formation through protodeboronation. The product of the reaction, either after hydrolysis to the boronic acid or in the ester form, can be further reacted with another aryl halide to give a biaryl. In certain cases the reaction might also be carried out in a one-pot manner.10... 

Boranes and, to a lesser extent, boronic acids can undergo slow hydrolysis (protode-boration) in the presence of protic solvents. This unwanted reaction can become predominant if a cross-coupling reaction only proceeds slowly (e.g. with electron-rich, sterically demanding, or unreactive halides Scheme 8.20 see also Scheme 8.14) or if the boron derivative is particularly sensitive, for example 2-formylphenylboronic acid. In such instances the reaction should be performed under anhydrous conditions in an aprotic solvent with a boronic acid ester [151] or a stannane. 

The diastereoselective alkylation of /V-acyloxazolidinones enolates was examined first. Lithium enolates of 107 were reacted with a variety of alkyl halides, and alkylation products were formed with excellent diastereoselectivities (94-99% de). Hydrolysis gave optically pure carboxylic acids, and the chiral auxiliary was recovered for reuse almost quantitatively.105-106 Highly diastereoselective bromination was also achieved by reaction of the boron enolate of 107 with /V-bromosuccinimide (NBS) (98% de). Optically pure amino acids could be accessed by simple synthetic transformations (Scheme 24.26).106... 

Preparation and Uses. Boric acid can be prepared in the laboratory by acid hydrolysis of a variety of boron compounds, including halides, esters, salts, and hydrides. It is prodnced commercially by reactions of snlfinic acid with sodium borates in the United States, and with sodium and calcium borates in Turkey. In Sonth America, boric acid is prodnced by reaction of sulfuric acid with ulexite, a mixed sodium-calcium borate. Boric acid is also produced in Rnssia from the borosilicate mineral datolite. 

Some of these reactions, particularly with the strongest Lewis acids, are rapid or even violent at room temperature. In general, boron triflnoride is significantly less reactive than the other halides. For example, it forms two distinct hydrates that are stable to 20 °C. This resistance to hydrolysis and strong Lewis acid character has led to the relatively wide use of boron triflnoride as a reaction catalyst in a nnmber of organic reactions. 

Suh et al.65 have reported a formal total synthesis of Mansonone F and this is described in Scheme 12. 5-Methoxy-a-tetralone (127) was converted to 1-methyl-5-hydroxy-naphthalene (128) by the standard organic reactions. Treatment of (128) with phenyl boronic acid, paraformaldehyde and propionic acid followed by catalytic hydrogenation yielded compound (129). This on alkylation gave the compound (130) which on alkaline hydrolysis was converted to acid. The acid halide underwent intramolecular Friedal-Crafts acylation affording an intermediate (131) whose transformation to Mansonone F has been accomplished by Best and Wege.59... 

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