Preparation of organoboron compounds

Some of the most useful organoboron compounds are ethers of boric acid, trialkyl(aryl)borates. There are several techniques for producing these ethers  

The formed sodium metaborate can be transformed back into borax with carbon dioxide  

Of practical interest are the last two techniques for producing trialkylbo-rates. It should be noted however, that the industrial reaction of boric anhydride with alcohols is fraught with difficulties. E.g., when powderlike boric anhydride is introduced into alcohol, clumps should be broken lest they kill the reaction. If boric anhydride is used in the form of pieces, the reaction should be conducted under an increased pressure and alcohol should be dehydrated beforehand. Thus, the most technological method is to obtain trialkyl(aryl)borates by the interaction of boric acid with alcohols. 

The synthesis of trimethylborate is based on the reaction of methyl alcohol with boric acid  

Trimethylborate forms an azeotropic mixture with the excess of methyl alcohol, which boils approximately at 55 °C. To separate the mixture and extract pure trimethylborate, there are several techniques to flush methyl alcohol with sulfuric acid to separate methyl alcohol with the help of calcium chloride, lithium chloride or other alcohol-soluble salts to distil methyl alcohol (in the form of azeotropic mixture with trimethylborate, which boils under a lower temperature than both components) with subsequent extraction of trimethylborate with mineral oil, etc. 

---

Secondary amines have been prepared from organoboron compounds R1315, R12 BC1 or R1BCI2 (R1 = Et, Bu, /-Bu,, v-Bu, 3-hexyl, cyclopentyl etc.) by treatment with azides R2N3 (R2 = Bu, /-Bu, i-Bu, cyclohexyl, Ph etc.) and aqueous work-up. It is suggested that the reactions proceed by way of anionotropic rearrangements (equation 61)176. 

Borazarophenanthrene was the first representative of a new class of heteroaromatic compounds containing boron atoms in six-membered aromatic rings.4 These compounds are of a different order of stability from previously known types of organoboron compounds, being chemically similar to normal aromatics, and their discovery has opened up a new field of aromatic chemistry. The procedure indicated here has been used to prepare a large number of related aromatic systems. 

These syntheses of all three elements have been widely used — those of organoboron compounds often as a prelude to further transformations (see Section 15.4, Ref. [1]), those of organosilicon compounds often to characterize organomagnesium reagents, and those of organophosphorus compounds often to prepare phosphine ligands. 

Boronic acids and boronate esters serve a myriad of purposes, and the discovery of the Suzuki-Miyaura reaction facilitated the widespread interest and application of organoboron compounds. This palladium-catalyzed C-C bond forming reaction initiated renewed interest in the preparation of diversely functionalized boronic acids that would lead to valuable products. From this synthetic standpoint, Suzuki coupling reactions have been employed in the production of natural products and the preparation of materials of interest. " The search for interesting starting materials for the Suzuki reaction produced a series of methods to prepare boronic acids so these species could be exploited in further applications. These compounds... 

What hydrocarbon would you use to prepare the organoboron compound of Problem 13 ... 

---