Tetrahydroxydiborone

Structural formula
General
Surname	Tetrahydroxydiborone
other names	Diboronic acid Hypoboric acid Subboric acid
Molecular formula	B 2 (OH) 4
Brief description	colorless crystals
External identifiers / databases
CAS number 13675-18-8 EC number 694-407-6 ECHA InfoCard 100.222.662 PubChem 10986154 Wikidata Q16294979
properties
Molar mass	89.6514 g mol −1
Physical state	firmly
density	1.657 g cm −3 (−173 ° C)
Melting point	143–148 ° C (decomposition)
solubility	very soluble in water, soluble in ethanol, DMF, DMSO, DMA
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302 + 332-315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Tetrahydroxydiboron is an inorganic chemical compound that belongs to the group of diboron compounds and can also be regarded as a boric acid . Diboron compounds can be seen formally as boron (II) compounds.

history

The compound was first described in 1937 by Egon Wiberg and Wilhelm Ruschmann as a new boric acid (subboric acid) . The synthesis started from boron trichloride , which was converted into the diester by a reaction with a substoichiometric amount of methanol .

${\displaystyle \mathrm {BCl_{3}+2\,CH_{3}OH\rightarrow B(OCH_{3})_{2}Cl+2\,HCl} }$

In the subsequent reduction with sodium , analogous to a Wurtz synthesis , the boron-boron bond was established in the tetramethoxydiboron formed .

${\displaystyle \mathrm {2\,B(OCH_{3})_{2}Cl+2\,Na\rightarrow B_{2}(OCH_{3})_{4}+2\,NaCl} }$

The tetrahydroxydiboron was then obtained by saponification of the tetramethoxydiboron.

${\displaystyle \mathrm {B_{2}(OCH_{3})_{4}+4\,H_{2}O\rightarrow B_{2}(OH)_{4}+4\,CH_{3}OH} }$

Extraction and presentation

In addition to the production from their esters, T. Wartik and EF Apple described syntheses from tetrachlorodiboron and R. Brotherton from tetra (dimethylamino) diboron in the 1950s .

properties

Physical Properties

Tetrahydroxydiboron forms colorless crystals that appear in a monoclinic crystal lattice with the space group P 2 ₁ / c (space group no. 14) . In the crystal lattice, the molecules are linked two-dimensionally via hydrogen bridges.

Chemical properties

Analogous to boric acid B (OH) ₃ , the dehydration of which gives boron trioxide B ₂ O ₃ , the dehydration of tetrahydroxydiboron leads to boron (II) oxide (BO) _x .

${\displaystyle \mathrm {B_{2}(OH)_{4}\rightarrow 2/x\,(BO)_{x}+2\,H_{2}O} }$

The water release starts at 90 ° C, with several hours of heating at 220 ° C being necessary for complete conversion.

The compound acts as a powerful reducing agent. A potassium permanganate solution is decolorized or silver is deposited from a silver nitrate solution. The aqueous solution is not stable. Even at room temperature, it slowly decomposes to boric acid with evolution of hydrogen .

${\displaystyle \mathrm {B_{2}(OH)_{4}+2\,H_{2}O\rightarrow 2\,B(OH)_{3}+H_{2}} }$

In the presence of atmospheric oxygen, boric acid is formed directly within two hours.

${\displaystyle \mathrm {B_{2}(OH)_{4}+H_{2}O+1/2\,O_{2}\rightarrow 2\,B(OH)_{3}} }$

use

In organic synthesis, the compound is used to introduce a boron substitution on the activated carbon in the molecule. A direct boronation of aromatics with palladium catalysis to form the corresponding phenyl boronic acids is possible.

In the presence of potassium hydrogen difluoride, the corresponding trifluorophenyl borates are formed

The phenyl boronic acids and the trifluorophenyl borates serve as starting materials in Suzuki couplings .

Individual evidence

1. ↑ ^{a b c d e} R. A. Baber, NC Norman, AG Orpen, J. Rossi: The solid-state structure of diboronic acid, B ₂ (OH) ₄ . In: New J. Chem. 27, 2003, pp. 773-775, doi: 10.1039 / B302496M .
2. ↑ ^{a b c} Datasheet Tetrahydroxydiboron from Sigma-Aldrich , accessed on February 28, 2014 ( PDF ).
3. ^ RJ Brotherton: The chemistry of compounds with B-B bond. In: H. Steinberg, AL McCloskey (Ed.): Progr. Boron Chem. Vol. 1, Pergamon 1964, ISBN 978-1-4832-1146-6 , pp. 1-82.
4. ↑ ^{a b c} e-EROS Encyclopedia of Reagents for Organic Synthesis , 1999-2013, John Wiley and Sons, entry for Tetrahydroxydiboron, accessed February 28, 2014.
5. ^ ^{A b c d e} E. Wiberg, W. Ruschmann: About a new boric acid ('subboric acid') of the formula H ₄ B ₂ O ₄ and its esters. In: Chem. Ber. 70, 1937, pp. 1393-1402, doi: 10.1002 / cber.19370700636 .
6. ↑ E. Wiberg, H. Smedsrud: To the knowledge of some compounds of the type BCl _{3 – n} (OR) _n . (Via alkoxyl-substituted boron chlorides). In: Z. anorg. general Chem. 202, 1931, pp. 1-21, doi: 10.1002 / zaac.19312020102 .
7. ^ H. Noeth, W. Meister: Contributions to the chemistry of boron, VI: About subcompounds of boron. Hypoboric acid tetrakis dialkylamides and hypoboric acid esters. In: Chem. Ber. 94, 1961, pp. 509-514, doi: 10.1002 / cber.19610940234 .
8. ↑ ^{a b} T. Wartik, EF Apple: A new modification of boron monoxide. In: J. Am. Chem. Soc. 77, 1955, pp. 6400-6401, doi: 10.1021 / ja01628a116 .
9. ↑ T. Wartik, EF Apple: The reactions of diboron tetrachloride with some hydrogen compounds of non-metallic elements and with dimethyl sulfide. In: J. Am. Chem. Soc. 80, 1958, pp. 6155-6158, doi: 10.1021 / ja01556a002 .
10. ^ RJ Brotherton: Method for preparing tetrahydroxydiboron. Patent US 3130009 A, priority date September 21, 1959.
11. ↑ NS Hosmane: Icons of Boron Chemistry. In: Chem. Int. Volume 34, No. 4, 2012, pp. 14-18, Link .
12. ↑ N. Turova: Inorganic Chemistry in Tables. Springer-Verlag, Berlin / Heidelberg 2011, p. 71, doi : 10.1007 / 978-3-642-20487-6_23 .
13. ^ ^{A b} S. M. Kennedy, GA Molander, SLJ Trice, SD Dreher, MT Tudge: Scope of the Palladium-Catalyzed Aryl Borylation Utilizing Bis-Boronic Acid. In: J. Am. Chem. Soc. 134, 2012, pp. 11667–11673, doi: 10.1021 / ja303181m .
14. ^ BG Davis, Z. Gao, V. Gouverneur: Enhanced Aqueous Suzuki-Miyaura Coupling Allows Site-Specific Polypeptide ¹⁸ F-Labeling. In: J. Am. Chem. Soc. 135, 2013, pp. 13612-13615, doi: 10.1021 / ja4049114 .