Tetrahydroxydiboron

Tetrahydroxydiboron
Names
	IUPAC name Hypoboric acid
	Other names (Dihydroxyboranyl)boronic acid; Hypoboric acid; Hypodiboric acid; Sub-boric acid (Unterborsäure in German); 1,1,2,2-Tetrahydroxydiborane
Identifiers
CAS Number	13675-18-8 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:38289;
ChemSpider	9161351;
ECHA InfoCard	100.222.662
PubChem CID	10986154;
UNII	D0Q7FO865W ;
CompTox Dashboard (EPA)	DTXSID40450702 ;
	InChI InChI=1S/B2H4O4/c3-1(4)2(5)6/h3-6H Key: SKOWZLGOFVSKLB-UHFFFAOYSA-N;
	SMILES B(B(O)O)(O)O;
Properties
Chemical formula	B2H4O4
Molar mass	89.65 g·mol−1
Appearance	White powder
Density	1.657
Solubility in water	very soluble
Solubility	ethanol, DMF, DMSO, DMA
Structure
Crystal structure	monoclinic P21/c
Thermochemistry
Std molar; entropy (S⦵298)	125.46 J K−1 mol−1
Std enthalpy of; formation (ΔfH⦵298)	−1410.43 kJ mol−1
Hazards
	GHS labelling:
Hazard statements	H302, H315, H319, H332, H335
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Related compounds
Related compounds	Diborane; Diboron tetrafluoride; Bis(pinacolato)diboron
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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Tetrahydroxydiboron is a chemical reagent which can be used to prepare boronic acids.^[2]

Synthesis

The reaction of boron trichloride with alcohols was reported in 1931, and was used to prepare dimethoxyboron chloride, B(OCH₃)₂Cl.^[3] Egon Wiberg and Wilhelm Ruschmann used it to prepare tetrahydroxydiboron by first introducing the boron–boron bond by reduction with sodium and then hydrolysing the resulting tetramethoxydiboron, B₂(OCH₃)₄, to produce what they termed sub-boric acid.^[4] The methanol used in this process can be recycled:

BCl₃

{\ce {->[{\text{+ }}{\ce {CH3OH}}][-{\text{ }}{\ce {HCl}}]}}

B(OCH₃)₂Cl

{\ce {->[{\text{+ }}{\ce {Na}}][-{\text{ }}{\ce {NaCl}}]}}

B₂(OCH₃)₄

{\ce {->[{\text{+ }}{\ce {H2O}}][-{\text{ }}{\ce {CH3OH}}]}}

B₂(OH)₄

Overall: 2 BCl₃ + 2 Na + 4 H₂O → B₂(OH)₄ + 2 NaCl + 4 HCl

Reactions

When heated to over 90 °C, tetrahydroxydiboron dehydrates to a polymeric boron(II) oxide. The temperature must rise to 220 °C to be totally free from water.^[5]

Tetrahydroxydiboron is a reducing agent. A water solution slowly gives off hydrogen gas.^[4]

References

^ "Hypodiboric acid". IUPAC.
^ Little, Sarah; Trice, Jane (2001). "Tetrahydroxydiboron". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289x.rn01181. ISBN 9780470842898.
^ Wiberg, Egon; Sütterlin, Walther (1931). "Zur Kenntnis einiger Verbindungen vom Typus BCl_3−n(OR)_n. (Über alkoxyl-substituierte Borchloride)" [Notes on some compounds of type BCl_3−n(OR)_n. (Via alkoxy-substituted boron chlorides)]. Z. anorg. allg. Chem. (in German). 202 (1): 1–21. doi:10.1002/zaac.19312020102.
^ ^a ^b Wiberg, Egon; Ruschmann, Wilhelm (1937). "Über eine neue Borsäure ('Unterborsäure'︁) der Formel H₄B₂O₄ und ihre Ester" [On a new boric acid ('Sub-boric acid') of the formula H₄B₂O₄ and its esters]. Ber. Dtsch. Chem. Ges. A/B (in German). 70 (6): 1393–1402. doi:10.1002/cber.19370700636.
^ Wartik, Thomas; Apple, Eugene F. (1955). "A New Modification of Boron Monoxide". J. Am. Chem. Soc. 77 (23): 6400–6401. doi:10.1021/ja01628a116.

[1] "Hypodiboric acid". IUPAC.

[2] Little, Sarah; Trice, Jane (2001). "Tetrahydroxydiboron". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289x.rn01181. ISBN 9780470842898.

[3] Wiberg, Egon; Sütterlin, Walther (1931). "Zur Kenntnis einiger Verbindungen vom Typus BCl_3−n(OR)_n. (Über alkoxyl-substituierte Borchloride)" [Notes on some compounds of type BCl_3−n(OR)_n. (Via alkoxy-substituted boron chlorides)]. Z. anorg. allg. Chem. (in German). 202 (1): 1–21. doi:10.1002/zaac.19312020102.

[Wiberg-4] Wiberg, Egon; Ruschmann, Wilhelm (1937). "Über eine neue Borsäure ('Unterborsäure'︁) der Formel H₄B₂O₄ und ihre Ester" [On a new boric acid ('Sub-boric acid') of the formula H₄B₂O₄ and its esters]. Ber. Dtsch. Chem. Ges. A/B (in German). 70 (6): 1393–1402. doi:10.1002/cber.19370700636.

[5] Wartik, Thomas; Apple, Eugene F. (1955). "A New Modification of Boron Monoxide". J. Am. Chem. Soc. 77 (23): 6400–6401. doi:10.1021/ja01628a116.

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