Tetrahydroxydiboron
{{Chembox
|IUPACName = Hypoboric acid{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/10986154#section=IUPAC-Name&fullscreen=true|title=Hypodiboric acid|work=IUPAC}}
|OtherNames = (Dihydroxyboranyl)boronic acid
Hypoboric acid
Hypodiboric acid
Sub-boric acid (Unterborsäure in German)
1,1,2,2-Tetrahydroxydiborane
|ImageFile = Tetrahydroxydiboron structure.svg
|Section1 = {{Chembox Identifiers
|CASNo = 13675-18-8
|CASNo_Ref = {{cascite|correct|CAS}}
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = D0Q7FO865W
|PubChem = 10986154
|ChemSpiderID = 9161351
|ChemSpiderID_Comment =
|ChEBI = 38289
|SMILES = B(B(O)O)(O)O
|InChI = 1S/B2H4O4/c3-1(4)2(5)6/h3-6H
|InChIKey = SKOWZLGOFVSKLB-UHFFFAOYSA-N
}}
|Section2 = {{Chembox Properties
|B = 2 | O = 4 | H = 4
|Appearance = White powder
|Density = 1.657
|Solubility = very soluble
|SolubleOther = ethanol, DMF, DMSO, DMA
}}
|Section3 = {{Chembox Structure
|CrystalStruct = monoclinic P21/c
}}
|Section4 = {{Chembox Thermochemistry
|DeltaHf = −1410.43 kJ mol−1
|Entropy = 125.46 J K−1 mol−1
|HeatCapacity =
}}
|Section7 = {{Chembox Hazards
| HPhrases = {{H-phrases|302|315|319|332|335}}
| PPhrases = {{P-phrases|261|264|270|271|280|301+312|302+352|304+312|304+340|305+351+338|312|321|330|332+313|337+313|362|403+233|405|501}}
}}
|Section8 = {{Chembox Related
|OtherCompounds = Diborane
Diboron tetrafluoride
Bis(pinacolato)diboron
}}
}}
Tetrahydroxydiboron is a chemical reagent which can be used to prepare boronic acids.{{Cite encyclopedia|encyclopedia = Encyclopedia of Reagents for Organic Synthesis|last1 = Little|first1 = Sarah|last2 = Trice|first2 = Jane|title = Tetrahydroxydiboron|year = 2001|publisher = John Wiley & Sons|isbn = 9780470842898|doi = 10.1002/047084289x.rn01181}}
Synthesis
The reaction of boron trichloride with alcohols was reported in 1931, and was used to prepare dimethoxyboron chloride, B(OCH3)2Cl.{{cite journal|last1 = Wiberg|first1 = Egon|last2 = Sütterlin|first2 = Walther|title = Zur Kenntnis einiger Verbindungen vom Typus BCl3−n(OR)n. (Über alkoxyl-substituierte Borchloride)|language = German|trans-title=Notes on some compounds of type BCl3−n(OR)n. (Via alkoxy-substituted boron chlorides)|journal = Z. anorg. allg. Chem.|year = 1931|volume = 202|issue = 1|pages = 1–21|doi = 10.1002/zaac.19312020102}} 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.{{cite journal|last1 = Wiberg|first1 = Egon|last2 = Ruschmann|first2 = Wilhelm|title = Über eine neue Borsäure ('Unterborsäure'︁) der Formel H4B2O4 und ihre Ester|journal = Ber. Dtsch. Chem. Ges. A/B|year = 1937|volume = 70|issue = 6|pages = 1393–1402|doi = 10.1002/cber.19370700636|language = de|trans-title=On a new boric acid ('Sub-boric acid') of the formula H4B2O4 and its esters}} The methanol used in this process can be recycled:
::BCl3
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.{{cite journal|last1 = Wartik|first1 = Thomas|last2 = Apple|first2 = Eugene F.|title = A New Modification of Boron Monoxide|journal = J. Am. Chem. Soc.|year = 1955|volume = 77|issue = 23|pages = 6400–6401|doi = 10.1021/ja01628a116}}
Tetrahydroxydiboron is a reducing agent. A water solution slowly gives off hydrogen gas.