Borinic acid

Borinic acid, also known as boronous acid, is an oxyacid of boron with formula H
₂BOH. Borinate is the associated anion of borinic acid with formula H
₂BO⁻
; however, being a Lewis acid, the form in basic solution is H
₂B(OH)⁻
₂.

Borinic acid

Names
IUPAC name Borinic acid
Systematic IUPAC name Boranol
Other names Boranol, Hydroxyborane, Dihydridohydroxidoboron
Identifiers
CAS Number	35825-58-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:38268 Y
ChemSpider	10706664
Gmelin Reference	141192
PubChem CID	13323622
InChI InChI=1S/BH3O/c1-2/h2H,1H2 Key: UYANAUSDHIFLFQ-UHFFFAOYSA-N
SMILES BO
Properties
Chemical formula	BH3O
Molar mass	29.83 g·mol−1
Solubility in water	reaction in water
Structure
Molecular shape	distorted trigonal bipyramid
Related compounds
Related compounds	Boronic acid Boric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N (what is YN ?) Infobox references

General chemical structure of borinic acids (organoborinic acids)

General chemical structure of borinate esters

Borinic acid can be formed as the first step in the hydrolysis of diborane:^[1]

BH₃ + H₂O → H₂BOH + H₂

Borinic acid itself is unstable and only lasts for a few seconds during the hydrolysis reaction. However, by using microwave spectroscopy various properties can be determined. The B-O distance is 1.352 Å, O-H distance 0.96 Å, B-H length is probably 1.2 Å. The angle between bonds at the oxygen atom BOH = 112° and the angles at boron are cis-HBO 121°, and trans-HBO = 117°. The dipole moment is 1.506 Debye.^[2]

Borinic acid can form esters such as methoxyborane. This too is unstable only lasting about ten seconds. It can be formed by heating diborane and methanol gas together.^[3]

By substituting organic components instead of hydrogen, more generic borinic acids (containing RR'BOH) or borinic esters (RR'BOR") can be formed. Esters will tend to be stable in acidic conditions, but in alkaline conditions the boron atom can gain a negative charge and attach two hydroxyl groups, or two ester bonds. RR'B⁻(OH)₂ or RR'B⁻(OR")₂. The anionic borinate ion can very easily form esters with diols such as ethylene glycol or sugars.^{[citation needed]}

Naming

The IUPAC name borinic acid is a unique name for the acid.^[4] The anhydrides are named diboroxanes, H₂BOBH₂, as the base compound and H being able to be substituted, e.g. tetraethyldiboroxane, as the anhydride for diethylborinic acid. Organic naming standard in the Bluebook allows skeletal replacement naming where the name is shorter, 3-borapentan-3-ol versus diethyl borinic acid. The grouping -BH-O-BH₂ is called diboroxanyl. Substituting sulfur for oxygen gives borinothioic acid (H₂BSH). (Dimethylboranyl)oxy is used for the group (CH₃)₂B-O− and methyl(hydroxy)boranyl for the grouping CH₃B(OH)-.

Formation

There are several ways to produce substituted borinic acids.^[5]

Firstly borinic acids can be made from oxidizing trialkylborane starting materials (R₃B) with exposure to moist air, or treatment with iodine, which makes a dialkyliodoborane (R₂BI). Hydrolysis then results in the boronic acid (R₂BOH).^[5] Trialkylborates [(RO)₃B] or trialkoxyboroxine [(ROBO)₃] can be reduced to borinic acid by us of a Grignard reagent. Grignard reagents can also reduce a boronic ester [RB(OR')₂] to a borinic ester.^[5]

Bu₃B + N2CHCOR → BuCH=C(R)OBBu₂

Bu₃B + CH2=CHCOCH₃ → BuCH₂CH=C(CH₃)OBBu₂

RCOC₂H₅ + R₂BOTf → RC(OBR₂)=CHCH₃

(Tf = Trifluoromethanesulfonate)

(Z)-Enolates give syn aldol product when reacted with an aldehyde, whereas (E)-enolates give and anti aldol products.

Dialkyl boron chloride (R₂BCl) with tertiary amine react with ketones to form an enol borinate.^[6]

A trialkoxyborane can react with lithium containing organic molecules to eliminate lithium and one or two alkoxy groups to make boronic and borinic esters.^[7]

Purification of the mixtures that result from the reactions is required, as often boronic esters will also be produced and mixed in with the borinic esters.^[5] The method of Letsinger is to dissolve the mixture in ether and precipitate the borinic ester by forming a complex with ammonia. Treatment with ethanolamine ends up making an aminoetylborinate.^[5]

Compounds

A wide variety of borinic acids, anhydrides ((R₂B)₂O), and esters (R₂BOR′) are known.^[8][9]

2-APB

2-aminoethyl-diphenylborinate

2-Aminoethoxydiphenyl borate (2-APB) inhibits transient receptor potential channels.^[10] This kind of inhibition, particularly inhibition of TRPM7, is being studied to find treatments for prostate cancer. 2-APB can work as a catalyst to add an alkyl group from an alkyl halide to a polyol or carbohydrate that contains a cis-vicinal diol to a precise position. It does this by first combining with the two hydroxy groups to make a ring containing OCCOB⁻.^[11] It can also calatlyse acid chloride or chloroformate reaction a specific region of the diol.^[12]

Diphenylborinic acid

Diphenylborinic acid was discovered in 1894 by Michaelis who produced it by hydrolyzing the chloride. Letsinger determined its properties in 1955.^[5]

Diphenylborinic acid has an extra high affinity for catechols compared with carbohydrates.^[13]

Diphenylborinic acid can catalyse the condensation of pyruvic acids with aldehydes to yield substituted isotetronic acid.^[14]

Diphenylborinic acid is an inhibitor of several enzymes such as α-chymotrypsin, subtilisin BPN', and trypsin.^[15]

Borinate radical

Borinate radicals (RR'BO^·) can be formed from peroxyborinate decomposition.^[16]

Other compounds

Other compounds include methoxy(dimethyl)borane, methoxy(methyl)boron, methoxy(methylidene)borane (with a C=B double bond).^[17]

[C₅H₅BR]⁻ uses a B⁻ to be equivalent to carbon in an aromatic benzene like ring. This too is called borinate. The 1-methyl and 1-phenyl borinates can form some of the few organo-thallium(I) compounds.^[18]

HB(C₆F₅)₂ + phosphino alcohol → ^tBu₂P⁺HCH₂C(CH₃)₂OB⁻H(C₆F5)₂ → H₂ + ^tBu₂PCH₂C(CH₃)₂OB(C₆F5)₂ and same for ^tBu₂PCH₂C(CF₃)₂OB(C₆F5)₂^[19]

di-Tris(tert-butoxy)siloxy borinic acid HOB[OSi(O(t)Bu)₃]₂ can be made from tributoxyborate and tributoxysiloxane. It can form a very complex crystal with Cp₂Zr(Me)[OB[OSi(O(t)Bu)₃]₂]₂.^[20]

Diborinic acids have two RBOH groups linked together by an organic connection such as diphenyl or phenyl.^[21]

Applications

1,1,1,3,3,3-Hexafluoroisopropylbis(pentafluorophenyl)borinate can greatly increase solubility of LiF by complexing the F⁻ anion.^[22] This has potential to improve lithium batteries.

Borinic esters are being researched as bacterial growth inhibitors^[23] due to their ability to disable some bacterial enzymes such as menaquinone methyltransferase and CcrM.^[24] This may result in development of treatments for topical application on skin.^[25]

References

1. Weiss, H. G.; Shapiro, I. (5 March 1953). "Mechanism of the Hydrolysis of Diborane in the Vapor Phase1". Journal of the American Chemical Society. 75 (5): 1221–1224. doi:10.1021/ja01101a061.
2. Kawashima, Yoshiyuki; Takeo, Harutoshi; Matsumura, Chi (1 January 1981). "Microwave spectrum of borinic acid BH₂OH". The Journal of Chemical Physics. 74 (10): 5430. Bibcode:1981JChPh..74.5430K. doi:10.1063/1.440947.
3. Kawashima, Y.; Takeo, H.; Matsumura, C. (1984). "Microwave Spectrum of Methoxyborane, CH₃OBH₂". Ohio State University. hdl:1811/16666.
4. Connelly, Neil G.; Damhus, Ture; Hartshorn, Richard M.; Alan T. Hutton (2005). "Table IR-8.1 Acceptable common names". Nomenclature of Inorganic Chemistry. International Union of Pure and Applied Chemistry. p. 127. ISBN 0-85404-438-8.
5. Povlock, Thomas Paul (August 1960). "Boroxines: Their Reactions and Ring Stability" (PDF). Archived from the original (PDF) on 5 March 2016. Retrieved 5 October 2013.
6. Brown, Herbert C; Rhaj K. Dhar (March 16, 1989). "Major Effect of the Leaving Group in Dialkyl Boron Chlorides and Triflates in COntrolling the Stereoscopic COnversion of Ketones into Either [E] or [Z]- Enol Borinates" (PDF). Archived from the original (PDF) on March 3, 2016. Retrieved 25 September 2013.
7. Delbrayelle, Dominique (15 June 2010). "Boronic Acids Manufacture at Industrial Scale" (PDF). Archived from the original (PDF) on 28 June 2013. Retrieved 5 October 2013.
8. US Abandoned 20020161230, Erbes, Michael; Forstinger, Klaus & Meudt, Andreas, "Process for preparing boronic and borinic acids", published 31 Oct 2002, assigned to Clariant GmbH
9. Povlock, Thomas Paul (August 1960). Boroxines: Their Reactions and Ring Stability (PDF) (PhD thesis). UFl. Archived from the original (PDF) on 5 March 2016. Retrieved 5 October 2013.
10. Carboxylic Acids—Advances in Research and Application. ScholarlyEditions. 2012. p. 93. ISBN 978-1-4649-9392-3.
11. Chan, Lina; Taylor, Mark S. (17 June 2011). "Regioselective Alkylation of Carbohydrate Derivatives Catalyzed by a Diarylborinic Acid Derivative". Organic Letters. 13 (12): 3090–3093. doi:10.1021/ol200990e. PMID 21591630.
12. Lee, Doris; Taylor, Mark S. (23 March 2011). "Borinic Acid-Catalyzed Regioselective Acylation of Carbohydrate Derivatives". Journal of the American Chemical Society. 133 (11): 3724–3727. doi:10.1021/ja110332r. PMID 21355584.
13. Chudzinski, Michael G.; Chi, Yuechuan; Taylor, Mark S. (1 January 2011). "Borinic Acids: A Neglected Class of Organoboron Compounds for Recognition of Diols in Aqueous Solution". Australian Journal of Chemistry. 64 (11): 1466. doi:10.1071/CH11294.
14. Lee, Doris; Newman, Stephen G.; Taylor, Mark S. (3 December 2009). "Boron-Catalyzed Direct Aldol Reactions of Pyruvic Acids". Organic Letters. 11 (23): 5486–5489. doi:10.1021/ol902322r. PMID 19904926.
15. Steiner, Steven J.; Bien, Jeffrey T.; Smith, Bradley D. (1 October 1994). "Diphenylborinic acid is a strong inhibitor of serine proteases". Bioorganic & Medicinal Chemistry Letters. 4 (20): 2417–2420. doi:10.1016/S0960-894X(01)80401-7.
16. Robin Hicks (2 August 2011). Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron Compounds. John Wiley and Sons. p. 518. ISBN 978-1-119-95696-9.
17. "Similar compounds". Retrieved 4 October 2013.
18. Janiac (1997). "(Organo) thallium (I) and (II) chemistry: syntheses, structures, properties and applications of subvalent thallium complexes with alkyl, cyclopentadienyl, arene or hydrotris (pyrazolyl) borate ligands". Coordination Chemistry Reviews. 163: 124. doi:10.1016/s0010-8545(97)00011-8.
19. Chapman, Andy M.; Haddow, Mairi F.; Orton, Jonathan P. H.; Wass, Duncan F. (1 January 2010). "Facile dihydrogen release from phosphino-borinate ester Lewis pairs". Dalton Transactions. 39 (27): 6184–6. doi:10.1039/c0dt00513d. PMID 20544115.
20. Fujdala, KL; Oliver, A. G.; Hollander, F. J.; Tilley, T. D. (Feb 24, 2003). "Tris(tert-butoxy)siloxy derivatives of boron, including the boronous acid HOB[OSi(O(t)Bu)(3)](2) and the metal (siloxy)boryloxide complex Cp(2)Zr(Me)OB[OSi(O(t)Bu)(3)](2): a remarkable crystal structure with 18 independent molecules in its asymmetric unit". Inorganic Chemistry. 42 (4): 1140–1150. doi:10.1021/ic0205482. PMID 12588150.
21. Suzuki, Akinobu Z.; Shoichiro Ozaki, Jun-Ichi Goto Katsuhiko Mikishiba (15 Feb 2010). "Synthesis of bisboron Compounds and their Strong Inhibitory Activity on Store-operated Calcium Entry". Bioorganic & Medicinal Chemistry Letters. 20 (4): 1395–1398. doi:10.1016/j.bmcl.2009.12.108. PMID 20097561.
22. McBreen, J.; H. S. Lee; X. Q. Yang (2003). "Borinates: A New Family of Anion Complexing Agents" (PDF). The Electrochemical Society, Inc. Retrieved 25 September 2013.
23. Bailey, P. J.; G Cousins; G A Snow; A J White (April 1980). "Boron-containing antibacterial agents: effects on growth and morphology of bacteria under various culture conditions". Antimicrobial Agents and Chemotherapy. 17 (4). American Society for Microbiology: 549–553. doi:10.1128/aac.17.4.549. PMC 283830. PMID 6994634.
24. Benkovic SJ, Baker SJ, Alley MR, Woo YH, Zhang YK, Akama T, Mao W, Baboval J, Rajagopalan PT, Wall M, Kahng LS, Tavassoli A, Shapiro L (1 November 2005). "Identification of Borinic Esters as Inhibitors of Bacterial Cell Growth and Bacterial Methyltransferases, CcrM and MenH". Journal of Medicinal Chemistry. 48 (23): 7468–7476. doi:10.1021/jm050676a. PMID 16279806.
25. Baker SJ, Akama T, Zhang YK, Sauro V, Pandit C, Singh R, Kully M, Khan J, Plattner JJ, Benkovic SJ, Lee V, Maples KR (2006). "Identification of a novel boron-containing antibacterial agent (AN0128) with anti-inflammatory activity, for the potential treatment of cutaneous diseases". Bioorg. Med. Chem. Lett. 16 (23): 5963–7. doi:10.1016/j.bmcl.2006.08.130. PMID 16997550.

Extra reading

• Dimitrijević, Elena; Taylor, Mark S. (3 May 2013). "Organoboron Acids and Their Derivatives as Catalysts for Organic Synthesis". ACS Catalysis. 3 (5): 945–962. doi:10.1021/cs4000848. Review of use borinic acids as a catalyst
• Roth, HJ; Miller, B (September 1964). "Synthesis of Phenyl- and Thienyl-Substituted Boronic and Borinic Acids". Archiv der Pharmazie. 297 (9): 513–523. doi:10.1002/ardp.19642970902. PMID 14341914. S2CID 95181696.