Sodium metaborate

Sodium metaborate monomer

Sodium metaborate trimer

Names
IUPAC name

Sodium metaborate

Identifiers

CAS Number

* 7775-19-1 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:75227

ECHA InfoCard | 100.028.992
EC Number |

* 231-891-6

PubChem CID

* 145326

RTECS number |

* ED4640000

UNII |

* Z6Q395A23R Y

CompTox Dashboard (EPA)

* DTXSID2034386

InChI

* InChI=1S/BO2.Na/c2-1-3;/q-1;+1

Key: NVIFVTYDZMXWGX-UHFFFAOYSA-N

SMILES

* B(=O)[O-].[Na+]

Properties

Chemical formula

| NaBO2
Molar mass | 65.80 g·mol−1
Appearance  | Colorless crystals
Odor | Odorless
Density | 2.464 g/cm3 (anhydrous)[1]
Melting point | 966 °C (1,771 °F; 1,239 K)
Boiling point | 1,434[2] °C (2,613 °F; 1,707 K)

Solubility in water

| 16.4 g/(100 mL) (0 °C)
28.2 g/(100 mL) (25 °C)
125.2 g/(100 mL) (100 °C)
Solubility | insoluble in ether, ethanol
Structure

Crystal structure

| trigonal
Thermochemistry

Heat capacity (C)

| 65.94 J/(mol·K)

Std molar
entropy (S⦵298)

| 73.39 J/(mol·K)

Std enthalpy of
formation (ΔfH⦵298)

| −1059 kJ/mol
Hazards
Lethal dose or concentration (LD, LC):

LD50 (median dose)

| 2330 mg/kg (rat, oral)

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Chemical compound

Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula NaBO2.[3] However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is Na3B3O6 or (Na+)3[B3O6]3−. The formula can be written also as Na2O*B2O3 to highlight the relation to the main oxides of sodium and boron.[2] The name is also applied to several hydrates whose formulas can be written NaBO2*nH2O for various values of n.

The anhydrous and hydrates are colorless crystalline solids. The anhydrous form is hygroscopic.[4]

## Hydrates and solubility

[edit]

The following hydrates crystallize from solutions of the proper composition in various temperature ranges:[5]

* tetrahydrate NaBO2*4H2O from −6 to 53.6 °C
* dihydrate NaBO2*2H2O from 53.6 °C to 105 °C
* hemihydrate NaBO2*0.5H2O from 105 °C to the boiling point.

Early reports of a monohydrate NaBO2*H2O have not been confirmed.[5]

## Structure

[edit]

### Anhydrous

[edit]

Solid anhydrous sodium metaborate has the hexagonal crystal system with space group R 3 ¯ c {\displaystyle R{\bar {3}}c} . It actually contains a six-membered rings with the formula [B3O6]3−, consisting of alternating boron and oxygen atoms with one negatively charged extra oxygen atom attached to each boron atom.[6][1] All nine atoms lie on a plane.[4] The six oxygen atoms are evenly divided into two distinct structural sites, with different B–O bond lengths: B–O(external) 128.0 pm and B–O(bridge) 143.3 pm.[6] The density is 2.348 ± 0.005 g/cm3.[4] The approximate dimensions of the hexagonal cell are a = 1275 pm, c = 733 pm.[4] However, the true unit cell is rhombohedral and has dimensions: ar= 776 pm, α = 110.6°, Z = 6 (5.98) molecules KB0[4]

### Dihydrate

[edit]

The dihydrate NaBO2*2H2O crystallizes in the triclinic crystal system, but is nearly monoclinic, with both α and γ very close to 90°. The cell parameters are a = 678 pm , b = 1058A pm, c = 588 pm, α = 91.5°, β = 22.5°, γ = 89°, Z = 4, density 1.905 g/cm3. The refractive indices at 25°C and wavelength 589.3 nm are α = 1.439, β = 1.473, γ = 1.484. The dispersion is strong, greater at red than at violet.[7]

The transition temperature between the dihydrate and the hemihydrate is 54 °C. However, the crystalline dihydrate will remain metastable until 106 °C to 110 °C, and change slowly above that temperature.[7]

### Vapor

[edit]

Infrared spectroscopy of the vapor from anhydrous sodium metaborate, heated to between 900 °C and 1400 °C, shows mostly isolated clusters with formula NaBO2, and some dimers thereof.[8] Electron diffraction studies by Akishin and Spiridonov showed a structure O=B−O−Na with linear anion O=B−O− and angle B−O−Na of 90-110°. The atomic distances are O=B: 120 pm, B−O: 136 pm,O−Na: 214 pm[9]

## Preparation

[edit]

Sodium metaborate is prepared by the fusion of sodium carbonate and boron oxide B2O3[1][4] or borax Na2B4O7. Another way to create the compound is by the fusion of borax with sodium hydroxide at 700 °C:

B2O3 \+ 2 NaOH → 2 NaBO2 \+ H2O

The boiling point of sodium metaborate (1434 °C) is lower than that of boron oxide (1860 °C) and borax (1575 °C) In fact, while the metaborate boils without change of composition, borax gives off a vapor of sodium metaborate with a small excess of sodium oxide Na2O.[2]

The anhydrous salt can also be prepared from the tetraborate by heating to 270 °C in vacuum.[10]

Although not performed industrially, hydrolysis of sodium borohydride Na[BH4] with a suitable catalyst gives sodium metaborate and hydrogen gas:[11]

Na[BH4] + 2 H2O → NaBO2 \+ 4 H2 (ΔH = −217 kJ/mol)

## Reactions

[edit]

### With water

[edit]

When sodium metaborate is dissolved in water, the anion combines with two water molecules to form the tetrahydroxyborate anion [B(OH)4]−.[11]

### Electrochemical conversion to borax

[edit]

Electrolysis of a concentrated aqueous solution of 20%[clarification needed] NaBO2*4H2O with an anion exchange membrane and inert anode (such as gold, palladium, or boron-doped diamond) converts the metaborate anion to tetraborate B4O2−7, and the sodium salt of the later (borax) precipitates as a white powder.[12]

BO2−2 \+ 2 OH− → B4O2−7 \+ H2O + 4 e−[clarification needed]

### Reduction to sodium borohydride

[edit]

Sodium metaborate can be converted to sodium borohydride by several methods, including the reaction with various reducing agents at high temperatures and pressure,[12] or with magnesium hydride MgH2 by ball milling at room temperature, followed by extraction of the Na[BH4] with isopropylamine.[13][10]

NaBO2 \+ 2 MgH2 → Na[BH4] + 2 MgO

Another method is the electrolytic reduction of a concentrated sodium metaborate solution,[10] namely

BO−2 \+ 6 H2O + 8 e− → [BH4]− \+ 8 OH−

However, this method is not efficient since it competes with the reduction of hydroxide:

4 OH− → 2 H2O + O2 \+ 4 e−

Nanofiltration membranes can effectively separate the borohydride from the metaborate.[11]

### Reaction with alcohols

[edit]

Anhydrous sodium metaborate refluxed with methanol yields the corresponding sodium tetramethoxyborate (melting point: 253-258 °C, CAS number: 18024-69-6[14]):[15]

Na+BO−2 \+ 4 CH3OH → Na+[B(OCH3)4]− \+ 2 H2O

The analogous reaction with ethanol yields the sodium tetraethoxyborate.[15]

## Uses

[edit]

Current and proposed applications of sodium metaborate include:

* Manufacture of borosilicate glasses, which are resistant to uneven or fast heating because of their small coefficient of thermal expansion.
* Composition of herbicides.[16]
* Raising the pH of injected fluids for oil extraction.[17]

## See also

[edit]

* Borate

## References

[edit]

1. ^ a b c Fang, Ssu-Mien (1938). "The Crystal Structure of Sodium Metaborate Na3 (B3 O6)". Zeitschrift für Kristallographie - Crystalline Materials. 99 (1–6): 1–8\. doi:10.1524/zkri.1938.99.1.1.1–6&rft.pages=1-8&rft.date=1938&rft_id=info:doi/10.1524/zkri.1938.99.1.1&rft.aulast=Fang&rft.aufirst=Ssu-Mien&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
2. ^ a b c Cole, Sandford S.; Taylor, Nelson W. (1935). "THE SYSTEM Na2O-B2O3, IV Vapor Pressures of Boric Oxide, Sodium Metaborate, and Sodium Diborate between 1150°C and 1400°C". Journal of the American Ceramic Society. 18 (1–12): 82–85\. doi:10.1111/j.1151-2916.1935.tb19358.x.1–12&rft.pages=82-85&rft.date=1935&rft_id=info:doi/10.1111/j.1151-2916.1935.tb19358.x&rft.aulast=Cole&rft.aufirst=Sandford+S.&rft.au=Taylor,+Nelson+W.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
3. ^ "Sodium metaborate" Substance page at the Chemister website. Accessed on 2022-06-28.
4. ^ a b c d e f Zachariasen, W. H. (1937). "The Crystal Structure of Potassium Metaborate, K3(B3O6)". The Journal of Chemical Physics. 5 (11): 919–922\. doi:10.1063/1.1749962.919-922&rft.date=1937&rft_id=info:doi/10.1063/1.1749962&rft.aulast=Zachariasen&rft.aufirst=W.+H.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
5. ^ a b Nies, Nelson P.; Hulbert, Richard W. (1967). "Solubility isotherms in the system sodium oxide-boric oxide-water. Revised solubility-temperature curves of boric acid, borax, sodium pentaborate, and sodium metaborate". Journal of Chemical & Engineering Data. 12 (3): 303–313\. doi:10.1021/je60034a005.303-313&rft.date=1967&rft_id=info:doi/10.1021/je60034a005&rft.aulast=Nies&rft.aufirst=Nelson+P.&rft.au=Hulbert,+Richard+W.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
6. ^ a b Marezio, M.; Plettinger, H. A.; Zachariasen, W. H. (1963). "The bond lengths in the sodium metaborate structure". Acta Crystallographica. 16 (7): 594–595\. Bibcode:1963AcCry..16..594M. doi:10.1107/S0365110X63001596.594-595&rft.date=1963&rft_id=info:doi/10.1107/S0365110X63001596&rft_id=info:bibcode/1963AcCry..16..594M&rft.aulast=Marezio&rft.aufirst=M.&rft.au=Plettinger,+H.+A.&rft.au=Zachariasen,+W.+H.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
7. ^ a b Krc, John (1951). "Crystallographic Data. 44. Sodium Metaborate Dihydrate". Analytical Chemistry. 23 (5): 806. doi:10.1021/ac60053a043.
8. ^ Alfred Büchler and Edward P. Marram (1963). "Gaseous Metaborates. II. Infrared Spectraof Alkali Metaborate Vapors". Journal of Chemical Physics. 39: 292. doi:10.1063/1.173424439 (inactive 1 November 2024).`{{cite journal}}`: CS1 maint: DOI inactive as of November 2024 (link)
9. ^ Akishin, P. A.; Spiridonov, V. P. (1962). "Electron diffraction study of the structure of LiBO2 and NaBO2 metaborate molecules in the vapor state". Journal of Structural Chemistry. 3 (3): 251–253\. doi:10.1007/BF01151477.251-253&rft.date=1962&rft_id=info:doi/10.1007/BF01151477&rft.aulast=Akishin&rft.aufirst=P.+A.&rft.au=Spiridonov,+V.+P.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
10. ^ a b c Kong, Lingyan; Cui, Xinyu; Jin, Huazi; Wu, Jie; Du, Hao; Xiong, Tianying (2009). "Mechanochemical Synthesis of Sodium Borohydride by Recycling Sodium Metaborate". Energy & Fuels. 23 (10): 5049–5054\. doi:10.1021/ef900619y.5049-5054&rft.date=2009&rft_id=info:doi/10.1021/ef900619y&rft.aulast=Kong&rft.aufirst=Lingyan&rft.au=Cui,+Xinyu&rft.au=Jin,+Huazi&rft.au=Wu,+Jie&rft.au=Du,+Hao&rft.au=Xiong,+Tianying&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
11. ^ a b c Atiyeh, H.; Davis, B. (2007). "Separation of sodium metaborate from sodium borohydride using nanofiltration membranes for hydrogen storage application". International Journal of Hydrogen Energy. 32 (2): 229–236\. Bibcode:2007IJHE...32..229A. doi:10.1016/j.ijhydene.2006.06.003.229-236&rft.date=2007&rft_id=info:doi/10.1016/j.ijhydene.2006.06.003&rft_id=info:bibcode/2007IJHE...32..229A&rft.aulast=Atiyeh&rft.aufirst=H.&rft.au=Davis,+B.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
12. ^ a b Park, E.; Ukjeong, S.; Hojung, U.; Kim, S.; Lee, J.; Woonam, S.; Hoonlim, T.; Junpark, Y.; Hoyu, Y. (2007). "Recycling of sodium metaborate to borax". International Journal of Hydrogen Energy. 32 (14): 2982–2987\. Bibcode:2007IJHE...32.2982P. doi:10.1016/j.ijhydene.2007.03.029.2982-2987&rft.date=2007&rft_id=info:doi/10.1016/j.ijhydene.2007.03.029&rft_id=info:bibcode/2007IJHE...32.2982P&rft.aulast=Park&rft.aufirst=E.&rft.au=Ukjeong,+S.&rft.au=Hojung,+U.&rft.au=Kim,+S.&rft.au=Lee,+J.&rft.au=Woonam,+S.&rft.au=Hoonlim,+T.&rft.au=Junpark,+Y.&rft.au=Hoyu,+Y.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
13. ^ Li, Z.P.; Liu, B.H.; Arai, K.; Morigazaki, N.; Suda, S. (2003). "Protide compounds in hydrogen storage systems". Journal of Alloys and Compounds. 356–357: 469–474\. doi:10.1016/S0925-8388(02)01241-0.469-474&rft.date=2003&rft_id=info:doi/10.1016/S0925-8388(02)01241-0&rft.aulast=Li&rft.aufirst=Z.P.&rft.au=Liu,+B.H.&rft.au=Arai,+K.&rft.au=Morigazaki,+N.&rft.au=Suda,+S.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
14. ^ "Product". sigmaaldrich.com.
15. ^ a b Kemmitt, T.; Gainsford, G.J. (2009). "Regeneration of sodium borohydride from sodium metaborate, and isolation of intermediate compounds". International Journal of Hydrogen Energy. 34 (14): 5726–5731\. Bibcode:2009IJHE...34.5726K. doi:10.1016/j.ijhydene.2009.05.108.5726-5731&rft.date=2009&rft_id=info:doi/10.1016/j.ijhydene.2009.05.108&rft_id=info:bibcode/2009IJHE...34.5726K&rft.aulast=Kemmitt&rft.aufirst=T.&rft.au=Gainsford,+G.J.&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">
16. ^ "BareSpot Monobor-Chlorate". Product safety data sheet at the BareSpot company website.Retrieved 2022-06-28.
17. ^ Chen, Fuzhen; Jiang, Hanqiao; Bai, Xiaohu; Zheng, Wei (2013). "Evaluation the performance of sodium metaborate as a novel alkali in alkali/Surfactant/Polymer flooding". Journal of Industrial and Engineering Chemistry. 19 (2): 450–457\. doi:10.1016/j.jiec.2012.08.029.450-457&rft.date=2013&rft_id=info:doi/10.1016/j.jiec.2012.08.029&rft.aulast=Chen&rft.aufirst=Fuzhen&rft.au=Jiang,+Hanqiao&rft.au=Bai,+Xiaohu&rft.au=Zheng,+Wei&rfr_id=info:sid/en.wikipedia.org:Sodium+metaborate" class="Z3988">

* v
* t
* e

Sodium compounds

Inorganic|

| Halides|

* NaF
* NaHF2
* NaCl
* NaBr
* NaI
* NaAt

|

Chalcogenides|

* NaO3
* NaO2
* Na2O
* Na2O2
* NaOH
* NaOD
* Na2S
* NaSH
* Na2Se
* NaSeH
* Na2Te
* NaHTe
* Na2Po

Pnictogenides|

* Na3N
* NaN3
* NaNH2
* Na3P
* Na3As

Oxyhalides|

* NaClO
* NaClO2
* NaClO3
* NaClO4
* NaBrO
* NaBrO2
* NaBrO3
* NaBrO4
* NaIO
* NaIO3
* NaIO4

Oxychalcogenides|

* Na2SO3
* Na2SO4
* NaHSO3
* NaHSO4
* Na2S2O3
* Na2S2O4
* Na2S2O5
* Na2S2O6
* Na2S2O7
* Na2S2O8
* Na2SeO3
* Na2SeO4
* NaHSeO3
* Na2TeO3

Oxypnictogenides|

* NaNO2
* NaNO3
* Na2N2O2
* NaH2PO4
* NaPO2H2
* Na2HPO3
* Na2PO3F
* Na3PS2O2
* Na3PO4
* Na5P3O10
* Na4P2O7
* Na2H2P2O7
* Na3AsO3
* Na3AsO4
* Na2HAsO4
* NaH2AsO4
* NaSbO3

Others|

* NaAlH4
* NaAlO2
* Na3AlF6
* NaAl(SO4)2
* NaAuCl4
* NaSbF6
* NaAsF6
* Na2TiF6
* NaBH4
* NaBH3(CN)
* NaBO2
* Na2B4O7
* Na2B2O9
* Na2B8O13
* NaBiO3
* NaCN
* NaCNO
* NaCoO2
* NaH
* NaHCO3
* Na4XeO6
* NaHXeO4
* NaMnO4
* NaOCN
* NaReO4
* NaSCN
* NaTcO3
* NaTcO4
* NaVO3
* Na2CO3
* Na2C2O4
* Na2C3S5
* Na2CrO4
* Na2Cr2O7
* Na2Cr3O10
* Na2GeO3
* Na2He
* Na2[Fe(CO)4]
* Na2MnO4
* Na2MoO4
* Na3IrCl6
* Na2PtCl6
* Na2O(UO3)2
* Na2S4O6
* Na2SiO3
* Na2TiO3
* Na2U2O7
* Na2WO4
* Na2Zn(OH)4
* Na3VO4
* Na6V10O28
* Na4Fe(CN)6
* Na3Fe(CN)6
* Na3Fe(C2O4)3
* Na4SiO4
* Na2SiF6
* Na3[Co(NO2)6]
* NaNSi2(CH3)6
* Na2PdCl4

Organic|

* CH3ONa
* C2H5ONa
* HCOONa
* C2H5COONa
* C3H7COONa
* Na2C4H4O6
* C4H5NaO6
* NaCH3COO
* NaC6H5CO2
* NaC6H4(OH)CO2
* NaC12H23O2
* NaC10H8
* Na2[Fe[CN5]NO]
* C6H16AlNaO4
* NaC6H7O6
* C5H8NO4Na
* C6H5Na
* C4H9Na
* NaC5H5
* C15H31COONa
* C17H33COONa
* C18H35O2Na
* C164H256O68S2Na2

* v
* t
* e

Borates

| H3BO3 |  |  |  | He

|
|
|
|

Li2B4O7 | Be  | B  | +(CO3)
+(C2O4) | (NH4)3BO3
+NO3 | O  | +F | Ne
Na2[B4O5(OH)4]·8H2O
NaBO2
NaBO3
Na3BO3
Na2B8O13 | Mg3(BO3)2 | AlBO3 | Si  | -PO4
+PO4 | +S
-SO4
+SO4 | +Cl | Ar
K2B4O7•4H2O
KB5O8•4H2O | Ca3(BO3)2 |  | ScBO3 | TiBO3 | -VO4 | Cr  | Mn3(BO3)2 | Fe3(BO3)2
FeBO3
FeB(OH)4 | Co3(BO3)2 | Ni3(BO3)2 | Cu3(BO3)2 | Znx(BO3)x | GaBO3
-GaO4 | -GeO4 | -AsO4 | -SeO4
-SeO3
+Se | +Br | Kr
Rb3BO3
RbB11O16(OH)2
Rb[B5O6(OH)4]•2H2O | Sr3(BO3)2 |  | YBO3 | ZrB2O5 | Nb  | Mo  | Tc  | Ru  | Rh  | Pd  | Ag3BO3 | Cd3(BO3)2 | InBO3 | Sn  | -SbBO4 | -TeO4
-TeO3 | +I | Xe
Cs3BO3
CsB5O8•4H2O | BaB2O4 | *  | Lu3B5O12 | HfB2O5 | Ta  | W  | Re  | Os  | Ir  | Pt  | Au  | Hg  | Tl3BO3 | Pb3(BO3)2 | BiBO3 | Po  | At  | Rn
Fr  | Ra  | **  | Lr  | Rf  | Db  | Sg  | Bh  | Hs  | Mt  | Ds  | Rg  | Cn  | Nh  | Fl  | Mc  | Lv  | Ts  | Og

*  | LaB3O6 | CeB3O6 | Pr4B10O21 | NdBO3 | Pm  | Sm  | Eu  | Gd  | Tb  | Dy4B6O15
Dy2B4O9 | Ho4B6O15
Ho2B4O9 | ErBO3 | Tm3B5O12 | Yb3B5O12
**  | Ac  | Th3(BO3)4 | Pa  | U(BO3)2 | Np  | Pu  | Am  | Cm  | Bk  | Cf[B6O8(OH)5] | Es  | Fm  | Md  | No
*[CID]: Compound ID
*[EPA]: U.S. Environmental Protection Agency
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template