Trimethyl borate

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Trimethyl borate
Other names
trimethoxyborane, boron trimethoxide
3D model (JSmol)
ECHA InfoCard 100.004.063
EC Number 204-468-9
Molar mass 103.91 g·mol−1
Appearance colourless liquid
Density 0.932 g/ml
Melting point −34 °C (−29 °F; 239 K)
Boiling point 68 to 69 °C (154 to 156 °F; 341 to 342 K)
Main hazards flammable
Related compounds
Other cations
Trimethyl phosphite
Tetramethyl orthosilicate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Trimethyl borate is the organoboron compound with the formula B(OCH3)3. It is a colourless liquid that burns with a green flame.[1] It is an intermediate in the preparation of sodium borohydride and is a popular reagent in organic chemistry. It is a weak Lewis acid (AN = 23, Gutmann-Beckett method). [2]

Green fire of boric acid in methanol

Borate esters are prepared by heating boric acid or related boron oxides with alcohols under conditions where water is removed.[1]


Trimethyl borate is the main precursor to sodium borohydride by its reaction with sodium hydride:

4 NaH + B(OCH3)3 → NaBH4 + 3 NaOCH3

It is a gaseous anti-oxidant in brazing and solder flux. Otherwise, trimethyl borate has no announced commercial applications. It has been explored as a fire retardant, as well as being examined as an additive to some polymers.[1]

Organic synthesis[edit]

It is a useful reagent in organic synthesis, as a precursor to boronic acids, which are used in Suzuki couplings. These boronic acids are prepared via reaction of the trimethyl borate with Grignard reagents followed by hydrolysis:.[3][4]

ArMgBr + B(OCH3)3 → MgBrOCH3 + ArB(OCH3)2
ArB(OCH3)2 + 2 H2O → ArB(OH)2 + 2 HOCH3


  1. ^ a b c Robert J. Brotherton, C. Joseph Weber, Clarence R. Guibert, John L. Little (2000), "Boron Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCHCS1 maint: Uses authors parameter (link)
  2. ^ M.A. Beckett, G.C. Strickland, J.R. Holland, and K.S. Varma, "A convenient NMR method for the measurement of Lewis acidity at boron centres: correlation of reaction rates of Lewis acid initiated epoxide polymerizations with Lewis acidity", Polymer, 1996, 37, 4629–4631. doi: 10.1016/0032-3861(96)00323-0
  3. ^ Kazuaki Ishihara, Suguru Ohara, Hisashi Yamamoto (2002). "3,4,5-Trifluorophenylboronic Acid". Organic Syntheses. 79: 176.CS1 maint: Multiple names: authors list (link); Collective Volume, 10, p. 80
  4. ^ R. L. Kidwell, M. Murphy, and S. D. Darling (1969). "Phenols: 6-Methoxy-2-naphthol". Organic Syntheses. 49: 90.CS1 maint: Multiple names: authors list (link); Collective Volume, 10, p. 80

External links[edit]