Trimethyl borate

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Trimethyl borate
Other names
trimethoxyborane, boron trimethoxide
3D model (Jmol)
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.

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] 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:.[2][3]

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 "Boron Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH. doi:10.1002/14356007.a04_309
  2. ^ Kazuaki Ishihara, Suguru Ohara, Hisashi Yamamoto (2002). "3,4,5-Trifluorophenylboronic Acid". Org. Synth. 79: 176.  ; Coll. Vol., 10, p. 80 
  3. ^ R. L. Kidwell, M. Murphy, and S. D. Darling (1969). "Phenols: 6-Methoxy-2-naphthol". Org. Synth. 49: 90.  ; Coll. Vol., 10, p. 80 

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