Trimethyl borate

• Ortho -boric acid trimethyl ester
• Trimethyl borate

Colorless liquid with a pleasant odor

Liquid

0.915 g · cm -3 ( 20 ° C)

-29.3 ° C

68.7 ° C

182 hPa ( 25 ° C)

Decomposition with water

1.3568 (20 ° C)

Attention

• 6140 mg · kg -1 ( LD50, rat, oral)
• 1850 mg · kg -1 ( LD50, Rabbit, transdermal)

Template: Infobox chemical / molecular formula search available

Trimethyl borate ( trimethyl ) is a chemical compound from the group of boric acid. It is the methyl ester of boric acid.

Representation

Trimethyl borate is produced by esterification of boric acid with methanol in the presence of acid catalysts in an equilibrium reaction:

To shift the equilibrium to the right side, however, it is necessary to escape the reaction mixture of the products ( Le Chatelier's principle ). Which often offering at esterification method is the binding of water by a dehydrating agent such as sulfuric acid, which simultaneously acts as an acid catalyst.

The reaction of boric oxide resulting in the formation of a mixture of various boric acid ester.

A third possibility is the reaction of boron halides with methanol in the presence of a base such as in the following example with boron tribromide:

The resulting hydrogen halide ( bromide in the example ) is bound by the base.

Properties

Trimethyl borate is a colorless, volatile liquid. In water, it is rapidly hydrolyzed in boric acid and methanol. The hydrolysis reaction is exothermic with -19.3 kJ · mol -1. It is the easiest boric acid. As the compound of boron burns with strong light green colored flame. Because no C-C bonds are present, no soot produced by the burning, the yellow glow in the flame and so drowns out the flame coloration (a large ethanol flame has a yellowish flame, alkanes burn more or less bright). The combustion of non-volatile, white boric oxide, the acid anhydride of boric acid, which can smoke the flame results:

The vapor pressure function is given by Antoine corresponding log10 (P) = A- ( B / ( T C )) ( P in bar, T in K) with A = 4.74371, B = 1476.192 and C = -29, 0 in the temperature range from 304 K to 340.5 K. The compound forms flammable vapor - air mixtures. The flash point is -18 ° C.

Use

Reiner trimethyl borate is technically little application. It is used to a small extent for the surface treatment of steel ( formation of a corrosion-inhibiting Fe2B layer) in specific plasma processes. Trimethyl borate is used as starting material for boric acid precursors of the Suzuki coupling using. Trimethyl borate is still used as fluxing agents for brazing in so-called " Gasflux " method.

The solid green flame coloration of the ester can analytically as an indication of the presence of boric acid / borates or methanol ( the boric acid esters of higher alcohols provide only green Flammensäume ) are used, however, is not unique. However, it is very sensitive and is already caused by traces of boric acid (for example, from the borosilicate glass is often used in laboratories to arise ).

In nuclear technology of trimethyl borate is used as an absorbent for neutron.