Sodium borohydride is a highly reactive substance. The study of its properties made it possible to significantly enrich organic and inorganic chemistry with information, as well as to solve a number of important analytical problems. This compound is one of the most industrialized among all alkaline earth metal borohydrides.
General Description
Sodium borohydride is a colorless, odorless crystalline substance. Unlike other alkali metal borohydrides, it is relatively stable in air and water. This is due to its widespread use in the chemical industry.
The empirical formula for sodium borohydride is: NaBH4.
Physical properties
This compound has the following physical properties:
- melting point - 500 °C;
- type of crystal lattice - cubic syngony;
- molecular weight – 37, 843 a.u. e. m.;
- density - 1.08 kg/m3;
- hygroscopicity – high;
- high electrical conductivity in solution with ammonia and diglyme.
Chemical properties
The main chemical properties of sodium borohydride are as follows:
- good solubility in water, alcohols, liquid ammonia, ammonia derivatives and oxoacids; bad - in diethyl ether, hydrocarbon compounds;
- in non-aqueous solutions, an exchange reaction with halides of lithium, magnesium, barium, aluminum is observed;
- from water the substance crystallizes in the form of dihydrate NaBH4-2H2O;
- when reacting with nitrogen, ammonia is reduced;
- drying the dihydrate can only be done under vacuum;
- in the reaction with dimethylformamide, acetamide, the formation of solvates occurs.
This substance is highly reactive and reducing. The second type of process goes with different parameters:
- no solvent;
- in aqueous solutions;
- in organic environments;
- in solutions with a wide range of acid-base index.
Receive
This compound is synthesized in several ways. The main types of reactions are described below:
diborane with hydride or sodium methylate:
2NaH + B2H6 → 2NaBH4 , 3CH3ONa + 2B2H6 → 3NaBH 4 + B(OCH3)3;
dimethoxyborane withsodium trimethoxyborohydride:
2NaBH(OCH3)3 + 3(CH3O) 2BH3=NaBH4 + 3B(OCH3) 3;
sodium hydride with ethyl boron ether:
4NaH + B(OCH2CH3)3 → NaBH 4 + 3NaOCH2CH3;
sodium hydride with boron trichloride or boric anhydride:
BX3 + 4NaH → NaBH4 + 3NaX, X=Cl, 1/2O.
The resulting technical substance is purified by extraction or recrystallization from various solvents.
Application
Sodium borohydride is used for the following purposes:
- fine inorganic and organic synthesis;
- obtaining metal sols;
- study of the structure of substances;
- determination of the kinetics of chemical reactions;
- obtaining borohydrides of other metals and their derivatives;
- regeneration of precious metals (platinum, palladium, silver, gold) from waste aqueous solutions, which are products of laboratory analysis or industrial production;
- obtaining pure gaseous hydrogen;
- foaming synthetic materials based on polyester, polyvinyl alcohol and foam;
- synthesis of boron compounds (diborane, boron triiodide, hydrazine monoborane, ethylamineborane, sodium borosulfide and others);
- obtaining porous heat-insulating coatings.
As catalysts for the release of hydrogen from borohydride in water, oxalic acid tablets are used,citric acid, succinic acid, hydrosulfates, hydrophosphates, carbon coated with s alts of cob alt, platinum or palladium.
Metal Coatings
Sodium borohydride is also used for high performance metal-boron coatings:
- high hardness;
- wear resistant;
- corrosion resistance;
- high melting point.
The borohydride method makes it possible to produce coatings at a low temperature (about 40 °C) based on copper, silver, gold, iron, nickel, cob alt, palladium, platinum and other metals. Various components (sulfites, sulfites, thiosulfates) can be used as additives, which makes it possible to obtain two- and three-component alloys with new properties.
