Sodium borohydride is a highly reactive substance. The study of its properties made it possible to significantly enrich the organic and inorganic chemistry with information, as well as solve a number of important analytical problems. This compound is one of the most industrially developed among all borohydrides of metals of the alkaline-earth group.
general description
Sodium borohydride is a colorless crystalline substance, odorless. Unlike other alkali metal borohydrides, it has relative stability in air and in water. This is due to its widespread use in the chemical industry.
The empirical formula of sodium borohydride is: NaBH 4 .
Physical properties
The following physical properties are characteristic of this compound:
- melting point - 500 ° C;
- type of crystal lattice - cubic syngony;
- molecular weight - 37.843 a. eat.;
- density - 1.08 kg / m 3 ;
- 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, in derivatives of ammonia and oxoacids; bad - in diethyl ether, hydrocarbon compounds;
- in non-aqueous solutions, an exchange reaction is observed with the halides of lithium, magnesium, barium, aluminum;
- from water, the substance crystallizes in the form of NaBH 4 -2H 2 O dihydrate;
- 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.
This substance has a high reactivity and reduction ability. The second type of process is with various parameters:
- lack of solvent;
- in aqueous solutions;
- in organic environments;
- in solutions with a wide range of acid-base indicator.
Getting
The synthesis of this compound is carried out in several ways. The main types of reactions are described below:
- Diborane with hydride or sodium methylate:
2NaH + B 2 H 6 → 2NaBH 4 ,
3CH 3 ONa + 2B 2 H 6 → 3NaBH 4 + B (OCH 3 ) 3 ;
- dimethoxyborane with sodium trimethoxyborohydride:
2NaBH (OCH 3 ) 3 + 3 (CH 3 O) 2 BH 3 = NaBH 4 + 3B (OCH 3 ) 3 ;
- sodium hydride with boron ethyl ether:
4NaH + B (OCH 2 CH 3 ) 3 → NaBH 4 + 3NaOCH 2 CH 3 ;
- sodium hydride with boron trichloride or boric anhydride:
BX 3 + 4NaH → NaBH 4 + 3NaX,
X = Cl, 1/2 * O.
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 that are products of laboratory analysis or industrial production;
- obtaining pure hydrogen gas;
- foaming of synthetic materials based on polyesters, polyvinyl alcohol and foam;
- synthesis of boron compounds (diborane, boron triiodide, hydrazine monoborane, ethylamine borane, sodium borosulfide and others);
- obtaining porous insulating coatings.
As catalysts for the evolution of hydrogen from borohydride in water, tablets of oxalic, citric, succinic acid, hydrosulfates, hydrophosphates, coal coated with cobalt, platinum or palladium salts are used.
Metal coatings
Sodium borohydride is also used to obtain coatings of the "metal-boron" type, characterized by good performance characteristics:
- high hardness;
- wear resistance;
- corrosion resistance;
- high melting point.
The borohydride method allows the manufacture of coatings at a low temperature (about 40 ° C) based on copper, silver, gold, iron, nickel, cobalt, palladium, platinum and other metals. Various additives (sulfites, sulfites, thiosulfates) can be used as additives, which makes it possible to obtain two- and three-component alloys with new properties.