Disodium hydrogen phosphate

Structural formula
General
Surname	Disodium hydrogen phosphate
other names	Sodium hydrogen phosphate; di-sodium phosphate; Disodium hydrogen orthophosphate; DISODIUM PHOSPHATE ( INCI ) ; E 339 ;
Molecular formula	Na 2 HPO 4
Brief description	colorless, crystalline substance
External identifiers / databases
EC number	231-448-7
ECHA InfoCard	100.028.590
PubChem	24203
ChemSpider	22625
DrugBank	DB09127
Wikidata	Q418448
properties
Molar mass	141.96 g mol −1 (anhydrous); 177.99 g mol −1 (dihydrate); 268.07 g mol −1 (heptahydrate); 358.14 g mol −1 (dodecahydrate);
Physical state	firmly
density	2.066 g cm −3 (20 ° C, dihydrate); 1.68 g cm −3 (20 ° C, heptahydrate); 1.52 g cm −3 (20 ° C, dodecahydrate);
Melting point	> 250 ° C (decomposition, anhydrous); 93 ° C (elimination of crystal water, dihydrate); 48 ° C (elimination of crystal water, heptahydrate); 35 ° C (elimination of crystal water, dodecahydrate);
pK s value	12.32
solubility	soluble in water (77 g l −1 at 20 ° C, anhydrous substance)
safety instructions
GHS labeling of hazardous substances	no GHS pictograms
	no GHS pictograms
H and P phrases	H: no H-phrases
	P: no P-phrases
Toxicological data	17,000 mg kg −1 ( LD 50 , rat , oral )
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Disodium hydrogen phosphate is a sodium - salt the phosphoric acid . It is also known as secondary sodium phosphate .

properties

Disodium hydrogen phosphate anhydrous is a colorless, crystalline, hygroscopic compound. In addition to the anhydrous compound, three hydrates are also known:

Dihydrate (Na ₂ HPO ₄ · 2 H ₂ O)
Heptahydrate (Na ₂ HPO ₄ 7 H ₂ O)
Dodecahydrate (Na ₂ HPO ₄ 12 H ₂ O)

One mole of anhydrous disodium hydrogen phosphate absorbs 2 moles of water from the air and binds it as crystal water . The higher hydrates, on the other hand, weather in air to form the dihydrate. This stability of the dihydrate is also the reason for its choice as a buffer substance. When heated, all of the water of crystallization is first given off (dodecahydrate at 35 ° C, heptahydrate at 48 ° C and dihydrate at 92.5 ° C), then (at approx. 250 ° C ) but also - from two molecules each - another water molecule, creating a pyrophosphate .

{\ displaystyle \ mathrm {2 \ Na_ {2} HPO_ {4} \ {\ xrightarrow {250 ^ {o} C}} \ Na_ {4} P_ {2} O_ {7} + H_ {2} O \ uparrow }}

Disodium hydrogen phosphate has a basic reaction in aqueous solution:

{\ displaystyle \ mathrm {HPO_ {4} ^ {2 -} + H_ {2} O \ rightleftharpoons H_ {2} PO_ {4} ^ {-} + OH ^ {-}}}

So there is an equilibrium between hydrogen and dihydrogen phosphate ions.

synthesis

Sodium hydrogen phosphate can be produced in the laboratory from sodium hydroxide solution and phosphoric acid.

{\ displaystyle \ mathrm {2 \ NaOH + H_ {3} PO_ {4} \ longrightarrow Na_ {2} HPO_ {4} +2 \ H_ {2} O}.}

use

In food technology, disodium hydrogen phosphate is used as a complexing agent , acid regulator and melting salt . Together with sodium dihydrogen phosphate and sodium phosphate, it is approved in the EU as a food additive under the common number E 339 ("sodium phosphate") for certain foods, each with different maximum quantity restrictions. According to the Additive Admissions Ordinance , these are - largely uniform for most of the approved phosphates - individual specifications for a wide range of numerous different types of food. The maximum permitted amounts vary from 0.5 to 50 grams per kilogram (in creamer for vending machines) or the lack of a fixed limit ( quantum satis - as required, for food supplements and sometimes for chewing gum). Phosphorus is suspected of causing hyperactivity , allergic reactions and osteoporosis . A permissible daily dose of 70 milligrams per kilogram of body weight was set for the total amount of phosphoric acid and phosphates ingested.

Phosphate buffer

Disodium hydrogen phosphate is used in biochemistry and molecular biology for the production of buffer solutions . By mixing sodium dihydrogen phosphate with disodium hydrogen phosphate solution or adding sodium hydroxide solution , a phosphate buffer with a specific pH value (pH 6-8) can be produced. It is also part of some drugs as a pH buffer.

Individual evidence

↑ Entry on DISODIUM PHOSPHATE in the CosIng database of the EU Commission, accessed on June 27, 2020.
↑ Entry on E 339: Sodium phosphates in the European database on food additives, accessed on June 27, 2020.
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Entry for CAS no. 7558-79-4 in the GESTIS substance database of the IFA , accessed on June 1, 2014(JavaScript required) .
↑ Entry on phosphoric acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 29, 2014.
↑ Data sheet disodium hydrogen phosphate (PDF) from Carl Roth , accessed on December 14, 2010.
^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 774.
↑ Jander, Blasius, Strähle: Introduction to the inorganic-chemical practical course . 14th edition. Hirzel, Stuttgart 1995, ISBN 978-3-7776-0672-9 , pp. 337-338.

[CosIng-1] Entry on DISODIUM PHOSPHATE in the CosIng database of the EU Commission, accessed on June 27, 2020.

[E-Nummer339-2] Entry on E 339: Sodium phosphates in the European database on food additives, accessed on June 27, 2020.

[GESTIS-3] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Entry for CAS no. 7558-79-4 in the GESTIS substance database of the IFA , accessed on June 1, 2014(JavaScript required) .

[roempp-4] Entry on phosphoric acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 29, 2014.

[roth-5] Data sheet disodium hydrogen phosphate (PDF) from Carl Roth , accessed on December 14, 2010.

[wiberg-6] AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 774.

[7] Jander, Blasius, Strähle: Introduction to the inorganic-chemical practical course . 14th edition. Hirzel, Stuttgart 1995, ISBN 978-3-7776-0672-9 , pp. 337-338.