Disodium dihydrogen diphosphate

Structural formula
General
Surname	Disodium dihydrogen diphosphate
other names	E 450a E 450 (i) Disodium dihydrogen pyrophosphate Sodium pyrophosphate dibasic DISODIUM PYROPHOSPHATE ( INCI )
Molecular formula	Na 2 H 2 P 2 O 7
Brief description	colorless and odorless powder
External identifiers / databases
CAS number 7758-16-9 EC number 231-835-0 ECHA InfoCard 100.028.941 PubChem 9837369 ChemSpider 8013090 Wikidata Q418498
properties
Molar mass	221.9 g mol −1
Physical state	firmly
density	1.86 g cm −3
Melting point	220 ° C (decomposition)
solubility	moderate in water (120 g l −1 at 20 ° C)
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 319 P: 305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium acid pyrophosphate Na ₂ H ₂ P ₂ O ₇ , a sodium salt of diphosphoric acid , belongs to the group of diphosphates . It is used as a food additive , among other things , and is often incorrectly referred to as disodium diphosphate .

Appearance and properties

Na ₂ H ₂ P ₂ O ₇ can be produced from sodium dihydrogen phosphate by heating it for several hours at about 210 ° C:

${\displaystyle \mathrm {2NaH_{2}PO_{4}\longrightarrow \ Na_{2}H_{2}P_{2}O_{7}+\ H_{2}O} }$

Alternatively, the representation takes place by reacting the diphosphoric acid with two equivalents of sodium hydroxide solution .

${\displaystyle \mathrm {H_{4}P_{2}O_{7}+2\ NaOH\longrightarrow \ Na_{2}H_{2}P_{2}O_{7}+2\ H_{2}O} }$

Above this temperature, the long-chain Maddrell salt (NaPO ₃ ) _n or sodium trimetaphosphate Na ₃ P ₃ O _{9 is formed} .

The salt is easily soluble in water and is slightly acidic .

The hexahydrate of the compound has a monoclinic crystal structure with the space group C 2 / c (space group no. 15) .

use

In food chemistry , Na ₂ H ₂ P ₂ O _{7 is used} as an additive for baking powder under the name E 450a ; as it reacts acidic, it promotes the decomposition of the leavening agents .

Since, as pyrophosphate, it strives to absorb water from its environment and thereby to regress the above-mentioned sodium dihydrogen phosphate

${\displaystyle \mathrm {Na_{2}H_{2}P_{2}O_{7}+\ H_{2}O\longrightarrow 2\ NaH_{2}PO_{4}} }$

it is also used as a dehydrating preservative for food.

literature

• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .

Individual evidence

1. ↑ Entry on DISODIUM PYROPHOSPHATE in the CosIng database of the EU Commission, accessed on February 11, 2020.
2. ↑ ^{a b c d e f} Entry on disodium dihydrogen pyrophosphate in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
3. ^ RN Bell: Sodium pyrophosphates . In: Ludwig F. Audrieth (Ed.): Inorganic Syntheses . tape 3 . McGraw-Hill, Inc., 1950, pp. 98-101 (English).
4. ^ DEC Corbridge: Phosphorus Chemistry, Biochemistry and Technology, Sixth Edition . CRC Press, 2016, ISBN 978-1-4398-4089-4 , pp. 234 ( limited preview in Google Book search).
5. ^ Arthur DF Toy: The Chemistry of Phosphorus Pergamon Texts in Inorganic Chemistry . Elsevier, 2016, ISBN 978-1-4831-3959-3 , pp. 513 ( limited preview in Google Book search).