Metaphosphate
A metaphosphate is a salt or an ester of metaphosphoric acid, HPO3. Metaphosphates are condensation products of orthophosphoric acid (H3PO4) with the sum formula (M'PO3)n, where n=1, 2, 3, ..., (M': univalent cation). Phosphoric acids can occur in rings (cyclic structures), chains (catena), branched, ultraphosphoric acids (cyclic and branched), or combinations, usually referred to as polyphosphoric acids. As an example trimetaphosphate can form a 6-membered ring. Tetrametaphosphates form a similar 8-membered ring.
Trimetaphosphates were used in former times in detergents; today due to the fertilization effect of the phosphates zeolites (stand silicates, as e.g. zeolite A) are used.
Sodium metaphosphates
Although sodium metaphosphate is the general term for any polyphosphate salt with four or more phosphate units, the four-phosphate unit version of sodium metaphosphate has been used commercially as an oral care agent; i.e., a chelating agent in cosmetic formulations.[1] The four-phosphate unit version is cyclic.[1]
Sodium trimetaphosphate has served as a buffering agent and sodium hexametaphosphate as a corrosion inhibitor.[1] Both of these sodium metaphosphates are staight chains.[1] Because of the corrosive nature of each of these sodium metaphosphates, these ingredients can be used safely if each formulation is prepared to avoid skin irritation.[1]
Alkali and alkali-earth metaphosphates
The chain metaphosphates NaCa(PO3)3 and NaSr(PO3)3 are isostructural, crystallise in space group P(-1), and contain anionic metaphosphate chains of (PO3)n with ionic contacts to Na+ ions in distorted octahedral sites and Ca2+ (or Sr2+) in distorted dodecahedral sites.[2]
Transition metal metaphosphates
Thyroxine has a catalytic effect on the oxidation of As(III) by Mn(III) metaphosphate, wherein the reaction rate can be increased by the presence of orthophosphoric acid.[3]
Metaphosphate glasses
In Pb-Al-metaphosphate glasses, (1 - x)Pb(PO3)2.xAI(PO3)3 with 0 < or = x < or = 1, the glass transition temperature and density vary as a function of the Al concentration, and the bonding preferences determined for Al are consistent with the behavior observed in Na-AI and Ca-AI metaphosphates.[4]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Lanigan RS (2001). "Final report on the safety assessment of Sodium Metaphosphate, Sodium Trimetaphosphate, and Sodium Hexametaphosphate". Int J Toxicol. 20 (Suppl 3): 75–89. PMID 11766135.
- ↑ Abrahams I, Hawkes GE, Ahmed A, Di Cristina T, Demetriou DZ, Ivanova GI (2008). "Structures of the chain metaphosphates NaM(PO3)3 (M = Ca or Sr)". Magn Reson Chem. 46 (4): 316–22. PMID 18306173. Unknown parameter
|month=ignored (help) - ↑ Pastor FT, Milovanović GA, Todorović M (2008). "Kinetic method for the determination of traces of thyroxine by its catalytic effect on the Mn(III) metaphosphate-As(III) reaction". Talanta. 74 (5): 1556–61. PMID 18371817. Unknown parameter
|month=ignored (help) - ↑ Tsuchida JE, Schneider J, Pizani PS, Oliveira SL (2008). "Lead and aluminum bonding in Pb-AI metaphosphate glasses". Inorg Chem. 47 (2): 690–8. PMID 18081273. Unknown parameter
|month=ignored (help)
Sources
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Von „http://de.wikipedia.org/wiki/Metaphosphate“ (German page)