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Phosphoric acids and phosphates
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Phosphoric acids and phosphates
In chemistry, a phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these PO4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is Hn+2−2xPnO3n+1−x, where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and n + 2/2.
Removal of protons (H+) from k hydroxyl groups –OH leaves anions generically called phosphates (if k = n − 2x + 2) or hydrogen phosphates (if k is between 1 and n − 2x + 1), with general formula [Hn−2x+2−kPnO3n+1−x]k−. The fully dissociated anion (k = n − 2x + 2) has formula [PnO3n−x+1](n−2x+2)−. The term phosphate is also used in organic chemistry for the functional groups that result when one or more of the hydrogens are replaced by bonds to other groups.
These acids, together with their salts and esters, include some of the best-known compounds of phosphorus, of high importance in biochemistry, mineralogy, agriculture, pharmacy, chemical industry, and chemical research.
The simplest and most commonly encountered of the phosphoric acids is orthophosphoric acid, H3PO4. Indeed, the term phosphoric acid often means this compound specifically (and this is also the current IUPAC nomenclature).[citation needed]
Two or more orthophosphoric acid molecules can be joined by condensation into larger molecules by elimination of water. Condensation of a few units yields the oligophosphoric acids, while larger molecules are called polyphosphoric acids. (However, the distinction between the two terms is not well defined.)
For example, pyrophosphoric, triphosphoric and tetraphosphoric acids can be obtained by the reactions
![{\displaystyle {\begin{aligned}{2\,\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {PO} {\vphantom {A}}_{\smash[{t}]{4}}}&\longrightarrow {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{4}}\mathrm {P} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} {\vphantom {A}}_{\smash[{t}]{7}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} }\\[2pt]{\mathrm {H} {\vphantom {A}}_{\smash[{t}]{4}}\mathrm {P} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} {\vphantom {A}}_{\smash[{t}]{7}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {PO} {\vphantom {A}}_{\smash[{t}]{4}}}&\longrightarrow {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}\mathrm {P} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {O} {\vphantom {A}}_{\smash[{t}]{10}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} }\\[2pt]{\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}\mathrm {P} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {O} {\vphantom {A}}_{\smash[{t}]{10}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {PO} {\vphantom {A}}_{\smash[{t}]{4}}}&\longrightarrow {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{6}}\mathrm {P} {\vphantom {A}}_{\smash[{t}]{4}}\mathrm {O} {\vphantom {A}}_{\smash[{t}]{13}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} }\end{aligned}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/d4c24f45d2f63419fa9f3ec8c03563abe3532b13)
The "backbone" of a polyphosphoric acid molecule is a chain of alternating P and O atoms. Each extra orthophosphoric unit that is condensed adds 1 extra H (hydrogen) atom, 1 extra P (phosphorus) atom, and 3 extra O (oxygen) atoms. The general formula of a polyphosphoric acid is Hn+2PnO3n+1 or HO[−P(O)(OH)−O−]nH.
Polyphosphoric acids are used in organic synthesis for cyclizations and acylations; an alternative is Eaton's reagent.
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Phosphoric acids and phosphates
In chemistry, a phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these PO4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is Hn+2−2xPnO3n+1−x, where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and n + 2/2.
Removal of protons (H+) from k hydroxyl groups –OH leaves anions generically called phosphates (if k = n − 2x + 2) or hydrogen phosphates (if k is between 1 and n − 2x + 1), with general formula [Hn−2x+2−kPnO3n+1−x]k−. The fully dissociated anion (k = n − 2x + 2) has formula [PnO3n−x+1](n−2x+2)−. The term phosphate is also used in organic chemistry for the functional groups that result when one or more of the hydrogens are replaced by bonds to other groups.
These acids, together with their salts and esters, include some of the best-known compounds of phosphorus, of high importance in biochemistry, mineralogy, agriculture, pharmacy, chemical industry, and chemical research.
The simplest and most commonly encountered of the phosphoric acids is orthophosphoric acid, H3PO4. Indeed, the term phosphoric acid often means this compound specifically (and this is also the current IUPAC nomenclature).[citation needed]
Two or more orthophosphoric acid molecules can be joined by condensation into larger molecules by elimination of water. Condensation of a few units yields the oligophosphoric acids, while larger molecules are called polyphosphoric acids. (However, the distinction between the two terms is not well defined.)
For example, pyrophosphoric, triphosphoric and tetraphosphoric acids can be obtained by the reactions
The "backbone" of a polyphosphoric acid molecule is a chain of alternating P and O atoms. Each extra orthophosphoric unit that is condensed adds 1 extra H (hydrogen) atom, 1 extra P (phosphorus) atom, and 3 extra O (oxygen) atoms. The general formula of a polyphosphoric acid is Hn+2PnO3n+1 or HO[−P(O)(OH)−O−]nH.
Polyphosphoric acids are used in organic synthesis for cyclizations and acylations; an alternative is Eaton's reagent.
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