7. Phosphorus and P-containing compounds 7.1. Elementary ...

7. Phosphorus and P-containing compounds

7.1. Elementary phosphorus
7.1.1. Physical properties. Allotropic modifications
7.1.2. Chemical properties
7.1.3. Occurrence
7.1.4. Use

7.2. Phosphorus containing compounds
7.2.1. Phosphine (phosphan)
7.2.2. Phosphorus halides
7.2.3. Oxides of phosphorus
7.2.4. Phosphorus containing oxyacids

7. Phosphorus and P-containing compounds

7.1. Elementary phosphorus

- electronic configuration: 3s23p3
- hybridisation: sp3d
- oxidation numbers: +III, +IV, +V

7.1.1. Physical properties.
Allotropic modifications

- white (yellow) phosphorus (P4)
- red phosphorus (Px)
- black phosphorus

structure of P4
molecules

7.1.2. Chemical properties

- combustion: P4 + 5O2 P4O10 (P2O5)

phosphorescence

- with nonmetals: 4PCl3 phosphorus trichloride
P4 + 6Cl2 4PCl5 phosphorus pentachloride

PCl3 + Cl2

- with metals: P4 + 6Ca 2Ca3P2

calcium phosphide

7.1.3. Occurrence Ca5(PO4)3F apatite (Cl, OH)
Ca3(PO4)2 phosphorite

7.1.4. Use

- production of fertilizers (phosphate),
- manufacture of safety match (phosphorus),
- foodstuff industry (phosphoric acid)

7.2. Phosphorus containing compounds

7.2.1. Phosphine (phosphan), PH3
- garlic like odour, very poisonous

- in air will be oxidized readily, ignites spontaneously

Ca3P2 + 6H2O 3 Ca(OH)2 + 2 PH3
calcium phosphide

7.2.2. Phosphorus halides

- phosphorus trichloride, -bromide, -triiodide PX3, (X= Cl, Br, I)
- phosphorus oxychloride, POCl3
- phosphorus pentachloride, -bromide, PX5, (X= Cl, Br)

- Use: important halogenating agents
(especially in organic transformations):

R-OH PX3 R-X

7.2.3. Oxides of phosphorus

Phosphorus(III) oxide, P4O6, Phosphorus(V) oxide, P4O10

OPO O
O
OPO
PO P
OPO O O P O
PO
OPO

O

- white cryst. substance

- strong dehydrating agent

Reaction of phosphorus(V) oxide with water

P4O10 + 2H2O (HPO3)4
HPO3 + H2O
metaphosphoric acid

H3PO4 ortophosphoric acid

P4O10 + 4H2O 2H4P2O7 diphosphoric acid

7.2.4. Phosphorus containing oxyacids

Phosphoric acid, H3PO4
- mp. 42oC, stable compound, well soluble in water

- dissociation in 3 steps: H2PO4- + H3O+ K1 = 1,1*10-2
HPO42- + H3O+ K2 = 1,2*10-7
H3PO4 + H2O PO43- + H3O+ K2 = 1,8*10-12
H2PO4- + H2O
HPO42- + H2O

- upon heating diphosphoric acid and
(poly)metaphosphoric acid

OO

2 H3PO4 215oC H4P2O7 HO P O P OH

- H2O OH OH

diphosphoric acid

n H3PO4 325oC (HPO3) n OOO
- nH2O
POPOPO
OH OH OH

polymetaphosphoric acid

- Salts of phosphorus acid, H3PO4
primary, secondary, tertiary phosphates

Sodium dihydrogenphosphate, NaH2PO4 primary sodium phosphate
Disodium hydrogenphosphat, Na2HPO4 secondary sodium phosphate
Trisodium phosphat, Na3PO4 tertiary sodium phosphate

Ca3(PO4)2 + 2H2SO4 Ca(H2PO4)2 + 2CaSO4
„Superphosphate”

Use: in agriculture (fertilizer)

Other P-containing oxyacids

H3PO2 phosphinic acid - phosphonous acid

- formation: 4P + 6H2O PH3 + 3H3PO2

H3PO3 phosphorous acid - phosphonic acid