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Phosphorus compounds mainly include phosphorus oxides, oxyacids and their salts, halides, sulfides, etc.
The most important of which is phosphorus oxyacids and their salts
.
12.
4.
1 Elemental Phosphorus
There are three main allotropes of phosphorus : white phosphorus , red phosphorus and black phosphorus
.
The molecular formula of white phosphorus is P4, tetrahedral structure, slightly yellow, also called yellow phosphorus; red phosphorus has a chain structure; black phosphorus has a flaky structure (Figure 12-10)
Figure 12-10 The structure of phosphorus elemental allotrope
In white phosphorus, ∠PPP is 60°, the p-orbital overlap of phosphorus is small, the tension is large, the bond energy is small (only 201 kJ·mol -1 ), and it is unstable
.
White phosphorus has high reactivity.
It oxidizes slowly in the air and then spontaneously ignites.
White phosphorus disproportionates in alkali to generate hypophosphite and phosphine
.
P 4 +3NaOH+3H 2 O=PH 3 +3NaH 2 PO 2
12.
4.
2 Phosphorus hydrides
Phosphorus hydrides mainly include phosphine (PH 3 , also known as Teng) and Lian Teng (P 2 H 4 )
.
Phosphorus hydride is highly toxic, has strong reducing power, and can spontaneously combust in the air
PH 3 is a colorless, highly toxic gas with garlic smell (boiling point -87.
78°C).
Its solubility in water is much lower than that of NH 3.
The pH of the solution has little effect on the solubility of PH 3
.
Because P has an empty d orbital, it can form dd π coordination bonds with transition metals, such as Cu(PH 3 ) 2 Cl, Cr(CO) 3 (PH 3 ) 3 and so on
.
The coordination ability of PH 3 with transition metals is stronger than that of NH 3 , but the coordination ability with H + is not as good as NH 3 , so PH 3 is extremely weak
12.
4.
3 Phosphorus oxides
1.
Phosphorus trioxide
Phosphorus oxide is formed on the basis of P 4 tetrahedron
.
The PP bond in the P 4 molecule is broken and an oxygen atom is inserted between every two P atoms to form a P 4 O 6 molecule (Figure 12-11).
P 2 O 3 is a creamy white solid (melting point 23.
8°C, boiling point 173°C).
It is toxic and easily soluble in organic solvents.
When dissolved in cold water, it slowly generates phosphorous acid and undergoes disproportionation reaction with hot water
.
Figure 12-11 Structure of P 4 O 6 and P 4 O 10
2.
Phosphorus Pentoxide
The chemical formula of P 4 O 10 is P 2 O 5 , abbreviated as phosphorus pentoxide.
Between P and terminal O in the molecule, there is a σ coordination bond (the P hybrid orbital electron is coordinated to the p orbital of O) and dp The π coordination bond (the electron of the p orbital of O is coordinated to the empty d orbital of P) is combined, so it can be considered that P and the terminal O form a double bond (Figure 12-11)
.
P 4 O 10 is a white powder (melting point 562°C), which is easy to sublime, has strong water absorption and dehydration, and is easy to deliquesce in the air.
It is a desiccant with the strongest drying ability
.
P 4 O 10 reacts with water to generate various oxygen-containing acids
The conversion rate of P 4 O 10 into H 3 PO 4 by the interaction of excess water is slow, and the conversion rate can be accelerated when HNO 3 is used as a catalyst
Related link: Preparation of nitric acid
