What is Phosphorus Triiodide Definition Structure Preparation and Reactions
Phosphorus triiodide is an inorganic compound composed of one phosphorus and three iodine atoms. Phosphorus forms two types of halides, phosphorus trihalides, and phosphorus pentahalides. The covalency of phosphorus in phosphorus trihalides is three and five in pentahalides. In this article, we will discuss the phosphorus triiodide structure PI3.
The chemical properties of phosphorus triiodide PI3 depend upon the electronic configuration and hybridization of the phosphorus. The uses of phosphorus PI3 are different from the other phosphorus trihalide, due to its chemical and physical properties. The chemical representation of phosphorus triiodide can be answered by the same question as what is the formula for phosphorus triiodide.
What is the Chemical Formula for Phosphorus Triiodide?
The most common question asked while studying harmful phosphorus compounds in inorganic chemistry is that what is the formula for phosphorus triiodide? The answer to this question is PI3.
Phosphorus Triiodide Structure PI3
(Image to be added soon)
The structure of phosphorus triiodide contains three single sigma bonds between phosphorus and iodine and one lone pair. The bond length is 243 pico meters and the bond angle between the two bonds is 102 degrees celsius. Due to the repulsion between the lone pair and bond pair the angle is less than tetrahedral. Phosphorus triiodide structure PI3 represents the distorted tetrahedral shape.
Preparation of Phosphorus Triiodide
Phosphorus triiodide is prepared by the free elements union method. Generally, iodine is mixed with the solution of white phosphorus in the neutral medium. Carbon disulfide is added in the preparation reaction of phosphorus triiodide. It provides a neutral medium for the reaction.
P4 + 6I2 → 4PI3
Another method for the preparation of phosphorus triiodide is the conversion of other phosphorus halides like phosphorus chloride and phosphorus bromide to the phosphorus triiodide by the addition of an iodide source (hydrogen iodide or metal iodide). The source of the iodine used in this reaction can be organic or inorganic.
PCl3 + 3HI → PI3 + 3HCl
Properties of Phosphorus Triiodide
Physical Properties of Phosphorus Triiodide PI3
Phosphorus triiodide exists in solid form.
It is generally found in the red colour.
It is corrosive in nature.
It acts as an irritant compound.
The molecular weight of the phosphorus triiodide is 411.6872 g/mol.
The density of phosphorus triiodide is 4.18 g/cm3.
The boiling point of phosphorus triiodide is 200 degrees celsius.
The melting point of the phosphorus triiodide is 61.2 degrees celsius.
Chemical Properties of Phosphorus Triiodide PI3
The dipole moment of Phosphorus triiodide is nearly zero.
The P-I bond is weak in nature.
Phosphorus triiodide is an unstable molecule. Therefore, reactive in nature.
Phosphorus triiodide reacts violently with water.
PI3 + 3H2O → H3PO3 + 3HI
Phosphorus triiodide is a good reducing agent in nature.
The standard enthalpy of formation of phosphorus triiodide is -46 KJ/mol.
The NMR chemical shift for phosphorus triiodide is 178 ppm.
Phosphorus triiodide reacts with methyl iodide in the presence of mercury and forms a complex (Trimethyl Phosphine Mercury) as a product.
PI3 + 3CH3I + Hg → [(CH3)3PHgI2]
Uses of Phosphorus Triiodide
The uses of phosphorus PI3 are discussed below:
Phosphorus triiodide is widely used in organic chemistry branch laboratories for converting alkane halide to alkane iodide.
It is used as various substitution reactions like the substitution of a hydroxyl group from alcohol.
Phosphorus triiodide is used in the manufacturing of phosphoric acid.
Phosphorus triiodide is used in the manufacturing of idopyrazines.
Did You Know?
Phosphorus triiodide can act as a nucleophile. Due to the presence of one lone pair, it can donate this pair to the electron-deficient compounds.
PI3 can also act as an electrophile. Due to the presence of an empty d orbital, it can accept electrons from electron-rich compounds and expands its valency to 5.
PI3 is highly toxic in nature.
PI3 violently reacts with water and produces large amounts of heat.
PI3 causes irritation to the eyes, skin, and respiratory system.
FAQs on Phosphorus Triiodide P I3 Properties and Chemistry
1. What is phosphorus triiodide?
Phosphorus triiodide is a covalent inorganic compound with the chemical formula PI3 composed of one phosphorus atom and three iodine atoms.
- It appears as a red or dark solid.
- It is mainly used in organic chemistry to convert alcohols into alkyl iodides.
- It reacts readily with water, undergoing hydrolysis.
2. What is the formula for phosphorus triiodide?
The chemical formula for phosphorus triiodide is PI3.
- "P" represents phosphorus.
- "I" represents iodine.
- The subscript 3 shows that three iodine atoms are bonded to one phosphorus atom.
3. How is phosphorus triiodide prepared in the laboratory?
Phosphorus triiodide is prepared by the direct combination of solid phosphorus and iodine according to the balanced equation 2P(s) + 3I2(s) → 2PI3(s).
- Red phosphorus is mixed with iodine crystals.
- The reaction is exothermic and forms solid PI3.
- The product is purified under dry conditions to prevent hydrolysis.
4. What is the structure and shape of phosphorus triiodide?
Phosphorus triiodide has a trigonal pyramidal molecular geometry due to one lone pair on the phosphorus atom.
- Phosphorus forms three single P–I covalent bonds.
- There are four electron domains (3 bonding pairs + 1 lone pair).
- According to VSEPR theory, this gives a tetrahedral electron geometry and trigonal pyramidal shape.
5. Is phosphorus triiodide ionic or covalent?
Phosphorus triiodide is a covalent compound because it is formed between nonmetals (phosphorus and iodine) sharing electrons.
- The P–I bonds involve shared electron pairs.
- It exists as discrete PI3 molecules rather than ions.
- It has relatively low melting and boiling points compared to ionic compounds.
6. What happens when phosphorus triiodide reacts with water?
Phosphorus triiodide undergoes hydrolysis with water to form phosphorous acid and hydrogen iodide according to PI3(s) + 3H2O(l) → H3PO3(aq) + 3HI(aq).
- The reaction is rapid and exothermic.
- Phosphorous acid (H3PO3) is produced.
- Hydrogen iodide (HI) is released as a strong acid.
7. What is phosphorus triiodide used for in organic chemistry?
Phosphorus triiodide is mainly used to convert alcohols into alkyl iodides via a substitution reaction.
- General reaction: 3ROH + PI3 → 3RI + H3PO3
- The –OH group of the alcohol is replaced by iodine.
- This reaction is useful for preparing primary and secondary alkyl iodides.
8. What is the oxidation state of phosphorus in phosphorus triiodide?
The oxidation state of phosphorus in PI3 is +3.
- Iodine typically has an oxidation state of −1.
- With three iodine atoms, total iodine charge = −3.
- To make the molecule neutral, phosphorus must be +3.
9. What is the molar mass of phosphorus triiodide?
The molar mass of phosphorus triiodide (PI3) is approximately 411.69 g/mol.
- Phosphorus (P): 30.97 g/mol
- Iodine (I): 126.90 g/mol × 3 = 380.70 g/mol
- Total = 30.97 + 380.70 = 411.67 g/mol (≈ 411.69 g/mol)
10. What is the difference between phosphorus triiodide and phosphorus pentaiodide?
Phosphorus triiodide (PI3) contains phosphorus in the +3 oxidation state, while phosphorus pentaiodide (PI5) would contain phosphorus in the +5 oxidation state.
- PI3 is a well-known stable compound.
- PI5 is not stable under normal conditions and readily decomposes to PI3 and I2.
- PI3 has trigonal pyramidal geometry, while PI5 (if formed) would have trigonal bipyramidal geometry.
