What is Phosphorus Triiodide?
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
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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
1. What is phosphorus triiodide?
Phosphorus triiodide is an inorganic compound with the chemical formula PI₃. It consists of one central phosphorus atom covalently bonded to three iodine atoms. It appears as a dark red solid and is known for being highly reactive, especially with water.
2. What are the main physical properties of phosphorus triiodide?
The key physical properties of phosphorus triiodide include:
- Appearance: It is a red to dark-red crystalline solid.
- Stability: It is an unstable compound, particularly at higher temperatures.
- Reactivity: It reacts violently with water.
- Molar Mass: Its molecular weight is approximately 411.69 g/mol.
- Nature: It is corrosive and can cause irritation.
3. What is phosphorus triiodide commonly used for?
In organic chemistry, phosphorus triiodide is a very useful reagent. Its primary use is to convert primary and secondary alcohols into alkyl iodides. This is an important step in many chemical synthesis processes. It also functions as a powerful reducing agent.
4. How is phosphorus triiodide typically prepared?
Phosphorus triiodide is usually made by reacting white phosphorus (P₄) with elemental iodine (I₂). To control the reaction, which is highly exothermic, it is often carried out in an inert solvent like carbon disulfide (CS₂).
5. Why is phosphorus triiodide a covalent compound, not an ionic one?
Phosphorus triiodide is a covalent compound because it is formed between two non-metals (phosphorus and iodine). The difference in electronegativity between them is too small for electrons to be transferred completely. Instead, they share electrons to form stable covalent bonds.
6. What is the molecular shape of PI₃ according to VSEPR theory?
According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the central phosphorus atom in PI₃ has three bonding pairs and one lone pair of electrons. This arrangement results in a trigonal pyramidal shape, similar to ammonia (NH₃).
7. Is the phosphorus triiodide molecule polar or non-polar, and why?
The PI₃ molecule is polar. Although the individual P-I bonds have very low polarity, the molecule's overall shape is asymmetrical due to the lone pair of electrons on the phosphorus atom. This uneven distribution of electron density creates a net dipole moment, making the entire molecule polar.
