Phosphorous Pentabromide (PBr5) Properties (25 Complete Facts)

PBr5 is the Penta-halogenated molecule of phosphorus where the central atom is sp3d hybridized along with five Br atoms. Let us explore PBr5 in detail.

All the axial and equatorial bond length is equal for the PBr5 as per Berry pseudorotation. Generally, the Br which are present in the axial site are less s character and for this reason, they are longer than equatorial. Due to sp3d hybridization, the 3d orbital of P is involved in the bond formation with Br atoms.

Phosphorus pentabromide also converts carboxylic acid to acetyl bromide.  Here we should discuss some basic properties of PBr5 with a proper explanation like oxidation state, crystal, acidity, and basicity in the following part of the article.

1. PBr5 IUPAC name

The IUPAC name of the PBr5 is phosphorus pentabromide as bromine is present as an anionic part, so “de” is added as a suffix, and five is called Penta which is added as the prefix of the anionic part. It is also known as pentabromophosphine.

2. PBr5 chemical formula

PBr5 is the chemical formula of phosphorus pentabromide, as there are phosphorous and bromine present a 1:5 proportion, as P bears the cationic part so it comes first followed by three bromide ions.

PBr5 Structure

3. PBr5 CAS number

7789-69-7 is the CAS number (up to 10 digits number given by chemical abstract service) of PBr5 and using this number we can get information about the molecule.

4. PBr5 Chem Spider ID

PBr5 has chem spider ID 56429 (given by the Royal Society of Science like the CAS number which is unique for each molecule).

5. PBr5 chemical classification

PBr5 is classified into the following categories,

  • PBr5 is strong lewis acid
  • PBr5 is a π-acidic ligand
  • PBr5 is an organic reagent
  • PBr5 is an inorganic covalent molecule

6. PBr5 molar mass

PBr5 has a molar mass of 430.49 g/mol which is the summation of the total atomic mass of one P and five Br atoms. P has an atomic mass of 30.97 g/mol and each Br has an atomic mass of 79.884 g/mol so in the PBr5 total molar mass is 30.97 + (79.884*5) = 430.49 g/mol as there are five Br atoms present.

7. PBr5 color

PBr5 has characteristics of yellow color due to the electronic transition between the d orbital of P and the p orbital of Br atoms.

8. PBr5 viscosity

The viscosity of PBr5 in liquid form is very low about 0.000954 pas at room temperature because it exists solid at room temperature. The solid or gaseous form did not have viscosity as it is the property for liquid only. 

9. PBr5 molar density

The molar density of solid PBr5 is 3.49 g/L as it has a molar mass of 430.49 g/mol and as per Avogardo’s calculation the volume of each element is 22.4L and here six elements are present, so the molar density of PBr5 will be 430.49/(22.4*6) = 3.49 g/L.

10. PBr5 melting point

The melting point of PBr5 is lower than 1000C due to its weak lattice crystal, so it can decompose into a liquid state under 1000C.

11. PBr5 boiling point

1060C or 279K is the boiling temperature for pentabromo phosphine, due to weak van der waal’s force of attraction it needs lower energy to get boiled off and converts into a gaseous state but higher than its melting temperature.

12. PBr5 state at room temperature

PBr5 is a yellow solid molecule at room temperature and on heating, it can decompose to PBr3 and Br2. It adopts orthorhombic crystal in a solid state at room temperature in its lattice form from the X-ray crystal it is confirmed.

13. PBr5 covalent bond

All bonds present in PBr5 are covalent in nature and they are formed due to the sp3d hybridization of central P like another covalent bond. So, here each Br and P share their electrons to construct each bond, and all the bonds are formed by the sharing of electrons.

14. PBr5 covalent radius

Phosphorous and bromine have covalent radii 195 and 185 pm as there is no covalent radius found for molecules so we can predict the covalent radius of individually substituent atoms.

15. PBr5 electron configurations

Electron configuration is the arrangement of electrons in a particular shell having a particular quantum number of an element. Let us find the electron configuration of PBr5.

The electronic configurations of P and Br are [Ne]3s23p3 and [Ar]3d104s24p5 which are the not electronic configuration of PBr5 itself because for molecules we cannot predict the configuration.

16. PBr5 oxidation state

The central P is in a +5 oxidation state in PBr5 where all the Br are in a -1 oxidation state. The oxidation state can be evaluated from their stable valency. Due to the -1 oxidation state of 5 Br atoms, the molecule has no charge appears and it is satisfied by the +5 oxidation state of P.

17. PBr5 acidity

PBr5 is acidic in nature rather it is strong lewis acid due to the presence of vacant d orbital of P, so it can accept electrons from the suitable lewis base or electron-rich system. Due to the five electronegative Br atoms, they pulled the electron density from the P site, and its lewis acidity further increases.

18. Is PBr5 odorless?

PBr5 has a pungent smell due to the hydrolysis of the molecule to the formation of hydrobromic acid.

19. Is PBr5 paramagnetic?

The paramagnetic nature of a molecule depends on the availability of unpaired electrons in the valence shell. Let us see whether PBr5 is paramagnetic or not.

PBr5 is neither paramagnetic nor diamagnetic because all five valence electrons for P are being used in the bond formation with five Br atoms. So, lacks electrons either unpaired or paired form we can not predict its magnetic property.

20. PBr5 hydrates

There is no such hydrated part present in the crystal form of the PBr5 molecule but it can undergo rapid hydrolysis from hydrobromic acid. It is a hydrophobic molecule. The electronegative F atoms can be attached to the water molecule by the H-bond because they form the best hydrogen bond.

21. PBr5 crystal structure

In the lattice form, PBr5 adopts orthorhombic crystal where a, b, and c values for the lattice crystal are 792, 836, and 1122 pm and α, β, and γ values are 900. There is a total of 16 atoms present in a single crystal which means four PBr5 molecules per crystal and it is a three-dimensional crystal lattice.

22. PBr5 polarity and conductivity

PBr5 is conductive and non-polar due to the following reason,

  • PBr5 can be ionized to PBr4+ and Br.
  • Due to the formed high electronegative bromide ions,PBr5 can easily carry electricity.
  • PBr5 will have dipole flows from electronegative Br to electropositive P atoms.
  • PBr5 has an asymmetric shape trigonal bipyramidal.
  • Although PBr5 has an asymmetric shape due to the arrangement the dipole will cancel out each other.
  • PBr5 has zero dipole-moment value.

23. PBr5 reaction with acid

PBr5 itself is an acid molecule so the reaction of acid is very little but it can react with the organic acid molecules to form corresponding acyl bromide and the reaction proceed via nucleophilic substitution bimolecular pathway (SN2 mechanism). It is also known as Hell-Volhard-Zelinsky halogenation.

Alpha Halogenation of PBr5

24. PBr5 reaction with base

Being a lewis acid it can react with lewis bases accept the lone pairs or electron density from them and formed an adduct or complex.

PBr5 + NH3 = H3N-PBr5

25. PBr5 reaction with oxide

PBr5 can react with the oxide of hydrogen to form hydrobromic acid, it can react very rapidly and vigorously with water. Also, it can convert to PBr3 and reacts with the -OH group in organic chemistry to form alkyl bromide.

  • PBr5 + H2O = HBr
  • CH3-CH2-OH + PBr5 = CH3-CH2-Br

26. PBr5 reaction with the metal

Due to the lower reduction potential of phosphorus than transition metal, it cannot reduce metal and not react with metal for displacement reaction.

Conclusion

PBr5 is a useful reagent in organic chemistry, it can supply PBr3 in a reaction that can convert -OH to alkyl bromide or acid to acetyl bromide. It can react with oxygen to form phosphorus pentaoxide.

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