Phosphorus tribromide

Structural formula
General
Surname	Phosphorus tribromide
other names	Phosphorus (III) bromide; Tribromophosphine;
Molecular formula	PBr 3
Brief description	clear, colorless liquid with a pungent odor
External identifiers / databases
EC number	232-178-2
ECHA InfoCard	100.029.253
PubChem	24614
ChemSpider	23016
Wikidata	Q416401
properties
Molar mass	270.69 g mol −1
Physical state	liquid
density	2.85 g cm −3
Melting point	−41.5 ° C
boiling point	173.2 ° C
Vapor pressure	2.9 h Pa (at 20 ° C)
solubility	violent decomposition in water
Refractive index	1.687 (25 ° C)
safety instructions
H and P phrases	H: 314-335
	EUH: 014
	P: 280-261-305 + 351 + 338-310
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Phosphorus tribromide is a corrosive chemical compound of phosphorus and bromine with the chemical formula PBr ₃ . It belongs to the phosphorus halides and is a clear, colorless liquid that has a characteristic, pungent odor and smokes in the air.

Extraction and presentation

Phosphorus tribromide can be prepared from the elements . The phosphorus tribromide formed acts as a solvent for the white phosphorus (P ₄ ). To avoid the formation of phosphorus pentabromide (PBr ₅ ), phosphorus is used in excess.

{\ displaystyle \ mathrm {P_ {4} +6 \ Br_ {2} \ longrightarrow 4 \ PBr_ {3}}}

properties

Molecular geometry of PBr ₃

Phosphorus tribromide can (similar to phosphorus trifluoride or phosphorus trichloride ) act in reactions, depending on the reactants, both as a Lewis acid and as a Lewis base .

The geometry of the phosphorus tribromide molecule is not flat but, as indicated in the figure, trigonal-pyramidal (pyramid with a triangular base). The lone pair of electrons on phosphorus also takes up space and prevents the three bromine atoms from being in one plane with the phosphorus atom. This geometry is similar to that of the ammonia molecule.

use

Phosphorus tribromide is used to replace the hydroxyl group of primary and secondary - but not tertiary - alcohols with bromine. This allows alkyl bromides to be prepared :

{\ displaystyle \ mathrm {R {-} CH_ {2} OH + PBr_ {3} \ longrightarrow R {-} CH_ {2} Br + PBr_ {2} OH}}

This reaction follows the mechanism of an S _N 2 reaction .

One molecule of PBr ₃ can convert up to three hydroxyl groups. It is converted into phosphonic acid :

{\ displaystyle \ mathrm {3 \ R {-} CH_ {2} OH + PBr_ {3} \ longrightarrow 3 \ R {-} CH_ {2} Br + H_ {3} PO_ {3}}}

Similarly, carboxylic acid bromides can be prepared from carboxylic acids using phosphorus tribromide :

{\ displaystyle \ mathrm {R {-} COOH + PBr_ {3} \ longrightarrow R {-} COBr + PBr_ {2} OH}}

Phosphorus tribromide is also used as a catalyst in the α-bromination of carboxylic acids , for example in the Hell-Volhard-Zelinsky reaction .

In microelectronics and for power semiconductors , PBr _{3 is used} for doping silicon in diffusion furnaces .

safety instructions

Phosphorus tribromide and its vapors are corrosive. It reacts violently with water and a number of other substances, such as white phosphorus, alkali metals , alcohols , amines and ammonia .

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h Entry on phosphorus tribromide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Liquids, pp. 4-140.
↑ Entry on Phosphorus tribromide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ K. Peter, C. Vollhardt, NE Schore: Organic chemistry. 4th edition, Wiley-VCH Verlag, Weinheim 2005, p. 393 ff.
↑ Junction Formation Dopants for Diffusion and Ion Implantation (Table 5) . In: Device Fabrication. osha.gov, accessed August 22, 2007.
↑ RV Knoell, SP Murarka: epitaxial growth induced by phosphorus tribromide doping of polycrystalline silicon films on silicon . In: Journal of Applied Physics . tape 57 , no. 4 , 1985, pp. 1322-1327 , doi : 10.1063 / 1.334533 .

[GESTIS-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Entry on phosphorus tribromide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .

[CRC90_4_140-2] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Liquids, pp. 4-140.

[CLP_100.029.253-3] Entry on Phosphorus tribromide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .

[4] K. Peter, C. Vollhardt, NE Schore: Organic chemistry. 4th edition, Wiley-VCH Verlag, Weinheim 2005, p. 393 ff.

[5] Junction Formation Dopants for Diffusion and Ion Implantation (Table 5) . In: Device Fabrication. osha.gov, accessed August 22, 2007.

[6] RV Knoell, SP Murarka: epitaxial growth induced by phosphorus tribromide doping of polycrystalline silicon films on silicon . In: Journal of Applied Physics . tape 57 , no. 4 , 1985, pp. 1322-1327 , doi : 10.1063 / 1.334533 .