Lead(II) chloride

Lead(II) chloride
IUPAC name Lead(II) chloride Lead dichloride
Other names Plumbous chloride Cotunnite
Identifiers
CAS number	7758-95-4 Y
PubChem	166945
ChemSpider	22867 Y
Jmol-3D images	Image 1
SMILES Cl[Pb]Cl
InChI InChI=1S/2ClH.Pb/h2*1H;/q;;+2/p-2 Y Key: HWSZZLVAJGOAAY-UHFFFAOYSA-L Y
Properties
Molecular formula	PbCl2
Molar mass	278.10 g/mol
Appearance	white odorless solid
Density	5.85 g/cm3
Melting point	501 °C
Boiling point	950 °C
Solubility in water	6.73 g/L (0 °C) 9.9 g/L (20 °C) 33.4 g/L (100 °C)
Solubility product, Ksp	1.7×10−5
Solubility	slightly soluble in dilute HCl, ammonia; insoluble in alcohol
Refractive index (nD)	2.199[1]
Structure
Crystal structure	Orthorhombic, oP12
Space group	Pnma, No. 62
Thermochemistry
Std enthalpy of formation ΔfHo298	-359.41 kJ/mol
Standard molar entropy So298	135.98 J K−1 mol−1
Hazards
MSDS	External MSDS
EU Index	082-001-00-6
EU classification	Repr. Cat. 1/3 Harmful (Xn) Dangerous for the environment (N)
R-phrases	R61, R20/22, R33, R62, R50/53
S-phrases	S53, S45, S60, S61
NFPA 704	0 3 0
Related compounds
Other anions	Lead(II) fluoride Lead(II) bromide Lead(II) iodide
Other cations	Lead(IV) chloride Tin(II) chloride Germanium(II) chloride
Related compounds	Thallium(I) chloride Bismuth chloride
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y chloride (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lead(II) chloride (PbCl₂) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mineral cotunnite.

Structure and properties

In solid PbCl₂, each lead ion is coordinated by 9 chloride ions – 6 lie at the apices of a trigonal prism and 3 lie beyond the centers of each prism face. The 9 chloride ions are not equidistant from the central lead atom, 7 lie at 280–309 pm and 2 at 370 pm.^[2] PbCl₂ forms white orthorhombic needles.

Vaporized PbCl₂ molecules have a bent structure with the Cl-Pb-Cl angle being 98° and each Pb-Cl bond distance being 2.44 Å.^[3] Such PbCl₂ is emitted from internal combustion engines that use ethylene chloride-tetraethyllead additives for antiknock purposes.

The solubility of PbCl₂ in water is low (9.9 g/L at 20 °C) and for practical purposes it is considered insoluble. Its solubility product constant (K_sp) is 1.7×10⁻⁵. It is one of only four commonly insoluble chlorides, the other three being silver chloride (AgCl) with K_sp = 1.8×10⁻¹⁰, copper(I) chloride (CuCl) with K_sp = 1.72×10⁻⁷ and mercury(I) chloride (Hg₂Cl₂) with K_sp = 1.3×10⁻¹⁸.^[4][5]

Occurrence

Crystal structure of cotunnite, PbCl₂

PbCl₂ occurs naturally in the form of the mineral cotunnite. It is colorless, white, yellow, or green with a density of 5.3–5.8 g/cm³. The hardness on the Mohs scale is 1.5–2. The crystal structure is orthorhombic dipyramidal and the point group is 2/m 2/m 2/m. Each Pb has a coordination number of 9. The composition is 74.50% Pb and 25.50% Cl. Cotunnite occurs near volcanoes: Vesuvius, Italy; Tarapacá, Chile; and Tolbachik, Russia.^[6]

Synthesis

Lead(II) chloride precipitates from solution upon addition of chloride sources (HCl, NaCl, KCl) to aqueous solutions of lead(II) compounds such as Pb(NO₃)₂.

Pb(NO₃)_2(aq) + 2 NaCl_(aq) → PbCl_2(s) + 2 NaNO_3(aq)

Pb(CH₃COO)_2(aq) + HCl_(aq) → PbCl_2(s) + 2 CH₃COOH_(aq)

basic PbCO₃ + 2 HCl_(aq) → PbCl_2(s) + CO_2(g) + H₂O^[7]

Pb(NO₃)_2(aq) + 2 HCl_(aq) → PbCl_2(s) + 2 HNO_3(aq)

Treatment of lead dioxide with hydrochloric acid gives lead(II) chloride as well as chlorine gas:

PbO₂(s) + 4 HCl → PbCl_2(s) + Cl₂ + 2 H₂O

Treatment of lead oxide with hydrochloric acid gives lead(II) chloride as well as water

PbO(s) + 2 HCl → PbCl_2(s) + H₂O

PbCl_2(s) also forms by the action of chlorine gas on lead metal:

Pb + Cl₂ → PbCl₂

Reactions

Addition of chloride ions to a suspension of PbCl₂ gives rise to soluble complex ions. In these reactions the additional chloride (or other ligands) break up the chloride bridges that comprise the polymeric framework of solid PbCl_2(s).

PbCl_2(s) + Cl^- → [PbCl₃]^-_(aq)

PbCl_2(s) + 2 Cl^- → [PbCl₄]^2-_(aq)

PbCl₂ reacts with molten NaNO₂ to give PbO:

PbCl_2(l) + 3 NaNO₂ → PbO + NaNO₃ + 2 NO + 2 NaCl

PbCl₂ is used in synthesis of lead(IV) chloride (PbCl₄): Cl₂ is bubbled through a saturated solution of PbCl₂ in aqueous NH₄Cl forming [NH₄]₂[PbCl₆]. The latter is reacted with cold concentrated sulfuric acid (H₂SO₄) forming PbCl₄ as an oil.^[8]

Lead(II) chloride is the main precursor for organometallic derivatives of lead, such as plumbocenes.^[9] The usual alkylating agents are employed, including Grignard reagents and organolithium compounds:

2 PbCl₂ + 4 RLi → R₄Pb + 4 LiCl + Pb

2 PbCl₂ + 4 RMgBr → R₄Pb + Pb + 4 MgBrCl

3 PbCl₂ + 6 RMgBr → R₃Pb-PbR₃ + Pb + 6 MgBrCl^[10]

These reactions produce derivatives that are more similar to organosilicon compounds, i.e. that Pb(II) tends to disproportionate upon alkylation.

Uses

• Molten PbCl₂ is used in the synthesis of lead titanate (PbTiO₃) and barium lead titanate ceramics by cation replacement reactions:^[11]

xPbCl_2(l) + BaTiO_3(s) → Ba_1-xPb_xTiO₃ + xBaCl₂

• PbCl₂ is used in production of infrared transmitting glass,^[7] and ornamental glass called aurene glass. Aurene glass has an iridescent surface formed by spraying with PbCl₂ and reheating under controlled conditions. Stannous chloride (SnCl₂) is used for the same purpose.^[12]
• Pb is used in HCl service even though the PbCl₂ formed is slightly soluble in HCl. Addition of 6–25% of antimony (Sb) increases corrosion resistance.^[13]
• A basic chloride of lead, PbCl₂·Pb(OH)₂, is known as Pattinson's white lead and is used as pigment in white paint.^[14]
• PbCl₂ is an intermediate in refining bismuth (Bi) ore. The ore containing Bi, Pb, and Zn is first treated with molten caustic soda to remove traces of acidic elements such as arsenic and tellurium. This is followed by the Parkes desilverization process to remove any silver and gold present. The ore now contains Bi, Pb, and Zn. It is treated with Cl₂ gas at 500 °C. ZnCl₂ forms first and is removed. Then PbCl₂ forms and is removed leaving pure Bi. BiCl₂ would form last.^[15]

Toxicity

Like other lead containing compounds, exposure to PbCl₂ may cause lead poisoning.

References

1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
2. ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
3. ^ Hargittai, I; Tremmel, J; Vajda, E; Ishchenko, A; Ivanov, A; Ivashkevich, L; Spiridonov, V (1977). "Two independent gas electron diffraction investigations of the structure of plumbous chloride". Journal of Molecular Structure 42: 147. doi:10.1016/0022-2860(77)87038-5. 
4. ^ CRC Handbook of Chemistry and Physics, 79th Edition, David R. Lide (Ed), p. 8-108
5. ^ Brown, Lemay, Burnsten. "Chemistry The Central Science". Solubility-Product Constants for Compounds at 25 °C. (ed 6, 1994). p. 1017
6. ^ Cotunnite
7. ^ ^{a b} Dictionary of Inorganic and Organometallic Compounds. Lead(II) Chloride. [1]
8. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 365. ISBN 978-0130399137. 
9. ^ Lowack, R (1994). "Decasubstituted decaphenylmetallocenes". J. Organomet. Chem. 476: 25. doi:10.1016/0022-328X(94)84136-5. 
10. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 524. ISBN 978-0130399137. 
11. ^ Aboujalil, Almaz; Deloume, Jean-Pierre; Chassagneux, Fernand; Scharff, Jean-Pierre; Durand, Bernard (1998). "Molten salt synthesis of the lead titanate PbTiO3, investigation of the reactivity of various titanium and lead salts with molten alkali-metal nitrites". Journal of Materials Chemistry 8 (7): 1601. doi:10.1039/a800003d. 
12. ^ Stained Glass Terms and Definitions. aurene glass
13. ^ Kirk-Othmer. "Encyclopedia of Chemical Technology". (ed 4). p 913
14. ^ Perry & Phillips. "Handbook of Inorganic Compounds". (1995). p 213
15. ^ Kirk-Othmer. "Encyclopedia of Chemical Technology". (ed 4). p 241

External links

• IARC Monograph: "Lead and Lead Compounds"
• IARC Monograph: "Inorganic and Organic Lead Compounds"
• National Pollutant Inventory – Lead and Lead Compounds Fact Sheet
• Case Studies in Environmental Medicine – Lead Toxicity
• ToxFAQs: Lead