Lead tetrachloride, also known as lead(IV) chloride, has the molecular formula PbCl₄. It is a yellow, oily liquid which is stable below 0 °C, and decomposes at 50 °C. It has a tetrahedral configuration, with

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

as the central atom. The Pb– Cl

covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

s have been measured to be 247 pm and the

bond energy In chemistry, bond energy (''BE'') is one measure of the strength of a chemical bond. It is sometimes called the mean bond, bond enthalpy, average bond enthalpy, or bond strength. IUPAC defines bond energy as the average value of the gas-phase b ...

is 243 kJ⋅mol⁻¹.

Synthesis

Lead tetrachloride can be made by reacting

lead(II) chloride 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 min ...

PbCl₂, and

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

HCl, in the presence of

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

gas (Cl₂), leading to the formation of chloroplumbic acid H₂PbCl₆. It is then converted to the

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

salt (NH₄)₂PbCl₆ by adding

ammonium chloride Ammonium chloride is an inorganic chemical compound with the chemical formula , also written as . It is an ammonium salt of hydrogen chloride. It consists of ammonium cations and chloride anions . It is a white crystalline salt (chemistry), sal ...

(NH₄Cl). Finally, the solution is treated with concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

H₂SO₄, to separate out lead tetrachloride. This series of reactions is conducted at 0 °C. The following equations illustrate the reaction: :PbCl₂ + 2HCl + Cl₂ → H₂PbCl₆ :H₂PbCl₆ + 2 NH₄Cl → (NH₄)₂PbCl₆ + 2HCl :(NH₄)₂PbCl₆ + H₂SO₄ → PbCl₄+ 2HCl + (NH₄)₂SO₄

Reaction with water

Unlike

carbon tetrachloride Carbon tetrachloride, also known by many other names (such as carbon tet for short and tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC), is a chemical compound with the chemical formula CCl4. It is a n ...

, another group IV (IUPAC: group 14) chloride, lead tetrachloride reacts with

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. This is because the central atom is bigger (Pb is bigger than C) so there is less

cluttering Cluttering is a speech and communication disorder characterized by a rapid rate of speech, erratic rhythm, and poor syntax or grammar, making speech difficult to understand. Classification Cluttering is a speech and communication disorder th ...

and water can easily access it. Also, because of the presence of empty d orbitals on the Pb atom,

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

can bind to it before a Pb–Cl bond has to break, thus requiring less

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

. The overall reaction is thus as follows: :PbCl₄ + 2H₂O → PbO₂(s) + 4HCl(g)

Stability

Lead tetrachloride tends to

decompose Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essen ...

further into lead dichloride and chlorine gas: :PbCl₄ → PbCl₂ + Cl₂(g) There are reports that this reaction can proceed explosively and that the compound is best stored under pure sulfuric acid at -80 °C in the dark.''The Chemistry of Germanium: Tin and Lead'' Elsevier, 2014, , The stability of the +4

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

decreases as we travel down this group of the periodic table. Thus while carbon tetrachloride is a stable compound, with lead the oxidation state +2 is favored and PbCl₄ quickly becomes PbCl₂. Indeed, the

inert pair effect The inert-pair effect is the tendency of the two electrons in the outermost atomic ''s''-orbital to remain unshared in compounds of post-transition metals. The term ''inert-pair effect'' is often used in relation to the increasing stability of o ...

causes lead to favor its +2 oxidation state: Pb atom loses all its outermost p electrons and ends up with a stable, filled s subshell.

Toxicity

Lead is a cumulative poison. Only limited evidence have been shown of lead's

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

ic effect, but lead tetrachloride, as well as all other lead compounds, is "reasonably anticipated to be human carcinogens" according to the ''Report on Carcinogens'', Twelfth Edition (2011). Lead can be absorbed by the body through several routes, primarily inhalation but also ingestion and dermal contact. Lead compounds are also teratogens.

References

{{Chlorides Lead(IV) compounds Chlorides Metal halides