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 with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

as the central atom. The Pb– Cl covalent bonds have been measured to be 247 pm and the

bond energy In chemistry, bond energy (''BE''), also called the mean bond enthalpy or average bond enthalpy is the measure of bond strength in a chemical bond. IUPAC defines bond energy as the average value of the gas-phase bond-dissociation energy (usually ...

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 mi ...

PbCl₂, and

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

HCl, in the presence of

chlorine Chlorine is a chemical element with the 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 them. Chlorine i ...

gas (Cl₂), leading to the formation of chloroplumbic acid H₂PbCl₆. It is then converted to the ammonium salt (NH₄)₂PbCl₆ by adding ammonium chloride (NH₄Cl). Finally, the solution is treated with concentrated sulfuric acid 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, another group IV (IUPAC: group 14) chloride, lead tetrachloride reacts with

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

. This is because the central atom is bigger (Pb is bigger than C) so there is less cluttering and water can easily access it. Also, because of the presence of empty d orbitals on the Pb atom,

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

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

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...

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

Stability

Lead tetrachloride tends to

decompose Decomposition or rot 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 ...

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 charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

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 ox ...

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 Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...

. Only limited evidence have been shown of lead's

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

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