Свинец(IV) ацетат

Описание

Lead (IV) acetate or lead tetraacetate is a chemical compound with chemical formula Pb(C₂H₃O₂)₄ and is a lead salt of acetic acid. It is commercially available often stabilized with acetic acid.

Химические свойства

Lead tetraacetate (plumbic acetate), Pb(C2H3O2)4, is a colorless, monoclinic crystalline solid that is soluble in chloroform and in hot acetic acid, but decomposes in cold water and in ethyl alcohol. Lead tetraacetate can be prepared by adding warm, water-free, glacial acetate acid to red lead, Pb3O4, and subsequent cooling. The salt decomposes with the addition of water to give PbO2, but the yield can be improved by passing in chlorine gas. Lead tetraacetate is available in laboratory quantities as colorless to faintly pink crystals stored in glacial acetic acid.

Использование

Oxidation with lead tetraacetate is often used in organic syntheses, because the lead salt is highly selective in the splitting of vicinal glycols. The rate of oxidation of cis glycols is more rapid than of the trans isomers, a property widely used in the structural determination of sugars and other polyols. Lead tetraacetate readily cleaves α-hydroxy acids as oxalic acid at room temperature. Another use is the introduction of acetoxy groups in organic molecules, as in the preparation of cyclohexyl acetate and the acetoxylation of cyclohexanol. At high temperature, methylation takes place. In these reactions, the organic molecule must contain double bonds or activating substituents.

Подготовка

Lead tetraacetate can be prepared by reaction of red lead with acetic acid The other main lead acetate is lead (II) acetate.

Определение

ChEBI: An acetate salt with formula Pb(OAc)4. It is used as a selective oxidising agent in organic synthesis.

прикладной

Lead tetraacetate is a strong oxidizing agent, a source of acetyloxy groups and a general reagent for the introduction of lead into organolead compounds. Some of its many uses in organic chemistry :
Acetoxylation of benzylic, allylic and α-oxygen ether C-H bonds, for example the photochemical conversion of dioxane to 1,4- dioxene through the 2-acetoxy-1,4-dioxane intermediate and the conversion of α-pinene to verbenone
* Oxidation of hydrazones to diazo compounds for example that of hexafluoroacetone hydrazone to bis(trifluoromethyl)diazomethane * Aziridine formation, for example the reaction of Naminophthalimide and stilbene
* Cleavage of 1,2-diols to the corresponding aldehydes or ketones often replacing ozonolysis, for instance the oxidation of di-nbutyl d-tartrate to n-butyl glyoxylate
* Reaction with alkenes to γ-lactones
* Oxidation of alcohols carrying a δ-proton to cyclic ethers.
* Oxidative cleavage of certain allyl alcohols in conjunction with ozone.

Общее описание

Faintly pink wet crystals with an odor of vinegar.

Реакции воздуха и воды

Unstable in air. Reacts with water to form brown lead dioxide and acetic acid [Merck 11th ed. 1989].

Профиль реактивности

Organometallics are strongly reactive with many other groups. Incompatible with acids and bases. Organometallics are good reducing agents and therefore incompatible with oxidizing agents. Often reactive with water to generate toxic or flammable gases. Generally highly toxic. Often react on contact with tissues to give toxic products.

Угроза здоровью

Early symptoms of lead intoxication by ingestion are most commonly gastrointestinal disorders, colic, constipation, etc.; weakness, which may go on to paralysis chiefly of the extensor muscles of the wrists and less often of the ankles, is noticeable in the most serious cases. Ingestion of a large amount causes local irritation of the alimentary tract; pain, leg cramps, muscle weakness, paresthesias, depression, coma, and death may follow in 1 or 2 days. Contact causes severe irritation of eyes and can burn skin.

Пожароопасность

Behavior in Fire: Can increase the intensity of a fire when in contact with combustible material. Cool containers with plenty of water.

Безопасность

Lead (IV) acetate may be fatal if ingested, inhaled, or absorbed through skin. It causes irritation to skin, eyes, and respiratory tract. It is a neurotoxin. It affects the gum tissue, central nervous system, kidneys, blood, and reproductive system.