Lead(II) acetate

Lead(II) acetate (Pb(CH3COO)2), also known as lead acetate, lead diacetate, plumbous acetate, sugar of lead, lead sugar, salt of Saturn, or Goulard's powder, is a white crystalline chemical compound with a sweet taste. It is made by treating lead(II) oxide with acetic acid. Like other lead compounds, it is toxic. Lead acetate is soluble in water and glycerin. With water it forms the trihydrate, Pb(CH3COO)2·3H2O, a colourless or white efflorescent monoclinic crystalline substance.

The substance is used as a reagent to make other lead compounds and as a fixative for some dyes. In low concentrations, it is the principal active ingredient in progressive types of hair colouring dyes. Lead(II) acetate is also used as a mordant in textile printing and dyeing, and as a drier in paints and varnishes. It was historically used as a sweetener and for cosmetics.

Production
Lead acetate can be made by boiling elemental lead in acetic acid and hydrogen peroxide. This method will also work with lead carbonate or lead oxide.

Pb(s) + H2O2(aq) +  2 H+(aq) →  Pb2+(aq) + 2 H2O(l) 
Pb2+(aq) + 2 CH3COO−(aq) → Pb(CH3COO)2(aq)

Lead(II) acetate can also be made via a single displacement reaction between copper acetate and lead metal:

Cu(CH3COO)2 + Pb → Cu + Pb(CH3COO)2

Uses

Sweetener
Like other lead(II) salts, lead(II) acetate has a sweet taste, which led to its historical use as a sugar substitute. The ancient Romans, who had few sweeteners besides honey, would boil must (grape juice) in lead pots to produce a reduced sugar syrup called defrutum, concentrated again into sapa. This syrup was used to sweeten wine and to sweeten and preserve fruit. It is possible that lead(II) acetate or other lead compounds leaching into the syrup might have caused lead poisoning in those who consumed it.  Lead acetate is no longer used in the production of sweeteners because of its recognized toxicity. Modern chemistry can easily detect it, which has almost completely stopped the illegal use that continued decades after legal use as a sweetener was banned.

Historical incidents
The earliest confirmed poisoning by lead acetate was that of Pope Clement II who died in October 1047. A toxicological examination of his remains conducted in the mid-20th century confirmed centuries-old rumors that he had been poisoned with lead sugar. It is not clear if he was assassinated.

In 1787 painter Albert Christoph Dies swallowed, by accident, approximately  of lead acetate. His recovery from this poison was slow and incomplete. He lived with illnesses until his death in 1822.

Although the use of lead(II) acetate as a sweetener was already illegal at that time, composer Ludwig van Beethoven may have died of lead poisoning caused by wines adulterated with lead acetate (see also Beethoven's liver).

In the 1850s, Mary Seacole applied lead(II) acetate, among other remedies, against an epidemic of cholera in Panama.

Cosmetics
Lead(II) acetate, as well as white lead, has been used in cosmetics throughout history.

It is still used in the USA in men's hair colouring products like Grecian Formula. The U.S. Food and Drug Administration considers this use safe because human testing showed lead did not enter the bloodstream and was not shown to be absorbed. It was, however, banned in cosmetics by Health Canada in 2005 (effective at the end of 2006) based on tests showing possible carcinogenicity and reproductive toxicity, and it is also banned in the European Union and has been on the California Proposition 65 warning list as a carcinogen since 1988.

Medical uses
Lead(II) acetate solution was a commonly used folk remedy for sore nipples. In modern medicine, for a time, it was used as an astringent, in the form of Goulard's Extract, and it has also been used to treat poison ivy.

Industrial uses
Lead(II) acetate paper is used to detect the poisonous gas hydrogen sulfide. The gas reacts with lead(II) acetate on the moistened test paper to form a grey precipitate of lead(II) sulfide.

An aqueous solution of lead(II) acetate is the byproduct of a 1/1 ratio of hydrogen peroxide and white vinegar (acetic acid) used in the cleaning and maintenance of stainless steel firearm suppressors (silencers) and compensators.  The solution is agitated by the bubbling action of the hydrogen peroxide, and the main reaction is the dissolution of lead deposits within the suppressor by the acetic acid, which forms lead acetate.  Because of its high toxicity, this chemical solution must be appropriately disposed by a chemical processing facility or hazardous materials centre. Alternatively, the solution may be reacted with sulfuric acid to precipitate nearly insoluble lead(II) sulfate. The solid may then be removed by mechanical filtration and is safer to dispose of than aqueous lead acetate.

It was also used in making of slow matches during the Middle Ages. It was made by mixing natural form of lead(II) oxide called litharge and vinegar.

Sugar of lead was a recommended agent added to linseed oil during heating to produce "boiled" linseed oil, the lead and heat acting to cause the oil to cure faster than raw linseed oil.

See also
 Saturn's Tree

References

External links

 Case Studies in Environmental Medicine - Lead Toxicity
 Essay on "Lead Poisoning and Rome"
 HowStuffWorks "What Kind of Hair Color Do Men Use?" discussion of progressive dyes containing lead acetate
 National Pollutant Inventory - Lead and Lead Compounds Fact sheet (Does Not Bring Up Lead)
 ToxFAQs: Lead
 US Food and Drug Administration (FDA) fact sheet "Lead Acetate in Hair Dye Products"
 US Food and Drug Administration (FDA)21CFR73.2396 "PART 73 -- LISTING OF COLOR ADDITIVES EXEMPT FROM CERTIFICATION, Subpart C--Cosmetics, Sec. 73.2396 Lead acetate"

Category:Acetates
Category:Alchemical substances
Category:Lead(II) compounds
Category:Sugar substitutes