Chemistry:Aluminium sulfacetate

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Short description: Chemical compound

Aluminium sulfacetate is a mixture of aluminium salts dissolved in water with formula Al2SO4(CH3CO2)4.[1][2]

Uses

It is an evenly balanced mixture of aluminium sulfate and aluminium acetate. It can be used as a mordant, which is a substance used to set dyes on fabrics[3] that typically contains a polyvalent metal ion like aluminium or iron,[4] In mixtures with basic aluminium diacetate or aluminium sulfacetate, aluminium triacetate has been used as a mordant with alizarin dye.[1] In 1899, Albert Ganswindt recommended that the use of impure sulfacetates that are empyreumatic liquids "should be abandoned" in favour of pure preparations.[5] Empyreuma is an obsolete chemical and medical term referring to "the smell and taste associated with burning vegetable and animal matter",[6] and likely results in this case from the use of pyroligneous acid (wood acid) or wood acid lime in the preparation of the mordant.[5]

Preparation

A common approach to preparing aluminium sulfacetate is by reaction of aluminium sulfate with lead(II) acetate. The relative amount of each reagent controls the composition of the resulting mixture.[1] When the stoichiometric ratio of lead acetate to aluminium sulfate exceeds 3:1, the process is theoretically driven to completion and aluminium triacetate is the sole product. With less lead acetate, a mixture of aluminium triacetate and aluminium sulfacetate results that becomes increasingly rich in the latter as the reagent mole ratio approaches 2:1. This approach is used to form various mixtures for mordant applications:[1]

Al2(SO4)3   +   3 Pb(CH3CO2)2   →   2 Al(CH3CO2)3   +   3 PbSO4

Basic aluminium sulfacetates can also be prepared, Al2SO4(CH3CO2)4 - n(OH)n, with hydroxide anions replacing some acetate ions. The extreme cases are aluminium sulfacetate itself (n = 0) and the double salt of aluminium sulfate and aluminium hydroxide (n = 4 case, Al2SO4(OH)4). Aluminium sulfacetate is made from the hydrates of aluminium sulfate and lead acetate:[2]

Al2(SO4)3•18H2O   +   2 Pb(CH3CO2)2•3H2O   →   Al2SO4(CH3CO2)4   +   2 PbSO4   +   24 H2O

The n = 1 and n = 2 cases, both of which are basic aluminium sulfacetates, are prepared using sodium bicarbonate along with the regents:[2]

2 Al2(SO4)3•18H2O   +   3 Pb(CH3CO2)2•3H2O   +   2 NaHCO3   →   Al2SO4(CH3CO2)3OH   +   3 PbSO4   +   Na2SO4   +   2 CO2   +   45 H2O
Al2(SO4)3•18H2O   +   Pb(CH3CO2)2•3H2O   +   2 NaHCO3   →   Al2SO4(CH3CO2)2(OH)2   +   PbSO4   +   Na2SO4   +   2 CO2   +   21 H2O

The n = 3 case, also a basic aluminium sulfacetate, is prepared using acetic acid instead of lead acetate, along with sodium bicarbonate:[2]

Al2(SO4)3•18H2O   +   CH3COOH   +   4 NaHCO3   →   Al2SO4(CH3CO2)(OH)3   +   2 Na2SO4   +   CO2   +   19 H2O

References