Aluminium sulfacetate is a mixture of aluminium salts dissolved in water with formula Al 2SO 4(CH 3CO 2) 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]
Basic aluminium sulfacetates can also be prepared, Al 2SO 4(CH 3CO 2) 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, Al 2SO 4(OH) 4). Aluminium sulfacetate is made from the hydrates of aluminium sulfate and lead acetate:[2]
Al 2(SO 4) 3•18H 2O + 2 Pb(CH 3CO 2) 2•3H 2O → Al 2SO 4(CH 3CO 2) 4 + 2 PbSO 4 + 24 H 2O
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 Al 2(SO 4) 3•18H 2O + 3 Pb(CH 3CO 2) 2•3H 2O + 2 NaHCO 3 → Al 2SO 4(CH 3CO 2) 3OH + 3 PbSO 4 + Na 2SO 4 + 2 CO 2 + 45 H 2O
Al 2(SO 4) 3•18H 2O + Pb(CH 3CO 2) 2•3H 2O + 2 NaHCO 3 → Al 2SO 4(CH 3CO 2) 2(OH) 2 + PbSO 4 + Na 2SO 4 + 2 CO 2 + 21 H 2O
The n = 3 case, also a basic aluminium sulfacetate, is prepared using acetic acid instead of lead acetate, along with sodium bicarbonate:[2]
Al 2(SO 4) 3•18H 2O + CH 3COOH + 4 NaHCO 3 → Al 2SO 4(CH 3CO 2)(OH) 3 + 2 Na 2SO 4 + CO 2 + 19 H 2O