Synthesis of potassium tris(oxalato)aluminate – Protocol H
Al2 (SO4 )3  6NaOH  3K 2 C2 O4  3H 2 C2 O4  2K 3 [Al(C2 O4 )3 ].3H 2 O  3Na 2SO4
Reaction. Dissolve 7 g (11.1 mmol) of aluminium sulphate hexadecahydrate (stoichiometric
proportions) in 100 mL of water and add to this, with stirring, a solution of 2.5 g (62.5 mmol) of
sodium hydroxide in 20 mL of water. Filter off the precipitated aluminium hydroxide, and wash with
water. Prepare a solution of 4 g (31.7 mmol) of oxalic acid dihydrate (stoichiometric proportions)
and 6 g (32.6 mmol) of potassium oxalate monohydrate (stoichiometric proportions) in 100 mL of
water, and boil this with the aluminium hydroxide.
Isolation. Filter off any unreacted aluminium hydroxide, and evaporate the filtrate to crystallization.
Dry the crystals.
Purification. Not prescribed.
Safety. See hazards associated with the reagents in Table 1.
Greenness Assessment. The evaluation was performed using the Green Star (GS) and the results are
shown in Figures 1 and 2. As no SDS file was found for potassium tris(oxalato)aluminate, two
alternatives were considered: one takes into account the maximum hazard of the product and the
other does not consider the product for greenness assessment.
REACTION
ISOLATION
P1
P12
GLOBAL
P1
P1
P2
P12
P10
P3
P9
P5
P8
P12
P5
P10
P6
P6
P2
P10
P3
P9
P5
P8
P6
P7
P7
P7
GSAI = 50.00
GSAI = 33.33
GSAI = 45.00
Figure 1. Greenness assessment (GS) for the synthesis of potassium tris(oxalato)aluminate (considering
maximum hazard of the product)
REACTION
P1
P12
ISOLATION
GLOBAL
P1
P1
P2
P12
P10
P3
P9
P5
P8
P12
P5
P10
P6
P6
P2
P10
P3
P9
P5
P8
P6
P7
P7
P7
GSAI = 50.00
GSAI = 41.67
GSAI = 45.00
Figure 2. Greenness assessment (GS) for the synthesis of potassium tris(oxalato)aluminate (not considering
the product)
Construction of the GS
Al2 (SO4 )3  6NaOH  3K 2 C2 O4  3H 2 C2 O4  2K 3 [Al(C2 O4 )3 ].3H 2 O  3Na 2SO4
Table 1 presents the hazards and scores associated with the substances involved and Tables 2 and 3
present the scores used to construct the green stars.
Table 1. Hazards for the synthesis of potassium tris(oxalato)aluminate, protocol H
Step
Substances involved
R
I
Hazard code
Pu
Stoichiometric reagents
Aluminium sulphate hexadecahydrate (CAS 16828-11-8)
H318

Oxalic acid dihydrate (CAS 6163-56-6)

H302, H312, H314
Potassium oxalate monohydrate (CAS 6487-48-5)

H302, H312
Sodium hydroxide (CAS 1310-73-2)
H314

Auxiliary substances
Solvents
Watera,b

Product
Potassium tris(oxalato)aluminate trihydrate
No data available


Waste
Aluminium hydroxide
H319

Sodium sulphate (aqueous solution)

Watera,b


R – Reaction; I – Isolation; Pu – Purification; HH – Human Health; E – Environment; P – Physical
a Renewable; b Degradable to innocuous products
Score: hazards to...
HH
E
P
3
3
2
3
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
Table 2. Scores used to construct the green star for the synthesis of potassium
tris(oxalato)aluminate, protocol H (considering maximum hazard of the product)
Green Chemistry
Principle
Isolation
Global
s
Explanation
s
Explanation
s
P1
Prevention
3
Waste is innocuous
2
Aluminium hydroxide,
H319
2
P2
Atom Economy
2
NA
2
P3
Less hazardous
chemical synthesis
1
NA
1
P5
Safer solvents and
auxiliary substances
P6
Increase energy
efficiency
P7
Use renewable
feedstocks
P8
Reduce derivatives
P9
Catalysts
P10
Design for degradation
P12
Safer chemistry for
accident prevention
s
Reaction
Stoichiometric
proportions of
reagents, formation of
by-products
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314,
oxalic acid dihydrate,
H314, and potassium
tris(oxalato)aluminate
trihydrate
Explanation
Aluminium hydroxide,
H319
Stoichiometric
proportions of
reagents, formation of
by-products
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314,
oxalic acid dihydrate,
H314, and potassium
tris(oxalato)aluminate
trihydrate
3
Water
3
Solvents and auxiliary
substances are not
used
3
Water
2
0 ºC ≤ T ≤ 100 ºC
2
0 ºC ≤ T ≤ 100 ºC
2
0 ºC ≤ T ≤ 100 ºC
1
Substances not
renewable
1
Substances not
renewable
1
Substances not
renewable
3
One stage
NA
3
One stage
3
Without catalysts
NA
3
Without catalysts
1
Substances not
degradable
1
1
Potassium
tris(oxalato)aluminate
trihydrate
1
1
1
– score; NA – Not applicable
Substances not
degradable
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314,
oxalic acid dihydrate,
H314, and potassium
tris(oxalato)aluminate
trihydrate
Substances not
degradable
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314,
oxalic acid dihydrate,
H314, and potassium
tris(oxalato)aluminate
trihydrate
Table 3. Scores used to construct the green star for the synthesis of potassium
tris(oxalato)aluminate, protocol H (not considering the product)
Green Chemistry
Principle
Isolation
Global
s
Explanation
s
Explanation
s
P1
Prevention
3
Waste is innocuous
2
Aluminium hydroxide,
H319
2
P2
Atom Economy
2
NA
2
P3
Less hazardous
chemical synthesis
1
NA
1
P5
Safer solvents and
auxiliary substances
P6
Increase energy
efficiency
P7
Use renewable
feedstocks
P8
Reduce derivatives
P9
Catalysts
P10
Design for degradation
P12
Safer chemistry for
accident prevention
s
Reaction
Stoichiometric
proportions of
reagents, formation of
by-products
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314, and
oxalic acid dihydrate,
H314
Explanation
Aluminium hydroxide,
H319
Stoichiometric
proportions of
reagents, formation of
by-products
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314, and
oxalic acid dihydrate,
H314
3
Water
3
Solvents and auxiliary
substances are not
used
3
Water
2
0 ºC ≤ T ≤ 100 ºC
2
0 ºC ≤ T ≤ 100 ºC
2
0 ºC ≤ T ≤ 100 ºC
1
Substances not
renewable
1
Substances not
renewable
1
Substances not
renewable
3
One stage
NA
3
One stage
3
Without catalysts
NA
3
Without catalysts
1
Substances not
degradable
1
2
Aluminium hydroxide,
H319
1
1
1
Substances not
degradable
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314, and
oxalic acid dihydrate,
H314
Substances not
degradable
Aluminium sulphate
hexadecahydrate,
H318, sodium
hydroxide, H314, and
oxalic acid dihydrate,
H314
– score; NA – Not applicable
References
Pass, G.; Sutcliffe, H. Practical Inorganic Chemistry – 2nd edition. Chapman and Hall: London, 1974, pp. 11.