Aluminium sulfacetate

Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH₄)₂SO₄, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen and 24% sulfur.

Uses

The primary use of ammonium sulfate is as a fertilizer for alkaline soils. In the soil the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil, while contributing essential nitrogen for plant growth. The main disadvantage to the use of ammonium sulfate is its low nitrogen content relative to ammonium nitrate, which elevates transportation costs.

It is also used as an agricultural spray adjuvant for water-soluble insecticides, herbicides, and fungicides. There, it functions to bind iron and calcium cations that are present in both well water and plant cells. It is particularly effective as an adjuvant for 2,4-D (amine), glyphosate, and glufosinate herbicides.

Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na₂SO₃. A pale yellow, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.

Preparation

Sodium sulfite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide. When conducted in warm water, Na₂SO₃ initially precipitates as a yellow solid. With more SO₂, the solid dissolves to give the disulfite, which crystallizes upon cooling.

SO₂ + 2 NaOH → Na₂SO₃ + H₂O

Sodium sulfite is made industrially by treating sulfur dioxide with a solution of sodium carbonate. The overall reaction is:

SO₂ + Na₂CO₃ → Na₂SO₃ + CO₂

Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a weak sulfurous odor. Although it is stable in the absence of air, it decomposes in hot water and in acid solutions.

Structure

Raman spectroscopy and single-crystal X-ray diffraction studies reveal that the geometry of the dithionite anion is flexible. The dithionite dianion has C ₂ symmetry, with almost eclipsed with a 16° O-S-S-O torsional angle. In the dihydrated form  the dithionite anion has a shorter S-S bond length and a gauche 56° O-S-S-O torsional angle.

A weak S-S bond is indicated by the S-S distance of 239 pm. Because this bond is fragile, the dithionite anion dissociates in solution into the [SO₂]⁻ radical anion, as has been confirmed by EPR spectroscopy. It is also observed that ³⁵S undergoes rapid exchange between S₂O₄²⁻ and SO₂ in neutral or acidic solution, consistent with the weak S-S bond in the anion.

Preparation

Sodium dithionite is produced industrially by reduction of sulfur dioxide. Several methods are employed, including reduction with zinc powder, sodium borohydride, and formate. Approximately 300,000 tons were produced in 1990.