Ammonium chloride dihydrate (NH₄Cl·2H₂O) is the hydrated crystalline form of ammonium chloride, carrying two molecules of water of crystallization per formula unit. It shares the same CAS registry number as the anhydrous salt (CAS 12125-02-9) but is specified separately where water content, dissolution behavior, and dusting characteristics matter in formulation and handling. The anhydrous form has a molecular weight of 53.49 g/mol; the dihydrate adds 36.03 g/mol of water, giving a theoretical formula weight of approximately 89.52 g/mol.
The underlying salt is well characterized: white crystalline solid, density 1.527 g/cm³, highly soluble in water (372,000 mg/L), and subliming/decomposing near 340 °C without melting. The dihydrate inherits these core characteristics while presenting a higher moisture load and a lower active NH₄Cl content per unit weight than the anhydrous grade.
| Property | Anhydrous NH₄Cl | Dihydrate NH₄Cl·2H₂O |
|---|---|---|
| CAS Number | 12125-02-9 | 12125-02-9 (shared) |
| Formula | NH₄Cl | NH₄Cl·2H₂O |
| Formula Weight | 53.49 g/mol | ≈ 89.52 g/mol |
| Appearance | White crystalline powder | White crystalline solid |
| Water Solubility | Very high (372 g/L) | High (water is already bound) |
| Key Handling Note | Hygroscopic; dust irritant | Higher bulk weight per unit NH₄Cl; moisture release on heating |
The practical consequence is straightforward: the dihydrate delivers less ammonium chloride per kilogram than the anhydrous material. Formulators specifying “NH₄Cl” on a weight basis must account for the water of crystallization when calculating active content, nitrogen contribution, or chloride load.
The distinction is not academic — it changes dosing, storage, and process behavior.
Active content. The dihydrate contains roughly 59.8% NH₄Cl by weight (53.49 / 89.52). A formulation calling for 100 kg of anhydrous NH₄Cl requires approximately 167 kg of the dihydrate to deliver the same ammonium chloride equivalents.
Dissolution and thermal behavior. Dissolving the dihydrate releases water of crystallization, which can slightly cool the solution and alter concentration kinetics. On heating, the hydrate loses water before the salt’s characteristic sublimation/decomposition near 340 °C.
Dusting and caking. Both forms are hygroscopic, but the dihydrate’s surface moisture profile can influence caking and flowability in bulk storage and pneumatic handling.
For applications where water is an acceptable or desirable component — fertilizer blends, certain flux formulations, and aqueous process streams — the dihydrate can be a practical and cost-effective input. Where maximum active concentration per unit weight is essential, anhydrous material is specified.
The application map is shared between the anhydrous and hydrated forms, with grade selection driven by water tolerance and purity requirements.
Dry cell batteries. Ammonium chloride is the classic electrolyte in zinc-carbon dry cells, and battery manufacture has historically been a principal volume outlet.
Metalworking fluxes. It functions as a flux in tinning, galvanizing, soldering, and brazing, removing oxide coatings from metal surfaces and improving solder adhesion.
Fertilizers. Agriculture-grade ammonium chloride supplies 24–26% nitrogen and is used on chlorine-tolerant crops including rice, wheat, maize, and cotton. The dihydrate form is compatible with bulk blend and granulation routes where its water content does not compromise the finished fertilizer’s storage stability.
Pharmaceuticals and food. Ammonium chloride is an expectorant in cough syrups and lozenges, and food-grade material (E510) serves as a yeast nutrient in breadmaking and a flavoring agent in licorice.
Chemical intermediate. It is a precursor to numerous ammonia compounds and appears in urea-formaldehyde resins and adhesives.
Yes — the hazards are moderate but require controlled handling. Under GHS, ammonium chloride is classified as Acute Toxicity Category 4 (H302, harmful if swallowed), Eye Irritation Category 2A (H319), and Specific Target Organ Toxicity Category 3 for respiratory irritation (H335); it also carries H290 (may be corrosive to metals) and H412 (harmful to aquatic life with long-lasting effects).
Practical controls include avoiding dust generation, using local exhaust ventilation, wearing gloves and eye/face protection, and keeping containers tightly closed in a dry, cool, well-ventilated area. Storage segregation from aluminium, lead, iron, and copper compounds is advised because of the metal-corrosivity classification. The dihydrate’s water content does not reduce these intrinsic hazards; the same precautionary framework applies.
The market data varies by scope, but the directional trend is consistent across sources. One forecast places the global ammonium chloride market at US 3.00 billion in 2026 and reaching US 2.03 billion, growing to US 2.18 billion in 2025, reaching US$ 3.19 billion by 2034 (CAGR 4.33%).
Growth is being pulled by fertilizer demand in rice- and wheat-growing regions, pharmaceutical expectorant manufacturing, dry-cell battery production, and metalworking flux consumption, with Asia-Pacific identified as the high-growth consumption region. The dihydrate form does not have a separately tracked market size; it is supplied as a specification variant within the broader ammonium chloride trade.
Is ammonium chloride dihydrate the same as anhydrous ammonium chloride?
No. Both share CAS 12125-02-9, but the dihydrate contains two molecules of water of crystallization per NH₄Cl unit, giving it a higher formula weight (≈89.52 vs. 53.49 g/mol) and lower active NH₄Cl content per kilogram. Dosing must be adjusted accordingly.
Can ammonium chloride dihydrate be used as a fertilizer?
Yes, agriculture-grade material is used as a nitrogen source (24–26% N) on chlorine-tolerant crops. However, the water of crystallization means more product is required to deliver the same nitrogen units as anhydrous ammonium chloride.
Does the dihydrate pose the same hazards as the anhydrous salt?
The GHS classification is shared: harmful if swallowed, serious eye irritation, respiratory irritation, and metal corrosivity. The presence of bound water does not remove these hazards, and the same ventilation, PPE, and dry-storage controls apply.
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