Ammonium citrate (3458-72-8) Physical and Chemical Properties
Ammonium citrate
The ammonium salt of citric acid used in industrial and agricultural applications for chelation, pH adjustment and as a nutrient source in formulated products.
| CAS Number | 3458-72-8 |
| Family | Ammonium salts / Citrates |
| Typical Form | Powder or crystalline solid |
| Common Grades | EP |
Ammonium citrate is an inorganic–organic salt formed from citric acid and ammonia; its stoichiometric molecular formula is \(\ce{C6H11NO7}\). Structurally it comprises the tricarboxylate/hydroxy backbone of citric acid (central tertiary alcohol flanked by three carboxylate functionalities) neutralized by ammonium counter‑species. The compound exists as a salt composed of discrete covalently bonded units (reported covalently-bonded unit count: 2) rather than a single covalent molecule; this manifests as high polarity, extensive hydrogen‑bonding, and a large polar surface area (TPSA = 133 Å^2) that strongly favors aqueous solvation and complex formation with metal cations.
Electronically, the citrate component provides multiple deprotonatable sites (three carboxyl groups and one hydroxyl), creating a chelating, polyvalent anion in deprotonated forms and enabling internal hydrogen‑bond networks in partially protonated states. The ammonium counterion contributes proton donation capacity and acid‑base buffering around near‑neutral \(\mathrm{pH}\) in aqueous media. The combination yields a highly hydrophilic, low‑lipophilicity salt with numerous hydrogen bond donors (5) and acceptors (8), and low expected partitioning into nonpolar phases.
Industrial relevance arises from its role as a benign, water‑soluble chelating/buffering salt and its utility in agricultural formulations and cleaning applications. Reported commercial grade: EP.
Basic Physical Properties
Solubility and Hydration
Physical description: Liquid.
As an ammonium salt of a polycarboxylic acid, the material is classically highly soluble in water and forms extensive hydrogen‑bonded hydrates; solubility behavior is governed by ionic dissociation of the ammonium/citrate components and \(\mathrm{pH}\)-dependent speciation of the citrate moiety. No experimentally established value for this property is available in the current data context.
Practical implication: expect rapid dissolution in aqueous media, complete dissociation to ammonium and citrate species under typical conditions used in formulation and processing.
Thermal Stability and Decomposition
No experimentally established value for this property is available in the current data context.
Qualitatively, ammonium salts of carboxylic acids commonly decompose on strong heating, releasing ammonia and producing carbonate/CO2 and residues derived from the organic acid; decomposition pathways and onset temperatures are dependent on hydration state, sample purity, and heating rate. Thermal decomposition under inert or oxidative atmospheres should be evaluated empirically for process safety.
Chemical Properties
Complex Formation and Coordination
Citrate is a tridentate/oligodentate ligand capable of forming stable chelates with a wide range of metal cations (alkaline earths, transition metals, rare earths), binding through carboxylate oxygens and, in some coordination modes, the hydroxyl oxygen. In the ammonium salt the ammonium ion acts solely as a charge‑balancing species (\(\ce{NH4+}\)) and does not compete for metal coordination in typical aqueous systems. Complexation reduces free metal activity and can affect solubility, bioavailability, and corrosion inhibition behavior in formulated products.
Reactivity and Stability
The compound is chemically stable in neutral to mildly acidic aqueous solutions where the citrate anion is predominant; oxidation under ambient conditions is generally slow because the citrate backbone lacks easily oxidizable aromatic or activated aliphatic centers. Hydrolytic cleavage of the carbon skeleton is not expected under typical storage or use conditions. Reducing or strongly oxidizing environments and prolonged exposure to elevated temperature can alter the organic fraction; compatibility testing is recommended when used with reactive oxidizers, strong bases, or catalytic metal surfaces.
Molecular Parameters
Molecular Weight and Composition
- Molecular formula: \(\ce{C6H11NO7}\)
- Molecular weight: 209.15
- Exact mass: 209.05355169
- Monoisotopic mass: 209.05355169
- Heavy atom count: 14
- Covalently‑bonded unit count: 2
- Formal charge: 0
- Complexity: 227
- Topological polar surface area (TPSA): 133
- Hydrogen bond donor count: 5
- Hydrogen bond acceptor count: 8
- Rotatable bond count: 5
These parameters reflect a highly polar, hydrogen‑bonding capable salt with high aqueous affinity and limited lipophilicity.
LogP and Ionization State
No experimentally established value for this property is available in the current data context.
Ionization state in the solid form corresponds to an ammonium/citrate salt pair; in aqueous solution the citrate moiety exists in pH‑dependent protonation states (mono‑, di‑, or tri‑deprotonated forms) while ammonium (\(\ce{NH4+}\)) provides a weakly acidic counterion. The reported formal charge for the covalent unit is 0, consistent with a neutral stoichiometric salt.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS RN: 3458-72-8
- EC number: 231-560-6
- InChI:
InChI=1S/C6H8O7.H3N/c7-3(8)1-6(13,5(11)12)2-4(9)10;/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12);1H3 - InChIKey:
BWKOZPVPARTQIV-UHFFFAOYSA-N - SMILES:
C(C(=O)O)C(CC(=O)O)(C(=O)O)O.N
Synonyms and Structural Names
Reported synonyms include: ammonium citrate; Citric acid, ammonium salt; Ammonium hydrogencitrate; monobasicammonium citrate; amine-citrate; azane;2-hydroxypropane-1,2,3-tricarboxylic acid. These names reflect the salt nature and various stoichiometric/structural descriptions used in supply and regulatory contexts.
Industrial and Commercial Applications
Use as Salt Form or Excipient
Ammonium citrate functions as a water‑soluble buffering and chelating salt, useful where controlled complexation of metal ions, gentle acidity, and high aqueous solubility are required. As an ammonium salt it may be selected over alkali metal salts when sodium or potassium content must be minimized. It is used in formulations that exploit citrate’s sequestration of hardness ions and mild acidity.
Representative Use Cases
- Cleaning agents and detergent formulations where sequestration of Ca2+/Mg2+ and pH control are required.
- Agricultural soil amendments and fertilizer blends to provide nitrogen and chelated micronutrients; listed uses include "Soil amendments (fertilizers)".
- Industrial formulations where a water‑soluble, non‑volatile chelator/buffer is preferred.
Regulatory/commercial status: reported active for commercial activity in relevant inventories.
If a concise application summary is required beyond the above, product‑specific technical data sheets should be consulted to match grade and purity to the intended use.
Safety and Handling Overview
Toxicological Considerations
The substance is reported as “Not Classified” under GHS hazard criteria in available company reports; aggregated notifications indicate that it does not meet classification thresholds in those submissions. Absence of classification implies a low acute hazard profile for typical industrial exposures, but specific toxicological endpoints (e.g., LD50, chronic toxicity) are not provided here. As with many ionic organic salts, exposure by ingestion or high concentrations in aerosols may produce irritation of mucous membranes; product‑specific toxicology should be reviewed prior to large‑scale use.
Storage and Handling Guidelines
Handle using standard industrial chemical precautions: avoid generation of dust/aerosols, provide local exhaust ventilation where finely divided material may be present, and use appropriate PPE (gloves, eye protection, protective clothing). Store in a cool, dry, well‑ventilated area away from strong oxidizers and incompatible reagents; avoid prolonged exposure to high temperature which can promote decomposition. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
