Metam (144-54-7) Physical and Chemical Properties
Metam
Low‑molecular‑weight organosulfur dithiocarbamic acid used industrially as the parent compound for commercially supplied metam salts and as a precursor in agrochemical formulations.
| CAS Number | 144-54-7 |
| Family | Dithiocarbamic acids |
| Typical Form | Powder or crystalline solid |
| Common Grades | EP |
Metam is an organosulfur dithiocarbamic acid, systematically named methylcarbamodithioic acid. Structurally it is an N‑methyl dithiocarbamic acid bearing a thiocarbonyl (C=S) linked to a terminal thiol functionality; the parent molecular formula is \(\ce{C2H5NS2}\). The neutral acid exists in equilibrium with its deprotonated dithiocarbamate anion, and the commercially and agriculturally important forms are the alkali and ammonium salts (e.g., metam‑sodium, metam‑potassium, metam‑ammonium), which are the water‑soluble, storage‑stable precursors to the active fumigant decomposition product methyl isothiocyanate under field conditions.
Electronically the molecule combines a polar N–C(=S)–S motif with a small alkyl substituent (N‑methyl). The thiocarbonyl confers nucleophilic sulfur character and susceptibility to hydrolysis/decomposition pathways that lead to isothiocyanate formation; the N–H/N–Me protonation state governs aqueous speciation (acid vs. anion). Computed descriptors indicate low-to-moderate lipophilicity and measurable polarity: the calculated XLogP is 0.7 and the topological polar surface area is 45.1 Ų, consistent with molecules that partition between aqueous and moderately polar organic phases and that form soluble salts when neutralization occurs.
Industrial relevance is dominated by its role in pest control: the parent acid functions as a pro‑pesticide, while its salts are formulated and applied as soil fumigants and precursors to broad‑spectrum nematicidal, fungicidal and herbicidal activity. Transformation to volatile toxicants under application conditions explains both efficacy and the need for controlled handling. Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting Point
No experimentally established value for this property is available in the current data context.
Boiling Point
No experimentally established value for this property is available in the current data context.
Vapor Pressure
No experimentally established value for this property is available in the current data context.
Flash Point
No experimentally established value for this property is available in the current data context.
Chemical Properties
Solubility and Phase Behavior
Metam in its neutral acid form is a small, polar organosulfur acid; the computed descriptors (XLogP = 0.7, TPSA = 45.1) indicate moderate polarity and the capacity to engage in hydrogen bonding (H‑bond donor count = 2, acceptor count = 2). In practical formulations and in environmental media it is typically handled as water‑soluble salts (e.g., sodium, potassium, ammonium), which dramatically increase aqueous solubility relative to the free acid. Under aqueous conditions, especially at elevated pH or in the presence of nucleophiles, the parent dithiocarbamic acid undergoes decomposition and transformation reactions; a notable environmental/technical transformation product is methyl isothiocyanate, a volatile electrophilic species responsible for much of the fumigant activity.
Phase behavior in formulated products therefore depends strongly on counterion, pH and temperature: salts favor aqueous solution, while the free acid and decomposition products may be more volatile and partition into the gas phase under field conditions.
Reactivity and Stability
The N‑methyl dithiocarbamate motif is chemically reactive toward hydrolysis, oxidation and thermal decomposition. Hydrolytic and base‑promoted pathways give rise to isothiocyanate formation; oxidative conditions can modify sulfur oxidation state and produce sulfoxide/sulfone‑like fragments or mixed sulfur oxides on more severe degradation. The compound readily forms stable ionic salts upon neutralization of the acidic thiol proton; these salts are the basis for agricultural formulations that are intentionally unstable under field conditions to release active volatile species. Standard precautions for reactive organosulfur acids apply: limit exposure to strong oxidants and bases, control temperature to reduce decomposition, and use materials of construction compatible with corrosive sulfur‑containing acids.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\ce{C2H5NS2}\)
- Molecular weight: 107.20 \(\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact mass: 106.98634151 \(\mathrm{u}\)
- Monoisotopic mass: 106.98634151 \(\mathrm{u}\)
Additional computed counts: heavy atom count = 5; formal charge = 0; covalently‑bonded unit count = 1.
LogP and Polarity
- XLogP (XLogP3‑AA): 0.7
- Topological polar surface area (TPSA): 45.1 Ų
- Hydrogen bond donor count: 2
- Hydrogen bond acceptor count: 2
- Rotatable bond count: 0
These descriptors indicate low-to-moderate lipophilicity with sufficient polar surface area and hydrogen‑bonding capacity to confer appreciable interaction with aqueous environments and to form soluble salts upon neutralization.
Structural Features
The core structural features are an N‑methylamino group bonded to a thiocarbonyl and a terminal thiol/thiolate: the functional groups of note are the thiocarbonyl (C=S), the adjacent sulfur substituent (–S– or –SH in the free acid), and the tertiary character introduced by N‑methylation. This arrangement favors deprotonation at sulfur to give dithiocarbamate anions that are resonance‑stabilized across the N–C–S system. The SMILES string for the neutral acid is provided as a compact structural identifier and corresponds to an N‑methyl dithiocarbamic acid skeleton.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 144-54-7
- European Community (EC) number: 205-632-2
- UNII: OA1I97689K
- ChEBI: CHEBI:141319
- ChEMBL: CHEMBL1413694
- DSSTox Substance ID: DTXSID5043970
- InChIKey:
HYVVJDQGXFXBRZ-UHFFFAOYSA-N - InChI:
InChI=1S/C2H5NS2/c1-3-2(4)5/h1H3,(H2,3,4,5) - SMILES:
CNC(=S)S
Synonyms and Structural Names
Reported synonyms and variant names include: Metam; methylcarbamodithioic acid; Methyldithiocarbamic acid; N‑Methylcarbamodithioic acid; Methyldithiocarbanic acid; methyldithiocarbamate; methyl‑dithiocarbamic acid; monopotassium methylcarbamodithioate (salt forms appear in related records). Salt forms and hydrates are commonly encountered in commerce and regulatory listings.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Metam is used primarily in agriculture as a pesticide active substance: it functions as a proherbicide, profungicide, proinsecticide and pronematicide. Commercial practice employs alkali or ammonium salts (notably metam‑sodium and metam‑potassium) which release volatile toxicants under application conditions, providing broad‑spectrum soil fumigation for control of weeds, nematodes, soil‑borne insects and fungi. Regulatory listings for the active substance and its salts reflect its role as an authorised pesticide active ingredient in relevant jurisdictions.
Role in Synthesis or Formulations
The free acid and, more commonly, its salts are formulated to exploit controlled decomposition to methyl isothiocyanate during soil treatment. As a technical chemical, metam is handled as a precursor salt in aqueous formulations or granular products; the parent acid is mainly of interest as the conceptual chemical entity and in mechanistic studies of decomposition and environmental fate. Commercial grades encountered include EP.
Safety and Handling Overview
Acute and Occupational Toxicity
Hazard classifications indicate significant acute and chronic risks. Available hazard class statements include (selection from classification metadata):
- Acute toxicity (oral) – Category 4
- Acute toxicity (inhalation: dusts and mists) – Category 4
- Skin corrosion/irritation – Category 1C
- Serious eye damage/eye irritation – Category 1
- Skin sensitization – Category 1
- Specific target organ toxicity — single exposure – Category 1 (nervous system and respiratory organs)
- Specific target organ toxicity — repeated exposure – Category 2 (liver), and Category 1 in some listings (nervous system, respiratory)
- Reproductive toxicity – Category 1B (in some classifications)
- Hazardous to the aquatic environment (acute and long‑term) – Category 1
Acute hazard statements reported include H302, H314, H317, H318, H332, H370, H373, H400 and H410 in various groupings; these reflect oral and inhalation toxicity, corrosivity, sensitization potential, organ toxicity and high aquatic toxicity. Occupational exposure controls should prioritize minimizing inhalation and dermal contact, given corrosivity and systemic toxicity potential.
Storage and Handling Considerations
Handle metam and its salts within closed systems where feasible; provide local exhaust ventilation and prevent formation of aerosols or dust. Appropriate personal protective equipment includes chemical‑resistant gloves, eye/face protection, and respiratory protection selected to match airborne concentrations and task‑specific risks. Store in cool, dry, well‑ventilated areas away from strong oxidizers, strong bases and sources of heat; segregate from incompatible materials and materials that catalyze decomposition. Given the propensity for decomposition to volatile toxicants under certain conditions, temperature control and spill containment are essential. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
