O,O-Dimethyl phosphorodithioate (dimethyl dithiophosphate, CAS 756-80-9) is a dark brown to pale purple liquid supplied at 92% minimum assay. It is the dimethyl member of the dialkyl dithiophosphoric acid family, and it serves two quite different industries: as a reactive intermediate for organophosphate synthesis, and as the acid precursor to dithiophosphate collectors used in sulphide ore flotation.
Specification
| Parameter | Limit | Why it matters |
|---|---|---|
| Appearance | Dark brown to pale purple liquid | The colour comes from the P=S chromophore and from trace polysulphides; a strong shift or heavy darkening indicates degradation |
| Assay | 92% min | The active dithiophosphate content. The balance is largely related sulphur species and hydrolysis products, which is normal for this chemistry |
Identity and properties
| Property | Value | Practical significance |
|---|---|---|
| Chemical name | O,O-Dimethyl phosphorodithioate (dimethyl dithiophosphoric acid) | Two methoxy groups and a P=S / P-SH pair on the phosphorus |
| Formula / molecular weight | C2H7O2PS2 / about 158 | Small, highly functional molecule – it is an acid, a ligand and a sulphur donor at once |
| Acidity | Strongly acidic | The P-SH proton is readily lost, which is why the acid is normally converted to a salt before use in flotation |
| Solubility | Organic-soluble; reacts with water | Handled in organic media; contact with water causes hydrolysis |
| Odour | Pungent, sulphidic | The odour is a warning property – the material evolves hydrogen sulphide on decomposition |
| Stability | Hydrolyses in the presence of water; sensitive to heat and alkali | Drives the storage requirements and the short shelf-life expectation |
The two industries it serves
| Sector | How it is used | What the chemistry relies on |
|---|---|---|
| Organophosphate synthesis | Reacted with an alkylating or acylating partner to build the P-S-C linkage of the finished active | The nucleophilic sulphur and the reactive phosphorus centre |
| Sulphide ore flotation | Converted to the sodium or potassium salt – a dithiophosphate collector, known generically as an aerofloat | The dithiophosphate anion chemisorbs on sulphide mineral surfaces and renders them hydrophobic |
| Lubricant additive chemistry | Structurally related dialkyl dithiophosphates are the basis of antiwear additives, generally with longer alkyl chains | The same P/S functionality provides the extreme-pressure film |
The flotation use deserves emphasis because it is often overlooked: the dimethyl acid is short-chain and therefore a relatively weak hydrophobiser compared with the diethyl, di-isopropyl or di-isobutyl homologues that dominate commercial collector ranges. Where the dimethyl grade is used in flotation it is usually for its selectivity rather than its collecting power.
How it is made
| Route | Chemistry | Note |
|---|---|---|
| Phosphorus pentasulphide route | P2S5 reacted with methanol | The classical industrial route; releases hydrogen sulphide, which must be scrubbed |
| Phosphorus trichloride route | PCl3 with methanol, followed by sulphur addition or hydrogen sulphide treatment | Alternative that avoids some of the P2S5 handling |
| Continuous vs batch | Both are operated commercially | Continuous operation gives more consistent colour and lower free sulphur |
Handling and storage
| Point | Requirement |
|---|---|
| Hydrogen sulphide | The material evolves H2S on hydrolysis and decomposition – one of the most dangerous gases in a chemical plant. Store and handle with ventilation, gas detection and no confined-space entry without testing |
| Materials | Polyethylene, glass-reinforced plastic or 316L stainless steel. Carbon steel corrodes and contaminates the product with iron |
| Moisture | Keep sealed and dry. Water causes hydrolysis to methanol and phosphate/sulphide species, with loss of assay and H2S evolution |
| Alkali | Never store in contact with alkalis unless forming the salt deliberately – the reaction is exothermic |
| Temperature | Store cool; heat accelerates both hydrolysis and the degradation that darkens the product |
| PPE | Acid-resistant gloves, face protection and respiratory protection where ventilation is not assured |
Packaging and documentation
Supplied in polyethylene drums or IBC with closures suitable for an acidic, sulphidic liquid. Each batch ships with a certificate of analysis covering assay, appearance and the relevant physical data, plus an SDS. Because the product degrades in storage, agree the remaining shelf life at delivery and order to consumption rate rather than holding stock.
For the two application routes in detail, see the dithiophosphate collectors for sulphide flotation page and the organophosphate intermediate page. The technical overview is in the dimethyl phosphorodithioate guide.
