Phosphonic Acid Phostones (1960)
U.S. Patent No. 2,953,591, granted on September 20, 1960, to Albert Y. Garner, describes a novel class of non-inflammable organophosphorus compounds termed “phostones.” Albert Garner, a research scientist at the Monsanto Chemical Company in St. Louis, Missouri, developed these intramolecular esters of phosphonic acids to serve as specialized, heavy-duty industrial fluids and additives.
This chemical invention solved a critical vulnerability in modern materials science: the extreme flammability of commercial plastics and hydraulic fluids when subjected to high temperatures. By synthesizing a phosphorus-based structural analog to traditional organic lactones, Garner created a molecule that intrinsically resists fire while maintaining exceptional physical stability.
The Chemistry: The Halide Distillation Pathway
Phostones are generated through a cyclic reaction between an organic phosphite and a dihalogenated hydrocarbon. Garner discovered that while these components theoretically react in equal parts, using an excess of the dihalogenated hydrocarbon significantly increases the overall chemical yield.
A critical element of the synthesis is the continuous removal of the reaction’s volatile by-products. By keeping the reaction temperature below 250°C, the lower-boiling organic halides are continuously boiled off, driving the equilibrium forward to optimize phostone production.
Why Phostones?
- Thermal Endurance: They exhibit an unusually broad liquid range, remaining highly stable and free-flowing at extreme temperatures. For instance, ethyl butylphosphonic acid phostone freezes below -80°C but will not boil until it reaches approximately 290°C under atmospheric pressure.
- Flame Retardancy: When incorporated into combustible polymers, the phosphorus structure acts as a built-in fire suppressant.
- Self-Extinguishing Properties: Under a direct flame, treated materials will slowly char rather than ignite into open blazes, completely extinguishing themselves the moment the external flame source is removed.
Key Chemical Components
The synthesis relies on a precise reaction matrix where molecular configuration dictates the properties of the final compound:
| Component | Function / Feature |
| Organic Phosphite | Mono-, di-, or tri-substituted esters of phosphorous acid (or their alkali metal salts). At least one attached group must be a hydrocarbon radical to form the ester backbone. |
| Dihalogenated Hydrocarbon | A 1,3-, 1,4-, or 1,5-dihalo-aliphatic hydrocarbon. The halogen atoms must be separated by 1 to 3 intervening carbon atoms to allow the ring structure to snap closed. |
| Volatile Halide By-Product (RX) | The organic or hydrogen halide formed during synthesis. Having a low boiling point allows it to be distilled out dynamically to push reaction yields higher. |
| The Resulting Phostone Ring | A cyclic organophosphorus compound where the phosphorus atom (P) and an oxygen atom (O) are chemically bound directly into a carbon ring. |
Performance: Fire Retardation in Plastics
Garner’s patent provides definitive experimental evidence of the phostone’s efficacy when blended into standard polystyrene molding powders.
Comparative Burn Test Results:
- Batch A (Formulated with 5% Phostone): When held directly inside a Bunsen burner flame, the plastic slab slowly charred but resisted rapid ignition. Upon removal from the flame, the specimen completely self-extinguished.
- Batch B (Untreated Polystyrene): When exposed to the identical Bunsen flame, the plastic slab ignited violently and rapidly. It continued to burn aggressively even after removal from the flame until it was entirely reduced to ash.
The Manufacturing Process
The patent outlines a straightforward, high-temperature synthesis sequence for isolating pure phostones:
- Charge the reaction vessel with the organic phosphite and a stoichiometric excess of the chosen dihalogenated hydrocarbon (e.g., 1,3-dibromopropane).
- Heat the mixture to an initial reaction temperature between 130°C and 155°C to initiate the cyclic transition.
- Maintain a uniform reaction environment within a strict window of 130°C to 200°C for a duration ranging from 2.5 to 20 hours.
- Distill the volatile alkyl halide by-products (such as ethyl bromide or ethyl chloride) out of the mixture continuously to optimize chemical equilibrium.
- Isolate the final product via fractional vacuum distillation at low pressure to capture the pure, colorless phostone liquid.
About the Inventor: Albert Y. Garner
Albert Y. Garner was an American research chemist whose mid-century work at the Monsanto Chemical Company significantly advanced the development of functional organophosphorus materials.
During the post-WWII industrial boom, the rapid proliferation of synthetic plastics created massive fire hazards across consumer goods, aviation, and manufacturing. Garner’s research focused heavily on polymer stabilizers, flame-retardant additives, and advanced synthesis techniques. His architectural approach to molecular design contributed directly to the foundational chemical libraries used today to manufacture flame-resistant electronics, safety insulation, and non-flammable aerospace hydraulic fluids.
Summary of Claims
The patent explicitly claims:
- Novel chemical compositions of matter comprising cyclic phostone structures where phosphorus and oxygen atoms are integrated into a divalent hydrocarbon chain.
- A synthesis process reacting mono-, di-, or tri-substituted esters of phosphorous acid with 1,3-, 1,4-, or 1,5-dihalo-aliphatic hydrocarbons.
- Conducting the chemical synthesis within a thermal range strictly limited between 100°C and 250°C.
