Chemistry informtion about  Butyl hydrogen phosphonate (16456-56-7) is:
IUPAC Name: Butoxy-hydroxy-oxophosphanium
Synonyms: Butyl Hydrogen Phosphonate;Phosphonic Acid, Monobutyl Ester;Butyl Phosphonate;Butylfosfit;Monobutyl Phosphite;Phosphorous Acid, Butyl Ester;Phosphonic Acid Butyl Ester
MF: C₄H₁₁O₃P
MW: 138.102101
EINECS: 240-508-1 
Density: g/cm3
Flash Point: 81.6 °C
Boiling Point: 211.3 °C at 760 mmHg
Enthalpy of Vaporization: 49.32 kJ/mol 
Vapour Pressure: 0.0725 mmHg at 25°C 
Following is the molecular structure of  Butyl hydrogen phosphonate (16456-56-7) is:

 Butyl hydrogen phosphonate (16456-56-7) can be used in the pharmaceutical, perfume synthesis, also used as lubricant additives, antiwear agent.

Reported in EPA TSCA Inventory.

Moderately toxic by an unspecified route. When heated to decomposition it emits toxic fumes of PO_x.

 Butyl hydrogen phosphonate (16456-56-7) is a clear colorless to slightly yellow liquid.
First Aid Measures:
Ingestion: Do not induce vomiting. If victim is conscious and alert, give 2-4 cupfuls of milk or water. Never give anything by mouth to an unconscious person. Get medical aid immediately.
Inhalation: Get medical aid immediately. Remove from exposure to fresh air immediately. If breathing is difficult, give oxygen. DO NOT use mouth-to-mouth respiration. If breathing has ceased apply artificial respiration using oxygen and a suitable mechanical device such as a bag and a mask.
Skin: Get medical aid immediately. Immediately flush skin with plenty of soap and water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. Destroy contaminated shoes.
Eyes: Get medical aid immediately. Do not allow victim to rub or keep eyes closed. Extensive irrigation is required (at least 30 minutes).
Handling and Storage:
Storage: Keep away from heat, sparks, and flame. Keep away from sources of ignition. Keep container closed when not in use. Flammables-area. Store protected from moisture.
Handling: Wash thoroughly after handling. Wash hands before eating. Remove contaminated clothing and wash before reuse. Ground and bond containers when transferring material. Use spark-proof tools and explosion proof equipment. Empty containers retain product residue, (liquid and/or vapor), and can be dangerous. Avoid contact with heat, sparks and flame. Do not get on skin or in eyes. Do not ingest or inhale. Use with adequate ventilation. Do not allow contact with water. Discard contaminated shoes. Do not pressurize, cut, weld, braze, solder, drill, grind, or expose empty containers to heat, sparks or open flames. Keep from contact with moist air and steam.