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Phosphonate esters are a class of organophosphorus compounds characterized by the presence of a phosphonate group (–PO(OR)_2), where phosphorus is bonded to two alkoxy groups and an alkyl or aryl group.
They are esters of phosphonic acid (R–PO(OH)_2) where the acidic hydrogens are replaced by alkyl or aryl groups.
Phosphonate esters are widely used as intermediates in organic synthesis, agricultural chemicals (e.g., pesticides, herbicides), plasticizers, flame retardants, and as additives in lubricants and fuels. Some are also precursors for phosphonates and related compounds.
CAS Number: 149-57-5
Synonyms
Organophosphonate ester,Dialkyl phosphonate,Dialkyl alkylphosphonate,Phosphonic acid diesters,Phosphorus acid esters
Introduction
Phosphonate esters are a class of organophosphorus compounds characterized by the presence of a phosphorus atom bonded to two alkoxy or aryloxy groups and a direct carbon-phosphorus (C–P) bond.
Their general formula is typically represented as (RO)2P(O)R', where R is an alkyl or aryl group and R' is a variable organic moiety.
These compounds are structurally similar to phosphates and phosphinates but differ in their oxidation states and bonding configurations.
Historically, the development of phosphonate esters dates back to the early 20th century, with significant advancements occurring post-World War II, particularly in the agricultural and pharmaceutical sectors.
Their versatility and chemical stability have led to extensive use across multiple industries.
Chemical Structure and Classification
Phosphonate esters are derivatives of phosphonic acids (RPO(OH)2) where the hydroxyl groups are replaced with alkyl or aryl groups.
They exist in several structural variations based on the nature of the R and R' groups:
Dialkyl phosphonates
Aryl phosphonates
Mixed alkyl-aryl phosphonates
The P=O bond imparts significant polarity, contributing to their unique reactivity and binding properties.
The distinction from phosphates (which have P–O–C linkages) lies in the direct P–C bond, which provides increased resistance to hydrolysis and enzymatic degradation.
Physicochemical Properties
Phosphonate esters possess distinctive physical and chemical properties, including:
Molecular Weight: Typically in the range of 150–300 g/mol
Solubility: Varies widely; dialkyl phosphonates are usually soluble in organic solvents, while others may exhibit aqueous solubility
Polarity: High due to the P=O bond
Thermal Stability: Good thermal resistance; often used in flame retardant formulations
Acid-Base Behavior: The phosphonate group can participate in acid-base equilibria, especially when deprotected
Synthesis of Phosphonate Esters
Several methodologies have been developed for synthesizing phosphonate esters:
Michaelis–Arbuzov Reaction: A classical route involving the reaction of trialkyl phosphites with alkyl halides
Pudovik Reaction: Involves the addition of dialkyl phosphites to aldehydes or ketones in the presence of a base or acid catalyst
Mannich-type Reactions: Formation of C–P bonds via iminium intermediates
Hydrophosphonylation: Addition of phosphites to unsaturated carbonyl compounds
Green Synthesis: Utilizing solvent-free, microwave-assisted, or catalyst-free conditions to minimize environmental impact
Spectroscopic and Analytical Characterization
Phosphonate esters are typically characterized using a suite of analytical tools:
NMR Spectroscopy:
1H NMR: Provides information on proton environments
13C NMR: Used for carbon skeleton analysis
31P NMR: Crucial for studying phosphorus environments; chemical shifts are highly diagnostic
Infrared (IR) Spectroscopy: Identifies P=O stretching frequencies (typically around 1250 cm^-1)
Mass Spectrometry (MS): Determines molecular weights and fragmentation patterns
UV-Visible Spectroscopy: Useful for conjugated phosphonates
Chromatographic Methods: GC, HPLC, and TLC for purity analysis and compound separation
Reactivity and Mechanism
Phosphonate esters exhibit diverse reactivity patterns:
Hydrolysis: Under acidic or basic conditions, esters can hydrolyze to phosphonic acids
Transesterification: Exchange of alkoxy groups under catalyzed conditions
Nucleophilic Substitution: Common with alkyl halides and epoxides
Coordination Chemistry: Can bind to metal centers forming chelates, useful in catalysis and materials science
Their reaction mechanisms often involve nucleophilic attack at the electrophilic phosphorus center or the alpha-carbon adjacent to it.
Industrial Applications
Phosphonate esters have widespread industrial significance:
Agriculture: Key ingredients in herbicides such as glyphosate and phosphinothricin
Pharmaceuticals: Used in the synthesis of bisphosphonates for bone-related disorders
Polymer Industry: Serve as flame retardants, plasticizers, and additives
Water Treatment: Employed as scale inhibitors and corrosion inhibitors
Lubricants and Coatings: Enhance durability and resistance properties
Biological Activities and Biomedical Uses
Enzyme Inhibition: Some phosphonate esters mimic transition states in enzymatic reactions, serving as potent inhibitors
Anticancer Agents: Certain derivatives exhibit cytotoxic activity
Antiviral Compounds: Effective against a range of viruses, including HIV and HBV
Bone Regeneration: Bisphosphonates accumulate in bone and inhibit resorption
Drug Delivery: Used as prodrugs or in conjugation with therapeutic agents
SAFETY INFORMATION ABOUT PHOSPHONATE ESTER
First aid measures:
Description of first aid measures:
General advice:
Consult a physician.
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
If inhaled:
If breathed in, move person into fresh air.
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately.
Wash off with soap and plenty of water.
Consult a physician.
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
If swallowed:
Do NOT induce vomiting.
Never give anything by mouth to an unconscious person.
Rinse mouth with water.
Consult a physician.
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment.
Avoid breathing vapours, mist or gas.
Evacuate personnel to safe areas.
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste.
Keep in suitable, closed containers for disposal.
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place.
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles.
Faceshield (8-inch minimum).
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin protection:
Handle with gloves.
Gloves must be inspected prior to use.
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product.
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
Wash and dry hands.
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls.
If the respirator is the sole means of protection, use a full-face supplied air respirator.
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions.
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company.
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product
