Chemical Identity and Physical Properties

2-Amino-4-iodobenzoic acid (CAS 13089-10-6) is an ortho-amino benzoic acid derivative in which an iodine atom is installed at the para position (C-4) relative to the carboxylic acid. Its molecular formula is C₇H₆INO₂ and its molecular weight is approximately 263.03 g/mol.

The compound presents as a crystalline solid, typically pale yellow to off-white in colour, and is sparingly soluble in water but more soluble in polar organic solvents such as methanol, ethanol, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF). The zwitterionic character arising from the opposing amino and carboxylic acid groups gives the molecule an amphoteric nature, and solubility can be improved by forming salts with dilute base or acid.

The aryl iodide bond (C–I) is notably weaker and more polarisable than C–Br or C–Cl bonds, conferring high reactivity in metal-catalysed coupling reactions while retaining stability under ordinary ambient storage conditions.

Synthetic Applications and Reactivity

The three orthogonal reactive handles on 2-Amino-4-iodobenzoic acid — the primary amine, the carboxylic acid, and the aryl iodide — allow it to participate in diverse synthetic transformations, making it a highly valued building block in complex molecule assembly.

Palladium-catalysed cross-coupling: The aryl iodide is an excellent electrophilic partner in Suzuki–Miyaura, Sonogashira, Heck, Buchwald–Hartwig, and Negishi reactions. The high oxidative addition rate of aryl iodides relative to aryl bromides or chlorides often allows milder reaction conditions and higher yields.

Heterocycle synthesis: The ortho amino group and carboxylic acid are geometrically pre-disposed for intramolecular cyclisation. This motif is commonly used to construct benzoxazoles, isatoic anhydride analogues, quinazolinones, and other nitrogen- or oxygen-containing heterocycles of pharmaceutical relevance.

Amide and ester formation: The carboxylic acid can be activated via standard coupling reagents (e.g., EDC/HOBt, HATU, or thionyl chloride) to deliver amides or esters, enabling fragment coupling in peptide-mimetic or prodrug synthesis.

Diazotisation: The amine can be diazotised and further converted to azo compounds, phenols (Sandmeyer), or used in diazo-coupling reactions.

Safe Handling, Storage, and Disposal

Personal protective equipment (PPE): Always wear appropriate PPE when working with 2-Amino-4-iodobenzoic acid, including nitrile gloves, safety glasses or goggles, and a laboratory coat. Work in a well-ventilated fume hood to minimise inhalation of dust or aerosols.

Storage: Store the compound in a tightly sealed container in a cool (typically 2–25 °C), dry location away from direct sunlight, strong oxidising agents, and incompatible bases or acids. Amber glass vials or HDPE containers are recommended to prevent photodegradation. Under recommended storage conditions the compound is expected to be stable for an extended period; consult the product specification sheet (CoA) for confirmed shelf-life data.

Handling precautions: Avoid generating fine dust during weighing. Use a micro-balance inside a containment enclosure where possible. Wash hands thoroughly after handling. In the event of skin contact, wash with soap and water; for eye contact, irrigate immediately with copious water and seek medical advice.

Disposal: Dispose of waste material and contaminated items in accordance with applicable local, national, and institutional regulations for halogenated organic waste. Do not discharge into drains or the environment.

Note: Consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific for complete hazard, first-aid, and regulatory information before use.

Practical Tips for Laboratory Use

Solution preparation: For coupling reactions, dissolve 2-Amino-4-iodobenzoic acid in anhydrous DMF or DMSO to prepare stock solutions. For aqueous applications, dissolve in dilute aqueous NaOH or K₂CO₃ (0.5–1 equiv.) and adjust pH as needed. Prepare solutions fresh or store at −20 °C under inert atmosphere to prevent decomposition.

Reaction optimisation for cross-coupling: Use palladium catalysts such as Pd(PPh₃)₄ or Pd(dppf)Cl₂ for Suzuki couplings. Aryl iodides typically do not require elevated temperatures; reactions can often be conducted at room temperature to 80 °C. Conduct reactions under nitrogen or argon atmosphere to protect the catalyst and prevent protodeiodination.

Protecting group strategy: When selectivity is required, the amine can be temporarily Boc- or Cbz-protected before performing transformations at the carboxylic acid or aryl iodide, and subsequently deprotected under standard conditions. Conversely, the carboxylic acid can be esterified before amine-directed steps.

Analytical characterisation: Confirm identity and purity by ¹H NMR (characteristic signals for the aromatic protons and broad NH₂ signal), ¹³C NMR, and HPLC (UV detection at 254 nm or 280 nm). ICP-MS or XRF may be used to verify iodine content if required.