1,1′-Bi-2-naphthol

1,1′-Bi-2-naphthol, commonly known as BINOL, is an organic compound that is of significant interest in the field of organic chemistry, particularly in asymmetric synthesis. This compound is a diol, meaning it contains two hydroxyl groups, and it is derived from the fusion of two naphthalene rings at their 1 and 1′ positions, hence the name 1,1′-Bi-2-naphthol. BINOL and its derivatives are widely used as chiral ligands and catalysts in various enantioselective reactions, making it a cornerstone in the production of chiral drugs and other chiral substances.

Structure and Properties

BINOL exists in two enantiomers due to its chiral axis, which runs through the point of fusion of the two naphthalene rings. These enantiomers are designated as (R)-BINOL and (S)-BINOL. The presence of the two hydroxyl groups allows for the formation of intramolecular hydrogen bonds, which significantly influence its physical properties and reactivity. BINOL is a white to off-white powder that is soluble in common organic solvents such as ethanol, diethyl ether, and chloroform.

Synthesis

The synthesis of BINOL can be achieved through various methods, with the most common being the oxidative coupling of 2-naphthol. This process involves the use of metal catalysts, such as copper(II) chloride, and an oxidizing agent. The reaction conditions and the choice of catalysts can influence the yield and the enantiomeric excess (ee) of the product. Advanced synthetic techniques allow for the preparation of BINOL with high ee, which is crucial for its application in asymmetric synthesis.

Applications

BINOL and its derivatives serve as powerful ligands and catalysts in a wide range of asymmetric reactions, including but not limited to aldol reactions, Michael additions, and Diels-Alder reactions. The ability of BINOL to induce chirality in the products of these reactions is invaluable in the synthesis of chiral drugs, agrochemicals, and other functional materials. Additionally, BINOL derivatives are used in the construction of MOFs (Metal-Organic Frameworks) and other supramolecular structures due to their ability to form complex coordination compounds.

Environmental and Health Considerations

While BINOL is not classified as a hazardous substance, its handling and disposal should be conducted with care to prevent environmental contamination. Safety data sheets (SDS) recommend wearing protective equipment and working in a well-ventilated area when handling BINOL. In case of spillage, it should be contained and collected for proper disposal according to local regulations.

See Also

• Chirality (chemistry)
• Catalysis
• Enantioselective synthesis
• Naphthalene