Phenyl isothiocyanate

Phenyl isothiocyanate (PITC) is an organic compound with the formula C₆H₅NCS. It is a colorless liquid with a pungent odor, commonly used in the synthesis of organic compounds and in biochemical applications, most notably in the Edman degradation method for sequencing amino acids in proteins. PITC reacts with the amino group of amino acids to form phenylthiocarbamyl (PTC) derivatives, which can be further cleaved and identified, allowing for the sequencing of proteins.

Properties

Phenyl isothiocyanate is characterized by its strong, pungent odor and its colorless appearance. It has a boiling point of 222°C and a density of 1.13 g/cm³. Being a liquid, it is soluble in organic solvents such as ethanol, acetone, and diethyl ether, but it is less soluble in water.

Synthesis

PITC can be synthesized through the reaction of aniline (C₆H₅NH₂) with carbon disulfide (CS₂) in the presence of an alkali, such as potassium hydroxide (KOH). The reaction proceeds through the formation of dithiocarbamate salt, which is then treated with lead(II) nitrate to yield phenyl isothiocyanate.

Applications

Edman Degradation

The primary application of phenyl isothiocyanate is in the Edman degradation process, a method of sequencing amino acids in peptides. In this process, PITC reacts with the N-terminal amino acid of a peptide to form a PTC derivative. This derivative can then be cleaved and identified, allowing for the sequential analysis of the peptide.

Organic Synthesis

Beyond its biochemical applications, PITC is also used in organic synthesis to introduce the isothiocyanate group into molecules, serving as a precursor to various pharmaceuticals and agrochemicals.

Safety

Phenyl isothiocyanate is a toxic compound and should be handled with care. It is irritating to the skin, eyes, and respiratory system. Proper protective equipment, such as gloves and goggles, should be worn when handling PITC, and work should be conducted in a well-ventilated area or under a fume hood.

See Also

• Amino acids
• Peptide sequencing
• Organic synthesis
• Toxicology