Sulfanyl

Sulfanyl, also known as a hydrosulfide or mercapto group, is a functional group in organic chemistry consisting of a sulfur atom bound to one hydrogen atom (–SH). It is the sulfur analogue of a hydroxyl group (–OH).

Nomenclature:

The sulfanyl group is commonly indicated in chemical nomenclature in several ways:

• As a prefix: mercapto- (less common in modern nomenclature).
• As a suffix: -thiol (used when the –SH group is the principal characteristic group).
• As a substituent using "sulfanyl-" (used when the –SH group is a substituent and other functional groups are present).

Properties:

Sulfanyl groups are weakly acidic, more acidic than alcohols but less acidic than carboxylic acids. They are also good nucleophiles. The sulfur atom has lone pairs of electrons, making sulfanyl groups capable of hydrogen bonding, although hydrogen bonding involving sulfur is weaker than that involving oxygen. Thiols, compounds containing sulfanyl groups, are often characterized by a strong and often unpleasant odor.

Occurrence and Significance:

Sulfanyl groups are found in a variety of biologically important molecules, including:

• Amino acids: Cysteine and methionine contain sulfur atoms. Cysteine contains a sulfanyl group that plays a crucial role in protein structure through disulfide bond formation.
• Coenzymes: Coenzyme A contains a sulfanyl group that is involved in acyl group transfer reactions.
• Enzymes: Some enzymes utilize sulfanyl groups in their active sites for catalysis.
• Various other biomolecules: Including certain vitamins and metabolic intermediates.

Reactions:

Sulfanyl groups undergo a variety of chemical reactions, including:

• Oxidation: Oxidation of thiols can lead to the formation of disulfides (R–S–S–R), sulfenic acids (R–S–OH), sulfinic acids (R–SO₂H), and sulfonic acids (R–SO₃H), depending on the oxidizing agent and reaction conditions.
• Alkylation: Thiols can be alkylated with alkyl halides to form thioethers (R–S–R').
• Reaction with carbonyl compounds: Thiols react with aldehydes and ketones to form thioacetals and thioketals, respectively.
• Deprotonation: The proton on the sulfur atom can be removed by a strong base to form a thiolate anion (–S⁻), which is a strong nucleophile.

Related Compounds:

• Thiols: Organic compounds containing one or more sulfanyl groups.
• Disulfides: Compounds containing a sulfur-sulfur bond (R–S–S–R).
• Thioethers (Sulfides): Compounds with a sulfur atom bonded to two alkyl or aryl groups (R–S–R').