18.7 Thiols and Sulfides
3 min read•may 7, 2024
Thiols and sulfides are sulfur-containing organic compounds that share similarities with alcohols and ethers. These molecules play crucial roles in various chemical processes and biological systems, with unique properties stemming from the sulfur atom's size and reactivity.
Synthesis of thiols and sulfides often involves nucleophilic substitution reactions, while their reactivity is influenced by the sulfur atom's properties. Understanding these compounds is essential for grasping organic sulfur chemistry and its applications in fields like biochemistry and pharmaceuticals.
Thiols and Sulfides
Structure and properties of thiols
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- Thiols (R-SH) are sulfur analogs of alcohols (R-OH) with a sulfur atom bonded to an R group and a hydrogen atom
- The hydrogen atom attached to the sulfur is called the
- Named as "alkanethiols" by replacing the "-ol" suffix of the corresponding alcohol with "-" (ethanethiol for CH3CH2SH)
- More acidic than alcohols due to greater charge stabilization by the larger sulfur atom, weaker S-H bond compared to O-H bond, and more stable (R-S⁻) than alkoxide anion (R-O⁻)
- Typical values: thiols ~10-11, alcohols ~16-18
- The functional group in thiols is known as the (-SH)
Synthesis of thiols and sulfides
- Thiols synthesized from alkyl halides via SN2 reaction with (HS⁻), a strong nucleophile (CH3CH2Br + HS⁻ → CH3CH2SH + Br⁻)
- Prepared by reducing sulfonic acids (R-SO3H) or sulfonyl chlorides (R-SO2Cl) with LiAlH4 to the corresponding thiol
- Sulfides (R-S-R') synthesized from thiols via SN2 reaction with alkyl halides
- Thiols deprotonated to form thiolate anion (R-S⁻), which acts as a nucleophile
- Thiolate anion reacts with alkyl halide (CH3CH2SH + NaOH → CH3CH2S⁻ + H2O; then CH3CH2S⁻ + R'-X → CH3CH2-S-R' + X⁻)
- Precautions: work with thiols in well-ventilated areas due to strong, unpleasant odors (similar to ); store thiols and sulfides under inert atmosphere to prevent oxidation
Sulfides vs ethers in reactions
- Sulfides (R-S-R') are sulfur analogs of ethers (R-O-R') with a sulfur atom bonded to two R groups
- Stronger nucleophiles than ethers due to the larger size and polarizability of sulfur, which is less electronegative than oxygen allowing for a more polarizable electron cloud
- Sulfides react more readily with alkyl halides via SN2 reactions compared to ethers
- More easily oxidized than ethers
- Sulfides oxidized to sulfoxides (R-SO-R') and sulfones (R-SO2-R') using oxidants (H2O2 or peroxyacids)
- Ethers generally resistant to oxidation under similar conditions
- Oxidation of sulfides to sulfoxides is stereoselective
- The lone pair on sulfur allows for two possible stereoisomers (R and S) when oxidized to a
- Stereochemistry of the product depends on the oxidant and reaction conditions
Organosulfur compounds and their properties
- are organic molecules containing sulfur atoms
- Sulfur can exist in various oxidation states, ranging from -2 to +6
- The of sulfur-containing compounds is generally higher than their oxygen analogs due to sulfur's larger size and polarizability
- Examples of organosulfur compounds include thiols, sulfides, disulfides, and sulfoxides, each with distinct reactivity and properties
Key Terms to Review (30)
Alkanethiol: An alkanethiol is an organic compound that contains a sulfur-hydrogen (S-H) functional group attached to an alkane backbone. These compounds are also known as mercaptans and are important in various chemical and biological processes.
Disulfide: A disulfide is a covalent bond formed between two sulfur atoms, typically found in the side chains of the amino acid cysteine. Disulfides play a crucial role in the structure and function of proteins, as well as in various biological processes involving thiols and sulfides.
Disulfides (R–S–S–R′): Disulfides are chemical compounds containing a pair of sulfur atoms linked together, attached to two different organic groups denoted R and R′. They are formed by the oxidation of thiols (sulfur-containing analogs of alcohols) and play a crucial role in stabilizing the structure of proteins by forming cross-links.
Disulfides (RSSR′): Disulfides are organic compounds that contain a pair of sulfur atoms linked together by a single bond, often derived from the oxidation of thiols. They play a crucial role in the structure and stability of proteins by forming cross-links between different parts of a molecule.
Hydrogen Sulfide: Hydrogen sulfide is a colorless, flammable gas with a characteristic rotten egg odor. It is an important compound in the context of thiols and sulfides, as it serves as a precursor and structural component for various sulfur-containing organic molecules.
Hydrosulfide: The hydrosulfide ion (HS-) is a chemical species that consists of a hydrogen atom bonded to a sulfur atom. It is an important intermediate in the chemistry of sulfur-containing compounds and plays a role in the topics of thiols and sulfides.
Mercaptan: Mercaptans, also known as thiols, are a class of organic compounds containing a sulfur-hydrogen (S-H) functional group. They are characterized by their distinctive unpleasant odor and play a significant role in the context of thiols and sulfides in organic chemistry.
Mercapto group: A mercapto group consists of a sulfur atom bonded to a hydrogen atom (-SH), functioning as a substituent or side chain in organic compounds. It is the sulfur analogue of the hydroxyl group (-OH) found in alcohols.
Nucleophilicity: Nucleophilicity refers to the ability of a species to donate electrons and form a covalent bond with an electrophilic center. It is a key concept in organic chemistry that governs the reactivity and selectivity of many important reactions, including substitution, addition, and elimination reactions.
Organosulfur Compounds: Organosulfur compounds are organic molecules that contain a sulfur atom covalently bonded to a carbon atom. They are a class of compounds that are important in various fields, including organic chemistry, biochemistry, and industrial applications.
Oxidation States of Sulfur: The oxidation state of sulfur refers to the degree of oxidation or reduction of a sulfur atom within a chemical compound. Sulfur can exhibit a wide range of oxidation states, which is crucial in understanding its behavior in organic chemistry, particularly in the context of thiols and sulfides.
Raney Nickel: Raney nickel is a highly active heterogeneous catalyst composed of nickel that is commonly used in organic chemistry for the selective hydrogenation of various functional groups. It is named after its inventor, Murray Raney, and is known for its ability to facilitate the reduction of alkenes, nitro compounds, and other reducible groups while maintaining selectivity.
Sulfhydryl Group: The sulfhydryl group, also known as the thiol group, is a functional group in organic chemistry consisting of a sulfur atom bonded to a hydrogen atom (–SH). It is an important structural feature in many biomolecules and plays a crucial role in various chemical reactions and biological processes.
Sulfide: A sulfide is an organic compound that contains a sulfur atom bonded to two alkyl or aryl groups. They are the sulfur analogs of ethers, where sulfur replaces the oxygen atom in the ether functional group.
Sulfide: A sulfide is a chemical compound containing sulfur in its negative or reduced oxidation state, typically bonded to a metal or other element. Sulfides are important in the context of organic chemistry, particularly in the study of thiols and sulfides.
Sulfone: A sulfone is a functional group in organic chemistry that consists of a sulfur atom double-bonded to two oxygen atoms. Sulfones are commonly found in various organic compounds and play important roles in the context of thiols and sulfides.
Sulfone (R2SO2): A sulfone is an organic sulfur compound characterized by a sulfonyl functional group connected to two alkyl or aryl groups. It is known for its stability and resistance to oxidation compared to other sulfur-containing compounds.
Sulfonic Acid: A sulfonic acid is a type of organic compound that contains a sulfonic acid functional group (-SO3H) attached to a carbon atom. These compounds are known for their acidic properties and have various applications in organic chemistry.
Sulfonium ions: Sulfonium ions are positively charged ions where sulfur is the central atom, bonded to three organic groups and carrying a positive charge. They are formed when sulfides react with alkyl halides, resulting in the addition of an alkyl group to the sulfur atom.
Sulfonyl Chloride: Sulfonyl chloride is a functional group consisting of a sulfur atom double-bonded to two oxygen atoms and single-bonded to a chlorine atom. It is a highly reactive species that is commonly used in organic synthesis, particularly in the formation of sulfones and other sulfur-containing compounds.
Sulfoxide: A sulfoxide is a functional group in organic chemistry that consists of a sulfur atom double-bonded to an oxygen atom. Sulfoxides are important intermediates in various organic reactions and have diverse applications in chemistry and biology.
Sulfoxide (R2SO): Sulfoxides are a class of organic sulfur compounds characterized by a sulfur atom bonded to two alkyl or aryl groups and one oxygen atom. They are derived from the oxidation of sulfides, where R represents any carbon-containing group.
Thioether: A thioether is a type of organic compound that contains a sulfur atom connected to two alkyl or aryl groups. These sulfur-containing compounds are structurally similar to ethers, but with the oxygen atom replaced by a sulfur atom.
Thiol: A thiol is an organic compound containing a sulfur-hydrogen (S-H) functional group. Thiols are the sulfur-containing analogues of alcohols, where the oxygen atom is replaced by a sulfur atom. They are important in organic chemistry and biochemistry, particularly in the context of protein structure and function.
Thiol Oxidation: Thiol oxidation is the process by which sulfur-containing functional groups known as thiols (R-SH) are converted to their oxidized forms, typically disulfides (R-S-S-R). This reaction is an important process in the chemistry of organic compounds and plays a crucial role in the structure and function of proteins.
Thiol Proton: The thiol proton refers to the hydrogen atom bonded to the sulfur atom in a thiol group (-SH). Thiols are organic compounds containing a sulfhydryl group, which is a key functional group in many biomolecules and plays a crucial role in various chemical reactions.
Thiolate Anion: A thiolate anion is the conjugate base of a thiol (R-SH), formed by the deprotonation of the sulfhydryl group. It is a negatively charged species with the general formula R-S⁻, where R represents an organic substituent. Thiolate anions are important intermediates in various organic reactions and play a crucial role in the chemistry of thiols and sulfides.
Thiolate ion: A thiolate ion is the conjugate base of a thiol, formed when a thiol loses a proton (H+) from its sulfur atom. It is represented by the formula R-S^-, where R is an organic group.
Zeisel Determination: The Zeisel determination is an analytical technique used to quantify the methoxyl (OCH3) group content in organic compounds. It is particularly useful in the analysis of various sulfur-containing compounds, such as thiols and sulfides, which are covered in the topics of Section 18.7 of organic chemistry.
Zinin: Zinin is a chemical reaction named after the Russian chemist Alexander Zinin, who developed the process in 1842. It is a method used to convert nitro compounds into their corresponding amino compounds through the reduction of the nitro group.