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General chemical structure of the thiol functional group
General chemical structure of the thiol functional group

In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Being the sulfur analogue of an alcohol group (-OH), this functional group is referred to either as a thiol group or a sulfhydryl group. In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon More traditionally, thiols are often referred to as mercaptans.

Contents

Nomenclature

When a thiol group is a substituent on an alkane, there are several ways of naming the resulting thiol:

Etymology

The term mercaptan comes from the Latin mercurius captans, meaning 'laying hold of mercury,' because the –SH group binds tightly to the element mercury. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum

Physical properties

Odor

Many thiols are colorless liquids having an odor resembling that of garlic. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Allium sativum L, commonly known as garlic, is a species in the Onion family Alliaceae. The odor of thiols is often strong and repulsive, particularly for those of low molecular weight. (A close selenium analog, butyl seleno-mercaptan, is responsible for the intolerable, persistent odor produced by the spraying of skunks. Seleno-mercaptan A seleno-mercaptan is an organic compound of the formula R-SeH Skunks (sometimes referred to as polecats) are Mammals best known for their ability to excrete a strong foul-smelling odor. ) Thiols bind strongly to skin proteins. The skin is the outer covering of living tissue of an animal (or plant Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Natural gas distributors began adding various forms of pungent thiols, usually ethanethiol, to natural gas, which is naturally odorless, after the deadly 1937 New London School explosion in New London, Texas. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Ethanethiol is the Organic compound with the formula CH3CH2SH Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Year 1937 ( MCMXXXVII) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar. The New London School explosion occurred on March 18, 1937, when a Natural gas leak caused an Explosion, destroying the New London School of New London is a city in Rusk County, Texas, United States. The population was 987 at the 2000 census. Thiols are also responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the "skunky" odor of beer which has been exposed to ultraviolet light. A wine fault or defect is an unpleasant characteristic of a Wine often resulting from poor Winemaking practices Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described However, not all thiols have unpleasant odors. For example, grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit. Grapefruit mercaptan is the common name for a natural Organic compound found in Grapefruit. Terpenes are a large and varied class of Hydrocarbons, produced primarily by a wide variety of plants particularly Conifers though also by some insects such The grapefruit is a subtropical Citrus Tree grown for its Fruit which was originally named the "forbidden fruit " of Barbados

Boiling points and solubility

Due to the small electronegativity difference between sulfur and hydrogen, an S-H bond is practically nonpolar covalent. " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons "Polar molecule" and "Non-polar" redirect here Therefore, the S-H bond in the thiols have a lower dipole moment as compared to the alcohol's O-H bond. Thiols show little association by hydrogen bonding, with both water molecules and among themselves. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen Hence, they have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. Thiols are as soluble and have similar boiling points to isomeric sulfides. The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation

Chemical properties

Synthesis

The methods used in making thiols are analogous to those used to make alcohols and ethers. The reactions are quicker and higher yielding because sulfur anions are better nucleophiles than oxygen atoms.

Thiols are formed when a halogenoalkane is heated with a solution of sodium hydrosulfide

CH3CH2Br + NaSH heated in ethanol(aq) → CH3CH2SH + NaBr

In addition, disulfides can be readily reduced by reducing agents such as lithium aluminium hydride in dry ether to form two thiols. The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane Sodium hydrosulfide is the Chemical compound with the formula NaSH In Chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms

R-S-S-R' → R-SH + R'-SH

Reactions

The thiol group is the sulfur analog of the hydroxyl group (-OH) found in alcohols. Hydroxyl in Chemistry stands for a molecule consisting of an Oxygen atom and a Hydrogen atom connected by a Covalent bond. In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Since sulfur and oxygen belong to the same periodic table group, they share some similar chemical bonding properties. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the In Chemistry a group, also known as a family, is a vertical column in the Periodic table of the Chemical elements There are 18 groups in A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic Like alcohol, in general, the deprotonated form RS− (called a thiolate) is more chemically reactive than the protonated thiol form RSH

The chemistry of thiols is thus related to the chemistry of alcohols: thiols form thioethers, thioacetals and thioesters, which are analogous to ethers, acetals, and esters. A thioether (similar to Sulfide) is a functional group in Organic chemistry that has the structure R1-S-R2 as shown on right Thioacetals are the Sulfur analogue of Acetals They are prepared in a similar way to acetals by reacting a Thiol with an Aldehyde Thioesters are compounds resulting from the bonding of Sulfur with an Acyl group with the general formula R-S-CO-R'. Ether is a class of Organic compounds which contain an ether group — an Oxygen Atom connected to two (substituted Alkyl An acetal is a Molecule with two single bonded oxygens attached to the same carbon atom Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least Furthermore, a thiol group can react with an alkene to create a thioether. In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon (In fact, biochemically, thiol groups may react with vinyl groups to form a thioether linkage. A vinyl compound is any Organic compound that contains a vinyl group (also called ethenyl) &minus C[[Hydrogen H]] =CH sub>2 A thioether (similar to Sulfide) is a functional group in Organic chemistry that has the structure R1-S-R2 as shown on right )

Acidity

The sulfur atom of a thiol is quite nucleophilic, rather more so than the oxygen atom of an alcohol. In Chemistry, a nucleophile (literally nucleus lover as in nucleus and phile) is a Reagent that forms a Chemical bond to The thiol group is fairly acidic with a usual pKa around 10 to 11. In the presence of a base, a thiolate anion is formed which is a very powerful nucleophile. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge The group and its corresponding anion are readily oxidized by reagents such as bromine to give an organic disulfide (R-S-S-R). Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state In Chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms

2R-SH + Br2 → R-S-S-R + 2HBr

Oxidation by more powerful reagents such as sodium hypochlorite or hydrogen peroxide yield sulfonic acids (RSO3H). Sodium hypochlorite is a Chemical compound with the formula NaClO Hydrogen peroxide (H2O2 is a very pale blue liquid which appears colorless in a dilute solution slightly more Viscous than water Sulfonic acid is an unstable Acid with the formula H-S(=O2-OH

R-SH + 3H2O2 → RSO3H + 3H2O

Biological importance

As the functional group of the amino acid cysteine, the thiol group plays an important role in biological systems. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Not to be confused with Cystine, its oxidized dimer Cysteine (abbreviated as Cys or C) is an α- Amino acid with When the thiol groups of two cysteine residues (as in monomers or constituent units) are brought near each other in the course of protein folding, an oxidation reaction can create a cystine unit with a disulfide bond (-S-S-). Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Cystine is the Amino acid Dimer formed when a pair of Cysteine molecules are joined by a Disulfide bond In Chemistry, a disulfide bond is a single Covalent bond derived from the coupling of Thiol groups Disulfide bonds can contribute to a protein's tertiary structure if the cysteines are part of the same peptide chain, or contribute to the quaternary structure of multi-unit proteins by forming fairly strong covalent bonds between different peptide chains. In Biochemistry and Chemistry, the tertiary structure of a Protein or any other Macromolecule is its three-dimensional structure as defined Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino In Biochemistry, quaternary structure is the arrangement of multiple folded Protein molecules in a multi-subunit complex The heavy and light chains of antibodies are held together by disulfide bridges. A heavy chain is the large Polypeptide subunit of a Protein complex, such as a Motor protein (e Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily Also, the kinks in curly hair are a product of cystine formation. Hair is a keratinised protein filament that grows through the epidermis from follicles deep within the Dermis. Permanents (perms) take advantage of the oxidizability of cysteine residues. The chemicals used in hair straightening are reductants that reduce cystine disulfide bridges to free cysteine sulfhydryl groups, while chemicals used in hair curling are oxidants that oxidize cysteine sulfhydryl groups to form cystine disulfide bridges. Hair straightening is a hair styling technique which involves the flattening and straightening of hair in order to give it a smooth streamlined and 'sleek' appearance A reducing agent (also called a reductant or reducer) is the element or a compound in a Redox (reduction-oxidation reaction (see Electrochemistry An oxidizing agent or oxidising agent (also called an oxidant, oxidizer or oxidiser) can be defined as either a Chemical compound Sulfhydryl groups in the active site of an enzyme can form noncovalent bonds with the enzyme's substrate as well, contributing to catalytic activity. The active site of an Enzyme contains the catalytic and Binding sites. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins A noncovalent bond is a type of Chemical bond, typically between Macromolecules that does not involve the sharing of pairs of electrons but rather involves more dispersed Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Active site cysteine residues are the functional unit in cysteine proteases. Proteases are Enzymes that degrade polypeptides. Cysteine proteases have a common catalytic mechanism that involves a nucleophilic Cysteine

Examples of thiols

See also

External links

Dictionary

thiol

-noun

  1. (organic chemistry) a univalent organic radical (-SH) containing a sulphur and a hydrogen atom; a compound containing such a radical
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