2-Mercaptobenzothiazole is an

organosulfur compound Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

with the formula . A white solid, it is a reagent in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

and in the

sulfur vulcanization Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into materials of varying hardness, elasticity, and mechanical durability by heating them with sulfur or sulfur-containing compounds. Sulfur forms cros ...

of rubber.

Structure

The molecule is planar with a C=S double bond, so the name ''mercapto''benzothiazole is a misnomer, a more appropriate name could be benzothiazoline-2-thione. Solution measurements by

NMR spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic f ...

could not measure the presence of the

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

that the name implies, instead it exists as a thione/

dithiocarbamate In organic chemistry, a dithiocarbamate is a chemical compound with the general formula . It contains the functional group with the Chemical structure, structure . It is the analog of a carbamate in which both oxygen atoms are replaced by sulfur ...

and the hydrogen appears on the nitrogen in the solid state, gas-phase, and in solution. Theory indicates that the thione tautomer is about 39 kJ/mol lower in energy than the thiol, and a hydrogen-bonded dimer of the thione has even lower energy. At alkaline pH greater than 7 the deprotonated

thiolate In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

form is most abundant. A protonated form could not be observed in the pH range 2-11.

Synthesis

The compound has been produced by many methods. The industrial route entails the high temperature reaction of

aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...

and

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is an inorganic compound with the chemical formula and structure . It is also considered as the anhydride of thiocarbonic acid. It is a colorless, flammable, neurotoxic liquid that is used as ...

in the presence of sulfur, which proceeds by this idealized equation: : The traditional route is the reaction of 2-aminothiophenol and carbon disulfide: : This method was developed by the discoverer of the compound, A. W. Hoffmann. Other routes developed by Hoffmann include the reactions of carbon disulfide with 2-aminophenol and of

sodium hydrosulfide Sodium hydrosulfide is the chemical compound with the formula NaSH. This compound is the product of the half-neutralization of hydrogen sulfide () with sodium hydroxide (NaOH). NaSH and sodium sulfide are used industrially, often for similar purp ...

with chlorobenzothiazole. Further synthetic advances were reported in the 1920s that included demonstration that phenyl

s pyrolyze to benzothiazole derivative.

Reactions

The compound is insoluble in water but dissolves upon the addition of base, reflecting deprotonation. Treatment with

Raney nickel Raney nickel , also called spongy nickel, is a fine-grained solid composed mostly of nickel derived from a nickel–aluminium alloy. Several grades are known, of which most are gray solids. Some are pyrophoric, but most are used as air-stable s ...

results in monodesulfurization, giving

benzothiazole Benzothiazole, or more specifically 1,3-benzothiazole, is an aromatic heterocyclic compound with the chemical formula . It is colorless, slightly viscous liquid. Although the parent compound, benzothiazole is not widely used, many of its derivativ ...

: : The benzo ring undergoes electrophilic aromatic substitution at the position para to nitrogen. S-alkylation of mercaptobenzothiazole gives thioether, which can be oxidized to the sulfone. This sequence sets the stage for the Modified Julia olefination. Oxidation gives mercaptobenzothiazole disulfide. This disulfide reacts with

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

s to give sulfenamide derivatives such 2-morpholinodithiobenzothiazole. These compounds are used in sulphur vulcanization, where they act as accelerators. File:Di(benzothiazool-2-yl)disulfide.svg, Mercaptobenzothiazole disulfide (MBTS) File:N,N-dicyclohexyl-2-benzothiazolesulfenamide.svg, Dicyclohexyl-2-benzothiazolesulfenamide (DCBS) File:Sodium mercaptobenzothiazole.svg, Sodium mercaptobenzothiazole

Uses

Using 2-mercaptobenzothiazole, rubber vulcanizes with less sulfur and at milder temperatures, both factors give a stronger product. This effect was reported by workers at Pirelli and at Goodyear Tire & Rubber. Lorin B. Sebrell won the 1942

Charles Goodyear Medal The Charles Goodyear Medal is the highest honor conferred by the American Chemical Society#Organization, American Chemical Society, Rubber Division. Established in 1941, the award is named after Charles Goodyear, the discoverer of vulcanization, ...

for his work on mercaptobenzothiazole. In polymerization, it finds use as a radical polymerization inhibitor, chain transfer agent, reforming agent, and additive for

photoinitiator In chemistry, a photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (Ultraviolet, UV or Visible spectrum, visible). Synthetic photoinitiators are key components in photopolymers ...

s. The compound has also been used in the past in the gold-mining industry for the froth flotation of gold from ore residue as part of the extraction process. Sodium salt is used as a biocide and preservative in adhesives (especially based on latex, starch, casein, and animal glues), paper, textiles. Often found together with sodium dimethyldithiocarbamate as e.g. Vancide 51. Zinc salt is used as a secondary accelerator in latex foam vulcanization. It can be added to oil-based

hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backho ...

s, heat-transfer fluids (

oils An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturat ...

antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allow ...

s),

cutting fluid Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists ...

s and other mixtures as a

corrosion inhibitor A corrosion inhibitor or anti-corrosive is a chemical compound added to a liquid or gas to decrease the corrosion rate of a metal that comes into contact with the fluid. The effectiveness of a corrosion inhibitor depends on fluid composition and ...

, effective for

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

and

copper alloys Copper alloys are metal Alloy, alloys that have copper as their principal component. They have high resistance against corrosion. Of the large number of different types, the best known traditional types are bronze, where tin is a significant addi ...

. It is also used in veterinary dermatology. In

electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...

it is used as a brightener for

copper sulfate Copper sulfate may refer to: * Copper(II) sulfate, CuSO4, a common, greenish blue compound used as a fungicide and herbicide * Copper(I) sulfate, Cu2SO4, an unstable white solid which is uncommonly used {{chemistry index Copper compounds ...

baths, at about 50-100 milligrams/liter. Also can be added to silver cyanide baths.

Safety

Mercaptobenzothiazole has a low toxicity in mice, with

LD50 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a given substance. The value of LD50 for a substance is the dose requ ...

of >960 mg/kg. In 2016, it was identified by the

World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...

as probably carcinogenic to humans. It causes

allergic contact dermatitis Allergic contact dermatitis (ACD) is a form of contact dermatitis that is the manifestation of an allergic response caused by contact with a substance; the other type being irritant contact dermatitis (ICD). Although less common than ICD, ACD ...

. The derivative morpholinylmercaptobenzothiazole is a reported allergen in protective gloves, including latex,

nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called " propionitrile" (or pr ...

, and

neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rub ...

gloves. It becomes air-borne as a result of wear on car tires, and is able to be

inhaled Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

. Evidence suggests that benzothiazoles

biodegrade Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...

readily.

History

Benzothiazoles were long ago found to strongly influence the course of the vulcanization of rubber.

References

{{Authority control Benzothiazoles Rubber Dithiocarbamates Veterinary drugs IARC Group 2A carcinogens