o-Phenylenediamine is a organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 with the formula C₆H₄(NH₂)₂. This aromatic diamine

Diamine

A diamine is a type of polyamine with exactly two amino groups. Diamines are mainly used as monomers to prepare polyamides, polyimides and polyureas. In terms of quantities produced, 1,6-diaminohexane, a precursor to Nylon 6-6, is most important, followed by ethylenediamine...

 is an important precursor to many heterocyclic compound

Heterocyclic compound

A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....

s. It is isomer

Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

ic with m-phenylenediamine

M-Phenylenediamine

m-Phenylenediamine, also called 1,3-diaminobenzene, is an organic compound with the formula C6H42. It is an isomer of o-phenylenediamine and p-phenylenediamine. It is a colourless solid.-Production:...

 and p-phenylenediamine

P-Phenylenediamine

p-Phenylenediamine is an organic compound with the formula C6H42. This derivative of aniline is a colorless solid, but typically samples can contain yellowish impurities arising from oxidation. It is mainly used as a component of engineering polymers and composites. It is also an ingredient in...

.

Preparation

Most commonly 2-nitrochlorobenzene is treated with ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, and the resulting 2-aminonitrobenzene is then hydrogenated:

ClC₆H₄NO₂ + 2 NH₃ → H₂NC₆H₄NO₂ + NH₄Cl

H₂NC₆H₄NO₂ + 3 H₂ → H₂NC₆H₄NH₂ + 2 H₂O

In the laboratory, the reduction of the nitroaniline

Nitroaniline

The term nitroaniline in chemistry refers to a derivative of aniline containing a nitro group There are three simple nitroanilines of formula C6H4 which differ only in the position of the nitro group:* 2-Nitroaniline* 3-Nitroaniline...

 is effected with zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 powder in ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

, followed by purification of the diamine

Diamine

A diamine is a type of polyamine with exactly two amino groups. Diamines are mainly used as monomers to prepare polyamides, polyimides and polyureas. In terms of quantities produced, 1,6-diaminohexane, a precursor to Nylon 6-6, is most important, followed by ethylenediamine...

 as the hydrochloride. This compound darkens in air; impurities may be removed by treating a hot aqueous solution with sodium dithionite

Sodium dithionite

Sodium dithionite is a white crystalline powder with a weak sulfurous odor. It is a sodium salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water and in acid solutions...

 (reducing agent) and activated carbon

Activated carbon

Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...

, and allowing the product to cool crystallize.

Reactions and uses

o-Phenylenediamine condenses with ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s and aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

s to give rise to a variety of useful products. Reactions with carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s and their derivatives afford benzimidazole

Benzimidazole

Benzimidazole is a heterocyclic aromatic organic compound. This bicyclic compound consists of the fusion of benzene and imidazole. The most prominent benzimidazole compound in nature is N-ribosyl-dimethylbenzimidazole, which serves as an axial ligand for cobalt in vitamin B12. Benzimidazole, in...

s. The herbicide benomyl

Benomyl

Benomyl is a fungicide which was introduced in 1968 by DuPont. It is a systemic benzimidazole fungicide that is selectively toxic to microorganisms and to invertebrates, especially earthworms. Benomyl binds to microtubules, interfering with cell functions such as meiosis and intracellular...

 is prepared in this manner. Also, quinoxaline

Quinoxaline

A quinoxaline, also called a benzopyrazine, in organic chemistry, is a heterocyclic compound containing a ring complex made up of a benzene ring and a pyrazine ring...

dione may be prepared by condensation of o-phenylenediamine with dimethyl oxalate. Condensation with xanthate esters affords mercaptoimidazoles, which are used as antioxidants in rubber products. Treatment with nitrous acid

Nitrous acid

Nitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...

 give benzotriazole, a corrosion inhibitor. Condensation of subtituted o-phenylenediamine with various diketone

Diketone

A diketone is a molecule containing two ketone groups. The simpliest diketone is diacetyl, also known as 2,3-butanedione. Diacetyl, acetylacetone, and hexane-2,5-dione are examples of 1,2-, 1,3-, and 1,4-diketones, respectively...

s is used in the preparation of a variety of pharmaceuticals.

In coordination chemistry, phenylenediamine is an important ligand precursor. Schiff base

Schiff base

A Schiff base, named after Hugo Schiff, is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, not hydrogen....

 derivatives, such as those derived from salicylaldehyde

Salicylaldehyde

Salicylaldehyde is the chemical compound with the formula C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almond odor at higher concentration and a characteristic buckwheat...

, are excellent chelating ligands. Oxidation of its metal-phenylenediamine complexes affords the diimine

Imine

An imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...

 derivatives, which are intensely colored and often exist in multiple stable oxidation states.

Safety

With an of 44 mg/L (aquatic), o-phenylenediamine is about 1000 times less toxic than the para-isomer. Anilines are typically handled as if they are carcinogenic. For many applications, OPD has been replaced by safer alternatives such as 3,3',5,5'-tetramethylbenzidine.