o-Phthalaldehyde or ortho-phthalaldehyde is the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula C₆H₄(CHO)₂. Often abbreviated OPA, the molecule is a dialdehyde

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....

, consisting of two formyl (CHO) groups attached to adjacent carbon centres on a benzene

Benzene

Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

 ring. This pale yellow solid is a building block in the synthesis of 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 and a reagent

Reagent

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

 in the analysis of amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s.

Synthesis

The molecule was first described in 1887 when it was prepared from α,α,α',α’-tetrachloro-ortho-xylene. A more modern synthesis is similar: the hydrolysis of the related tetrabromoxylene using potassium oxalate

Oxalate

Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...

, followed by purification by steam distillation

Steam distillation

Steam distillation is a special type of distillation for temperature sensitive materials like natural aromatic compounds....

. The reactivity of OPA is complicated by the fact that with water it forms both a mono- and dihydrate, C₆H₄(CHO)(CH₂OH) and C₆H₄(CH₂OH)₂, respectively.

Isomeric phthalaldehydes

Related to o-phthalaldehyde are the meta and para 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...

s, which are respectively named isophthalaldehyde (m.p. 87-88 °C, CAS# 626-19-7) and terephthalaldehyde (m.p. 114-116 °C, CAS# 623-27-8).

Biochemistry

Ortho-phthalaldehyde (OPA) is well soluble, and stable in water solution at pH<11.5. It is however sensitive to UV illumination and air oxidation.

OPA is used as a very sensitive fluorescent reagent for assaying amine

Amine

Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s or sulfhydryls in solution, notably contained in proteins, peptides, and aminoacids, by capillary electrophoresis

Capillary electrophoresis

Capillary electrophoresis , also known as capillary zone electrophoresis , can be used to separate ionic species by their charge and frictional forces and hydrodynamic radius. In traditional electrophoresis, electrically charged analytes move in a conductive liquid medium under the influence of an...

 and chromatography

Chromatography

Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....

. OPA reacts specifically with primary amines above their isoelectric point Pi in presence of thiols. OPA reacts also with thiols in presence of an amine such as n-propylamine or 2-aminoethanol. The method is spectrometric (optical absorbance at 436-475nm (max 455nm) with excitation at 330-390nm (max.340nm))
.

Disinfection

Ortho-phthalaldehyde is commonly used as a high-level disinfectant for medical instruments. Disinfection with OPA is indicated for semi-critical instruments that come into contact with mucous membranes or broken skin, such as specula, laryngeal mirrors, and internal ultrasound probes.

Poly(phthalaldehyde)

Phthalaldehyde can be polymerized. In the polymer, one of the oxygen atoms forms a bridge to the other non-ring carbon of the same phthalaldehyde unit, while the other bridges to a non-ring carbon of another phthalaldehyde unit. Poly(phthalaldehyde) is used in making a photoresist

Photoresist

A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....

.http://www.journalarchive.jst.go.jp/jnlpdf.php?cdjournal=photopolymer1988&cdvol=6&noissue=4&startpage=491&lang=en&from=jnlabstract