Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the chemical compound with the formula C₆H₄(CHO)₂. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is a building block in the synthesis of

heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

s and a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

in the analysis of amino acids. OPA dissolves in water solution at pH < 11.5. Its solutions degrade upon UV illumination and exposure to air.

Synthesis and reactions

The compound 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

tetrabromo-o-xylene α,α,α',α'-Tetrabromo-o-xylene is an organobromine compound with the formula C6H4(CHBr2)2. Three isomers of α,α,α',α'-Tetrabromoxylene exist, but the ortho derivative is most widely studied. It is an off-white solid. The compound is prep ...

using potassium oxalate, followed by purification by

steam distillation Steam distillation is a separation process that consists in distilling water together with other volatile and non-volatile components. The steam from the boiling water carries the vapor of the volatiles to a condenser; both are cooled and ret ...

. The reactivity of OPA is complicated by the fact that in water it forms both a mono- and dihydrate, C₆H₄(CHO)(CH(OH)₂) and C₆H₄(CH(OH))₂O, respectively. Its reactions with nucleophiles often involves the reaction of both carbonyl groups. Orthophthalaldehyde and hydrated forms 001

Orthophthalaldehyde and hydrated forms 001

Biochemistry

OPA is used in a very sensitive fluorescent reagent for assaying amines or

sulfhydryl 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 ...

s in solution, notably contained in proteins, peptides, and amino acids, by capillary electrophoresis and chromatography. 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 (fluorescent

emission Emission may refer to: Chemical products * Emission of air pollutants, notably: **Flue gas, gas exiting to the atmosphere via a flue ** Exhaust gas, flue gas generated by fuel combustion ** Emission of greenhouse gases, which absorb and emit radi ...

at 436-475 nm (max 455 nm) with excitation at 330-390 nm (max. 340 nm)).

Disinfection

OPA is commonly used as a

high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer scienc ...

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...

for medical instruments, commonly sold under the brand names of Cidex OPA or TD-8. 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)

OPA 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.

In winemaking

The Nitrogen by O-Phthaldialdehyde Assay (NOPA) is one of the methods used in winemaking to measure yeast assimilable nitrogen (or YAN) needed by wine yeast in order to successfully complete

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

.B. Zoecklein, K. Fugelsang, B. Gump, F. Nury ''Wine Analysis and Production'' pgs 152-163, 340-343, 444-445, 467 Kluwer Academic Publishers, New York (1999) {{ISBN, 0834217015

Isomeric phthalaldehydes

* isophthalaldehyde (benzene-1,3-dicarbaldehyde) *

terephthalaldehyde Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the chemical compound with the formula C6H4(CHO)2. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is ...

(benzene-1,4-dicarbaldehyde)

References

Benzaldehydes