Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one ele ...

with the formula C₆H₄(CHO)₂. It is one of three isomers of benzene dicarbaldehyde, related to

phthalic acid Phthalic acid is an aromatic dicarboxylic acid, with formula C6H4(CO2H)2. Although phthalic acid is of modest commercial importance, the closely related derivative phthalic anhydride is a commodity chemical produced on a large scale. Phthalic ac ...

. This pale yellow solid is a building block in the synthesis of heterocyclic compounds and a reagent in the analysis of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s. 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 Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...

, 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 re ...

. 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

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

s 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 Capillary electrophoresis (CE) is a family of electrokinetic separation methods performed in submillimeter diameter capillaries and in micro- and nanofluidic channels. Very often, CE refers to capillary zone electrophoresis (CZE), but other elect ...

and

chromatography In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system ( ...

. 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 A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...

(fluorescent emission 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

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 s ...

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 A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry. ...

In winemaking

The Nitrogen by O-Phthaldialdehyde Assay (NOPA) is one of the methods used in

winemaking Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and ...

to measure

yeast assimilable nitrogen Yeast assimilable nitrogen or YAN is the combination of free amino nitrogen (FAN), ammonia (NH3) and ammonium (NH4+) that is available for a yeast, e.g. the wine yeast ''Saccharomyces cerevisiae'', to use during fermentation. Outside of the fe ...

(or YAN) needed by

wine yeast The role of yeast in winemaking is the most important element that distinguishes wine from fruit juice. In the absence of oxygen, yeast converts the sugars of the fruit into alcohol and carbon dioxide through the process of fermentation.Jeff Cox ...

in order to successfully complete fermentation.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 (benzene-1,4-dicarbaldehyde)

References

Benzaldehydes