1,2-Naphthoquinone-4-sulfonic acid reagent

The reaction mechanism has not been elucidated. It is possible that formaldehyde reacts by oxidation as in the Marquis reaction (see formaldehyde — sulfuric acid reagent), whereby colored salts are formed with naphthoquinone sulfonic acid. 

Reagent 3 Spray solution 3 A saturated solution of 1,2-naphthoquinone-sulfonic acid sodium salt in ethanol — water (1+1). 

Naphthoquinone-4-sulfonic Acid- Perchloric Acid - Formaldehyde Reagent... 

Naphthoquinone-4-sulfonic Acid-Perchloric Acid-Formaldehyde Reagent 353... 

The second method is that described above /3-naphthol is converted through the nitroso derivative and i-amino-2-naph-thol-4-sulfonic acid into naphthoquinone sulfonate, and this is subjected to acid hydrolysis. The sulfonate can be converted directly into hydroxynaphthoquinone by the action of concentrated sulfuric acid,3,4 but the process is not so easily controlled as when the quinone is etherified as it is formed, and the ether subsequently hydrolyzed.4 The overall yield from /3-naphthol is 46 per cent of the theoretical amount, but all the reagents are inexpensive, and with ordinary apparatus, 150 g. of hydroxynaphthoquinone can be made conveniently in one run (from 300 g. of /3-naphthol). 

Salts of 1,2-naphthoquinone-4-sulfonate have been prepared by the oxidation of 2-amino-i-naphthol-4-sulfonic acid with nitric acid,2 or by the oxidation of the more readily available i-amino-2-naphthol-4-sulfonic acid with the same reagent.3,4 5... 

A number of other reagents have been used to give colored derivatives of amino acids, among these being Folin s reagent, 1,2-naphthoquinon-4-sulfonic acid and o-phthalaldehyde. However, the ninhydrin reaction is so easy to perform and sensitive that other reactions are of very limited importance. Derivatization of amino acids to give colored and/or fluorescent products subsequently subjected to chromatographic procedures can be mentioned in connection with the discussion of color reactions for amino acids. 

Other highly sensitive reagents are 2,4,6-trinitro-benzosulfonic acid, l,2-naphthoquinone-4-sulfonic acid (Folin s reagent), and 4,4 -tetramethyldiaminodi-phenylmethane (TDM). Intensely fluorescing amino acid derivatives are formed by reaction with o-phthal-aldehyde in the presence of reducing agents with pyr-idoxal and zinc ions and with dansyl chloride (5-di-methylaminonaphthalene sulfonyl chloride). 

Glutathione does not react with 1,2-naphthoquinone-4-sodium sulfonate (30, 49). Cysteine (30) and cysteinylglycine (50), however, react to form a red color which is not destroyed by sodium hyposulfite. Many compounds form a colored condensation product with naphthoquinone sulfonate. However, these are all decolorized by sodium hyposulfite (30). Glutathione may be determined indirectly following hydrolysis. Glutamyl-cysteine (51), homocysteine (52), and isocysteine (52) do not react with the reagent. Thioglycolic acid (49) produces one fifteenth of the color produced by cysteine. The method is not specific for the reduced form and the results indicate the total of reduced plus oxidized compoimds. Approximately 0.1 mg. is required for analysis (49). 

An analogous reaction occurs with 1,2-naphthoquinone-4-sulfonic acid Folin reagent) but, instead of a yellow color (cf. Formula 1.36), a red color develops ... 

Cabero et al. [80] developed a method based on the conversion of cyclamate to cyclo-hexylamine and the subsequent reaction with l,2-naphthoquinone-4-sulfonate, yielding a spectrophotometrically active derivative, which is detected at 480 nm thus, other sweeteners, such as saccharin or aspartame, do not interfere in these determinations. The hydrolysis step is performed batchwise by treatment of cyclamate with hydrogen peroxide and hydrochloric acid, while the cyclohexylamine derivatization is carried out in the flow injection system (Figure 24.9). Rocha et al. [81] reported a flow system based on multicommutation for fast and clean determination of cyclamate. The procedure exploits the reaction of cyclamate with nitrite in an acidic medium and the spectrophotometric determination of the excess of nitrite by iodometry. The flow system was designed with a set of solenoid micropumps to minimize reagent consumption and waste generation (Figure 24.10). 

Reagents saturated sodium l,2-naphthoquinone-4-sulfonate solution in 50% ethanol 0.5 N NaOH, 2 n acetic acid. 

Reagents 10% solution of monochloroacetic acid, 0.5% aqueous sodium 1,2-naphthoquinone-4-sulfonate, 2 n NaOH,... 

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