Purpald

The use of an acidic solution of p-anisaldehyde in ethanol to detect aldehyde functionalities on polystyrene polymer supports has been reported (beads are treated with a freshly made solution of p-anisaldehyde (2.55 mL), ethanol (88 mL), sulfuric acid (9 mL), acetic acid (1 mL) and heated at 110°C for 4 min). The colour of the beads depends on the percentage of CHO content such that at 0% of CHO groups, the beads are colourless, -50% CHO content, the beads appear red and at 98% CHO the beads appear burgundy [Vdzquez and Albericio Tetrahedron Lett 42 6691 200]]. A different approach utilises 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald) as the visualizing agent for CHO groups. Resins containing aldehyde functionalities turn dark brown to purple after a 5 min reaction followed by a 10 minute air oxidation [Coumoyer et al. J Comb Chem 4 120 2002]. 

Aldehydes 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald reagent) Aldehydes yield violet chromatogram zones on a whitish-yellow background. Some alcohols form yellow to orange-colored chromatogram zones. [2]... 

Qualitative spot tests for aldehydes, in the presence of ketones, are generally only reliable for water-soluble compounds. This problem can be overcome by the use of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald , Aldrich Chemical Company) in the presence of Aliquat (Scheme 5.27). Under aerial oxidation, the initially formed colourless cyclic adduct changes colour through red to purple. The colourless cyclic aminal can also be formed by ketones, but only the adducts derived from the aldehydes are oxidized to the purple bicyclic aromatic system [28]. Weakly electrophilic aldehydes, e.g., 4-methoxybenzaldehyde, reacts slowly, but will give the positive coloration upon gentle heating to ca. 70°C for one or two minutes. 

The aldehydic material under test (ca. 0.1 ml) is added to Purpald (50 mg) and Aliquat (0.11 g, 0.25 mmol) in PhMe (5 ml). Aqueous NaOH (10%, 1 ml) is added and the mixture is shaken well. The initial yellow coloration of the organic phase rapidly changes to a deep rust colour to confirm the presence of the aldehyde, but remains yellow for ketones. 

Experimental Procedure. The resin is washed with MeOH and a small portion (ca. 5 mg) is transferred to a disposable syringe (1 ml) fitted with a polypropylene filter disc. To the resin is added of DMF (1 ml) and the syringe is capped and shaken for 5 min. The DMF is then drained and a freshly prepared solution of Purpald dissolved in 1 M NaOH (250 pi) is added. The syringe is capped and shaken for 5 min. The solution is drained and the resin is washed with DCM (3x1 ml). The resin is then left uncapped for 10 min. The presence of free aldehydes is indicated by brown or purple beads. At lower values of resin loading, a longer air oxidation time may be required for color to develop (up to 20 min). 

Notes. Due to the instability of Purpald in solution, it is imperative that only freshly prepared reagent solution be used. 

Functional group Kaiser TNBS NF-31 Chloranil first amine Chloranil second amine TosCl- PNBP TCT Methyl red Ellman MG Vazquez Purpald... 

M. S. Quesenberry and Y. C. Lee, A rapid formaldehyde assay using purpald reagent Application under periodation conditions, Anal. Biochem., 234 (1996) 50-55. 

Figure 1.8. Chemistry of the purpald assay for bacterial polysaccharides (PS). The substituent groups R and R" must be released during treatment with NaOH and H2S04, before the periodate reaction.

One month after pressing, the boards were cut and triplicate samples for each duplicate board tested according to the dessicator method, using Purpald solution and a colorimeter, for formaldehyde emission over a period of 24 hours and 30 minutes Purpald development. After this initial assessment the samples were placed in a laboratory fan-exhaust oven at a temperature of 50 C to accelerate the test for a period of two months. The samples were tested at regular intervals of three weeks over the two months period. The formaldehyde emission results obtained are shown in Table I. 

Amino-3-hydrazino-5-mercapto-l,2,4-triazine (Purpald ) 402 is a well-established reagent for qualitative and quantitative detection of aldehydes. In the presence of an aldehyde or ketone, Purpald is transformed into a fused tetrahydrotetrazine intermediate 403. However, only with aldehydes, further oxidation of 403 takes place to give a deeply purple colored [l,2,4]triazolo[4,3-. ][l,2,4,5]tetrazine-3-thiol 404 (Scheme 95) <2000ALD28>. 

Five combinations of reagents are utilized. The copolymer and the mediator are added to 2mL of the laccase/buffer solution (Img/mL) placed in SmL vials and the resulting mixture was vigorously stirred for S min. The veratryl alcohol is added and vials 2 through 4 are stirred at 10°C for 24 h. Vial 1 is allowed to stir at 2S°C for 24 h. Purpald (Aldrich) in 1 N NaOH is used as an indicator to assess the concentration of veratryl aldehyde produced during the reaction (IT). 

Jendral JA, Monakhova YB, Lachenmeier DW. Formaldehyde in Alcoholic Beverages Large Chemical Survey Using Purpald Screening Followed by Chromotropic Acid Spectrophotometry with Multivariate Curve Resolution. Int J Anal Chem 2011 2011 1-11 Article ID 797604. 

Detection Methods. - The use of purpald (4-amino-3-hydrazino-5-nicrcsq)to-l,2,4-triazole) as a reagent for post-column derivatization of neutral nwnosaccharides has been repented. ... 

Amino-5-thioxo-l,2,4-triazolidin-3-one 3-hydrazone, 9CI. 4-Amino-5-hydrazino-4H-1,2,4-triazole-3-thiol, SCI. 4-Amino-3-hydrazino-1,2,4-triazoline-5-thione. Purpald [1750-12-5]... 

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