Ninhydrin, alkylation with

The use of triflic acid in the alkylation with other dicarbonyl compounds, such as isatins,258 parabanic acid,259 and ninhydrin,260 has also been explored. A significant acidity dependence was found in the reaction of isatin with benzene.258 Alkylation does not take place in the presence of trifluoroacetic acid (Ho = —2.7) at 25°C in 12 h. Adding 22% of triflic acid (//0 10.6) brings about a 90% yield of the 3,3-... 

The ninhydrin treatment caused a 25 % increase in work needed to extend by 30 % (Cockburn et al., 1953, Cockburn and Speakman, 1956a,b), and Feughelman and Watt (1964) conclude that ninhydrin-treated fibers behave in water like untreated fibers at 90 % R.H. Likewise, fibers containing adsorbed dye are stiffened (Speakman and Elliott, 1946) and alkylation of reduced fibers with benzyl chloride gives stiffer fibers (in water) than alkylation with methyl iodide (Harris et al., 1942). 

In the case of amino acid analysis, the quantification of cysteine can be difficult because it is oxidized to cystine during acid hydrolysis. To circumvent this problem, cysteine can be oxidized to cysteic acid with performic acid prior to analysis. Alternatively, cysteine can be converted to the pyridyl ethyl derivative and subsequently detected by postcolumn reaction with ninhydrin. Still another method involves the production of carboxymethyl cysteine following alkylation with iodoacetic acid. All of these cysteine derivatives can be separated by either reversed-phase precolumn or ion-exchange postcoT umn methods. 

Table 38.2. Ninhydrin assays for surface amines on APS-SBA-15 materials, all materials were alkylated after polymer removal determined from elemental analysis frefluxed in 10% HCl in ethanol for 24 hours stirred with 25 wt%...

Normally the reaction Is useful for the conversion of alkyl halides to primary amines without concomitant formation of secondary amines.29 Treatment of polymer 17 with hexamethylenetetramine in a mixture of ethanol/THF afforded an insoluble resin. Using diazabicyclooctane (DABCO), we demonstrated that the reaction could be limited to attack by a single nitrogen in a multifunctional amine, so we did not anticipate crosslinking via bis-quat salt formation. Hydrolysis of 2 with anhydrous HC1 in ethanol generated free amino groups as evidenced by a positive ninhydrin test, but quantitative hydrolysis could not be achieved and the product remained insoluble. One would have expected a simple bis-quat to hydrolyse and open the crosslinked structure. 

Fmoc-Rink-Nle-pMeBHA-resin (1 g, 0.55 mmol g ) was swollen for 1.5 h in NMP in a reaction vessel equipped with a sintered glass bottom, and placed on a shaker. The Fmoc group was removed with 20% piperidine in NMP (8mL, 2 x 15 min) and after washing with NMP (8mL, 5 x 2 min), the Fmoc removal was monitored by the ninhydrin Kaiser test. Coupling of building blocks such as iV -Fmoc-/Va>-carb-oxyalkyl(OAl)Xaa-OH or /V -Fmoc-/V" -aminoalkyl(Aloc)Xaa-OH, or N -alkylated amino acids such as... 

The procedure was applied to additional dipeptides, and the course of the alkylation at 35-40°C followed by argentometric titration (Toennies and Kolb, 1945a). With over 90% formation of carbamylmethylsulfonium salts only 8% of peptide cleavage occurred at 40°C however, on brief heating at 95°C the yields of liberated amino acid increased to 54-85 % (Table XVI). Paper chromatography and paper electrophoresis of such reaction mixtures showed that in each case the hberated amino acid was the only ninhydrin-positive substance present. 

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