Hydrazones, aldehyde detection

Hydrates, enthalpies of formation, 156, 157 Hydrazones, aldehyde detection, 670 Hydrocarbons autoxidation, 320... 

Igawa et al. (1989) have reported analysis of formaldehyde and other aldehydes in cloud and fogwater samples by HPLC with a postcolumn reaction detector. The aldehydes were separated on a reversed-phase C18 column, derivatized with 3-methyl-2-benzothiazolinone hydrazone, and detected at 640 mn. 

Reagent A is particularly useful for the treatment of the lower aliphatic aldehydes and ketones which are soluble in water cf. acetaldehyde, p. 342 acetone, p. 346). The Recent is a very dilute solution of the dinitrophenylhydrazine, and therefore is used more to detect the presence of a carbonyl group in a compound than to isolate sufficient of the hydrazone for effective recrystallisation and melting-point determination. 

Figure 23.10 Glycoproteins may be oxidized with sodium periodate to generate aldehyde residues. These may be specifically labeled using a hydrazide-streptavidin derivative through hydrazone bond formation. Subsequent detection may be done using biotinylated enzymes.

Hydrazide groups can react with carbonyl groups to form stable hydrazone linkages. Derivatives of proteins formed from the reaction of their carboxylate side chains with adipic acid dihydrazide (Chapter 4, Section 8.1) and the water-soluble carbodiimide EDC (Chapter 3, Section 1.1) create activated proteins that can covalently bind to formyl residues. Hydrazide-modified enzymes prepared in this manner can bind specifically to aldehyde groups formed by mild periodate oxidation of carbohydrates (Chapter 1, Section 4.4). These reagents can be used in assay systems to detect or measure glycoproteins in cells, tissue sections, or blots (Gershoni et al., 1985). 

Eberhardt and Sieburth [133] also devised a spectrophotometric procedure for the determination of aldehydes in seawater. The method is based on the reaction of aldehydes with 3-methyl-2-benzothiazolinone, hydrazone hydrochloride, and ferric chloride to produce a coloured compound. A detection limit of0.072 jlM formaldehyde per litre was obtained using a 5 cm path-length. 

Carboxylates and other negatively charged functional groups can be detected by treatment with a positively charged dye, such as malachite green [71]. Polystyrene-bound aldehydes can be visualized by treatment with 4-methoxybenzaldehyde under acidic conditions [72]. Quantification of resin-bound carbonyl compounds has been achieved by conversion into dansyl hydrazones [73],... 

Diphenylacetyl-l,3-indandione-l-hydrazone, first prepared by Braun and Mosher [143], reacts readily with carbonyl compounds such as aldehydes and ketones in weakly acidic media. The derivatives are separated by paper or thin-layer chromatography [144]. The derivatives are excited at 400-415 nm and emit at ca. 525 nm. The limit of detection is 2 ng per spot. 

Fig. 5.13. HPLC separation of a reference mixture of 4-hydroxy-2-alkenal dinitrophen-yl hydrazones. The numbers indicate the chain length of the aldehyde thus 7 4-hydr-oxy-2-heptenal 8 4-hydroxy-2-octenal etc. Lichrosorb 5-RP-I8, (4.6 nm x 20 cm) methanol/water 80 20 (v/v) 1.0 ml/min detection 378 nm. (Benedetti et al., 1986.)...

When the ozonization of cinnamyl alcohol was carried out in methyl chloride at —70° C., followed by removal of the solvent at —10° and immediate reduction of the residue with sodium bisulfite and conversion of the aldehydes to their corresponding 2,4-dinitrophenyl-hydrazones, benzaldehyde and glycolic aldehyde were obtained in yields of 98 and 70%, respectively. No formaldehyde was detected. 

This reaction can be used for the recognition and detection of aldehydes and ketones. In order to prepare a hydrazone, formerly a solution of I part of phenyl hydrazine hydrochloride and ii parts of crystallised sodium acetate in 10 parts of water was used as a reagent. If this is added to an aldehyde or ketone, there is formed, in many cases at the ordinary temperature, but in others only on heating, the hydra-zone. Since, at present, perfectly pure free phenyl hydrazine may be purchased in the market, a mixture of equal volumes of phenyl hydrazine and 50 % acetic acid, diluted with three times its volume of water, is used as the reagent. 

Formaldehyde and other aldehydes are receiving increasing attention both as toxic substances and as promoters in the photochemical formation of ozone in the atmosphere. They are released into residential buildings from plywood and particle board, insulation, combustion appliances, tobacco smoke, and various consumer products. Aldehydes are released into the atmosphere in the exhaust of motor vehicles and other equipment in which hydrocarbon fuels are incompletely burned. A sensitive method for analyzing aldehydes and ketones is based on the sorption of these compounds to an SPE sorbent and their subsequent reaction with 2,4-dinitrophenylhydrazine (DNPH) on the sorbent. They are then analyzed as their hydrazones by HPLC (Fig. 7.9). A gradient analysis by HPLC may separate as many as 17 components with detection by ultraviolet (UV) light. 

Low concentrations of volatile aldehydes in air samples have been analyzed by collection on porous glass impregnated with 5-dime-thylaminonaphthalene-l-sulfohydrazide with which they react to form hydrazones that were analyzed online using HPLC with fluorescence detection (Nondek et al. 1992). 

Let us focus here on determining the various carbony compounds. Figure 4.46 shows a HPLC chromatogram for the separation and detection of the first six homologous series of aldehydes as their 2,4-dinitrophenylhydrazone derivatives accomplished in the author s laboratory. The reaction of aldehydes and ketones with 2,4-nitrophenylhydrazine under mildly acidic conditions in water to form stable hydrazones is a well-known reaction in organic chemistry. The homologous series with R representing Ci, C2, C3, C4, C5, and Cg react as follows ... 

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