Identification, 2,105 ketones

Their semicarbazones and 2,4-dinitrophenylhydrazones, on the other hand, all differ in their melting points. By making these derivatives of the ketones, identification was made much easier, Of course, all ofthis has been totally superseded by NMRr However these crystalline derivatives are still useful in the purification of volatile... 

Wheeler, J. W., Evans, S. L., Blum, M. S. and Torgerson, R. L. (1975). Cyclo-pentyl ketones identification and function in Azteca ants. Science, 187, 254-5. 

NH2-C0-NH NH2,CH5N30. Colourless crystalline substance m.p. 96" C. Prepared by the electrolytic reduction of nitrourea in 20% sulphuric acid at 10 "C. Forms crystalline salts with acids. Reacts with aldehydes and ketones to give semicarbazones. Used for the isolation and identification of aldehydes and ketones. 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Dinitrophenylhydrazine is a very important reagent for the identification of aldehydes and ketones (pp. 342, 346). It is readily prepared from chloro-2,4-dinitrobenzene (I). In the latter compound the chlorine is very reactive in... 

When the compound for identification fails to respond to test 4 (aldehyde or ketone), the next class reactions to apply are the hydroxatnic acid teat and saponification, i.e., hydrolysis in alkaline solution. These are the class reactions for esters and anhydrides the rarely-encountered lactones react similarly. 

An enol is usually characterised by treatment with ketonic reagents or with phenylhydrazme (compare Section IV,114 and Table IV,114A), or by hydrolysis with acid, followed by the identification of the ketone. 

In general however, ozonolysis is of limited synthetic importance. For quite some time ozonolysis has been an important tool for structure elucidation in organic chemistry, but has lost its importance when spectroscopic methods were fully developed for that purpose. The identification of the aldehydes and/or ketones obtained by ozonolysis of unsaturated compounds allowed for conclusions about the structure of the starting material, but has practically lost its importance since then. 

Methyl-heptenone also forms a bromine derivative which is well suited for the identification of the ketone. This body, which has the formula CgHjjBrgO. OH, melts at 98° to 99°, and is obtained as follows Three grams of methyl-heptenone are mixed with a solution containing 3 grams of caustic soda, 12 grams of bromine, and 100 c c. of water. After a time an oily substance is deposited, which is extracted with ether. The solvent is evaporated, and the residue, redissolved in ether, is treated with animal charcoal and filtered. On slow evaporation the product is obtained in well-defined crystals. 

Bayer and Henrich have prepared a bisnitrosopulegone, which is very useful for the identification of the ketone. A solution of 2 c.c. of pulegone in 2 c.c. of petroleum ether is cooled in a freezing mixture and 1 c.c. of amyl nitrite and a trace of hydrochloric acid are added. Fine needles of the bisnitroso compound quickly separate, which, when dried on a porous plate and washed with petroleum ether, melt at 81 5°. 

To distinguish between azobenzene and benzophenone, assuming reference spectra are not available for these compounds, it is a good idea to examine the mass spectra of aromatic ketones, such as acetophenone, butyrophenone, diphenyldiketone, and so forth. Complete identification is assured by obtaining or synthesizing the suspected component and analyzing it on the GC/MS system under the same GC conditions. If the retention time and the mass spectrum agree, then the identification is confirmed. 

Many impurities are present in commercial caprolactam which pass into the liquid wastes from PCA manufacture from which caprolactam monomer may be recovered. Also, the products of die thermal degradation of PCA, dyes, lubricants, and other PCA fillers may be contained in the regenerated CL. Identification of die contaminants by IR spectroscopy has led to the detection of lower carboxylic acids, secondary amines, ketones, and esters. Aldehydes and hydroperoxides have been identified by polarography and thin-layer chromatography. 

The identification of a novel BVMO from Mycobacterium tuberculosis (BVMOMtbs) complements this toolbox, as this particular biocatalyst performs a classical kinetic resolution instead of a regiodivergent oxidation vith complete consumption of substrate [140]. Notably, this enzyme accepts only one ketone enantiomer and converts it selectively to the abnormal lactone while the antipodal substrate remains unchanged (Scheme 9.24) [141]. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

Hydrocarbons oxidize to give a complex mixture of products which include hydroperoxides, alcohols, ketones, acids, esters, etc. (1). Polyolefins similarly can be oxidized by heat, radiation or mechano-initiated processes. The precise identification and quantification of these oxidation products are essential for the complete understanding and control of these destructive reactions. Conventional methods for the identification of oxidation products include iodome-... 

Figure 10.16 Total ion current chromatogram obtained for sample 1484 after headspace SPME. Peak labels correspond to compound identification given in Table 10.6. Ax, acid with x carbon atoms. Kx, ketone with x carbon atoms...

For those aldehydes and ketones which are volatile enough, gas chromatography of the headspace gases can be used, and this has been used to measure acetone, butyraldehyde, and 2-butanone in oceanic waters. In a gas chromatography-mass spectrometry analysis of a single sample of volatile materials concentrated from inshore waters onto Tenax GC, MacKinnon [ 139] reported tentative identification of methyl isopropyl ketone, bromoform, 4-methyl-2-pentanone, 2-hexanone, and 2-hexanal. 

If a sample contains one or more members of a homologous series, identifications can be made using a plot of log tR against the number of carbon atoms, previously prepared from standards. The plot, which is valid for one temperature only, is linear and can be used for alkanes, alkenes, alcohols, aldehydes, ketones, esters and ethers. 

The infrared spectrum of erythromycin is commonly used for its identification. Figure 2 shows the spectrum of a 75 mg./ml. chloroform solution. The bands at 1685 and 1730 cm- are due to the ketone carbonyl and the lactone carbonyl, respectively. The absorption peaks between 1000 and 1200 cm-1 are due to the ethers and amine functions. The CH2 bending is evidenced by peaks between 1340 and 1460 cm-, and alkane stretching peaks appear between 2780 and 3020 cm-. Hydrogen bonded OH and water appear as bands between 3400 and 3700 cm-1. 

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