Mass spectrometry aldehydes and ketones

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

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. 

For more volatile compounds in soils, such as aromatic hydrocarbons, alcohols, aldehydes, ketones, chloroaliphatic hydrocarbons, haloaromatic hydrocarbons, acetonitrile, acrylonitrile and mixtures of organic compounds a combination of gas chromatography with purge and trap analysis is extremely useful. Pyrolysis gas chromatography has also found several applications, heteroaromatic hydrocarbons, polyaromatic hydrocarbons, polymers and haloaromatic compounds and this technique has been coupled with mass spectrometry, (aliphatic and aromatic hydrocarbons and mixtures of organic compounds). 

Peters R, Hellenbrand J, Mengerink Y, Wal Van der S. 2004. On-line determination of carboxylic acids, aldehydes and ketones by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionization mass spectrometry after derivatization with 2-nitrophenylhydrazine. J Chromatogr A 1031 35. 

Abbreviations Amberlite IRA 400 borohydride resin, commercially available resin for selective reduction of a,/3-unsaturated aldehydes and ketones DBU, 1,8-diazabicyclo [5.4.0]undec-7-en DCM, dichloromethane DMF, dimethylformamide EtOAc, ethyl acetate Et2NH, diethylamine Et3N, triethylamine HBr, hydrobromic acid HC1, hydrochloric acid MS, mass spectrometry MeOH, methyl alcohol NH4OH, ammonium hydroxide NaBHj, sodium borohydride NaOH, sodium hydroxide NaOMe, sodium methanolate PAMAM, polyaminoamide resin (commercially available) RT, room temperature THF, tetrahydrofuran. 

Olson KE, Swarin SJ. 1985. Determination of aldehydes and ketones by derivatization and liquid chromatography-mass spectrometry. J Chromatogr 333 337-347. 

Welti (9). The quality of the spectra is uniformly good as exemplified retention times are C02, H20, formaldehyde, acetaldehyde, methanol, propylene, isobutylene, acetone, hexene, and other unsaturated aldehydes and ketones. The actual chemical structures of these ketones and of several other products are being determined by mass spectrometry. 

D. W. Johnson, A modified Girard derivatizing reagent for universal profiling and trace analysis of aldehydes and ketones by electrospray ionization tandem mass spectrometry. Rapid. Commun. Mass. Spectrom., 21 (2007) 2926-2932. 

Blake, R.S., Patel, M., Monks, P.S., EUis, A.M., Inomata, S., Tanimoto, H. (2008) Aldehyde and ketone discrimination and quantification using two-stage proton transfer reaction mass spectrometry. International Journal of Mass Spectrometry, 278,15-19. 

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

Regarding ozonation processes, the treatment with ozone leads to halogen-free oxygenated compounds (except when bromide is present), mostly aldehydes, carboxylic acids, ketoacids, ketones, etc. [189]. The evolution of analytical techniques and their combined use have allowed some researchers to identify new ozone by-products. This is the case of the work of Richardson et al. [189,190] who combined mass spectrometry and infrared spectroscopy together with derivatization methods. These authors found numerous aldehydes, ketones, dicarbonyl compounds, carboxylic acids, aldo and keto acids, and nitriles from the ozonation of Mississippi River water with 2.7-3 mg L 1 of TOC and pH about 7.5. They also identified by-products from ozonated-chlorinated (with chlorine and chloramine) water. In these cases, they found haloalkanes, haloalkenes, halo aldehydes, haloketones, haloacids, brominated compounds due to the presence of bromide ion, etc. They observed a lower formation of halocompounds formed after ozone-chlorine or chloramine oxidations than after single chlorination or chlorami-nation, showing the beneficial effect of preozonation. 

A series of Vap GC analyses on approximately 50 mg of all the aged resin samples was conducted. Ethanal, propanal, isobutyraldehyde, propenal, butenal, methyl ethyl ketone (MEK), and methyl penetenal were positively identified by mass spectrometry. With the exception of MEK, all compounds identified (the major products) were aldehydes. Methyl ethyl ketone, the solvent used in MY720, remains even after cure. The aldehydes, however, are not impurities in either the MY720 or DOS and represent compounds which are characteristic of the resin alone. These compounds are either produced during the curing process or are formed from the thermal decompositon of a labile compound which is formed during cure. 

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