Methoxime derivatives

Hint To distinguish these compounds without elemental composition or standards for GC retention time, split the GC effluent to a FID, a nitrogen-phosphorus detector, and the mass spectrometer, simultaneously. Using this splitter system, it is easy to determine if the GC peak contains nitrogen. Also, the analyst can differentiate between azobenzene and benzophenone by using the methoxime derivative. 

For low molecular weight aliphatic acids, try TMSDEA reagent. Otherwise, use MSTFA, BSTFA, or TRI-SIL BSA (Formula P). For analysis of the keto acids, methoxime derivatives should be prepared first, followed by the preparation of the trimethylsilane (TMS) derivatives using BSTFA reagent. This results in the meth-oxime-TMS derivatives. 

This derivative is useful for determining the presence and number of keto groups as well as for protecting the ketone from enolization. Some diketones that polymerize readily, such as 2,3-butanedione. should be freshly distilled and the methoxime derivatives should be prepared. 

Preparation of methoxime derivatives Add 0.5 ml of MOX reagent to the sample. Heat at 60° for 3 hours. Evaporate the reaction mixture to dryness with clean, dry nitrogen. Dissolve in the minimum amount of ethyl acetate. Some solids will not dissolve. 

Molecular ion The MW of aliphatic ketones can be determined from its prominent molecular ion. In general, the intensity of the molecular ions of ketones is greater for C3-C8 than for CVC u. A molecular ion is usually observed for methoxime derivatives. 

In the mass spectrum of 2-hexanone (Figure 20.1), the molecular ion is apparent at m/z 100, which can be confirmed by preparing the methoxime derivative. The compound type is verified by the presence of m/z 43 and 58. 

The Oxamyl in this extract is then determined by gas chromatography using on-column reaction with trimethylphenyl ammonium hydroxide, the derivative so formed being determined by a flame photometric detector operated in the sulphur mode. Both Oxamyl and Oxamyl oxime in the soil react with trimethylphenyl ammonium hydroxide to form the same methoxime derivative (CH3)2NCOC(SCH3) -NOCH3. 

Mason and Slover187 studied the separation of monosaccharides as the O-trimethylsilyl derivatives of the oximes, as an alternative method to analyzing for sugars in foods, and Clayton and H.G. Jones188 used trimethylsilylated D-glucose oxime. Both groups of workers referred to the instability of these derivatives, as noted in Section III (see p. 23). Laine and Sweeley189 proposed a similar method that used the methoxime derivatives. 

Naturally occurring antibiotics of the aglycone type were subjected to analysis by combined GC-MS as their pertrimethylsilyl methoxime derivatives [528]. Persilylation is performed by treatment for several minutes with BSTFA—TMCS—TMSIM (3 3 2) at room temperature. Preliminary methoximation is carried out by reaction with methoxylammonium chloride in pyridine at 75°C for 45 min. Some of the aglycones are methoximated incompletely, however, and provide two peaks for both derivatives. 

Gas Chromatography-Mass Spectrometry. Prepare methoxime derivatives by heating the extract from the thin-layer chromatographic plate with 100 xl of an 8% solution of methoxyamine hydrochloride in dry pyridine at 60° for 30 minutes, and evaporate in a rotary film evaporator. Silylate by dissolving the residue in 100 Lll of chloroform, adding 100 Lll of A,0-bis(trimethylsilyl)acetamide and 20 Lll of trimethylchlorosilane, then seal, and heat for 2 hours at 60°. When only 5a-estrane-3P,17a-diol is to be confirmed the methoxime formation can be omitted. Prepare a 2-cm column of Sephadex LH-20 in a Pasteur pipette with a cotton wool plug, using a... 

Measurement by stable isotope dilution was introduced for quantitative SIM using a deuterated methoxime derivative of prostaglandin Ei... 

In conclusion, oxime or methoxime derivatives showed significant lOP-lowering activ-... 

Homing, M.G., Moss, A.M. and Homing, E.C. (1968b), Formation and gas-liquid chromatographic behaviour of isomeric steroid ketone methoxime derivatives. Anal Biochem., 22,284. 

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