Derivatization with methyl iodide

Bovine NHs/hydroxylamine kidney treatment, EtOAc extn, liq-liq partn, SPE cleanup, derivatization with methyl iodide, liq-liq partns... 

Figure 9 shows a commercial drug mixture in human urine underivatized and derivatized with methyl iodide. In Figure 9a the propoxyphene and methamphetamine are not observed from the urine. However, upon derivatization, molecular ions from both can be seen and the ion intensity from methadone and quinine have been increased by a factor of ten. 

A method for the dcicnnination of DAPs in water has been described (Chang etal., 20(X)). This method uses a strong anion exchange disk to isolate DAPs from water and DAPs arc derivatized with methyl iodide in acetonitrile. Capillary GC with FPD was used for determination. A residue analytical method for the determination of DEP... 

For the preparation of derivatives on a micro scale (at the microgram and picogram levels) reaction with methyl iodide was recommended [510] 100—200 /il of an acetone solution of barbituric acids was mixed with a 3- to 1000-fold molar excess of methyl iodide and refluxed with 3—5 mg of potassium carbonate. After about 30 min, 0.2 /A of the supernatant was injected directly into a column with 3% of OV-225, with temperature programming at 8°C/min from 100 to 240°C. The advantage of the method is that no toxic and hazardous chemicals are used. The method was further modified for the micro-determination of barbiturates in blood [511]. Only 20-25 /d of blood were necessary for the determination, and with the use of a detector sensitive to nitrogen down to 1 ng of barbiturate could be determined in this sample. The derivatization reaction was performed in a micro-refluxer (see Fig. 2.6). 

GC separation of the isolated phenolic compounds occurs prior to identification and quantification using ECD- and MS-coupled detectors (Sect. 4.3). However, phenolic compounds are polar, and derivatization gives better GC peak shapes in the most commonly used types of GC columns. Hitherto the standard method of derivatization of OH-PCBs retained in blood has been methylation by diazomethane to form the corresponding methoxy-PCB (MeO-PCB) [39,43, 135]. OH-PCB methylation by ion-pair alkylation with methyl iodide is an alternative to the diazomethane technique [43,140]. Acetylation has been shown to give comparable recoveries of OH-PCB derivatization as the methyl iodide and diazomethane approaches to OH-PCB methylation [139]. Silylation reactions have also been applied for the derivatization of various OH-PCBs [137]. 

Permethylation of hydroxyl groups is used widely in the analysis of sugar derivatives and usually involves reaction with a strong base, such as sodium hydride, followed by treatment with methyl iodide. Alternative bases can be used and the efficiency of the derivatization varies from compound to compound. Permethylated derivatives are stable and can be purified without breakdown. However, except for experienced investigators, analysis of permethylated plant hormones has received relatively little attention, primarily beeause derivatization is time consuming and complex. Nonetheless, once effective derivatization is achieved, permethylated GA glycosyl ether can be analysed by GC-MS [74] while cytokinins are best analysed as their permethyl derivatives [6]. 

Benzyloxygermanium compounds also undergo the 0- C anionic rearrangement (34), and in this case rearranged products are obtained exclusively even with methyl iodide as derivatizing agent (Table III). Apparently the equilibrium in Eq. (23) lies even farther to the right... 

Today, silanes are available or can be synthesized for a one-step surface thesis of all the different types of ion-exchangets. However, the preparation of some of the older types is likely to involve multiple surface reactions. The details of the preparation of many commercial products is not public knowledge, so it is difB t to know which products are made by which procedure. When multiple reactions are carried out on the surface, a more heterogeneous product is obtained. For example, if the silica is first derivatized with propylamino silane, and the product is subsequently quatemized with methyl iodide, an appreciable amount of tertiary amino groups will remain on the surface. Such an ion exchanger has properties different from those of an ion exchanger that contains purely quaternary amino groups. 

Silica-based strong anion exchangers can also be obtained directly by derivatization of the silica with the appropriate silane. However, the more common approach is to derivatize the silica first with an amino silane, which is then quatemized by reaction with methyl iodide. 

The uracil heterocycles are readily prepared in high yields from the corresponding aryl isocyanates 44 and from ethyl trifluoromethylaminocrotonate (45) in the presence of a base [72]. The uracil heterocycle is then directly N-methylated with methyl iodide in a one-pot reaction (Scheme 3.1). The uracil ring is stable to treatment with strong acids such as HBr and weak bases such as potassium carbonate, both reagents used in the further derivatization of the intermediate 46 with the benzyl chloride 47 to produce benzfendizone (41). 

These transformations are satisfactory for derivatizing most primary and secondary amines, but tertiary amines do not undergo such reactions. However, such amines form salts that constitute solid derivatives. Thus a useful crystalline salt is formed upon reaction with methyl iodide to afford a methiodide (Eq. 25.59). 

Transfer the residue with 2 x 1 mL of DMSO into a 10-mL centrifuge vial. Add 20 iL of methyl iodide and 200 pL of 1M sodium hydroxide solution, mix and plug the vial with a stopper. Derivatization is done at 70 °C for 1 h. After addition of 45 mL of aqueous 10% sodium chloride, extract the reaction mixture with 10 or 2 x 10 mL of n-hexane. Transfer the n-hexane phase on to the chromatographic column prepared as described below. 

The O-methylated extract was derivatized with 99 percent C-enriched methyl iodide. The NMR spectrum of the extract showed a strong absorption at 56 ppm (relative to TMS), which can be attributed to unhindered aryl methyl ethers (67%), a smaller absorption at 60 ppm, attributable to hindered aryl methyl ethers (23%), and a resonance at 51 ppm, assignable to methyl esters derived from carboxylic acids (10%).(16) TTiese results are consistant with those of Liotta l al, who studied the alkylation of whole Illinois No. 6 coal.(12)... 

Other derivatization procedures involve alkylation and silylation [486]. The latter is carried out with the aid of BSTFA and provides simple products, whereas alkylation with a methyl iodide—sodium hydride—dimethyl sulphoxide mixture (50°C, 10 min) leads to two peaks due to various products. 

The first involves a known functional group derivatization to quantify specific types of carbons found in humic substances, the derivatization being carried out by chemical reactions with l C-labeled reactants.( d-27) For example, methylation with C-labeled diazomethane or methyl iodide has been used to distinguish between and quantify hydroxyl functionalities in humic acids. The second labeling methodology involves the use of C-labeled reactants to follow the course of a complex reaction or association such as the interaction of pollutants with humic acids.(6-9,22,2J) The first structural evidence for the type of interaction of pollutants with humic substances was provided using and site specific labeling in combination with and NMR, respectively. 

To the dried mixture of acids (up to 20 mg) are added 2 ml of dried acetone, 2 ml of methyl iodide and 30-50 mg of anhydrous K2CO3. After refluxing at 60-70 °C under a calcium chloride drying tube for 20-30 minutes, the solution is made up to 5 ml with acetone and analysed by GC [80]. Serum free fatty acids have been derivatized for analysis by very similar versions of this procedure [81, 82]. 

Polymers from 16C and 18C, and presumably 17C, may be hydrogenated to form the corresponding poljrvinylpiperidines (6), or oxidized to the corresponding water-soluble N-oxide. The polyvinylpyridines may also be readily derivatized via quaternization with an appropriate alkylating agent, such as methyl iodide. The monomeric quats are readily water-soluble but can be prone to spontaneous polymerization above critical concentrations (216). The nature of the counterion can also affect the propensity of the quaternized monomers to autopolymerize. 

The majority of anal)4ical procedures employ silylation as the derivatization reaction. Many reagents and combinations have been described. Depending on the catalyst present in a silylation mixture, keto functional groups can be converted into enol-trimethylsilyl (TMS) derivatives. Iodine ions (I ) in the well known N-methyl-N trimethylsilyltrifluoroacetamide (MSTFA) with ammonium iodide and dithioerythritol (1000 2 4 v/w/w) mixture are often used for this purpose [10, 18,19]. 

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