Diazomethane stabilization

TMS production involves one specific functional group (-OH, -COOH, =NH, -NH2, or -SH), which loses an activated hydrogen and is replaced by a trimethylsilyl group (Proestos et ah, 2006). To achieve silylation, some authors have used BSTFA (N,0-hA(trimethyl-silyl)trifluoroacetamide) and TMCS (trimethylchlorosilane) successfully in several matrices (e.g. aromatic plants, cranberry fixiit) (Zuo et ah, 2002 Proestos et ah, 2006). Using silylated derivatives is advantageous for several reasons phenols and carboxylic acids are prone to silylation, these compounds can be derivatized in the same part of the process, and the minor products do not impede analysis and are well documented (Little, 1999 Stalikas, 2008). A two-step methylation procedure was used to analyze catechins and tannins in plant extracts. The first step used trimethylsilyl diazomethane (TMS-diazomethane) to pre-methylate the sample, and the second step used thermally assisted hydrolysis and methylation (THM). The pre-methylation step with TMS-diazomethane stabilized the dimer molecule m/z 540) by minimizing isomerization and reducing reactivity. (Shadkami et ah, 2009). 

In a first step, the carboxylic acid 1 is converted into the corresponding acyl chloride 2 by treatment with thionyl chloride or phosphorous trichloride. The acyl chloride is then treated with diazomethane to give the diazo ketone 3, which is stabilized by resonance, and hydrogen chloride ... 

Carbenes from Diazo Compounds. Decomposition of diazo compounds to form carbenes is a quite general reaction that is applicable to diazomethane and other diazoalkanes, diazoalkenes, and diazo compounds with aryl and acyl substituents. The main restrictions on this method are the limitations on synthesis and limited stability of the diazo compounds. The smaller diazoalkanes are toxic and potentially explosive, and they are usually prepared immediately before use. The most general synthetic routes involve base-catalyzed decomposition of V-nitroso derivatives of amides, ureas, or sulfonamides, as illustrated by several reactions used for the preparation of diazomethane. 

The way biotin participates in carbon dioxide fixation was established in the early 1960s. In 1961 Kaziro and Ochoa using propionyl CoA carboxylase provided evidence for 14C02 binding in an enzyme-biotin complex. With excess propionyl CoA the 14C label moved into a stable position in methyl malonyl CoA. In the same year Lynen found biotin itself could act as a C02 acceptor in a fixation reaction catalyzed by B-methylcrotonyl CoA carboxylase. The labile C02 adduct was stabilized by esterification with diazomethane and the dimethyl ester shown to be identical with the chemically synthesized molecule. X-ray analysis of the bis-p-bromanilide confirmed the carbon dioxide had been incorporated into the N opposite to the point of attachment of the side chain. Proteolytic digestion and the isolation of biocytin established the biotin was bound to the e-NH2 of lysine. 

Acceptor-substituted diazomethanes can be explosive, and low-molecular-weight diazo compounds, in particular, should be handled with care. Ethyl diazoacetate has a half-life of 109h at 100°C in inert solvents [984, p 425], but traces of acid or catalytically active salts can dramatically accelerate the thermal decomposition. Monoacyldiazomethanes are thermally less stable than diazoacetates [985], whereas bis-acceptor-substituted diazomethanes generally have high thermal and chemical stability. 

Acyl substituents at the 3- and/or 4-positions result in decreased hydrolytic stability compared with the alkyl and aryl derivatives described above. Despite this constraint most of the usual reactions of the carbonyl group are possible. Aldehydes <9ILA1211> and ketones are oxidized to the carboxylic acid, borohydride reduction affords the expected alcohols, and epoxides are formed on reaction with diazomethane. Oximes and arylhydrazones are formed with hydroxylamine and arylhydrazines, and the products may subsequently undergo monocyclic rearrangement involving the oxadiazole to give the corresponding isomeric furazans and 1,2,3-triazoles (Section 4.05.5.1.4). 

A second and related consequence in aliphatic nitro compounds is the acidification of the directly bonded CH unit through the attendant stabilization of the derived conjugate bases (5,6). As with all delocalized anions, reprotonation gives rise to tautomers, the original C-nitro compound (I) and the oci-nitro or isonitro form (II), Eq. 2.1. The aci-nitro tautomers are typically present in very minor concentrations, with equilibrium constants (A eq) between 10 and 10 (7). Alkylation of the delocalized anion leads to both a-substituted nitro compounds and the regioisomeric nitronic esters (nitronates). Nitronates were described as early as 1894 (8), however, the first isolated nitronic ester was obtained several years later upon the addition of diazomethane to phenylazonitromethane (1), Eq. 2.2 (9). 

Diazomethylene)phosphoranes 33 (Scheme 8.10), which represent another type of diazocumulenes (12) are easily obtained by the oxidative ylidation of the corresponding phosphanyl(trimethylsilyl)diazomethane with CCI4. The increased stability of these compounds as compared with diazocumulenes (R2C=C=N2) is probably due to the ylidic character of the P=C bond. These diazo compounds exhibit the expected dipolar reactivity toward electron-deficient alkenes, alkynes, phosphaalkenes, and heterocumulenes (12). Thus, 33 reacts with TCNE to form A -pyrazoline 35 (60). Furthermore, 33 could be converted into the phosphonio-borate-substituted diazo compound 34, which underwent subsequent cycloaddition with electron-deficient alkenes (e.g., 34 36) (61). 

The kinetically stabilized azacyclobutadiene 78 (Scheme 8.19) reacts with diazomethane at the C=C bond with formation of 79, while 1-diazo-1-phenyl-ethane adds across the sterically less hindered C=N bond to furnish the bicyclic... 

Onium-Salze sind in der Literatur nur vereinzelt beschrieben worden, so bei der Ringoffnung von 1,3-Benzoxazinen mit Hydroxylamin358 oder als stabile Zwischenprodukte bei der Isomerisierung von 3-(Aryl-nitrono-mcthyl)-l,2,4-oxadiazolcn, die mit Diazomethan N-methyliert werden konnen253 ... 

To probe the stability of 16b under normal conditions, the precursor diazomethane was photolyzed in degassed benzene at room temperature. The bands due to 16b decayed cleanly, showing isosbestic points, persisting for more than 3h before disappearing completely. The decay curve was analyzed in terms of second-order kinetics 2k/zl = 5.2 x lO s ). The half-life for 16b was estimated to be 19 min. This carbene is the longest-lived triplet thus far generated in our research group. 

Homo-l//-azepines (29), unlike their carbocyclic counterparts, show little tendency to isomerize to the thermodynamically less favoured bicyclic aziridine tautomers (30). Presumably, the homoazepine gains its stability from delocalization of the nitrogen lone pair through the dienamine system <71AG(E)ll). However, the aziridine tautomers (30 R1 = C02Me, R2 = Ac, C02Me or p-Ts) have been trapped as their all-cTs bis-l,3-dipolar cycloadducts with diazomethane (76CB3505). 

The chemistry of a fourth coenzyme was at least partially elucidated in the period under discussion. F. Lynen and coworkers treated P-methylcrotonyl coenzyme A (CoA) carboxylase with bicarbonate labelled with 14C, and discovered that one atom of radiocarbon was incorporated per molecule of enzyme. They postulated that an intermediate was formed between the enzyme and C02, in which the biotin of the enzyme had become car-boxylated. The carboxylated enzyme could transfer its radiolabelled carbon dioxide to methylcrotonyl CoA more interestingly, they found that the enzyme-COz compound would also transfer radiolabelled carbon dioxide to free biotin. The resulting compound, carboxybiotin [4], was quite unstable, but could be stabilized by treatment with diazomethane to yield the methyl ester of N-carboxymethylbiotin (7) (Lynen et al., 1959). The identification of this radiolabelled compound demonstrated that the unstable material is N-carboxybiotin itself, which readily decarboxylates esterification prevents this reaction, and allows the isolation and identification of the product. Lynen et al. then postulated that the structure of the enzyme-C02 compound was essentially the same as that of the product they had isolated from the reaction with free biotin, but where the carbon dioxide was inserted into the bound biotin of the enzyme (Lynen et al., 1961). Although these discoveries still leave significant questions to be answered as to the detailed mechanism of the carboxylation reactions in which biotin participates as coenzyme, they provide a start toward elucidating the way in which the coenzyme functions. 

E. I. du Pont de Nemours and Co., Gibbstown, New Jersey, under the tradename EXR-101. The 30% white mineral oil acts as a stabilizer. The material may be stored indefinitely at room temperature. Details concerning the properties of the compound and recommended precautions in its use are provided in a products bulletin available from the supplier. EXR-101 sometimes turns green on long standing, but this does not affect the yield of diazomethane (private communication from Dr. . C. McKusick). 

Gas chromatographic methods have been successfully used for the determination of penicillin molecules bearing neutral side-chains in milk and tissues (95, 97), but cannot be used for amphoteric -lactams. Gas chromatography of penicillin residues is further complicated by the necessity for derivatization with diazomethane. This derivatization step is particularly important because it not only leads to formation of the volatile penicillin methyl esters but also improves their chromatographic properties (thermal stability and decreased polarity). Using a fused-silica capillary column in connection with a thermionic nitrogen-selective detector, excellent separation and sensitivity figures were obtained. 

Gas chromatographic separation has not gained wide acceptance in spite of being quite sensitive and specific. This mode of separation is complicated by the need for derivatization of sulfonamide residues before gas chromatographic analysis. These drugs are subjected to derivatization via methylation with diazomethane (223, 224, 253, 254, 271), or double derivatization via methylation followed either by silylation with Ai-methyl-Ai-trimethylsilytrifluoroacetamide (261) or by acylation with A-methyl-bis(trifluoroacetamide) (256). This derivatization step is required not only to form the volatile derivatives of the sulfonamides but also to improve their chromatographic properties (thermal stability and decreased polarity). 

Because of the low cost of the starting materials and the stability in storage of the nitrosoaminoketone, this substance is an excellent intermediate for preparing diazomethane. One of the submitters (Redemann) reports that a sample of the crude material was kept in the laboratory in a brown bottle for... 

Electron-withdrawing substituents generally increase diazo compounds stability toward decomposition. Dicarbonyl diazomethane, which bears two carbonyl groups flanking the diazomethane carbon, are more stable than diazo compounds with only one carbonyl substituent. In general, metal catalysed decomposition of dicarbonyl diazomethane requires higher temperature than does monocarbonyl substituted diazomethane. As indicated before, rhodium(II) carboxylates are the most active catalysts for diazo decomposition. With dicarbonyl diazomethane, the rhodium(II) carboxylate-promoted cyclopropanation process can also be carried out under ambient conditions to afford a high yield of products. 

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