Pyridine as a solvent

The data discussed above can be summarized as follows NaBH4 is more prone to saturate conjugated double bonds than LiAlH4 the double bond in a l-en-3-one steroid is especially sensitive use of pyridine as a solvent favors formation of the saturated alcohol use of methanol with NaBH4, Na(OCH3)3BH in tetrahydrofuran, Li[OC(CH3)3]3AIH and aluminum hydride favor formation of the allylic alcohol. 

There are other gains, as well. Pyridine as a solvent is difficult to remove from the products, and it smells quite awful. In this reaction, a catalytic amount of DMAP is all that is necessary, and a more acceptable solvent can be employed. 

Acyl and sulfonyl halides and anhydrides react instantaneously with pyridine to form quaternary salts which are excellent acylating and sulfonylating agents. The familiar use of pyridine as a solvent in such reactions reflects this. While usually used in situ, stable A-acylpyridinium and N-acylisoquinolinium salts, e.g. (63), have been isolated and their structures confirmed by single crystal... 

Used to introduce chromophores into alcohols and amines using pyridine as a solvent efficient means for the isolation of carbohydrates in complex mixtures Reference 3... 

A kinetic study of the hydrogenation of benzhydrol to diphenyl-methane (Wender, Greenfield, Metlin, Markby and Orchin, 21) in different solvents showed that the rate decreased in the following order ethanol > benzene > cyclohexane. This is the solvent effect to be expected in a reaction with an ionic intermediate. Furthermore, the reduction is completely inhibited with pyridine as a solvent, a fact consistent with acid catalysis. 

Pyridine is also toxic and has a foul smell—so there are disadvantages in using pyridine as a solvent. But it is cheap and remains a popular solvent in spite of the problems. 

Systematic examination of the catalytic properties of dimeric complexes was initiated shortly after the identification of dinuclear iron sites in metalloenzymes. The first report of a reactive dimeric system came from Tabushi et al. in 1980, who examined the catalytic chemistry of [Fe3+(salen)]20, 1 (salen is N,N -(salicylaldehydo)-l,2-ethylenediamine) (12). They reported interesting stereoselectivity in the oxidation of unsaturated hydrocarbons with molecular oxygen in the presence of mercaptoethanol or ascorbic acid and pyridine as a solvent ([l]<<[alkane]<<[2-mercaptoethanol]). With adamantane as substrate, they observed the formation of a mixture of (1- and 2-) adamantols and adamantanone (Table I) (12). Both the relative reactivity between tertiary and secondary carbons (maximum value is 1.05) and final yield ( 12 turnovers per 12 hr) were dependent on the quantity of added 2-mercaptoethanol. Because autoxidation of adamantane gave a ratio of 3°/2° carbon oxidation of 0.18-0.42, the authors proposed two coexisting processes autooxidation and alkane activation. 

Acetamides. Reflux about 0.5 millimole of the unknown with 0.2 mL of acetic anhydride for 5 min, cool, and dilute the reaction mixture with 2.5 mL of water. Initiate crystallization by scratching, if necessary. Remove the crystals by filtration and wash thoroughly with dilute hydrochloric acid to remove unreacted amine. Recrystallize the derivative from alcohol-water. Amines of low basicity, e.g., p-nitroaniline, should be refluxed for 30 to 60 min with 1 mL of pyridine as a solvent. The pyridine is removed by shaking the reaction mixture with 5 mL of 2% sulfuric acid solution the product is isolated by filtration and recrystallized. 

Typical fragmentation of both types of base involves the loss of small neutral molecules such as HCN, CO, and CH3CN, as well as some extensive rearrangements in aromatic compounds. The most common derivatization, silylation under normal conditions (TMSC, HMDS/TMSC, BSA, or BSTFA/TMSC, V, 20 min - 2 hr), with or without pyridine as a solvent and base catalyst, usually leads to the enolic forms of the bases via the corresponding silyl ether. The persilylated derivatives are volatile enough to be used in gas chromatography-mass spectrometry (GC-MS). This enhancement of volatility compared to that of the free bases is the key factor making GC-MS a widely used analytical method in this area. 

N-Formylation of 2-aminobenzothiazoles is achieved by treatment with 7V-phenyl formamide and two equivalents of benzenesulfonyl chloride in pyridine as a solvent <88CCC3ii>. Condensation of 2-aminobenzothiazole with dimethylacetylendicarboxylate in ethanol affords pyrimido-benzo-thiazolones (172). Similar heterocyclic systems are obtained when 2-aminobenzothiazoles are treated with ethylbenzoyl acetate in polyphosphoric add (Scheme 42) <88jhC949>. 

B.i. Chromium Trioxide—Pyridine. In 1948, Sisler and co-workers isolated and characterized a stable complex from the reaction of chromium trioxide and pyridine. Sisler did not use this reagent for the oxidation of organic molecules but Sarett and co-workers recognized its utility in the synthesis of steroids. In this connection, alcohol 24 was oxidized to 26 in 89% yield. The reagent, which probably has the trigonal bipyramidal structure shown in 25, proved useful for the general oxidation of primary and secondary alcohols, even in the presence of double bonds and thioethers,. The oxidation usually requires pyridine as a solvent and... 

Draw the product of the reaction between pyrrole with sulfur trioxide (SO3) using pyridine as a solvent at lOO C. 

The absorbance of the red quinonamine dye formed in the reaction of phenol and 4-amino-l,5-dimethyl-2-phenyl-3-pyrazolone (4-aminoantipyrine) with periodate ions has been used in the estimation of periodate consumption in the oxidation of starch and other carbohydrates. The evaluation of the use of pyridine as a solvent in the oxidation of water-insoluble carbohydrates by periodate has been reported. The three types of dialdehydes produced by this oxidation were converted to the TMS ethers of the dithioacetals and measured by g.l.c. Oxidation proceeded in a normal Malapradian fashion but more slowly than it does in water. 

If a colorant can be solubilized, it can be evaluated by means of TLC. This technique is commonly employed for ink analysis but not for paints. A 1982 report described the use of TLC in isolating pigments in house paint, followed by IR identification of separated spots, but this is one of few such reports and TLC is infrequently used this way. However, for inks, TLC is an accepted and widely used discriminatory tool that is applicable to a variety of pens and toners. The ASTM guide for ink analysis (E 1422) recommends pyridine as a solvent for glycol-based ballpoint inks and an ethanol-water (1 1) combination for nonballpoint inks. The stationary phase is typically silica gel and the solvent S) tems are based on ethanol and water. There are still many inks in which the colorants can be separated with nothing more than water and filter paper. Dyes in textiles can be similarly examined, a topic discussed in Chapter 14. 

The intramolecular oxa-Michael strategy is shown in Fig. 3.22. Using pyridine as a solvent, the cw-diol 3.5a and triphosgene could react to create a carbonate product 3.48 in 85 % yield. The alkynyl lithium intermediate attacked the carbonyl group of 3.48, obtained a pair of diastereoisomer 3.47 and 3.49 which were produced depending on the different ring opening site. The main product was the... 

Silver(I) fluoride can also be used as a fluoride source. For example, a Cu-catalyzed orf/zo-fluorination process employing 8-aminoquinoline as an auxiliary was reported. Copper(I) iodide was chosen as the catalyst and NMO performed superiorly compared with other oxidants. A-methyl-protected indoles and pyridyl-derived carboxamides could be fluorinated in good yield (54 and 62%, respectively) however, the p)ridyl substrate required pyridine as a solvent to prevent product decomposition (eq 28). 

Tricyclic laddersiloxanes with 8-8-8-membered rings were the first laddersiloxanes those structures were determined. Synthesis of Me,Ph-tricyclic laddersiloxane (Me8Ph4Si80io) was reported hy Brown in 1965 (1), and later the structure was determined to have the syn-form hy Shklover (2). First nnh-tricyclic laddersiloxane was reported hy Shklover in 1981 (3). All these compounds were obtained by the reaction of chlorosilanes and silanols in the presence of base. Our group applied this method to obtain l-Pr,Ph-tricyclic laddersiloxane in 85% yield (4). In this synthesis, using pyridine as a solvent afforded better yield than using stoichiometric amount of pyridine. 

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