Pyridine, reactions with—continued

A iridine traces in aqueous solution can be determined by reaction with 4-(p-nitroben25l)pyridine [1083-48-3] and potassium carbonate [584-08-7]. Quantitative determination is carried out by photometric measurement of the absorption of the blue dye formed (367,368). Alkylating reagents interfere in the determination. A iridine traces in the air can be detected discontinuously by absorption in Folin s reagent (l,2-naphthoquinone-4-sulfonate) [2066-93-5] (369,370) with subsequent chloroform extraction and hplc analysis of the red dye formed (371,372). The detection limit is ca 0.1 ppm. Nitrogen-specific thermal ionisation detectors can be used for continuous monitoring of the ambient air. 

A solution of a 2-aminobenzophenone (0.1 mol) and an z-amino acid ethyl ester hydrochloride (0.15 mol) in pyridine (200 mL) was refluxed. During the first 4h, 20-50 mL of liquid was allowed to distill and was replaced by fresh pyridine. Heating was continued for a further 11 h, the mixture was evaporated under reduced pressure and H20 and Et20 were added. In most cases some of the reaction product remained undissolved and was filtered off. The aqueous layer was separated, made alkaline and extracted with Et20. The comhined F.t20 phases were washed with H20. dried and evaporated and the reaction product was separated from unchanged amino ketone by crystallization. 

Another SBU with open metal sites is the tri-p-oxo carboxylate cluster (see Section 4.2.2 and Figure 4.2). The tri-p-oxo Fe " clusters in MIL-100 are able to catalyze Friedel-Crafts benzylation reactions [44]. The tri-p-oxo Cr " clusters of MIL-101 are active for the cyanosilylation of benzaldehyde. This reaction is a popular test reaction in the MOF Hterature as a probe for catalytic activity an example has already been given above for [Cu3(BTC)2] [15]. In fact, the very first demonstration of the catalytic potential of MOFs had aheady been given in 1994 for a two-dimensional Cd bipyridine lattice that catalyzes the cyanosilylation of aldehydes [56]. A continuation of this work in 2004 for reactions with imines showed that the hydrophobic surroundings of the framework enhance the reaction in comparison with homogeneous Cd(pyridine) complexes [57]. The activity of MIL-lOl(Cr) is much higher than that of the Cd lattices, but in subsequent reaction rans the activity decreases [58]. A MOF with two different types of open Mn sites with pores of 7 and 10 A catalyzes the cyanosilylation of aromatic aldehydes and ketones with a remarkable reactant shape selectivity. This MOF also catalyzes the more demanding Mukaiyama-aldol reaction [59]. 

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

B. 4-Aaetylpyridine oxime toeylate. Pure E-oxime (27.1 g, 0.20 mol) and p-toluenesulfonyl chloride (47.9 g, 0.22 mol) (Note 6) are added to 100 mL of anhydrous pyridine (Note 7) in a 1-L, round-bottomed flask fitted with a drying tube and a large magnetic stirring bar. The reaction mixture is stirred at 25°C for 24 hr a precipitate of pyridine hydrochloride forms. A 500-mL portion of ice water is added with continued stirring. The initial precipitate dissolves and a voluminous white precipitate soon forms. This is collected by suction filtration, washed with three 150-mL portions of cold water and dried under reduced pressure and over Drierite to constant weight. The yield of pure tosylate, mp 79-81°C (Note 8), is 55.1 g (95%). 

A stirred solution of 8.8 g 2,5-dimethoxy-3,4-methylenedioxy-l-propenylbenzene and 3.9 g pyridine in 45 mL acetone was cooled to ice-bath temperatures, and treated with 7.9 g tetranitromethane. This extremely dark reaction was stirred at 0 °C for 5 min, then quenched with a solution of 2.6 g KOH in 45 mL Hp. With continued stirring, there appeared yellow crystals of l-(2,5-dimethoxy-3,4-methylenedioxyphenyl)-2-nitropropene which, after filtering, washing with 50% acetone and air drying, weighed 8.0 g and had a mp of 110-111 °C. 

In the course of the continuing study [9a,b] on the enantioselective addition of dialkylzincs to aldehydes by using chiral amino alcohols such as diphenyl(l-methyl-2-pyrrolidinyl)methanol (45) (DPMPM) [48] A. A -dibutylnorephedrine 46 (DBNE) [49], and 2-pyrrolidinyl-l-phenyl-1-propanol (47) [50] as chiral catalysts, Soai et al. reacted pyridine-3-carbaldehyde (48) with dialkylzincs using (lS,2/ )-DBNE 46, which gave the corresponding chiral pyridyl alkanols 49 with 74-86% ee (Scheme 9.24) [51]. The reaction with aldehyde 48 proceeded more rapidly (1 h) than that with benzaldehyde (16 h), which indicates that the product (zinc alkoxide of pyridyl alkanol) also catalyzes the reaction to produce itself. This observation led them to search for an asymmetric autocatalysis by using chiral pyridyl alkanol. 

Addition of a base (pyridine or methoxyethylamine), which can mix with the continuous phase to the cyclohexane-salt miniemulsion under stirring, provides reaction to oxides and hydroxides, e.g., from iron(III) chloride hexahydrate to iron(III) oxide. Here the crystal water steps into the reaction, while pyridine from the continuous phase neutralizes the eliminated HCl. Obviously, the interface area of the miniemulsion is high enough in order to allow this reaction. 

In 70% HF/pyridine (70 mL). maintained in a polyethylene flask at — 70 C, was dissolved N02BF4 (14 g, 0.1 mol). Then cyclohexenc (4.2 g, 0.05 mol) was added to the stirred solution over 10 min. at — 70 C. When the addition was complete the mixture was warmed to 0 C over 10 min, and then the reaction was continued for 1 h at 0 C. The mixture was poured into ice water and extracted with Et20. The Et20 layer was washed with H20. aq NaHC03, and H20, then dried (anhyd Na2S()4). After evaporation of the solvent, the residue was distilled, and l-fluoro-2-nitrocyelohexane was obtained yield 5.1 g (70%). 

The photocycloaddition chemistry of pyridines substituted with electron-donor and electron-acceptor groups at the 2- and 3- positions continues to be exploited. The results of irradiation of such pyridines in the presence of 2-cyanofuran have now been described. The yields of the (47r+47r) cycloadducts (29) and (30), the pyridine dimer (31) and the transposition isomer (32) are dependent on the level of methyl substitution on the heteroarene and are given in Scheme 2. Other photocycloadditions to heteroarenes reported within the year include the reactions of benzodithiophene (33) with butadiyne derivatives and dimethyl acetylene dicarboxylate, giving low yields of (34) and (35) respectively, the latter from photorearrangement of the primary adduct (36). The (271+471) photocycloaddition of indoles (37) to cyclohexa-1,3-dienes (38) is sensitized by the aromatic ketones (39), and yields (14-46%) of the exo and endo isomers of the adduct (40) in ratios which are dependent on the substituents on the addends. 

A solution of 62 g. of dry pyridine in 350 ml. of dry chloroform is placed in a three-necked flask fitted with a thermometer, mechanical stirrer, and a dropping funnel. The flask is cooled by an ice-salt mixture while 38.5 g. of chlorosulfonic acid is slowly added to the solution, with continuous stirring. The rate of addition is regulated so that the temperature of the reaction mixture is kept in the neighborhood of 0°. At the end of the reaction, the solid pyridine-sulfur trioxide (pyridiniuin chloride remains in solution) is filtered on a Buchner funnel and quickly washed four times with 30- to 40-ml. portions of ice-cold chloroform. The product is then placed between porous... 

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