Aromatic nitriles, effective

An unusual solvent effect was observed in cycloadditions of aromatic nitrile N-oxides with alkyl-substituted p-benzoquinones in ethanol-water (60 40) the reaction rates were 14-fold greater than those in chloroform (148). The use of ion pairs to control nitrile oxide cycloadditions was demonstrated. A chiral auxiliary bearing an ionic group and an associated counterion provides enhanced selectivity in the cycloaddition the intramolecular salt effect controls the orientation of the... 

The most widely used method for the dehydration of primary nitroalkanes involves their treatment with phenyl isocyanate and triethylamine, introduced in 1960 by Hoshino and Mukaiyama (7). A probable mechanism for the formation of the nitrile oxide is shown in Scheme 6.4. This method is known to be very effective for the preparation of aliphatic or aromatic nitrile oxides. In some cases, the separation of the byproduct A,A -diphenylurea from the reaction mixture may be troublesome. In order to circumvent this problem, 1,4-phenylene diisocyanate was introduced (82,83). The polymeric urea that is formed as a byproduct is largely insoluble in the reaction mixture and can easily be removed. 

A common and effective direct approach to unsubstituted or multiply substituted oxazolines is the Lewis acid catalyzed reaction of nitriles with amino alcohols in an alcoholic or aromatic solvent (chlorobenzene) at reflux. The most common Lewis acids employed include ZnCl2, ZnBr2, NiBr2, CuCl2, and kaolinitic clay. Microwave irradiation has also been reported to facilitate the transformation. Alternatively, the condensation can be carried out in the presence of catalytic amounts of potassium carbonate. The method works well for both aliphatic and aromatic nitriles, with retention of stereochemistry. Some representative examples from the recent literature are listed in Table 8.16 (Scheme 3 40),2 35.2oi-2i3... 

Aryl nitriles The most satisfactory route to the naphthalenecarbonitrile 3 is addition of (CH3)3SiCN to the 1-tetralone 1 followed by conversion to the a,(l-unsuturated nitrile 2. Dehydrogenation to the fully aromatic nitrile can be effected with DDQ, but is effected preferably with palladium-on-charcoal in combination with sulfur. 

Estimation methods for the hydrolysis rates of several types of carboxylic acid esters, carbamates, aromatic nitriles, and phosphoric acid esters have been reported. Hydrolysis rates are subject to substituent effects, and consequently LFERs, as represented by Hammett or Taft correlations, have been applied to their estimations. Reviews (e.g., Harris, 1990 Peijnenburg, 1991 Nendza, 1998) reveal that QSARs are available only for a few compound classes and are based mostly on... 

Nitrile oxide cycloaddition with mono- and trisubstituted alkenes affords almost exclusively 5-mono- and 4,5,5-trisubstituted isoxazolines, respectively, the regioselectivity being determined by steric effects. Reverse regioselectivity in nitrile oxide cycloaddition to terminal alkenes has been reported <1997CC1517> for example, 4-A t/-butylbenzoni-trile oxide was forced to reverse alignment for the cycloaddition by formation of the inclusion complex 470 with /3-cyclodextrin. Under these conditions, 90% of the 3,4-disubstituted cycloadducts were obtained, whereas in the absence of cyclodextrin the aromatic nitrile oxide afforded only the 5-substituted isoxazoline. 

Aromatic nitriles. Newman added pyridine to a mixture of a-bromonaph-thalene and cuprous cyanide and noticed an exothermic effect (due to formation of... 

The most frequently used and widely known appheation of a,p-unsaturatcd nitriles is their conversion into a,p-unsaturated aldehydes. This is also the most extensively studied reaction for the formation of a,p-unsaturated nitriles. In 1957 it was reported that simple aliphatic or aromatic nitriles are effectively converted to aldehydes in high yields via reduction to intermediate imines with DIBAL-H followed by hydrolysis of the imines. This transformation has been introduced... 

The key to the success of this process is a combination of specific catalysts and optimum reaction conditions. Effective catalysts for trimerization of aromatic nitriles are listed in Table I (4 ). Optimum reaction conditions for processing the aromatic nitrile-modified imide precursors depend on the chemical structure and characteristic property of the individual precursor of concern. In general, yield of the polymeric products increases with the increase of reaction temperature, pressure, time, and concentration of catalyst within the range of practical experimental limits (5 ). 

Table I. EFFECTIVE CATALYSTS FOR TRIMERIZING AROMATIC NITRILES CATALYST FORMULA...

Conventional organic synthesis for aromatic nitriles [e. g. 10], for example the Rosenmund-von Braun reaction, the Sandmeyer reaction, or the oximation of aldehydes in the presence of dehydrating agents, performed in batch processes, are cumbersome and result in different amounts of by- and waste products. The ineffectiveness of such processes with regard to the amount of feedstock necessary per formed nitrile and the waste produced is rather high (in terms of the effectiveness factor defined by Sheldon [11]). 

Solvent effects on the weak exciplex emission from systems containing an aromatic nitrile and furan or an alkene are reported. The 1,2-photocycloaddi-tion reactions of methyl phenanthrene-9-carboxylate with styrenes are proposed to go by way of singlet exciplexes, partly on the basis of results from fluorescence studies of compounds such as (48). 6-Cyanophenanthridine (49) behaves like its... 

An interesting and effective synthesis of 1,2,4-thiadiazoles is the direct condensation at high temperatures of aromatic nitriles and sulfur under the influence of suitable catalysts. Benzonitrile, for example, reacts with sulfur in the presence of tri-n-octylamine in closed vessels at 250°C to afford 3,5-diphenyl-1,2,4-thiadiazole in 75% yield. The effectiveness of the catalysts increases with their chain length, tri-n-octylamine being five times as active as triethylamine.250... 

Aromatic nitriles can give mixtures of the primary amine and dibenzylamines (via the condensation reaction), but this depends on the catalyst. Rhodium hydroxide [Rh(OH)3] is very effective for production... 

In addition, this reaction is an auto-catalyzed reaction, as demonstrated by the reaction between / -bromotoluene and CuCN, which at 250°C completes only 15% within the first 60 min, while 60% more product is formed in the subsequent 30 min of reaction. Moreover, the presence of a small amount of nitrile effectively reduces the induction period. Some nitrogenous bases such as tertiary amine and pyridine also promote this reaction. It has been found that CUSO4 has a catalytic effect for this reaction, whereas hydroquinone retards the formation of aromatic nitrile, indicating that this reaction involves the divalent copper ion. However, this reaction also has a few associated problems the requirement for extreme reaction conditions (150-280°C) a harsh work-up process by heating with HCl and FeCb a stoichiometric amount of cuprous cyanide which leads to the formation of equivalent amount of copper halide which may complicate the product separation and cause the problem of waste disposal as well. ... 

Aromatic nitriles may be trimerized at moderate temperature and pressure with p-toluenesulfonic acid as catalyst. Studies were conducted to establish the effect of the reaction temperature, pressure, time, and catalyst concentration on yield of the trimerized product. Trimerization studies were also conducted to establish the effect of substituting electron donating or withdrawing groups on benzonitrile. Preliminary results of using the catalytic trimerization approach to prepare s-triazine cross-linked polyimide/graphite fiber composites are presented. 

The aromatic nitrile and catalyst selected for this study were benzonitrile and PTSA, respectively. Studies were conducted to establish the effect of reaction conditions on yield of trimerized product. Figure 1 shows the... 

Another important class of reactions involves the introduction of a cyano group by substitution in an Ar-Z precursor. In fact, novel pathways leading to aromatic nitriles-for example, photosubstitution reactions-are desirable in view of the many applications of aryl cyanides as agrochemicals and pharmaceuticals. Today, the classical copper(l)-mediated Rosenmund-von Braun and Sandmeyer reactions, from aryl halides and aryldiazonium salts respectively, have been supplanted by reactions which employ palladium- or copper-catalysis [57]. The rather common use of excess cyanide anion may lead to a deactivation of the catalyst, and affect to a remarkable extent each of the key steps of the catalytic cycle [58aj. Although the use of complex iron cyanide has been shown to offer an effective solution to this limitation [58b,c], photocyanation provides an equally useful alternative [10],... 

The hydrolysis of aliphatic and aromatic nitriles into amides and/or carboxylic acids is an area of rapidly increasing interest. Already the Nitto Chemical Industry Co. Ltd. has developed a large-scale process for the conversion of acrylonitrile into acrylamide using Rhodococcus cells (see Section 6.7.2). Many other organisms, as well as the nitrilases, nitrile hydratases and amidases derived from them, can effect similar conversions. It is interesting to note that for dinitriles, only one of the nitrile groups... 

Takeuchi and coworkers reported an iridium-catalyzed cycloaddition of a,o -diynes and nitriles to give pyridines in 2012 [57]. With [Ir (cod)Cl]2/DPPF or BINAP as the catalytic system, pyridines were formed effectively (Scheme 3.24). A wide range of nitriles (aliphatic and aromatic nitriles) can be applied and reacted smoothly with Q ,a -diynes to give the pyridines. In the case of unsymmetrical diyne bearing two different internal alkyne moieties, high regioselectivity can be achieved which can be explained by the different reactivities of the a-position in iridacyclopentadiene. Terpyridine and quinquepyridine were prepared as well. [Ir(cod)Cl]2/chiral diphosphine catalyst can be applied to enantioselective synthesis. Kinetic resolution of the racemic... 

Inoue, Y., Araki, K. and Shiraishi, S., Unusual solvent effect on the cycloadditions of aromatic nitrile n-oxide with alkyl-substituted p benzoquinones in ethanol-water systems. Bull Chem. Soc. Jpn., 1991, 64, 3079-3083. 

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