Nitriles selectivity

Despite acetonitrile s feeble acidity (pATa ca 29) compared with enolizable aldehydes (67, pA s 16-17), the combination of a simple ruthenium complex, [RuCp(PPli3)2]+, and diazabicycloundecane (DBU) brings about a nitrile-selective deprotonation to give /I-hydroxynitriles (68).274 A mechanism is proposed in which DBU, aldehyde, and acetonitrile can displace triphenylphosphines, with the metal centre activating acetonitrile to convert it to an NC-CFU- ligand (proposed intermediate, 69). A nickel-diarylamidodiphosphine complex (70) also catalyses this transformation in the presence of DBU.275... 

The product distribution between nitrile and imide depends upon the reaction conditions and the nature of the catalyst used [105]. The influence of various reaction parameters such as (i) reaction temperature (ii) water vapor addition in the feed gas (iii) NH3/o-xylene mole ratio and (iv) space velocity, were studied [105]. The removal of water vapor from the feed gas has a highly pronounced promotional effect on the selectivity of phthalonitrile. The nitrile selectivity increased from 2.1 to 34% at the expense of phthalimide (which decreased from 53 to 9%) with the complete removal of water vapor in the reactant feed mixture. This observation gives an indication that phthalonitrile being formed in the reaction is further hydrolyzed to phthalimide via the amide intermediate in presence of water... 

Pagni and Kabalka reported acid-catalyzed hydrolysis of nitrile selectively into amide on the surface of unactivated AI2O3. The AI2O3 surface is polar and contains a layer of OH groups, which could serve as the source of water in this reaction (Scheme 5.30). 

The anunoxidation of substituted toluenes and methylheteroi cles to the corresponding nitriles is an industriedly important reaction [e.g. 1]. The synthesized nitriles are valuable intermediates in the organic synthesis of different dyestuffs, pharmaceuticals and pesticides. Recent studies have shown that the conversion rate of the substrate and the nitrile selectivity are strongly determined by the position, size and electronic effects of one or more substituents... 

Toluene can be readily ammoxidized to benzonitrile, usually over supported vanadium oxide and vanadium phosphate catalysts [e. g. 9,57]. Besides catalyst choice, catalytic performance mainly depends on the reaction conditions. Excess ammonia, as mentioned above, significantly increases nitrile selectivity by blocking sites responsible for consecutive oxidation ammonia also frequently reduces catalyst activity [1]. Water vapor in the reactant stream can also improve selectivity by blocking sites for total oxidation [38] or providing Brdnsted sites for the activation of ammonia [51]. 

The reaction of dichloro-substituted toluenes is much more influenced by the position of the substituents-closer proximity of the substituents to the methyl group results in lower conversion and nitrile selectivity (2,6-di-Cl < 2,5-di-C1 < 2,3-di-Cl < 2,4-di-Cl 3,4-di-Cl) [39,77], Because, however, 2,6-dichloro-benzonitrile has special importance as an intermediate for pesticides, catalysts and conditions have been described which afford acceptable yields [29,78]. Thus 2,6-dichlorobenzonitrile is formed in 85 % yield by use of a fluid-bed reactor with separate introduction of the educt gases over a vanadium-molybdenum-containing multicomponent catalyst [79]. 

High selectivity was also reported for the ammoxidation of 4-methylpyridine, e. g. over vanadium-molybdenum oxides [90] highly dispersed vanadia on sili-cated alumina [91] or on vanadium-containing molecular sieves (VSAPO, VAPO [92], also used for the ammoxidation of 3-methylpyridine [93,94]). The ammoxidation of 2-methylpyridine leads to the formation of large amounts of pyridine, by total oxidation of the methyl group and subsequent decarboxylation, in addition to the desired nitrile [95]. Yields in excess of 90% can, nevertheless, be achieved, e. g. over vanadium-tin oxide at ca 670 K [23] or over molybdenum phosphates [96]. When the ammoxidation of 2-, 3- and 4-methylpyridine over vanadium phosphates was compared catalyst activity and the nitrile selectivity reflected the reactivity order 4- > 3- > 2-methylpyridine, probably as a result of different sterie hindranee [41]. 

Hansen et al. (1988) reported that YBa2Cu3CV A catalyzes the ammoxidation of toluene. A sharp change in selectivity occurred in their system at a given partial pressure of oxygen. The bulk composition of the nitrile-selective catalyst was close to YBa2Cu30(,. When x > 0, the catalyst became C02-selective. These results seem to suggest that the oxygen stoichiometry plays a key role in the catalyst selectivity for this reaction. 

Coupling of Alkenes and Alkynes. The highly reactive [Cp2Zr] fragment, generated through trapping of an alkyne complex with Lewis base (240), forms metallacycles with alkenes, alkynes, ketones, aldehydes, and nitriles (selected reactions shown in Scheme 14). 

The reaction conditions required for acid-catalyzed hydrolysis of a cyano group are typically more vigorous than those required for hydrolysis of an amide, and in the presence of excess water, a cyano group is hydrolyzed first to an amide and then to a carboxylic acid. It is possible to stop at the amide by using sulfuric acid as a catalyst and one mole of water per mole of nitrile. Selective hydrolysis of a nitrile to an amide, however, is not a good method for the preparation of amides. They are better prepared from acid chlorides, acid anhydrides, or esters. 

Sodium tetrahydridoborate Nitriles from a,j( -unsatd. nitriles Selective and preferential hydrogenation of carbon-carbon double bonds... 

Hie IS Meldrum s acid derivatives and 31 nitriles selected for the final libraiy are given in Figures 2 and 3. The majority of the molecules were predicted to have MW between 325 and 425 g/mol and log P values between 0.5 and 3.5, consistent with good lead-like and ag-lite properties. 

NHases are widely found in bacteria, which thereby make use of nitriles as sole source of nitrogen by coupling with an amidase (hydrolases acting on amides that yield the corresponding carboxylic acid). This feature provides a means for new biocatalyst discovery via nitrile-selective saeening [6,7]. An iron-based colorimetric assay for NHase/amidase-activity was recently developed and optimized for high throughput discovery [8]. 

A classical way to achieve regioselectivity in an (a -i- d -reaction is to start with a-carbanions of carboxylic acid derivatives and electrophilic ketones. Most successful are condensations with 1,3-dicarbonyl carbanions, e.g. with malonic acid derivatives, since they can be produced at low pH, where ketones do not enolize. Succinic acid derivatives can also be de-protonated and added to ketones (Stobbe condensation). In the first example given below a Dieckmann condensation on a nitrile follows a Stobbe condensation, and selectivity is dictated by the tricyclic educt neither the nitrile group nor the ketone is enolizable (W.S. Johnson, 1945, 1947). 

The conversion of carboxylic acid derivatives (halides, esters and lactones, tertiary amides and lactams, nitriles) into aldehydes can be achieved with bulky aluminum hydrides (e.g. DIBAL = diisobutylaluminum hydride, lithium trialkoxyalanates). Simple addition of three equivalents of an alcohol to LiAlH, in THF solution produces those deactivated and selective reagents, e.g. lithium triisopropoxyalanate, LiAlH(OPr )j (J. Malek, 1972). 

Even ia 1960 a catalytic route was considered the answer to the pollution problem and the by-product sulfate, but nearly ten years elapsed before a process was developed that could be used commercially. Some of the eadier attempts iacluded hydrolysis of acrylonitrile on a sulfonic acid ion-exchange resia (69). Manganese dioxide showed some catalytic activity (70), and copper ions present ia two different valence states were described as catalyticaHy active (71), but copper metal by itself was not active. A variety of catalysts, such as Umshibara or I Jllmann copper and nickel, were used for the hydrolysis of aromatic nitriles, but aUphatic nitriles did not react usiag these catalysts (72). Beginning ia 1971 a series of patents were issued to The Dow Chemical Company (73) describiag the use of copper metal catalysis. Full-scale production was achieved the same year. A solution of acrylonitrile ia water was passed over a fixed bed of copper catalyst at 85°C, which produced a solution of acrylamide ia water with very high conversions and selectivities to acrylamide. 

Physical properties for naphthalene mono-, di-, tri-, and tetracarboxyhc acids are summari2ed in Table 9. Most of the naphthalene di- or polycarboxyLic acids have been made by simple routes such as the oxidation of the appropriate dior polymethylnaphthalenes, or by complex routes, eg, the Sandmeyer reaction of the selected antinonaphthalenesulfonic acid, to give a cyanonaphthalenesulfonic acid followed by fusion of the latter with an alkah cyanide, with simultaneous or subsequent hydrolysis of the nitrile groups. 

Adhesives. Contact adhesives are blends of mbber, phenoHc resin, and additives suppHed in solvent or aqueous dispersion form they are typically appHed to both surfaces to be joined (80). Evaporation of the solvent leaves an adhesive film that forms a strong, peel-resistant bond. Contact adhesives are used widely in the furniture and constmction industries and also in the automotive and footwear industries. The phenoHc resins promote adhesion and act as tackifiers, usually at a concentration of 20—40%. In solvent-based contact adhesives, neoprene is preferred, whereas nitrile is used in specialty appHcations. The type and grade of phenoHc resin selected control tack time, bond strength, and durabiHty. 

With solvents having a nitrile group like acetonitrile, the selectivity of y-butyrolactone is increased, resulting in a yield of 60%. 

Nitrile mbber compounds have good abrasion and water resistance. They can have compression set properties as low as 25% with the selection of a proper cure system. The temperature range for the elastomers is from —30 to 125°C. The compounds are also plasticized using polar ester plasticizers. The main dilemma is the selection of a heat-stable, nonfugitive plasticizer that also gives good low temperature properties. 

Amino Acids. The formation of A/-halo-a-amino acids involves halogenation of the acid anion (13). /V-Cb1oro-CX-amino acids decompose to aldehydes and nitriles, the selectivity depending on pH and stoichiometry (110). For example, AJ-chloroalanine decomposes in the 6.5—10 pH range. 

Nitrile A-oxides, under reaction conditions used for the synthesis of isoxazoles, display four types of reactivity 1,3-cycloaddition 1,3-addition nucleophilic addition and dimerization. The first can give isoxazolines and isoxazoles directly. The second involves the nucleophilic addition of substrates to nitrile A-oxides and can give isoxazolines and isoxazoles indirectly. The third is the nucleophilic addition of undesirable nucleophiles to nitrile A-oxides and can be minimized or even eliminated by the proper selection of substrates and reaction conditions. The fourth is an undesirable side reaction which can often be avoided by generating the nitrile A-oxide in situ and by keeping its concentration low and by using a reactive acceptor (70E1169). 

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