Bis-nitrile

Some researchers have elaborated synthesis of PCSs employing bis(nitrile oxide)s as 1,3-dipoles and diynes, dinitriles, and a number of other compounds as dipolaro-philes154-156). 

Organic peroxides and hydroperoxides decompose in part by a self-induced radical chain mechanism whereby radicals released in spontaneous decomposition attack other molecules of the peroxide.The attacking radical combines with one part of the peroxide molecule and simultaneously releases another radical. The net result is the wastage of a molecule of peroxide since the number of primary radicals available for initiation is unchanged. The velocity constant ka we require refers to the spontaneous decomposition only and not to the total decomposition rate which includes the contribution of the chain, or induced, decomposition. Induced decomposition usually is indicated by deviation of the decomposition process from first-order kinetics and by a dependence of the rate on the solvent, especially when it consists of a polymerizable monomer. The constant kd may be separately evaluated through kinetic measurements carried out in the presence of inhibitors which destroy the radical chain carriers. The aliphatic azo-bis-nitriles offer a real advantage over benzoyl peroxide in that they are not susceptible to induced decomposition. 

The latter procedure was used in syntheses of stable nitrile oxides such as P,P-diphenylacrylonitrile oxide and 2,6-diphenylbenzonitrile oxide (22), a series of functionally substituted 2,6-dimethylbenzonitrile oxides (29), as well as 2,4,6-triethylbenzene-l,3-dicarbonitrile oxide (29), stable bis(nitrile oxides) of a novel structure 6, in which two benzene rings, bearing hindered fulmido groups are connected with a bridge (30), tetrachloroisophthalo- and terephthalonitrile oxides (31). Stable o-sullamoylbenzonitrile oxides with only one shielding substituent were also prepared using NaOCl/NaOH in a two-phase system (20, 32). 

Stable furoxans are convenient starting compounds for generating short-lived nitrile oxides XCNO (X = ONC, NC, Cl, Br, and Me) by thermolysis (10, 11, 80, 81). The thermolysis of benzotrifuroxan (200°, in excess PhCN) proceeds (Scheme 1.6) with the cleavage of the C-C and 0-N(0) bonds in only one furoxan ring to give bifuroxan bis(nitrile oxide). The latter undergoes further reactions such as cycloaddition with PhCN or conversion to bisisocyanate (82). 

Silacyclophanes 414, were synthesized (Scheme 1.52) by using quadruple macrocyclization of bis(vinyldimethyl)disiloxane with an aromatic bis(nitrile oxide) formed from bis(hydroxymoyl chloride) 415 (452). 

I.4.2.I. Synthesis and Modification of Polymers Unstable bis(nitrile oxide), generated by dichloroglyoxime dehydrochlorination, polymerizes in solution to give poly(furoxan) or (in the presence of 1,3-dienes) gives rise to their being cross-linked (500). Polymerization of terephthalonitrile dioxide and its... 

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

Bis(nitrile oxides) obtained from dialkylbenzenes have been claimed as low-temperature rubber vulcanization agents (517). Curing of poly(butadiene-co-acrylonitrile) with 2,4,6-trimethylisophthalodinitrile N-oxide produces rubbery material of good quality, however, curing of (polybutadiene) was unsuccessful (518). The solubility of dinitrile oxides and stability of their ketone solutions has been studied for their application as vulcanizing agents in the production of mbberized materials (519). 

Borodachev IV, Volkhonskaya EV, Guk YuV, Zhukov AYu, Tsypin GI, Chernysheva SYu, Antipova VF, Panova NV. Bis(nitrile oxides) of dialkylbenzenes as low-temperature rubber vulcanization agents with low unsaturation and their manufacture from dialkylbenzenes, RU Patent No. 2042664 1995 [Chem. Abstr. 1996 124 263170],... 

Overberger, C. G., and A. Lebovits Azo-bis Nitriles. Decomposition of Azo Compounds. A Special Case of Carbon-Carbon Hyperconjugation in a Free Radical Reaction. J. Amer. chem. Soc. 76, 2722 (1954). 

Trifluoromethyl substituted 1 -oxadiazoles 113 were prepared by heating the bis(oximes) 112 with dry silica <99H(51)627>. l -Oxadiazole-2-oxides(furoxans)are often produced by dimerisation of nitrile oxides and some novel examples of the method, which produces 3,4-disubstituted derivatives bearing medium and large rings, have been described <99JOC8428>. Two examples of compounds prepared in this way from bis(nitrile oxides) are the ftiroxans 114 (84%) and 115 (86%). 

PhS, p-tolS) initially yields the bis(nitrile) complexes [MI2(CO) (NCMe)2(i72-RC2R )]. which dimerize to yield the iodo-bridged complexes [ M(/t-I)I(CO)(NCMe)(T)2-RC2R ) 2].245 The reactions of the diphenylacet-ylene molybdenum complex with donor ligands and alkynes are shown in Scheme 6. 

Reactions which generate nitrile oxides can lead to isoxazoles and iso-xazolines by cycloaddition to acetylenes and olefins, respectively. The cleavage of the furoxan ring into two nitrile oxide molecules (or to a bis-nitrile oxide, in the case of a fused furoxan) is described in Section IV,A,... 

Thermolysis yields a bis-nitrile oxide which, in the absence of dipolarophiles, isomerizes to a diisocyanate. 

Acylhydrazides are oxidized to iV,V -diacylhydrazines in high yields with aqueous Oxone (eq 66), although only aromatic hydrazides were effective. The oxidation of alkylcyano-hydrazines to azo-bis nitriles can be carried out with an Oxone/ JCBr system (eq 67). Nitriles can also be hydrolyzed to amides in moderate to good yields with Oxone/acetone (eq 68). ... 

The binuclear compounds as well as the mononuclear seven-coordinate bis(nitrile) compounds are catalysts for the polymerisation of terminal alkynes such as phenylacetylene (PA) or ferf-butylacetylene (f-BA) and for the ROMP of norbornene (NBE) and norbornadiene (NBD) [20, 38-42]. The first step in all catalytic reactions is the coordination of the organic substrate to metal and the formation of a complex. Sometimes it was possible to isolate the products in crystalline form but frequently such adducts were observed only in situ by NMR investigations. 

Primary product of this thermal transformation presumably is a bis-nitrile oxide 4, which in the absence of dipolarophiles isomerizes to diisocyanate 5. 

Conjugate reduction of a,/8-unsaturated nitriles has long been a synthetic problem owing to over-reduction therefore new methodology is welcome. Copper hydride, formed from cuprous bromide, Vitride, and butan-2-ol in THF effectively converts the bis-nitrile (1) into the desired reduction product (Scheme 2). ... 

---