4,4 Azobis synthesis

The carboxyl terminated ACPA, 4,4 -azobis-(4-cya-nopentanoic acid), turned out to be a suitable reagent in condensation reactions. This compound can be prepared by Strecker s synthesis from levulinic acid following the method of Haines and Waters [12]. Regarding the formation of polymeric azo initiators, Matsakuwa et al. [13] reported on the condensation of ACPA with various diols and diamines in the presence of a condensation agent, I-methyl-2-chlorpyridinium iodide, and a cata-... 

RAFT polymerization of two anionic acrylamido monomers sodium 2-acrylamido-2-methylpropane-sulfonate, AMPS, and sodium 3-acrylamido-3-methyl-butanoate, AMBA, (Scheme 29) was conducted in water at 70 °C using 4,4/-azobis(4-cyanopentanoic acid) as the initiator and 4-cyanopentanoic acid dithiobenzoate as the RAFT chain transfer agent [80]. The synthesis was initiated either from one monomer or the other leading to narrow molecular weight distributions in both cases (Mw/Mn < 1.2). 

Monofunctional and difunctional xanthates, shown in Scheme 30, were employed as chain transfer agents in the synthesis of block and triblock copolymers of acrylic acid, AA and acrylamide, AAm PAA-fr-PAAm, PAAm-fr-PAA-fo-PAAm and P(AA-sfaf-AAm)-fr-PAAm [81]. The polymerizations were conducted in aqueous solutions at 70 °C with 4,4 -azobis(4-cyanopentanoic acid) as the initiator. The yields were almost quantitative,... 

Free radical polymerization combined with anionic ring polymerization was employed for the synthesis of poly(N-vinylpyrrolidone)-fr-poly(D,L-lactide), PVP-fr-PDLLA, as shown in Scheme 49 [121]. The free radical polymerization of VP was conducted using 2,2/-azobis[2-methyl-M-(2-hydroxyethyl)propionamide] as the initiator, isopropyl alcohol and 2-... 

A Although it would be possible to convert 3-bromo-4-melhylani-line (7.2) into the corresponding hydrazine, by diazotization and reduction, react it with cyclohexanone, and then subject the product hydrazone to a Fischer indolization, the bromine substituent would still remain in the indole (note two isomers would form). Of course, this substituent could be displaced reductively using tributyltin hydride and a radical initiator [AIBN, azobis(isobuty-ronitrile)], but the overall synthesis is clumsy and non-selective and there should be a simpler route. 

A concise free radical cyclization process has been applied to the synthesis of new cyclopentanone-annulated azepines 204 from chiral vinylogous amides (Scheme 26). The free radical was generated from the phenylselenide group in 203 (made in turn by N-acylation of 202) using Bu3SnH and l,l -azobis(cyclohexanecarbonitrile) (ACN), as the initiator <2004SL1917>. 

Amino-terminated telechelic polybutadiene was prepared by LiAlH4 reduction of amidino end-group in polybutadiene, which was polymerised by a water-soluble initiator, 2,2 -azobis(amidinopropane)dihydrochloride. The structure was analysed by 1H- and 13C-NMR, but functionality of 2.0 was obtained by a titration method [70]. Synthesis of co-epoxy-functionalised polyisoprene was carried out by the reaction of 2-bromoethyloxirane with living polymer that was initiated with sec-butyl lithium. The functionality of the resulting polyisoprene was 1.04 by 1H-NMR and 1.00 by thin layer chromatography detected with flame ionisation detection [71]. 

Refluxing treatment of a mixture of cyclohexyl bromide and Bu3SnH in the presence of a catalytic amount of 2,2 -azobis (isobutyronitrile) (AIBN) in benzene produces cyclohexane in good yield as shown in Scheme 1.6. The Bu3SnH/AIBN system is the most popular radical reaction system in organic synthesis. 

Matsugi, M. et al. Highly Stereoselective Synthesis of Carbocycles via a Radical Addition Reaction Using 2,2 -Azobis(2,4-dimethyl-4-methoxyvaleronitrile) [V-70LJ. 2.1 1999 [149]... 

Direct Synthesis of Hydroxytelechelic Polymers a) 4,4 -Azobis(4-cyano-n-pentanol) as initiator... 

The oldest and probably the most widely used initiator is 4,4 -azobis(4-cyano-n-pentanol). Synthesized from 5-keto-n-pentanol as starting material (Strecker synthesis), this initiator was used in hydroxytelechelic polystyrene, polyacrylonitrile, and polymethacrylate syntheses, 4). Dienes were also polymerized with this initiator by a different method the molecular weights of liquid hydroxytelechelic polymers are between 2000 and 20000, their functionality is usually higher than two 15,16) (Table 1.1). The polymerization has been studied in dependence on reaction time, monomer and initiator concentrations, temperature, and solvent. The molecular weight increases with decreasing initiator concentration or increasing reaction time. The yield is a function of the nature of monomer and solvent. It decreases in the series chloroprene > butadiene > isoprene and dioxane > toluene. 

The reaction of AIBN with different diols (1,4-butanediol, 1,3-butanediol, 1,2-propylene glycol, ethylene glycol) leads to di(x-hydroxyalkyl)-2,2 -azobisisobutyrate 34). The di(4-hydroxybutyl)-2,2 -azobisisobutyrate has many advantages compared to 4,4 -azobis (4-cyano-n-pentanol) an easy synthesis, a good solubility in hydrocarbons, no transfer reactions. This initiator yields functionalized polyisoprenes with a high molecular weight 26). Its catalytic efficiency is similar to that of the other initiators. 

The x,x -azobis(x-cyano-alkanol)s are prepared by the Strecker synthesis followed by oxidation of the hydrazo intermediate. The same method was also used for 4,4 -azobis(4-cyano-n-pentanol) and 5,5 -azobis(5-cyanohexane-2-ol). The former one was a good initiator for secondary hydroxyl-terminated polydienes. Similar results were reported by Reed (see Sect. 1.1.2. a) for hydroxytelechelic polybutadienes (the functionality was 1.9 to 2.5, generally higher than 2, M < 5000). 

Monomethacrylate-functionalized POSS reagents are capable of being polymerized into novel linear silsesquioxane-based materials. Efforts to copolymerize these methacrylate-functionalized POSS with other acryhc comonomers have been successful [96,112]. In a typical polymer synthesis, a 0.5 M toluene solution of macromonomer was prepared, to which 2,2 -azobis(iso-butyronitrile) (AIBN) based on macromonomer was added from a stock solution. The clear solution was heated at 60 °C for 24 h and then precipitated into methanol. Further purification was performed by reprecipitation from toluene into methanol to yield white powder. 

The photoreduction of aromatic ketones by polymeric systems having tertiary amine end groups provides an ele nt way for the preparation of block copolymers with high efficiency [138]. The method consists of the synthesis of the bifimctional azo-derivative 4,4 -azobis (iV,i -dimethylaminoethyl-4-cyano pentanoate) (ADCP), successively used as fiee radical thermal initiator for the preparation of tertiary amine-terminated poly(styrene). 

Indeed, 4,4 -azobis-(4-cyanopentanoyl)-bis-benzoin (ACPB) and 4,4 -azobis-(4-cyano ntenoyl)-bis-(a-methylolbenzoin methyl ether) (ABME) have been used in the synthesis of poly(styrene )s possessing benzoin or benzoin methyl ether end groups (Scheme 38) ... 

Different vinyl monomers have also been reported to give block copolymers, in combination with other bifiinctional initiators, provided that the two photolabile groups differ sufficiently in the selective absorption of the light to jwrmit a two-step synthesis. Indeed, an azo-oligoperoxyester has been iM-epared [55] by reaction of hydrogen peroxide with 4,4 -azobis-(4-cyanopentanoic acid chloride) ... 

Regarding the initiation process of polymerization, it can be started by y-radiation. It is a method that has been used for the synthesis of hydrogels of PEO as well as hydrogels based on vinyl monomers " in this latter case, azo-compounds such as 2,2-azo-isobutyroni-trile (AIBN)f or 2,2 -azobis (2-amidine-propane) dihydrochloride or V-SO, and aqueous salt solutions such as aqueous ammonium peroxodisulfate are also used. Among the monomers most used in the preparation of hydrogels through free-radical polymerization are 2-hydroxyethyl methacrylate (HEMA) and A-vinyl-2-pyrrolidone (VP). ... 

By means of related procedures grafting from and onto radical VFA polymerization with functionalized silica are also possible. It was found that these methods are ineffective for the synthesis of PVFA/silica hybrid materials [103]. Hence, radical copolymerization of VFA with vinylsilane-function-alized silica particles was chosen [99]. The functionalization of silica particles with VTS yields, with good reproducibility, hybrid particles (VTS-silica) with an average carbon content of 3.4 w/w-%. Co-polymerization of VFA with VTS-silica particles was performed in aqueous suspensions containing 2,2 -azobis-(2-amidinopropene) dihydrochloride (ABAC) as initiator. The... 

This methodology was applied to synthesis of 2/,3/-didehydro-2/,3/-dideoxy-nucleosides, potent anti-HIY agents. The bis-xanthate of the V3-methyluridine derivative was subjected to radical reaction conditions in water, giving the corresponding alkene in 82% yield. Similar results were also achieved in the case of the adenosine derivative (76% yield). However, Kita et al. found that the combination of a water-soluble radical initiator, 2,2 -azobis[2-(2-imid-azolin-2-yl)propane] (VA-061), a water soluble chain carrier, 1-ethylpiperidine hypophosphite (EPHP), and a surfactant, cetyltrimethylammonium bromide (CTAB), resulted in a radical cyclisation that occurred in water with a variety of hydrophobic substrates16 (Table 5.2). 

In other examples of the use of azo compounds in pyridazine synthesis, dialkyl azodicarboxylates undergo cycloaddition with dienes to give 1,2,3,6-tetrahydropyridazines. Azobis(formamidine) reacts similarly. Diethyl azodicarboxylate also reacts with furans to give an adduct which is transformed into a pyridazine by acid. In a photochemical synthesis,... 

M. Matsugi, K. Gotanda, C. Ohira, M. Suemura, A. Sano, and Y. Kita, Stereoselective synthesis of carbocycles via a radical addition reaction using 2,2 -azobis(2,4-dimethyl-4-methoxyvaleronitrile), J. Org. Chem., 64 (1999) 6928-6930. 

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