Radical 2,2’ -azobis

Such reactions can be initiated by free radicals, derived from compounds (initiators) such as benzoyl peroxide, ammonium persulphate or azobis-isobutyronitrile or by ionic mechanisms... 

DIITIATORS - FREE-RADICAL INITIATORS] (Voll4) l,ly-Azobis(cyanocyclohexane) [2094-98-6]... 

There has also been a trend in recent years to the use of free-radical initiators that decompose more rapidly than the traditional initiators such as caproyl and lauryl peroxides. Currently used initiators include peroxydicarbonates, t-butylperpiva-late, azobis-(2,4-dimethylvaleronitrile) and acetyl cyclohexylsulphonyl peroxide. 

Azo compounds having functional groups that stabilize the radical products are especially reactive. The stabilizing effect of the cyano substituent is responsible for the easy decomposition of azobis(isobutyronitrile) (AIBN), which is frequently used as a radical initiator. 

Generation of radicals by redox reactions has also been applied for synthesizing block copolymers. As was mentioned in Section II. D. (see Scheme 23), Ce(IV) is able to form radical sites in hydroxyl-terminated compounds. Thus, Erim et al. [116] produced a hydroxyl-terminated poly(acrylamid) by thermal polymerization using 4,4-azobis(4-cyano pentanol). The polymer formed was in a second step treated with ceric (IV) ammonium nitrate, hence generating oxygen centered radicals capable of starting a second free radical polymeriza-... 

Both S polymerization initiated by AlBMe176 180 (i.e. PS + 4) and MMA polymerization initiated by 1 J -azobis-l-phenylethane176 (i.e. PMMA + 1-phenylethyl radical) are reported lo give predominantly combination. Ito,7e has concluded that cross termination is not particularly favored over homotermination in S-MMA copolymerization. 

Ueno and coworkers10 have found that the facile displacement of sulfonyl group from a-alkylated allyl p-tolyl sulfones 18 by tri-n-butyltin radical in the presence of 2,2 -azobis[2-methylpropanenitrile] (AIBN) occurs smoothly in refluxing benzene (equation 11). In contrast, vinyl sulfones undergo the radical substitution reaction to give vinylstannanes in the presence of AIBN at a higher temperature11. 

The radical alkylation of ketones is achieved by their conversion into the desired N-silyloxy enamines 81 (Scheme 13). The reaction of 81 with diethyl bromomalonate in the presence of EtsB (0.5 equiv) in benzene was performed in open air and stirred at room temperature for 3h. With nitro compounds it is achieved by their conversion into the desired ]V-bis(silyloxy)enamines (82) (Scheme 13). When the reaction is carried out with 82 and alkyl iodides with an electron-withdrawing substituent at the a-position, using V-70 as radical initiator (2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile)), it underwent a clean radical alkylation reaction to yield an oxime ether. Successful radical alkylation of... 

Products that are likely to form free radicals also start a very violent polymerisation if the mixture is made in uncontrolied conditions. Primers are usually tert-butyl or benzoyl peroxide or azobis-isobutyronitrile. 

To conclusively disprove the involvement of the chromanol methide radical, the reaction of a-tocopherol with dibenzoyl peroxide was conducted in the presence of a large excess of ethyl vinyl ether used as a solvent component. If 5a-a-tocopheryl benzoate (11) was formed homolytically according to Fig. 6.6, the presence of ethyl vinyl ether should have no large influence on the product distribution. However, if (11) was formed heterolytically according to Fig. 6.9, the intermediate o-QM 3 would be readily trapped by ethyl vinyl ether in a hetero-Diels-Alder process with inverse electron demand,27 thus drastically reducing the amount of 11 formed. Exactly the latter outcome was observed experimentally. In fact, using a 10-fold excess of ethyl vinyl ether relative to a-tocopherol and azobis(isobutyronitrile) (AIBN) as radical... 

Skinner, W. A. Vitamin E oxidation with free radical initiators Azobis(isobutyronitrile). Biochem. Biophys. Res. Commurt. 1964, 15, 469 472. 

Attempts to promote radical reactions by adding azobis-isobutyronitrile to HMDS polymerizations gave no marked effect. 

Radical cyclization of perhydro-l,3-benzoxazines 518, promoted by Bu vSnI I in the presence of 2,2 -azobis(2-methylpro-pionitrile) (AIBN) gave a mixture of perhydropyrido[2,T ][l,3]benzoxazin-9-ones 519 and 520 and the seven-membered tricyclic derivatives 521 and 522, formed by a 6-exo- and a 7-rwr/o-cyclization process, respectively (Scheme 54) < 1999TL2421 >. Cyclization of parent acrylamide 518 (R = R1 = H) occurred with moderate regioselectivity (()-exo/7-endo ratio = 65 35) and poor stereoselectivity (519/520 ratio = 42 43). The presence of a [1-methyl group in crotylamide 518 (R = Me, R1 = H) disfavored the 7-/w/ -cyclization process, but did not influence the stereoselectivity of the cyclization (519/520 ratio = 66 34). The presence of an a-methyl group in methylacrylamide 518 (R=H, R1 Me) caused a retardation of the 6-oeo-attack, favoring the 7-/w/ -cyclization with a higher stereoselectivity (521/522 ratio = 75 12). 

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-... 

Meso- and (+ )-azobis[6-(6-cyanododecanoic acid)] were synthesized by Porter et al. (1983) as an amphipathic free radical initiator that could deliver the radical center to a bilayer structure controllably for the study of free radical processes in membranes. The decomposition pathways of the diazenes are illustrated in Fig. 36. When the initiator was decomposed in a DPPC multilamellar vesicle matrix, the diazenes showed stereo-retention yielding unprecedented diastereomeric excesses, as high as 70%, in the recombination of the radicals to form meso- and (+ )-succinodinitriles (Brittain et al., 1984). When the methyl esters of the diazene surfactants were decomposed in a chlorobenzene solution, poor diastereoselectivity was observed, diastereomeric excesses of 2.6% and 7.4% for meso- and ( )-isomers respectively, which is typical of free radical processes in isotropic media (Greene et al, 1970). 

In this section, we review the properties of a series of PNIPAM-b-PEO copolymers with PEO blocks of varying length, with respect to the PNIPAM block. Key features of their solutions will be compared with those of PNIPAM-g-PEO solutions. PNIPAM-b-PEO copolymers were prepared by free-radical polymerisation of NIPAM initiated by macroazoinitiators having PEO chains linked symmetrically at each end of a 2,2/-azobis(isobutyronitrile) derivative [169,170]. The polydispersities of PEOs were low, enabling calculations of the number-average molar mass for each PNIPAM block from analysis of their H-NMR spectra (Table 2). 

This assay measures the ability of antioxidant components in test materials to inhibit the decline in (3-phycoerythrin ((3-PE) fluorescence that is induced by 2,2 -azobis(2-amidinopropane) dihydrochloride (AAPH) as peroxyl radical generator (ORACroo.X H202-Cu2+ as hydroxyl radical generator (ORACho.X and Cu2+ as a transition metal oxidant (ORACcu)-... 

In vitro Antioxidant capacity was measured by the method of Trolox equivalent antioxidative capacity (TEAC) [12]. The TEAC assay used 20 pL of the extract sample mixed with a 980 pL solution of ABTS + [2.2 -azobis-(3-ethylenebenzothia-zohne-6-srrlfonic) acid], the decolorization of ABTS ", which is a long-life radical cation and bine-green chromophore, measrrred at 734 nm. Results are expressed as millimoles of Trolox equivalent per kilograms of fresh weight. 

---