Free radicals from toluene

Butadiene reacts readily with oxygen to form polymeric peroxides, which are not very soluble in Hquid butadiene and tend to setde at the bottom of the container because of their higher density. The peroxides are shock sensitive therefore it is imperative to exclude any source of oxygen from butadiene. Addition of antioxidants like /-butylcatechol (TBC) or butylated hydroxy toluene (BHT) removes free radicals that can cause rapid exothermic polymerizations. Butadiene shipments now routinely contain about 100 ppm TBC. Before use, the inhibitor can easily be removed (247,248). Inert gas, such as nitrogen, can also be used to blanket contained butadiene (249). 

A novel cross-linked polystyrene-divinylbenzene copolymer has been produced from suspension polymerization with toluene as a diluent, having an average particle size of 2 to 50 /rm, with an exclusive molecular weight for the polystyrene standard from about 500 to 20,000 in gel-permeation chromatography. A process for preparing the PS-DVB copolymer by suspension polymerization in the presence of at least one free-radical polymerization initiator, such as 2,2 -azo-bis (2,4-dimethylvaleronitrile) with a half-life of about 2 to 60 min at 70°C, has been disclosed (78). 

What are the three products resulting from free-radical chlorination of toluene Why are only three hydrogens replaced ... 

Abramovitch, Roy, and Uma 51> disagreed with this, pointing out a number of inconsistencies with that conclusion. Thus, while the total rate ratios are not much different from unity, as expected for a homolytic substitution, the values of °h A = 1.0, °HeA = 0.96, and °hA = 0.80 do not support this mechanism since such electron-donating substituents should facilitate attack by an electrophilic free radical 59-60> and lead to total rate ratios greater than unity. Also, the partial rate factor calculated for attack at the meta position of toluene was unusually low, and it is not clear why this position should be deactivated towards attack either by a free radical or by an electrophilic species. 

A bulky methacrylate, triphenylmethyl methacrylate (TrMA), is a unique monomer which gives an almost 100% isotactic polymer in anionic polymerization with n-butyllithium both in nonpolar and polar solvents. Moreover, even free-radical polymerization affords a highly isotactic polymer from this monomer.23 The isotactic specificity of TrMA polymerization is ascribed to the helical formation of the main chain. When TrMA is polymerized in toluene at —78°C... 

For example, in the photolysis of (30) in toluene solution, the product of insertion of DPC into the benzylic C—H bonds, 1,1,2-triphenylmethane (31), was accompanied by substantial amounts of 1,1,2,2-tetraphenylethane (32) and bibenzyl (33).When solvents such as cyclohexane are used, tetraphenylethane (32) is formed as the major product, indicating that direct C—H insertion in the singlet state is not the main process in most diarylcarbenes (Scheme 9.7). ° In contrast, 9-cyclohexylfluorene (37) is produced by photolysis of diazofluorene (36) in cyclohexane as a main product (65%) along with a small amount of escaped products (38 and 39). One can estimate in this case that at most 14% of 37 arises from free radical processes. Similarly, direct or sensitized photolysis of diazomalonate in 2,3-dimethylbutane gives C—H insertion products, but in the triplet-sensitized... 

The understanding of polar effects on free radical reactions arose from studies of free radical polymerization where transition state effects were empha-sized. Further studies involved diacyl peroxide reactions (equation 45), hydrogen abstraction from ring-substituted toluenes, and reactions of peresters involving transition state 38 (equation 57). ... 

Polymethylstyrene (PMS) and PCMS (both prepared from mixtures of meta and para isomers) were prepared by free radical polymerization of the respective monomers in toluene initiated by benzoyl peroxide at 85°C (12). Chlorination of P-p-MS was carried out in carbon tetrachloride (CC14) at 60 °C in presence of AIBN using the desired amount of S02C12 (13). Chlorination of PMS was carried out in CC14 at 50 °C under irradiation from a 60W incandescent light with the requisite amount of t-BuOCl (14). 

Intuitively, the idea of an influence of the size of the substituent on the stereocontrol in free radical polymerization is very appealing. However, it is not supported by quantitative data. Table I shows the probabilities p of the formation of isotactic and syndiotactic diads at existing iso- and syndiotactic diads for the free radical polymerization of the methacryl type monomers CH2=CH(CH3)COOR in toluene at —78°C. These probabilities have been calculated from published mole fractions of iso- and syndiotactic diads (Xi, X8) and iso-, syndio-, and heterotactic triads (Xu, X88 and Xu) via... 

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