Peroxide, dibenzoyl

Rapid side-chain chlorination of toluene proceeds in the dark with sulphuryl chloride in the presence of dibenzoyl peroxide (0-001-0 005 mol per mol of SOjCl,) as catalyst ... 

Method 2. In a 500-ml. rovmd-bottomed flask, fitted with an efficient reflux condenser, place 92 g, (106 ml.) of toluene, 68 g. (41 ml.) of redistilled sulphuryl cldoride and 1 g, of dibenzoyl peroxide (Section IV,196). Reflux gently, when a vigorous reaction takes place the reaction is complete in 30 minutes. Isolate the benzyl chloride as described in Method 1. The yield is 50 g. 

The extent of decarboxylation primarily depends on temperature, pressure, and the stabihty of the incipient R- radical. The more stable the R- radical, the faster and more extensive the decarboxylation. With many diacyl peroxides, decarboxylation and oxygen—oxygen bond scission occur simultaneously in the transition state. Acyloxy radicals are known to form initially only from diacetyl peroxide and from dibenzoyl peroxides (because of the relative instabihties of the corresponding methyl and phenyl radicals formed upon decarboxylation). Diacyl peroxides derived from non-a-branched carboxyhc acids, eg, dilauroyl peroxide, may also initially form acyloxy radical pairs however, these acyloxy radicals decarboxylate very rapidly and the initiating radicals are expected to be alkyl radicals. Diacyl peroxides are also susceptible to induced decompositions ... 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

Tetrachloroethylene reacts with formaldehyde and concentrated sulfuric acid at 80°C to form 2,2-dichloropropanoic acid [75-99-0] (8). Copolymers with styrene, vinyl acetate, methyl acrylate, and acrylonitrile are formed in the presence of dibenzoyl peroxide (9,10). 

Formation of an fV,fV -linked bipyrazole was observed during the oxidation of 5-amino-3-aniIino-4-ethoxycarbonyIpyrazoIe by means of dibenzoyl peroxide (82ZC56). 

Fig. 12.3. NMR spectra recorded during thermal decomposition of dibenzoyl peroxide. Singlet at high field is due to benzene other signals are due to dibenzoyl peroxide. [From H. Fischer and J. Bargon, Acc. Chem. Res. 2 110 (1969). Reproduced by permission of the American Chemical Society.]...

The oxidation of norhomadiene by i-butyl perbenzoate and Cu(I) leads to 1-t-butoxynorbomadiene. Similarly, oxidation with dibenzoyl peroxide and CuBr leads to 7-benzyloxynorbomadiene. In both cases, when a 2-monodeuterated sample of norbomadiene is used, the deuterium is found distributed at all seven carbons in the product. Provide a mechanism which could account for this result. In what w s does this mechanism differ from the general mechanism discussed on pp. 724-725 ... 

Dimethyl peroxide Diethyl peroxide Di-t-butyl-di-peroxyphthalate Difuroyl peroxide Dibenzoyl peroxide Dimeric ethylidene peroxide Dimeric acetone peroxide Dimeric cyclohexanone peroxide Diozonide of phorone Dimethyl ketone peroxide Ethyl hydroperoxide Ethylene ozonide Hydroxymethyl methyl peroxide Hydroxymethyl hydroperoxide... 

Detection and result The chromatogram was freed from mobile phase in a stream of cold air, immersed in the reagent solution for 1 s and then dried in a stream of cold air for 15 min. At first reddish and then after 60 min violet chromatogram zones developed on a pink background (detection limit of dibenzoyl peroxide ca. 500 ng). 

Fig. 1 Reflectance scans of 5 gg dibenzoyl peroxide (/l = 620 nm) after dipping the chromatogram was dried in (A) a stream of cold air and (B) in a stream of nitrogen.

While these results support the ionic orthoester mechanism, it was originally suggested that an oxygen radical may participate since it was claimed that the reaction proceeds in the presence of dibenzoyl peroxide instead of zinc, and that the presence of hydroquinone or exclusion of oxygen completely inhibits the reaction. Later work, however, could not confirm the previously observed influence of hydroquinone or oxygen. 

A distinction between these four possibilities can be made on the basis of the kinetic isotope effect. There is no isotope effect in the arylation of deuterated or tritiated benzenoid compounds with dibenzoyl peroxide, thereby ruling out mechanisms in which a C5— bond is broken in the rate-determining step of the substitution. Paths (ii) and (iii,b) are therefore eliminated. In path (i) the first reaction, Eq. (6), is almost certain to be rate-determining, for the union of tw o radicals, Eq. (7), is a process of very low activation energy, while the abstraction in which a C—H bond is broken would require activation. More significant evidence against this path is that dimers, Arz, should result from it, yet they are never isolated. For instance, no 4,4 -dinitrobiphenyl is formed during the phenylation of... 

It is understandable that dihydro adducts should be formed by polycyclic compounds and not by benzene or pyridine, because the loss of aromatic resonance energy is smaller in the former than in the latter process, (c) When dibenzoyl peroxide is decomposed in very dilute solution (0.01 Af) in benzene, 1,4-dihydro biphenyl is produced as well as biphenyl, consistent with addition of the phenyl... 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

The quantitative phenylation of pyridine has been studied by two groups of workers. Dannley and Gregg showed that 2-, 3-, and 4-phenylpyridine are formed in relative amounts 58 28 14 in the phenylation of pyridine with dibenzoyl peroxide, as estimated by infrared spectrophotometry. Hey and his co-workers obtained the ratios shown in Table I for the phenylation of pyridine using four different sources of phenyl radicals. ... 

The phenylation of quinoline with dibenzoyl peroxide was studied by Pausacker, who obtained all seven monophenylated quinolines in relative amounts shown in (4).- He also examined the phenylation of pyridine-iV-oxide with diazoaminobenzene and obtained the results shown in (5). ... 

Pyridlne-A -oxide may be formed in a manner analogous to the reaction of dibenzoyl peroxide with tertiary phosphines, i.e., Eq, (18)... 

Pyridine has been phenylated with the following free-radical sources benzenediazonium chloride with aluminum trichloride the Gomberg reaction " phenylhydrazine and metal oxides A -nitroso-acetanilide dibenzoyl peroxide phenylazotriphenylmethane di-phenyliodonium hydroxide and electrolysis of benzoic acid. ° Although 2-phenylpyridine usually accounts for over 50% of the total phenylated product, each of the three phenyl derivatives can be obtained from the reaction by fractional recrystallization of the... 

The phenylation of quinoline with dibenzoyl peroxide has been reported to give a mixture of 4- and 5-phenylquinoline which can be separated by the fractional recrystallization of their picrates, In a later investigation, the other five phenylquinolines have also been identified among the products, the relative reactivities of the nuclear positions being 8- > 4- > 3-, 5- > 2-, 6-, 7-... 

There is an early report that thiophene reacts at the 3-position in phenylation with benzenediazonium chloride and aluminum trichloride, but in the Gomberg reaction thiophene has been found to substitute mainly at the 2-position both with p-tolyl and with p-chloro-phenyl radicals.Bcnzothiazole is phenylated at the 2-position in low yield by dibenzoyl peroxide a small quantity of the 4-isomcr is also obtained. ... 

To a solution of 279 g of o-chloroacetophenone in 2 liters of anhydrous diethyl ether were added about 3 g of dibenzoyl peroxide. 5 g of bromine were added to the resulting solution, and after 3 minutes, the color of bromine had been discharged, indicating that the formation of oj-bromo-o-chloroacetophenone had been initiated. A further amount of 288 g of bromine was added dropwise to the reaction mixture over a VA hour interval. After the addition of the bromine had been completed, the reaction mixture was stirred for one-half hour and poured over about 1 kg of crushed ice. 

---