Benzoylation process, solvent-free

On the basis of their earlier work with benzoyl nitrate and zeolites [16] Smith et al. [17,18] described a method for the nitration of simple aromatic compounds such as benzene, toluene, and halobenzenes. Using 90 % nitric acid, H-beta zeolite as catalyst, and acetic anhydride as water-trapping agent these aromatics are nitrated in quantitative yield with high para selectivity in a solvent-free process by use of a stoichiometric quantity of nitric acid and acetic anhydride at... 

Rabek and Ranby (22) have shown that a free radical induced degradation of polystyrene occurs in the presence of oxygen, that leads to rapid chain scission. Benzoyl radicals derived from Type 1 initiators abstract hydrogen atoms from the polymer and thereby start a chain degradation process. Berner, Kirchmayr and Rist (6) and others have shown that when initiator I is irradiated in solution, the benzoyl radical abstracts a hydrogen from the surrounding solvent to form benzalkdehyde and a free radical. 

The rate of decomposition also depends on the solvent. Benzoyl peroxide, for example, after 60 min at 79.8" C, is 13% decomposed in CCI4, 15.5% in benzene, 51% in cyclohexane, and 82.2% in dioxane. After only 10 min in i-propanol the decomposition is 95.1 %, and in amines decomposition occurs explosively. Thus, solvents can intervene in the free-radical-forming process. 

Conventional free radical techniques are applicable and conunonly solution polymerization is carried out, using water as the solvent. In a typical process a water-soluble initiator such as potassium persulphate is added to an aqueous solution of the acid together with an activator, e.g., sodium thiosulphate, and a transfer agent, e.g., mercaptosuccinic acid a reaction temperature of 50 100°C is used. Alternatively, if solid polymer is required, it is convenient to conduct the polymerization in a solvent such as benzene in which the polymer is insoluble in this case benzoyl peroxide is a suitable initiator. Salts of acrylic and methacrylic acids may also be polymerized in aqueous solution by treatment with free radical initiators. In addition to the polymerization of the appropriate monomer, the hydrolysis of a suitable polymer represents a further method of preparation of polymeric acids and salts. (See Sections 6.4,6.6.3 and 6.7.)... 

From related studies with diacetyl peroxide, Homer and Anders conclude that oxidation of primary aromatic amines is an entirely heterolytic process. They find, for instance, that no carbon dioxide is evolved as would be expected if acetoxy radicals were formed in the oxidation process (CHgCOO-COg + CHg-). Since the products are analogous to those obtained with benzoyl peroxide, the same conclusion may also apply to the latter reagent. More recent studies , however, claim to detect the presence of free radicals in the oxidation of aniline with benzoyl peroxide in solvent benzene. 

In a broad sense radical-induced decomposition may be considered as the reaction of any substrate promoted by a free radical, but the more common usage is to restrict consideration to those cases in which the molecule undergoing reaction is a free radical initiator (1, ). Thus radical-induced decomposition may be de-fTned as reaction of a free radical with the primary source of the radical. This phenomenon is particularly noticeable when a free radical initiator does not react with first-order kinetics, but is consumed by the radicals it generates in chain processes. This case was originally elucidated for the kinetics of benzoyl peroxide decomposition in solvents such as ethyl ether ( - ), and was found to occur with radical displacement (the SH2 reaction) (S) by solvent derived radicals on the peroxidic oxygen of benzoyl peroxide as shown in Fig. 1. 

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