Phenyl salicylate, reactions

Benzoxazin-4-ones have been known for many years and are made by the cyclization of O-benzoylsalicylamides or reactions between phenyl salicylates and benzamidines (l5LA(409)305>. The first of these two methods obviously has wide applicability and when 2-acyl-mercaptobenzamides are used l,3-benzothiazin-4-ones are obtained (Scheme 77) (67BSF4441). 

Other solvents tried and the liquid temperatures of the refluxing mixtures are stearic acid (340-365°), di- -butyl phthalate (320-325°), phenyl salicylate (290°). The first two solvents are unsatisfactory because of side reactions consuming some of the tetraphenylcyclopentadienone, the third because the addition reaction is too slow. 

Khan and Arifin reported a study involving the kinetics and mechanism of an intramolecular general base-catalyzed methanolysis of phenyl salicylate in cationic micellar media [12]. The authors showed the participation of methanol in the reaction via its partitioning into the micellar pseudophase and thereby modifying the overall aggregate microenvironment. 

The aminolysis and methanolysis of ionized phenyl salicylate (189) have been examined under micellar conditions. The effect of CTABr on the rates of aminolysis of (189) by -butylamine, piperidine, and pyrrolidine is to bring about a rate decrease (up to 17-fold with pyrrolidine). The results are interpreted in terms of binding constants for the amines with CTABr and the pseudo-phase model.The effects of mixed surfactants SDS and CTABr on the methanolysis of (189) and the alkaline hydrolysis of phenyl benzoate suggest that micellar aggregates are involved in the processes.The effects of NaOH and KBr on the intramolecular general base-catalysed methanolysis of (189) in the presence of CTABr has been investigated. Pseudo-first-order rate constants were not affected by either additive but other changes were noted. The effect of mixed MeCN-water solvents on the same reaction has also been probed. 

The H-bond strength of the third group—nonlumlnescent molecules—is similar to that of the salicylic derivatives, and no ground state tautomers are observed. Tremendous pK changes are necessary in order to facilitate proton transfer in the excited state. The deactivation path is still a matter of speculation. It is worth noting that a substance of the fluorescent class (phenyl salicylate, Table 2) has been the first ultraviolet stabilizer (9) used on a technical scale, despite its poor absorption intensity (screening effect). This substance is photo-chemlcally converted into 2,2 -dlhydroxy benzophenone (87) in a photo-Fries reaction. This can, however, not explain the total efficiency of this stabilizer (93). 

Benzo-l,3-dioxan-4-ones. Phenyl salicylates form cyclic acetals on reaction with HCHO and DABCO in chloroform. The corresponding methyl esters do not react. 

M. Niyaz Khan [Int. J. Chem. Kinet., 19, 757-776 (1987)] studied the kinetics of the alcoholysis of phenyl salicylate in aqueous mixed solvents. For reaction at 30°C in basic (0.05 M NaOH) solution containing 5% (v/v) methanol and 0.8% methyl cyanide, the reaction network can be described as follows ... 

The effect of cetyltrimethylammonium bromide on the rate constants of hydrolysis of ethyl glycinate hydrochloride has been reported. " Cationic and non-ionic micelles inhibited and anionic micelles accelerated the acid hydrolysis of A-p-tolyl-benzohydroxamic acid (189). The rates of acid hydrolysis of acetohydroxamic acid, MeCONHOH, benzohydroxamic acid, PhCONHOH, and A-phenylbenzohydroxamic acid, PhCON(OH)Ph, were increased by perfiuorooctanoic acid and by sodium 1-dodecanesulfonate and sodium dodecyl sulfate (SDS). " The effects of micelles of SDS upon the rates of reaction of ionized phenyl salicylate with Bu"NH2, piperidine and pyrroiidine have been reported. 

Figure 5.191 uses the sodium benzoate-induced melt crystallization of bisphenol A-polycarbonate to illustrate its catalyzed decomposition. There are kinetic and product specific indications that rearrangements of phenyl salicylates are forming o-phenoxybenzoates. The phenyl salicylates are created by sodium salicylates that form from carboxylate ions of sodium phenolate. Pyrolysis/mass spectroscopic investigations showed the ultimate formation of cyclical trimmers, dimers, and/or tetramers of bisphenol A-polycarbonate caused by intermolecular transesterifications and/or homolytic reactions [673]. 

The reactions of salicylate esters in aprotic solvents are also intra-molecularly catalysed. Thus the reactions of phenyl salicylate and phenyl o-methoxybenzoate with n-butylamine in acetonitrile are both second-order in amine but phenyl salicylate reacts 132 times faster [31]. These reactions are also catalysed by triethylenediamine and the rate constant for the reaction which is first-order in n-butylamine and first-order in triethylenediamine is over one hundred times greater for phenyl salicylate than for phenyl o-methoxybenzoate. The reaction of phenyl o-methoxybenzoate, but not that of phenyl salicylate, is catalysed by n-butylamine hydrochloride, which suggests that the phenolic hydroxyl group of the latter acts as an internal acid catalysis. Since the rate-limiting step in the aminolysis of esters in acetonitrile solutions is the breakdown of tetrahedral intermediate [32], a reasonable mechanism for the reaction of phenyl salicylate is one in which breakdown of the tetrahedral intermediate is catalysed intermolecularly by a second molecule of amine and intramolecularly by the phenolic hydroxyl group as shown in 25. The reaction of... 

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