Propionate-based phenolic

In doing their job phenolic antioxidants are converted each phenolic group can scavenge at least two radicals (Scheme 18.7). However, the chemistry is not finished after the formation of quinones. These molecules are still reactive and can undergo several side reactions. For propionate-based phenolic antioxidants the quinone can rearrange and form a phenolic antioxidant back (Scheme 18.9), which causes that each phenolic group can react with at least four radicals. 

Methylphenol is converted to 6-/ f2 -butyl-2-methylphenol [2219-82-1] by alkylation with isobutylene under aluminum catalysis. A number of phenoHc anti-oxidants used to stabilize mbber and plastics against thermal oxidative degradation are based on this compound. The condensation of 6-/ f2 -butyl-2-methylphenol with formaldehyde yields 4,4 -methylenebis(2-methyl-6-/ f2 butylphenol) [96-65-17, reaction with sulfur dichloride yields 4,4 -thiobis(2-methyl-6-/ f2 butylphenol) [96-66-2] and reaction with methyl acrylate under base catalysis yields the corresponding hydrocinnamate. Transesterification of the hydrocinnamate with triethylene glycol yields triethylene glycol-bis[3-(3-/ f2 -butyl-5-methyl-4-hydroxyphenyl)propionate] [36443-68-2] (39). 2-Methylphenol is also a component of cresyHc acids, blends of phenol, cresols, and xylenols. CresyHc acids are used as solvents in a number of coating appHcations (see Table 3). 

A large number of hindered phenoHc antioxidants are based on the Michael addition of 2,6-di-/ f2 -butylphenol and methyl acrylate under basic catalysis to yield the hydrocinnamate which is a basic building block used in the production of octadecyl 3-(3,5-di-/ f2 butyl-4-hydroxyphenyl)propionate, [2082-79-3], tetrakis(methylene-3(3,5-di-/ f2 butyl-4-hydroxylphenyl)propionate)methane [6683-19-8], and many others (63,64). These hindered phenolic antioxidants are the most widely used primary stabilizers in the world and are used in polyolefins, synthetic and natural mbber, styrenics, vinyl polymers, and engineering resins. 2,6-Di-/ f2 -butylphenol is converted to a methylene isocyanate which is trimerized to a triazine derivative... 

Many papers concerning salt effect on vapor-liquid equilibrium have been published. The systems formed by alcohol-water mixtures saturated with various salts have been the most widely studied, with those based on the ethyl alcohol-water binary being of special interest (1-6,8,10,11). However, other alcohol mixtures have also been studied methanol (10,16,17,20,21,22), 1-propanol (10,12,23,24), 2-propanol (12,23,25,26), butanol (27), phenol (28), and ethylene glycol (29,30). Other binary solvents studied have included acetic acid-water (22), propionic acid-water (31), nitric acid-water (32), acetone-methanol (33), ethanol-benzene (27), pyridine-water (25), and dioxane-water (26). 

Crystal structures have been reported for the octahedral phenolate [Tc(dppo)3] (307), thiolate [Tc(dppbt)3] (307, 308), and propionate [Tc(dppp)3]-2dmso (306). In each case the three P atoms occupy mer positions. For the amine ligand (25) (R = NH2) an acid-base equilibrium is established and either the triply deprotonated [Tc(dppba)3] or salts of the doubly deprotonated [Tc(dppba)2(dppbaH)]+ may be isolated depending on the pH. The crystal structure of [Tc(dppba)2(dppbaH)]-... 

Silylatlon The reagent silylates alcohols, phenols, mercaptans, carboxylic acids, and amides at 15-55° in the absence of a base, acid, or catalyst. Only methyl propionate (b.p. 80°) is formed as by-product. 

Sulfonic acid resins can be used as solid catalysts for esterifications and other acid-catalyzed reactions. Am-berlyst 15 was a more effective catalyst for the preparation of esters of phenethyl alcohol and cyclohexanol than sulfated zirconia, an acid clay, and dodecatungstophos-phoric acid.113 (Amberlyst and Amberlite are trademarks of Rohm Haas.) (See Chap. 6 for more detail on solid acids and bases.) The same catalyst gave 86-96% yields of hydroxyesters when a lactone was stored with a hy-droxyacid.114 Diols can be monoacylated in 58-92% yields by transesterification with ethyl propionate in the presence of Dowex 50W (a product of the Dow Chemical Co.).115 Modification of the sulfonic acid resin with 2-mercaptoethylamine produced a catalyst for the reaction of phenol with acetone to produce bisphenol A (5.30) in 99.5% yield.116 After 20 cycles the yield was still 98.7%. When used as catalysts, ion-exchange resins can last for 6 months to 2 years. 

Polymer bound acrylic ester is reacted in a Baylis-Hillman reaction with aldehydes to form 3-hydroxy-2-methylidenepropionic acids or with aldehydes and sulfonamides in a three-component reaction to form 2-methylidene-3-[(arylsulfonyl)amino]propionic acids. In order to show the possibility of Michael additions, the synthesis of pyrazolones was chosen. The Michael addition was carried out with ethyl acetoacetate and BEMP as base to form the resin bound p-keto ester. This was then transformed into the hydrazone with phenylhydrazine hydrochloride in the presence of TMOF and DIPEA [28]. The polymer bound phenol was readily coupled to a variety of allyl halides by using the Pl- Bu to generate a reactive phenoxide [29]. 

The stabilizer systems for polyacetals are invariably composed of a hindered phenol with a costabilizer. The hindered phenols in use are 2,2 -methylenebis-(4-methyl-6-tert-butyl-phenol), 1,6-hexamethyle-nebis-3-(3,5-di-rert-butyl-4-hydroxyphenyl)-propionate, and pentaerythrityl-tetrakis-3-(3,5-di-fert-butyl-4-hydroxyphenyl)-propionate. A large number of nitrogen-containing organic compounds have been described as costabiKzers for polyacetals, e.g., dicyandiamide, melamine, terpolyamides, urea, and hydrazine derivatives. The effectiveness of these compounds is based on their ability to react with formaldehyde and to neutralize acids, especially formic acid, formed by oxidation. In addition to nitrogen compounds, salts of long-chain fatty acids (e.g., calcium stearate, calcium ricinoleate, or calcium citrate) are also used as acid acceptors. The practical concentrations are 0.1-0.5% for the phenolic antioxidant and 0.1-1.0% for the costabilizer. 

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